Circulatory System for AP Biology
Practice problems for these concepts can be found at:
Welcome to the heart. The human heart is a four-chambered organ whose function is to circulate blood by rhythmic contraction. The heart pumps oxygenated blood from the left ventricle out to the aorta (Figure 15.1). From there it travels through arteries to feed the organs, muscles, and other tissues of the body. The blood returns to the heart via the veins. The vena cava system of veins returns deoxygenated blood from the body to the lungs to pick up more oxygen. The blood reenters the heart into the right atrium, passes through to the right ventricle, and from there flows to the lungs to pick up more oxygen. At this point, the blood has made a complete cycle through the body. The blood is at its most oxygenated stage just after leaving the lungs as it enters the left side of the heart and travels into the aorta. The blood is in its least oxygenated stage as it reenters the right atrium of the heart.
Structure–function relationships come up often on the AP Biology exam, and the circulatory system provides a good example you could add to an essay on the topic. The left ventricle of the heart is the thickest and most muscular part of the heart, and the most pressure is exerted on it. Why does this make sense functionally? Because the left ventricle is the portion of the heart that needs to pump the blood into the aorta and to the rest of the body. The left ventricle is structurally designed to fit its function. The right ventricle is smaller and less muscular because it only pumps blood a short distance to the lungs for reoxygenation.
If you look off to your right, you will see some of the blood and its components passing us now. If you look closely, you will see little red blood cells traveling in the bloodstream, which carry oxygen. Thanks to a molecule termed hemoglobin, the red blood cells are able to carry and deliver oxygen throughout the body to hardworking organs and tissues. Iron is a major component of hemoglobin. If you do not have enough iron in your diet, your ability to deliver oxygen via the blood can be compromised, and you may develop anemia.
Blood is able to flow so efficiently because it contains primarily water. The liquid portion of the blood, the plasma, contains minerals, hormones, antibodies, and nutritional materials. Another common cell seen in the bloodstream is the platelet, which is involved in the clotting of blood. You might ask, "What are the white cells flowing around?" The white blood cells are the protection system for our body. We will be seeing those up close when we talk about the immune system.
The lymphatic system is worth a brief mention here because it is an important part of the circulatory system. When blood flows through the capillaries of the body, proteins and fluid leak out during the exchange. The lymphatic system functions as the route by which these poor lost souls find their way back into the bloodstream. The lymphatic system also functions as a protector for the body because of the presence of structures known as lymph nodes, which are full of white blood cells that live to fight infection. If your neck sometimes swells when you are sick with the flu, for instance, it is probably the multiplication of white blood cells in the lymph node.
Diseases of the Cardiovascular System
Two diseases that you should be familiar with for the exam are hypertension and arteriosclerosis. Hypertension is high blood pressure and is a major cause of strokes and heart attacks. Arteriosclerosis is a big word that means hardening of the arteries. These hardened arteries become narrower and are a prime risk factor for death by embolism—the breaking off of a piece of tissue that lodges in an artery, blocking the flow of blood to vital tissues.
Practice problems for these concepts can be found at: Human Physiology Review Questions for AP Biology
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