Ch 19 Cardiovascular Syste Essay

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Chapter 19

The Cardiovascular System: Blood Vessels:

Part A

Blood Vessels

Delivery system of dynamic structures that begins and ends at heart

Arteries: carry blood away from heart; oxygenated except for pulmonary circulation and umbilical vessels of fetus

Capillaries: contact tissue cells; directly serve cellular needs

Veins: carry blood toward heart

Structure of Blood Vessel Walls


Central blood-containing space

Three wall layers in arteries and veins

Tunica intima, tunica media, and tunica externa


Endothelium with sparse basal lamina


Tunica intima

Endothelium lines lumen of all
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tinuous with thoroughfare channel (intermediate between capillary and venule)

Thoroughfare channel ( postcapillary venule that drains bed

Capillary Beds: Two Types of Vessels

Vascular shunt (metarteriole—thoroughfare channel)

Directly connects terminal arteriole and postcapillary venule

True capillaries

10 to 100 exchange vessels per capillary bed

Branch off metarteriole or terminal arteriole

Blood Flow Through Capillary Beds

True capillaries normally branch from metarteriole and return to thoroughfare channel

Precapillary sphincters regulate blood flow into true capillaries

Blood may go into true capillaries or to shunt

Regulated by local chemical conditions and vasomotor nerves

Venous System: Venules

Formed when capillary beds unite

Smallest postcapillary venules

Very porous; allow fluids and WBCs into tissues

Consist of endothelium and a few pericytes

Larger venules have one or two layers of smooth muscle cells


Formed when venules converge

Have thinner walls, larger lumens compared with corresponding arteries

Blood pressure lower than in arteries

Thin tunica media; thick tunica externa of collagen fibers and elastic networks

Called capacitance vessels (blood reservoirs); contain up to 65% of blood supply


Adaptations ensure return of blood to heart

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