(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

Comments

Post a Comment

Popular posts from this blog

Explain how structures of the human ear are adapted to their functions. (20 marks)

-
Image
The pinna;- is funnel shaped to trap sound waves; cartilaginous to maintain the funnel shape; collects and directs sound waves into the external auditory meatus ear; The external auditory canal; - a tube connected to the pinna that directs sound waves from the pinna to the eardrum lining the auditory canal; has hair that trap foreign particles; The canal contains wax-secreting cells; and hair which traps dust particles; and pathogenic bacteria hence prevent them from getting into the ear; The eardrum; - has a thin tough membrane; that easily vibrates when hit by sound waves; transferring them into vibrations. The ear ossiscles; - they act like a layer and they easily move forward and backward to amplify sound vibrations that hit them; The suspensory ligaments; - suspends the ear ossicles and prevents excessive vibration that would otherwise damage the inner parts of the ear; The eustachian tube - it connects the middle ear with the pharynx; and it equalises air pressure between
Read more

DESCRIBE THE ADAPTATIONS OF THE ILEUM TO ITS FUNCTION (20 MARKS)

-
Has secretory glands/crypts of lieberkuhn which secretes enzymes (maltase/sucrase/lactase/peptidase/lipase to complete digestion of sugars/proteins/lipids. Goblet cells secrete mucus which allows for smooth movement of food and protect wall of ileum from action of digestive enzymes Very long to provide large surface area for absorption. Highly folded/coiled to slow movement of food to allow more time for digestion/absorption/ and to increase surface area for absorption. Has numerous villi which increase surface area for absorption/microvilli which further increase surface area for absorption. Ileum wall/villi have thin epithelium which is only one cell thick to reduce distance over which digested food has to diffuse. Villi are highly vascularised/have a rich network of blood capillaries for rapid transport from small intestines and maintain a steep concentration gradient for rapid absorption. Villi have lacteals for absorption of fatty acids and glycerol Cells of ileum wall h
Read more

(a) Define digestion. [2 m] (b) Describe the digestion of a piece of ugali in a human digestive system from the mouth until its assimilation. [18mks]

-
(a) Define digestion It is break down of complex insoluble; v food substance into simple soluble food substances; v 2max (b) Describe the digestion of ugali; Digestion of ugali begins in the mouth;v ugali is chewed by the teeth to increase large surface areav for action of salivary amylase / ptyalin; vThe food mixes with saliva produced by salivary glands;v Saliva contains mucus and enzyme ptyalin. Mucus moistens, softens and lubricates the food;v ptyalin speeds up the conversion of starch to maltose;v ugali is made into bolus in the mouth;v The bolus moves along the oesophagus and prestalsis / by contraction and relaxation of circular and longitudinal muscles into the stomach;v The digestion continues until ugali become acidic since the stomach does not contain carbohydrase / carbohydrate digesting enzymes no digestion of ugali takes place here.v Ugali now
Read more