homeostasis and hormonal control

• what is homeostasis ?

  it is the maintenance of a constant internal environment
• what does the internal environment of the human body include ?

  it includes the blood and tissue fluids that surrounds the cells in the body
• what are some examples of homeostasis in humans ?

  • regulating body temperature
  • regulating the water potential of blood and tissue fluid
  • regulating blood glucose concentration
• how does homeostasis work ?

  • if the blood concentration of a substance increases above the normal level, it is detected by a receptor
  • the body will respond by returning the blood concentration of the substance back to normal level
• what is the negative feedback process ?

  it is when the body reacts to bring about an opposite effect to the changes in the internal body detected, setting off a sequence of events that restores the system
• what is any change from normal condition called ?

  stimulus
• what are the conditions for negative feedback to take place ?

  • a normal level to be maintained
  • a stimulus
  • a receptor to detect the stimulus and send signals to the control centre
  • a corrective mechanism to bring about the reverse effect of the stimulus
• what are hormones ?

  they are chemical substances produced in minute quantities by an endocrine gland and is transported in the bloodstream to target organs where it exerts its effects
• where are hormones produced ?

  endocrine glands
• what is the difference between endocrine and exocrine glands ?

  exocrine glands have ducts or tubes for carrying away their secretion but endocrine glands are ductless and secrete their secretions directly into the blood stream
• which organ is both an endocrine and exocrine gland ?

  pancreas
• what happens if there is a normal amount of insulin secretion ?

  decrease blood concentration by

  • making cell membranes more permeable to glucose, allowing more glucose to diffuse into the liver and muscle cells
  • stimulating liver and muscle cells to convert excess glucose into glycogen for storage
  • increasing the use of glucose for respiration
• what happens if there is a lack of secretion of insulin ?

  • increase blood glucose concentration as
  • glucose cannot be stored or utilised by tissue cells
  • glucose concentration rises and some glucose is lost in the urine
  • gives rise to a disease called diabetes mellitus
  • muscle cells have no reserves of glycogen, the body grows weak and continuously loses weight
• what happens if there is an oversecretion of insulin ?

  abnormal decrease in blood glucose concentration such that

  • low blood glucose concentration results in a condition called shock
  • seizures or fits, collapsing or passing out may follow
• what are the effects of glucagon ?

  • increasing blood glucose concentration by stimulating:
  • conversion of glycogen into glucose
  • conversion of fats and amino acids into glucose
• describe the homeostatic control of BGC when it increases above normal level

  1. the islets of langerhans in the pancreas are stimulated to secrete more insulin into the bloodstream
  2. the blood transports the insulin to the liver muscles to
  3. increase the permeability of the cell membrane to glucose so it is absorbed more quickly by the cells
  4. increase the rate of respiration
  5. causes the liver and muscles to convert the excess glucose to glycogen where it is stored there
  6. BGC decreases, providing a feedback to the receptor to reduce insulin production
• describe the homeostatic control of BGC when it falls below normal level

  1. the islets of langerhans in the pancreas are stimulated to secrete more glucagon into the bloodstream
  2. blood transports the glucagon to the liver and muscles which
  3. causes the conversion of stored glycogen back to glucose which enters the bloodstream from the liver
  4. BGC increases, providing feedback to the receptor to reduce glucagon production
• what are the 2 mainly types of diabetes ?

  • type 1 diabetes
  • develops early in a person's life
  • inherited condition
  • islets of langerhans are unable to produce or secrete sufficient insulin
  • type 2 diabetes
  • occurs later in a person's life
  • overweight people are more likely to develop it
  • develops when the target cells, such as the muscle cells, do not respond well to insulin
• what are the signs and symptoms of diabetes ?

  • persistently high blood glucose level
  • presence of glucose in the urine
  • healing of wounds is slow or difficult
  • frequent urination
  • weight loss
  • thirst
• what are the risk factors of type 2 diabetes ?

  • obesity
  • age
  • the risk if higher as you get older
  • family history
  • blood lipid levels
  • risk is increased if you have high levels of 'bad' cholesterol or LDH and low levels of 'good' cholesterol or HDL in the blood
  • sedentary lifestyle
  • physical activities uses up the excess glucose to provide energy for muscular contractions and make the liver and muscle cells more sensitive to insulin
• how can we reduce the risk of getting type 3 diabetes ?

  • eat healthily
  • foods that are low in calories and high in fibre
  • engage in more active physical activities
  • avoid being inactive for long periods of time
  • maintain a healthy body weight
• describe the homeostatic control of body temperature when it rises

  1. thermoreceptors in the skin and the hypothalamus are stimulated
  2. this causes the
  3. arterioles in the skin to dilate, allowing more blood to flow through the blood capillaries in the skin so more heat will be lose through the skin
  4. sweat glands to become more active and produce more sweat
  5. more water in the sweat evaporates from the surface of the skin, more heat is lost from the body via latent heat
  6. metabolic rate decreases, reducing the amount of heat released within the body
  7. body temperature decreases
• describe the homeostatic control of the body temperature when it falls

  1. thermoreceptors in the skin and the hypothalamus are stimulated
  2. this causes the
  3. the arterioles in the skin to constrict, allowing less blood to flow through the blood capillaries in the skin so less heat will be lost through the skin
  4. sweat glands to become less active and produce less sweat, so less heat is lost from the body
  5. metabolic rate is increased, increasing the heat released within the body
  6. the rapid contraction and relaxation of the skeletal muscles increases the amount of heat released (shivering)
• what is the dilation of arterioles called ?

  vasodilation
• what is the constriction of arterioles in the skin called ?

  vasoconstriction