Human Reproduction

1. In birds and mammals internal fertilisation takes place. In uterus of the female, the male gamete fuses with the female gamete. Here zygote develops to form an embryo inside the female body.

2. After the birth of a child Colostrum is the first milk form produced by the mammary glands. It is full of nutrients, antibodies and provides immunity boost in the child.

3.Polyspermy is the phenomenon in which an egg meets more than one sperm. In mammals, polyspermy is not prevented by chemical changes. Once the sperm attaches to the zona pellucida layer of the ovum, it brings about physiological changes in the ovum’s membrane and blocks the entry of other sperms.

4.In the human female implantation occurs about seven days after fertilisation.

Only statement ‘c’ is incorrect. Hence option ‘c’ is the correct answer.

1. High levels of oestrogen increases the surge of LH and FSH which in turn leads to ovulation.

2. Oogonial cells are added in the foetal stage only and not after the birth.

3. The sperms become highly motile and fertile in the head of the epididymis. They are not highly motile when they are released from the seminiferous tubules.

4. The ruptured follicle closes after the release of egg and leads to the formation of corpus luteum. This corpus luteum produces progesterone. Hence the progesterone level is high during the post ovulatory phase of menstrual cycle.

Therefore, only option ‘d ’is correct.

Rete testis, Epididymis and Vasa Efferentia are all parts of the male reproductive system. Isthmus is the part of female reproductive system hence, it is the odd one out.

Seminal plasma is the fluid part of the semen that consists of secretions of prostate gland, urethra and bulbourethral gland. This fluid is rich in calcium, fructose and carries sperm to the ovum.

1) Spermiation is the process of sperm formation from the Seminiferous tubules.

2) Vas Deferens: Transfers the produced sperm to the urethra.

3) Epididymis: Stores the sperm until it is ejaculated.

4) Prostate Gland: It helps to propel the seminal fluid into the urethra.

Mature Graafian follicle is generally present in the ovary of a healthy human female from 11th to 17th day of menstrual cycle.

The interaction of the sperm with zona pellucida causes the release of fertilizin and hence the reaction.

Secretion from male accessory gland provides nutrients to the sperm and activates the spermatozoa. These glands consist of Seminal vesicle, Prostate and Bulbourethral gland.

Ampulla is the part of female reproductive system.

1) Spermatogonia have 46 chromosomes but always undergo mitotic division not meiotic division.

2) Primary spermatocytes divide by meiotic division not mitotic division.

3) Secondary spermatocytes have 23 chromosomes and undergo second meiotic division.

4) Spermatids are transformed into Spermatozoa.

Spermatogonia, zygote and oogonia are all diploids and have 46 chromosomes.

Only Secondary oocyte has 23 chromosomes.

Placenta is the temporary organ that attaches the embryo to the uterine wall through an umbilical cord and provides nutrition to the developing embryo. It also releases hormones like hCG, Oestrogen and Progesterone.

LH or Luteinizing hormone is released from Pituitary Gland.

The vas deferens receives duct from the seminal vesicle and opens into urethra as Ejaculatory Duct.

Urethral meatus is the opening of the urethra. It is the point from where urine exits the urethra and is also known as External opening of the urinogenital tract.

The Morula is the globular mass having 16-32 blastocysts and is the developmental stage between the zygote and blastocyst.

1. The membranous cover of the ovum at ovulation is Corona radiata. When sperm enters the ovum, it first comes in contact with corona radiata and zona pellucida.

2. Zona radiata is a striated membrane.It is situated next to the yolk of an ovum.

3. Zona pellucida is adjacent to corona radiata.

4. Chorion is an embryonic foetal membrane which forms the placenta.

Infundibulum, Fimbriae and Isthmus are parts of fallopian tube of the female reproductive system whereas Labia minora is the part of external genitalia.

The sequential order is as follows:

1. Gametogenesis: It is the process through which the precursor cells undergo cell division in order to form male (sperm) and female gamete (ovum).

2. Insemination: The entry of the semen into female either sexually or artificially.

3. Fertilisation: This is the fusion process of male and female gametes for the formation of an embryo.

4. Implantation: During this event, the embryo gets embedded into the uterus wall. This adherence of embryo to mother’s uterus provides nutrition and oxygen to the embryo.

5. Gestation: The period during which the growing embryo stays in mother’s womb is called gestation period. For humans, this period is about 9 months.

6. Parturition: The process of delivering the child is called parturition.

1. Seminiferous tubules : Here the sperms are produced via spermatogenesis. Sperms are then transported to rete testis.

2. Rete testis: These are a network of tubes which carries sperms to vasa efferentia.

3. Vasa efferentia: It transports sperm by connecting rete testis to the upper part of epididymis.

4. Epididymis: In epididymis sperms mature and are transported to vas deferens.

5. Vas Deferens: Carries the mature sperm to the urethra.

6. Urethra: From here the sperm gets released.

Cervix is the part of female reproductive system that connects uterus to womb. Cervix has the following roles including:

1) It allows the passage of sperm.

