- Related Topics:
- cardiovascular disease
- hypertension
- stroke
- heart valve transplant
- hemangioma
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- Biology LibreTexts - Cardiovascular System (Oct. 16, 2026)
human cardiovascular system
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What is the human cardiovascular system?
The human cardiovascular system is an organ system responsible for transporting blood throughout the body. This closed tubular system consists of the heart, which acts as a muscular pump, and a network of blood vessels, including arteries, arterioles, capillaries, venules, and veins.
The arteries carry blood away from the heart to the tissues, where capillaries facilitate the exchange of oxygen, nutrients, and waste products. The veins then return the blood back to the heart. The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes.
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What are the main parts of the cardiovascular system?
The human cardiovascular system is an organ system responsible for transporting blood throughout the body. Its primary parts include the heart, arteries, and veins.
- The heart is a muscular pump that propels blood through vessels to all parts of the body.
- Arteries are thick-walled vessels that receive blood from the heart at high pressure, transporting it to the body. They branch into smaller vessels called arterioles, which connect to capillaries.
- Capillaries are thin, microscopic vessels that allow the exchange of nutrients and waste products with tissues.
- Veins are vessels that carry blood back to the heart. Venules collect blood from the capillaries and converge to form veins.
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What is the function of the heart in the cardiovascular system?
The primary function of the heart in the human cardiovascular system is to act as a muscular pump. It propels blood into and through vessels, circulating it to all parts of the body to deliver nutrients and oxygen to tissues and remove carbon dioxide and other wastes. The heart ensures that oxygenated blood from the lungs is distributed to the body and deoxygenated blood is sent back to the lungs.
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What are arteries, veins, and capillaries?
The cardiovascular system includes arteries, veins, and capillaries, all of which are part of a closed system of vessels that transport blood throughout the body.
- Arteries are strong, elastic vessels that transport blood from the heart to the body's tissues under high pressure.
- Veins transport blood from the body's tissues back to the heart. Veins have thinner walls than arteries and contain valves to prevent the backflow of blood.
- Capillaries are microscopic tubules that connect arterioles and venules. Their primary function is to exchange fluids, nutrients, and waste between the blood and tissues.
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How does blood move through the heart and body?
The human cardiovascular system ensures blood circulates efficiently throughout the body. The heart, divided into right and left halves, features two chambers in each half: the upper atria and lower ventricles, separated by the interatrial and interventricular septa, respectively.
The right atrium receives deoxygenated blood from the body via the superior and inferior venae cavae and the coronary sinus. This blood then flows into the right ventricle, which pumps it through the pulmonary artery to the lungs for oxygenation. Oxygenated blood returns to the left atrium via the pulmonary veins and moves into the left ventricle. The left ventricle, with its thick walls, forcefully ejects blood through the aorta into the systemic circulation, supplying oxygen to all body tissues. Valves in the heart and veins prevent backflow, ensuring unidirectional blood movement.
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How do the structures of the heart and blood vessels help them do their jobs?
The structure of the heart and blood vessels are closely related to their functions in the cardiovascular system.
- Heart The heart is mostly muscle tissue arranged in a way that allows it to contract rhythmically. The contraction of individual heart cells results in a decrease in the heart chamber size and ejection of blood into the vessels. Valves in the heart, like the atrioventricular and semilunar valves, ensure that blood flows in one direction, preventing backflow.
- Blood vessels Arteries have strong, elastic walls to withstand high pressure and ensure efficient blood flow. Veins have thinner walls and valves to prevent backflow, assisting blood return to the heart. The pulmonary trunk has thin walls that can accommodate the stroke volume of the right ventricle.
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human cardiovascular system, organ system that conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes. It is a closed tubular system in which the blood is propelled by a muscular heart. Two circuits, the pulmonary and the systemic, consist of arterial, capillary, and venous components.
The primary function of the heart is to serve as a muscular pump propelling blood into and through vessels to and from all parts of the body. The arteries, which receive this blood at high pressure and velocity and conduct it throughout the body, have thick walls that are composed of elastic fibrous tissue and muscle cells. The arterial tree—the branching system of arteries—terminates in short, narrow, muscular vessels called arterioles, from which blood enters simple endothelial tubes (i.e., tubes formed of endothelial, or lining, cells) known as capillaries. These thin, microscopic capillaries are permeable to vital cellular nutrients and waste products that they receive and distribute. From the capillaries, the blood, now depleted of oxygen and burdened with waste products, moving more slowly and under low pressure, enters small vessels called venules that converge to form veins, ultimately guiding the blood on its way back to the heart.
