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Circulation

Where does the Cardiac Output go?

The Path of blood through the vascular system

• Heart• Arteries • Arterioles• Capillaries• Venules• Veins• Heart

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Arteries

• Transport blood under high pressure

Cardiac Output is pulsatile,this is reflected in the arterial

pressure• Systolic pressure = high point• Diastolic pressure = low point

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Vascular Compliance

Compliance = ∆volume/∆pressure

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Calculating Mean Arterial Pressure from direct

measurements

MAP = DP + 1/3 (SP-DP)

DP = diastolic pressureSP = systolic pressure

Arterioles

• Branches of artery system• Act as control valves to the capillaries• Determines the to total peripheral

resistance

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What determines the Variable resistance in the individual

Arterioles?

Factors that influence the diameter of individual arterioles

• Local controls– Hyperemia– Flow Autoregulation

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Arteriolar resistance

• Local controls– Hyperemia– Flow Autoregulation

• Extrinsic controls– Sympathetic nerves– Hormones

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Capillaries

• Exchange fluids, nutrients, hormones, and all other important things, between blood and tissues

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If all the blood circulates ~ once per minute how does it slow down to exchange gasses and nutrients?

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Movement of fluids in and out of the capillaries

Hydrostatic pressure

moves fluids out of the capillaries into the interstitial fluid

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Osmotic pressure

Moves fluids back into the capillaries

This system is not perfectly balanced

About 4L/day of fluid accumulates in the interstitial fluid

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Veins

• Conducts blood back to the heart• Serves as a major reservoir for blood

volume

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Regulation of total systemic arterial pressure

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F = ∆P/RFlow = change in Pressure ÷ Resistance

oror

∆∆P = F P = F xRxR

Mean arterial pressure = Cardiac Output X Total Peripheral

Resistance

MAP = CO x TPR

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Short Term Regulation of blood pressure

Baroreceptor Reflexes

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Hemorrhage

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Relationship of Blood Volume to interstitial fluid volume

Long term Regulation of blood pressure

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A final note about circulation