20.7 Blood Flow Distribution During Exercise

During exercise, there is an increase in total blood flow due to

a faster and stronger heartbeat and because blood is shifted from the “reservoirs” of the veins to more quickly circulate. There is also a redistribution of blood.

both of these changes help ensure that the most metabolically active tissues are receiving adequate blood flow to meet the needs of the tissue cells.

increases in blood to specific regions or organs:

• Heart. Blood flow to the coronary arteries of the heart increases approximately three-fold (from 250 mL/min to 750 mL/min), a change that helps to ensure that sufficient oxygen reaches the cardiac muscle within the heart wall (see ( section 19.3f).

• Skin. The percentage of blood flow to the skin increases to almost five times its resting level (from 400 mL/min to 1900 mL/min) to dissipate heat (see L section 1.6b and ( section 6.1d).

• Skeletal Muscle. Blood flow to skeletal muscle increases an amazing 11-fold (from 1100 mL/min to 12,500 mL/min)-which is approximately 70% of the total cardiac output-a change needed to meet the high metabolic demands experienced by skeletal muscle during exercise

relatively less total blood flow is distributed to

the kidneys and abdominal organs

less total blood flow to the kidneys leads to

decreases urine ouput to maintain blood volume and blood pressure

less total blood flow to the abdominal organs leads to

slowed down digestive processes.