Blood Flow in the Body

1. General Features
1. delivery of oxygen and removal of carbon dioxide
2. gas exchange in the lungs
3. absorption and delivery of nutrients from GI tract
4. processing/waste removal in the kidneys
5. normal blood flow at rest
• abdominal organs 24%
• skeletal muscle 20%
• kidneys 20%
• brain 13%
• heart 4%
• other 15%
2. Velocity of Blood Flow
1. velocity directly related to the TOTAL cross-sectional area of the vessel(s)
• FASTEST aorta 40-50 cm/s
• arteries 20-40 cm/s
• arterioles 1-20 cm/s
• SLOWEST capillaries 0.1-1 cm/s
3. Local Regulation of Blood Flow
1. autoregulation - regulation of blood flow by altering arteriole diameter
• oxygen and carbon dioxide levels
• prostaglandins, histamines, kinins
• needy areas --> more blood flow
2. myogenic response - change in flow through arteriole in response to stretch of smooth muscle
3. reactive hyperemia - increase in blood flow to area where an occlusion has occurred
4. increased vasculature - results from prolonged lack of oxygen/nutrients to an area (eg. heart)
4. Blood Flow to Skeletal Muscles
1. active (exercise) hyperemia - increased blood flow to muscles during heavy activity
2. decreased oxygen and increased lactic acid
3. visceral organ blood flow is decreased
5. Blood Flow to The Brain
1. MUST maintain constant blood flow (750 ml/min)
2. sensitive to low pH and high carbon dioxide
3. blood pressure tightly regulated in the brain
• fainting -> below 60 mm Hg
• edema (brain swelling) -> above 180 mm Hg
6. Blood Flow to The Skin
1. intimately involved in temperature regulation
• increased body temperature -> hypothalamic inhibition of vasomotor area -> vasodilation of vessels in skin -> increased blood flow -> sweating -> (bradykinin -> more vasodilation)
7. Blood Flow to the Lungs
1. short pathway from heart, less pressure required
2. low oxygen level --> vasoconstriction
8. Blood Flow to the Heart
1. blood to coronary arteries during diastole
2. vasodilation from ADP and carbon dioxide

Category: Physiology Notes