Homeostasis

B M Subramanya Swamy M.Sc. B.Ed.

CIE Co ordinator & Examination OfficerKanaan Global School

Jakarta Indonesia

swamy@kanaanglobal.sch.id

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

Rise abovenormal value

Fall below normal value

normal value

Corrective Mechanis

m

Corrective Mechanis

m

NEGATIVE FEEDBACK

MECHANISM

normal

value

negative

feedback

negative

feedback

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

Examples of organ involved in HomeostasisOrgan 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

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

Temperature control in the hypothalamusHeat 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

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

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

Method of heat gain/ lossHeat 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

Epidermis

Dermis

Outermost layerMiddle layerInnermost layer

Sweat gland

Blood capillaries

Subcutaneous fat

Receptors

Erector muscle

Nerve fibres

Sebaceous gland

Hair follicle

Structure of Mammalian Skin

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

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

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

much heat lostVasodilation

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

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