integration of the cardio mechanisms Flashcards
what are the major resistance vessels?
arterioles
how is systemic vascular resistance controlled?
- regulated by smooth muscles
- main site are arterioles
- contraction of smooth muscles causes vasoconstriction and increases SVR and MAP
- vascular smooth muscles are controlled by extrinsic and intrinsic mechanisms
what is the equation of resistance to blood flow?
Resistance proportional to (blood viscosity x length of blood vessel)/ (radius of blood vessel)4
what are the extrinsic control of vascular smooth muscles?
- nerves are important for bp regulation - baroreceptor reflex
- vascular smooth muscles are supplied by sympa nerve fibres - noradrenaline acting on a receptors
- they are partially constricted at rest - vasomotor tone
what are the NERVE extrinsic control of vascular smooth muscles?
- vasomotor tone is caused by tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
- increased sympa discharge will increase vasomotor tone resulting in vasoconstrictions
- decreased sympa discharge will decrease the vasomotor tone = vasodilation
- there is no significant para innervation of arterial smooth muscle - exceptions include penis and clitoris
what are the HORMONE extrinsic control of vascular smooth muscle?
- adrenaline from the adrenal medulla
- effect of adrenaline is largely organ specific - depends on the predominant type of receptor
- adrenaline acting on a receptors = vasoconstriction
- a receptors are predominant in skin, gut, kidney arterioles
- B2 receptors are predominant in cardiac and skeletal muscle arterioles
- this helps strategic redistribution of blood during exercise
- angiotensin 2 causes vasoconstriction
- antidiuretic hormon causes vasoconstriction
what are the intrinsic controls of vascular smooth muscle?
- blood flow is matched to the tissues metabolic needs
- they can over-ride the extrinsic control
- they include local chemical and physical factors
what are the CHEMICAL: LOCAL METABOLITES intrinsic controls of vascular smooth muscles?
- local metabolic changes within an organ influences the contraction of arteriolar smooth muscles
- the following cause relaxation of arteriolar smooth muscles = vasodilation and metabolic hyperaemia
1. decreased locals PO2
2. increased local PCO2
3. increases local H+
4. increased EC K+
5. increased osmolarity of ECF
5. increased adenosine (from ATP)
what are the CHEMICAL: LOCAL HUMORAL AGENTS intrinsic control of vascular smooth muscles?
- they influence the contraction of arterial and arteriolar smooth muscles
- they can be released in response to tissue injury or inflammation
- eg that result in vasodilation =
1. histamine
2. bradykin
3. nitric oxide
what is the role of NO?
- continuously produced b y VE from L-arginine through action of NOsynthase
- NO is a vasodilation (short life), it is important in the regulation of blood flow and maintenance of vascular health
- stress on VE as a result on increased flow causes release of Ca in VE cells, and activates NOS
- chemical stimuli can induce NO formation
- NO diffuses from the VE into the adjacent smooth muscle cells where it activates the formation of cGMP
what are some examples f humoral agents which cause contraction of arteriolar smooth muscles resulting in vascocontriction?
- serotonin
- thromboxane A2
- leukotrienes
- endothelin
what is the endothelium?
- important in maintaining vascular health
- endothelial damage can be caused by high BP, high cholesterol, smoking
- endothelial produced vasodilators are anti-thrombotics, anti-inflammatory, anti-oxidants
- endothelial produced vasoconstrictors are the opposite
what are the PHYSICAL intrinsic controls of vascular smooth muscles?
- temperature
- myogenic response
- sheer stress
what happens to blood vessels when you are cold?
vasoconstrict
what is the myogenic response to stretch?
- if MAP rises resistance vessels constrict
