Chapter 16 Human Reproduction Part 1 by TEACHING CARE online tuition and coaching classes

Chapter 16 Human Reproduction Part 1 by TEACHING CARE online tuition and coaching classes


   Reproduction and its type.

Reproduction : Reproduction is the ability of living organism to produce a new generation of living individuals similar to themselves.

Basic features of reproduction : All organisms reproduce. Modes of reproduction vary in different organisms. However, all modes have certain common basic features. These are

  • Replication of This is the molecular basis of reproduction.
  • Cell division, only mitotic, or both mitotic and This is cytological basis of reproduction.
  • Formation of reproductive bodies or
  • Development of reproductive bodies into

Types of reproduction : These are of two main types

(i) Asexual (Non-gametic)                     (ii) Sexual (gametic)

(i) Asexual reproduction

  • Definition : Production of offspring by a single parent without the formation and fusion of gametes is called asexual The young one receives all its genes from one parent.
  • A sexual reproduction is also known as agamogenesis or
  • It involves only mitotic cell divisions, and also termed somatogenic reproduction.
  • Asexual reproduction produces identical offspring commonly referred to as a Today, the scientists have been able to produce clones of multicellular animals (e.g., boar calf names as Frosty, and Finn Dorset lamb named as the famous Dolly) artificially in the laboratory.
  • Occurrence : Asexual reproduction occurs in protozoans and some lower animals such as sponges, coelentrates, certain worms and It is absent among the higher non-vertibrates and all vertibrates.
  • Types : Asexual reproduction takes place in five principal ways :
    • Binary fission : Binary fission is the division of the parent into two small, nearly equalized daughter Examples – Protozoans (Amoeba, Euglena etc.) Bacteria and Planarians.

Modes of binary fission : In Binary fission, the nucleus divides first and the cytoplasm next. Subsequently, the mother cell splits into two equal sized daughter halves or cells. There are three modes of binary fission.

  • Simple binary fission : If the plane of cytoplasmic division passes through any direction, the fission is called simple Example – Amoeba.





Fig. – Simple binary fission in

  • Transverse binary fission : If the plane of cytoplasmic division concides with the transverse axis of the individual, the fission is termed transverse binary Example – Paramoecium and Planaria.






Fig. – Transverse binary fission in

  • Longitudinal binary fission : It the plane of cytoplasmic division concides with the longitudinal axis of the This kind of fission is designated as longitudinal binary fission. Example – Euglena and vorticella.

Fig. – Longitudinal binary fission in euglena

Binary fission involves mitotis only and consequently, the resultant offspring’s are genetically identical to the parent and each other.

  • Multiple fission : Multiple fission is the division of the parent into many small daughter individuals Examples – Multiple fission occurs in many protozoans such as Plasmodium, Amoeba and Monocytis.




SCHIZONT               NUCLEI           MEROZOITES


Fig. Multiple fission of malarial parasite in RBC of man

Mode of multiple fission : Sometimes, the nucleus divides several times by amitosis to produce many nuclei, without involving any cytokinesis. Later, each nucleus gathers a small amount of cytoplasm around it and the mother individual splits into many tiny daughter cells.

In course of time, each of these daughter cells starts a free life and transforms into an adult individuals. This kind of fission is called multiple fission.

  • Encystation : In response to unfavourable living condition, an Amoeba withdraws its pseudopodia and secretes a three-layered hard covering or cyst around This phenomenon is termed as encystation.
  • Sporulation : During favourable condition, the encysted Amoeba divides by multiple fission and produces many minute amoebae or pseudopodiospores; the cyst wall burst out, and the spores are liberated in the surrounding medium to grow up into many This phenomenon is known as sporulation.
  • Schizogony : It is a type of multiple fission present in plasmodium. Schizogonies are of two type. Liver schizogony and blood
    • Plasmotomy : Plasmotomy is the division of a multinucleate protozoan into several small, multinucleate daughters without nuclear division. The daughters grow and regain the normal number of nuclei by nuclear The daughters grow and regain the normal number of nuclei by nuclear division. It takes place in Opalina and Pelomyxa.





  • Budding : Formation of a daughter individual from a small projection, the bud, arising on the parent body is called budding. It is a common method of asexual reproduction. In budding new individual form by mitosis. Examples – Budding occurs in some protozoans and certain lower animals such as sponges (Scypha), coelenterates (Hydra), annelids (chaetopterus) and tunicates (Salpa).

Types of budding : There are two types of budding

  • Exogenous or External budding : Initially, a small outgrowth of the parent’s body develops into a miniature It then separates from the mother to lead a free life. This type of budding is recognised as exogenous budding. Example – Hydra.


  • Endogenous or Internal budding : In fresh water sponges (g. – Spongilla) and marine sponge






(e.g. – Sycon), the parent individual releases a

Fig. – External budding in hydra


specialised mass of cells enclosed in a common opaque envelope, called the gemmule, on germination. Each


gemmule gives rise to an offspring gemmules are thought to be internal buds. This type of budding recognised as endogenous budding. Example – Sycon and Spongilla.

  • Fragmentation : It is the breaking up of an animal’s body into two or more pieces, each of which grows into a new individual. Examples – It occurs in the flatworm,
  • Special asexual reproductive bodies : Archeoocytes of sponges are totipotent cells. They take part in the formation of Gemmules form new sponges.



















Fig. – A gemmule






4 3 4 2 4

3 4 1

4    3   4    2

4   3   4




Fig. – Fragmentation in microstomum (a flatworm)


  • Reproductive units in asexual reproduction : Reproductive units vary in different forms of asexual These are entire parent bodies in binary and multiple fission’s and are small parts of parent body in budding and fragmentation. An asexual reproductive unit is called blastos.
  • Characteristics of asexual reproduction : All forms of asexual reproduction have certain common basic These are under –
    • A single parent produces offspring, that is, asexual reproduction is
    • Gametes are not
    • Cell divisions are only mitotic.




  • The new individuals formed are usually genetically identical to the parent. Variability, if it occurs, is restricted to mutation
  • Multiplication occurs
  • The offspring are often formed in large numbers near the
  • Significance of asexual reproduction : Asexual reproduction brings multiplication of the species only. It does not play a role in evolution as no variation is introduced into the new individuals formed by it. Asexual reproduction is theoretically most advantageous in stable, favourable environment because it perpetuates successful genotypes

(ii) Sexual reproduction

  • Definition : It is the production of offspring usually by two parents, male and Involving four processes :
    • Formation of special haploid cells, the gametes, by (Gametogenesis)
    • Fusion of the gametes in pairs, forming diploid cells, the zygotes (Fertilization)
    • Repeated mitotic divisions of zygotes to form embryos (Embryogenesis)
    • Growth of Embryos into a new individuals (Development)
  • Sexual reproduction is also called
  • Occurrence : Sexual reproduction occurs nearly in all mammals, including those which reproduce Some protozoans, such as Amoeba, Euglena lack sexual reproduction. In most and female, and the difference between them is determined genetically. In sexual reproduction offsprings resemble the parent.
  • Types : Sexual reproduction is of two main types –
    • Amphigony (2) Parthinogenesis
  • Amphigony : It involves the complete and permanent fusion of two gametes from differents or from the same parent to form a composite cells, the It is further of two kinds :

(i) Syngamy                         (ii) Conjugation

  • Syngamy : It involves the fusion of two entire gametes to form a zygote. It is further of two types with regard to the source of fusing gametes :
  • Endogamy : It involves self-fertilization, e., the fusion of two gametes of the same parent. It is, thus uniparental. It is not common. It is found in Taenia, a tapeworm. Tapeworm is a bisexual (hermaphrodite, monoecious) animal.
  • Exogamy : It involves cross-fertilization, e., the fusion of two gametes formed by different parents. It is, thus, biparental. It is very common. It is found in frog, rabbit and man. Syngamy is also of two kinds with regard to the structure of the fusing gametes :
  • Isogamy : The fusing gametes are similar morphologically as in Monocytis, a Such gametes are known as isogametes, and their fusion is termed isogamy. Although the isogametes are similar in structure, they have behavioural differences. The gametes produced by one parent do not fuse with each other.





  • Anisogamy or Heterogamy : The fusing gametes are different in form, size structure and behaviour as in frog and humans. Such gametes are known as anisogametes, or heterogametes, and their fusion is termed anisogamy, or

Special forms of syngamy : These are two special forms of syngamy :

  • Neoteny : Development of gonads and sexual reproduction in the larval stage of an animal is called It is found in the axolotl larva of the salamander Ambystoma.
  • Polyembryony : The blastomeres formed by division of the zygote separate in early stages of development, each producing in a complete individual (fasciola liver fluke). Armadillo regularly produces four young ones per Identical twins in human beings is another example.
  • Conjugation : Some acellular protist animals (g. Paramaecium) exhibit sexual reproduction by forming male and female gamete nuclei, which they exchange through temporary cytoplasmic bridge; later, the cytoplasmic bridge disappears and the gamete nucleus of one individual fuses with that of the other to form zygote nuclei. This mode of sexual reproduction is known as conjugation.
  • Parthenogenesis (Virgin birth) : It is a modification of sexual reproduction in which an egg develops into a complete offspring without fertilization. It is monoparenta Parthinogenesis was discovered by Bonnet (1745).

Occurrence : Parthinogenesis is found in many non vertebrates such as rotifers, aphids, bees and crustaceans. It also occur in a few vertebrates.

Types : Parthenogenesis is of two main types –

  • Natural parthenogenesis : It is a regular phenomenon in the life history at some It may be three type.
  • Complete (Obligatory) parthenogenesis : Males are absent, females develop parthenogenetically, g., rotifers, Typhlina brahmina (small lizard, 15 cm long), Lacera saxicola-armeniaca (Caucasian Rock Lizard), Cnemidophorus (Whiptail Lizards of America).
  • Incomplete (cyclic) parthenogenesis : Some animals have both sexual and parthenogenetic individuals, which may In these animals, female can produce unfertilized or fertilized eggs, depending upon environmental conditions. In Daphina, a fresh water crustacean, female lays unfertilized eggs that develop parthenogenetically under favourable conditions, and fertilized eggs during times of environmental stress. In aphids, the insects pests or crops, females produce many parthenogenetic generations from unfertilized eggs alternating with a biparental generation from fertilized eggs.

In honeybee, unfertilized eggs develop into male bees (drones) with haploid cells, and fertilized eggs give rise to females (queen bees and worker bees) with diploid cells. Spermatogenesis in drones is peculiar in lacking reduction division. In turkey, about 40% males are produced by parthenogenesis whereas 60% males and all females develop from fertilized eggs.

