Chapter-2
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Human Reproduction
1. The mature sperms are stored in the
(a) Seminiferous tubules
(b) Vas deferens
(c) Epididymis
(d) Seminal vesicle
[Ans. (c) Epididymis]
2. The male sex hormone testosterone is secreted from
(a) Sertoli cells
(b) Leydig cell
(c) Epididymis
(d) Prostate gland
[Ans. (b) Leydig cell]
3. The glandular accessory organ which produces the largest proportion of semen is
(a) Seminal vesicle
(b) Bulbourethral gland
(c) Prostate gland
(d) Mucous gland
[Ans. (a) Seminal vesicle]
4. The male homologue of the female clitoris is
(a) Scrotum
(b) Penis
(c) Urethra
(d) Testis
[Ans. (b) Penis]
5. The site of embryo implantation is the
(a) Uterus
(b) Peritoneal cavity
(c) Vagina
(d) Fallopian tube
[Ans. (a) Uterus]
6. The foetal membrane that forms the basis of the umbilical cord is
(a) Allantois
(b) Amnion
(c) Chorion
(d) Yolk sac
[Ans. (a) Allantois]
7. The most important hormone in intiating and maintaining lactation after birth is
(a) Oestrogen
(b) FSH
(c) Prolactin
(d) Oxytocin
[Ans. (c) Prolactin]
8. Mammalian egg is
(a) Mesolecithal and non cleidoic
(b) Microlecithal and non cleidoic
(c) Alecithal and non cleidoic
(d) Alecithal and cleidoic
[Ans. (c) Alecithal and non cleidoic]
9. The process which the sperm undergoes before penetrating the ovum is
(a) Spermiation
(b) Cortical reaction
(c) Spermiogenesis
(d) Capacitation
[Ans. (d) Capacitation]
10. The milk secreted by the mammary glands soon after child birth is called
(a) Mucous
(b) Colostrum
(c) Lactose
(d) Sucrose
[Ans. (b) Colostrum]
11. Colostrum is rich in
(a) Ig E
(b) Ig A
(c) Ig D
(d) Ig M
[Ans. (b) Ig A]
12. The Androgen Binding Protein (ABP) is produced by
(a) Leydig cells
(b) Hypothalamus
(c) Sertoli cells
(d) Pituitary gland
[Ans. (c) Sertoli cells]
13. Which one of the following menstrual irregularities is correctly matched?
(a) Menorrhagia - excessive menstruation
(b) Amenorrhoea - absence of menstruation
(c) Dysmenorrhoea - irregularity of menstruation
(d) Oligomenorrhoea - painful menstruation
[Ans. (b) Amenorrhoea - absence of menstruation]
14. Find the wrongly matched pair
(a) Bleeding phase - fall in oestrogen and progesterone
(b) Follicular phase - rise in oestrogen
(c) Luteal phase - rise in FSH level
(d) Ovulatory phase - LH surge
[Ans. (c) Luteal phase - rise in FSH level]
Answer the following type of questions
Assertion (A) and Reason (R)
(a) A and R are true, R is the correct explanation of A
(b) A and R are true, R is not the correct explanation of A
(c) A is true, R is false
(d) Both A and R are false
15. A – In human male, testes are extra abdominal and lie in scrotal sacs.
R – Scrotum acts as thermoregulator and keeps temperature lower by 2°C fornnormal sperm production .
[Ans. (a) A and R are true, R is the correct explanation of A]
16. A – Ovulation is the release of ovum from the Graafian follicle.
R – It occurs during the follicular phase of the menstrual cycle.
[Ans. (c) A is true, R is false]
17. A – Head of the sperm consists of acrosome and mitochondria.
R – Acrosome contains spiral rows of mitochondria.
[Ans. (d) Both A and R are false]
18. Mention the differences between spermiogenesis and spermatogenesis.
Spermiogenesis |
Spermatogenesis |
Spermiogenesis is a part of spermatogenesis in which the haploid spermatids formed from secondary spermatocytes are transformed into mature spermatozoa. |
Spermatogenesis is the sequence of all the events involved in the formation of male gametes or the sperms in the seminiferous tubule of the testis. |
It is a stage in the maturation phase of spermatogenesis. |
It includes multiplication, growth and maturation phase. |
19. At what stage of development are the gametes formed in new born male and female?
(i) In a new born male, spematogenesis (formation of sperms) starts at the age of puberty. It is initiated due to the increase in the release of Gonadotrop in Releasing hormone.
