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

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

• kidneys :

Parts of Body involved

skin – regulate water & mineral salts concentration • skin : – regulate body temperature • liver & pancreas : – regulate blood glucose level liver + blood pancreas tissue cells kidney

Osmoregulation (Water & Mineral salts)

• Regulate water potential in Tissue Fluid • Organ involved: KIDNEYS

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

After Drinking Normal Water Content in Blood 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

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

Epidermis Hair follicle Sebaceous gland Erector muscle Receptors Dermis Outermost layer Middle layer 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)

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

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