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the fluid that circulates through the heart, arteries, capillaries, and veins and is the chief means of transport within the body. It transports oxygen from the lungs to the body tissues, and carbon dioxide from the tissues to the lungs. It transports nutritive substances and metabolites to the tissues and removes waste products to the kidneys and other organs of excretion. It has an essential role in the maintenance of fluid balance.

In an emergency, blood cells and antibodies carried in the blood are brought to a point of infection, or blood-clotting substances are carried to a break in a blood vessel. The blood distributes hormones from the endocrine glands to the organs they influence. It also helps regulate body temperature by carrying excess heat from the interior of the body to the surface layers of the skin, where the heat is dissipated to the surrounding air.

Blood varies in color from a bright red in the arteries to a duller red in the veins. The total quantity of blood within an individual depends upon body weight; a person weighing 70 kg (154 lb) has about 4.5 liters of blood in the body.

Blood is composed of two parts: the fluid portion is called plasma, and the solid portion or formed elements (suspended in the fluid) consists of the blood cells (erythrocytes and leukocytes) and the platelets. Plasma accounts for about 55 per cent of the volume and the formed elements account for about 45 per cent. ( and table.)

Chemical analyses of various substances in the blood are invaluable aids in (1) the prevention of disease by alerting the patient and health care provider to potentially dangerous levels of blood constituents that could lead to more serious conditions, (2) diagnosis of pathologic conditions already present, (3) assessment of the patient's progress when a disturbance in blood chemistry exists, and (4) assessment of the patient's status by establishing baseline or “normal” levels for each individual patient.

In recent years, with the increasing attention to preventive health care and rapid progress in technology and automation, the use of a battery of screening tests performed by automated instruments has become quite common. These instruments are capable of performing simultaneously a variety of blood chemistry tests. Some of the more common screening tests performed on samples of blood include evaluation of electrolyte, albumin, and bilirubin levels, blood urea nitrogen (BUN), cholesterol, total protein, and such enzymes as lactate dehydrogenase and aspartate transaminase. Other tests include electrophoresis for serum proteins, blood gas analysis, glucose tolerance tests, and measurement of iron levels.
Composition of the blood, which constitutes 8% of total body weight. From Applegate, 2000.
blood bank
1. a place of storage for blood.
2. an organization that collects, processes, stores, and transfuses blood. In most health agencies the blood bank is located in the pathology laboratory. It is operated by medical technologists under the direction of a pathologist.
blood bank technologist a clinical laboratory scientist/medical technologist who has postgraduate education in blood banking and is certified by the Board of Registry of the American Society of Clinical Pathologists; designated as MT(ASCP)SBB. Specialists in blood bank technology perform both routine and specialized tests in blood bank immunohematology and perform transfusion services. The address of the American Association of Blood Banks is 8101 Glenbrook Road, Bethesda, MD 20814 (telephone 301-907-6582). The address of the Board of Registry of the American Society of Clinical Pathologists is P.O. Box 12270, Chicago, IL 60612. Their telephone number is 312-738-1336 and their web site is
blood-brain barrier BBB; the barrier separating the blood from the brain parenchyma everywhere except in the hypothalamus. It is permeable to water, oxygen, carbon dioxide, and nonionic solutes, such as glucose, alcohol, and general anesthetics, and is only slightly permeable to electrolytes and other ionic substances. Some small molecules, e.g., amino acids, are taken up across the barrier by specific transport mechanisms.
citrated blood blood treated with sodium citrate or citric acid to prevent its coagulation.
cord blood the blood contained in the umbilical vessels at the time of delivery of the infant. It is rich in stem cells that could be used in place of bone marrow for a transplant; thus, it is sometimes collected and stored for future use.
blood count determination of the number of blood cells in a given sample of blood, usually expressed as the number in a cubic millimeter; it may be either a complete blood count or a count of just one of the elements such as an erythrocyte count, leukocyte count or a platelet count. Methods include manual counts using a hemacytometer and automated counts using a flow cytometer, a Coulter counter, or other means. The blood count is useful in the diagnosis of various blood dyscrasias, infections, or other abnormal conditions and is one of the most common tests done on the blood. Called also blood cell count. (See accompanying table.)
defibrinated blood whole blood from which fibrin has been separated during the clotting process.
blood gas analysis laboratory studies of arterial and venous blood for the purpose of measuring oxygen and carbon dioxide levels and pressure or tension, and hydrogen ion concentration (pH). (See accompanying table.) Analyses of blood gases provide the following information:ƒ

PaO2—partial pressure (P) of oxygen (O2) in the arterial blood (a)

SaO2—percentage of available hemoglobin that is saturated (Sa) with oxygen (O2)

PaCO2—partial pressure (P) of carbon dioxide (CO2) in the arterial blood (a)

pH—an expression of the extent to which the blood is alkaline or acidic

HCO3—the level of plasma bicarbonate; an indicator of the metabolic acid-base status

These parameters are important tools for assessment of a patient's acid-base balance. They reflect the ability of the lungs to exchange oxygen and carbon dioxide, the ability of the kidneys to control the retention or elimination of bicarbonate, and the effectiveness of the heart as a pump. Because the lungs and kidneys act as important regulators of the respiratory and metabolic acid-base balance, assessment of the status of a patient with any disorder of respiration and metabolism includes periodic blood gas measurements.

The partial pressure of a particular gas in a mixture of gases, as of oxygen in air, is the pressure exerted by that gas alone. It is proportional to the relative number of molecules of the gas, for example, the fraction of all the molecules in the air that are oxygen molecules. The partial pressure of a gas in a liquid is the partial pressure of a real or imaginary gas that is in equilibrium with the liquid.

