Free Human Reproductive System MCQs with Answers

1. Spermatogenesis in the human male takes place in the

• A. seminiferous tubules
• B. epididymis
• C. prostate gland
• D. vas deferens

Explanation: The germinal epithelium lining the seminiferous tubules of the testis divides by mitosis and then meiosis to form spermatids, which mature into spermatozoa. The epididymis is where sperm are stored and gain motility after leaving the testis, so it is the tempting answer, but no division occurs there. The prostate and the vas deferens contribute secretions and transport, not gamete formation.

2. Testosterone is secreted by the

• A. Sertoli cells
• B. interstitial cells of Leydig
• C. germinal epithelium
• D. seminal vesicles

Explanation: The Leydig cells lie in the connective tissue between the seminiferous tubules and secrete testosterone in response to luteinising hormone from the anterior pituitary. Sertoli cells sit inside the tubules and nourish the developing sperm, which is why they are the usual confusion. Testosterone maintains sperm production and the secondary sexual characters such as voice and body hair.

3. Fertilisation of the human ovum normally occurs in the

• A. uterus
• B. cervix
• C. ampulla of the fallopian tube
• D. ovary

Explanation: The secondary oocyte is swept into the oviduct at ovulation and meets sperm in the wide upper third, the ampulla, within about a day. The zygote then divides as it travels down and reaches the uterus as a blastocyst several days later, so the uterus is the site of implantation rather than of fertilisation. Fertilisation in the ovary or in the abdominal cavity is possible but is an abnormal ectopic pregnancy.

4. The blastocyst implants itself in the

• A. myometrium
• B. perimetrium
• C. cervix
• D. endometrium

Explanation: The endometrium is the inner glandular lining of the uterus, thickened and richly supplied with blood by progesterone during the secretory phase, which is exactly what implantation requires. The myometrium is the thick smooth muscle layer whose contractions expel the baby at birth, and the perimetrium is the outer covering. Implantation in the cervix or oviduct is an ectopic pregnancy and is dangerous.

5. The hormone detected by a standard urine pregnancy test is

• A. luteinising hormone
• B. follicle stimulating hormone
• C. progesterone
• D. human chorionic gonadotropin

Explanation: The chorion of the young embryo secretes hCG, which keeps the corpus luteum alive so that progesterone continues and the endometrium is not shed. Because only a pregnancy produces it, hCG is specific, whereas progesterone is high in the luteal phase of every cycle and so would give false positives. It appears in urine within about two weeks of fertilisation.

6. Which of the following is NOT a function of the placenta?

• A. Production of the fetus's red blood cells
• B. Exchange of oxygen and carbon dioxide
• C. Secretion of progesterone and hCG
• D. Transfer of nutrients from mother to fetus

Explanation: The fetus makes its own blood cells, first in the yolk sac and liver and later in the bone marrow, and maternal and fetal blood never actually mix in the placenta. What the placenta does is bring the two circulations close enough for exchange of gases, nutrients, wastes and antibodies, and it also works as an endocrine gland from about the third month. It further acts as a partial barrier, though alcohol, nicotine and many viruses cross it.

7. The acrosome of a spermatozoon contains

• A. the mitochondria that power the tail
• B. hydrolytic enzymes that digest the coverings of the egg
• C. the haploid nucleus
• D. contractile proteins of the flagellum

Explanation: The acrosome is a lysosome like cap over the front of the head, and its enzymes, including hyaluronidase, break down the corona radiata and zona pellucida so that one sperm can reach the egg membrane. The nucleus lies behind it in the head, and the mitochondria are packed into the middle piece. A sperm whose acrosome reaction fails cannot fertilise even a normal egg.

8. The mitochondria of a spermatozoon are concentrated in the

• A. head
• B. acrosome
• C. middle piece
• D. tip of the tail

Explanation: A spiral sheath of mitochondria wraps the middle piece and supplies the ATP that the flagellum needs for the long journey to the oviduct. Placing them immediately behind the head puts the energy source next to the machinery that uses it. Almost none of these mitochondria enter the egg at fertilisation, which is why human mitochondrial DNA is inherited from the mother alone.

9. The number of chromosomes in a human secondary oocyte is

• A. 23
• B. 46
• C. 44
• D. 92

Explanation: The first meiotic division is completed before ovulation and halves the chromosome number, so the secondary oocyte is haploid with 23 chromosomes, each still made of two chromatids. Forty six is the diploid number of the primary oocyte and of every body cell, which is why it is the common error. The second division is completed only if a sperm actually penetrates the egg.

10. Meiosis of one human primary oocyte finally produces

• A. four functional ova
• B. two ova and two polar bodies
• C. one ovum and three polar bodies
• D. four polar bodies and no ovum

Explanation: Cytoplasmic division in oogenesis is deliberately unequal, so almost all the cytoplasm and stored food goes to one cell while the other products are tiny polar bodies that soon degenerate. This gives the single ovum the reserves an early embryo needs before implantation. Spermatogenesis, by contrast, divides the cytoplasm evenly and yields four functional sperm from each primary spermatocyte.