🏥 Chapter 9 - Homeostasis and Hormonal Control

• homeostasis

  • the maintenance of a constant internal environment (blood and tissue fluids)
  • allows organism to be independent from changes in the external environment (surroundings)

  e.g. regulating water potential, temperature and blood glucose conc
• negative feedback

  • the process whereby a change in the system triggers a corrective mechanism to bring about an opposite effect to the change detected and restores the system to its original state
• negative feedback

  • for negative feedback to take place, there must be

  • a normal level or set point to be maintained

  • a stimulus, which is a change in the internal environment

  • a receptor that can detect the stimulus and send signals to the

  control centre

  • a corrective mechanism, which brings about the reverse effect of

  the stimulus

  
• Regulating Water Potential (I)

  • decrease in water potential due to loss of water (profuse sweating)
  • hypothalamus detects this decrease in water potential
  • more ADH is released into the bloodstream by the pituitary gland
  • more ADH is transported to the kidneys
  • cells in the wall of the collecting duct become more permeable to water, leading to more water being reabsorbed
  • less water excreted, more concentrated urine, less urine produced
  • water potential in blood increases to normal level
  • feedback is given to the hypothalamus to stop corrective mechanism
• Regulating Water Potential (II)

  
  

  • there is an increase in water potential (large intake of water)
  • hypothalamus detects this change of water potential
  • less ADH is released by pituitary glands into the bloodstream
  • less ADH is transported to the kidneys
  • cells in the wall of the collecting duct becomes less permeable to water
  • less water reabsorbed into bloodstream
  • more water excreted, more urine produced, more dilute urine
  • water potential of blood decreases to normal level
  • feedback is given to the hypothalamus to stop corrective mechanism
• hormones

  • chemical substances produced in minute quantities by an endocrine gland
  • is transported directly in the bloodstream to target organ(s) where it exerts its effect(s)
  • production must be carefully controlled so as to prevent disastrous results
• exocrine glands

  • secretes substances via a duct (e.g. sweat and salivary glands)
• endocrine glands(I)

  • secretes hormones directly into the bloodstream (ie. without a duct)
• pancreas

  • can be both an endocrine and exocrine gland since
  • pancreatic juice is carried by the pancreatic duct into the duodenum
  • insulin and glucagon secreted by the Islets of Langerhans flow directly into the bloodstream
• Endocrine glands (II)

  1. Pituitary Gland ("master gland")

  - secretes a number of hormones which controls secretion of hormones of several other endocrine glands

  - secretes ADH

  2. Hypothalamus

  -endocrine gland that regulates secretion of some hormones

  3. Pancreas

  - islets of Langerhans in the pancreas secrete insulin and glucagon

  
  

  4. Ovary

  - secretes oestrogen and progesterone

  
  

  5. Testis

  - secretes testosterone
• effects of insulin(I)

  • secreted by islets of Langerhans

  In normal levels of insulin, it decreases blood glucose concentration by:

  • make cell membranes more permeable to glucose
  • more glucose to diffuse from blood to liver and muscle cells
  • stimulates liver and muscle cells to convert glucose to glycogen for storage
  • increases use of glucose for respiration
• effects of insulin (II) [UNLIKELY TO BE TESTED]

  when a lack of insulin is secreted it increases blood glucose concentration because:

  • glucose cannot be stored or utilized by tissue cells
  • causes excess glucose to be removed in the urine
  • causing diabetes mellitus
  • muscle cells have no reserve of glycogen
  • body grows weak and continuously loses weight
• effects of insulin (III) [UNLIKELY TO BE TESTED]

  when insulin is oversecreted, there is an abnormal decrease in blood glucose concentration which causes:

  • condition called shock
  • collapsing and passing out may follow
• what happens when blood glucose concentration rises above normal

  1. the islets of Langerhans in the pancreas are stimulated
  2. islets of Langerhans secrete more insulin into the blood stream, which is transported to liver and muscle cells
  3. insulin increases permeability of cell membranes to glucose
  4. cells absorb more glucose from blood plasma
  5. insulin increases rate of respiration
  6. insulin causes liver and muscle cells to convert excess glucose into glycogen
  7. glycogen is stored in liver and muscles
  8. blood glucose concentration decreases, causing receptor to reduce insulin production

  
• diabetes mellitus (I)

