Blood Flow in the Heart and Blood Pressure

Need help preparing for the Biology section of the MCAT? MedSchoolCoach expert, Ken Tao, will teach everything you need to know about Blood Flow in the Heart and Blood Pressure of the Circulatory System. Watch this video to get all the MCAT study tips you need to do well on this section of the exam! The heart is responsible for pumping blood throughout the body. For the MCAT exam, understanding the pathway of blood through the heart is important. The structure of the heart has significant components, and contains the pathway of blood flow. Blood first enters the heart through the superior and inferior vena cava. These blood vessels carry deoxygenated blood from the systemic circulation to the heart. Both the inferior and superior vena cava empty into the right atrium. From the right atrium, the blood is pumped into the right ventricles, passing through the right atrioventricular valve or the tricuspid valve. The heart has a number of these valves to prevent the backflow of blood. For example, when the right ventricle contracts, the tricuspid valve prevents the blood from shooting back into the right atrium. With the valve closed, the blood can move into the pulmonary artery. Once again, the pulmonary artery has a valve called the pulmonary valve that prevents the backflow of blood back into the right ventricle. From the pulmonary artery, the deoxygenated blood will reach the lungs where gas exchange occurs. At this point, the blood becomes oxygenated. Afterward, it will move through the pulmonary veins into the left atrium of the heart. From the left atrium, the oxygenated blood will travel to the left ventricles, passing through the left atrioventricular valve. This valve is also known as the bicuspid or mitral valve. Like the tricuspid valve, the bicuspid valve also prevents the backflow of blood from the ventricle to the atrium. When the left ventricle contracts, blood is pushed into the aorta and then to the rest of the body. Similar to the pulmonary artery, the aorta has a valve, called the aortic valve, that prevents the backflow of blood. Blood Pressure Blood pressure is the measure of the pressure, or force, of the blood circulating throughout the body on the walls of the blood vessels. Blood pressure is directly related to the heart. When the heart contracts, the pressure of blood in the vessels increases. When the heart relaxes, the pressure of blood in the vessels decreases. There are two important terms when it comes to blood pressure – systolic blood pressure and diastolic blood pressure. The systolic blood pressure is the highest pressure in one heartbeat. It is the highest pressure when the ventricles contract. The diastolic blood pressure is the lowest pressure in two heartbeats. In other words, it is the pressure when the ventricles are relaxing and filling with blood. In normal, healthy humans, the expected systolic pressure over diastolic pressure as about 120 over 80 mm Hg. Sometimes an individual's blood pressure may be too high or too low, and many times this can be caused by an underlying disease, such as hypertension or kidney disease. However, many times changes in blood pressure are normal physiological responses and are not the sign of disease. Changes in Blood Pressure Three different factors can change blood pressure. The first factor is changes in blood volume. Blood vessels are sort of like a container for blood, and drinking more fluid, such as water, will increase the blood in the container. More volume in the same-sized container will increase the pressure in the container. In this way, drinking more fluids increases blood pressure. Similarly, drinking less fluids means there is less volume in the container. In this way, dehydration leads to a decrease in blood pressure. Another factor that can affect blood pressure is peripheral resistance. Instead of changing the volume of blood in the container, changing the size of the container can also lead to blood pressure fluctuations. Constricting the blood vessels decreases the vessel diameter. Decreasing the vessel diameter increases the peripheral resistance, which in turn increases the blood pressure. Contrastingly, dilating the blood vessels increases the vessel diameter, which in turn decreases the peripheral resistance and blood pressure. The third factor that can affect blood pressure is cardiac output. Cardiac output is defined as the volume of blood pumped from the heart per minute. MEDSCHOOLCOACH To watch more MCAT video tutorials like this and have access to study scheduling, progress tracking, flashcard and question bank, download MCAT Prep by MedSchoolCoach IOS Link: play.google.com/store/apps/details?id=com.htd.meds… Apple Link: apps.apple.com/us/app/mcat-prep-by-medschoolcoach/… #medschoolcoach #MCATprep #MCATstudytools

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