Blood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells.
In vertebrates, it is composed of blood cells suspended in a liquid called blood plasma. Plasma, which comprises 55% of blood fluid, is mostly water (90% by volume),[1] and contains dissolved proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), platelets and blood cells themselves. The blood cells present in blood are mainly red blood cells (also called RBCs or erythrocytes) and white blood cells, including leukocytes and platelets. The most abundant cells in vertebrate blood are red blood cells. These contain hemoglobin, an iron-containing protein, which facilitates transportation of oxygen by reversibly binding to this respiratory gas and greatly increasing its solubility in blood. In contrast, carbon dioxide
is almost entirely transported extracellularly dissolved in plasma as bicarbonate ion.
Vertebrate blood
is bright-red when its hemoglobin is oxygenated. Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, instead of hemoglobin. Insects and some molluscs use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed
circulatory system. In most insects, this "blood" does not contain oxygen-carrying molecules
such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen.
Jawed vertebrates have an adaptive immune system, based largely on white blood cells. White blood cells help to resist infections and parasites. Platelets are important in the clotting of blood.[2] Arthropods, using hemolymph, have hemocytes as part of their immune system.
Blood is circulated
around the body through blood vessels by the pumping action of the heart. In animals having lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, and venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled.
Medical
terms related to blood often begin with hemo- or hemato- (also spelled haemo- and haemato-) from
the Ancient Greek word αἷμα (haima) for "blood".
In terms of anatomy and histology, blood is considered a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers
in the form of fibrinogen.
http://en.wikipedia.org/wiki/Blood#Cardiovascular_system
What is the Blood composed of?
One microliter of blood contains:
- 4.7 to 6.1 million (male), 4.2 to 5.4 million (female) erythrocytes:[6] In mammals, mature red blood cells lack a nucleus and organelles. They contain the blood's hemoglobin and distribute oxygen. The red blood cells (together with endothelial vessel cells and other cells) are also marked by glycoproteins that 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.[7]
- 4,000-11,000 leukocytes:[8] White blood cells are part of the immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances. The cancer of leukocytes is called leukemia.
- 200,000-500,000 thrombocytes:[8] thrombocytes, also called platelets, are responsible for blood clotting (coagulation). They change fibrinogen into fibrin. This fibrin creates a mesh onto which red blood cells collect and clot, which then stops more blood from leaving the body
and also helps to prevent bacteria from entering the body.
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 litres 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, and fatty acids (dissolved in the blood or bound to plasma proteins), and removes waste products, such as carbon dioxide, urea, and lactic acid.
Other important components include:
One microliter of blood contains:
- 4.7 to 6.1 million (male), 4.2 to 5.4 million (female) erythrocytes:[6] In mammals, mature red blood cells lack a nucleus and organelles. They contain the blood's hemoglobin and distribute oxygen. The red blood cells (together with endothelial vessel cells and other cells) are also marked by glycoproteins that 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.[7]
- 4,000-11,000 leukocytes:[8] White blood cells are part of the immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances. The cancer of leukocytes is called leukemia.
- 200,000-500,000 thrombocytes:[8] thrombocytes, also called platelets, are responsible for blood clotting (coagulation). They change fibrinogen into fibrin. This fibrin creates a mesh onto which red blood cells collect and clot, which then stops more blood from leaving the body
and also helps to prevent bacteria from entering the body.
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 litres 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, and fatty acids (dissolved in the blood or bound to plasma proteins), and removes waste products, such as carbon dioxide, urea, and lactic acid.
Other important components include:
In vertebrates, the various cells of blood are made
in the bone marrow in a process called hematopoiesis, which includes erythropoiesis, the production of red blood cells; and myelopoiesis, the production of white blood cells and platelets. During childhood,
almost every human bone produces red blood cells; as adults, red blood cell production is limited to the larger bones: the
bodies of the vertebrae, the breastbone (sternum), the ribcage, the pelvic bones, and the bones of the upper arms and legs.
In addition, during childhood, the thymus gland, found in the mediastinum, is an important source of lymphocytes.[10] The proteinaceous component of blood (including clotting proteins) is produced predominantly by the liver, while hormones are produced by the endocrine glands and the watery fraction is regulated by the hypothalamus and maintained by the kidney.
Healthy erythrocytes have a plasma life of about 120 days before they are degraded by the spleen, and the Kupffer cells in the liver. The liver also clears some proteins, lipids, and amino acids. The kidney actively secretes waste products into the urine.
