"can be used to ignore the success or failure of a sequence of other commands, as in the example: make … && false Setting a user's login shell to false, in /etc/passwd, effectively denies them access to an interactive shell, but their account may still be valid for other services, such as FTP. (Although /sbin/nologin, if available, may be more fitting for this purpose, as it prints a notification before terminating the session.) The programs take no ""actual"" parameters; in most Linux versions, the standard parameter codice_5 displays a usage summary and codice_6 displays the program version. The ""true"" command"
"between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart. The word ""vascular"", meaning relating to the blood vessels, is derived from the Latin ""vas"", meaning vessel. A few structures (such as cartilage and the lens of the eye) do not contain blood vessels and are labeled. The arteries and veins have three layers. The middle layer is thicker in the arteries than it is in the veins: Capillaries consist of little more than a layer of endothelium and occasional connective tissue. When blood vessels connect to form a region of"
"ways by which the blood is returned to the heart itself; and that the blood in the members and extremities does pass from the arteries into the veins (either mediately by an anastomosis, or immediately through the porosities of the flesh, or both ways) as before it did in the heart and thorax out of the veins, into the arteries…"" Marcello Malpighi was the first to observe directly and correctly describe capillaries, discovering them in a frog's lung in 1661. Capillary A capillary is a small blood vessel from 5 to 10 micrometres (µm) in diameter, and having a wall"
"the venae cavae. Individual capillaries are part of the ""capillary bed"", an interweaving network of capillaries supplying tissues and organs. The more metabolically active a tissue is, the more capillaries are required to supply nutrients and carry away waste products. There are two types of capillaries: true capillaries, which branch from arterioles and provide exchange between tissue and the capillary blood, and metarterioles, found only in the mesenteric circulation. They are short vessels that directly connect the arterioles and venules at opposite ends of the beds. Metarterioles are found primarily in the mesenteric microcirculation. The physiological mechanisms underlying precapillary resistance"
"cells called tunica intima. The precise location of veins varies much more from person to person than that of arteries. Veins serve to return blood from organs to the heart. Veins are also called ""capacitance vessels"" because most of the blood volume (60%) is contained within veins. In systemic circulation oxygenated blood is pumped by the left ventricle through the arteries to the muscles and organs of the body, where its nutrients and gases are exchanged at capillaries. After taking up cellular waste and carbon dioxide in capillaries, blood is channeled through vessels that converge with one another to form"
"Capillary A capillary is a small blood vessel from 5 to 10 micrometres (µm) in diameter, and having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and venules. These microvessels are the site of exchange of many substances with the interstitial fluid surrounding them. Substances which exit include water (proximal portion), oxygen, and glucose; substances which enter include water (distal portion), carbon dioxide, uric acid, lactic acid, urea and creatinine. Lymph capillaries connect with larger lymph vessels to drain lymphatic fluid collected in the microcirculation. During early"
"Vein Veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart. In contrast to veins, arteries carry blood away from the heart. Veins are less muscular than arteries and are often closer to the skin. There are valves in most veins to prevent backflow. Veins are present throughout the body as tubes that carry blood back to the heart. Veins are classified in a number of ways, including superficial vs. deep, pulmonary"
"arteries, arterioles, and ultimately capillaries. In the capillaries, oxygen and nutrients from blood are supplied to body cells for metabolism, and exchanged for carbon dioxide and waste products. Capillary blood, now deoxygenated, travels into venules and veins that ultimately collect in the superior and inferior vena cavae, and into the right heart. The cardiac cycle refers to the sequence of events in which the heart contracts and relaxes with every heartbeat. The period of time during which the ventricles contract, forcing blood out into the aorta and main pulmonary artery, is known as systole, while the period during which the"
"person's skin, how much oxygen is being carried in the blood, and how big and deep the vessels are. When a vein is drained of blood and removed from an organism, it appears grey-white. The largest veins in the human body are the venae cavae. These are two large veins which enter the right atrium of the heart from above and below. The superior vena cava carries blood from the arms and head to the right atrium of the heart, while the inferior vena cava carries blood from the legs and abdomen to the heart. The inferior vena cava is"
"6339.6 km (modern value is c. 6,371 km), the best estimate at that time. In the cardiovascular system, Ibn al-Nafis in his ""Commentary on Anatomy in Avicenna's Canon"" was the first known scholar to contradict the contention of the Galen School that blood could pass between the ventricles in the heart through the cardiac inter-ventricular septum that separates them, saying that there is no passage between the ventricles at this point. Instead, he correctly argued that all the blood that reached the left ventricle did so after passing through the lung. He also stated that there must be small communications,"
"fluid and blood, they tend to have large surface area and short diffusion path. Normally, capillaries consist of a central lumen lined with an endothelium, a single layer of smooth epithelial cells. In contrast, deep neurovascular bundles, with arteries in them, have a more complicated composition. Arteries are the vessels that transfer the blood pumped by the heart to the entire body. Arteries have high intraluminal blood pressure, relative to capillaries and veins. To compensate arteries have a smooth muscle and a connective tissue structure outside the endothelium. This composition allows arteries to contract/relax, be flexible under pressure, and transfer"
