HL Sexual reproduction

Question 1

Where does Spermatogenesis take place?

Answer 1

within seminiferous tubules in the testes. Cells in gaps between tubules are called interstitial or “leydig” cells.

Question 2

What is the order of events in spermatogenesis?

Answer 2

1. The outer layer, “germinal epithelium cells” (diploid) divide via mitosis producing diploid cells.
2. These diploid cells become large, and are now referred to as “primary spermatocyte”.
3. Each primary spermatocyte goes through the FIRST DIVISION of meiosis, producing TWO secondary spermatocytes (haploid).
4. Each secondary spermatocyte goes through the SECOND DIVISION of meiosis, producing two spermatids.
5. Each spermatid becomes associated with SERTOLI CELLS (nurse cells) which helps them differentiate and develop into spermatoza (also grow tail).
6. Spermatoza/Sperm detach from stroll cells and are carried out of the testes by fluid eventually.

Question 3

What is the order of events in Oogenesis?

Answer 3

1. Primary follicle consists of a central oocyte surrounded by a single layer of follicle cells that begin developing, and oocyte completes FIRST DIVISION of MEIOSIS
2. In secondary follicle, follicle cells proliferate (grow in number), a fluid cavity develops, and oocyte begins SECOD MEIOTIC DIVISION. Only one of these usually goes on to produce a mature follicle with secondary oocyte.
3. Mature follicle is released from ovary via exocytosis, “ovulation”, and the corpus luteum is maintained.

Question 4

What is the order of events in fertilisation? (And how is polyspermy prevented)

Answer 4

ACROSOME REACTION:
- Acrosome in sperm head contains digestive enzymes that break down the zona pellucida.

PENETRATION OF EGG MEMBRANE:
- membranes of sperm and egg membrane fuse and the nucleus of sperm enters the egg cell (fertilisation)

CORTICAL REACTION:
- Sperm activates egg - cortical granules in eggs are vesicles filled with enzymes released by exocytosis, and digest binding proteins so no further sperm can bind; zone pellucid hardens.

Question 5

Explain the mechanisms involved in parturition (birth)

Answer 5

• During the pregnancy, progesterone inhibits oxytocin production in the pituitary gland.
• At the end of pregnancy, foetus produces hormone that signals the placenta to STOP PRODUCING PROGESTERONE, so that oxytocin production is no longer inhibited.
• Oxytocin -> muscular contractions of uterine muscles.
• Stretch receptors signal to pituitary gland to produce MORE OXYTOCIN - POSITIVE FEEDBACK
• Cervix dilates as muscle fibres relax, amniotic sac bursts.

Question 6

Role of Human growth Hormone (hCG)

Answer 6

• Produced by Embryo, stimulates corpus leuteum to continue producing progesterone and oestrogen, maintaining the endometrium.