Biology Forums - Study Force

Help please :)

1.  Why do you think body position has an affect on blood pressure & heart rate?  Is this direct or via neutral control?
3.  How are veins different from arteries in structure & function?
4.  What is the purpose of plotting EKG amplitudes in Einthovens triangle?

Thanx!!

Arteries - transports oxygenated blood from the heart (except in pulmonary artery which contains deoxygenated blood).

Arteries have:

• thick muscular wall
• much elastic tissue
• small lumen relative to diameter
• not permeable
• valves in pulmonary artery and Aorta only
• blood under high pressure (10-16kPa)
• blood moves in pulses
• blood flows rapidly

Veins transport deoxygenated blood back to the heart (except in pulmonary vein which carries oxygenated blood)

• thin muscular wall
• little elastic tissue
• large lumen relative to diameter
• not capable of constriction
• not permeable
• valves throughout all veins
• blood under low pressure (1kPa)
• no pulses
• blood flows slowly

Arteries: flow from heart, thick elastic muscle layer, no valves, oxygenated

Veins: flow to heart, thin elastic muscle layer, has valves, deoxygenated

(http://library.thinkquest.org/22016/circ/vessy.gif)

Looking at the image you can see that they have different wall thicknesses. The capillary wall is only 1 cell thick - this is to allow substances to diffuse across it(ie to give oxygen to cells and retrieve the CO2 from cells. One of the reason the blood is at higher pressure in the arteries is that there is a thick muscle layer and this creates a small volume for the blood to pass through. The thick muscle layer is there to withstand the high pressure. In the veins, the semilunar valves stop the blood from flowing backwards, as it is traveling at a very low pressure and is often moving against gravity. The contraction of the muscles also helps the blood in the veins to be pushed up.