  • Paedogenetic parthenogenesis : In certain insects, larvae lay eggs which develop parthenogenetically into a new generation of Parthenogenesis is larvae is called paedogenesis.
  • Artificial parthenogenesis : Eggs of certain animals, such as annelids, mollusks, starfish, frog, hen, rabbit, etc., can be induced to develop parthenogenetically by artificial stimuli. Artificial stimuli may be (i) physical, , prick of a needle, electric shock, change in temperature or pH; or (ii) chemical such as addition of urea, fatty acids, ether, chloroform, to water.




On the basis of chromosome sets parthinogenesis is of two types –

  • Arrhenotoky (Haploid parthenogenesis) : Haploid eggs grow to form haploid males g., Arachnids, some insects (honey bees).
  • Thelotoky (Diploid parthenogenesis) : Diploid eggs grow without fertilization in to diploid individuals, generally e.g.Gall fly.

Advantages of parthenogenesis

  • This avoids the wastage of germplasm as sperms and Adult organism is devoted exclusively to feeding and reproduction so is a mode of high reproduction e.g., aphids.
  • There is no chance of separation of useful combination of genes by crossing over and are transmitted as
  • The offsprings are exactly similar to
  • Haploid parthenogenesis is the direct proof of chromosomal theory of sex-determination.

Disadvantages of parthenogenesis : It stops the chances of new combinations of genes and thus avoids selection in population. It decreases the chances of adaptability followed by extinction.

  • Reproductive unit in sexual reproduction : The reproductive units in sexual reproduction are specialised cells called The gametes are generally of two kinds –
    • Microgametes or Spermatozoa (2) Macrogametes or Ova

Both are well developed for their role in reproduction. The male gametes are mostly minute and motile so that they may swim to the female gametes for fertilization. The female gametes are usually large, non motile and often have a store of food to nourish the developing embryo.

  • Maintenance of chromosome number : The gametes are usually formed by meiotic divisions. Therefore, they are haploid, e., have halved or reduced (n) number of chromosomes. In sexual reproduction, the male and female gametes fuse to form a single cell, the zygote formed by the fusion of two haploid gametes in naturally diploid, i.e., has double or normal number (2n) of chromosomes. The zygote gives rise to the offspring by mitotic divisions. Thus, the offspring is also diploid like its parents which formed haploid gametes by meiosis for its creation. Meiosis and fertilization are the two important events in sexual reproduction that keep the number of chromosomes constant from generation to generation.
  • Reproduction pattern : Sexual reproduction shows three patterns depending on whether fertilization and embyronic development occur within or outside the maternal body –
  • External fertilization and External development : This pattern is found in many aquatic animals, such as Obelia, Nereis, Labeo and frog. Parents release sperms and eggs into the surrounding water, where fertilization occurs and zygotes develop into offspring. For this pattern to succeed, male and female must shed their gametes at the same time and place and in large numbers. the parents may or may not make a physical contact for releasing the
  • Internal fertilization and External development : Sperms are passed from the male into the female with an intromittent organ, such as a penis as in shark and lizard, or otherwise, for example, by cloacal apposition in birds, with modified arm in cuttle fish. Internal fertilization has several The female reproductive tract provides a confines, protected place where sperm and egg can easily meet without the danger of being eaten up by predators or washed away by water currents. The zygote passing down the female reproductive tract to the exterior can acquires secretions, membranes, or shell for the protection of the developing embryo.




Animals with internal fertilization usually produce fewer zygotes because of protection provided by egg shells or internal development.

  • Internal fertilization and Internal development : Internal development provides additional advantages to the embryo. The mother’s body provides exactly the right chemical conditions and, in mammals, warmth and nourishment As the mother carries the embryo wherever she goes, it is not vulnerable to predators who attack externally developing eggs.
  • Characteristics of sexual reproduction : Sexual reproduction has the following important basic features –
    • It is generally
    • It involves formation of male and female
    • Mostly there is fusion of male and female gametes (fertilization).
    • Cell divisions are meiotic during gamete formation and mitotic during development of zygote into an
    • The offspring are not genetically identical to the They show variation as they receive characters (chromosomes) from two different parents. Sexual reproduction is, thus, a source of variety in population.
  • Significance of sexual reproduction : Sexual reproduction has a dual significance for the species –
    • It results in multiplication and perpetuation of the
    • It contributes to evolution of the species by introducing variation in a population much more rapidly than asexual

Difference between sexual and asexual reproduction


S.No. Asexual reproduction Sexual reproduction
1. It is always uniparental. It is generally biparental.
2. It invariably results in increase in the number of individuals. It may not


result in increase in the number of
3. Gametes are not formed. It always involves the formation and fusion of gametes.
4. There is no fertilization. Fertilization generally occurs.
5. It involves only mitotic cell divisions. It involves meiotic divisions during gamete formation and mitotic divisions during development of zygote into an offspring.
6. Daughter individuals are genetically identical to the parent. Daughter individuals genetically differ from the parents.
7. It occurs


in only lower invertebrates and lower It occurs nearly in all animals.
8. It contributes little to evolution. It contributes to evolution by introducing variation in offspring.
9. It often causes rapid increase in number. It causes slower increase in number.
  • Blastogenesis and Embryogenesis : Development of the offspring from reproductive units, such as buds or fragments, in asexual reproduction is called blastogenesis. Development of the embryo from the zygote in sexual reproduction is termed
  • Unisexual or dioecious : Organism in which the two sexes occur in different individuals, g., humans, mammals, birds, lizards.





  • Bisexual / Hermaphrodite or monoecious : Organism in which the two types of sex organs (testes and ovaries) occur in the same individual, g., Earthworm, Taenia.
  • Deviations in the reproductive strategies : Although asexual and sexual reproductions are the two major trends of breeding, many deviations are also observed in the reproductive strategies of One such variation in reproductive strategy in hermaphroditism, found in tapeworms and earthworms. Tapeworms are self- fertilising; the sperm produced in the testes of one individual can fertilise the eggs produced by the same individual. The earthworms employ cross, fertilisation; the sperm of one individual fertilises the eggs of the other.

Sexual dimorphism : Differentiation in morphology of the two sexes of the same species is called sexual dimorphism. Example – Ascaris, Oryctolagus and humans etc.

Human reproductive system

In human beings, reproduction takes place by sexual method and the sexes are separate. The primary sexual organs of males and females are the testes (sing. testis) and the ovaries (sing. ovary)., respectively. The males are also different from the females in the secondary sexual features or accessory sex organs. Also, the humans exhibit sexual dimorphism. For example, the mammary glands are well developed in the females are rudimentary in males; the females do not develop beard and moustache but males do; the voice in females is pitched higher than in males.

  • Sex organs : Human are unisexual. The reproductive system of each sex consists of many organs. The latter are distinguishable into primary and secondary sex Besides these, there are some accessory sex characters –
  • Primary sex organs : Gonads which form gametes are called primary sex organs – testis (plural testes) in males and ovary (plural ovaries) in females. Testis produces sperms and secrets testosterone (formation and maintenance of secondary sex organs, accessory male glands and external sex characters). Ovary produces Maturing Graffian follicles secrete estrogens for development and maintenance of secondary sex organs, accessory or external sex characters and part of menstrual cycle. Projesterone produced by ruptured Graffian follicles or corpus luteum controls a part of menstrual cycle, implantation and development of placenta.
  • Secondary sex organs : Sex organs, glands and ducts which do not produce gametes but are otherwise essential for sexual reproduction are known as secondary sex organs. In human male reproductive system, the secondary sex organs are vasa efferentia, epididymes, vasa deferentia, ejaculatory ducts, seminal vesicles, urethra, prostate glands, Cowper’s glands and penis. Secondary sex organs of a human female include fallopian tubes, uterus, vagina, external genitalia, Bartholin’s gland and mammary glands.
  • Accessory / External / Secondary sex characters : They are traits which do not have any direct role in reproduction but provide specific features and structures to the two sexes. The important external / accessory sex characters of human male are beard, moustaches, body hair on shoulder and chest, pubic hair on both lateral and vertical directions, comparatively more height with more muscular body, larynx apparent externally, voice low pitched with breathing more by means of diaphragm. The important accessory sex character of human females are high pitched voice, breast, broader pelvis, lateral pubic hair, rounded body contours with more subcutaneous fat in thighs buttocks and face and sternal
  • Puberty : Beginning of sexual maturity or ability to reproduce is known as puberty. Primary sex organs begin Secondary sex organs develop fully under the influence of sex hormones produced by primary sex organs. Growth is rapid. It is accompanied by slow development of accessory/external sexual characters. Puberty occurs at the age of 10 – 14 years in girls and 13 – 15 years in boys.

(vi)  Characteristics of human reproduction :






  • Human beings are non-seasonal breeders.
  • There is no oestrus / heat.
  • In human females the ability to produce young ones begins at menarche (beginning of menses) and ends at menopause (stoppage of menses).
  • In human females the reproductive phase has 28 day repeated menstrual
  • Fertilization is internal.
  • There is vivipary, e., giving birth to young ones.
  • Foetus develops inside uterus and is nourished by joint special structure called placenta.
  • Infants can be fed on mother’s
  • Parental care is very well

 Male reproductive system


The male reproductive system consists of a scrotum, a pair of testes, vasa efferentia, a pair of epididymis, a pair of vasa deferentia, a pair of ejaculatory ducts, a urethra, a penis and certain glands.

(i) Reproductive organ

  • Scrotum : The scrotum is a pouch of pigmented skin arising from the lower abdominal wall and hanging between the legs. Its dermis contains almost a continuous layer of smooth muscle fibres called dartos tunic. The scrotum is divided internally into right and left scrotal sacs by a muscular partition, the septum scroti. A scar like raphae marks the position of the septum externally. The testes originate in the abdominal but latter, during the seventh month of development, descend permanently into the respective scrotal sac through passages termed










































inguinal canal. If an inguinal canal remains open or is torn, a loop of intestine may descent in the scrotum to produce the disorder of inguinal hernia.

  • A spermatic cord connects testis with abdominal It

Fig. Male reproductive system (front view)





consists of connective tissue that encloses an artery, a vein, a lymph vessel, a nerve, cremaster muscle and a vas deferens. A testis rests in it chamber over pad called gubernaculum.

  • Descent of testes in scrotum provides a low temperature (of 2Cº) for maintenance of spermatogenic tissue and formation of sperms. Failure of testes to descend in scrotum is cryptorchidism, the disorder that causes sterlity because sperm formation does not occur at the abdominal
  • Men persistently wearing tight underpants or taking very


























Fig. – Testes of man






hot baths may have a reduced sperm count almost leading to infertility.

