Day 2 Mammalian Circulation Superior systemic pulmonary systemic Inferior What do blue vs. red areas represent?

Vertebrate cardiovascular system Chambered heart atrium = receive blood ventricle = pump blood out Blood vessels arteries = carry blood away from heart Arterioles (small artery) veins = return blood to heart Venules (small vein) capillaries = thin wall, exchange / diffusion capillary beds = networks of capillaries Arteries, veins, and capillaries are the three main kinds of blood vessels, which in the human body have a total length of about 100,000 km. Notice that arteries and veins are distinguished by the direction in which they carry blood, not by the characteristics of the blood they contain. All arteries carry blood from the heart toward capillaries, and veins return blood to the heart from capillaries. A significant exception is the hepatic portal vein that carries blood from capillary beds in the digestive system to capillary beds in the liver. Blood flowing from the liver passes into the hepatic vein, which conducts blood to the heart.

Blood vessels arteries arterioles capillaries venules veins veins artery arterioles venules arterioles capillaries venules veins

Physical principles govern blood circulation Blood flow rate (F) is determined by many factors: F = ∆Pπr4 8Lµ ∆P – change in blood pressure r – radius of blood vessel L – length of blood vessel µ – viscosity of blood

Arteries: Built for high pressure pump thicker walls provide strength for high pressure pumping of blood narrower diameter elasticity elastic recoil helps maintain blood pressure even when heart relaxes

Veins: Built for low pressure flow Blood flows toward heart Veins thinner-walled wider diameter blood travels back to heart at low velocity & pressure lower pressure distant from heart blood must flow by skeletal muscle contractions when we move squeeze blood through veins valves in larger veins one-way valves allow blood to flow only toward heart Open valve Closed valve

The Upright Posture Gravity acting on blood in veins Harder to move blood from lower extremities up to the heart

Capillaries: Built for exchange very thin walls lack 2 outer wall layers only endothelium enhances exchange across capillary diffusion exchange between blood & cells

Capillaries Efficient gas exchange F = ∆Pπr4 8Lµ Large surface area Low velocity (speed) of blood flow Lower blood pressure F = ∆Pπr4 8Lµ

Controlling blood flow to tissues Blood flow in capillaries controlled by pre-capillary sphincters supply varies as blood is needed after a meal, blood supply to digestive tract increases during strenuous exercise, blood is diverted from digestive tract to skeletal muscles capillaries in brain, heart, kidneys & liver usually filled to capacity Why? sphincters open sphincters closed

Exchange across capillary walls http://www.youtube.com/watch?v=Q530H1WxtOw Exchange across capillary walls Lymphatic capillary Fluid & solutes flows out of capillaries to tissues due to blood pressure “bulk flow” Interstitial fluid flows back into capillaries due to osmosis plasma proteins  osmotic pressure in capillary BP > OP BP < OP Interstitial fluid About 85% of the fluid that leaves the blood at the arterial end of a capillary bed reenters from the interstitial fluid at the venous end, and the remaining 15% is eventually returned to the blood by the vessels of the lymphatic system. Blood flow 85% fluid returns to capillaries Capillary 15% fluid returns via lymph Arteriole Venule