This article describes the structure and function of the heart and blood vessels, and the technologies that are used to evaluate and monitor the health of these fundamental components of the human cardiovascular system. For a discussion of diseases affecting the heart and blood vessels, see the article cardiovascular disease. For a full treatment of the composition and physiologic function of blood, see blood, and for more information on diseases of the blood, see blood disease. To learn more about the human circulatory system, see systemic circulation and pulmonary circulation, and for more about cardiovascular and circulatory function in other living organisms, see circulation.
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The heart
Description
Shape and location
The adult human heart is normally slightly larger than a clenched fist, with average dimensions of about 13 × 9 × 6 cm (5 × 3.5 × 2.5 inches) and weight approximately 10.5 ounces (300 grams). It is cone-shaped, with the broad base directed upward and to the right and the apex pointing downward and to the left. It is located in the chest (thoracic) cavity behind the breastbone (sternum), in front of the windpipe (trachea), the esophagus, and the descending aorta, between the lungs, and above the diaphragm (the muscular partition between the chest and abdominal cavities). About two-thirds of the heart lies to the left of the midline.
Pericardium
The heart is suspended in its own membranous sac, the pericardium. The strong outer portion of the sac, or fibrous pericardium, is firmly attached to the diaphragm below, the mediastinal pleura on the side, and the sternum in front. It gradually blends with the coverings of the superior vena cava and the pulmonary (lung) arteries and veins leading to and from the heart. (The space between the lungs, the mediastinum, is bordered by the mediastinal pleura, a continuation of the membrane lining the chest. The superior vena cava is the principal channel for venous blood from the chest, arms, neck, and head.)
Smooth, serous (moisture-exuding) membrane lines the fibrous pericardium, then bends back and covers the heart. The portion of membrane lining the fibrous pericardium is known as the parietal serous layer (parietal pericardium), that covering the heart as the visceral serous layer (visceral pericardium or epicardium).
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The two layers of serous membrane are normally separated by only 10 to 15 ml (0.6 to 0.9 cubic inch) of pericardial fluid, which is secreted by the serous membranes. The slight space created by the separation is called the pericardial cavity. The pericardial fluid lubricates the two membranes with every beat of the heart as their surfaces glide over each other. Fluid is filtered into the pericardial space through both the visceral and parietal pericardia.
Chambers of the heart
The heart is divided by septa, or partitions, into right and left halves, and each half is subdivided into two chambers. The upper chambers, the atria, are separated by a partition known as the interatrial septum; the lower chambers, the ventricles, are separated by the interventricular septum. The atria receive blood from various parts of the body and pass it into the ventricles. The ventricles, in turn, pump blood to the lungs and to the remainder of the body.
The right atrium, or right superior portion of the heart, is a thin-walled chamber receiving blood from all tissues except the lungs. Three veins empty into the right atrium, the superior and inferior venae cavae, bringing blood from the upper and lower portions of the body, respectively, and the coronary sinus, draining blood from the heart itself. Blood flows from the right atrium to the right ventricle. The right ventricle, the right inferior portion of the heart, is the chamber from which the pulmonary artery carries blood to the lungs.
The left atrium, the left superior portion of the heart, is slightly smaller than the right atrium and has a thicker wall. The left atrium receives the four pulmonary veins, which bring oxygenated blood from the lungs. Blood flows from the left atrium into the left ventricle. The left ventricle, the left inferior portion of the heart, has walls three times as thick as those of the right ventricle. Blood is forced from this chamber through the aorta to all parts of the body except the lungs.
External surface of the heart
Shallow grooves called the interventricular sulci, containing blood vessels, mark the separation between ventricles on the front and back surfaces of the heart. There are two grooves on the external surface of the heart. One, the atrioventricular groove, is along the line where the right atrium and the right ventricle meet; it contains a branch of the right coronary artery (the coronary arteries deliver blood to the heart muscle). The other, the anterior interventricular sulcus, runs along the line between the right and left ventricles and contains a branch of the left coronary artery.
On the posterior side of the heart surface, a groove called the posterior longitudinal sulcus marks the division between the right and left ventricles; it contains another branch of a coronary artery. A fourth groove, between the left atrium and ventricle, holds the coronary sinus, a channel for venous blood.