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Biology 12 10.1 The Blood Vessels The circulatory system has ____ types of blood vessels. • ____________: carry blood _________ from the heart to the capillaries • ____________: permit exchange of material with the tissues • ____________: return blood from the capillaries ____ the heart All three blood vessel types have an inner endothelium, a simple squamous epithelium attached to a connective tissue basement membrane that has elastic fibres. The Arteries The _________ artery in the body is the ________, which carries O2-rich blood _________ the heart to other parts of the body. The arterial wall has three layers. • Inner layer: ________________ • Middle layer: ___________ muscle that contracts and relaxes to regulate blood flow and pressure • Outer layer: ____________ connective tissue ________________ are small arteries that branch off from an artery. Arterioles have three layers. • Inner layer: endothelium • Middle layer: some elastic tissue but mostly smooth muscle o Smooth muscle contracts: blood vessel constricts, resulting in higher blood pressure o Smooth muscle relaxes: blood vessel relaxes, resulting in lower blood pressure • Outer layer: fibrous connective tissue The Capillaries Capillaries are ____________ blood vessels that join _____________ to ____________. • Composed of a _____________ layer of epithelium with a basement membrane • Form vast _______________ (capillary beds) throughout the body • Only certain capillary beds are ________ at any given time. • After ____________, capillary beds that serve the digestive system are ________, and those that serve the muscles are mostly ____________ Biology 12 • • • ______________ muscles relax to _________ the bed and allow blood flow Sphincter muscles contract to _________ the bed and prevent blood flow • When the bed is closed, blood flows through ________________ (arteriovenous shunts) ______________ from arterioles to venules, bypassing the bed ______________ of substances takes place across the ________ walls of the capillaries. • Oxygen and nutrients _____________ out of the capillary and into the tissue fluid that surrounds cells • ____________ (carbon dioxide) diffuse into the capillary • Some water _____________ the capillaries, and excess is picked up by _______________vessels The Veins Veins and _____________ (small veins) take blood _________ the capillary beds to the __________. • Veins and venules have the same ________ layers as arteries, but there is ________ smooth muscle and connective tissue • Veins have _________, which allow blood to flow toward the heart when open and ___________ blood from flowing backward when closed • Veins act as a blood ______________ • Since their walls are ____________, they can _____________ to a greater extent • About ___% of blood is in the veins • The largest veins in the body are the ____________ __________ (superior vena cava, inferior vena cava), which deliver O2-poor blood to the heart