[edit] Oxygen transport
Basic hemoglobin saturation curve. It is moved to the right in higher acidity (more dissolved carbon dioxide) and to
the left in lower acidity (less dissolved carbon dioxide)
About 98.5% of the oxygen in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with the Hgb.
About 1.5% is physically dissolved in the other blood liquids and not connected to Hgb. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species (for exceptions, see below). Hemoglobin has an oxygen binding capacity of between 1.36 and 1.37 ml
O2 per gram Hemoglobin [11], which increases the total blood oxygen capacity seventyfold[12], compared to if oxygen solely was carried by its solubility of 0.03 mL O2 per litre blood per mmHg partial pressure of oxygen (approximately 100 mmHg in arteries). [12]
With the exception of pulmonary and umbilical arteries and their corresponding veins, arteries carry oxygenated blood away from the heart and deliver it to the body via arterioles and capillaries, where the oxygen is consumed; afterwards, venules, and veins carry deoxygenated blood back to the heart.
Under normal conditions in humans at rest, hemoglobin in blood leaving
the lungs is about 98-99% saturated with oxygen. In a healthy adult at rest, deoxygenated blood returning to the
lungs is still approximately 75% saturated.[13][14] Increased oxygen consumption during sustained exercise reduces the oxygen saturation of venous blood, which can reach
less than 15% in a trained athlete; although breathing rate and blood flow increase to compensate, oxygen saturation in arterial
blood can drop to 95% or less under these conditions.[15] Oxygen saturation this low is considered dangerous in an individual at rest (for instance, during surgery under anesthesia.
Sustained hypoxia (oxygenation of less than 90%), is dangerous to health, and severe hypoxia (saturations of less than 30%)
may be rapidly fatal.[16]
A fetus, receiving oxygen via the placenta, is exposed to much lower oxygen pressures (about 21% of the level found in an adult's lungs), and, so, fetuses produce
another form of hemoglobin with a much higher affinity for oxygen (hemoglobin F) in order to function under these conditions.[17]
[edit] Carbon dioxide transport
When blood flows through capillaries, carbon dioxide
diffuses from the tissues into the blood. Some carbon dioxide is dissolved in the blood. Some carbon dioxide reacts with hemoglobin
and other proteins to form carbamino compounds. The remaining carbon dioxide is converted to bicarbonate and hydrogen ions through the action of RBC carbonic anhydrase. Most carbon dioxide is transported through the blood in the form of bicarbonate ions.
Carbon dioxide (CO2),
the main cellular waste product is carried in blood mainly dissolved in plasma, in equilibrium with bicarbonate (HCO3-) and carbonic acid (H2CO3). 86%-90% of CO2 in the body is converted into carbonic acid, which can quickly turn into bicarbonate, the chemical equilibrium being important in the pH buffering of plasma.[18] Blood pH is kept in a narrow range (pH between 7.35-7.45).[
What is the Blood composed of?
One microliter of blood contains:
- 4.7 to 6.1 million (male), 4.2 to 5.4 million (female) erythrocytes:[6] In mammals, mature red blood cells lack a nucleus and organelles. They contain the blood's hemoglobin and distribute oxygen. The red blood cells (together with endothelial vessel cells and other cells) are also marked by glycoproteins that 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.[7]
- 4,000-11,000 leukocytes:[8] White blood cells are part of the immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances. The cancer of leukocytes is called leukemia.
- 200,000-500,000 thrombocytes:[8] thrombocytes, also called platelets, are responsible for blood clotting (coagulation). They change fibrinogen into fibrin. This fibrin creates a mesh onto which red blood cells collect and clot, which then stops more blood from leaving the body
and also helps to prevent bacteria from entering the body.
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 litres 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, and fatty acids (dissolved in the blood or bound to plasma proteins), and removes waste products, such as carbon dioxide, urea, and lactic acid.
Other important components include:
One microliter of blood contains:
- 4.7 to 6.1 million (male), 4.2 to 5.4 million (female) erythrocytes:[6] In mammals, mature red blood cells lack a nucleus and organelles. They contain the blood's hemoglobin and distribute oxygen. The red blood cells (together with endothelial vessel cells and other cells) are also marked by glycoproteins that 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.[7]
- 4,000-11,000 leukocytes:[8] White blood cells are part of the immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances. The cancer of leukocytes is called leukemia.
