Cardiovascular System: Circulation Pathways and BP Regulation Anatomy & Physiology II Tony Serino, Ph.D. Biology Department Misericordia University

Blood Vessels Arteries –conduct blood away from heart Elastic arteries, Muscular arteries, arterioles Veins –conduct blood toward heart Venules, small and large veins Capillaries –thinnest blood vessel; used in exchange, is the functional unit of circulatory system (Microcirculation) AV shunts, metarterioles, pre-capillary sphincters, and capillary bed

Blood Vessels Types

Capillary Anatomy Three types: tight, fenestrated and sinusoids

Capillary Types Tight Capillary Fenestrated Capillary Sinusoidal Capillary

Capillary Bed (blood flowing)

Capillary Bed (blood shunted)

Capillary Transport Pathways

Forces Affecting Bulk Flow across the Capillary Wall

Arteries and Veins Arteries are known as resistance vessels, especially the arterioles Arteries withstand the greatest BP Veins are capacitance vessels, they are able to change the diameter to hold more or less blood

Artery vs. Vein

Artery Anatomy (CT) (Smooth Muscle) (Controlled by sympathetic system = vasomotor nerves)

BP through Vascular Tree Small changes in arteriolar diameter produce big changes in resistance; termed total peripheral resistance (TPR)

TPR (total peripheral resistance) TPR is the opposition to blood flow through the vessel (caused by friction) Arteries with their smaller lumen resist blood flow Arteriolar diameter contribute the most to TPR Arteriolar compliance (the ability of the vessel to distend) controls the TPR Sympathetic innervation controls arteriolar radius The viscosity of the blood also affects resistance

Blood Flow Velocity in Vascular Tree

Blood Flow Changes During Exercise

Arterial Side

Blood flow in a healthy system is Laminar (smooth –no sound) Blood flow in a unhealthy system is Turbulent (rough –noisy)

Atherosclerotic plaques

Pressure Points

Venous Side

Skeletal Muscle Pump

Factors Affecting CO (Review) Starling Forces

Blood Pressure BP = SP/DP Systolic Pressure (SP) –the pressure in the artery during systole Diastolic Pressure (DP) –the pressure in the artery during diastole Mean Arterial Pressure (MAP) (weighted average) MAP = DP + 1/3 (PP) Pulse Pressure (PP) = SP - DP MAP = CO x TPR

SP DP

Renal Hormonal Control of BP

Summary of MAP Factors