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

2. 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.

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

4. 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

5. 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

6. 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

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

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

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

10. 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

11. Exchange across capillary walls
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