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  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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