Circulatory system -----is an organ system that passes nutrients (such as amino acids,electrolytes and lymph), gases, hormones, bloods, cells, etc. to and from cellsin the body to help fight diseases, stabilize body temperature and pH, and tomaintain homeostasis. This system may be seen strictly as a blood distribution network, butsome consider the circulatory system as composed of the cardiovascularsystem, which distributes blood, and the lymphatic system, which returnsexcess filtered blood plasma from the interstitial fluid (between cells) aslymph. The lymphatic system, on the other hand, is an open system providingan accessory route for excess interstitial fluid to get returned to the blood.Two types of fluids move through the circulatory system: blood and lymph.Lymph is essentially recycled blood plasma after it has been filtered from theblood cells and returned to the lymphatic system. The blood, heart, and blood vessels form the cardiovascular (fromLatin words meaning heart-vessel) system. The lymph, lymph nodes, andlymph vessels form the lymphatic system. The cardiovascular system and thelymphatic system collectively make up the circulatory system.
Human cardiovascular system The main components of the human cardiovascular system are theheart, blood, and blood vessels. It includes: the pulmonary circulation, a"loop" through the lungs where blood is oxygenated; and the systemiccirculation, a "loop" through the rest of the body to provide oxygenatedblood. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters)of blood, which consists of plasma, red blood cells, white blood cells, andplatelets. Also, the digestive system works with the circulatory system toprovide the nutrients the system needs to keep the heart pumping.
Pulmonary Circulation The pulmonary circulatory system is the portion of thecardiovascular system in which oxygen-depleted blood is pumped awayfrom the heart, via the pulmonary artery, to the lungs and returned,oxygenated, to the heart via the pulmonary vein. Oxygen deprived blood from the vena cava, enters the rightatrium of the heart and flows through the tricuspid valve (rightatrioventricular valve) into the right ventricle, from which it is thenpumped through the pulmonary semilunar valve into the pulmonaryartery to the lungs. Gas exchange occurs in the lungs, whereby CO2 isreleased from the blood, and oxygen is absorbed. The pulmonary veinreturns the now oxygen-rich blood to the heart.Systemic CirculationSystemic circulation is the portion of the cardiovascular system whichtransports oxygenated blood away from the heart, to the rest of thebody, and returns oxygen-depleted blood back to the heart. Systemiccirculation is, distance-wise, much longer than pulmonary circulation,transporting blood to every part of the body.
View from the front, which means the right side of the heart is on the left of the diagram (and vice-versa)
Coronary circulation The coronary circulatory system provides a blood supply to theheart. As it provides oxygenated blood to the heart, it is by definition apart of the systemic circulatory system.Heart The heart pumps oxygenated blood to the body anddeoxygenated blood to the lungs. In the human heart there is oneatrium and one ventricle for each circulation, and with both a systemicand a pulmonary circulation there are four chambers in total: leftatrium, left ventricle, right atrium and right ventricle. The right atriumis the upper chamber of the right side of the heart. The blood that is returned to the right atrium is deoxygenated(poor in oxygen) and passed into the right ventricle to be pumpedthrough the pulmonary artery to the lungs for re-oxygenation andremoval of carbon dioxide. The left atrium receives newly oxygenatedblood from the lungs as well as the pulmonary vein which is passed intothe strong left ventricle to be pumped through the aorta to thedifferent organs of the body.
Oxygen transportation About 98.5% of the oxygen in a sample of arterial blood in ahealthy human breathing air at sea-level pressure is chemicallycombined with haemoglobin molecules. About 1.5% is physically dissolved in the other blood liquidsand not connected to haemoglobin. The haemoglobin molecule is theprimary transporter of oxygen in mammals and many other species.
Measurement techniquesElectrocardiogram—for cardiac electrophysiologySphygmomanometer and stethoscope—for blood pressurePulse meter—for cardiac function (heart rate, rhythm, dropped beats)Pulse—commonly used to determine the heart rate in absence of certain cardiacpathologiesHeart rate variability -- used to measure variations of time intervals betweenheart beatsNail bed blanching test—test for perfusionVessel cannula or catheter pressure measurement—pulmonary wedge pressure orin older animal experiments.
Other vertebrates Two-chambered heart of a fish The circulatory systems of all vertebrates, as well as of annelids(forexample, earthworms) and cephalopods(squids, octopuses and relatives) areclosed, just as in humans. Still, the systems of fish, amphibians, reptiles, and birdsshow various stages of the evolution of the circulatory system. In fish, the system has only one circuit, with the blood being pumpedthrough the capillaries of the gills and on to the capillaries of the body tissues.This is known as single cycle circulation. The heart of fish is therefore only a singlepump (consisting of two chambers). In amphibians and most reptiles, a double circulatory system is used, butthe heart is not always completely separated into two pumps. Amphibians have athree-chambered heart.
