Chapter 20- Blood Vessels

arteries, veins, capillaries

tunica interna, tunica media, tunica externa

Lines the blood vessel and is exposed to blood

• Simple squamous epithelium • Selectively permeable barrier • Secretes chemicals that stimulate dilation or constriction • Normally repels blood cells and platelets to prevent clotting • When tissue around vessel is inflamed, endothelial cells produce cell-adhesion molecules • Causes leukocytes to adhere to surface and congregate in tissues where their defensive actions are needed

• Middle layer • Consists of smooth muscle, collagen, and elastic tissue • Strengthens vessels and prevents blood pressure from rupturing them • Contraction of muscle controls blood vessel diameter • This layer is more prominent in arteries compared with veins in general

• Outermost layer • Consists of loose connective tissue that often merges with that of neighboring blood vessels, nerves, or other organs • Anchors the vessel and provides passage for small nerves, lymphatic vessels • Vasa vasorum: small vessels that supply blood to outer part of the larger vessels

• Biggest arteries • Examples: aorta, common carotid, subclavian, pulmonary trunk, and common iliac arteries • Internal elastic lamina at the border between interna and media • External elastic lamina at the border between media and externa • Expand during systole, recoil during diastole • Expansion takes pressure off smaller downstream vessels • Recoil maintains pressure during relaxation, keeps blood flowing

• Distribute blood to specific organs • Examples: brachial, femoral, renal, and splenic arteries • Smooth muscle layers constitute three-fourths of wall thickness

• Thicker tunica media in proportion to their lumen than large arteries and very little tunica externa • Arterioles: smallest of the resistance arteries • 200 μm diameter; only 1-3 layers of smooth muscle • Control amount of blood to various organs

• Short vessels that link arterioles directly to venules in some places (for example, in mesenteries) • Provide shortcuts allowing blood to bypass capillary beds

• weak point in artery or heart wall • Forms a thin-walled, bulging sac that pulsates with each heartbeat and may rupture at any time

blood accumulates between tunics of artery and separates them, usually because of degeneration of the tunica media

abdominal aorta, renal arteries, and arterial circle at base of brain

• Can cause pain by putting pressure on other structures • Can rupture causing hemorrhage • Result from congenital weakness of blood vessels, trauma, or bacterial infections • Most common cause is atherosclerosis and hypertension

In walls of internal carotid artery, monitor blood pressure, allow for baroreflex, innervation is glossopharyngeal n (CN IX

• Oval bodies near branch of common carotids • Monitor blood chemistry, CNIX to brainstem respiratory centers; adjust respiratory rate to stabilize pH, CO2, and O2

One to three bodies in walls of aortic arch, same structure and function as carotid bodies, but innervation is by vagus n.

Where gasses, nutrients, wastes, and hormones pass between the blood and tissue fluid * The “business end” of the cardiovascular system * Composed of endothelium and basal lamina * Absent or scarce in tendons, ligaments, epithelia, cornea, and lens of the eye * Three capillary types distinguished by permeability

• Continuous capillaries • Fenestrated capillaries • Sinusoids

• Occur in most tissues • Endothelial cells have tight junctions • Form a continuous tube with intercellular clefts • Allow passage of solutes such as glucose • Pericytes wrap around the capillaries and contain the same contractile protein as muscle • Contract and regulate blood flow

• Organs that require rapid absorption or filtration - Examples: kidneys, small intestine • Endothelial cells riddled with holes called filtration pores (fenestrations) • Spanned by very thin glycoprotein layer • Allow passage of only small molecules • Proteins and larger particles stay in bloodstream

• Found in liver, bone marrow, spleen • Irregular blood-filled spaces with large fenestrations • Allow proteins (albumin), clotting factors, and new blood cells to enter the circulation

• Thin-walled and flaccid • Collapse when empty, expand easily • Greater capacity for blood containment than arteries • At rest, about 64% of blood is in veins, 15% in arteries • Have steady blood flow (unlike pulses in arteries) • Have valves to prevent back flow (except in head and most of neck region) – formed from tunica interna • Subjected to relatively low blood pressure

• Smallest veins (10 to 20 mm diameter) • Even more porous than capillaries • Also exchange fluid with surrounding tissues • Tunica interna with only a few fibroblasts around it • No muscle • Leukocytes (WBCs) leave bloodstream through venule walls