Importance of Homeostasis in Mammals  metabolic reactions are controlled by enzymes  enzymes work best in a narrow range of temperature & pH only  ∴ important to keep internal environment as steady as possible

Definition: Keeping the internal environment in a Steady state It is controlled by Negative Feedback Mechanism

Rise above normal value Fall below normal value Corrective Mechanism NEGATIVE FEEDBACK MECHANISM normal value negative feedback

kidneys : –regulate water & mineral salts concentration skin : –regulate body temperature liver & pancreas : –regulate blood glucose level Parts of Body involved kidney liver pancreas + skin tissue cells blood

Osmoregulation (Water & Mineral salts) Regulate water potential in Tissue Fluid Organ involved: KIDNEYS

Normal Water Content in Blood After Sweating Concentrated Blood Larger proportion of water is reabsorbed Concentrated Urine is produced

Normal Water Content in Blood After Drinking Diluted Blood Smaller proportion of water is reabsorbed Diluted Urine is produced

Osmoregulation (Water & Mineral salts) After having a very salty meal  produce concentrated urine to remove excess salts in solution form  extra water is needed to be excreted along with the excess salts  sensation of thirst (drink more water to compensate for the water loss)

Thermoregulation (Regulation of Body Temperature) poikilotherms (cold-blooded animals) –body temperatures vary with that of the environment –e.g. reptiles, fish, amphibians

Homoiotherms (warm-blooded animals) –keep body temperature constant even in winter by increasing metabolic rate –e.g. birds, mammals Thermoregulation (Regulation of Body Temperature)

Maintenance of Body Temperature

Epidermis Dermis Outermost layer Middle layer Innermost layer Sweat gland Blood capillaries Subcutaneous fat Receptors Erector muscle Nerve fibres Sebaceous gland Hair follicle Structure of Mammalian Skin

Epidermis dead outer layer –relatively impermeable –easily peeled off –protect the underlying tissues to prevent mechanical injury to prevent bacterial entry to reduce water loss

middle layer –made up of living cells –become dead as they approach the surface black inner layer –with pigment (melanin) to absorb ultra- violet ray for sunlight –have cell division to repair the lost outer layers Epidermis

Dermis  Blood capillaries –to nourish the cells of the skin –branch into superficial blood capillaries  Sweat gland –surrounded by a network of capillaries –secrete sweat (consists of water, mineral salts, urea & some waste materials) –characteristic of mammals

 Hair follicles & Hairs –each hair has a nerve & a capillary attached to it –nerve: receives stimuli –capillary: supply food & oxygen –hairs reduce heat loss & assist in temperature regulation  Erector muscle –controls the hair movement for temperature regulation Dermis

 Sebaceous gland –secretes oily substance to make the skin waterproof to prevent bacterial entry  Receptors –detect pain, pressure, temperature & touch Dermis

 beneath the Dermis  for fat storage  acts as insulator of heat Subcutaneous Fat

Functions of Our Skin  protect the body (epidermis)  to provide mechanical protection  to prevent bacterial entry  to reduce water loss  temperature regulation (hair)

Functions of Our Skin  excretion of sweat (sweat gland)  store fats (subcutaneous fat)  sensation (numerous receptors )  production of vitamin D under ultra-violet light (inner epidermis)

Control Body Temperature in Hot Conditions

 More sweat is produced by sweat glands –evaporation of sweat takes away heat which produces a cooling effect  Vasodilation of skin arterioles –arterioles near the surface of the skin dilates –to let more blood flows near the skin surface –to have more heat lost by conduction & radiation.

 Erector muscles relax –hairs lie flat on the skin –reduce thickness of air trapped among the hairs (not effective in human because human’s hairs are short)

 Develop thinner subcutaneous fat & shed their fur –as long term responses –increase heat loss  Decrease metabolic rate & muscle contraction –gain less heat

Control Body Temperature in Cold Conditions

 Vasoconstriction of skin arterioles –arterioles near the surface of the skin constrict –to let less blood flows near the skin surface –to have less heat lost by conduction & radiation

 Erector muscles contract –pull hairs erect for trapping more air –thicker layer of air acts as a good insulator of heat  Less sweat is produced by sweat glands –reduce heat loss by evaporation

 Develop thicker subcutaneous fat & thicker fur –as long term responses –reduce heat loss  Increase metabolic rate & muscle contraction –gain more heat

Regulation of Blood Glucose Level  controlled by Negative feedback mechanism  controlled by insulin secreted from the islets of Langerhans in pancreas  Diabetes - malfunction of pancreas (does not secrete enough insulin)

Liver converts glycogen to glucose normal blood glucose level Blood glucose level falls Soon after a meal Long after a meal Blood glucose level rises normal blood glucose level Too High Too Low Pancreas secretes insulin Pancreas secretes less insulin Liver coverts glucose to glycogen

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