Human Reproduction

1. Write down the events in human reproduction.

Ans: As you are aware, humans are sexually reproducing and viviparous. The reproductive events in humans include
a. Gametogenesis: formation of gametes (gametogenesis), i.e., sperms in males and ovum in females,
b. Insemination: transfer of sperms into the female genital tract.
c. Fertilization: fusion of male and female gametes leading to formation of zygote.
d. Implantation: attachment of blastocyst to the uterine wall.
e. Gestation: embryonic development.
f. Parturition: delivery of the baby.
2. Draw a neat labelled diagram of male reproductive system OR explain the male reproductive system.
Ans:

OR
• humans are sexually reproducing and viviparous. The reproductive events in humans include gametogenesis,
insemination, fertilization, implantation, gestation and parturition.
• The human reproductive system includes-
o Primary sex organ o Associated glands
o Accessory ducts o External genitalia
• Primary sex organ (The Testis)-
o The testes are situated outside the abdominal cavity within a pouch called scrotum.
o The scrotum helps in maintaining the low temperature of the testes (2–2.5o C lower than the normal internal body
temperature) necessary for sermatogenesis.
o In adults, each testis is oval in shape, with a length of about 4 to 5 cm and a width of about 2 to 3 cm.
o The testis is covered by a dense covering.
o Each testis has about 250 compartments called testicular lobules and has 1-3 highly coiled seminiferous tubule and
the site for spermatogenesis in testes
• The male sex accessory ducts:
o The male sex accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens.
o The seminiferous tubules of the testis open into the vasa efferentia through rete testis.
o Vas deferens receives a duct from seminal vesicle and opens into urethra as the ejaculatory duct.
o These ducts store and transport the sperms from the testis to the outside through urethra.
o The urethra originates from the urinary bladder and extends through the penis to its external opening called urethral
meatus.
• The male sex accessory glands:
o The male accessory glands include paired seminal vesicles, a prostate and paired bulbourethral glands.
o Secretions of these glands constitute the seminal plasma which is rich in fructose, calcium and certain enzymes.
o The secretions of bulbourethral glands also help in the lubrication of the penis.
• Male external genitalia:
o The penis is the male external genitalia.
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 o It is made up of special tissue that helps in erection of the penis to facilitate insemination.
o The enlarged end of penis called the glans penis is covered by a loose fold of skin called foreskin.
3. Draw a neat labelled diagram of female reproductive system OR write an account on female reproductive system.
Ans:

OR
• The female reproductive system consists of the followings and
o a pair of ovaries o vagina and
o a pair of oviducts, o external genitalia
o uterus, o mammary
o cervix,
• Ovaries:
o Ovaries are the primary female sex organs that produce the female gamete (ovum) and several steroid hormones
(ovarian hormones).
o The ovaries are located one on each side of the lower abdomen.
o Each ovary is about 2 to 4 cm in length and is connected to the pelvic wall and uterus by ligaments.
o Each ovary is covered by a thin epithelium which encloses the ovarian stroma.
o The stroma is divided into two zones – a peripheral cortex and an inner medulla.
• Oviducts/fallopian tube:
o The oviducts (fallopian tubes), uterus and vagina constitute the female accessory ducts.
o Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus,
o the part closer to the ovary is the funnel-shaped infundibulum.
o The edges of the infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum
after ovulation.
o The infundibulum leads to a wider part of the oviduct called ampulla.
o The last part of the oviduct, isthmus has a narrow lumen and it joins the uterus.
• The uterus:
o The uterus is single and it is also called womb.
o The shape of the uterus is like an inverted pear.
o It is supported by ligaments attached to the pelvic wall.
o The uterus opens into vagina through a narrow cervix.
o The cavity of the cervix is called cervical canal which along with vagina forms the birth canal. The wall of the uterus
has three layers of tissue.
o The external thin membranous perimetrium, middle thick layer of smooth muscle, myometrium and inner glandular
layer called endometrium that lines the uterine cavity.
o The endometrium undergoes cyclical changes during menstrual cycle while the myometrium exhibits strong
contraction during delivery of the baby.
• The female external genitalia:
o The female external genitalia include mons pubis, labia majora, labia minora, hymen and clitoris.
o Mons pubis is a cushion of fatty tissue covered by skin and pubic hair.
o The labia majora are fleshy folds of tissue, which extend down from the mons pubis and surround the vaginal opening.
o The labia minora are paired folds of tissue under the labia majora.

