Double circulatory system
Overview
 
In a first order circulatory circuit, blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 is pumped to the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s, thus acquiring oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 while simultaneously releasing carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

. Fully oxygenated blood then enters the second order circuit, going to the brain and body. The second order systemic output blood is selectively deoxygenated by the needs of the peripheral organs, returning once again to the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

.

The double circulatory system of blood flow references two distinct and separate systems. This distinction is shared by most vertebrates to varying degrees to include amphibians, bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s (including human
Human
Humans are the only living species in the Homo genus...

s.) In contrast, fish
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...

 have a single circulation system because they lack lungs.
Encyclopedia
In a first order circulatory circuit, blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 is pumped to the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s, thus acquiring oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 while simultaneously releasing carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

. Fully oxygenated blood then enters the second order circuit, going to the brain and body. The second order systemic output blood is selectively deoxygenated by the needs of the peripheral organs, returning once again to the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

.

The double circulatory system of blood flow references two distinct and separate systems. This distinction is shared by most vertebrates to varying degrees to include amphibians, bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s (including human
Human
Humans are the only living species in the Homo genus...

s.) In contrast, fish
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...

 have a single circulation system because they lack lungs. Most animals living above the water require a double circulatory system to allow the added benefit of direct oxygenation from a developed pulmonary circuit. Embryology
Embryology
Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...

 of the human circulatory system is an advanced study of the double circulatory system as the distinction between the right and left portions of the heart is founded.

For example, the adult human heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 consists of two separated pumps or flow circuits. One side is dedicated to the right atrium
Right atrium
The right atrium is one of four chambers in the hearts of mammals and archosaurs...

 and right ventricle
Right ventricle
The right ventricle is one of four chambers in the human heart. It receives deoxygenated blood from the right atrium via the tricuspid valve, and pumps it into the pulmonary artery via the pulmonary valve and pulmonary trunk....

 (which pumps deoxygenated blood into the pulmonary circulation). This circuit is very low in pressure incumbent upon systemic resistance. The left circuit inclusive of the left atrium and ventricle (which pumps oxygenated blood into the systemic circulation) is better gated to high pressure. Blood in one circuit must go through the heart to enter the other circuit.

Mathematics remain murky but it appears that summation of imaged Right Ventricular Ejection Fraction plus Left Ventricular Ejection Fraction may not allow a solution of 100% in many cases. European models of Windkessel
Windkessel
Windkessel literally means air chamber and is a German translation of a concept described previousy by Stephen Hales, who likened the effect of the elastic arteries in dampening the arterial pulse to that of an air chamber in some 18th century fire engines...

 physiology appear to offer additional mathematical illumination of Diastolic Performance.

Blood circulates through the body at speeds which vary by a factor of one hundred, from 1.2 m/s in the aorta to approximately 1.1 cm/s in the capillaries. Blood velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...

 is similarly highly variable. Velocities generated within the large bore heart chambers vary considerable from velocities within the smaller bore vessels of the periphery and lungs. The circulatory system features numerous return paths (out to the kidneys and back, to the liver and back, to the legs and back, etc.), so it is incorrect to think of blood cells travelling the entire circulatory distance. The average adult heart pumps approximately 5 L/min of blood at rest (the cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...

); with a total blood volume of approximately 5L in an average adult, a blood cell will run through the complete circuit about once a minute, though this depends on what tissue it circulates to. For example, blood supplying the coronary circulation
Coronary circulation
Coronary circulation is the circulation of blood in the blood vessels of the heart muscle . The vessels that deliver oxygen-rich blood to the myocardium are known as coronary arteries...

 of the heart muscle itself will return to the pulmonary loop much faster than blood supplying the toes. During intense exercise, the cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...

 can increase fivefold.

Regulation of circulation

Throughout the circulatory system there are many valves. There are 3 main types. The first is the bicuspid valve (mitral valve) which is found between the left atrium (auricle) and the left ventricle. This valve allows oxygenated blood to flow from the left atrium into the left ventricle during ventricular relaxation diastole
Diastole
Diastole is the period of time when the heart fills with blood after systole . Ventricular diastole is the period during which the ventricles are relaxing, while atrial diastole is the period during which the atria are relaxing...

. The bicuspid valve also prevents the backflow of blood into the left atrium during ventricular contraction (systole). Then there is the tricuspid valve which is found between the right atrium and the right ventricle. This valve allows deoxygenated blood to flow from the right atrium into the right ventricle during ventricular relaxation. It prevents the backflow of blood into the right atrium during ventricular contraction. Finally there are the two semilunar valves, found at the beginning of the arteries leaving the heart. It is called a double circulatory system because it has two loops, one from the heart to the lungs and one from the heart to the rest of the body.

The advantage of a double circulatory system is that blood can be pumped simultaneously into low pressure/compliance (pulmonary/right) and high pressure/compliance (systemic/left) loops.

See also

  • Circulatory system
  • Pulmocutaneous circulation
    Pulmocutaneous circulation
    Pulmocutaneous circulation is part of the amphibian circulatory system. It is responsible for directing blood to the skin and lungs. Blood flows from the ventricle into an artery called the conus arteriosus and from there into either the left or right truncus arteriosus. They in turn each split...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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