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

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(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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