In an organism, circulation is the flowing of sap or blood through the veins or channels, by means of which the perpetual and simultaneous movements of composition and decomposition manifested in organic life are carried on. Although Galen, who had observed the opposite directions of the blood in the arteries and veins, may be said to have been upon the very point of discovering the circulation, the discovery was reserved for William Harvey, who in 1628 pointed out the continuity of the connections between the heart, arteries, and veins, the reverse directions taken by the blood in the different vessels, the arrangements of valves in the heart and veins so that the blood could flow only in one direction, and the necessity of the return of a large proportion of blood to the heart to maintain the supply.
In 1661 Malpighi exhibited microscopically the circulation in the web of a frog's foot, and showed that the blood passed from arteries to veins by capillaries or intermediate vessels. This finally established the theory with regard to animals, but the movements of sap in vegetables were only traced with difficulty and after numerous experiments.
Many physiologists were reluctant to ascribe the term 'circulation' to this portion of the economy of plants; but though sap, unlike the blood, does not exhibit movements in determinate vessels to and from a common centre, a definite course is observable. In the stem of a dicotyledonous tree, for example, the sap describes a sort of circle, passing upwards from the roots through the newer woody tissue to the leaves, where it is elaborated under the action of air and light; and thence descending through the bark towards the root, where what remains of it is either excreted or mixed with the new fluid, entering from the soil for a new period of circulation.
In infusorial animalcules the movement of the fluids of the body is maintained by that of the animal itself and by the disturbing influence of nutritive absorption. In the Coelentera (zoophytes, etc) the movement receives aid besides from the action of cilia on the inner walls of the body. The Annelids, as the earth-worm, possess contractile vessels traversing the length of the body. The Insects, Crustaceans, Myriapods, and Spiders have a dorsal tube, a portion of which may be specially developed as a heart. The blood is driven to the tissues, in some cases along arterial trunks, being distributed not in special vessels, but simply through the interstices of the tissues. From the tissues it is conveyed, it may be by special venous trunks to a venous sinus which surrounds the heart and opens into it by valvular apertures. The Mollusca have the heart provided with an auricle and a ventricle, as in the snail and whelk; two auricles, one on either side of the ventricle, as in the fresh-water mussel; or two auricles and two ventricles, as in the ark-shells. Among the ascidians, which stand low in that division of animals to which the molluscs belong, the remarkable phenomenon is encountered of an alternating current, which is rhythmically propelled for equal periods in opposite directions.
All vertebrated animals (except Amphioxus) have a heart, which in most fishes consists of an auricle and ventricle, but in the mud-fishes (Lepidosiren) there are two auricles and one ventricle; and this trilocular heart is found in the amphibians, and in most reptiles except the crocodiles, which, like birds and mammals, have a four-chambered organ consisting of two auricles and two ventricles. In these two last-named classes the venous and arterial blood are kept apart; in the trilocular hearts the two currents are mixed in the ventricle. Research Circulation
The left atrium is a small upper cavity of the heart. Oxygen rich blood returns from the lungs through the four pulmonary veins into the smooth chamber of the left atrium. The chamber is constructed of two overlapping layers of muscle: a superficial layer and an inner layer, composed of many small bundles. The wall of the chamber is slightly thicker and more powerful than the right atrium. As the heart contracts (ventricular systole), blood flows into the ascending aorta through the aortic arch. As the heart relaxes (ventriclediastole), the blood flows through the mitral valve to the left ventricle. The right atrium is a small upper cavity of the heart that holds about three-and-a-half tablespoons of blood. It serves as the receiving chamber for all the venous blood (short of oxygen and laden with carbon dioxide) returning through the superior and inferior vena cava, and from many minute blood vessels that drainblood from the walls of the chamber itself. The right atrium is slightly larger than the left atrium, which is slightly more powerful. The walls of the right atrium are less than an eighth of an inch thick. Two layers of muscle form the wall. The superficial layer spans both atria, and the inner layer, composed of many small bundles, arches over the atrial cavity at right angles to the superficial layer. As the heart contracts (ventricular systole), the blood is pushed through the pulmonary valve into pulmonary circulation. As the heart relaxes (ventricular diastole), the blood exits the right atrium through the tricuspid valve to the right ventricle. In the upper part of the right atrium there is a small patch of special hearttissue called the sinus node or the sinoatrial node. It is the heartspacemaker, triggering the heartbeat and establishes its rate. Research Atrium
The coronary vein is often referred to as the great cardiac vein of the heart. It is a large vein with two branches, the left coronary vein and the right coronary vein. The vein commences at the apex of the heart and ascends along the heart to the base of the ventricles. It then curves left to the back part of the heart and opens into the left coronary sinus, which is about 2.5 centimeters in length and terminates in the right atrium near the inferior vena cava. Research Coronary Vein
The hilus is the slit-like opening in the middle of the concave medial border of the kidney. Nerves and blood vessels pass through the hilus into the renal sinus within. Research Hilus
Oxymetazoline is a chemical which constricts blood vessels in the body.
Oxymetazoline is used as a topical drug available without prescription for the temporary relief of both eye irritations and nose and sinus irritations. The nasal formulation acts directly on the blood vessels of the nasal tissues. Constriction of the blood vessels in the nose and sinuses leads to a drainage of the areas and a decrease in congestion. Most people experience a temporary burning or stinging sensation in the nose when using oxymetazoline, but no other serious side-effects are known, though the drug will apparently react with monoamine oxidase inhibitors, and according to the American Yale New Haven Health System may be very dangerous, though this is not a view shared widely by British doctors and pharmacists. Research Oxymetazoline
The posterior cardiac vein (often referred to as the middle cardiac vein) extends from the apex of the heart, receiving blood from both ventricles, and continues along the base of the heart to the coronary sinus, where the blood is then delivered to the right atrium of the heart. Research Posterior Cardiac Vein
The renal sinus is the cavity within the kidney which houses the renal pyramid. Nerves and blood vessels pass into the renal sinus through the hilus. Research Renal Sinus
The veins in the brain return blood from the dura mater and partially from the bones. They terminate in various sinuses, among which are the inferior sagittal sinus, the superior sagital sinus, and the straight sinus. The sagital sinuses are situated near the parietal bone. Research Sagittal Sinus Vein
Abbreviations
Research Circulation