2) It also acts as a reservoir for the sperm.

3) It prevents the entry of bacteria into the uterus during pregnancy.

4) It forms the birth canal during parturition.

Once a woman gets pregnant, the placenta starts producing Human Gonadotropin Hormone (hCG). This hormone starts developing Corpus Luteum that secretes a hormone called progesterone which maintains the thickness of the endometrium lining and prevents it from shedding. High level of oestrogen and progesterone during pregnancy results in the absence of menstrual cycle.

In the above diagram, the female reproductive organs are matched with their respective functions.

1. In ovaries ovulation takes place.

2. The fusion of male and female gametes (known as fertilisation) takes place in the oviduct.

3. Uterus is also known as womb. In the womb development of the foetus takes place.

4. The baby passes through the birth canal which is the vagina.

Parturition is a term that is used to describe the delivery of baby and placenta from mother's uterus to the outside world. The signals of parturition arise from the foetus. Oxytocin is the principal

(main) hormone involved in parturition.

Epididymis is a coiled structure within the scrotum that plays a significant role in male fertility:

1) Sperms mature physiologically, their motility and fertilising capacity increases within the epididymis.

2) It also helps in the transportation of sperms.

Spermatogenesis is the process of sperm formation that takes place within the seminiferous tubules. This process starts at the age of puberty. Hormones involved in spermatogenesis are:

1. Oogonia results in the formation of primary oocyte.This primary oocyte is surrounded by granulosa cells to form a primary follicle.

2. This primary follicle gets surrounded by more granulosa cells to form a secondary follicle.

3. The secondary follice gets converted to tertiary follicle by addition of more granulosa cells.

4. The primary oocyte within the tertiary follicle than undergoes meiotic division to form a secondary oocyte or ovum and a polar body.

5. The tertiary follicle matures to form graafian follicle.

6. The graafian follicle than ruptures to release the secondary occyte or ovum.

7. This process is known as Ovulation.

During gametogenesis, the chromosome number (2n) reduces to half (n) and the actual number (2n) of chromosomes are restored in the offspring after fertilisation.

Ovum fertilization takes place at the ampullary-isthmic junction in the female reproductive tract.

Polyspermy refers to the fertilization of an egg through more than one sperm. Proteases destroy the protein link between the cell and vitelline membrane as well as between the receptor protein and any other sperm bound to it, hence, prevents polyspermy.

LH or luteinizing hormone surge leads to the rupture of graafian follicle and releases ovum into the fallopian tube. LH surge is responsible for luteal phase in the ovarian cycle.

In the first meiotic (meiosis I) division, the primary spermatocyte divides into two secondary spermatocytes. Each secondary spermatocyte formed, then divides into spermatids through second meiotic division (meiosis II)

Menarche is the beginning of menstrual cycle in a female’s life that starts at the age of puberty and marks the attainment of sexual maturity.

Menopause is the end stage of a woman’s menstrual cycle that marks the end of reproductive stage.

(a) Two spermatozoa are formed from one secondary spermatocyte.

(b) The first cleavage division of zygote takes place in the fallopian tube or oviduct.

During pregnancy, corpus luteum releases a large amount of progesterone and oestrogen due to the neural signal given by the maternal endometrium to the hypothalamus.

This sustains the release of Luteinising hormone and maintains the embryo until the gestation period. If the fertilisation does not occur, corpus luteum would not be able to remain active for more than 10-12 days because of the lack of progesterone which is required to maintain the corpus luteum.

Parturition is the delivery of foetus into the outside world. Foetal ejection reflex are the signals given by the completely developed foetus and the placenta which causes mild uterine contractions.

1. When the foetal ejection reflex occurs, mild uterine contractions takes place.

2. These mild uterine contractions trigger the release of oxytocin.

3. The release of oxytocin in turn, leads to stronger uterine contractions. This process continues until a stronger contraction leads to the expulsion of baby through the birth canal or parturition.

Placenta is the temporary organ that:

1) Attaches uterus to the uterine wall.

2) Provides nutrients to the growing foetus.

3) Provides oxygen to the foetus.

4) Helps in waste removal from the foetus.

Doctors recommend breast feeding during the initial period of infant growth because for a few days during the start of lactation, the milk produced by colostrum (the female mammary glands), is full of antibodies. This improves the immunity of baby and provides resistance against various diseases.

The events that take place in the ovary and uterus during follicular phase of the menstrual cycle are:

1. The primary follicle matures into graafian follicle.

2. After this the secretion on oestrogen takes place.

3. The endometrium lining of the uterus regenerates through proliferation.

4. Shedding of the endometrium lining starts taking place.

A: LH and FSH (Follicle Stimulating Hormone)

B: LH (Luteinizing hormone)

C: Progestrone

To understand why that is so, observe the following diagram

1. The mature follicle is also known as the Graafian follicle. As in evident from the diagram above, during this phase i.e. the follicular phase, the primary follicles in the ovary grow and become a Graafian follicle. These changes are induced by changes in the levels of pituitary and ovarian hormones: LH and FSH and Estrogen. LH and FSH levels increase during the follicular phase, which stimulates the development of follicles.

