Homeostasis Flashcards
How is homeostasis maintained
- Negative feedback mechanism
- the internal body enviro are regulated by negative feedback mech
( glucose; CO2; H2O; Salt )
- Explain the principle of negative feedback
- Works on the principle that any deviation from the normal state is rectified by causing a change to occur in the opposite direction so that the deviation is cancelled
Explain the above/below normal state
- Normal state
- Rise above normal
- Receptor detects the change
- Control center processes info
- Reaction from effector eg. gland
Explain the feedback in the control of thyroxin levels ( incr )
- When the thyroxin level in the blood rises abv normal
- Pituitary gland detects the rise and stops secreting TSH
- Decr in secretion of TSH causes thyroid gland to decrease is production of thyroxin.
- As excess thyroxin is destroyed in the liver, levels of thyroxin in the blood will fall back to normal
- Rise abv normal
- PT Gland detects rise in thyroxin levels
- PT Gland stops secreting TSH
- Thyroid gland stops secreting thyroxin
Explain the feedback in the control of thyroxin levels ( decr )
- When the thyroxin level in the blood drops below normal
- PT Gland detects this drop and secretes TSH into the bloodstream
- The incr in TSH causes thyroid gland to secrete more thyroxin
- Drop below normal
- PT Gland detects drop thyroxin levels
- PT Gland secretes TSH
- Thyroid gland secretes more thyroxin
Explain the feedback in the control of blood glucose levels ( rises )
- When level rises abv normal
- Pancreas detects rise in glucose level
- Beta cells of Islets of L in pancreas secrete hormone insulin
- Insulin converts excess glucose to glycogen.
- Insulin promotes entry of glucose into body cells - Islets of L in pancreas detect high BG levels and secrete insulin
- Insulin stimulates 2 different responses to reduce BG
1) Promoting absorption of glucose into all cells for use during rest
2) Stimulating the liver to convert excess glucose into glycogen to be stored in the liver and muscles
Explain the feedback in the control of blood glucose levels ( too low )
- When level drop below normal
- Pancreas detects drop in glucose levels
- Alpha cells in Islets of L in pancreas secrete the hormone glucagon
- Glucagon convert stored glycogen to glucose
- Islets of L in pancreas detect low BG level and secrete more Glucagon
- Glucagon causes incr BG levels by:
- Stim liver and muscles to convert stored glycogen into glucose ( in turn released into bloodstream )
- BG levels = back 2 normal
Explain the feedback in the control of water levels ( rises )
- When H2O level in the blood rises abv normal ( water intake or less sweating )
- Hypothalamus detects rise in H20 level in blood stimulated to send impulse to :
- PT Gland to secrete less ADH into blood
- Tubules in kidney become less permeable to H20
- Less H20 is reabsorbed from these tubules
- More H20 leaves body as dilute urine
Explain the feedback in the control of water levels ( drops )
- When water level in blood drops below normal ( sweating )
- Hypothalamus detects drop in H20 levels in blood and is stimulated to send impulse to :
- PT Gland to secrete more ADH into blood
- Tubules in kidney become more permeable to H20
- More H20 is reabsorbed from tubules into blood capillaries incr H20 in the blood
- Urine becomes more conc and less leaves the body
Explain the feedback in the control of sodium levels ( drops )
- Low sodium level detected by receptors in kidney
- Adrenal Gland
Explain thermoregulation when blood temp is higher than normal in BV
- Heat receptors in hypothalamus and skin are stimulated
- Hyp sends impulses to surface blood vessels
- Causing them to widen ie. vasodilation
- More blood flows to skin surface and more heat is lost by radiation
Explain thermoregulation when blood temp is lower than normal in BV
- Cold receptors in hypo and skin are stimulated
- Hypo sends impulses to surface blood vessels
- Causes them to narrow ie . vasoconstriction
- Less blood flows to skin surface and less heat is lost from skin by radiation
Explain thermoregulation when blood temp is higher than normal in SWEAT GLANDS
- Heat receptors in hypothalamus and skin are stimulated
- Hyp sends impulses to surface blood vessels
- Vasodilation also incr amount of blood flowing to sweat glands
- Sweat glands become more active and more sweat is released
- More heat is lost through evaporation of sweat causing cooling of the skin
Explain thermoregulation when blood temp is lower than normal in SWEAT GLANDS
- Vasoconstriction decr amount of blood flowing to sweat glands
- Sweat glands become less active and less sweat is released
- Less heat is lost through evaporation of sweat
Effects of temperature on the body
- Hypothermia = body temp drops and remains below 36.9 degrees for a long period
- Hyperthermia = body temp rises and remains above 36.9 degrees for a long period ( dehydration )