  • The scrotal sac of male homologous to female’s labia

Variations in position of testes : In some mammals (lion, bull, horse), the testes remain permanently in the scrotum and keep functioning throughout the year as in man. In certain seasonally breeding mammals, such as bat, otter and llama, (Insectivora, Tubulidentata, chiroptera and most Rodentia) the testes enlarge, become functional, and descent into the scrotum in the breeding season, but thereafter ascent into the abdominal cavity, and become reduced and inactive. In a few cases (elephant, whale, seal) the testes remain permanently in the abdomen as the body temperature is low enough for sperm maturation. Scrotum is absent in such cases. Scrotum is in front of penis in Kangaroo.

  • Testes : The testes are the primary sex organs. They are about 4 – 5 cm long, 5 cm wide and 3 cm thick. They are suspended in the scrotal sacs by spermatic cords.
    • Protective coats (Tunicae) : Each testis has three coverings – tunica vaginalis, tunica albuginea and tunica vasculosa. On one side each testis is covered by hollowed tunica vaginalis, a bilayer of peritoneum with a narrow coelomic cavity having coelomic fluid for sliding. The actual covering of testis is a fibrous connective tissue sheath called tunica albuginea. Tunica albuginea also projects inside testis to form a vertical coloumn called mediastinum and a number of transverse septa.
    • Testicular lobules : In growth of the tunica albuginea, called septa, divide the testis into some 200 to 300 lobules. Each testicular lobule contains 1 – 4 highly convoluted seminiferous tubules, blood vessels and nerve embedded in loose connective A total of about 1000 seminiferous tubules occur in each testis. Each tubule is


about 70 – 80 cm long. In seminiferous tubules lumen develop after puberty. The ends of the seminiferous tubules converge toward the middle of the posterior surface of the testis and join to form short straight tubules called tubuli recti. The tubuli recti open into a network of wider, irregular tubules called rete testis. Here some of the epithelial cells bear a single cilium to aid sperm transport.

Seminiferous tubules : Each seminiferous tubules













Fig. – T.S. A seminiferous tubule (diagrammatic)


is lined by germinal epithelium, seminiferous tubules is the site of spermatogenesis. The process occurs in waves along the length of the tubule, taking about 9 weeks (63 days) to complete in man. Seminiferous tubules contain 2 types of cells –

  • Germ cells : These are spermatogenic cells by mitotic divisions, produce spermatogonia into the lumen of the seminiferous The spermatogonia grow into primary spermatocytes which undergo meiosis, producing haploid cells, first secondary spermatocytes and then spermatids. Spermatids differentiate by a process of spermiogenesis into dimorphic haploid sperm (containing X or Y chromosome). Mature spermatozoa lie free in the cavity of the seminiferous tubules.
  • Somatic cells / Sertoli cells / Sustentacular cells / Nurse cells : These are supportive nutritive and secrete a polypeptide hormone called inhibin and a steroid estradiol which interferes with spermatogenic activity and kinetics of sperm
    • These are scattered irregularly between
    • They also phagocytose damaged germ cells and secrete enzymes for sperm maturation.





  • Rest on the basement membrane of the seminiferous tubule and its cytoplasm fills all the narrow spaces between the cells of the spermatogenic They have ovoid nucleus; exhibits deep identation and has large nucleolus. It has mitochondria, rough endoplasmic reticulum, and lipid droplets.
  • Sertoli cells is the characteristics of mammalian testis.
  • Sertoli cell acts as ‘Nurse cell’ and provide mechanical and metabolic support to developing germ
  • These cells mediate some important regulatory processes. Sertoli cells produce androgen binding protein (ABP) which serves as vector for androgen and thus generate a hormonal milieu synergistically with FSH to facilitate
  • They do not divide and thus their number is constant.
  • They are resistant to exogenous / endogenous

(3)  Leydig cells ( = Interstitial cell)

  • These are endocrine cell of testes which lie in the form of clusters or singly in the interstitum (=space between seminiferous tubules).
  • They are stimulated by LH (=ICSH) elaborated by luteotroph cells of adenohypophysis which themselves are triggered into activity by LHRH.
  • Leydig cells secrete a sex steroids called androgen by using cholesterol. The cells contain a rich repertoire of enzymes which facilitate formation of pathways for steroid biosynthesis and These enzymes are called steroid-dehydrogenases.
  • Leydig cells are large, have voluminous eosinophilic cytoplasm, lipid, vacuoles. In humans (but in no other species) they contain elongated cytoplasmic crystals called crystals of Reinke.
  • Testosterone is the principal It acts in tandem with FSH to promote spermiogenesis. During pubertal changes it plays a critical anabolic role. It facilitates differentiation of secondary sex characters (change of voice, development of penis, spermatogenic activity, formation of facial hair/beard, pubic and axillary hair, moods, libido etc.)

Rete testis : This is a plexiform arrangement (Network) of space supported by highly vascular collagenous connective tissue. It is lined by cuboidal epithelial cells some of which bear flagella whose activity assists in forward migration of testicular sperm (which are immotile at this stage).

  • The seminiferous tubules open into rete
  • Vasa efferentia : Rete testis is connected to caput epididymis by 12 – 20 fine tubules called vasa efferentia or ductuli Their lining epithelium is ciliated for conducting sperms.
    • Tubuli recti, rete testis and ductuli efferents constitutes an intertesticular genital duct system. The cells of vasa efferens are columnar ciliated.
  • Epididymis : On the inner wall of the testis, a highly coiled tubule is present called the They are two long (4 – 6 m), narrow (0.4 mm) tubules which lie compacted along the testes from their upper ends to lower back sides.

Epididymes has 3 parts

  • Upper part (Heads) : Caput epididymis or globus major.
  • Middle part : Corpus epididymis or globus norma
  • Basal part (Tail) : Cauda epididymis or globus minor.





  • In the head of epididymis, the sperms undergo physiological maturation, acquiring increased motility and fertilizing capacity. Then they pass down into the tail of the epididymis where they are stored for a short period before entering the vas
  • In epididymis the sperms are stored for a few hours to a few days till sent out through
  • Spermatozoa are produced whether ejaculation takes place or
  • The spermatozoa not ejaculated are reabsorbed in the vas
  • The epididymis shows peristaltic and segmenting contraction at intervals to push the spermatozoa away from the
  • Testis and epididymis are together called testicle.
  • Vasa deferentia (Singular-vas dererens) : The vas deferens is a continuation of the cauda epididymis. It is about 40cm. long and is slightly coiled at first but becomes straight as it enters the abdominal cavity through the inguinal cana Here, it passes over the urinary bladder, curves round the ureter and joins the duct of a seminal vesicle to form an ejaculatory duct. Near its end, the vas deferens is enlarged to form a spindle-like ampulla for the temporary storage of spermatozoa. At its distal end the ampulla receives a duct from seminal vesicle.
    • Vasa deferentia (ducti deferentes) conduct sperms from epididymis to urethra.
    • Surgical interference (vasectomy) of vas deferens ensure successful non-reversible male

Difference between Vasa efferentia and Vasa deferentia


S.No. Vasa efferentia Vasa deferentia
1. Arise from the rete testes. Arise from the cauda epididymides.
2. Vary from 15 to 20 in number. Are only 2 in number.
3. Are fine and convoluted Are thick slightly coiled in the scrotum, straight in the abdomen
4. Lining bears many ciliated cells. Lining has sterocilia on many cells.
5. Carry spermatozoa from rete testes to caput epididymides Carry spermatozoa from cauda epididymides to ejaculatory ducts.
  • Ejaculatory ducts : They are short (2 cm) straight muscular tubes each formed by union of a vas deferens and duct of seminal vesicle where ejaculate is formed by mixing of sperms with secretion of seminal The two ejaculatory ducts join the urethra within prostate gland.
  • Urethra : It is the urinary duct leading from the bladder. From the point it is joined by ejaculatory ducts, it carries urine as well as spermatozoa and secretions of the seminal vesicles. It also receives secretion of the prostate and cowper’s Urethra is some 20cm long and passes through the penis. The urethra has 4 regions –
    • Urinary urethra : It carries only urine.
    • Prostatic urethra : It is a short proximal part which is surrounded by prostate gland.
    • Membranous urethra : It is a short middle part, without any covering.
    • Penile urethra : It is a long distal part that passes through the penis.
    • The penile part is also called spongiose urethra because it lies inside corpus spongiosum.
    • Epididymis, vasa deferentia and urethra transport sperms towards penile meatus or They are collectively called excretory genital ducts.
    • The urethra opens out at the tip of the
    • The urethra has 2 sphincters : Internal sphincter of smooth muscle fibres at its beginning and external sphincter of striated muscle fibres around its membranous






  • Penis : The penis is an erectile copulatory organ. It consist of a long shaft that enlarges to form an expanded tip, the glans penis. It is covered by a loose, retractable fold of skin, the prepuce or foreskin. Under the skin, the penis contains three columns of erectile tissue : two cylinders of the corpora cavernosa of the penis, placed dorsally, and one cylinder, the corpus spongiosum, along the ventral side. The corpora cavernosa of the penis and the urethra are covered by dense connective tissue, the tunica albuginea. Both urine and semen are carried out of the body through the penis.
    • Prominent blood vessels are present in these erectile These vessels are thick walled and have arteries and arteriole called helicine arteries (since they follow a spiral course in flaccid state). During erection dilation of these vessels causes enlargements of corpora cavernosum.












Fig. – T.S. penis


  • Penis is made up of fibrous connective tissue endoskeleton is absent in But in penis of some animals a bone is present called Baculum and such penis is called Osso-penis. Example – Whale, Bat, Rat, etc.
  • The penis of opposum, bandicoot is doubled branched.

Sperm storage : Sperms are stored for the most part in the vasa efferentia, epididymes and proximal parts of vasa deferentia.


  • Accessory sex glands : The substances secreted by the accessory, sex glands help in reproduction these are –
  • Seminal vesicles : The seminal vesicles are long pouches with muscular wall; they secrete spermatozoa activating substances, such as fructose, citrate, inositol, prostaglandins and several proteins, sperms use fructose as a respiratory substrate. Seminal fluid maintains viability and motility of sperms.



























  • Seminal vesicle secretes a nutritive fluid which forms main part e. 60 – 80% of the semen.


