Blood Flow and Pressure Exchange. Outline. Overview of circulation Components of the Vascular system Medical physics of blood flow Vascular distensibility and compliance Arterial damping of pressure pulses Veins as reservoirs of blood Capillary exchange. Learning Objectives.
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Elastin fibersComponents of the Vascular System - Blood Vessels
Thick, muscular walls
Diameter varies in response to neural stimuli and local chemical influences.
Consist of a single tunica interna
Gas, nutrient, and waste exchange
Shunting of blood
Venules—porous—free movement of fluids and white blood cells.
3 tunics—but thin
Maintenance of Blood Pressure
Shunting and vasoconstriction.
Carotid and aorta
Higher brain centers
Histamine—other vasodilatorsVenous System
Causes heart failure, vascular disease, renal failure, stroke, and blindness.
Enlargement falled by hypertrophy of the myocardium
Diet (sodium, saturated fat, cholesterol)
Smoking—nicotine is a vasoconstrictor.Hypertension
Fatty streak stage
tPA—tissue plasminogen activator
HDL—removes cholesterol from vessel walls.Atherosclerosis
Function of Circulatory System: To carry nutrients and hormones to tissues and wastes products away from tissues.
- e.g., during exercise, blood flow to skeletal muscle increases.
- In most tissues, blood flow increases in proportion to the metabolism of that tissue.
Aorta receives blood from left ventricle.
Arteries transport under high pressure, strong vascular walls.
Arterioles control conduits, last branch of arterial system, strong muscular walls that can strongly constrict or dilate.
Capillaries exchange substances through pores.
Venules collect blood from capillaries.
Veins low pressure, transport blood back to the heart, controllable reservoir of extra blood.
Cross-sectional area (cm2)
Small Arteries 20
Small Veins 80
- Typically measured as mm Hg.
- E.g., 100 mm Hg is the force needed to push a column of Hg to a level of 100 mm.
- If ΔP = 1 mm Hg and F = 1 ml/sec, then R = 1 PRU (peripheral resistance unit).
- In the adult systemic circulatory system, ΔP = 100 mm Hg, and F = 100 ml/sec; so R = 1 PRU.
- In the pulmonary system, ΔP = 14 mm Hg and F = 100 ml/sec; so R = 0.14 PRU.
Conductance = 1/resistance
- Increases blood blow as pressure increases.
- In arteries, averages out pulses.
- Allows veins to act as reservoirs
Vascular = Increase in Volume
DistensibilityIncr in P xorigVol
If 1mm Hg increases a vessel from 10mm to 11mm, the distensibility would be 0.1 per mm Hg or 10% per mm Hg.
Vascular compliance = Increase in volume
Increase in pressure
Can distend to hold large amounts of blood.
Contraction of skeletal muscles can constrict the veins and propel blood to the heart and increase cardiac output.
The contraction-induced constriction and the valves prevent the venous pressure from building up on the feet of standing adults.