1. The document discusses homeostasis and temperature regulation in the human body. It defines homeostasis as the maintenance of constant internal conditions and describes how the skin, blood flow, sweating, and shivering help regulate body temperature. 2. The hypothalamus acts as the thermoregulatory center that detects temperature changes and coordinates responses like vasodilation and vasoconstriction to increase or decrease blood flow to the skin. 3. Other examples of homeostasis discussed include blood glucose regulation by the liver, pancreas, and hormones like insulin and glucagon. The kidneys also help regulate water, salts, and acid levels in the blood.

1. Made by: TAHIRA PASHA

2. Let’s exercise!!
• Heart rate before, after and during exercise
• Why does heart rate change?
• How does your heart rate become normal?
• What evidence shows that homeostasis was disturbed in
this activity?
• Discuss how long it took your heart rate to return to its
state of homeostasis.
• What might cause differences in the time it took for
different people?
• Why do athletes typically have a quicker recovery time in
their heart rate compared to the average person?

3. Examples from daily life
• Body temp
• Water content
• Glucose Conc.
• Attack by immune system
• The maintenance of healthy blood pressure
• Urinating

4. Learning objectives
• Define homeostasis
• Skin structure
• Control of body temperature
• Homeostasis
• Negative feedback

5. Definition:
Homeostasis is the maintainance of
constant internal conditions in
the body.

6. Skin structure:
• In the basal layer some
of the cells are
continually dividing and
pushing the older cells
nearer the surface. Here
they die and are shed at
the same rate as they are
replaced.
• The basal layer and the
cells above it constitute
the epidermis.
• The basal layer also
contributes to the hair
follicles. The dividing
cells give rise to the hair.
The skin and temperature control

7. • There are specialized
pigment cells in the
basal layer and
epidermis. Melanin
• The thickness of the
epidermis and the
abundance of hairs
vary in different parts
of the body
• The dermis contains
connective tissue
with hair follicles,
sebaceous glands,
sweat glands, blood
vessels and nerve
endings.
• There is usually a
layer of adipose
tissue

8. The structure of human skin

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

10. Skin function
1. Protection
• The outermost layer of dead cells of the epidermis helps to reduce water loss and
provides a barrier against bacteria.
• The pigment cells protect the skin from damage by the uv rays in sunlight.
• Why do white ppl tan?
2. Sensitivity
• sense receptors in skin- touch, pressure, heat, cold and pain. ??
3. Temperature regulation
• Help in maintaining body temp by adjusting the flow of blood near the skin
surface and by sweating.

11. Temperature control
• Normal human body temperature?? What if it fluctuates?
• Hands, feet, head or internal organs, will be at different temperatures but temp
under the tongue, will vary by only 1 or 2 degrees.
• Heat is lost from the body surface by conduction, convection, radiation and
evaporation.
• The amount of heat lost is reduced to an extent due to the insulating properties of
adipose (fatty) tissue in the dermis.
• Some mammals - whales and seals, have thick layers of blubber to reduce heat
loss more effectively.
• How much insulation the blubber gives?? Water : fat
• Heat is gained, internally, from the process of respiration and, externally, from the
surroundings or from the Sun.

12. Overheating
• - More blood flows near the surface of the skin,
• - Sweating – the sweat glands secrete sweat on to the skin surface. When this layer of
liquid evaporates, it takes heat (latent heat) from the body and cools it down
• Overcooling
• Less blood flows near the surface of the skin
• Sweat production stops – thus the heat lost by evaporation is reduced.
• Shivering –rapid muscular contraction in the limbs release heat as a result of respiration
in the muscles.
• 37 °C but control our temperature by adding or removing clothing or deliberately taking
exercise.
• Whether we feel hot or cold depends on the sensory nerve endings in the skin, which
respond to heat loss or gain.
• No conc control on body temp
• The brain detects change in body temp
• hypothalamus - thermoregulatory centre - temperature receptors detect
temperature changes in the blood and co-ordinate a response to them.
• Temperature receptors are also present in the skin. They send information
to the brain about temperature changes.

