Importance of Homeostasis in Mammals

2. 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

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

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

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

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

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

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

9. 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)

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

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

12. Maintenance of Body Temperature SKIN

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

14. 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

15. 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

16. 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

17. 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

18. Dermis • Sebaceous gland • secretes oily substance • to make the skin waterproof • to prevent bacterial entry • Receptors • detect pain, pressure, temperature & touch

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

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

21. 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)

22. Control Body Temperature in Hot Conditions

23. 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.

24. 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)

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

26. Control Body Temperature in Cold Conditions

27. 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

28. 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

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

30. 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)

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

32. ~END~