Cardiovascular Physiology 2

Blood distribution

Organ or system Percent of blood flow
digestive system 21%
liver 6%
kidneys 20%
skin 9%
brain 13%
heart 3%
skeletal muscle 15%
bone 5%

Vessel functions

arteries

rapid-transit passageways

pressure reservoirs

elastic recoil and arterial pressure fluctuation

pulse pressure

mean arterial pressure as driving force

Part = dbp + 1/3 pp

arterioles

major resistance vessels

pressure drop from 93 mm Hg → 37 mm Hg

provides the ΔP

damps out the pulsatile pressure swings

vasoconstriction

increased O2
decreased CO2 and metabolites
sympathetic stimulation 
epinephrine 
vasopressin 
angiotensin II

vasodilatation

adenosine acts as a vasodilator in the heart;
it triggers the reactive hyperemia seen following occlusion/reperfusion of a coronary artery
and ameliorates reperfusion-induced injury

vascular tone

local control determines distribution of cardiac output

active hyperemia and vasodilatation

extrinsic control regulates arterial blood pressure

sympathetic tone

local control to override vasoconstriction

particularly skeletal muscle and skin

generally no parasympathetic innervation

exceptions:  penis and clitoris

cardiovascular control center

hormones

capillaries

10–40×109

sites of exchange

walls thin:  1 μm

small diameter:  7 μm

extensive branching:  no cell is more than 100 μm away

surface area of about 600 m2, only 250 mL of blood

slow velocity of flow

calculation of the cross-sectional areas:

Acapillary = π × r2
Acapillary = 3.14 × ((7.5 ÷ 2) μm)2
Acapillary = 3.14 × 14.06 μm2
Acapillary = 44.2 μm2
Atotal = Ncapillaries × Acapillary
Atotal = 35×109 × 44.2 μm2
Atotal = 1.5×1012 μm2
Atotal = 1.5 m2
Aaorta = π × r2
Aaorta = 3.14 × ((2.5 ÷ 2) cm)2
Aaorta = 3.14 × 1.56 cm2
Aaorta = 4.9 cm2
Aaorta = 4.9×10-4 m2

diffusion across capillary wall for solute exchange

there are no carrier-mediated transport systems

bulk flow across capillary wall and ECF distribution

ultrafiltration

reabsorption

driving forces

Type of pressure Pressure value
capillary blood pressure 37 mm Hg → 17 mm Hg
blood colloid osmotic pressure (oncotic pressure) 25 mm Hg
interstitial-fluid hydrostatic pressure 1 mm Hg
interstitial-fluid:  colloid osmotic pressure ~ 0 mm Hg

lymphatic system and interstitial fluid return

structure of lymphatic capillaries

muscle contractions and valves

functions

return of excess filtered fluid

defense against disease

transport of absorbed fat

return of filtered protein

edema

reduced concentration of plasma proteins

urine loss

decreased synthesis

protein deficiency

massive skin loss

increased permeability of capillary walls

inflammation, blisters, hives

increased venous pressure

blockage of lymph vessels

filariasis 1

elephantiasis

veins

capacitance vessels:  >60% in systemic veins

venous return

sympathetic activity

contrast results of arteriolar constriction

skeletal-muscle pump

gravity

venous pressure

fainting

venous valves

varicose veins 2

respiratory pump

cardiac suction

Questions for thought
1.   Distinguish between elastic arteries, muscular arteries, and arterioles with respect to location, structure, and functional adaptations.
2.   Describe the relationships of the various pressures affecting fluid movement through the capillary wall. How would allowing plasma proteins to leak out of the capillary affect this balance?
3.   Describe the role of lymphatic vessels in modulating edema.
4.   Explain how blood is returned via the caval veins to the atria of the heart.
5.   Explain how arterioles are used to control both blood distribution and blood pressure.

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