Circulatory System

The circulatory system is the system that comprises of the heart at the center, blood vessels, including arteries, veins, capillaries, blood, the pulmonary vessels and the circulation of blood in the body.

Circulatory System

Other names[edit | edit source]

Cardiovascular system
The cardiovascular system
Blood-vascular

Parts of circulatory system[edit | edit source]

It consists of the heart, which is a muscular pumping device, and a closed system of vessels called arteries, veins, and capillaries.

Pump[edit | edit source]

As the name implies, blood contained in the circulatory system is pumped by the heart around a closed circle or circuit of vessels as it passes again and again through the various "circulations" of the body.
The heart is a muscular pump that provides the force necessary to circulate the blood to all the tissues in the body.
Three layers of the heart are: the epicardium, the myocardium, and the endocardium.
The four chambers of the heart are: the right atrium, the right ventricle, the left atrium, and the left ventricle.
Two types of valves of the heart are the atrioventricular valves and semilunar valves.
Blood flows from the right atrium to the right ventricle and then is pumped to the lungs to receive oxygen. From the lungs, the blood flows to the left atrium, then to the left ventricle. From there it is pumped to the systemic circulation.

Vital role[edit | edit source]

The vital role of the cardiovascular system in maintaining homeostasis depends on the continuous and controlled movement of blood through the thousands of miles of capillaries that permeate every tissue and reach every cell in the body.

Blood volumes at different levels of the circulatory system

Physiology[edit | edit source]

Numerous control mechanisms help to regulate and integrate the diverse functions and component parts of the cardiovascular system in order to supply blood to specific body areas according to need. These mechanisms ensure a constant internal environment surrounding each body cell regardless of differing demands for nutrients or production of waste products.

Arteries[edit | edit source]

Arteries carry blood away from the heart.

Pulmonary arteries[edit | edit source]

Pulmonary arteries transport blood that has a low oxygen content from the right ventricle to the lungs.

Systemic arteries[edit | edit source]

Systemic arteries transport oxygenated blood from the left ventricle to the body tissues.

Major Systemic Arteries

All systemic arteries are branches, either directly or indirectly, from the aorta. The aorta ascends from the left ventricle, curves posteriorly and to the left, then descends through the thorax and abdomen. The aorta divides the aorta into three portions: ascending aorta, arotic arch, and descending aorta. The descending aorta is further subdivided into the thoracic arota and abdominal aorta.

Capillaries[edit | edit source]

Capillaries, the smallest and most numerous of the blood vessels, form the connection between the vessels that carry blood away from the heart (arteries) and the vessels that return blood to the heart (veins). The primary function of capillaries is the exchange of materials between the blood and tissue cells.

Circulatory system

Veins[edit | edit source]

Veins carry blood toward the heart. After blood passes through the capillaries, it enters the smallest veins, called venules. From the venules, it flows into progressively larger and larger veins until it reaches the heart. In the pulmonary circuit, the pulmonary veins transport blood from the lungs to the left atrium of the heart. This blood has a high oxygen content because it has just been oxygenated in the lungs. Systemic veins transport blood from the body tissue to the right atrium of the heart. This blood has a reduced oxygen content because the oxygen has been used for metabolic activities in the tissue cells.

Major Systemic Veins

After blood delivers oxygen to the tissues and picks up carbon dioxide, it returns to the heart through a system of veins. The capillaries, where the gaseous exchange occurs, merge into venules and these converge to form larger and larger veins until the blood reaches either the superior vena cava or inferior vena cava, which drain into the right atrium.

Blood Flow[edit | edit source]

Blood flow refers to the movement of blood through the vessels from arteries to the capillaries and then into the veins. Pressure is a measure of the force that the blood exerts against the vessel walls as it moves the blood through the vessels. Like all fluids, blood flows from a high pressure area to a region with lower pressure. Blood flows in the same direction as the decreasing pressure gradient: arteries to capillaries to veins.

rate of flow[edit | edit source]

The rate, or velocity, of blood flow varies inversely with the total cross-sectional area of the blood vessels. As the total cross-sectional area of the vessels increases, the velocity of flow decreases. Blood flow is slowest in the capillaries, which allows time for exchange of gases and nutrients.

Human Heart and Circulatory System

Resistance[edit | edit source]

Resistance is a force that opposes the flow of a fluid. In blood vessels, most of the resistance is due to vessel diameter. As vessel diameter decreases, the resistance increases and blood flow decreases.

Capillary pressure[edit | edit source]

Very little pressure remains by the time blood leaves the capillaries and enters the venules. Blood flow through the veins is not the direct result of ventricular contraction. Instead, venous return depends on skeletal muscle action, respiratory movements, and constriction of smooth muscle in venous walls.

Pulse and Blood Pressure[edit | edit source]

Pulse refers to the rhythmic expansion of an artery that is caused by ejection of blood from the ventricle. It can be felt where an artery is close to the surface and rests on something firm.

In common usage, the term blood pressure refers to arterial blood pressure, the pressure in the aorta and its branches. Systolic pressure is due to ventricular contraction. Diastolic pressure occurs during cardiac relaxation. Pulse pressure is the difference between systolic pressure and diastolic pressure. Blood pressure is measured with a sphygmomanometer and is recorded as the systolic pressure over the diastolic pressure. Four major factors interact to affect blood pressure: cardiac output, blood volume, peripheral resistance, and viscosity. When these factors increase, blood pressure also increases.

Arterial blood pressure is maintained within normal ranges by changes in cardiac output and peripheral resistance. Pressure receptors (barareceptors), located in the walls of the large arteries in the thorax and neck, are important for short-term blood pressure regulation.

Circulatory System Resources
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