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 o The opening of the vagina is often covered partially by a membrane called hymen.
o The clitoris is a tiny finger-like structure which lies at the upper junction of the two labia minora above the urethral
opening.
• Mammary gland:
o A functional mammary gland is characteristic of all female mammals.
o The mammary glands are paired structures (breasts) that contain glandular tissue and variable amount of fat.
o The glandular tissue of each breast is divided into 15-20 mammary lobes containing clusters of cells called alveoli.
o The direction of milk in them is as follows-
Mammary lobes>Alveoli>mammary tubule>mammary duct>ampulla>lactiferous duct>nipple
4. Briefly explain the process of spermatogenesis. OR give a schematic representation spermatogenesis.
Ans: Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing
hormone (GnRH).
• In testis, the immature male germ cells (spermatogonia) produce sperms by spermatogenesis.
• The spermatogonia (sing. spermatogonium) present on the inside wall of seminiferous tubules multiply by mitotic division
and increase in numbers.
• Each spermatogonium is diploid and contains 46 chromosomes.
• Some of the spermatogonia called primary spermatocytes periodically undergo meiosis.
• A primary spermatocyte (2n) completes the first meiotic division (reduction division) leading to formation of two equal,
haploid (n) cells called secondary spermatocytes, which have only 23 chromosomes each.
• The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids.
• Spermiogenesis: The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis.
• Spermiation: After spermiogenesis, sperm heads become embedded in the Sertoli cells, and are finally released from the
seminiferous tubules by the process called spermiation.
OR

5. Explain the structure of sperm. OR draw a neat labelled diagram of sperm OR draw sectional view of seminiferous tubule.
Ans: Structure of sperm: -
• It is a microscopic structure composed of
o a head,
o neck,
o a middle piece and
o a tail.
• A plasma membrane envelops the whole body of sperm.
• The sperm head contains an elongated haploid nucleus, the anterior portion of which is covered by a cap-like structure,
acrosome.
• The acrosome is filled with enzymes that help fertilisation of the ovum.
• The middle piece possesses numerous mitochondria, which produce energy for the movement of tail that facilitate sperm
motility essential for fertilisation.

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6. Fill in the blanks given bellow in the statements a. to e. -
(maturation and motility, 200 to 300 million, accessory ducts, androgens, semen, 60 per cent, 40 per cent)
a. The human male ejaculates about _____________ sperms during a coitus of which, for normal fertility, at least
_________ sperms must have normal shape and size and at least _________ of them must show vigorous motility.
b. Sperms released from the seminiferous tubules, are transported by the_____________.
c. Secretions of epididymis, vas deferens, seminal vesicle and prostate are essential for _____________ of sperms.
d. The seminal plasma along with the sperms constitute the__________.
e. The functions of male sex accessory ducts and glands are maintained by the testicular hormones (____________).
7. Differentiate between primary, secondary, tertiary and Graafian follicle.
Ans:
• Primary follicle: Each primary oocyte gets surrounded by a layer of granulosa cells and is called the primary follicle.
• Secondary follicles: The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called
secondary follicles.
• Tertiary follicle:
o The secondary follicle transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum.
o The theca layer is organised into an inner theca interna and an outer theca externa.
o At this stage the primary oocyte completes its first meiotic division (unequal).
o Resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.
o The secondary oocyte retains bulk of the nutrient rich cytoplasm of the primary oocyte.
• Graafian follicle:
o The tertiary follicle further changes into the mature follicle or Graafian follicle.
o The secondary oocyte forms a new membrane called zona pellucida surrounding it.
o The Graafian follicle now ruptures to release the secondary oocyte (ovum) from the ovary by the process called
ovulation.
8. Explain the process of Oogenesis. OR give a schematic representation of oogenesis.
Ans: Oogenesis-
• The process of formation of a mature female gamete is called oogenesis.
• Oogenesis is initiated during the embryonic development stage.
• No more oogonia (egg mother cell) are formed and added after birth.
• oogonia start division and enter into prophase-I of the meiotic division and get temporarily arrested.
• The prophase-I arrested oogonia are called primary oocytes and are present in primary follicles.
• After puberty the primary follicle transform into secondary follicle and soon transforms into a tertiary follicle.
• Tertiary follicle:
o Is characterised by a fluid filled cavity called antrum.
o The theca layer is organised into an inner theca interna and an outer theca externa.
o The 1st meiotic division completes in tertiary follicle.
o First meiotic division is an unequal division resulting in the formation of
▪ a large haploid secondary oocyte and a
▪ tiny first polar body.

