Homeostasis refers to the body's ability to maintain stable internal conditions such as temperature and glucose levels. It is regulated by negative feedback mechanisms. For example, temperature receptors in the skin sense changes and send signals to the hypothalamus in the brain. If body temperature rises, the hypothalamus activates sweating and blood vessel dilation to cool the body through evaporation. Conversely, it triggers shivering and vessel constriction when temperatures fall to conserve heat. Various organs also help regulate variables through hormones, like the liver controlling glucose with insulin secretion. The skin plays an important role in homeostasis through insulation, sweating, and temperature reception.

1. Homeostasis
B M Subramanya Swamy M.Sc. B.Ed.
CIE Co ordinator & Examination Officer
Kanaan Global School
Jakarta
Indonesia
swamy@kanaanglobal.sch.id

2. Introduction
• Homeostasis is the maintenance of a constant
internal environment
• The internal environment of the human body is
tissue
• Cells functions within narrow limits of fluctuation
of temperature, pressure and gaseous
concentration
• In living organisms, a state of dynamic equilibrium
exists ensuring that constant movement of material
in and out tissues
• It is controlled by Negative Feedback Mechanism

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

4. A Feedback loop
• Feedback is needed to maintain homeostasis
• One system would then play a role in influencing
another system
• E.g. when in a hot environment. Thermo
receptor send information to the brain
• This is processed and information sent to cooling
system in the body to be activated
• When adjusted, another feedback is sent to
inform the body and the loop continues

5. Examples of organ involved in Homeostasis
Organ Variable factors Mode of control
Lungs Carbon di oxide & Oxygen Regulated by respiratory centre of brain
Skin Temperature Controlled by hypothalamus of brain
Liver Glucose Regulated by insulin
Kidney Water urea and excess of
mineral salts
• Water regulated by anti diuretic
hormone
• Urea and excess salts lost in urine

6. Role of Brain
• Thermo receptor are sensory receptors
sensitive to change in temperature
• The skin has heat and cold receptors
• They are connected to the temperature
control center in the brain called the
hypothalamus

7. Temperature control in the hypothalamus
Heat center Cooling center
Rise in the temperature of blood stimulates
hypothalamus
Fall in temperature of blood stimulates
hypothalamus
Neurons activated by increase in
temperature
Neurons activated by decrease in
temperature
Increases the production of sweat Shivering occurs
Hair erector muscles relax Hair erector muscles contract
Blood capillaries dilates Blood capillaries constricts
Metabolic reaction decreases Metabolic reaction increases
Temperature of blood decreases with
negative feedback
Temperature of the blood increases with the
negative feedback

8. Regulation of body temperature
• Homoiotherms (endotherms) are animals which are able to
regulate their body temperature by physiological means
• They are often referred to as warm blooded animals
• E.g. humans birds & mammals
• Poikilotherms (ectotherms) are animals which are unable
to regulate their body temperature. They gain heat from
environment
• They are often referred as cold blooded animals
• E.g. reptiles fishes & amphibians
• A constant body temperature is very important for enzymes
– catalysed reaction to take place at an optimum

9. Effect of temperature changes on ectotherms
High temperature Low temperature
Blood temperature rises Blood temperature lowered
Heart beat faster Body activities slow
Metabolic rate increases Metabolic rate slow
Maintain temperature by moving in and
out of sunshine
Muscles function slowly
Speed of movement increases Movement is sluggish

10. Method of heat gain/ loss
Heat gain / loss Mode of action
Radiation Transfer of heat from hot object to cold through the air
Conduction Transfer of heat when in contact with each other
Convection Movement of air in which the warmer air is replaced by cooler air
Evaporation Change of liquid to vapour accompanied by cooling

11. 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

12. Structure and Function of Skin Component
Structure Function
Epidermis Consist of three layer
• Cornified layer • Contains keratin an effective waterproof layer
• Protected body from microbial infection, mechanical and
thermal damage
• Granular layer • Replaces dead cells from the cornified layer
• Malphigian layer • Cells undergo cell division
• Contains melanin to protect genetic material from UV
radiation
Dermis
• Blood vessel In temperature regulation
• Sebaceous gland Secretes sebum which act as a lubricant
• Sweat gland Produces sweat which is an excretory product as well as cooling
agent
• Hair Involves in heat control
• Erector muscle Contract and relaxes to control position of hair
• Receptors Detect changes such as heat temperature and pressure
• Elastic fibre Has collagen which affects elasticity of skin

13. Functions of skin
Function Mode of Action
Protection • Cushions skin from mechanical damage
• Insulates from thermal damage
• Prevents chemical damage
• Surface prevents bacterial infection
Water loss • Keratin is an effective waterproof agent
Heat loss • Capillary network regulates heat loss from body surface
Excretory organ • Removes urea excess water and salts
Sensory organ • Sensory receptor allow skin to respond to change in the
environment
Vitamin D • Produced when skin is exposed to sunlight

14. Response of skin to heat and cold
Response to heat Response to cold
• Hair is lowered as erector muscles
relax
• Does not trap air, reducing insulation
• Hair is raised as erector muscles
contracts
• Air around hair forms a thick layer of
insulation
• More blood is transported to the skin
as blood vessels dilated
• Shunt vessels are dilated, blood
bypasses skin surface
• Sweat is secreted by sweat glands
• Evaporation of sweat causes cooling
• Absence of sweating
• Reduction of metabolic rate reduces
heat generated
• Increases in metabolic rate
• Shivering

15. much heat lost
Vasodilation
If the body temperature rises, the blood
vessels in the skin dilate (become wider)
and allow more blood to flow near the
surface. The heat loss from the blood
through the skin helps cool the
circulating blood
Vasoconstriction little heat lost
If the body temperature falls. The blood
vessels in the skin constrict. Less warm
blood flows near the surface so less heat
is lost
Vasoconstriction & dilation
7