Course 13.2Lesson 3 of 3
In the human heart the blood makes two loops. The pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs and brings oxygenated blood to the left atrium. The systemic circulation carries oxygenated blood from the left ventricle to the body and brings deoxygenated blood to the right atrium. The hepatic portal system and the coronary system are two special pathways.
Try the code and the simulations beside the lesson.
In the lesson on animals you saw that a mammal has a double circulation. Now follow the blood through the human heart. The path has two loops that meet in the heart.
The oxygenated blood enters the aorta from the left ventricle. A network of arteries, arterioles and capillaries carries it to the tissues. There the blood gives up oxygen and takes up carbon dioxide. The deoxygenated blood is collected by venules, veins and the vena cavae. It is emptied into the right atrium.
The deoxygenated blood is pumped from the right ventricle into the pulmonary artery. It goes to the lungs. In the lung capillaries, it gives up carbon dioxide and takes up oxygen. The oxygenated blood returns by the pulmonary veins to the left atrium.
An artery carries blood away from the heart. A vein carries blood towards the heart. The rule is about the direction, not about the oxygen. The pulmonary artery carries deoxygenated blood, and the pulmonary veins carry oxygenated blood.
The two sides of the heart pump the same volume of blood, and the oxygenated and the deoxygenated blood never mix. The right ventricle sends blood only to the lungs, so its wall is thinner.
You should find that the blood is rich in oxygen only on the way from the lungs to the body, and that it passes the heart twice in one round.
A special connection joins the digestive tract and the liver. It is called the hepatic portal system. The hepatic portal vein carries blood from the intestine to the liver. There it enters capillaries once more. So the blood from the intestine passes through the liver before it is delivered to the systemic circulation. The liver can then store, change or remove the substances absorbed from the food. The hepatic vein carries the blood out of the liver.
The heart muscle is thick, and it needs its own blood. The coronary circulation is the system of vessels that supplies the cardiac muscle. The coronary arteries take blood from the aorta to the heart muscle, and the coronary veins bring it back to the right atrium. The blood in the chambers does not feed the heart wall.
The program lists the stops of one round of the blood and the state of the oxygen at each stop.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
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