Blood vessels

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Classification based on size and function1. Elastic (conducting) arteries            a. Characteristics                        i. Thick-walled                        ii. Near heart                        iii. Largest diameter                        iv. More elastic                        v. Large lumen            b. Properties                        i. Dampen BP changes associated with heart contraction                        ii. Passive accommodation results in smooth flow of blood            c. 1.0 - 2.5 cm2. Muscular arteries-distributing arteries            a. Distal to elastic arteries            b. Deliver blood to specific organs            c. Thick media layer                        i. More smooth muscle            d. 0.3 - 1.0 cm3. Arterioles            a. Determine flow into capillary beds            b. Mostly smooth muscle            c. 10 µm - 0.3 cm

Venous

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em A. Types of vessels

1. Venules            a. 8 - 100 µm            b. Characteristics vary with size                        i. Little muscle                        ii. Thin externa2. Veins            a. Formed from venules            b. Thinner walls and less muscle than arteries            c. Little muscle in media                        i. Mostly elastin            d. Externa is thickest wall layerB. Capacitance vessels1. Veins act as reservoirs            a. Large lumens            b. Low blood pressure allows walls to thin2. Venous valves            a. Prevent backflow            b. Folds of interna

Capillaries

Smallest blood vessels 8 - 10 µm one cell thick

Exchange of materials

Very low blood pressure

Where gas exchange takes place.

They can carry oxygenated and deoxygenated blood

Types of capillaryC

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s • Uninterrupted endothelial cells

• Incomplete tight junctions

• Intercellular clefts

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d • Endothelial cells have oval pores (Fenestrations)

• Pores permit greater permeability S

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al • Modified,

leaky capillaries

• Large molecules can pass through

(a) continuous, (b) frenestrated, (c) sinusoid