Fig. – Male reproductive organs


  • It is also called uterus-masculinus. It forms from the mullerian duct of the embryo. In females, these ducts form the ovi-ducts.
  • The seminal vesicle do not store sperms.
  • Seminal vesicles are found between urinary bladder and

Test for rape : Fructose, which is present in the seminal fluid and is not produced anywhere else in the body, provides a forensic test for rape. Its presence in the female’s genital tract confirms sexual intercourse.




  • Prostate gland : The prostate gland surrounds the first portion of the urethra. This gland secretes an alkaline fluid which forms 15 – 30% part of the The secretion nourish and activates the spermatozoa to swim. It is essential for sperm motility (removal causes sterlity).
    • In the secretion of prostate–gland citric acid, calcium and phosphate, Fibrinogen and Fibrinolysin is present. The secretion of the prostate gland combines with the secretion of seminal vesicle and so the semen gets In the coagulated semen, the mobality of sperms is reduced and so their energy is conserved. After sometime due to fibrinolysins, semen again liquefies and in this semen now the sperms can move.
  • Cowper’s glands : These are also termed as Bulbourethral glands. 1st pair of Cowper’s glands are attached to They secrete alkaline mucus which is discharged into the membranous part of urethra. The mucus lubricates the reproductive tract. This serves to neutralize any acid of urine remaining in the urethra. Secretion of Cowper’s glands is produced before the ejaculation of semen.

Secretion of Cowper’s glands carries some spermatozoa released before ejaculation. This is one of the reasons for the high failure rate of the withdrawal method of birth control.

  • Perineal or Rectal glands : These are found both in males and females during the breeding season, these glands secrete and odoriferous liquid which has pheromones or Ectohormones in it. Its smell attracts the animal of opposite sex.
Note :

In man, Perineal or Rectal glands are absent.

  • Other glands : Prepuce contains preputial glands which produce a sebaceous substance which together with desquamated epidermal cells forms a whitish, pasty, foul-smelling accumulation, called smegma, about the base of the glans penis beneath the
  • Semen : The products of the testes (spermatozoa) and prostate gland, alongwith fluid from the seminal vesicle, are collectively knows as semen. Release of spermatozoa from urethra is known as ejaculation.
    • It is a milky, viscus and alkaline (pH 3 – 7.5) fluid ejaculated by male reproductive system during orgasm. The volume of ejaculate varies from person to person. Abstinence play a role in this. Each ejaculate measures 3.5 ml and contains 50 – 150 million sperm/ml i.e. 250 million – 525 million (average – 400 million).
    • Nearly 25% of these sperms have abnormal shapes, lack motility. The life span of human sperm after ejaculation is 24 – 48 hrs. Crayopreservation enhances the longevity of sperm. The rate of active moment of sperm is 5 – 3.0 mm per minute in uterine endometrium.
    • Semen has chemicals for nourishing the sperms (g. fructose), neutralizing the acidity of urethra and vagina (e.g.bicarbonate), stimulating movements in female tract (e.g.prostaglandins). pH of semen – 7.35 – 7.55.
    • Testicular sperm cannot fertilize ovum. They undergo maturational changes in epididymal segment and acquire fertilizing ability (capacitation). However, these sperm are masked by decapacitation factor (protein) when deposited in vagina of female, this mask is dissolved and they re-acquired fertilising ability (second phase of capacitation).





A person with a sperm count below 20 million will be physiologically sterlile. Fusion of defective sperm (e.g. 22+xy) with ovum causes many birth defects e.g. klinefelter’s syndrome.

  • Penis conducts urine as well as But the two cannot pass through it at the same time.
  • Sperm can survive in the female reproductive tract for 1 to 3 days.
  • Hormonal control of male reproductive system : The growth, maintenance and functions of secondary sex organs (epididymis, vasa deferentia, accessory glands and penis) are under the control of testosterone hormone secreted by Leydig’s cells of testis, while those of seminiferous tubules and Leydig’s cells are controlled by Follicular Stimulating Hormone (FSH) and Interstitial Cells Stimulating Hormone (ICSH) of anterior pituitary lobe respectively.

Sertoli cells also secretes two proteins



  • Androgen Binding Protein (ABP) that concenterates testosterone in the seminiferous
  • (Inhibin) protein which suppress FSH Release of FSH, LH or ICSH, in turn, are controlled by release of hypothalamic













gonadotropin releasing hormone (GnRH).

Fig. – Hormonal control of male reproductive system


  • Onset of puberty in the male : Puberty is the period when reproductive organs become functional. It is triggered by the secretion of the hormone testosterone in the testes. This hormone brings about growth and maturation of the secondary sex organs and development of the accessory sex characters. The latter induce –
  • Enlargement of the penis and
  • Broadening of the shoulders.
  • Growth of body and facial
  • Deepening of the voice duce enlargement of layrnx and thickening of vocal-cords.
  • Increased development of musculature and bones.
  • Increase in height so characteristic of male
  • Male sex act : The male sex act involves 3 phases : erection of the penis, copulation (often called sexual intercourse in humans) and subsidence of
  • Erection : Erection of the penis is caused by rush of arterial blood into the empty sinuses of its spongy tissue on sexual excitement. As the spongy tissue distends, it compress the veins, inhibiting the flow of blood out of the tissue. Filling of tissue with blood is called vasocongenstion. Erection makes the penis long and stiff for entry into the female’s vagina for Stiffness is due entirely to the hydraulic pressure of blood filling the sinuses.






  • Copulation : Mucus from the urethral glands, Cowper’s glands and vaginal glands provides lubrication for Friction due to rhythmic movements of sexual intercourse stimulate the sensory cells of the glans penis. This stimulation releases semen into the proximal part of urethra by contraction of reproductive glands and ducts. This process is called emission. Then the rhythmic, wavelike contractions of the muscles at the base of the penis cause forceful discharge, called ejaculation, of semen into the vagina. One ejaculate (about 3 ml.) contains 200 to 400 million spermatozoa. Ejaculation marks the climax of copulation.

Orgasm : At the peak of sexual stimulation, pleasurable sensation, called orgasm, occurs. It usually last only a few seconds.

  • Subsidence of erection : After ejaculation, the arterioles to the penis contract, reducing the blood flow to the penis, and erection This often takes a few minutes.
  • Movement of spermatozoa to site of fertilization : In the female genital tract, alkalinity of the semen helps neutrilize acidity in the vagina. This protects the sperms and increase their motility, prostaglandins of the semen thin the mucus at the opening of the uterus, and also stimulate contractions of the uterine These contractions help the semen move up the uterus called syring absorption mechanism. When ejaculated, the semen first coagulates, making it easier for uterine contractions to push up; and is then liquefied by the anticoagulating enzymes, enabling the sperms to start swimming in the uterus. From here, they reach the oviduct. In the oviduct, the spermatozoa are capacitated (attain the ability to penetrate the ovum). Somewhere in the ampulla of the oviduct, an ovum, if present, may be fertilized by a sperm, and procreation of the special starts.
  • Disorders of male reproductive system : Only a few are
  • Prostatomegaly (Prostatic hypertrophy) : This is enlargement of prostate gland. If often occurs in old


age. The enlarged gland may block the urethra, causing frequent night urination (nocturia) or difficult or painful micturition. Prostate cancer is very common in men. It is treated surgically or with drugs.

  • Impotence : This is inability of the male to achieve and or maintain erection of the penis long enough to engage in or complete
  • Sterility : Inability of the male’s sperm to fertilized the ovum, it may or may not be associated with Sterlity also results from immobility and morphological abnormality of the sperms, and

from low sperm count in the semen.
























Fig. – Human female reproductive system

 Female reproductive system

The female reproductive system consists of a pair of ovaries, a pair of fallopian tubes, uterus, vagina, external genitalia or vulva and breasts.

(i) Reproductive organ

  • Ovaries : Ovaries are the primary sex organs of
    • Size and form : The ovaries are almond shaped bodies, about 3 cm long, 5 cm wide and 1 cm thick.






  • Role : The ovaries, like the tests, have both an exocrine function (production of ova) and an endocrine role (secretion of female sex hormones : estrogen and progesterone). After menupause, the ovaries become small and lose
  • Location : Each ovary is located close to the lateral walls of the pelvic cavity, being suspended from the dorsal body wall just behind the kidney, by a section of peritonium, the mesovarium. It is held in position by several connective tissue Each ovary is connected by an ovarian ligamemt to the uterus, and by a suspensory ligament to the lateral pelvic wall. It has hilus where nerves and blood vessels are connected.
  • Structure : Each ovary is a compact or solid organ, consisting of an outer cortex and inner medulla. The


stroma of the cortical region is composed of spindle      shaped          fibroblasts.    A        poorly





delineated dense connective tissue layer, the

tunica albuginea, covers the cortex. It imparts the whitish colour to the ovary. Located outside the tunica albuginea, the germinal epithelium, formed of simple squamous or cuboidal epethelial cells, covers the surface of the ovary.

Cells of germinal epithelium give rise to groups of oogonia that project into cortex as cords called egg tubes of Pfluger, each with a round terminal mass of oogonia called egg

nest. Egg nests give rise to ovarian follicles. In




























neonate female baby the ovary contains about 2 million follicles but 50% of them are






atretic or degenerate. Atresia continues and

Fig. – L.S. human ovary


by the time of puberty some 3,00,000 – 4,00,000 ovarian follicles are present in an ovary. However, only 450 ovarian follicloes mature, one by one alternately in the two ovaries at intervals of 28 days. A mature ovarian follicle is called Graffian follicle. It has a diameter of 10 mm. Outer fibrous theca externa and inner cellular theca interna are derived from spindle cells of cortex. Estrogen secreted by the internal theca of graffian follicle. Other constituents are follicular cells (nourishing cells formed from undifferentiated oogonia), an antrum or follicular cavity having liquor folliculi and an eccentrically placed oocyte. Follicular cells form a cellular sheath (below theca interna) called


membrane granulosa and cellular mass called cumulus ovaricus covering the oocyte. Cumulus oophorus or cumulus ovaricus differentiates into outer discus proligerous and inner corona radiata. Alongwith oocyte it also secretes a mucoprotein membrane called zona pellucida. Oocyte (secondary oocyte with metaphase of meiosis II) is 50 – 100 mm. It is microlecithal (alecithal according to some workers). Oocyte membrane is called vitelline membrane. There are three coverings around the egg – inner zona pellucida, middle corona radiata and outer discus proligerous. A polar body is found between viteline membrane and zona pellucida. Graffian follicle develops under influence of FSH of anterior pituitary. Its follicular cells secrete estrogen. Estrogen brings about proliferation













of lining layer of uterus, vagina and fallopian tubes. Rising level of

Fig. – Matured graffian follicle






estrogen decreases production of FSH and stimulates secretion of LH. The two cause the mature Graffian follicle to rise to the ovarian surface and burst open releasing ovum (ovulation). It occurs 10 – 14 days of mestrual cycle. The empty ruptured Graffian follicle is called corpus haemorrhagic. It usually contains a blood clot. The ruptured follicle shows proliferation of cells of membrana granulosa, deposition of yellow pigment or luteum and formation of yellow body called corpus luteum. It grown in size to about 2.5 cm. Corpus luteum secretes progesterone Ultimately corpus luteum loses its yellow colour, becomes changed to corpus albicans and then degenerates. Some thecal cells located around the follicle become active interstial cells which secrete small amount of androgen.

