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. 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

4. 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

5. 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

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

7. 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

8. 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

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

12. Maintenance of Body Temperature
SKIN

13. 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

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. 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

32. ~ END ~