Peter, Sam and Alex

Blood Vessels

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?

SourcesBianco, 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.