"differing physical structure: veins and arteries contains a hollow channel, but nerves do not. Vesalius describes the route by which air travels through the lungs and the heart. He describes this process as ""a tree whose trunks divide into branches and twigs"". He also describes how the body contains four veins (the portal vein, the venae cavae, the artery-like vein [now understood as the Pulmonary Vein], and the umbilical vein) and two arteries (the aorta, and the vein-like artery [now understood as the Pulmonary Artery] as being the main vessels which branch out into smaller veins and arteries. Vesalius lists"
"circulates about 5 liters of blood at a rate of approximately 6 l/m. The pulmonary and the systemic circulations are the two parts of the vasculature. The pulmonary circulation system consists of the network of blood vessels from the right heart to the lungs and back to the left heart. The rest of the blood flow loop is called systemic circulation system. The pulmonary and systemic circulations take the blood through large arteries first and then branches into smaller arteries before reaching arterioles and capillaries. After capillaries, the blood enters the venules before joining smaller veins first and then larger"
"Blood vessel The blood vessels are the part of the circulatory system, and microcirculation, that transports blood throughout the human body. These vessels are designed to transport nutrients and oxygen to the tissues of the body. They also take waste and carbon dioxide and carry them away from the tissues and back to the heart. Blood vessels are needed to sustain life as all of the body’s tissues rely on their functionality.There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals"
"the body. Similar to the atrium, the arteries are composed of thick elastic muscles to withstand the pressure of the ventricular constriction, and become more rigid as they move away from the heart. Blood moves through the arteries, which undergo vasoconstriction, and into arterioles which act as a transportation system to distribute primarily oxygen as well as nutrients to all tissues of the body. As the arterioles move away from the heart and into individual organs and tissues they are further divided to increase surface area and slow blood flow. Travelling through the arterioles blood moves into the capillaries where"
"149,000 km. There is a decline in total length with age of about 10% each decade such that a man at 80 years of age has 97,200 km and a female 82,000 km. Most of this reduction is due to the loss of thinner fibers. White matter is the tissue through which messages pass between different areas of gray matter within the central nervous system. The white matter is white because of the fatty substance (myelin) that surrounds the nerve fibers (axons). This myelin is found in almost all long nerve fibers, and acts as an electrical insulation. This is"
"due to the effect of the wall and the no-slip condition. Moreover, it can be shown that the transient forces become relatively more important than viscous forces as the animal size increases. The Heart, arteries, and veins (a network of tubes to carry blood) constitute the cardiovascular system or circulatory system of our body which transports the blood throughout the body. The heart can be thought of as a muscular pump, consisting of four chambers, and pulsatile muscles which pump and circulates the blood through the vasculature. Arteries, arterioles, capillaries, venules, and veins make up the vasculature. The cardiovascular system"
"volume. The vascular volume is divided into the venous volume and the secreted arterial volume; and the arterial volume has a conceptually useful but unmeasurable subcompartment called the effective arterial blood volume. There are approximately 6 to 10 liters of lymph in the body, compared to 3.5 to 5 liters of blood. By type: By location: In plants: Body fluid is the term most often used in medical and health contexts. Modern medical, public health, and personal hygiene practices treat body fluids as potentially unclean. This is because they can be vectors for infectious diseases, such as sexually transmitted diseases"
"pain and lead to serious medical problems. Although AVMs are often associated with the brain and spinal cord, they can develop in any part of the body. Normally, the arteries in the vascular system carry oxygen-rich blood, except in the case of the pulmonary artery. Structurally, arteries divide and sub-divide repeatedly, eventually forming a sponge-like capillary bed. Blood moves through the capillaries, giving up oxygen and taking up waste products, including , from the surrounding cells. Capillaries in turn successively join together to form veins that carry blood away. The heart acts to pump blood through arteries and uptake the"
"combines from capillaries around the gastrointestinal tract where the blood absorbs the various products of digestion; rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in the liver. The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle. The right atrium is the upper chamber of the right side"
"veins and arteries lose themselves by subdivision into the tiny capillary vessels. It was in 1660, three years after Harvey's death, that Marcello Malpighi saw the blood moving in the capillaries of a frog's lung, and thus supplied the missing link in Harvey's proof of the circulation of the blood. Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (Latin for ""An Anatomical Exercise on the Motion of the Heart and Blood in Living Beings""), commonly called De Motu Cordis, is the best-known work of the physician William Harvey. The book"
"mandatory which is a huge problem for many countries today. The great saphenous vein,(GSV) a superficial vein, is the longest vein in the body. It has its origin in the dorsal venous arch of the foot, a superficial vein which connects the small saphenous vein with the GSV. It travels up the leg and medial side of the thigh to reach the groin, where it drains into the common femoral vein. Along the length of the GSV, it receives numerous tributaries, (from the subcutaneous layer) and drains into the deep veins via the perforator veins. When seen in a scan,"