  • Fallopian tubes / Uterine tubes / Oviducts : Each ovary is located in front of a funnel shaped opening of the uterus, the The oviduct is a muscular tube, measuring about 12 cm in length. Its lumen is lined by ciliated epithelium.
    • Oviducts develop from the mullarian duct of the
    • It conveys the egg from the ovary to the uterus, and provides the appropriate environment for its fertilization.
    • It is supported by a double fold of peritoneum called mesosalpinx.
    • The wall of oviduct is made of three layers –
  • Serosa : It is the outermost layer of visceral-peritoneum.
  • Muscle-layer : The middle layer of the oviduct is made up of unstriped-muscle.
  • Mucous membrane : It is the innermost This layer is made up of ciliated epithelium and the connective tissue.


The oviduct shows 4 regions –





  • Infundibulum : It is the broad, funnel-shaped proximal part. Its margin bears motile, finger-like processes called fimbriae. It opens into the body cavity by an aperture called ostium. The latter lies close to the ovary to receive the egg released from the ovary. The fimbriae bear cilia which beat toward the ostium













to direct the egg into the infundibulum.

  • Ampulla : It is the long, wide, thin-walled, tortuous major part of the fallopian tube next to the
  • Isthmus : It is the very short,















narrow, thick-walled, straight part that follows the ampulla.

Fig. – Female reproductive system


  • Uterine part : It is also narrow and passes through the uterine wall, and communicates with the uterine
    • The oviduct is ciliated usually in its ampullary Eggs are propelled along the oviduct by peristaltic and ciliary action.
    • The oviducts open into the upper corners, the cornua (singular-conru), of the

In most vertebrates both the ovaries and oviducts are functional. In birds the right ovary and right oviduct are atrophied (Degenerated). Being nonmammalian, the birds also lack mammalian sex organs and characters like uterus, external genitalia and mammary glands.





(c)  Uterus

  • Structure of uterus : It is pyriform, hollow muscular thick-walled but distensible median structure located above and behind urinary bladder that is meant for nourishing and development of foetus. For this uterus is capable of tremendous enlargement. The empty uterus is 5 cm long and 5 cm broad and 2.5 cm thick. Lining layer of uterus, called endometrium (mucous membrane), consists of an epithelium and lamina propria of connective tissue. Epithelium is a mixture ciliated and secretory columnar cells. Lamina propria contains tubular glands, fibroblasts and blood vessels.
    • It is attached to the body wall by a double fold of peritoneum, the mesometrium (broad-ligament). It varies in In a nulliparous woman (who has not borne any child), It is about 8 cm long, 5 cm wide and 2 cm thick. It is some what larger in a multiparous woman (who has borne two or more child).

It has four regions –

  • Upper wide, domeshaped fundus that receives the fallopian tubes.
  • Cornua, the upper corners where the oviducts enter the
  • Middle large body or corpus which is the main
  • Lower narrow cervix that projects into the vagina. The cervix communicates above with the body of the uterus by an aperture, the internal os, and with the vagina below by an opening, the external os.

The line demarcating the body and the cervix is called isthmus. It corresponds to the internal os.

The uterus has a thick, highly vascular wall composed of three tissues : outer peritoneal covering called perimetrium, middle smooth muscle layer termed myometrium, and inner mucous membrane known as endometrium. Longest unstriped muscles of the body are found in the walls of uterus.

  • Antiflexion : The normal position of the uterus is anteflexed, that is, it is bent forward on itself at the level of the internal os so as to lie almost horizontally over the bladder. The cervix is composed largely of the biggest and the most powerful sphincter muscle in the It is strong enough to hold about 7 kg. of foetus and fluid in the uterus against the pull of gravity during pregnancy.
  • Capacity of uterus : The cavity of the uterus can expand 500 times during pregnancy, from 10 cm3 to 5,000 cm3.

(4)  Types of uterus

  • Duplex : These are the simplest type of In it both the uteri are completely separated and open independently into the vagina through two separate openings e.g. Rat.
  • Biparite : In these uteri, the lower part of the two uteri are fused and there is a septa in between the two,

e.g., Carnivore mammals.

  • Bicornuate : The lower parts of the 2 uteri are fused with each other but the partition wall is absent, g. Rabbit.
  • Simplex : When both the uteri are completely fused with each-other to form only one structure, these are the most developed uteri g. Man.
  • Functions of uterus : The uterus plays multiple It receives the ovum from the fallopian tubes, forms placenta for the development of the foetus and expels the young one at birth.
  • Vagina : It is tubular female copulatory organ, passageway for menstrual flow as well as birth canal of about 7 – 9 cm length between external opening (vaginal orifice) in vestibule and cervix with depression or fornix





around cervix, two longitudinal ridges and numerous transverse folds or vaginal rugae. Vaginal wall is made of an internal mucosa, muscular layer and an outer adventitia. Its mucous membrane is nonkeratinised stratified squamous epithelium. Glands are absent. However, cervical glands do pass on some mucus into it during ovulation. the epithelial cells contain glycogen (from puberty to menopause) which shows cyclic changes. Certain bacteria (species of Lactobacillus and Lactoneustroc, also called Doderlein’s Bacillus) bring about fermentation and produce acid which inhibits growth of other microorganisms. In virgins the vaginal orifice is partially covered by an annular centrally perforate membrane called hymen.

  • External genitalia / vulva : There is a depression, the


vestibule, in front of the anus. It is flanked by two pairs of fleshy folds of skin : the inner small, thin, moist, labia minora and outer larger, hair-covered labia majora. All the labial folds have numerous sebaceous and sweat glands on both sides. A small erectile organ, the clitoris, lies at the anterior junction of the labia minora. It is homologous to the penis in the male but is very small and solid, having no passage through it. It consists of a short shaft with erectile tissue. It ends in a rounded glans












clitoridis. The latter is covered by a small hook of skin, the prepuce. Rubbing of clitoris during intercourse produces a

Fig. – Female external genitalia vulva


pleasurable sensation. This seems to be its only function. A membranous fold, called fourchette, connects the posterior ends of the labia minora. The area between the fourchette and the anus is termed perineum. Urethra and vagina open by separate apertures, the upper urethral and lower vaginal orifices, into the vestibule. The vaginal orifice is normally covered in the virgin by a membrane, the hymen. A slit in the hymen allows menstrual flow to pass out. The hymen is ruptured during first copulation, or due to some other reason. The hymen presumably has a protective role, but is absent in many women. A fleshy elevation above the labia major is known as mons veneris or mons pubis. It bears pubic hair.

  • Bartholins or vestibular glands : They are a pair of small glands which open in the vestibule lateral to vaginal orifice. The secretion is thick, viscid and alkaline for lubrication and counteracting urinary acidity (similar to Cowper’s glands in males).


  • Breasts / Mammary glands : The breasts are rounded eminences located over the pectoral muscles on the front wall of the These enlarge considerably in the adult female. Each breast has near its middle a nipple surrounded by a circular, pigmented (deep pink to brown) area called areola. The breasts contain fatty and connective tissues and mammary (milk) glands. The latter are compound saccular glands and are modified sweat glands. The connective tissue supports the mammary glands and the adipose tissue covers them. The glands open on the nipples, the lactiferous ducts. Just under the nipples, the lactiferous ducts widen to form lactiferous sinuses, to store milk during lactation. A nursing mother produces 1 to 2 litres of milk per day.






















  • Milk secretion is under the control of prolactin (of anterior pituitary) while milk ejection is under control of oxytocin

Fig. – Human female mammary gland






(of posterior pituitary).

  • First or premilk after parturition is called colustrum.
  • Each mammary gland consists of 15 – 25 lobules of the compound tubulo alveolar type. The lobules secrete
  • In a nonpregnant woman, the glandular tissue is scanty. During pregnancy, the glands grow under the influence of oestrogen and progesterone. On the infant’s birth, the hormone prolactin stimulates the production of milk and the hormone oxytocin causes release of milk as the infant sucks the breast. After menopause, the glands
  • Rudimentary milk glands are present in the male also. Low level of estrogen in males checks the development of secretory tissue as well as fat
  • Onset of puberty in the females : Woman attains puberty about the age of Its onset it triggered by the production of the anterior pituitary’s follicle-stimulating hormone (FSH) which promotes growth of the ovarian follicles. The follicles then secrete the hormone estrogen from the follicle cells in the ovaries. This hormone brings about the growth and maturation of the reproductive tract and the development of accessory sex character. The latter include growth of breasts and external genitalia, broadening of pelvis, growth of pubic and axillary hair, increase in the subcutaneous fat, particularly in thighs, shoulders, buttocks and face to give a typical feminine contour and initiation of menstruation and ovulation.
  • Hormonal control of female reproductive system : Ovary is regulated by pituitary gonadotropins or Gn Anterior


pituitary secretes follicular stimulating hormone (FSH) which controls of the transformation of young primary follicle into Graffian follicle, maturation of ovum and secretion of estrogens by its follicular cells. The Luteinizing Hormone (LH) of anterior pituitary regulates the ovulation from the Graffian follicle, transformation of empty Graffian follicle into yellowish, conical corpus luteum and secretion of progesterone hormone from the corpus luteum.

       Growth and function of secondary sex organs are regulated by estrogens and








Fig. – Hormonal control of female reproductive system



progesterone. Estrogens control the growth, maintenance and functioning of secondary sex organs of female. Progesterone suspends ovulation during pregnancy, promotes implantation of foetus on the endometrium and development of foetus in the uterus.

At the end of pregnancy, the corpus luteum secretes relaxin which broadens the pelvis for easy parturition.

  • Reproductive cycle in female : The events involved in reproduction in female mammals occur in a cyclic Constituting the reproductive cycle or ovarian cycle. The reproductive cycle is of two types :
  • Oestrous cycle (b) Menstrual cycle

Oestrous cycle : The oestrous cycle consists of a few days of oestrus or “heat” followed by a few days of anoestrus of “quiescence”.

