The circulatory system functions to deliver oxygen, nutrients, and hormones as well as transporting waste products. In mammals it is divided into two major pathways. The systemic circuit and the pulmonary circuit. Both circuits have arteries which lead away from the heart capillaries which connect arteries to veins and veins which carry blood toward the heart. In the systemic circuit arteries carry blood rich in oxygen from the left side of the heart toward the extremities. They are injected with red latex. In the organs capillary beds connect arteries to veins that return blood depleted in oxygen to the right side of the heart. Veins are injected with blue latex.

Now examine the pulmonary circuit, which transports blood between the heart and lungs. Note that blood low in oxygen enters the right side of the heart. Arteries carry blood low in oxygen from the right side of the heart to the lungs to be oxygenated. Blood high in oxygen enters the left side of the heart in the pulmonary vein and is pumped into the systemic circuit.

The pulmonary arteries and veins are unique in the type of blood they carry.

Click here to examine circulation about the heart.

(Optional) Click here if you would like to examine the internal structures of a pork heart. Use the back button to return to this tutorial.

Click to follow the path taken by blood toward the anterior extremities. Note the two large veins lying on either side of the neck these are the cranial vena cavas. They return blood to the right side of the heart. Click for an alternate view.

Click to test you knowledge of the movement of material through the thoracic cavity. In the image the pathways are coded as follows: air, food, oxygenated blood, deoxygenated blood.

In addition to the pulmonary and systemic circuit there are also portal systems. Portal systems move blood between organs before it is returned to the heart. They begin in the capillary beds of one organ and terminate in the capillary beds of another organ. Because latex does not move through capillary beds portal systems must be injected separately.

Nutrients processed by the digestive organs enter the circulatory system through the hepatic portal system, which carries them from the capillary beds in the digestive organs directly to the capillary beds in the liver. The nutrients will be further processed in the liver and stored or circulated. The capillary beds of the liver are continuous with the hepatic portal system on one side and the systemic venous system on the other side. Vessels that are part of the hepatic portal system have been injected with yellow latex in some specimens.

Click to see the veins of the hepatic portal system.

Click to follow the path taken by blood as it returns to the heart.

(Optional) Click to follow the path taken by blood as it returns from the posterior extremities. Note that in this region many arteries parallel veins of the same name. Only the veins are numbered.

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