2. During Ovulation, the mature follicle releases the Ova. This happens because of a surge in LH levels.

3. The luteal phase follows ovulation. During the luteal phase, the Graafian follicle transforms into the corpus luteum. The corpus luteum secretes large amounts of progesterone and the surge of progesterone can be observed in the diagram given above.

Changes that occur in the oogonia during the transition of a primary follicle to Graafian follicle are:

1) Germinal epithelial cells divide repeatedly to form multiple diploid oogonia.

2) These oogonia grow to form primary oocyte.

3) These primary oocytes get surrounded by granulosa cells and form a primary follicle

4) Primary oocyte gets surrounded by more granulosa cells and forms a primary follicle.

5) Now this primary follicle, gets surrounded by more granular cells in order to form secondary follicle.

6) This secondary follicle converts into tertiary follicle by adding more granulosa cells.

7) The primary oocyte within the tertiary follicles, undergoes meiotic division in order to form secondary oocyte and a haploid polar body.

8) This tertiary follicle then, matures into graafian follicle which in turn, ruptures to release secondary oocyte or ovum.

1. The two main pituitary gonadotropins are LH (luteinising hormone) and FSH (Follicle stimulating hormone). At the end of menstrual cycle, the amount of FSH increases that leads to the development of the follicles in the ovaries.

2. As follicles mature, oestrogen production increases. This in turn, increases the LH and FSH secretions.

3. The increased LH leads to ovulation and starts the formation of corpus luteum or luteinising.

4. Corpus luteum secretes progesterone and oestrogen which further maintains the endometrium lining.

1. Meiotic division during oogenesis is different from the one that occurs in spermatogenesis in terms of unequal division during oogenesis.

2. In spermatogenesis, all the four spermatids formed are equally functional in nature.

3. Whereas in oogenesis, unequal division takes place. In which major part of the cytoplasm remains in one ovum only.

4. Only a minor part of the ovum is separated as a polar body.

5. This division forms only one such ovum which is functional in nature.

This shows that, in spermatogenesis, all four spermatids formed are functional whereas in oogenesis only one ovum is functional.

The various stages of the zygote before implantation are:

In the stage ‘a’ as shown in the diagram, a zygote is formed after the fusion of male and female gametes. In stage ‘b’ as shown in the diagram, zygote enters the isthmus.

CLEAVAGE STAGE: Within the isthmus, the zygote formed by the fusion of the male and female gamete, enters the two-cell stage known as cleavage.

BLASTOMERE: The cleavage formed, undergoes mitosis. At first, to form a 2 then 4, then 8 and finally 16 cells stage. These daughter cells are called as blastomere.

MORULA: The 8-16 cell blastomere are known as morula. This morula divides continuously to form a blastocyst and moves into the uterus.

The blastomere present within the blastocyst are arranged into a layer known as trophoblast. There are cluster of interior cells attached to the trophoblast known as interior cell mass.

(5) The trophoblast layer gets attached to the endometrium lining of the uterus, the inner cells than forms an embryo after differentiation.

(6) After the attachment the uterine cells divide to cover the blastocyst.

(7) This blastocyst then, gets embedded in the endometrium of the uterus known as implantation.

(a) Site for Production of gametes: Ovary

(b) Site of fertilisation: Isthmus-ampullary junction.

(c) Site of implantation: Uterine endometrium

(d) Birth canal: Cervix and vagina

The female reproductive system includes:

1. Uterus: It is a muscular pear-shaped organ and is also known as the womb. It is the part where the zygote develops into an embryo and then grows into the foetus.

2. Fallopian tubes: These are funnel shaped muscular tubes that extends from both right and left side of the uterus extended to the edge of the ovaries. These tubes have finger-like projections called fimbriae. These fimbriae extend to the ovary and pick up ova that is produced by ovary into the infundibulum and finally reaches the uterus.

3. Vagina: It is an elastic and muscular tube that acts as a receptor for sperms during sexual intercourse and delivers the sperm to the fallopian tube as well as to the uterus.

1. Mammary glands or breasts are paired structure that have undeveloped duct system and adipose tissue.

2. When a woman gets pregnant, the secretion of oestrogen and progesterone increases. This develops a glandular system in the mammary glands which leads to the production of milk.

3. The glandular tissue of each breast, forms mammary lobes consisting of clusters of cells known as alveoli.

4. These alveoli cells start secreting milk that is stored within the cavities of the alveoli.

5. These cells further open into mammary tubules and join to form a mammary duct.

6. A number of mammary ducts join together in order to form a mammary ampulla from which the milk is sucked out.