- 200,000-500,000 thrombocytes:[8] thrombocytes, also called platelets, are responsible for blood clotting (coagulation). They change fibrinogen into fibrin. This fibrin creates a mesh onto which red blood cells collect and clot, which then stops more blood from leaving the body
and also helps to prevent bacteria from entering the body.
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 litres 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, and fatty acids (dissolved in the blood or bound to plasma proteins), and removes waste products, such as carbon dioxide, urea, and lactic acid.
Other important components include:
In vertebrates, the various cells of blood are made
in the bone marrow in a process called hematopoiesis, which includes erythropoiesis, the production of red blood cells; and myelopoiesis, the production of white blood cells and platelets. During childhood,
almost every human bone produces red blood cells; as adults, red blood cell production is limited to the larger bones: the
bodies of the vertebrae, the breastbone (sternum), the ribcage, the pelvic bones, and the bones of the upper arms and legs.
In addition, during childhood, the thymus gland, found in the mediastinum, is an important source of lymphocytes.[10] The proteinaceous component of blood (including clotting proteins) is produced predominantly by the liver, while hormones are produced by the endocrine glands and the watery fraction is regulated by the hypothalamus and maintained by the kidney.
Healthy erythrocytes have a plasma life of about 120 days before they are degraded by the spleen, and the Kupffer cells in the liver. The liver also clears some proteins, lipids, and amino acids. The kidney actively secretes waste products into the urine.
[edit] Oxygen transport
Basic hemoglobin saturation curve. It is moved to the right in higher acidity (more dissolved carbon dioxide) and to
the left in lower acidity (less dissolved carbon dioxide)
About 98.5% of the oxygen in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with the Hgb.
About 1.5% is physically dissolved in the other blood liquids and not connected to Hgb. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species (for exceptions, see below). Hemoglobin has an oxygen binding capacity of between 1.36 and 1.37 ml
O2 per gram Hemoglobin [11], which increases the total blood oxygen capacity seventyfold[12], compared to if oxygen solely was carried by its solubility of 0.03 mL O2 per litre blood per mmHg partial pressure of oxygen (approximately 100 mmHg in arteries). [12]
With the exception of pulmonary and umbilical arteries and their corresponding veins, arteries carry oxygenated blood away from the heart and deliver it to the body via arterioles and capillaries, where the oxygen is consumed; afterwards, venules, and veins carry deoxygenated blood back to the heart.
Under normal conditions in humans at rest, hemoglobin in blood leaving
the lungs is about 98-99% saturated with oxygen. In a healthy adult at rest, deoxygenated blood returning to the
lungs is still approximately 75% saturated.[13][14] Increased oxygen consumption during sustained exercise reduces the oxygen saturation of venous blood, which can reach
less than 15% in a trained athlete; although breathing rate and blood flow increase to compensate, oxygen saturation in arterial
blood can drop to 95% or less under these conditions.[15] Oxygen saturation this low is considered dangerous in an individual at rest (for instance, during surgery under anesthesia.
Sustained hypoxia (oxygenation of less than 90%), is dangerous to health, and severe hypoxia (saturations of less than 30%)
may be rapidly fatal.[16]
A fetus, receiving oxygen via the placenta, is exposed to much lower oxygen pressures (about 21% of the level found in an adult's lungs), and, so, fetuses produce
another form of hemoglobin with a much higher affinity for oxygen (hemoglobin F) in order to function under these conditions.[17]
[edit] Carbon dioxide transport
When blood flows through capillaries, carbon dioxide
diffuses from the tissues into the blood. Some carbon dioxide is dissolved in the blood. Some carbon dioxide reacts with hemoglobin
and other proteins to form carbamino compounds. The remaining carbon dioxide is converted to bicarbonate and hydrogen ions through the action of RBC carbonic anhydrase. Most carbon dioxide is transported through the blood in the form of bicarbonate ions.
Carbon dioxide (CO2),
the main cellular waste product is carried in blood mainly dissolved in plasma, in equilibrium with bicarbonate (HCO3-) and carbonic acid (H2CO3). 86%-90% of CO2 in the body is converted into carbonic acid, which can quickly turn into bicarbonate, the chemical equilibrium being important in the pH buffering of plasma.[18] Blood pH is kept in a narrow range (pH between 7.35-7.45).[
