Blood Vessels Peter, Sam and Alex

Arteries – Structure Outer layer of connective tissue Layer of elastic tissue Smooth muscle Another elastic tissue layer Bottom layer is endothelium Arterioles: Smaller branches of arteries, thinner, lead to capillaries

Arteries - Function Carry oxygen-rich blood to the body and head and deoxygenated blood to lungs Muscles contract when heart relaxes and expand when it pumps to regulate flow and pressure Wide diameter allows fast, easy blood flow Thick and elastic to withstand blood pressure Muscle in arterioles contract and expand to control flow speed and volume

Capillaries – Structure 10-40 billion in body .001 cm from every cell at farthest 3-7 micrometers wide (red blood cells 8) 1 epithelial cell thick

Capillaries – Function Provide oxygen and nutrients to organs while removing wastes like carbon dioxide Thinness allows easy diffusion of oxygen (out), carbon dioxide (in) and other nutrients/wastes Pressure inside capillary can lead to bulk flow of water and solutes out Small diameter (red blood cells pressing against wall) and slowed blood flow make diffusion easier High number and closeness to cells allows almost every cell access

Veins – Structure Outer layer of connective tissue Smooth muscle with elastic fibers Endothelium is innermost layer Valves Venules: small veins, thin, allow some diffusion, help control capillary pressure

Veins – Function Return deoxygenated blood to to heart (which pumps it to the lungs) Heart cannot pump blood in veins so skeletal muscles alongside contract to move it Valves allow flow of blood only towards heart Valves closed by blood backflow, can hold/store blood

Questions?

Sources Bianco, Carl.  "How Your Heart Works." 1 April 2000. 27 October 2008. <http://health.howstuffworks.com/heart.htm>. “The Human Heart” The Franklin Institute. 2008. The Franklin Institute. 28 October 2008 <http://www.fi.edu/learn/heart/index.html> “Circulatory System” Microsoft Encarta Online Encyclopedia. 2008. Encarta Encyclopedia. 27 October 2008 <http://encarta.msn.com/>. Starr, Cecie and Ralph Taggart, Biology: The Unity and Diversity of Life. Pacific Grove: Brooks/Cole, 2000.