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The heart is divided into four chambers. The left and right sides of the heart are divided by a vertical muscular wall called the septum, which blood does not cross unless a person has a heart defect. The top and bottom chambers of the heart are divided by valves, which prevent the backflow of blood in the heart. The top chambers of the heart are called atria (singular “atrium”) and the bottom chambers are called ventricles. The valve between the left atrium and left ventricle is called the bicuspid valve because it has two valve flaps. The valve between the right atrium and the right ventricle is called the tricuspid valve, because it has three.
The heart muscle functions to pump blood throughout the body, getting oxygen where it is needed. You can think of the circulatory system as having two circuits. One circuit involves the right side of the heart and the blood vessels that take blood to and from the lungs. The other circuit involves the left side of the heart and the blood vessels that take blood to and from the rest of the body. Because of this asymmetry of the heart’s functions, the left ventricle is much stronger than the right and has a thicker muscular wall. The blood goes from the right side of the heart through the first circuit to pick up oxygen, then it goes through the second circuit to deliver the oxygen to organs and tissues. Afterwards, the blood returns back to the right side of the heart, and so on. Looking at a diagram of the heart with arrows indicating blood flow may help clarify the description:
The circulatory system is set up so that the right side of the heart pumps deoxygenated blood to the lungs via arteries called the pulmonary arteries. The pulmonary arteries are “backwards” from the other arteries in the body in that they carry deoxygenated blood instead of oxygenated blood; usually, veins carry deoxygenated blood and arteries carry oxygenated blood. Once the blood goes through the pulmonary arteries, the hemoglobin in red blood cells picks up oxygen from the air sacs of the lungs. This blood, now full of oxygen, is pumped through the pulmonary veins back to the left side of the heart, where it is pumped through the largest artery in the body, called the aorta, to the rest of the body.
Pulmonary hypertension involves high blood pressure specifically in the pulmonary arteries, the blood vessels that carry deoxygenated blood from the right side of the heart to the lungs. Pulmonary hypertension can have many causes, but it starts with inflammation in the pulmonary arteries, stiffening or tightening of the pulmonary arteries or blood clots in the pulmonary arteries. All of these factors have the potential to raise blood pressure in the pulmonary arteries and these changes may be triggered by different medical conditions. Pulmonary hypertension is different from the type of hypertension that affects all of the blood vessels in the body. It is more localized, but it is potentially serious because it can lead to heart failure.
The type of heart failure that can result from pulmonary hypertension is called cor pulmonale, and it affects the right side of the heart. Due to increased blood pressure in the pulmonary arteries, the right ventricle has to work harder to force blood into the pulmonary arteries to the lungs. Over time, this results in the muscle of the right ventricle weakening and stretching out. If the condition is allowed to worsen, this eventually leads to the heart muscle not being strong enough to pump enough blood to the lungs.
People with pulmonary hypertension may report symptoms, but these symptoms vary and may not be constant. Possible symptoms of pulmonary hypertension include lightheadedness and shortness of breath. A fast or irregular heart beat may also be present. At first, these symptoms may only occur during strenuous activity, but as the pulmonary hypertension gets worse the symptoms can occur when a person is resting. In some cases, people with pulmonary hypertension may experience chest pain. Fatigue, muscle weakness, dizziness, fainting, and swelling of the ankles may occur. A person who has a lowered oxygen saturation due to weakening of the right side of the heart may appear cyanotic, or have a blue tint to their lips, fingernail beds or skin. Pulmonary hypertension will become worse over time if left untreated.