Describe the structure and function of the mammalian skin.

-
   It  has  a  cornified  layer  made  up  of  dead  cells  and  is  tough  and  impermeable  to  water;  to  protect the  skin  against  mechanical  damage;  bacterial  infections  and  water  loss;  granular  layer;  whose cells  divide  to  form  the  cornified  layer;  malpighian  layer;  which  is  made  up  of  diving  cells  that give  rise  to  a  new  granular  layer;  contains  melanin;  to  protect  skin  against  ultra-violet rays/radiations;  Sebaceous  glands;  which  secrete  sebum;  to  make  the  skin  supple/soft  and waterproof;  sebum  is  also  antiseptic;  Blood  vessels;  dilate  during  hot  weather;  increasing  blood flow  near  the  skin  surface;  heat  loss  is  enhanced;  constrict;  in  cold  weather;  less  blood  flow; minimize  heat  loss;  Sensory  nerve  endings  and  receptors;  enable  detection  of  external environmental  changes;  Highly  coiled  sweat  glands;  secrete  sweat;  to  control  body temperature;  when  hot  sweat  evaporates  cooling  the  body;  sweat  contains  excretory  products; subcutaneous  fat/adipose  tissue  in  dermis;  for  insulation;  hair;  to  regulate  body  temperature;  in cold  weather  erector  pili  muscles  contract;  hair  is  raised,  air  trapped  to  insulate  the  body;  in  hot weather,  erector  pili  muscles  relax;  hair  lies  flat  reducing  insulation;  dense  network  of  blood capillaries;  supply  nutrients/oxygen  to  skin  tissues;  as  well  as  carrying  away  wastes  and  carbon (IV)  oxide  away  from  the  skin  tissues;  adipose  tissue/sub-cutaneous  layer;  serves  as  an insulator;  helping  in  temperature  control;  helps  in  manufacture  of  vitamin  D;  Max.  20  mks

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