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

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

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

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

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

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

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

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

Maintenance of Body Temperature SKIN

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

Epidermis 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

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

Dermis 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

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

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)

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

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