Adrenalin and thyroxine Flashcards
What are the levels of thyroxine in the blood controlled by?
negative feedback
What is negative feedback?
if a factor falls below a normal level, a corrective mechanism takes place to bring it back up to a normal level
if a factor rises above a normal level, a corrective mechanism takes place to lower the levels back to normal
What is adrenalin released in response to?
sudden stress
it causes the fight or flight response
What does thyroxine control?
metabolic rate
also growth and development
What is metabolic rate?
the rate at which cells respire
it is measured as the rate of energy transfers in the body
What are the target organs of adrenalin?
liver
heart
blood vessels
skin
What are the effects of adrenalin?
- increases heart rate
- constricts some blood vessels to increase blood pressure
- dilates other blood vessels to increase blood flow to muscles
- causes the liver to convert glycogen to glucose, which is released into the blood
Explain how the production of thyroxine is controlled by negative feedback
When the concentration of thyroxine in the blood is too low a corrective mechanism is stimulated
the hypothalamus secretes more TRH which causes the pituitary gland to produce more TSH
as a result the thyroid produces more thyroxine
if the thyroxine production is too high, TRH production is inhibited by the hypothalamus
this results in less production of thyroxine
Explain two ways in which adrenalin is useful for preparing skeletal muscles for fight or flight
the heart beats faster, so oxygen is carried around the body quicker
this allows faster respiration in muscle cells
energy is released for cell contraction faster
blood glucose concentration increases
more glucose is available for respiration in muscle cells
Name two target cells or organs that adrenalin affects.
Explain how it affects them.
heart, lungs, liver, blood vessels
speeds up heart rate, speeds up breathing rate, increases blood glucose, increases blood pressure, constricts blood vessels
Beta blockers are drugs that reduce the effect of adrenalin on the heart.
Explain why they are prescribed for people with heart disease.
stops heart rate increasing / keeps heart rate low,
so stress on heart is reduced
blood pressure is reduced
People who produce too much thyroxine tend to eat a lot but generally do not get fat.
They also feel very warm most of the time.
Explain why.
thyroxine stimulates cellular response
uses more glucose so they eat more to replace it
respiration releases heat therefore they feel warmer
Is adrenalin controlled by negative feedback?
no
