Explain how the skin is adapted to protection, excretion and homeostasis.

a)Protection.
-The cornified layer is made of dead cells; which protects the body against physical/mechanical injury/ damage; prevents entry of pathogens and poisonous chemicals;
-The sebaceous gland produces an oily secretion /sebum; that protects the skin against invasion by micro-organisms (acts as antiseptic).
-Malpighian layer contains melanin; which protects the body against harmful ultra-violet rays;
b)Excretion.
-Sweat glands secrete sweat; containing excess water, mineral salts, ammonia, traces of urea, lactic acid; Sweat flows through the sweat duct to the skin surface and the wastes are lost;
c)Homeostasis.
Osmoregulation.
-The skin has sweat glands; that secrete sweat containing excess water and mineral salts/ ions and other wastes e.g. urea hence maintaining water and ions balance;
Thermoregulation.
-It has blood arterioles/ vessels that vasodilate (vasodilation) when it is hot/ when the body temperature rises above normal; the hypothalamus is stimulated which sends impulse to the skin causing more blood flows near the skin surface hence more heat is lost through conduction and convection; When it is cold/ when the body temperature falls below normal, the arterioles constrict/ vasoconstrict (vasoconstriction); less blood flows near the skin surface hence less heat is lost/ heat is conserved;
-It has erector pili muscles which contract when it is cold/ when the body temperature falls below normal; this causes hairs to stand erect trapping more air; Air which is a poor conductor of heat insulates the body against heat loss/ prevents heat loss; when the temperature is raised above the normal/when it is hot, erector pili muscles relax; hair lies flat on the skin surface; less air is trapped and more heat is lost;
-It has sweat glands which secrete more sweat when the temperature is raised above the normal/when it is hot; water in sweat evaporates/sweat evaporates; taking up heat from the body hence the body is cooled/temperature lowered; when it is cold/ when temperature drops below normal sweat glands are less stimulated/there is less sweating; leading to less vaporization of water/less heat loss;