  • disease in which the body is unable to control its blood glucose concentration in order for it to remain within normal limits
  • blood glucose concentration can rise to a level that exceeds the kidney's ability to completely reabsorb all the glucose.
  • The glucose that is not reabsorbed is excreted in the urine.
• diabetes mellitus (II)

  Type 1 diabetes:

  • early-onset diabetes
  • islets of Langerhans secrete insufficient amounts of insulin
  • is inherited

  Type 2 diabetes:

  • late-onset diabetes
  • when muscle cells do not respond well to insulin
  • mostly overweight people develop this

  symptoms:

  • persistent high glucose level
  • glucose in urine
  • slowing healing of wounds
  • frequent urination
  • thirst
  • excessive weight loss
• how can diabetes be treated

  • measure blood glucose concentration and test urine regularly
  • watch diet
  • for type 1 diabetes, insulin has to be injected regularly into the fat tissue under skin
  • ensure glucose concentration does not drop too low by always carrying sugary snacks
  • take medicine which increase uptake of glucose from bloodstream into cells
• risk factors of diabetes (type 2)

  • when muscles dont respond well to insulin, its called insulin resistance
  • muscle cells unable to take in excess glucose in the blood

  1. obesity
  2. age (as age increase, risk is higher)
  3. family history
  4. blood lipid levels (risk increased if there's high levels of "bad" cholesterol and low levels of "good" cholesterol)
  5. sedentary lifestyle (physical activities use up excess glucose to provide energy for muscular contraction)
• vasodilation


  • when arterioles dilate, more blood is sent to the blood capillaries in the skin, and skin turns red
  • shown when we blush after vigorous activities
  • decreases body temperature
• vasoconstriction

  • when arterioles constrict, it reduces the amount of blood flowing through blood capillaries in the skin
  • causes us to become pale
  • increases body temperature
• sweat glands

  • secreted flows through a sweat duct/pore that opens at the skin surface
  • consists of water, mineral salts, and small amounts of urea, hence skin is an excretory organ
  • sweat production varies on external and internal environmental conditions
  • small quantities of sweat evaporate almost immediately
  • large quantities of sweat appear as droplets on your skin or as 'running streaks' of liquid
  • sweat is continuously produced
• sensory receptors

  • structures in the body that detect changes in the environment
  • enable you to sense pain, pressure and temperature change in the external environment
  • receptors that detect temperature changes are thermoreceptors

  
• how is heat gained in the body?

  • result of metabolic activities such as cellular respiration
  • vigorous muscular exercise
  • being in warm environments
• how is heat lost in the body

  • through skin
  • evaporation of sweat from the surface of the skin
  • in faeces and urine
  • in exhaled air
• how is temperature in the body regulated

  • hypothalamus in the brain regulates and monitors the body's temperature
  • receives information from thermoreceptors in skin (external env.)
  • receives information from thermoreceptors in the hypothalamus that detect temperature of blood (internal env.)
• what happens when body temperatures begin to rise (I)

  • rise in body temperatures can be caused by vigorous activity, and on a warm day, where body absorbs heat from surroundings when surrounding temperature is higher than our body temperature
• what happens when our body temperature begins to rise (II)

  1. body temperature rises above normal
  2. thermoreceptors in the skin and in the hypothalamus are stimulated
  3. vasodilation occurs to allow more blood to flow through blood capillaries in the skin, hence more heat is lost through skin
  4. sweat glands become more active and produce more sweat
  5. as more water in sweat evaporates from the surface of the skin, more heat is loss from the body
  6. metabolic rate is decreased, and reduces amount of heat released in the body
  7. body temperature decreases

  
• What happens when our body temperature begins to fall

  1. body temperature falls
  2. thermoreceptors in skin and in hypothalamus are stimulated, and nerve impulses are transmitted to hypothalamus
  3. vasoconstriction occurs to allow less blood to flow through capillaries in the skin, and less heat will be lost through skin
  4. sweat glands become less active and produce less sweat
  5. metabolic rate is increased, releasing more heat within body
  6. shivering may occur if the responses are insufficient, as rapid contraction and relaxation of skeletal muscles release more heat
  7. body temperature increases to normal

  
• yt video on chapter

  https://www.youtube.com/watch?v=XMsJ-3qRVJM&t=123s