12. Blood flow and regulation- vasocontriction Flashcards
What changes in circulation occur during exercise?
20 fold increase in blood to skeletal muscles
cardiac output to skeltal muscle becomes 80%
What is the myogenic response?
Found in resistance arteries, this reponse allows for a reduction in flow at higher pressures.
This allows constant tissue blood flow when perfusion pressure changes
What induces the myogenic response?
Vessel wall tension e.g. stretching
What is responsible for the myogenic response?
Depolorisation of membrane potential
Extracellular calcium
What are the two main hypothesis for transmural pressure and membrane potential?
Stretch activated cat-ion channels: transient effect, didnt implement sodium which is one of the main factors
Phospholipase A activation and HETE formation.
Discuss how HETE is produced?
Increase in tension leads to an increase in phospholipase A2 activation
This leads to an increasde production of arachonoric acid which activated cytochrome p450 4A
cytochrome p450 4A helps form HETE
What does HETE stand for?
Hydroxyeicosatetraenoic acid
How does HETE regulate transmural pressure?
HETE closes potassium channels leading to a de-polarised membranes causing an icrease of intracellular calcium and therefore contraction of smooth muscle
What is the evidence of HETE regulating transmural pressure?
PLA2 inhibitors reduce myogenic response in some vessels
P-450 inhibitors reduce myogenic response
Other unrelated Ca2+ activated potassium channels blocks the myogenic response.
How does NO and HETE interact
Nitric oxide binds to cytochrome p450 via the heame group and de-naturing the enzyme
This inactivates the myogenic response.
How does neural input effect vasocontriction
When pressure builds the nerve impulses reduce to promote relaxation
What nervous system effects blood vessels
Sympathetic
