homeostasis and hormonal control

• properties of hormones:

  1. transported via bloodstream to target specific organs
  2. regulate, growth, activity and development
  3. chemical substances that are secreted in minute quantities by endocrine glands
  4. broken down in liver and excreted by kidneys
• effects of insulin

  1. make cells more permeable to glucose
  2. stimulates the liver and muscle cells to convert glucose into glycogen
  3. increase usage of glucose for cellular respiration
• general structure of homeostasis:

  1. stimulus -> receptor -> control centre -> effector-> corrective mechanism
• exocrine gland :

  1. ducts present to transport hormones to targeted organs (eg. pituitary gland)
• endocrine glands :

  1. ductless glands that transport their secretions via the bloodstream (eg. pancreas)
• lack of secretion of insulin :

  • increases blood glucose concentration
  • muscle cells have no reserves of glycogen, the body grows weak and continues to lose weight
• over secretion :

  • abnormal decrease in blood glucose level/concentration such that low blood glucose concentration results in a condition called "shock"
  • seizures or fits, collapsing or passing out may follow
• type 1 diabetes :

  • develops early in a person's life
  • cause : islets of langerhans are unable to produce insulin
• type 2 diabetes :

  • occurs later on in a person's life
  • cause : when target cells such as the muscle cells do not respond well to insulin
• treatment for diabetes :

  1. measure blood glucose concentration and test urine
  2. inject insulin regularly into the fat skin under their tissue
  3. need to be ready with a supply of sugary sweets
• risk factors of diabetes :

  1. obesity
  2. age
  3. family history
  4. blood lipid levels
  5. sedentary lifestyle
• how to reduce the risk factors ?

  1. eat healthily
  2. engage in more physical activities
  3. avoid being inactive for too long
  4. try to maintain healthy weight and BMI
• anatomy of the skin :

  • sweat pore
  • nerve ending
  • sweat gland
  • hair erector muscle
  • hair
  • hair follicle
  • blood capillaries
  • arterioles
  • sebaceous gland
• vasodilation :

  • when blood vessels dilate, more blood flows to the skin surface
• when the body temperature increases :

  1. arterioles in the skin dilate (allows more blood to flow through the blood capillaries in the skin and more heat will be lost)
  2. shunt vessels become narrower to allow for more blood to pass through the blood capillaries
  3. sweat glands become more active, as more water in the sweat evaporates from the surface of the skin causing more heat to be lost from the body
  4. the metabolic rate is decreased/rate of respiration is decreased and this reduces the amount of heat produced within the body
• when the body temperature decreases :

  1. arterioles in the skin constrict (allows less blood to flow through the blood capillaries in the skin therefore less heat will be lost)
  2. shunt vessels become wider
  3. sweat glands become less active
  4. metabollic rate is increased
  5. hairs stand up because of the hair erector muscle to trap more air
  6. when the above is not enough, the body also shivers
• anti-diuretic hormone - signals the body to reabsorb water from the urine and the kidneys back into the bloodstream
• antidiuretic hormone makes the collecting duct of the nephron more permeable to water
• negative feedback - a change from the normal setpoint causes the body counteract the change with an opposite effect to return it back to normal
• what is the general structure of homeostasis ?

  stimulus -> receptor -> control centre -> effector -> corrective mechanism