Physiology 6 - Integration of CV Mechanisms Flashcards
What are the major resistance vessels in the circulation?
The arterioles
What vessels contain most of the blood volume during rest?
The veins (the capacitance vessels)
What is the main regulator of the HR?
Autonomic nervous system
What are the main regulators of the stroke volume? (3)
Pre-loadAfter-loadMyocardial contractility
Where is the main site of TPR?
Arterioles
How is resistance to blood flow related to blood viscosity and length of blood vessel?
Directly proportional to blood viscosity and length of blood vessel
How is resistance to blood flow related to the radius of the blood vessel?
Inversely proportional to the radius of the blood vessel to the power of 4
Equation for what resistance to blood flow is related to?
blood viscosity X length of blood vessel divided by radius of blood vessel to the power of 4
How is the resistance to blood flow mainly controlled?
By vascular smooth muscle that changes the radius of arterioles
What is involved in the extrinsic control of vascular smooth muscle?
Hormones and nerves
What branch of the autonomic nervous system supplies the vascular smooth muscle?What receptors on the smooth muscle does the released neurotransmitter act on?
SympatheticAlpha 1 (noradrenaline)There is no significant parasympathetic innervation of arterial smooth muscle except in the penis and clitoris
what is the state of the vascular smooth muscle at rest?Why?
It is partially constricted due to the vasomotor tone - tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
What effect does increased sympathetic stimulation have on vascular smooth muscle?
Increased vasomotor tone = increase vasoconstriction and vice versa
What hormones are involved in the control of vascular smooth muscle? (3)
AdrenalineAngiotensin 2Vasopressin (ADH)All cause vasoconstriction
What effect dies adrenaline have on vascular smooth muscle?
Adrenal is released from the adrenal medullaAdrenal acting on B2 adrenoceptors causes vasodilation (cardiac and skeletal muscle arterioles) Adrenaline acting on alpha 1 adrenoceptors causes vasoconstriction (predominant in skin, gut and kidney arterioles)
What is the purpose of intrinsic controls of vascular smooth muscle?
To match the blood flow of different tissues to their metabolic needs (they can over red the extrinsic control mechanisms)They include local chemical and physical factors
What local metabolites (chemicals) cause vasodilation? (6)
Decreased local pO2Increased local pCO2Increased local [H+] (decreased pH)Increased extra-cellular [K+]increased osmolarity of ECFadenosine release (from ATP)
What are local humoral agents released in response to?
Tissue injury or inflammation
What are examples of local humoral agents which cause relaxation of arteriolar smooth muscle resulting in vasodilation? (3)
HistamineBradykinNO
Where is NO released from?What causes its release?
Continuously produced by the vascular endothelium from the amino acid L-arginine through enzymatic action of nitric oxide synthase (NOS)Shear stress on vascular endothelium as a result of increased flow causes release of of calcium in vascular endothelial cells and the subsequent activation of NOSChemical stimuli can also induce NO formation
How does NO causes vasodilation?
NO diffuses from the vascular endothelium into the adjacent smooth muscles where it activates the formation of cGMP that serves as a second messenger for signalling smooth muscle relaxation
Examples of humoral factors that cause vasocontraction? (4)
SerotoninThromboxane A2leukotrienesEndothelin
In terms for thrombotic, inflammatory and oxidant effect, what are endothelial produced vasodilators?
Anti-thrombotic, anti-inflammatory, anti-oxidants (and vice versa for endothelial produced vasoconstrictors
Apart from chemicals, what else can intrinsically control vascular smooth muscle?
Physical factors:Sheer stresstemperatureMyogenic response to stretch
What effect does temperature have on vascular smooth muscle?
Cold = vasoconstrictionWarmth = vasodilation
What is the myogenic response to stretch?
If MAP rises, resistance vessels automatically constrict to limit flowIf MAP falls resistance vessels automatically dilate dilate to increase flow (especially important in tissues lie the brain and kidneys)
When is the maximal force generated in myocytes?
At optimal fibre length
What 5 factors increase venous return? (5)
Increased venomotor tone Increased skeletal muscle pumpIncreased respiratory pumpIncreased stroke volume = increased arterial pressureIncreased blood volume
What branch of the autonomic nervous system supplies your blood vessels?
Sympathetic
What does increased venomotor tone cause?
Due to increased sympathetic stimulation - increased venous constructionBlood driven to the right atrium increases (venous return), SV and MAP also increase
What does increased muscle activity cause in terms of venous return?
Increased venous return to the heart due to skeletal muscle pump
What effect does exercise have on the CVS?
Sympathetic nerve activity increasesHR and SV increase = increased COSympathetic vasomotor nerves reduce flow to kidneys and gut = vasoconstrictionIn skeletal and cardiac muscle, metabolic hyperaemia overcomes vasomotor tone = vasodilationIncrease in CO increases systolic BP The increase in CO increases systolic BP and the metabolic hyperaemia decreases TPR and decreases DBP (pulse pressure increases)Post exercise hypotensive response
