(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;
·         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.
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; stimulates development of Graafian follicle; in the ovary; it also stimulates the ovary to produce hormone oestrogen ; oestrogen causes healing and repair of uterine wall after menstruation; oestrogen also stimulates pituitary gland to secrete Luteinizing hormone (LH).
LH causes ovulation; and stimulates conversion of Graafian follicle into a corpus luteum; it also 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

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