(ii) Oogenesis is the process of development of the female gamete or egg in the ovaries. During foetal development, certain cells in the germinal epithelium of foetal ovary divide by mitosis and produce millions of oogonia or egg mother cells.
(iii) No more oogonia are added after birth. The oogonial cells enter into prophase I of meiosis to form primary oocytes which are temporarily arrested at this stage.
(iv) The primary oocytes then become primary follicles. From birth to puberty, a large number of follicles degenerate. At puberty the primary follicle undergoes further development and finally releases the ovum.
20. Expand the acronyms
a. FSH b. LH c. hCG d. hPL
(a) FSH – Follicular Stimulating Hormone
(b) LH – Leutinising Hormone
(c) hCG – Human Chorionic Gonadotropin
(d) hPL – Human Placental Lactogen.
21.How is polyspermy avoided in humans?
(i) During the process of fertilization in humans, the acrosome of the sperm enters through the corona radiata and zona pellucida layers of the ovum by releasing a enzyme called hyaluronidase. which is called acrosomal reaction.
(ii) Once fertilization is accomplished, cortical granules from the cytoplasm of the ovum form a barrier called the fertilization membrane around the ovum. This prevents further penetration of other sperms. Thus polyspermy (entry of more than one sperm into an egg) is prevented.
22. What is colostrum? Write its significance.
The mammary glands of a female secrete a yellowish fluid called colostrum during the initial days after parturition.
Significance:
(i) It has less lactose than milk and almost no fat, but it contains more proteins, vitamin A and minerals.
(ii) It is rich in IgA antibodies. It helps to protect the infants digestive tract against bacterial infections.
(iii) It is the ideal food for infants since it contains all constituents in suitable concentration and is easily digestable.
(iv) It is loaded with immune, growth and tissue repair factors.
(v) It acts as a natural antimicrobial agent to actively stimulate the maturation of the infant’s immune system.
(vi) It is fully sufficient till 6 months of age for all infants.
23. Placenta is an endocrine tissue. Justify.
(i) Human embryo is surrounded by 3 embryonic membranes. The chorionic villi and uterine tissues form the disc shaped placenta. It is a temporary endocrine organ formed during pregnancy and connects the foetus to the uterine wall through the umbilical cord.
(ii) During pregnancy, the placenta acts as a temporary endocrine gland and produces large quantities of human Chorionic Gonadotropin (hCG), human Chorionic Somatomammotropin (hCS) or human Placental Lactogen (hPL), oestrogens and progesterone which are essential for a normal pregnancy.
(iii) A hormone called relaxin is also secreted during the later phase of pregnancy which helps in relaxation of the pelvic ligaments at the time of parturition. It should be noted that hCG, hPL and relaxin are produced only during pregnancy.
(iv) Thus placenta is a endocrine tissue.
24. Draw a labeled sketch of a spermatozoan.
25. What is inhibin? State its functions.
(i) Inhibin is a hormone secreted by the sertoli cells in the stratified epithelium of the seminiferous tubule in the testis.
(ii) Function: It is involved in the negative feedback control of sperm production.
26. Mention the importance of the position of the testes in humans.
Testes are the primary male sex organs. They are a pair of ovoid bodies lying in the scrotum. The scrotum is a sac of skin that hangs outside the abdominal cavity. Since viable sperms cannot be produced at normal body temperature, the scrotum is placed outside the abdominal cavity to provide a temperature 2-3°C lower than the normal internal body temperature. Thus, the scrotum acts as a thermoregulator for spermatogenesis.
27. What is the composition of semen?
(i) Semen is a milky white fluid which contains sperms and the seminal plasma secreted from the seminal vesicles, prostate gland and bulbourethral glands.
(ii) The seminal plasma contains fructose sugar, ascorbic acid, prostaglandins and a coagulating enzyme called vesiculase which enhance sperm mobility. It also contains citrate, several enzymes and prostate specific antigens. It also provides nutrients and contains chemicals that protect and activate the sperms.
(iii) It acts as a transport medium for the sperms.
28. Name the hormones produced from the placenta during pregnancy.
Hormones produced by the placenta during pregnancy are:
(i) human Chorionic Gonadotropin (hCG)
(ii) human Chorionic Somatomammotropin (hCS)
(iii) human Placental Lactogen (hPL)
(iv) Oestrogens
(v) Progesterone
(vi) Relaxin
29.Define Gametogenesis.
Gametogenesis is the process of formation of gametes i.e., sperms and ovary from the primary sex organs in all sexually reproducing organisms. Meiosis plays the most significant role in the process of gametogenesis.
