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Flowing of blood in Heart

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 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

pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide.

The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which

is passed into the strong left ventricle to be pumped through the aorta to the different organs of the

body.

Blood vessels

The blood vessels are the part of the circulatory system that transports blood throughout the body.

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 between the blood and the

tissues; and the veins, which carry blood from the capillaries back toward the heart.

Types

There are various kinds of blood vessels:

1)Arteries:- Arteries are blood vessels that carry blood away from the heart. This blood is normally

oxygenated, exceptions made for the pulmonary and umbilical arteries. 

The circulatory system is extremely important for sustaining life. Its proper functioning is responsible

for the delivery of oxygen and nutrients to all cells, as well as the removal of carbon dioxide and waste

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products, maintenance of optimumpH, and the mobility of the elements, proteins and cells of

the immune system. In developed countries, the two leading causes of death, myocardial

infarction and stroke, each may directly result from an arterial system that has been slowly and

progressively compromised by years of deterioration. (See atherosclerosis).

2)arteriole:- An arteriole is a small diameter blood vessel in the microcirculation that extends and

branches out from an artery and leads to capillaries.[1]

 

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. This reduces the pressure and velocity of flow for gas and

nutrient exchange to occur within the capillaries. Arterioles receive autonomic nervous

system innervation and respond to various circulating hormones in order to regulate their diameter.

Further local responses to stretch, carbon dioxide, pH, and oxygen also influence tone. Bloodpressure in the arteries supplying the body is a result of the work needed to pump the cardiac

output (the flow of blood pumped by the heart) through the vascular resistance , usually termed total

peripheral resistance by physicians and researchers.

3)Capillaries:-Capillaries are the smallest of a body's blood vessels and are parts of

the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter,

connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many

other nutrient and waste chemical substances between blood and surroundingtissues.[1]

 During

embryological development, new capillaries are formed by vasculogenesis, the process of blood

vesselformation occurring by a de novo  production of endothelial cells and their formation into

vascular tubes The termangiogenesis denotes the formation of new capillaries from pre-existing blood

vessels.

4)venule:-A venule is a small blood vessel in the microcirculation that allows deoxygenated blood to

return from the capillary beds to the larger blood vessels called veins. Venules range from 8 to 100μm

in diameter and are formed when capillaries unite.

Venules are blood vessels that drain blood directly from the capillary beds. Many venules unite to

form a vein.

Structure

Venule walls have three layers: An inner endothelium composed of squamous endothelial cells that

act as a membrane, a middle layer of muscle and elastic tissue and an outer layer of fibrous

connective tissue. The middle layer is poorly developed so that venules have thinner walls

than arterioles. They are extremely porous so that fluid and blood cells can move easily from the

bloodstream through their walls.

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5)veins:-In the circulatory system, veins (from the Latin vena ) are blood vessels that

carry blood towards 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. Veins differ from arteries in structure and function; for example, arteries are more muscular

than veins, veins are often closer to the skin and contain valves to help keep blood flowing toward the

heart, while arteries carry blood away from the heart.

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Function of blood

Blood performs many important functions within the body including:

Supply of oxygen to tissues (bound to hemoglobin, which is carried in red cells)

  Supply of nutrients such as glucose, amino acids, and fatty acids (dissolved in the blood or bound

to plasma proteins (e.g.,blood lipids))

  Removal of waste such as carbon dioxide, urea, and lactic acid 

Immunological functions, including circulation of white blood cells, and detection of foreign

material by antibodies 

  Coagulation, which is one part of the body's self-repair mechanism (blood clotting after an open

wound in order to stop bleeding)

Messenger functions, including the transport of hormones and the signaling of tissue damage

Regulation of body pH 

  Regulation of core body temperature 

  Hydraulic functions

Constituents of human blood

Blood accounts for 8% of the human body weight,[3]

 with an average density of approximately

1060 kg/m3, very close to pure water's density of 1000 kg/m

3.[4]

 The average adult has a blood

volume of roughly 5 liters (1.3 gal), composed of plasma and several kinds of cells (occasionally

called corpuscles ); these formed elements of the blood are erythrocytes (red blood cells, RBCs),

leukocytes (white blood cells), and thrombocytes (platelets). By volume, the red blood cells constitute

about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%.

Whole blood (plasma and cells) exhibits non-Newtonian, viscoelastic fluid dynamics; its flow

properties are adapted to flow effectively through tiny capillary blood vessels with less resistance than

plasma by itself. In addition, if all human hemoglobin were free in the plasma rather than being

contained in RBCs, the circulatory fluid would be too viscous for the cardiovascular system to function

effectively.

Cells

  4.7 to 6.1 million (male), 4.2 to 5.4 million (female) Erythrocytes:[5]

 Red blood cells contain the

blood's hemoglobin and distribute oxygen. Mature red blood cells lack

a nucleus and organelles in most mammals (the exception is camels). The red blood cells

(together with endothelial vessel cells and other cells) are also marked by glycoproteins that

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define the different blood types. The proportion of blood occupied by red blood cells is referred to

as the hematocrit, and is normally about 45%. The combined surface area of all red blood cells of

the human body would be roughly 2,000 times as great as the body's exterior surface.

Plasma

About 55% of whole blood is blood plasma, a fluid that is the blood's liquid medium, which by itself is

straw-yellow in color. The blood plasma volume totals of 2.7 –3.0 liters (2.8 –3.2 quarts) in an average

human. It is essentially an aqueous solution containing 92% water, 8% blood plasma proteins, and

trace amounts of other materials. Plasma circulates dissolved nutrients, such as glucose, amino

acids, andfatty acids (dissolved in the blood or bound to plasma proteins), and removes waste

products, such as carbon dioxide, urea, and lactic acid. 

Blood in non-human vertebrates

Human blood is typical of that of mammals, although the precise details concerning cell numbers,

size, protein structure, and so on, vary somewhat between species. In non-mammalian vertebrates,

however, there are some key differences:[11]

 

Red blood cells of non-mammalian vertebrates are flattened and ovoid in form, and retain their

cell nuclei

There is considerable variation in the types and proportions of white blood cells; for example,

acidophils are generally more common than in humans

Platelets are unique to mammals; in other vertebrates, small, nucleated, spindle cells are

responsible for blood clotting instead