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 o The tertiary follicle further changes into the mature follicle or Graafian follicle.
• The secondary oocyte forms a new membrane called zona pellucida surrounding it.
• The Graafian follicle ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation.
• Second meiotic division completes at fertilization
OR

9. Write an account of menstrual cycle. OR give a schematic representation of menstrual cycle.

Ans:
• The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is called menstrual cycle.
• The first menstruation at puberty is called menarche.
• It is of 28 day and may vary depending upon the health status.
• It has four phases namely-
o Menstrual phase o Ovulatory phase
o Follicular or proliferative phase o Luteal phase
• Pituitary hormones (LH & FSH) control ovarian events and the ovarian hormones (Estrogen & Progesterone) control
uterine events
• Menopause: In human beings, menstrual cycle ceases around 50 years of age; that is termed as menopause.
OR

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 10. Write the significance of phases of menstrual cycle.
Ans:
o Menstrual phase:
▪ The cycle starts with the menstrual phase.
▪ It lasts for 3-5 days.
▪ The menstrual flow results due to breakdown of endometrial lining of the uterus and its blood vessels which forms
liquid that comes out through vagina due to lack of fertilization and low level of progesterone.
o Follicular or proliferative phase:
▪ During this phase, the primary follicles in the ovary grow to become a fully mature Graafian follicle and
simultaneously the endometrium of uterus regenerates through proliferation.
▪ These changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones.
▪ The secretion of gonadotropins (LH and FSH) increases gradually during the follicular phase, and stimulates
follicular development as well as secretion of estrogens by the growing follicles.
o Ovulatory phase:
▪ Both LH and FSH attain a peak level in the middle of cycle (about 14th day).
▪ Rapid secretion of LH leading to its maximum level during the mid-cycle called LH surge induces rupture of Graafian
follicle and thereby the release of ovum (ovulation).
o Luteal phase:
▪ The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian
follicle transform as the corpus luteum.
▪ The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium.
11. Define the term insemination.
Ans: During copulation (coitus) semen is released by the penis into the vagina (insemination).
12. Draw a well labelled diagram of a mammalian ova.
Ans:

13. Why not all copulations lead to fertilisation and pregnancy?

Ans: Fertilisation can only occur if the ovum and sperms are transported simultaneously to the ampullary region
14. Briefly explain the process of fertilization.
Ans: Fertilization-
• The process of fusion of a sperm with an ovum is called fertilisation.
• Fertilisation can only occur if the ovum and sperms are transported simultaneously to the ampullary region.
• During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the
membrane that block the entry of additional sperms.
• Thus, it ensures that only one sperm can fertilise an ovum.
• The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the
plasma membrane.
• This induces the completion of the meiotic division of the secondary oocyte.
• The second meiotic division is also unequal and results in the formation of a second polar body and a haploid ovum (ootid).
• Soon the haploid nucleus of the sperms and that of the ovum fuse together to form a diploid zygote.

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15. How many chromosomes will be there in the zygote?
Ans: 46 (2n)
16. How does sex-determination take place in human?
Ans: sex- determination in human-
• Male is heterogametic, i.e., he produces two types of sperms
o Sperm with autosomes and an X-chromosome and
o a sperm with autosome and a Y-chromosome
• Females are Homogametic i.e., she produces only one type of gamete
o An egg with autosomes and an X-chromosome
• If the egg fertilizes with the sperm having X-chromosome will produce a female
• Likewise, if an egg fertilizes with sperm having Y-chromosome will produce a male
• The XX/XY pattern of sex-determination is seen Human and in Drosophila
17. What is cleavage?
Ans: The mitotic division in the zygote when it moves through the isthmus of the oviduct towards the uterus is called cleavage.
18. What is blastomere?
Ans: cleavage leads to formation of 2, 4, 8, 16 and so on daughter cells called blastomeres.
19. What is morula?
Ans: The embryo with 8 to 16 blastomeres is called a morula.
20. What is blastocyst? Explain its structure.
Ans: The mammalian blastula is called blastocyst.
• The morula continues to divide and transforms into blastocyst as it moves further into the uterus.
• The blastomeres in the blastocyst are arranged into
• an outer layer called trophoblast and
• an inner group of cells attached to trophoblast called the inner cell mass. And
• a fluid filled cavity called blastocoel.
21. What is implantation? How does it occur?
Ans: The attachment of blastocyst to the endometrial wall of uterus is called implantation.
• The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo.
• After attachment, the uterine cells divide rapidly and covers the blastocyst.
• As a result, the blastocyst becomes embedded in the endometrium of the uterus.

