(a) EXPLAIN THE ROLES OF THE MAMMALIAN PLACENTA. (7 MKS) (b) (DESCRIBE HOW HORMONES REGULATE THE MENSTRUAL CYCLE IN HUMAN FEMALES. (13 MKS)

(a) Explain the roles of the mammalian placenta. (7 mks)
  • Prevents mixing of maternal and foetal blood;
  • Protects the foetus against microorganisms;
  • Protects the foetus against mechanical injury and shock;
  • Prevents some chemicals/hormones passing to the foetus;
  • Protects foetal blood vessels from damage by high blood pressure of maternal blood.
  • Allows exchange of gases
  • Allows supply of nutrients and water to the foetus;
  • Removes metabolic wastes from the foetus to be excreted through maternal blood
  • Produces progesterone and oestrogen;
  • Encloses the amniotic fluid;
  • Attach the fetus to the uterine wall;
Total 8 marks
Max 7 marks

(b) Describe how hormones regulate the menstrual cycle in human females. (13 mks)
  • Follicle stimulating hormone; produced by pituitary gland; causes development of Graafian follicle; in the ovary; stimulates the ovary to produce hormone oestrogen ; 
  • Oestrogen causes healing and repair of uterine wall after menstruation; It stimulates pituitary gland to secrete lutenizing hormone (LH).
  • LH causes ovulation; and stimulates conversion of Graafian follicle into a corpus luteum; it stimulates corpus luteum to secrete hormone progesterone; 
  • Progesterone causes thickening of uterine wall; If fertilization occurs, it inhibits production of FSH; it also inhibits production of LH and stops ovulation.
  • If the implantation does not occur, the level of progesterone falls; due to disintegration of corpus luteum causing menstruation.

Total – 18 marks
Max. 13 marks

GRAND TOTAL 20 MARKS

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