  • During oestrus, the female is sexually responsive, allows a male to copulate, eggs are released and pregnancy is
  • During anoestrus, the female become passive and does not accept a






  • The oestrus occurs in most species of mammals. Many mammals reproduce in the breeding season The oestrus cycles run only during the breeding season in these mammals and anoestrus spreads over the entire non breeding season.
  • Except primates, oestrous cycle is found in all mammals.
  • Some mammals, such a cow and buffalo experience oestrous cycles throughout the year. They have no specific breeding
  • In rabbit the oestrous cycle is of 7 days.
  • Oestrous cycle of rat is of 5 days only.
  • Dog has one cycle per year.
  • Oestrous is also found in the new-age monkeys.
  • During the oestrous-cycle, the wall of uterus does not dissolve e. no bleeding takes place.
  • Mono – oestrous animals : In the breeding period of some animals only one oestrous cycle is

e.g. Rabbit, Hare, Dog, Fox, Bat, Deer etc.

  • Poly Oestrous animals : In many animals many oestrous cycles are found in the breeding e.g. Rats squirrels, Cow, Sheep, Pig, Horse etc.
  • Menstrual cycle : The gamete formation in females is a cyclic activity that takes about 28 days and


involves changes in the structure and function of the entire reproductive system. It is called menstrual cycle.

  • The menstrual cycle occur only in primates.
  • Period : The length of menstrual cycle varies widely in women, but on average it is completed in 28 days (mensem means a month). In a female, successive cycles may vary in length by 1 to 2 It is absent during pregnancy, may be













suppressed during lactation and permanently stops at menopause.

  • Phase : Menstrual cycle is divided into four phases –
    • Follicular (Proliferative) phase or Post-menstrual or Pre-ovulatory phase : It follows the menstrual phase and lasts for about 10 – 12 days (from 5th to 14th day of menstrual cycle). It involves following changes :












  • Under the stimulation of FSH-RF of hypothalamus, there is increased secretion of FSH from anterior
  • FSH stimulates the change of a primary follicle of the ovary into a Graffian follicle.
  • Follicular cells of Graffian follicle secrete estrogens. Estrogens have the following effects :
  • Stimulate the growth, maintenance and normal functioning of secondary sex
  • Uterne endometrium becomes thick (about 2-3 mm thick), more vascular and more glandular cork-screw shaped. So it prepares itself for



























Fig. Sexual cycle


  • The epithelium of Fallopian tubes becomes thick and densely ciliated to conduct the ovum /
  • Inhibit the secretion of FSH and stimulate the secretion of luteinising hormone (LH) from the anterior pituitary.
  • Glycogen and fat accumulate in the endometrial cells.











  • Ovulatory phase or fertility phase : It involves the ovulation from the Graffian follicle of ovary. The mature graffian follicle rises to the surface of the ovary and ruptures

to release ovum. The phenomina is called ovulation. It occurs midway between two menstrual cycles on 14th day of the onset of the menstrual cycle. it is caused by increasing turgidity and contraction of smooth muscles fibres around the Graffian follicle.


Ovum is received by the fimbriad of the fallopian tube. Ovum is

viable for two days. Ovulation is controlled by the increased level of LH in the blood. Egg at that time is in the secondary oocyte state.


LH also starts the change of empty Graffian follicle into corpus











luteum and secretion of progesterone from corpus. There is no much change in uterine endometrium during ovulatory phase. In animals the ovulation follow three patterns –

Fig. – Graphical representation of menstrual cycle


  • Fix or spontaneous ovulators : In these animals ovulation takes place a fix time in the midway of There is no need of coitus for ovulation. e.g. Primates (Human, Ape and Monkey)
  • Induced or reflex ovulators : In these animals copulation or ciotus is necessary for e.g. – Rabbit.
  • Seasonal ovulators : Ovulation occur in breeding season g. – Frog.
    • Luteal or progestational or Pre-menstrual or Secretory or Post-ovulatory phase : It lasts for about 12 – 14 days and extends from 16th to 28th day of menstrual It is characterised by following changes –
  • Corpus luteum (Yellow body) : Formed from empty Graffian follicle, increase in size, so is called luteal
  • Corpus luteum begins to secrete hormone called The latter reaches its peak about 22nd day after the beginning of cycle.
    • Progesterone induce following changes –
  • Decreases the secretion of FSH and LH (gonadotropins) from anterior pituitary so inhibits the maturation of follicle and ovulation.
  • Uterine endometrium further proliferates (about 5 mm thick) and is ready for Uterine glands secrete Uterine milk for the foetus.
  • Reduces the uterine
    • In the absence of fertilization, corpus luteum degenerates LH levels Progesterone level is reduced.


Reduced level of both progesterone and estrogen causes mensus.


3      4           5       6

2                                       7

1                                                    8


(iv)   Menstrual phase or bleeding phase : It

st          th

28           MENSTRUAL PHASE

POST                9



lasts for about 3 – 5 days and extends from 1 to 4  

day of the menstrual cycle. When the ovum remains unfertilized, then the corpus luteum starts degenerating. The level of progesterone in the blood declines. The uterine tissues fail to be maintained. Then the unfertilized ovum along with ruptured uterine epithelium, about 50 – 100 ml of blood and












25               PHASE


























some mucus is discharged out through the vaginal


20    19


18    17





orifice and is called menstrual flow or menstruation.

Decrease in the level of progesterone and estrogens in the blood stimulates the hypothalamus and anterior pituitary to release FSH-RF and FSH respectively (Positive feedback). FSH starts the follicular phase of next menstrual cycle.

  • Effect of fertilization : If fertilization occurs and foetus is implanted in the endometrium, the trophoblast cells of the developing placenta secrete a hormone human chorionic gonadotrophin (hCG). This hormone, like LH, maintains the corpus luteum and the secretion of progesterone and estradiol by it. These two hormones check the breakdown of the endometrium of the uterus. the absence of menstrual bleeding (the ‘period’) is the earliest sign of By the 16th week of pregnancy, the placenta produces enough progesterone and estradiol for a normal pregnancy, and the now unnecessary corpus luteum undergoes shrinkage.
  • Miscarriage : Prematuredegeneration of corpus luteum is the common cause of miscarriage at about 10 – 12 weak of pregnancy (miscarriage means abortion)

(5)  Menopause (Climacteric period)

Definition : It is the period when ovulation and menstrual cycle stop in human female.

Period : Between 45 to 55 years. The average period of menopause is currently 52 years. In some, this occurs gradually (in between a period of 1-5 years) while in some this occur abruptly.

Characters : Menopause is characterized by hot flushes (sensation of warmth spreading from the trunk to the face) and a number of psychic symptoms. FSH is secreted in the urine.

Note    :

Cause : Decline in the estrogen level.

  • The function of the testes


declines slowly with advancing age, especially in their late 40 yrs or 50 yrs due to decrease in testosterone secretion and is called male climacteric.

(v)   Disorders of female reproductive








GERM CELL                 2n



2n                                           2n



  • Sterlity : Inability of the female to conceive, due to inadequacy in structure or function of the genital

(b)  Menstrual irregularity

  • Amenorrhoea :       Absence   of

2n                        2n






2n                        2n











  • Hypermenorrhoea : Excessive or prolonged bleeding of


n                                             n




  • Dysmenorrhoea :  Painful
    • Pregnancy test : During pregnancy, HCG may be detected in the urine, and this forms the basis of pregnancy
  • Oral contraceptive checks ovulation

n                          n                 n                          n







Fig. – Spermatogenesis


and implantation (for more information see endocrine system).






The process of the formation of haploid gametes from the undifferentiated, diploid germ cells in the gonads for sexual reproduction is called gametogenesis.

  • As a result of this process, male gamete sperm and female gamete egg is
  • The process of Gametogenesis is stimulated by the FSH or Follicle Stimulating Hormone and for this process Vitamin “A” and “E” are also
  • The process of Gametogenesis has been divided into 3 substages –
    • Multiplication
    • Growth
    • Maturation

Types of gametogenesis

  • Spermatogenesis
  • The process of formation of sperms in the germinal-epithelium of the testis of the male animal is termed as spermatogenesis.
  • In mammals, testis have several coiled tubules in it called the seminiferous tubules.
  • Sperms are formed in these The inner wall of seminiferous tubules is made up of germinal epithelium whose cells are cuboidal.
  • Some special cells are present in this germinal epithelium which are called the primordial germ cells. Due to the division of these cells sperms are
  • Some large cells are also found in this germinal These are called the “Sertoli cells or Subtentacular cells“.
  • These cells provide nutrition to the maturing sperms in the form of Glycogen.
  • For getting nutrition, the head of the sperms are submerged in the cytoplasm of sertoli cells.
  • When sperms fully mature, they move away from sertoli cells and get liberated in the cavity of seminiferous
  • Liberation of sperms from sertoli cells is termed as Spermiation.
  • Liberation of sperms from the testis is termed as Semination.
  • Liberation of sperms into the vagina of the female is termed as Insemination.
  • Sertoli cells are also endocrine in nature and they secrete 2 hormones –

AMH (Anti Mullarian Hormone) : This hormone stimulates degradation of female gonads in a male embryo.

Inhibine hormone : This hormone is secreted in adult stages and it stops the secretion or FSH.

