Transport systems in mammals: Direction of blood flow and the lungs

Blood flow through the heart

Deoxygenated blood enters the right atrium through the vena cava → right ventricle → pulmonary artery → lungs. Oxygenated blood returns through the pulmonary veins → left atrium → left ventricle → aorta → body.

Pulmonary system

The system that transports deoxygenated blood from the heart to the lungs, where gas exchange takes place, and returns oxygenated blood to the heart.

Alveoli

Tiny air sacs in the lungs surrounded by capillaries where oxygen and carbon dioxide are exchanged.

Gas exchange in the lungs

Carbon dioxide diffuses from the blood capillaries into the alveoli, while oxygen diffuses from the alveoli into the blood capillaries.

Systemic system

The circuit that transports oxygenated blood from the left ventricle to all body cells and returns deoxygenated blood to the right atrium.

Hepatic portal system

A branch of the systemic circuit in which the hepatic portal vein carries blood rich in digested nutrients to the liver.

Hepatic portal vein

The vein that carries blood rich in digested nutrients from the digestive system to the liver.

Hepatic vein

The vein that carries blood away from the liver and joins the inferior vena cava.