"arterioles, capillaries, and venules —constitutes most of the area of the vascular system and is the site of the transfer of O, glucose, and enzyme substrates into the cells. The venous system returns the de-oxygenated blood to the right heart where it is pumped into the lungs to become oxygenated and CO and other gaseous wastes exchanged and expelled during breathing. Blood then returns to the left side of the heart where it begins the process again. In a normal circulatory system, the volume of blood returning to the heart each minute is approximately equal to the volume that is"
"they were for transport of air. The Greek physician, Herophilus, distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Greek anatomist Erasistratus observed that arteries that were cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood. In 2nd century AD Rome, the Greek physician Galen knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner)"
"Artery An artery (plural arteries) () is a blood vessel that takes blood away from the heart to all parts of the body (tissues, lungs, etc). Most arteries carry oxygenated blood; the two exceptions are the pulmonary and the umbilical arteries, which carry deoxygenated blood to the organs that oxygenate it. The effective arterial blood volume is that extracellular fluid which fills the arterial system. The arteries are part of the circulatory system, which is responsible for the delivery of oxygen and nutrients to all cells, as well as the removal of carbon dioxide and waste products, the maintenance of"
"air to all of the cells of the body, and venous blood carries carbon dioxide, a waste product of metabolism by cells, to the lungs to be exhaled. However, one exception includes pulmonary arteries, which contain the most deoxygenated blood in the body, while the pulmonary veins contain oxygenated blood. Additional return flow may be generated by the movement of skeletal muscles, which can compress veins and push blood through the valves in veins toward the right atrium. The blood circulation was famously described by William Harvey in 1628. In vertebrates, the various cells of blood are made in the"
"Arteriole An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. Arterioles have muscular walls (usually only one to two layers of smooth muscle) and are the primary site of vascular resistance. The greatest change in blood pressure and velocity of blood flow occurs at the transition of arterioles to capillaries. In a healthy vascular system the endothelium lines all blood-contacting surfaces, including arteries, arterioles, veins, venules, capillaries, and heart chambers. This healthy condition is promoted by the ample production of nitric oxide by the endothelium, which requires"
"into individual organs and tissues they are further divided to increase surface area and slow blood flow. Blood travels through the arterioles and moves into the capillaries where gas exchange can occur. Capillaries are organized into capillary beds in tissues; it is here that blood exchanges oxygen for carbon dioxide waste. In the capillary beds blood flow is slowed to allow maximum diffusion of oxygen into the tissues. Once the blood has become deoxygenated it travels through venules then veins and back to the heart. Veins, unlike arteries, are thin and rigid as they do not need to withstand extreme"
"Neurovascular bundle A neurovascular bundle (neuro: nerve, vascular: veins, lymph vessels, and arteries) is the combination of nerves, arteries, veins, and lymphatics in the body that travel together. There are two types of neurovascular bundles: superficial neurovascular bundles and deep neurovascular bundles. As arteries do not travel within the superficial fascia (loose connective tissue under the skin), superficial neurovascular bundles differ from deep neurovascular bundles in both composition and function. A superficial neurovascular bundle, without arteries in it, is mostly made up of capillaries running through different body tissues. Because capillaries function as the sites for material exchange between interstitial"
"will form the internal iliac arteries. The human venous system develops mainly from the vitelline veins, the umbilical veins and the cardinal veins, all of which empty into the sinus venosus. About 98.5% of the oxygen in a sample of arterial blood in a healthy human, breathing air at sea-level pressure, is chemically combined with hemoglobin molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species. Many diseases affect the circulatory system. These include a number of cardiovascular diseases,"
"blood pressure throughout the body. When the aorta receives almost five litres of blood from the heart, it recoils and is responsible for pulsating blood pressure. Moreover, as aorta branches into smaller arteries, their elasticity goes on decreasing and their compliance goes on increasing. Arteries branch into small passages called arterioles and then into the capillaries. The capillaries merge to bring blood into the venous system. After their passage through body tissues, capillaries merge once again into venules, which continue to merge into veins. The venous system finally coalesces into two major veins: the superior vena cava (roughly speaking draining"
"arteries as well as the veins. It is obvious that this hypothesis was supported by the fact that the network of arteries and veins becomes thinner and thinner as they get farther from the heart. It was also assumed that the networks are not connected, so the blood cannot pass from one network to the other. (The microscope was not yet invented, so one could not view capillary arteries without aid.) Dr. Amatus Lusitanus described in the Centuria I, paragraph (Curatio) 513, how, in 1547, he performed an experiment before some scholars from the University of Ferrara. He blew air"
"vary somewhat between species. In non-mammalian vertebrates, however, there are some key differences: Blood is circulated around the body through blood vessels by the pumping action of the heart. In humans, blood is pumped from the strong left ventricle of the heart through arteries to peripheral tissues and returns to the right atrium of the heart through veins. It then enters the right ventricle and is pumped through the pulmonary artery to the lungs and returns to the left atrium through the pulmonary veins. Blood then enters the left ventricle to be circulated again. Arterial blood carries oxygen from inhaled"