  • Sertoli cells mainly provide nutrition and conserve the various stages of Spermatogenesis is a continuous process. To make it easier for study, it has been divided into the following steps –
  • Formation of
  • Spermiogenesis or





  • Formation of spermatids : This process begins as the animal attains sexual maturity. The cells of the germinal epithelium of the seminiferous tubules which participate in this process are termed as the primordial germ cells. The process of formation of spermatids from primordial germ cells are termed as spermatocytosis. It has 3 sub-stages –
    • Multiplication phase : During this process the primordial germ cells repeatedly undergo mitosis division, and as a result of these divisions spermatogonia are formed spermatogonia are diploid.
    • Growth phase : Some spermatogonia either due to growth or due to food storage become 2 or 3 times of their original size, and are now known as primary spermatocytes. The remaining spermatogonia remain in the seminiferous tubules in the form of reserved The primary – spermatocytes formed during the growth phase are diploid. Growth phase is the longest.
    • Maturation phase : Primary – spermatocytes undergo Meiosis-I and as a result 2 haploid secondary spermatocytes are formed. This division is termed as First Maturation Division or Reductional division. Secondary spermatocytes undergo Meiosis II or equational division, and as result, 2 spermatids are formed from each secondary Thus, from 1 diploid primary spermatocytes 2 secondary spermatocytes are formed on meiosis I and from 2 haploid secondary spermatocytes 4 spermatids are formed on meiosis-II. Metamorphosis of spermatids into sperms in known as Spermiogenesis or Spermatoliosis.
  • Spermatoliosis : The process of transformation of a round non-motile and haploid spermatid obtained from spermatocytosis into thread-like, motile and haploid sperm is termed as spermatoliosis. From different parts of the spermatid different parts of the sperm are These are as follows –
  • From nucleus and glogibody -> Head part
  • From mitochondria -> Middle part
  • From distal centriole -> Tail
  • The structure of the head of the sperm mainly depends on the structure of the nucleus. During spermatoliosis, nucleus contracts and acquires different
  • RNA and nucleolus disappear from nucleus or their major part is given out from the nucleus. DNA also contracts / shrinks e. now the nucleus contains only those materials which are responsible for the hereditery characters.
  • Centrosome divides into 2 centrioles e. 1 distal and 1 proximal centriole.
  • Many golgi-bodies aggregate on the posterior side and their vacuoles enlarge.
  • In some vacuoles of the golgi-bodies. Some dense-bodies can be seen, which are termed as Acroblast.
  • In any one vacuole the Acroblast enlarges by aggregating with These are termed as “Acrosomal Granules”.
  • The rest part of the golgi-body is given out and this is termed as Golgi-rest.
  • This acroblast reaches the anterior most tip of the sperm and acquires a cap shaped structure on the nucleus which is termed as the Acrosome.
  • Acrosome is surrounded by a double membrane e. the tonoplast and cell-membrane.
  • The acrosome along with this membrane is termed as Galea-capatis. Acrosome, at the tip of the nucleus has an important role in breaking the egg.






  • Mitochondria from different parts of spermatid, collect around the growing axonema and form a dense In mammals, they form a spiral structure called Nebenkern sheath. In other animals, they collect and form mitochondrial clumps.
  • The part of the axonema surrounded by mitochondria is known as Middle-piece.
  • Around the middle-piece cytoplasm is present in the form of a thin layer called Manchette.
  • Behind the middle piece, axonema surrounded only by plasmalemma is This is called the tail part.
  • Shape of the sperm is so that it can move easily in a liquid
  • Structures and functions of sperms parts –
    • Acrosome : Breaking the egg
    • Middle piece : For providing energy
    • Tail :     For locomotion

Above structures are formed during spermatoliosis and the remaining substances are given out in the form of cytoplasmic residue, which is ingested by the “Cells of Sertoli”.

  • Structure of sperm : Structure of sperm has three parts

(a) Head          (b) Middle piece        (c) Tail

  • Head : It is flat ant oval in human It is composed of a large posterior nucleus and a small anterior acrosome.



  • Acrosome is formed from the golgi complex. It contains digestive enzyme “spermlysin“. It is the caplike covering above the It is surrounded by double membrane. Acrosome + its membrane are together called Galea-capatis. Acrosome plays important role in penetration of ovum by sperm.
  • Remaining part of the head is nucleus. Narrow space between the nucleus and the acrosome is termed as “perforatorium“.
  • Nucleus of the sperm is very small. In it nucleoplasm and nucleolus are absent. It contains only chromatin.
  • At the base of the nucleus in a pit like depression













































proximal centriole is present.

Fig. – Structure of sperm


  • In between the head and the middle piece a small neck is In this neck part a distal centriole is located. Both the centrioles are at right angles to each other.
  • Proximal centriole first induce cleavage in a fertilized First spindle fibre forms from it.
  • Distal centriole gives rise to the axial filament of the It has (9+2) microtubular arrangement.

(b)       Middle piece






  • This is known as the energy-chamber of the Many mitochondria spirally surround the axonema, this is called “Nabenkern sheath“. This part provides energy to the sperm for locomotion.
  • In middle-piece, cytoplasm is found in the form of a thin-sheet called Manchett.
  • In middle-part, axonema is surrounded by 9 solid fibres made up of
  • At the posterior end of the middle-piece a Ring centriole is Its function is not known.

(c)        Tail

  • The longest and the fibrous part of the sperm is termed its
  • Sperm moves with the help of its tai
  • Basal granule of the tail is Distal centriole. Tail has 2 parts
  • Main part : This part is It contains cytoplasm and is surrounded by 2 solid fibres.
  • End piece : This part is narrow in it cytoplasm is absent only axonema is In it solid fibres are also absent. In the sperm of certain animals, tail is absent. e.g.


  • Ascaris : Tailless, ameboid sperms
  • Cray fish : Tailless, stellate (star shape) sperms.
  • Crab and lobser : Tailless
















sperms with 3 spines at apex.

  • Biflagellage sperms : In Toad fist (Opsanus)
  • In Opposum : Many sperms fuse together by their heads to form a “sperm-boat”.
  • Gastrapods have hexaflagellated sperms.
  • Oogenesis : Oogenesis takes place in the ovaries. Unlike sperm formation that starts at puberty, egg formation begins before birth but is completed only after fertilization. Oogenesis consists of three phases –

(a)    Multiplication phase



GROWTH        46



























23                   BODY



23                    ENTRY






















  • During foetal development, certain cells in the germinal epithelium of the ovary are larger than others and also have larger

SPERM 23                               23                 23

46                                 SECONDARY




Fig. – Stages in oogenesis







  • These cells undergo mitotic divisions, producing undifferentiated germ cells called oogonia or egg mother cells in the
  • The oogonia have diploid, number of chromosome, 46 in humans.
  • The oogonia multiply by mitotic divisions and produce ovigerous cords or egg tubes of pfluger in
  • Growth phase : It is prolonged and Oogonia form rounded masses or egg nests at the tips of egg tubes of pfluger.
  • An egg nest forms ovarian follicle (Graffian follicle) one central oogonium grows and functions as primary oocyte. The others form the covering follicular cells. the latter provide nourishment to primary oocyte. Some nourishment also comes from outside. Yolk is deposited in this state. This phenomenon is called vetellogenesis.
  • In cooperation with follicular cells, the enlarged primary oocyte secrete mucoprotein membrane or zona pellucida outside its own plasma membrane or vitelline membrane. There is increase in reserve food, size of nucleus, number of mitochondria; functioning of golgi apparatus and complexing of endoplasmic

(c)  Maturation phase

  • Meosis occurs. Nucleus shifts towards animal pole and undergoes meosis – I. A daughter nucleus alongwith small quantity of cytoplasm is extruded as primary polar body or polocyte below zona pellucida. Simultaneously primary oocyte is changed into haploid secondary It proceeds with meosis – II but stops at metaphase-II. Ovum is generally shed in secondary oocyte stage.
  • After fertilization, the second meotic division is completed with unequal cytoplasmic cleavage. This forms a large cell the ootid with essentially whole of the cytoplasm, and a very small cell, the second polar body. The ootid and the second polar body are haploid as the second meotic division is equationa The first polar body may divide at about the same time into two polar bodies.
  • One primary oocyte forms, after two meiotic division, one haploid ootid and three haploid polar bodies. The ootid grows into a functional haploid ovum.
  • The polar bodies have no function and disintegrate due to lack of cytoplasm and
  • The formation of non functional polar bodies enables the egg to get rid of excess chromosomes. The unequal cytoplasmic division enables the ovum to retain the whole of cytoplasm of the primary oocyte in it for the development of the future
  • In humans, ova are released from the ovary in the secondary oocyte stage. Their maturation is completed in the mother’s genital tract, usually after the sperm has


entered for fertilization.

  • Structure of ovum : An ovum is generally spherical, nonmotile gamete with yolky cytoplasm and enclosed in one or

more egg envelops. Size of ovum varies in different animals and                              depends upon the amount of yolk. Size of ovum varies from 10m

to a few cm. Largest sized egg is of ostrich and is about 170 ´135 mm. Egg size and yolk amount are interdependent. It is about 50m in many polychaete worms, 150m in tunicates but very large sized in birds and reptiles. In mammals, it is generally









microlecithal and about 100m.

Fig. – Structure of ovum






Human ovum is microlecithal with large amount of cytoplasm. Cytoplasm is differentiated into outer, smaller and transparent exoplasm or egg cortex and inner, larger and opaque endoplasm or ooplasm.

Egg cortex is with some cytoskeletal structures like microtubules and microfilaments (Balinsky, 1981), pigment granules and cortical granules of mucopolysaccharides. Endoplasm is with cell-organelles, informosomes tRNAs, histones, enzymes etc. Nucleus of ovum is large, bloated with nucleoplasm and is called germinal vesicle. Nucleus is excentric in position so human ovum has a polarity. The side of ovum with nucleus and polar body is called animal pole, while the opposite side is called vegetal pole.

Egg envelopes. Human ovum is surrounded by a number of egg envelopes :

  • Vitelline membrane : It is inner, thin, transparent and is secreted by ovum itself.
  • Zona pellucida : It is middle, thick, transparent and non-cellular.
  • Corona radiata : It is outer, thicker coat formed of radially elongated follicular cells. Between the vitelline membrane and zona pellucida, there is a narrow perivitelline space.

Differences between Spermatogenesis and Oogenesis


S.No. Characters Spermatogenesis Oogenesis
1. Site of occurrence In the seminiferous tubules of testes. In the ovaries.
2. Total period It is a continuous process and completed in 74 days in humans It is a discontinuous process and completed in a

few days to years.

3. Growth phase Of shorter duration Of longer duration
4. Yolk synthesis No yolk is synthesized in growth phase Vitellogenesis occurs in growth phase.
5. Nuclear changes Nucleus becomes condensed by the loss of superfluous materials. Nucleus is bloated due to increase in necleoplasm.
6. Number of gametes One spermatogonium forms 4 haploid sperms. One oogonium forms only one ovum.
7. Polar bodies Not formed. Two or three polar bodies are formed.
8. Site of completion It is started and completed within the testes. It is started inside the ovary but is generally completed outside the ovary.
9. Size of gametes formed Sperm is much smaller than spermatogonium. Ovum is much larger than oogonium.

(vi) Types of eggs

(a)  On the basis of amount and distribution of yolk

  • Alecithal or Microleithal or Oligolecithal or Meolecithal and Isolecithal or Homolecithal : The amount of yolk is very small in these types of eggs. (Oligolecithal or Microlecithal or Alecithal)


and yolk is evenly distributed in these eggs (Isolecithal or Homolecithal). Examples – Egg of Amphioxus, Eutheria (Human egg), Metatheria and Sea-urchin.