30.Describe the structure of the human ovum with a neat labelled diagram.
Human ovum is non-cleidoic, alecithal and microscopic in nature. Its cytoplasm called ooplasm contains a large nucleus called the germinal vesicle. The ovum is surrounded by three coverings namely an inner thin transparent vitelline membrane, middle thick zona pellucida and the outer thick coat of follicular cells called corona radiata. Between the vitelline membrane and zona pelludica is a narrow perivitelline space.
31.Give a schematic representation of spermatogenesis and oogenesis in humans.
32. Explain the various phases of the menstrual cycle.
The menstrual or ovarian cycle occurs approximately once in every 28/29 days during the reproductive phase of a female from menarche (Puberty) to menopause except during pregnancy. The cycle of events starting from one menstrual period till the next one is called the menstrual cycle during which cyclic changes occur in the endometrium every month. Cyclic menstruation is an indicator of normal periodic phase.
Menstrual cycle comprises of the following phases
1. Menstrual phase
2. Follicular or proliferative phase
3. Ovulatory phase
4. Luteal or secretory phase
1. Menstrual phase
The cycle starts with the menstrual phase when menstrual flow occurs and lasts for 3-5 days. Menstrual flow is due to the breakdown of endometrial lining of the uterus, and its blood vessels due to decline in the level of progesterone and oestrogen. Menstruation occurs only if the released ovum is not fertilized. Absence of menstruation may be an indicator of pregnancy. However it could also be due to stress, hormonal disorder and anaemia.
2. Follicular or proliferative phase
The follicular phase extends from the 5th day of the cycle until the time of ovulation. During this phase, the primary follicle in the
ovary grows to become a fully mature Graafian follicle and simultaneously, the endometrium regenerates through proliferation. These changes in the ovary and the uterus are induced by the secretion of gonadotropins like FSH and LH, which increase gradually during the follicular phase. It stimulates follicular development and secretion of oestrogen by the follicle cells.
3. Ovulatory phase
Both LH and FSH attain peak level in the middle of the cycle (about the 14th day). Maximum secretion of LH during the mid cycle called LH surge induces the rupture of the Graafian follicle and the release of the ovum (secondary oocyte) from the ovary wall into the peritoneal cavity. This process is called as ovulation.
4. Luteal or secretory phase
During luteal phase, the remaining part of the Graafian follicle is transformed into a transitory endocrine gland called corpus luteum. The corpus luteum secretes large amount of progesterone which is essential for the maintenance of the endometrium. If fertilisation takes place, it paves way for the implantation of the fertilized ovum. The uterine wall secretes nutritious fluid in the uterus for the foetus. So, this phase is also called as secretory phase. During pregnancy all events of menstrual cycle stop and there is no menstruation. In the absence of fertilisation, the corpus luteum degenerates completely and leaves a scar tissue called corpus albicans. It also initiates the disintegration of the endometrium leading to menstruation, marking the next cycle.
33.Explain the role of oxytocin and relaxin in parturition and lactation.
1. Relaxin is the hormone secreted by placenta that cause the contraction of pelvic joints and promotes parturition (Child birth)
2. Oxytocin causes the Let-down-reflex - the actual ejection of milk from alveoli of mammary glands. Oxytocin also stimulates the uterus to regain its pre-pregnancy size after child birth.
34.Identify the given image and label its parts marked as a, b, c and d.
The given image is the diagram of human egg cell or ovum.
a – vitelline membrane
b – nucleus
c – zona pellucida
d – Corona radiata
35. The following is the illustration of the sequence of ovarian events (a-i) in a human female.
a) Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents.
b) Name the ovarian hormone and the pituitary hormone that have caused the above-mentioned events.
c) Explain the changes that occurs in the uterus simultaneously in anticipation.
d) Write the difference between C and H.
(a) The figure ‘F’ illustrates ovulation. It represents the maturation stage of oogenesis.
(b) The pituitary hormone leutinising hormone and the ovarian hormone oestrogen are responsible for the above mentioned events.
(c) (i) The endometrium of the uterus becomes thicker to receive the fertilized ovum in anticipation. (Implantation)
(ii) The uterine wall secretes nutritious fluid in the uterus for the foctus.
(d) ‘C’ indicates developmental stage of follicle in the Ovary when the ovum has not been released. ‘H’ indicates a stage where the ovum has been released and the remaining part of the ruptured graafian follicle has transformed into a temporary endocrine gland called corpus luteum to produce additional hormones for pregnancy.
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