Circulatory System Functions Circulatory Systems Of Different

The circulatory system of arthropods and most mollusks is open, meaning that there are no capillaries and veins: one or more hearts pump the blood (more properly called hemolymph in this case) through the arteries to spaces called sinuses which surround the organs, allowing the tissues to exchange materials with the hemolymph. The hemolymph is drawn back into the heart as the heart relaxes.

The circulatory systems of all vertebrates as well as of earthworms, squidThis article is about the sea animal. For other uses of "squid", see Squid (disambiguation). Myopsina Oegopsina The squid is a marine mollusk of the class Cephalopoda, subclass Coleoidea, order Teuthida of which there are two major suborders, Myopsina ands and octopus14 in two suborders, see text For other meanings of "octopus", see Octopus (disambiguation). The octopus is a cephalopod of the order Octopoda that inhabits many diverse regions of the ocean, especially coral reefs. The term may also refer to only those ces are closed, meaning that the blood never leaves the system of blood vessels consisting of arteries, capillaries and veins.

The systems of fishAtlantic herring, Clupea harengus one of the most abundant species in the world Photo A fish is a poikilothermic (cold-blooded) water-dwelling vertebrate with gills. There are over 27,000 species of fish, making them the most diverse group of vertebrates., amphibians, reptileCrocodilia Crocodilians Rhynchocephalia Tuataras Squamata Suborder Sauria Lizards Suborder Serpentes Snakes Testudines Turtles Superorder Dinosauria Saurischia Ornithischia The reptiles are a group of vertebrate animals. Most reptiles are tetrapods, and ts, birdFor other meanings of bird see bird (disambiguation). Many see text Birds are bipedal, warm-blooded, egg-laying vertebrates characterized primarily by feathers, forelimbs modified as wings, and hollow bones. There are almost 9000 known species of birds ins and mammalSubclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorps show various stages of evolutionThis article is about biological evolution. For other possible meanings, see Evolution (disambiguation). Evolution generally refers to any process of change over time. However, in the context of the life sciences, evolution is a change in the genetic make. In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as single circulation. The heart of fish is therefore only a single pump (consisting of two chambers). In amphibians and reptiles, a double circulation is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart. Birds and mammals show complete separation of the heart into two pumps, for a total of four heart chambers; it is thought that the four-chambered heart of birds evolved independently of that of mammals.

All circulatory systems frequently employ countercurrent exchange systems to drive the diffusion of chemicals into or out of the bloodstream.

2.1.1 No Circulatory system

An example of an animal with no circulator system is the flatworm (class Tubellaria). They have a mouth leading into a digestive system. The digestive system is very branched, and because the worm is so flat, digested materials can be diffused to all the cells of the flat worm. Oxygen can diffuse from water into the cells of the flatworm. Thus every cell is able to obtain nutrients, water and oxygen without the need of a transport system.

2.2 Humans

The human circulatory system is comprised of the blood, the vascular system, and the heart.

The heart is the muscular organ which pumps the blood. The vascular system is made up of arteries, veins, and capillaries. Arteries are blood vessels that carry blood away from the heart. Veins are blood vessels that return blood to the heart. Capillaries are the smallest blood vessels, and are where the exchange of nutrients and gases takes place between the red blood cells and the body tissues.

Humans have a double circulatory system which consists of separate but connecting circulations: the pulmonary circulation and the systemic circulation.

2.2.1 Pulmonary circulation

The right ventricle pumps deoxygenated blood into the pulmonary arteries. These arteries carry the blood to the lungs, where it passes through a capillary network close to air-filled alveoli. This enables the release of carbon dioxide and the uptake of oxygen from the air. The now oxygenated blood returns to the left atrium in the pulmonary veins.

2.2.2 Systemic circulation

Oxygenated blood from the lungs returns to the heart via the pulmonary veins, flows into the left atrium and then into the left ventricle, which then pumps the blood through the aorta, the major artery which supplies blood to the body.

There are also unique braches of the systemic circulation that are given their own names due to their unique physiology.

2.2.3 Portal circulation

There are two exceptions to the system of double circulation.

The deoxygenated blood from the capillaries of the gastrointestinal tract drains into the portal vein which, instead of going directly back to the heart, leads to the liver. This allows the liver to take up the nutrients that were extracted by the intestines from food. The liver also neutralizes some toxins taken up by the intestines. Blood from the liver drains via the hepatic veins into the inferior vena cava and then the right side of the heart.

There is also a small portal flow from the hypothalamus to the anterior pituitary gland.

2.2.4 Fetal circulation

The circulatory system of the fetus is different, as the fetus does not use its lungs yet and obtains oxygen and nutrients from the placenta through the umbilical cord. After birth, the fetal circulatory system undergoes several anatomical changes, including closure of the ductus arteriosus and foramen ovale.

3 History of discovery

The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BC. However their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for transport of air.

Herophilus distinguished veins from arteries but thought that pulse is a property of arteries themselves. 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. Galen in the 2nd century AD knew that blood vessels carry blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.

Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through ' pores' in the interventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created 'sooty' vapors were created and passed to the lungs also via the pulmonary artery to be exhaled.

Ibn Nafis in 1268 was the first person to accurately describe the process of blood circulation in the human body. Contemporary drawings of this process have survived. In 1552 Servetus described the same and Realdo Colombo proved the concept. All these results were not widely accepted however.

Finally William Harvey, a pupil of Hieronymus Fabricius (who had earlier described the valves of the veins without recognizing their function), performed a sequence of experiments and announced in 1628 the discovery of the human circulatory system as his own and published an influential book about it. This work with its essentially correct exposition slowly convinced the medical world. Harvey was not able to identify the capillary system connecting arteries and veins; these were later described by Marcello Malpighi.

4 See also

5 External links

The Circulatory System, a comprehensive overview
Studies on Hemodynamics and Coronary Circulation

Cardiovascular system

Heart - Aorta - Arteries - Arterioles - Capillaries - Venules - Veins - Venae cavae - Pulmonary arteries - Lungs - Pulmonary veins - Blood

Human organ systems

Cardiovascular system - Digestive system - Endocrine system - Immune system - Integumentary system - Lymphatic system - Muscular system - Nervous system - Skeletal system - Reproductive system - Respiratory system - Urinary system

Physiology Anatomy Cardiovascular system Blood

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Home > Circulatory system

1 Functions

2 Circulatory systems of different species

2.1 Non-human animals