PHYL3002 Lecture Notes - Lecture 11: Hypercapnia, Hyperkalemia, Vasopressin
LECTURE ELEVEN: Vascular Reactivity
Blood Flow:
• Arterial system converts intermittent/pulsatile outflow from the heart to
a steady flow of blood through the capillaries
• Wall thickness and diameter decreases as you go through the different
levels of the arterial system
• Differences in composition of tissues through arterial system
o Proportion of elastic tissue decreases through different levels of
arterial system
o Proportion of smooth muscle tissue increases
• Aorta and large arteries → larger diameter and an elasticity that allows
them to handle a considerable volume of blood
• Arterioles → high resistance vessels with relatively large amounts of
smooth muscle → regulate distribution of blood flow to capillaries
• Blood flow velocity is inversely proportional to cross-sectional area of all
the vessels at a given level of the vascular tree
• Blood flows faster in large diameter vessels facilitating rapid transfer of
blood from heart to organs
• Elasticity of aorta/large vessels allows them to stretch when the blood is
ejected from the ventricles during systole
• Recoil of vessel walls during diastole provides energy to maintain a
steady blood flow when heart is relaxing
• Although the diameter of each capillary is very small, due to vast number
of capillaries in the body total CSA is very large
• Blood flows very slowly through the capillaries facilitating the exchange
of gases and nutrients between blood and tissue cells
• Rate of blood flow is directly proportional to the pressure gradient and
inversely proportional to vascular resistance
o F = ∆P/R
• Laminar flow → frictional force
• Turbulent flow → uneven flow of fluid, occurs when disturbance of wall
occurs
Blood Pressure:
• Force exerted against a vessel wall
• Depends on the volume of blood and compliance of the vessel
• Affected by the cardiac output (stroke volume x heart rate) and stiffness
of large vessels
• SBP → BP increases during systole as blood is ejected from left ventricle
into aorta
• DBP → BP decreases during diastole due to peripheral runoff from the
arteries into microcirculation
• PP → pulse pressure, difference between SBP and DBP → directly
affected by SV and arterial compliance (stiffness)
• MAP → mean arterial pressure → average pressure during a cardiac cycle
→ DBP + PP/3
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Document Summary
Influences smooth muscle tone, endothelial function and vascular health. Increases in oxygen: myogenic activity, decreases in carbon dioxide, angiogensin ii, vasopressin, decreases blood flow, vasodilation, caused by the opposite of what causes vasoconstriction, affected by ans output and inflammation, increases blood flow. Flow mediation dilatation: blood flow through a vessel exerts a shear stress on the vessel wall leading to vasodilation. Impaired in smokers: requires intact endothelium, decreases with age earlier in males than females, endothelial function important for vascular health, can be assessed from measurements of flow mediated dilatation. Impaired endothelial function independently predicts long term cardiovascular events in patients with peripheral arterial disease. Increased level of endogenous inhibitor adma: increased breakdown of no. Increased production of superoxide anions by cyclo- oxygenase and nadph-oxidase. Auto-regulation of blood flow: change in perfusion pressure bring about a change in vascular resistance to maintain blood flow, tone of smooth muscle is regulated by stretch of arterial walls, myogenic response.
