Cardiovascular System
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The cardiovascular system consists of the heart, which is a muscular pumping organ, a closed system of blood vessels called arteries, veins, and capillaries, and lymphatic vessels. Blood contained in the cardiovascular system is pumped by the heart alternately through the systemic and pulmonary circulations (blood vasculature). The circulation of blood allows for delivery of oxygen, nutrients, hormones, etc. to tissues of the body, and removal of carbon dioxide and other metabolic waste products. The gas exchange between ambient air and blood in the pulmonary circulation occurs in the alveolar walls of the lungs. The lymphatic vessels drain excess interstitial fluid, and transport lymph and chyle.
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Other Names
Synonyms
- Circulatory system
Related terms
- Blood-vascular system
- Lymphatic system
Description
The cardiovascular system comprises the heart, blood, blood vessels, lymph, and lymphatic vessels. These structural elements are arranged to form the systemic circulation, pulmonary circulation and lymphatic drainage.
The blood vessels of the systemic and pulmonary circulations are classified as arteries, veins and capillaries. Arteries conduct blood away from the heart; veins return blood to the heart. Capillaries and arteriolovenular anastomoses connect arteries and veins within peripheral tissues.
The lymphatic vessels include lymphatic capillaries, small and medium-sized lymphatic vessels, lymphatic ducts, and lymphatic trunks. The lymphatic vessels drain interstital fluid, and convey lymph and chyle into tributaries of the superior vena cava. (Lymph nodes, which are associated with lymphatic vessels, are now considered by anatomists to be part of the lymphoid system rather than the lymphatic system.)
Role of the Cardiovascular System in the Body
As in the adult, survival of the developing embryo depends on the circulation of blood to maintain homeostasis and a favorable cellular environment. In response to this need, the circulatory system makes its appearance early in development and reaches a functional state long before any other major organ system. Incredible as it seems, the primitive heart begins to beat regularly early in the fourth week following fertilization.
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. It is in the microscopic capillaries that blood performs its ultimate transport function. Nutrients and other essential materials pass from capillary blood into fluids surrounding the cells as waste products are removed.
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.
How the Cardiovascular System Works
The heart, and blood and lymphatic vessels make up the cardiovascular system. The blood vasculature makes two subsystems: the systemic and pulmonary circulations. The heart pumps two parallel streams of blood through itself into these circulations. Blood from the left side of the heart is pumped into the systemic circulation, and blood from the right side is pumped into the pulmonary circulation. Lymphatic vessels form a single system that drains excess interstitial fluid, and conveys that fluid (lymph) to veins that empty into the right atrium.
Heart
Systemic circulation
The systemic circulation carries oxygenated blood from the heart to peripheral tissues, and then returns the deoxygenated blood to the heart. Blood pumped out of the left ventricle of the heart enters the aorta, a large elastic artery, which distributes the blood to its many branches, including large elastic arteries, medium-sized muscular arteries and small arteries (arterioles). Healthy arteries are strong and elastic. They narrow between beats of the heart, which helps to keep the blood pressure consistent. This helps blood circulate efficiently through the body. Arteries and arterioles have strong, flexible walls that allow them to adjust to the amount and rate of blood flowing to different parts of the body.
Arterioles supply blood to capillaries, where oxygen, nutrients, and waste pass between the blood and body tissues. Capillaries are very small blood vessels that connect the arterial and venous vessels. The importance of capillaries lies in their very thin walls. Unlike arteries and veins, capillary walls are thin enough that oxygen and nutrients in the blood can pass through the walls to the parts of the body that need them to function normally. Capillaries' thin walls also allow waste products like carbon dioxide to pass from the body's organs and tissues into the blood, where it's taken away to the lungs.
Veins of the systemic circulation drain capillaries and carry deoxygenated blood back to the right atrium of the heart. Veins have thinner walls than arteries and can increase in width as the amount of blood passing through them increases.
Pulmonary circulation
Pulmonary circulation is the movement of deoxygenated blood from the heart to the lungs and the return of oxygenated blood back to the heart. Oxygen-poor blood is pumped to the lungs from the right ventricle of the heart via the pulmonary arteries and their branches. The pulmonary arterioles supply capillaries in the walls of alveoli, where gas exchange occurs between air in the alveoli and blood in the capillaries. Oxygen diffuses into the blood while carbon dioxide diffuses out of the blood. Oxygen-rich blood moves from the lungs to the heart through the pulmonary veins to the left atrium of the heart.
Lymphatic drainage
Lymphatic capillaries drain excess interstitial fluid. Lymphatic vessels, which roughly resemble veins, convey lymph to certain large veins. The course of lymphatic vessels is interrupted by lymph nodes. In lymph nodes, lymph passes through lymphatic sinuses and lymph-borne antigens are exposed to lymphoid tissues.
Chyle is also transported by lymphatic vessels. Chyle is a milky form of lymph taken up by lymphatic vessels called lacteals in the walls of the small intestine.
Chyle is milky because it contains chylomicrons, lipd droplets containing triglycerides, phospholipids, and apolipoproteins.
Diseases of the Cardiovascular System
Some diseases of the circulatory system are the following:
For diseases specific to the heart, visit the heart page.
Symptoms
Symptoms of diseases of the circulatory system include the following:
Related Professions
- A hematologist is a medical doctor trained in treating diseases of the heart.
- A vascular surgeon is a surgeon with special training in operating on the blood vessels.
- A cardiothoracic surgeon is a surgeon with special training in heart surgery.
History
How the circulatory system was discovered
The circulatory system came to be understood in the 17th century. William Harvey (1578-1657) is the physician most commonly credited with the first description of the circulatory system. Others described components of the circulatory system before Harvey's time, however. Galen (born around 129 C.E.) is credited as the first to discover that arteries carried blood (previously thought to contain air). Iranian physician Abu Bakr Mohammad Zakariya al-Razi (865–925 C.E.) wrote a highly accurate anatomical description of the heart and blood vessels, and Ali ibn al-Abbas al-Majusi (known as Ahwazi), another Iranian physician (10th century C.E.), expounded a similar view to Galen regarding the circulation of blood. Physician and philosopher Ibn Al-Nafis Damashqi (1210–1285 C.E.) added to this knowledge when he described the pulmonary circulation. Harvey's description was the most complete, but did not explain the exchange of blood between arteries and veins away from the heart. In 1661, Italian anatomist Marcello Malpighi (1628 – 1698) described the capillaries, which completed the understanding of the circulation.[1]
How the circulatory system was named
The term circulate is derived from the Latin circulare, which means to make round.
Research
One popular area of research today is in the area of angiogenesis. This term describes the formation of new blood vessels by the body, which allows tumors to receive enough nutrient-containing blood to grow to large sizes. Research has yielded insights into how this works, and a great deal of effort is spent today to try to find drugs that interfere with this process.[2]
References
- ↑ Azizi MH, Nayernouri T, Azizi F. A brief history of the discovery of the circulation of blood in the human body. Arch Iran Med. 2008 May;11(3):345-50. Abstract | PDF
- ↑ National Cancer Institute. Angiogenesis.
External Links
American Association for Thoracic Surgery
National Heart, Lung, and Blood Institute[[Category:|Category:]]
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