13. Homeostasis extended
• Enzymes & temperature
• The cell membrane controls the substances that enter and leave the cell,
but it is the tissue fluid that supplies or removes these substances, so composition of the
• Tissue fluid should be maintained.
• If the tissue fluid were to become too concentrated?
• If the tissue fluid were to become too dilute?
• The kidneys, which remove substances that might poison the enzymes.
• The kidneys also control the level of salts, water and acids in the blood.
• The composition of the blood affects the tissue fluid which, in turn, affects the cells.
• Role of liver in maintaining blood glucose in body
• Glucose and the brain
• The lungs play a part in homeostasis by keeping the concentrations of 02 and carbon
CO2 in the blood at the best level for the cells’ chemical reactions, especially respiration.
• The skin regulates the temperature of the blood.
• If the cells were to get too cold Or If they became too hot?
• The brain checks the composition of the blood flowing through it and if it is too
warm, too cold, too concentrated or has too little glucose, nerve impulses or
hormones are sent to the organs concerned, causing them to make the necessary
adjustments.

14. • 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

15. Homeostasis and negative feedback
• Temperature regulation
• Maintenance of a constant body temperature important so the reactions do not
speed up or slow down when the surrounding temperature changes.
• The constant-temperature or homoiothermic (‘warm-blooded’) animals, the
birds and mammals, therefore have an advantage over the variable temperature
or poikilothermic (‘cold-blooded’) animals.
• Poikilotherms such as reptiles and insects can regulate their body temperature to
some extent by, for example, basking in the sun or seeking shade. Nevertheless,
if their body temperature falls, their vital chemistry slows down and their
reactions become more sluggish. They are then more vulnerable to predators.
• The ‘price’ that homoiotherms have to pay is the intake of enough food to
maintain their body temperature, usually above that of their surroundings.

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

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

18. • In the hypothalamus-
thermoregulatory centre.
• temperature receptors in the
skin.
• A rise in body temperature
• vasodilation and sweating.
• A fall in body temperature
• vasoconstriction and shivering.
• Negative feedback.

19. CAIE question
• https://pmt.physicsandmathstutor.com/down
load/Biology/GCSE/Past-Papers/CIE/Paper-
4/November%202018%20(v2)%20QP%20-
%20Paper%204%20CIE%20Biology%20IG
CSE.pdf

20. Regulation of blood sugar
• Role of insulin and glucagon
• Insulin increases the uptake
of glucose in all cells for use
in respiration; it promotes
the conversion of
carbohydrates to fats and
slows down the conversion
of protein to carbohydrate.
• The level of glucose in the
blood to within narrow
limits –homeostasis.

21. • FBG- between 90 and 100 mg 100 cm−3 blood.
• After a meal, 140 mg 100 cm−3
• 2 hours later, 95 mg- why??
• About 100 g glycogen is stored in the liver of a healthy man.
• If the concentration of glucose in the blood falls below about 80 mg 100
cm−3 blood?
• If the blood sugar level rises above 160 mg 100 cm−3, glucose is excreted by the
kidneys.
• A blood glucose level below 40 mg 100 cm−3??
• Liver helps in maintaining BGC between 80 and 150 mg,
• What if production or function of insulin is not proper?

22. 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)

23. Liver
converts
glycogen to
glucose
normal blood
glucose level
Blood glucose
level fallsSoon
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

24. Type 1 diabetes
• It results from a failure of the islet cells to produce sufficient
insulin.
• Need regular injections of the hormone
• ‘insulin-dependent’ diabetes.
• The patient is unable to regulate the level of glucose in the blood-
excreted in the urine, or fall so low that result is coma.
• feeling tired, feeling very thirsty, frequent urination and weight
loss.
• Weight loss is experienced because the body starts to break down
muscle and fat.
• Diabetics need a carefully regulated diet
• Need regular blood tests and take regular exercise.

25. Temperature control
• Skin maintains a constant body temperature.
• Dilation or constriction of arteriole blood to flow near the skin surface through the blood
capillaries.
• Vasodilation – the widening of the arterioles in the dermis allows more warm blood to
flow through blood capillaries near the skin surface and so lose more heat
• Vasoconstriction – narrowing (constriction) of the arterioles in the skin reduces the
amount of warm blood flowing through blood capillaries near the surface

26. Control Body
Temperature in
Hot Conditions

27. 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.

28. 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)

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

30. Control Body
Temperature in
Cold Conditions

31.  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

32.  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

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

34. ~END~