  • Mesolecithal or Telolecithal eggs : In this type of egg the amount of yolk is moderate and yolk is concentrated in the basal part of egg (telolecithal egg). Examples – Egg of Amphibia, Petromyzon and Lung fishes.
  • Polylecithal or Macrolecithal or Megalecithal eggs : Eggs are with large amount of yolk and this yolk is concentrated in the centre and cytoplasm is in the form of superficial layer around the yolk (centrolecithal eggs). Example – Insect’s

In discoidal or highly telolecithal eggs, the yolk is enormous in amount and cytoplasm is confined to a disc like area on yolk. This disc of cytoplasm is called germinal disc. Example

Eggs of reptiles, birds, protherian mammals.























Note :

Majority eggs are oval but the eggs of insects are long and cylindrical.

  • Smallest eggs are of 50m in the polychaeta and the largest eggs are of an ostrich.

(b)  On the basis of fate

  • Determinate / Mosaic eggs : Every part of fertilize egg has a definite fate, so that fate of every blastomere is determined from the It is found in invertebrates except echinoderms.
  • Indeterminate / Regulative eggs : The fate of different parts of egg or its blastmeres is not Example – Echinodermes, Vertebrates.

(c)  On the basis of shell

  • Cleidoic eggs : Eggs surrounded by a hard shell are know as cleidoic eggs. These eggs are found in those animals which have a terrestrial mode of life of which lay eggs on land. These eggs have more amount of yolk. These are adaptations to terrestrial mode of life. Shell prevents the egg from e.g. Eggs of “Reptiles”. “Birds”. “Insects” and “Prototherians”.
  • Non Cleidoic eggs : Eggs which are not surrounded by a hard shell are called Non-cleidoic These eggs are found in all oviperous animals which lay eggs in water and all viviperous animals. e.g. All viviperous animals (Mammals) and all oviperous animals which lay eggs in water (Amphibians).

Structure of an oocyte : Oocyte is a large yolk containing cell. The nucleus is large and swollen and is termed as the “Germinal Vasicle“. Oocyte is surrounded by membranes termed as the egg-membranes. Oocyte / Ovum alongwith the egg-membrane are termed as the egg. Egg = Ovum / Oocyte + Egg membrane.

Classification of egg – membranes : On the basis of origin, egg-membranes are of 3 types –

  • Primary egg membrane : This membrane is secreted by the egg (ovum) e.g. Vitelline membrane, of human egg.
  • Secondary egg membrane : This is found outside the primary egg membrane and is secreted by the e.g. Chorion of insect eggs, corona radiata and zona pellucida of human egg.
  • Tertiary egg membrane : This present outside the primary and the secondary egg It is either secreted by the uterus or the oviduct. Egg jelly coat around frog’s egg; albumen, shell membrane and shell of bird egg.

Functions of egg membranes

(1) To provide protection.                                        (2) To check polyspermy.

(3) To provide buoyancy to the amphinian eggs.               (4) To provide nutrition (Birds, Reptiles)

(5) To help in excretion (Allantois)

Different types of eggs

  • Insect egg : Eggs of insects are megalecithal or polylecithal in them yolk is present in the centre, so the eggs are also centrolecithal. Eggs of insects are cigar Along with plasma-membrane the egg has 2 egg-membranes.
  • Vitelline membrane : This is a primary egg membrane and the egg itself secretes it
  • Chorion : This is a secondary egg membrane and is secreted by the In Insect’s egg tertiary egg- membranes is absent. Chorion of insect’s egg is ornamented i.e. there are specific markings on its egg membrane which are characters of Taxonomic importance. In the egg, a hole termed as micropyle is present which is the port of entry for sperms. Its cytoplasm is divided into 2 parts –

(a) Central                  (b) Peripheral cytoplasm

  • Central cytoplasm : It is present in a very small amount in the centre of the Egg nucleus is located in it.
  • Peripheral cytoplasm : It is present in a very small amount along the periphery of the






Yolk : In insect’s egg yolk is present in a very large amount and this yolk is concentrated between the central and the Peripheral cytoplasm.

  • Frog’s egg : Eggs of frog are Teloecithal and Mesolecithal. The egg has 2 egg
  • Vitelline membrane : This is a primary membrane, secreted around by the egg
  • Jelly – coat : This is a tertiary egg-membrane. It is secreted by the Secondary egg-membrane are absent in these egg’s. Internally, the egg is divided into 2 areas –

(a) Animal pole                     (b) Vegetal pole

  • Animal pole : This part has more amount of cytoplasm in it and the egg nucleus is also located in In this part melanin granules are found which prevent the egg from harmful radiations. Due to these melanin granules the frog’s egg is partly white and partly black. This helps in Camouflage. Sperm


















Fig. – Insect egg


always enters inside the egg through the animal pole. The part from where the sperm enters inside the frog’s egg in future forms the ventral part of the embryo. As the sperm enters inside the egg. The part directly opposite to the entry point becomes a clear-zone due to the rapid movement of melanin granules. this clear-zone is termed as the

Grey-Crescent. This part with Grey-Crescent forms the dorsal part of


the embryo in future.

  • Vegetal pole : Here the yolk is concentrated in frog’s egg, the part with cytoplasm in future forms the ectoderm. The Grey crescent part in future the Mesoderm and the part with yolk in future forms the

Jelly-coats of all the eggs of a frog absorb water and swell up, to form a cluster of eggs termed as Spawn. Jelly-coat has air-bubbles, due to which the eggs don’t drown. Jelly-coat is bilter in taste and so the eggs are protected from the enemies.

Important tips











Fig. – Frog’s egg












  • Cat and Rabbit are both induced
  • The life span of eggs in female reproductive organs is different g. in humans it is 48 hours.
  • Nucleus of the egg is termed as Germinal
  • The asexual process replaced by the sexual method is known as
  • Phallic organs in cockroach are related to male reproductive
  • No natural death in organisms showing binary fision g. Amoeba, so are called immortal.
  • The croaking sound made by frog is sex call for female
  • Leuvenhock (1677) saw human
  • In frog bidder canal help in sperm
  • Gynandromorph : An animal having male characteristics on one part and female characteristics on the
  • Gynaecomastia : Enlarged functional mammary gland in
  • Azoospermia : No sperms in
  • Oligospermia : Sperms less than 20 million in per ml
  • V. Graf (1672) : Androgenesis discovered follicles in human ovary.
  • Androgenesis : Development in which embryo has only paternal chromosomes, male
  • Gynogenesis : Development in which embryo has only maternal chromosomes, female
  • Gland of Tyson : Modified sebaceous glands present around corona of
  • In many birds (exception some birds of prey) only the left ovary and left oviduct are The right ones are non-functionsl.
  • Seminiferous tubules : Structural and functional unit of
  • Hysterectomy : Surigcal removal of
  • Castration / Chidectomy : Removal of It produce eunuchs. Castration changes aggressiveness of male into docile nature.
  • Corpus luteum : Persists for two weeks in case of non pregnancy and four months when pregnancy has taken
  • Prostatitis : Inflammation of prostate Prostate cancer is common in ageing males.
  • Human egg : 1 mm in diameter.
  • Prostatectomy : Surgical removal of prostate
  • Peculiar spermatozoa : Ascaris has amoeboid spermatozoa devoid of Some crustaceans also have atypical sperms.
  • Sperms form about 10% of the ejaculated
  • Protandry : Spermatozoa mature earlier than ova in bisexual animals g. – Hydra, Earthworm.
  • Andrology : Branch of medicine concerned with diseases peculiar to male
  • Spermatorrhoea : An involuntary discharge of semen, without
  • Spermatophore : A capsule containing spermatozoa, as in cuttle fish and
  • Menarche : Beginning of menstrual cycle and other bodily
  • Oophoritis : Inflammation of an
  • Vitellogenesis : Process of laying down of yolk in the primary It occurs in the prophase of meosis-I.
  • Metagenesis : Alternation of sexually and asexually reproducing forms in the life cycle of an animal g. Obelia.
  • Protogyny : Ova mature earlier than sperm in abisexual animal g. Herdmania.
  • Spermathecae : Small sacs that form a part of female reproductive system of earthworm and store spermatozoa received from the male for use in
  • Oviparous : Animals that lay eggs g. – Birds.
  • Viviparous : Animals which give birth to young ones, g. most mammals.
  • Ovoviviparous : Animals that produce eggs which hatch within their
  • Ovipositor : A specialised female organ for laying eggs, specially in
  • Rutting season : It is a brief period of pronounced sexual activity in
  • Tubectomy (Salpingectomy) : Surgical removal of
  • Von bear : Discovered





  • Strobilation : Asexual multiplication by transverse fusion and is found in Scyphistoma of Aurelia and also found in
  • Richard owen gave term
  • Testes are also called
  • Vaginal coelom : Cavity of scrotal
  • Leydig cells are absent from the testes of frog and are characteristics of mammalian
  • To-gene : Testicular organisation gene located on Y-chromosome and is a male determining
  • Adiposogenital syndrome : Hypogonadism in male and characterised by obesity and child like sexual
  • No man – no woman syndrome : Characterised by male-female pseudohermaphroditism in which external sexual characters are opposite to genetic and gonadal
  • Wolffian duct : Acts as male genital duct, while mullarian duct is
  • Mesosalpinx : Mesentry suspending the fallopian
  • Mesometrium : Mesentry suspending the
  • Uterus : It is also called
  • Cervix of uterus is formed of most powerful smooth
  • Vestibule : Acts as a urinogenital
  • Perineum : Area between the fourchette and
  • Bartholin’s or Bulvo vestibular glands of female homolegous to Cowper’s glands of
  • Precocious puberty : Puberty attained before the normal
  • Hypermastia : More than normal number of
  • Number of breasts in female depends upon the number of young ones born at a
  • Female ascaris has paired ovaries so is called
  • In seasonally breedings animals, testes show testicular
  • Spermatogenesis is continous process, while oogenesis is a discontinuous
  • In spermatogenesis, spermatogonium produces four sperms while in oogenesis, one oogonium produces one ovum and 2 or 3 polar
  • Golgi rest : Part of golgi body which is lost during
  • Gynosperm : Sperm with 22 A+X
  • Androsperm : Sperm with 22 A+Y
  • Yolk nucleus : Also called Balbiani A mass of mitochondria and golgibody near the nucleus which controls vitellogenesis.
  • Redundancy : Gene amplification of r-RNA genes for rapid RNA and protein
  • Ring centriole : Also called annulus or Jensen’s  ring. Menstruation is  also called “Weeping of uterus  for the lost ovum  or funeral of unfertilized egg”.
  • Menstrual cycle is associated with withdrawal or