Homeostasis in Mammals Prepared by WS Kwan

Definition: Keeping the internal environment in a Steady state

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 How? Controlled by Negative Feedback Mechanism

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

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 Regulate water potential in Tissue Fluid Why important? Cells will be damaged by absorbing or losing too much water Omoregulation is achieved by Organ : KIDNEYS

Nephron (kidney tubule) renal artery renal vein capillaries around nephron Loop of Henle afferent arteriole glomerulus efferent arteriole collecting duct

Normal Water Content in Blood After Sweating Concentrated Blood Larger proportion of water is reabsorbed in kidney tubule Small volume of Concentrated Urine is produced How kidneys maintain a constant water level in the body?

Normal Water Content in Blood After Drinking Diluted Blood Smaller proportion of water is reabsorbed in kidney tubule Large volume of Diluted Urine is produced How kidneys maintain a constant water level in the body?

Osmoregulation (Water & Mineral salts) After having a salty meal  Salt concentration in blood increase  Excess salts removed by kidney  Salts excreted in solution form, hence extra water is needed (How to compensate)  High blood salt concentration gives body the sensation of thirsty. (Drink more water)  As a result, large volume of concentrated urine is produced. How kidneys maintain a constant salt level in the body?

Osmoregulation Summary: Osmoregulation It is a process to maintain the water potential of the tissue fluid constant. It is done by regulating the amount of water in relation to that of salt in body. It is achieved by the kidneys. Kidneys regulate both water level & salt level.

Thermoregulation (Regulation of Body Temperature) Why important ? Most metabolic reactions are enzymatic reactions Enzymes work best at limited range of temperature Enzymes are inactivated at low temperatures Enzymes are denatured at high temperatures

Poikilotherms (cold-blooded animals) –body temperatures vary with that of the environment –e.g. reptiles, fish, amphibians

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

Maintenance of Body Temperature

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

Functions of Our Skin  protect the body (epidermis)  To provide mechanical protection  To prevent bacterial entry  To kill germs (antiseptic secretion)  To protect from harmful UV  to reduce water loss (epidermis)

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)  temperature regulation

Control Body Temperature in Hot Conditions

Avoid overheating by  More sweat is produced by sweat glands –evaporation of sweat takes away heat  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. When body is Hot:

 Erector muscles relax –hairs lie flat on the skin –reduce thickness of air trapped among the hairs

 Decrease metabolic rate & muscle contraction –gain less heat Long-term response :  Develop thinner subcutaneous fat & shed their fur to –increase heat loss

Control Body Temperature in Cold Conditions

Body reduce heat loss by  Vasoconstriction of skin arterioles –arterioles near the surface of the skin contract –to let less blood flows near the skin surface –to have less heat lost by conduction & radiation When body is Cold:

 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

 Increase metabolic rate & muscle contraction (e.g. Shivering) –gain more heat Long-term response  Develop thicker subcutaneous fat & thicker fur to reduce heat loss

Regulation of Blood Glucose Level  controlled by Negative feedback mechanism  controlled by insulin secreted from the islets of Langerhans in pancreas

Liver converts glycogen to glucose Body cells take up less 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 Body cells take up more glucose

Diabetes  Malfunction of pancreas (does not secrete enough insulin)  Cannot control Blood glucose level  Symptoms: Urine with glucose, excessive thirsty (When glucose level is too high)  Treatment: injection of insulin

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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