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Chapter 21

The Cardiovascular SystemPeripheral Circulation and Regulation

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Types of Blood Vessels

• Arteries– Elastic– Muscular– Arterioles

• Capillaries: site of exchange with tissues• Veins: thinner walls than arteries, contain less

elastic tissue and fewer smooth muscle cells– Venules– Small veins– Medium or large veins

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Capillaries

• Capillary wall consists of endothelial cells (simple squamous epithelium), basement membrane and a delicate layer of loose C.T.

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Capillary Network

• Blood flows from arterioles through metarterioles, then thoroughfare channel

• Smooth muscle in arterioles, metarterioles, precapillary sphincters regulates blood flow

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Structure of Arteries and Veins• Tunica intima

– Endothelium– Basement membrane– Lamina propria (C.T. layer)– Internal elastic membrane.

Fenestrated layer of elastic fibers.• Tunica media: smooth muscle cells

arranged circularly around the blood vessel.– Vasoconstriction: smooth muscles

contract, decrease in blood flow– Vasodilation: smooth muscles relax,

increase in blood flow• Tunica externa (adventitia):

connective tissue, varies from dense regular near the vessel to loose that merges with the surrounding C.T.

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Photomicrograph of Artery and Vein

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Elastic Artery• Elastic or conducting arteries

– Largest diameters, pressure high and fluctuates between systolic and diastolic. More elastic tissue than muscle.

– Relatively thick tunica intima, thin tunica intima

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Muscular Artery

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Medium and Large Veins

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Other Vessel Types

• Vasa vasorum: blood vessels that supply the walls of arteries and veins. Penetrate vessel walls from the exterior. Branches of arteries.

• Vasa vasorum: blood vessels that supply the walls of arteries and veins. Penetrate vessel walls from the exterior. Branches of arteries.

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Pulmonary Circulation

• From right ventricle into pulmonary trunk

• Pulmonary trunk divides into left and right pulmonary arteries.

• Two pulmonary veins exit each lung and enter left atrium

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Systemic Circulation• Aorta: exits left ventricle and is divided into three

parts– Ascending aorta: right and left coronary arteries

branch from here– Aortic arch: arching posteriorly and to the left and has

three branches• Brachiocephalic artery• Left common carotid• Left subclavian artery

– Descending aorta• Thoracic aorta: portion in thorax• Abdominal aorta: inferior to diaphragm. Ends as two

common iliac arteries

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Branches of the Aorta

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Major Arteries

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Head and Neck Arteries

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Major Arteries of the Head and Thorax

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Arteries of Upper Limb and Shoulder

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Arteries of Abdomen

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Arteries of Abdomen and Pelvis

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Arteries of Pelvis and Lower Limb

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Arteries of Lower Limb

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Systemic Circulation: Veins

• Return blood from body to right atrium

• Major veins– Coronary sinus (heart)– Superior vena cava (head, neck, thorax, upper

limbs)– Inferior vena cava (abdomen, pelvis, lower

limbs)

• Types of veins– Superficial, deep, sinuses

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Major Veins

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Venous Sinuses Associated with the Brain

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Veins of Head and Neck

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Head and Thorax Veins

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Veins of Shoulder and Upper Limb

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Veins of Thorax

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Inferior Vena Cava and Its Tributaries

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Hepatic Portal System• Portal system: vascular system that

begins and ends at a capillary bed with no pumping mechanism in between.

• Hepatic portal- liver; renal portal- kidney; hypothalamohypophyseal portal between hypothalamus and pituitary.

• Blood entering the hepatic portal vein is rich with nutrients collected from the intestines, but may also contain toxic substances. Both nutrients and toxic substances will be regulated by the liver–Nutrients: either taken up and stored or modified chemically and used by other parts of the body–Biotransformation: Toxic substances can be broken down by hepatocytes or can be made water soluble. To be transported in blood and excreted by the kidneys.

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Veins of Abdomen and Pelvis

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Veins of Pelvis and Lower Limb

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Veins of Lower Limb

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