22. What is placenta? How does it form?

Ans: A structural and functional unit between developing embryo (foetus) and maternal body called placenta.
After implantation, finger-like projections appear on the trophoblast called chorionic villi which are surrounded by
the uterine tissue and maternal blood. The chorionic villi and uterine tissue become interdigitated with each other and jointly
form placenta.

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23. What are the functions of the placenta?
Ans: functions of placenta-
• The placenta facilitate the supply of oxygen and nutrients to the embryo and also removal of carbon dioxide and
excretory/waste materials produced by the embryo.
• The placenta is connected to the embryo through an umbilical cord which helps in the transport of substances to and from
the embryo.
• Placenta also acts as an endocrine tissue (temporary endocrine gland) and produces several hormones like
o human chorionic gonadotropin (hCG), o estrogens,
o human placental lactogen (hPL), o progestogens, etc.
24. Name the hormones produced only during pregnancy.
Ans: hCG, hPL and relaxin are produced in women only during pregnancy.
25. What is relaxin? What is its function?
Ans: In the later phase of pregnancy, a hormone called relaxin is also secreted by the ovary. It helps in parturition by dilating
the pubis symphysis.
26. Name the other hormones essential for supporting the fetal growth, metabolic changes in the mother and maintenance of
pregnancy.
Ans: Estrogens, progestogens, cortisol, prolactin, thyroxine, etc., are increased several-folds in the maternal blood. And are
essential for supporting the fetal growth, metabolic changes in the mother and maintenance of pregnancy.
27. Write a brief note on embryogeny/embryological development in human.
Ans:
• Immediately after implantation, the inner cell mass (embryo) differentiates into an outer layer called ectoderm (1st germ
layer) and an inner layer called endoderm.
• A mesoderm soon appears between the ectoderm and the endoderm.
• These three layers give rise to all tissues (organs) in adults.
• It needs to be mentioned here that the inner cell mass contains certain cells called stem cells which have the potency to
give rise to all the tissues and organs.
• The major features of embryonic development at various months of pregnancy-
o The human pregnancy lasts 9 months.
o In human beings, after one month of pregnancy, the embryo’s heart is formed.
o The first sign of growing foetus may be noticed by listening to the heart sound carefully through the stethoscope.
o By the end of the second month of pregnancy, the foetus develops limbs and digits.
o By the end of 12 weeks (first trimester), most of the major organ systems are formed, for example, the limbs and
external genital organs are well-developed.
o The first movements of the foetus and appearance of hair on the head are usually observed during the fifth month.
o By the end of about 24 weeks (end of second trimester), the body is covered with fine hair, eye-lids separate, and
eyelashes are formed.
o By the end of nine months of pregnancy, the foetus is fully developed and is ready for delivery.
28. What is parturition? Explain the.
Ans: This process of delivery of the foetus (childbirth) is called parturition.
29. What is foetal ejection reflex? Explain the process of parturition.
Ans: The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine
contractions called foetal ejection reflex.
Process of parturition: -
• Parturition is induced by a complex neuroendocrine mechanism.
• Parturition is initiated by foetal ejection reflex.
• This triggers release of oxytocin from the maternal pituitary.
• Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of
oxytocin.
• The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger
contractions.
• This leads to expulsion of the baby out of the uterus through the birth canal – parturition.
• Soon after the infant is delivered, the placenta is also expelled out of the uterus.

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30. Define the term lactation.
Ans: Lactation is the process in which the mammary gland in female undergo differentiation during pregnancy and produce
milk in them.
31. What is colostrum? What are its significances?
Ans: The milk produced during the initial few days of lactation is called colostrum.
Significance/importance-
• Contains several antibodies absolutely essential to develop resistance for the new-born babies.
• Breast-feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby.

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