Cardiovascular Systemfunctions

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Abnormalities or injuries to any or all parts of the cardiovascular system can result in serious health complications. Common conditions that can affect the cardiovascular system include coronary artery disease, heart attack, high blood pressure, and stroke.

There are two blood circulatory systems in the body. The first is the systemic circulatory system. This is the main blood circulatory system that transports blood to the organs, tissues, and cells throughout the body.

The second is the pulmonary circulatory system. This circulatory system moves blood between the heart and lungs. It is where oxygen enters the blood and carbon dioxide leaves the blood.

The heart pumps blood through closed vessels to every tissue within the body. The blood itself then delivers nutrients and oxygen to all cells in the body. Without blood, the cells and tissues would not function at their total capacity and would begin to malfunction and die.

The first phase is diastole, in which the ventricles fill with blood. It begins when the aortic or pulmonary valve closes and ends when the mitral or tricuspid valve closes. During diastole, blood vessels return blood to the heart in preparation for the next contraction of the ventricles.

The second phase is systole, in which the ventricles contract and eject blood. It begins when the mitral or tricuspid valve closes and ends when the aortic or pulmonary valve closes. The pressure inside the ventricles becomes greater than the pressure inside adjacent blood vessels, thereby forcing the blood from the ventricles to the vessels.

A heart attack happens when a part of the heart muscle does not receive enough blood. This can occur due to a blockage, a tear in an artery around the heart, or if the heart requires more oxygen than is available.

The treatment for stroke will depend on the type. A person who experiences ischemic stroke may receive medications to help break up the blood clot and restore blood flow to their brain. A person who experiences a hemorrhagic stroke may require surgery to fix the blood vessel that is bleeding out.

As a person ages, their heart begins to work less effectively than it used to. For example, it cannot beat as fast during physical activity, although the resting heart rate remains steady. Arrhythmias can also develop as the heart ages.

Another common condition of aging is more stiffness in the large arteries and stiffness of the heart muscle. This stiffness can cause high blood pressure, increasing the risk of heart attacks, stroke, and heart failure. Stiffness of the heart can also cause congestive heart failure.

The cardiovascular system consists of the heart, veins, arteries, and capillaries. These components make up two circulatory systems: the systemic and pulmonary circulatory systems. The cardiac cycle consists of two phases: systole (relaxation) and diastole (contraction).

As the body ages, the heart functions less effectively, especially during periods of high physical activity. The arteries also have a higher likelihood of becoming stiff with age, which increases the possibility of high blood pressure and associated cardiovascular issues.

The cardiovascular system delivers oxygen, nutrients, hormones, and other important substances to cells and organs in the body. It plays an important role in helping the body meet the demands of activity, exercise, and stress. It also helps maintain body temperature, among other things.

In most of these types of procedures, a catheter is inserted through the skin into a large blood vessel. In most cases, such procedures do not need general anesthesia. Patients often do not need to stay in the hospital overnight. They recover in 1 to 3 days and can most often return to their normal activities within a week.

Cardiac rehabilitation is therapy used to prevent heart disease from getting worse. It is usually recommended after major heart-related events such as a heart attack or cardiac surgery. It may include:

Go MR, Starr JE, Satiani B. Development of a multispecialty practice and operation of multispecialty cardiovascular centers. In: Sidawy AN, Perler BA, eds. Rutherford's Vascular Surgery and Endovascular Therapy. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 197.

Herrmann HC. Transcatheter mitral valve repair and replacement. In: Otto CM, Bonow RO, eds. Valvular heart disease: A companion to Braunwald's Heart Disease. 5th ed. Philadelphia, PA: Elsevier; 2021:chap 20.

Updated by: Michael A. Chen, MD, PhD, Associate Professor of Medicine, Division of Cardiology, Harborview Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

The cardiovascular system provides blood supply throughout the body. Responding to various stimuli can control the velocity and amount of blood carried through the vessels. The cardiovascular system comprises the heart, arteries, veins, and capillaries. The heart and vessels work intricately to provide adequate blood flow to all body parts. The regulation of the cardiovascular system occurs via a myriad of stimuli, including changing blood volume, hormones, electrolytes, osmolarity, medications, adrenal glands, kidneys, and much more. The parasympathetic and sympathetic nervous systems also play a key role in regulating the cardiovascular system.[1][2][3]

The heart is the organ that pumps blood through the vessels. It pumps blood directly into arteries, specifically the aorta or the pulmonary artery. Blood vessels are critical because they control the amount of blood flow to specific parts of the body. Blood vessels include arteries, capillaries, and veins. Arteries carry blood away from the heart and can divide into large and small arteries. Large arteries receive the highest blood flow pressure and are thicker and more elastic to accommodate the high pressures. Smaller arteries, such as arterioles, have more smooth muscle, which contracts or relaxes to regulate blood flow to specific body portions. Arterioles face a smaller blood pressure, meaning they don't need to be as elastic. Arterioles account for most of the resistance in the pulmonary circulation because they are more rigid than larger arteries. Furthermore, the capillaries branch off of arterioles and are a single-cell layer. This thin layer exchanges nutrients, gases, and waste with tissues and organs. Also, the veins transport blood back to the heart. They contain valves to prevent the backflow of blood.

The cardiac output (CO) is the amount of blood ejected from the left ventricle; normally, it equals the venous return. The calculation is CO = stroke volume (SV) x heart rate (HR). CO also equals the rate of oxygen consumption divided by the difference in arterial and venous oxygen content.

The SV is the amount of blood pumped out of the heart after 1 contraction. It is the difference between end-diastolic (EDV) and end-systolic (ESV) volume. It increases with increased contractility, increased preload, and decreased afterload. Also, the left ventricle's contractility increases with catecholamines by increasing intracellular calcium ions and lowering extracellular sodium.

Frank-Starling law describes the relationship between EDV and SV. This law states that the heart attempts to equalize CO with venous return. As venous return increases, a larger EDV in the left ventricle leads to further stretching of the ventricle, leading to a larger contraction force and a larger SV. A larger SV leads to a larger CO, thus equalizing CO with venous return.

Afterload is the pressure the left ventricular must exceed to push blood forward. Mean arterial pressure best estimates this. Also, afterload can be estimated by the minimum pressure needed to open the aortic valve, equivalent to the diastolic pressure. Thus, diastolic blood pressure is one of the better ways to index afterload.

Vasculature plays a significant role in regulating blood flow throughout the body. In general, blood pressure decreases from arteries to veins, and this is because of the pressure overcoming the resistance of the vessels. The greater the change in resistance at any point in the vasculature, the greater the pressure loss. Arterioles have the most increase in resistance and cause the largest decrease in blood pressure. The constriction of arterioles increases resistance, which causes a decrease in blood flow to downstream capillaries and a larger decrease in blood pressure. Dilation of arterioles causes a decrease in resistance, increasing blood flow to downstream capillaries and a smaller decrease in blood pressure.

Diastolic blood pressure (DP) is the lowest pressure in an artery at the beginning of the cardiac cycle while the ventricles are relaxing and filling. DP is directly proportional to total peripheral resistance (TPR). Also, the energy stored in the compliant aorta during systole is now released by the recoil of the aortic wall during diastole, thus increasing diastolic pressure.

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