Circulation and Gas Exchange

Page
3

Systemic capillaries

Reptiles

Lung capillaries

Pulmonary

circuit

Right

systemic

aorta

Right

Left

Left

systemic

aorta

Systemic capillaries

A

A

V

V

Systemic capillaries

Pulmonary

circuit

Systemic

circuit

Right

Left

A

A

V

V

Lung capillaries

Mammals and

Birds

Slide 18

In reptiles and mammals, oxygen-poor blood flows through the pulmonary circuit to pick up oxygen through the lungs.

In amphibians, oxygen-poor blood flows through a pulmocutaneous circuit to pick up oxygen through the lungs and skin.

Oxygen-rich blood delivers oxygen through the systemic circuit.

Double circulation maintains higher blood pressure in the organs than does single circulation.

Slide 19

Adaptations of Double Circulatory Systems

Amphibians:

Frogs / amphibians have a three-chambered heart: 2 atria and 1 ventricle.

The ventricle pumps blood into a forked artery that splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit.

Underwater, blood flow to the lungs is nearly shut off.

Slide 20

Reptiles (Except Birds)

Turtles, snakes, and lizards have a three-chambered heart: two atria and one ventricle.

In alligators, caimans, and other crocodilians a septum - partially or fully divides the ventricle.

Reptiles have double circulation, with a pulmonary circuit - lungs and a systemic circuit.

Slide 21

Mammals

Mammals and birds have a four-chambered heart with two atria and two ventricles.

The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood.

Mammals and birds are endotherms and require more O2 than ectotherms.

RA --> RV --> LUNGS --> LA --> LV --> Body

Slide 22

Coordinated cycles of heart contraction drive double circulation in mammals

Blood begins its flow with the right ventricle pumping blood to the lungs.

In the lungs, the blood loads O2 and unloads CO2

Oxygen-rich blood from the lungs enters the heart at the left atrium and is pumped through the aorta to the body tissues by the left ventricle.

The aorta provides blood to the heart through the coronary arteries.

Slide 23

Blood returns to the heart through the superior vena cava (deoxygenated blood from head, neck, and forelimbs) and inferior vena cava (deoxygenated blood from trunk and hind limbs).