Pages 370-379

Flow is unidirectional

Vessels that carry blood away from the heart: (from largest to smallest)◦ Arteries > arterioles > Capillary beds

exchanges between tissues and blood take place at the capillary beds

Vessels that return blood toward the heart:◦ Venules and veins

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Three tissue layers (tunics) in blood vessels from deep to superficial:

◦ Tunica intima- innermost endothelium◦ Tunica media- middle smooth muscle◦ Tunica externa- outermost fibrous connective

All vessels possess this arrangement except capillaries

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Arteries:◦ thicker tunica media for larger volume and pressure◦ Stronger and more elastic

Capillaries: one cell layer thick for diffusion between blood and tissues

Veins:◦ thinner tunica media than arteries◦ operate under low pressure◦ valves to prevent backflow of blood against gravity◦ Larger lumen (channel)◦ Skeletal muscle helps move blood toward the heart

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VeinArtery Tunica intima• Endothelium• Loose connective tissue

Tunica media• Smooth muscle

• Collagen fibersTunica externa

LumenArteriole Capillary

network

Venule

Valve

Lumen

Basement membraneEndothelial cells

Capillary(b)

Valve (open)

Contractedskeletalmuscle

Valve (closed)

Vein

Direction ofblood flow

Precapillary sphinctersVascular shunt

Truecapillaries

Terminal arteriole Postcapillaryvenule

(a) Sphincters open; blood flows throughtrue capillaries.

Terminal arteriole Postcapillaryvenule

(b) Sphincters closed; blood flows throughvascular shunt.

Varicose veins: ◦ structural defect due to incompetent valves◦ Common in people who:

Are obese stand for long periods of time

◦ Predisposing factor for thrombophlebitis: inflammation of a vein resulting from a clot can lead to pulmonary embolism

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circulation between the heart and tissues

◦ Aorta (oxygenated blood) Largest artery in the body Leaves from the left ventricle of the heart

◦ Superior and inferior venae cavae (deoxygenated) enter the right atrium of the heart Superior drains the head and arms Inferior drains the lower body

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Superior vena cava Aorta

Left atrium

Left ventricle

Right atrium

Right ventricle

Inferior vena cava

CEREBRUM:◦ Blood supply branches from

internal carotid arteries Basilar artery

BRAIN STEM AND CEREBELLUM:◦ Blood supply branches from

Basilar artery

This system of arteries branches to form a circle which supplies the major brain structures

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Frontal lobe

Internal carotidartery

Temporal lobe

Pons

Occipital lobe

Anterior

Posterior

Cerebral arterial circle(circle of Willis)

Basilar arteryVertebral artery

Cerebellum

(a)

(b)

sends blood from certain organs (digestive, pancreas, spleen) for processing by the liver

The hepatic portal vein is the transport vessel

After nutrients are removed and stored, blood is returned to systemic circulation◦ via the hepatic portal vein to the inferior vena cava

veins are supplying the liver with blood for processing while arteries supply the liver with oxygen

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Arterialblood

Venousblood

Stomach and intestine Liver

Inferiorvena cava

Liver cells (hepatocytes)

Nutrientsand toxinsleave

Nutrients andtoxins absorbed

Hepaticportal vein

Hepaticvein

First capillary bed Second capillary bed(liver sinusoids)

Hepatic portal system

Liver

Hepaticportal vein

Smallintestine

Inferior vena cava(not part of hepaticportal system)

Gastric veins

SpleenStomach

Splenic vein

Inferiormesenteric vein

Superiormesenteric vein

Large intestine

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