regulation of arteriolar resistance Flashcards
what is used to vary total peripheral resistance?
radius of vessels
what does varying the radius of vessels affect?
mean arterial pressure (the difference in pressure)
increasing TPR does what to mean arterial pressure?
increases it
what is the function of intrinsic mechanisms of controlling arteriolar constriction?
they are concerned with meeting the selfish needs of each individual tissue
what is the function of extrinsic mechanisms of controlling arteriolar constriction?
they are concerned with ensuring that total peripheral resistance of the whole body stays in the right ball park
what are the extrinsic mechanisms for controlling arteriolar constriction
- sympathetic nerve innervation
- hormonal control (adrenaline, ADH, angiotensin II, atrial natriuretic peptide and brain natriuretic petide)
describe how sympathetic innervation affects the constriction of arterioles
- they release noradrenaline
- this binds to alpha-1 receptors
- this causes smooth muscle contraction and arteriolar constriction.
- decreases flow through that tissue and increases TPR
does the parasympathetic system have an effect of arteriolar constriction?
no
how does adrenaline affect arteriolar radius?
- binds to alpa-1 receptors in most tissues causing a arteriolar constriction, decreased flow and increased TPR
- in some tissues like skeletal and cardiac muscle it binds to beta 2 receptors causing arteriolar dilation therefore increasing flow and decreasing TPR
how does angiotensin II affect arteriolar constriction?
produced in response to low blood volume it causes arteriolar constriction
how does antidiuretic hormone affect arteriolar radius?
released response to low blood volume it causes arteriolar constriction
how do atrial and brain natriuretic peptide affect arteriolar radius?
released in response to high blood volume
causes arteriolar dilation
what are the intrinsic contol mechanisms for arteriolar constriction?
- active (metabolic) hyperaemia
- pressure (flow) autoregulation
- reactive hyperaemia
- injury response
describe the process of metabolic hyperaemia?
- as metabolic activity increases the conc. of metabolits in the blood increases
- this triggers the release of EDRF
- this causes arteriolar dilation to wash out the metabolites
describe the process of pressure (flow) autoregulation?
- a decrease mean arterial pressure causes a decrease in flow through arterioles and capillaries
- this reduces the movement of metabolites away from tissues
- this causes metabolites to accumulate
- EDRF is released and causes vasedilation to wash out metabolites
describe the process of reactive hyperaemia?
occlusion of blood supply causes a subsequent increase in blood flow
describe the process of injury response?
1 injury to an area sends a action potential up a C-fibre
- a branch of the C-fibre releases substance P
- this substance stimulates mast cells to release histamine which causes arteriolar dilation
- this aids the delivery of blood-borne leucocytes to the injured area
when is blood supply to the heart interrupted?
during systole
how does the heart deal with increased demand during exercise with its interrupted blood supply?
- it shows excellent active hyperaemia
- also expresses many beta 2 receptors which swamp any arteriolar constriction
what sort of arteriolar regulation do the arterioles in the brain show?
excellent pressure autoregulation in order to keep a stable circulation
what happens to the arterioles in the lungs when oxygen conc. decreases?
they constrict (opposite to most other tissues to ensure blood gets to the best ventilated parts)
what sort sort of arteriole constriction are the arterioles in the kidneys particularly good at?
pressure autoregulation, as changes in MAP would have big effects on blood volume
