BActive hyperemia

- Blood flow to an organ is proportional to its metabolic activity.

Table 3-2. Causes and Examples of Edema

Cause Examples

T Pc Arteriolar dilation

Venous constriction Increased venous pressure Heart failure

Extracellular volume expansion Standing (edema in the dependent limbs)

1 ttc Decreased plasma protein concentration

Severe liver disease (failure to synthesize proteins) Protein malnutrition

Nephrotic syndrome (loss of protein in urine)

T Kf Burn

Inflammation (release of histamine; cytokines)

Table 3-3. Summary of Control of Special Circulations

Circulation*

(% of resting cardiac output)

Local Metabolic Control

Vasoactive Metabolites

Sympathetic Control

Mechanical Effects

Coronary (5%)

Most important mechanism

Hypoxia Adenosine

Least important mechanism

Mechanical compression during systole

Cerebral (15%)

Most important mechanism

C02 H+

Least important mechanism

Increases in intracranial pressure decrease cerebral blood flow

Muscle (20%)

Most important mechanism during exercise

Lactate K+

Adenosine

Most important mechanism at rest (a receptor causes vasoconstriction; p receptor causes vasodilation)

Muscular activity causes temporary decrease in blood flow

Skin (5%)

Least important mechanism

Most important mechanism (temperature regulation)

Pulmonaryt (100%)

Most important mechanism

Hypoxia vaso-constricts

Least important mechanism

Lung inflation

*Renal blood flow (25% of resting cardiac output) is discussed in Chapter 5. tPulmonary blood flow is discussed in Chapter 4.

*Renal blood flow (25% of resting cardiac output) is discussed in Chapter 5. tPulmonary blood flow is discussed in Chapter 4.

- For example, if metabolic activity in skeletal muscle increases as a result of strenuous exercise, blood flow to the muscle will increase proportionately to meet metabolic demands.

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