chapter 11

• Homeostasis

  -maintenance of the constant internal environment of an living organism despite the changes of the external environment and internal environment .It is achieved by negative feedback mechanism.

  -basic function of organism to survive

  -to maintain the physically and chemically condition in the body for enzymatic and other cellular activities.

  -enables biological system to function effectively and smoothly with minimum wastage of energy.
• When the environment is hot

  Skin temperature increases
• Heat receptor


  Detects skin temperature increase
• Superficial capillary


  Capillary near to the skin surface
• Latent heat of vaporisation


  Heat required for evaporation
• Cooling effect occurs to cool the skin
• These responses increase the heat loss to the surrounding and decrease the heat production
• Body temperature decreases and returns to the normal set point
• When the environment temperature decreases

  The skin temperature will decrease
• Response to cold

  1. Cold receptors detect temperature

  2. Send nerve impulses to posterior hypothalamus

  3. Sphincter muscle contracts

  4. Vasoconstriction occurs

  5. Less blood flows to superficial capillaries

  6. Decrease heat release by radiation

  7. Hair erector muscle contracts

  8. Hair traps insulating air

  9. Shivering occurs

  10. Adrenaline released for shivering

  11. Thyroid gland releases thyroxine

  12. Increase metabolic rate
• Responses to decrease heat loss

  • Decrease heat loss to surroundings
  • Increase heat production
• Less blood flows to the superficial capillary which is near to the surface of the skin
• Increased heat is released to the surrounding by radiation
• Hair on the skin will erect and trap a thicker layer of heat insulating air
• Shivering occurs to increase production of heat
• Adrenaline is released by adrenal glands for shivering to gain heat from the contracting muscles
• Thyroid gland will also release thyroxine to increase the metabolic rate
• More energy and heat are generated in the body
• These responses

  Decrease heat loss to the surrounding and increase heat production to increase body temperature to return to the normal set point
• Importance to miantain body temperature

  -to provide optimum body temperature.

  -to provide optimum activity of enzyme

  -provide optimum medium of biochemical reactions.
• Importance to maintain blood osmotic pressure

  -maintain electrolyte balance in the cell

  -maintain blood volume in cell

  -maintain the blood pressure
• Ectothermic: organism that rely on heat obtained from the environment than metabolic heat to raise their body temperature.

  -exapmle : fish ,amphibian and reptiles.
• Endothermic -organism that rely on metabolic heat to maintain their body temperature

  Example: birds, mammals
• physiological- the body's automatic response to a stimulus.

  behavioural - you respond to a stimulus
• Glycogenesis

  -glucose ---->glycogen
• Glycogenolysis

  • glycogen----> glucose
• Gluconeogenesis

  • pyruvate---->glucose
• Characteristics of liver

  • Liver is the largest visceral organ in the body
  • liver cell is called as hepatocyte
  • The hepatic artery supply oxygenated blood to the liver from the aorta to the hepatocytes
  • The hepatic vein transports deoxygenated blood from hepatocytes to vena cava
  • hepatic portal vein transport deoxygenated blood which is rich in soluble nutrients absorbed from the intestine to the liver
• • Hepatic artery and hepatic portal vein fuse together to form sinusoid
• A group of hepatocytes with its associated blood supply is know as liver acinus
• Kupffer cell are attached to the wall of sinusoid

  -They are phagocytic macrophage to ingest and destroy the worn out erythrocytes and foreign particles .
• Canaliculus

  • a channel that transport bile juice secreted by hepatocytes to the branch of bile duct
• Glycogenesis


  The formation of glycogen from glucose
• Glycogenesis process

  1. Insulin control

  2. Insulin production from Beta-cells

  3. Insulin binds to liver cell receptor

  4. Increase permeability of liver cell to glucose

  5. Glucose is phosphorylated by hexokinase

  6. Glucose-6-phosphate conversion by glucose-1-phosphate uridyltransferase

  7. Glucose converted to glycogen by glycogen synthase
• The process of glycogenesis is under control by insulin
• Insulin is produced from the Beta-cells of the islets of Langerhans of the pancreas
• Insulin binds to the receptor on the plasma membrane of the liver cell


  Increases the permeability of the liver cell to glucose
• Phosphorylation of glucose

  1. Add phosphate group from ATP

  2. Form glucose-6-phosphate

  3. With the help of hexokinase
• Conversion of glucose-6-phosphate

  1. Converted to glucose-1-phosphate

  2. With the help of glucose-1-phosphate uridyltransferase
• Conversion of glucose to glycogen

  By glycogen synthase