Heart The human heart is about the size of a clenched fist. It contains fourchambers: two atria and two ventricles. Oxygen-poor blood enters the right atrium through a major vein calledthe vena cava. The blood passes through the tricuspid valve into the rightventricle. Next, the blood is pumped through the pulmonary artery to the lungsfor gas exchange. Oxygen-rich blood returns to the left atrium via thepulmonary vein. The oxygen-rich blood flows through the bicuspid (mitral) valve into theleft ventricle, from which it is pumped through a major artery, the aorta. Twovalves called semilunar valves are found in the pulmonary artery and aorta.
The ventricles contract about 70 times per minute, which represents apersons pulse rate. Blood pressure, in contrast, is the pressure exerted againstthe walls of the arteries. Blood pressure is measured by noting the height towhich a column of mercury can be pushed by the blood pressing against thearterial walls. A normal blood pressure is a height of 120 millimeters of mercuryduring heart contraction ( systole), and a height of 80 millimeters of mercuryduring heart relaxation ( diastole). Normal blood pressure is usually expressedas “120 over 80.”Coronary arteries------ supply the heart muscle with blood. The heart is controlled by nervesthat originate on the right side in the upper region of the atrium at thesinoatrial node. This node is called the pacemaker. It generates nerve impulses that spread to the atrioventricular nodewhere the impulses are amplified and spread to other regions of the heart bynerves called Purkinje fibers.
Blood Blood is the medium of transport in the body. The fluid portion of theblood, the plasma, is a straw-colored liquid composed primarily of water. All theimportant nutrients, the hormones, and the clotting proteins as well as the wasteproducts are transported in the plasma. Red blood cells and white blood cells arealso suspended in the plasma. Plasma from which the clotting proteins have beenremoved is serum.Red blood cells Red blood cells are erythrocytes. These are disk-shaped cells producedin the bone marrow. Red blood cells have no nucleus, and their cytoplasm is filledwith hemoglobin.Hemoglobin is a red-pigmented protein that binds loosely to oxygen atoms andcarbon dioxide molecules. It is the mechanism of transport of these substances.(Much carbon dioxide is also transported as bicarbonate ions.) Hemoglobin alsobinds to carbon monoxide. Unfortunately, this binding is irreversible, so it oftenleads to carbon-monoxide poisoning.
A red blood cell circulates for about 120 days and is then destroyedin the spleen, an organ located near the stomach and composed primarily oflymph node tissue. When the red blood cell is destroyed, its iron componentis preserved for reuse in the liver. The remainder of the hemoglobin converts to bilirubin. This ambersubstance is the chief pigment in human bile, which is produced in the liver. Red blood cells commonly have immune-stimulatingpolysaccharides called antigens on the surface of their cells. Individualshaving the A antigen have blood type A (as well as anti-B antibodies);individuals having the B antigen have blood type B (as well as anti-Aantibodies); individuals having the A and B antigens have blood type AB (butno anti-A or anti-B antibodies); and individuals having no antigens haveblood type O (as well as anti-A and anti-B antibodies).
White blood cells White blood cells are referred to as leukocytes. They are generallylarger than red blood cells and have clearly defined nuclei. They are alsoproduced in the bone marrow and have various functions in the body. Certain white blood cells called lymphocytes are essentialcomponents of the immune system. Other cells called neutrophils andmonocytes function primarily as phagocytes; that is, they attack and engulfinvading microorganisms. About 30 percent of the white blood cells are lymphocytes, about60 percent are neutrophils, and about 8 percent are monocytes. Theremaining white blood cells are eosinophils and basophils. Their functionsare uncertain; however, basophils are believed to function in allergicresponses.
Platelets Platelets are small disk-shaped blood fragments produced in the bonemarrow. They lack nuclei and are much smaller than erythrocytes. Also knowntechnically as thrombocytes, they serve as the starting material for bloodclotting. The platelets adhere to damaged blood vessel walls, andthromboplastin is liberated from the injured tissue. Thromboplastin, in turn,activates other clotting factors in the blood. Along with calcium ions and otherfactors, thromboplastin converts the blood protein prothrombin into thrombin. Thrombin then catalyzes the conversion of its blood protein fibrinogeninto a protein called fibrin, which forms a patchwork mesh at the injury site.As blood cells are trapped in the mesh, a blood clot forms.