Integration of Cardiovascular Mechanisms Flashcards
the capillaries are the site of exchange of gas, nutrients and water between….
the blood and the tissues
what is the main factor affecting the regulation of heart rate?
Mainly autonomic nervous system but an have some hormonal control
how is the TPR controlled?
it is regulated by vascular smooth muscles
what is the main site of TPR?
the arterioles
what does contraction of vascular smooth muscles cause?
vasoconstriction and increase TPR and MAP (i.e. pressure upstream)
relaxation causes the opposite
resistance to blood flow is directly proportional to____ and ____
blood viscosity and length of blood vessel
resistance to blood flow is inversely proportional to ____
the radius of the blood vessel to the power 4
what is the Resistance to flow equation?
R ∝ η.L
r4
what is the main way that resistance t flow is regulated?
by changes in the radius of arterioles
the smaller the radius …..
the higher the resistance
what are 2 examples of extrinsic control of vascular smooth muscle?
nerves and hormones
what reflex regulates the innervation which is important to blood pressure regulation?
baroreceptor reflex
The vascular smooth muscles are supplied by SYMPATHETIC nerve fibers. What is the neurotransmitter?
noradrenaline
what is the receptor for vascular smooth muscle for noradrenaline
alpha receptors
resistance is _____ proportional to the radius ^4
inversely
flow is _____ proportional to the radius ^4
directly
there is a constant constriction on the blood vessels even at rest. what is this called?
vasomotor tone
what causes the vasomotor tone?
caused by tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
what will increased sympathetic discharge do?
increase the vasomotor tone resulting in vasoconstriction
what will decreased sympathetic tone do?
decrease the vasomotor tone
what is the effect of parasympathetic innervation of arterial smooth muscles?
there is no significant innervation
what hormone controls vascular smooth muscle
adrenaline
what is the effect of adrenaline largely dependent on?
the organ it is acting on. It is organ specific
what does adrenaline acting on alpha receptors do?
causes vasoconstriction
what does adrenaline acting on beta receptors do?
causes vasodilation
where are alpha receptors predominant?
in skin, gut, kidney arterioles
where are beta receptors predominant?
in cardiac and skeletal muscle arterioles
what does this organ specific effect of adrenaline mean during exercise?
that there is strategic redistribution of blood
what are the other hormones that can affect vascular smooth muscles?
angiotensin II: causes vasoconstriction
ADH : causes vasoconstriction
these are important in the intermediate control of blood pressure
what kind of factors are involved in the intrinsic control of vascular smooth muscle?
chemical and physical factors
what do the intrinsic mechanisms do?
match the blood flow of different tissues to their metabolic needs. They can OVER_RIDE the extrinsic control mechanisms in specific tissues
what are examples of factors which chemical factors causing local metabolic changes which influence the contraction of arteriolar smooth muscles causing relaxation and thus vasodilation?
Decreased local PO2
Increased local PCO2
Increased local [H+] (decreased pH)
Increased extra-cellular [K+]
Increased osmolality of ECF
Adenosine release (from ATP)
what does decreased local PO2 cause in pulmonary circulation and what does it cause in systemic circulation?
decreased local Po2 will cause vasoconstriction in the pulmonary circulation and vasodilatation in the systemic circulation
what other local chemicals released within an organ influence the contraction of arteriolar and arterial smooth muscles?
local humoral agents
when are local humoral agents released?
can be released in response to tissue injury or inflammation
what are some examples of humoral agents which cause RELAXATION and thus VASODILATATION?
histamine
bradykinin
NO
how often and where is NO released from?
this is released continuously by endothelial cells of arteries and arterioles
how is NO produces?
NO is continuously produced by the vascular endothelium from the amino acid L-arginine through enzymatic action of Nitric Oxide Synthase (NOS)
what does NO do?
NO is a potent vasodilator (with a short life of few seconds) which is important in the regulation of blood flow and maintenance of vascular health
what are the two main stimuli which can up regulate the production of NO?
- shear stress on the vascular endothelium as a result of increased flow (flow dependent NO formation)
- chemical stimuli can also induce NO formation (receptor stimulated NO formation)
what happens in flow dependent No formation as a result of increased flow?
this causes the release of calcium in vascular endothelial cells and the subsequent activation of NOS - the NOS makes NO
what happens in receptor stimulated NO formation?
stimulators like bradykinin and things are vasoactive stimulators which can stimulate NO formation
what does NO do once formed?
diffuses from the vascular endothelium into the adjacent smooth muscle cells where it activates the formation of cGMP that serves as a second messenger for signalling smooth muscle relaxation
what are some examples of humoral agents which cause contraction and thus VASOCONSTRICTION?
serotonin
thromboxane A2
leukotrienes
endothelin
what is endothelin?
this is a potent vasoconstrictor released from endothelial cells. Its production is stimulated by various agents which cause vasoconstriction
what sometimes produce serotonin and thromboxane A 2
platelets
what factors can cause endothelial damage/ dysfunction?
high BP,
high cholesterol
diabetes and smoking
what are some of the functions of endothelial vasodilatores?
anti-thrombotic, anti-inflammatory, anti-oxidants
what are some of the functions of endothelial vasoconstrictors?
pro-thrombotic, pro-inflammatory, pro-oxidants
what are 3 examples of physical intrinsic factors that control smooth muscle
- temperature
- myogenic response
- sheer stress
what is the myogenic response if MAP rises (in a specific organ) ?
resistance vessels automatically constrict to limit flow
what is the myogenic response if MAP falls (in a specific organ) ?
resistance vessels automatically dilate to increase flow
which organs if myogenic response important for?
brain and kidneys
what effect does sheer stress have?
Dilatation of arterioles causes sheer stress in the arteries upstream to make them dilate. This increases blood flow to metabolically active tissues
what is the main controller of BP in the cerebrum?
myogenic response - this helps to keep a relatively constant blood flow in relation to a changing BP
Sympathetic nervous system plays the primarily role on the control of arteriolar radius and TPR (the brain is an exception, where vasoconstriction will increase the TPR )
yes