PaO2 measures the oxygen content of the arterial blood, most of which is bound to hemoglobin, forming oxyhemoglobin. The SaO2 measures the oxygen in oxyhemoglobin as a percentage of the total hemoglobin oxygen-carrying capacity.

A PaO2 of 60 mm Hg represents an SaO2 of 90 per cent, which is sufficient to meet the needs of the body's cells. However, as the PaO2 falls, the SaO2 decreases rapidly. A PaO2 below 55 indicates a state of hypoxemia that requires correction. Normal PaO2 values at sea level are 80 mm Hg for elderly adults and 100 mm Hg for young adults.

However, some patients with chronic obstructive pulmonary disease can tolerate a PaO2 as low as 70 mm Hg without becoming hypoxic. In caring for patients with this condition, it is important to know that attempts to elevate the PaO2 level to the normal level can be dangerous and even fatal. It is best to establish a baseline for each individual patient before supplementary oxygen is given, and then to assess his condition and the effectiveness of his therapy according to this baseline.

The PaCO2 gives information about the cellular production of carbon dioxide through metabolic processes, and the removal of it from the body via the lungs. The normal range is 32 to 45 mm Hg. Values outside this range indicate a primary respiratory problem associated with pulmonary function, or a metabolic problem for which there is respiratory compensation.

In the newborn the normal PaO2 is 50 to 80 mm Hg. At 40 to 50 mm Hg cyanosis may become apparent. Respiratory distress in an infant who is unable to ventilate the lungs adequately will produce a drop in PaO2 level. However, there is no marked increase in PaCO2 level in some infants as in adults with respiratory distress because many infants can still eliminate carbon dioxide from the lungs even though weakness prevents inhaling an adequate oxygen supply. All infants being ventilated and receiving oxygen therapy require frequent blood gas analyses and also pH, base excess, and oxygen saturation levels to avoid oxygen toxicity and acid-base imbalance.

Blood pH gives information about the patient's metabolic state. A pH of 7.4 is considered normal; a value lower than 7.4 indicates acidemia and one higher than 7.4 alkalemia.

Because the amount of CO2 in the blood affects its pH, abnormal PaCO2 values are interpreted in relation to the pH. If the PaCO2 value is elevated, and the pH is below normal, respiratory acidosis from either acute or chronic hyperventilation is suspected. Conversely, a PaCO2 below normal and a pH above normal indicates respiratory alkalosis. When both the PaCO2 and the pH are elevated, there is respiratory retention of CO2 to compensate for metabolic acidosis. If both values are below normal, there is respiratory elimination of CO2 (hyperventilation) to compensate for metabolic acidosis.

Abnormal levels of bicarbonate (HCO3) in the plasma are also interpreted in relation to the pH in the diagnosis of disturbances in the metabolic component of the acid-base balance. The normal range for HCO3 is 22 to 26 mEq per liter. Abnormally low levels of both HCO3 and pH indicate acidosis of metabolic origin. Conversely, elevations of both of these values indicate metabolic alkalosis. The kidneys maintain bicarbonate levels by filtering bicarbonate and returning it to the blood; they also produce new bicarbonate to replace that which is used in buffering. Therefore, a decreased HCO3 and an increased pH level indicate either retention of hydrogen ions by the kidneys or the elimination of HCO3 in an effort to compensate for respiratory alkalosis. Conversely, if the HCO3 level is increased and the pH is decreased, the kidneys have compensated for respiratory acidosis by retaining HCO3 or by eliminating hydrogen ions.
blood gas analysis, mixed venous blood gas analysis performed on a blood sample obtained from the pulmonary artery.
blood gas analysis, transcutaneous the determination of PO2 and PCO2 by placement of a heated electrode over the skin to get an inference of PaO2 and PaCO2.
blood group the phenotype of erythrocytes defined by one or more cellular antigenic structural groupings under the control of allelic genes. In clinical practice there are four main blood groups or blood types: A, B, O, and AB (see table). In addition to this major grouping there is an Rh-hR system that is important in the prevention of erythroblastosis fetalis resulting from incompatibility of blood groups in mother and fetus.

The ABO blood group system was first introduced in 1900 by Karl Landsteiner; in 1920 group AB was discovered by van Descatello and Sturli. Identification of these four major blood groups represented a major step toward resolving the problem of blood transfusion reactions resulting from donor-recipient incompatibility. In 1938 Landsteiner and Weiner discovered another blood factor related to maternal-fetal incompatibility. The factor was named Rh because the researchers were using rhesus monkeys in their studies. Further research has uncovered additional factors in the Rh group.

Although more than 90 factors have been identified, many of these are not highly antigenic and are not, therefore, a cause for concern in the typing of blood for clinical purposes.

The term factor, in reference to blood groups, is synonymous with antigen, and the reaction occurring between incompatible blood types is an antigen-antibody reaction. In cases of incompatibility, the antigen, located on the red blood cells, is an agglutinogen and the specific antibody, located in the serum, is an agglutinin. These are so named because whenever red blood cells with a certain factor come in contact with the agglutinin specific for it, there is agglutination or clumping of the erythrocytes.

In determining blood group, a sample of blood is taken and mixed with specially prepared sera. One serum, anti-A agglutinin, causes blood of group A to agglutinate; another serum, anti-B agglutinin, causes blood of group B to agglutinate. Thus, if anti-A serum alone causes clumping, the blood is group A; if anti-B serum alone causes clumping, it is group B. If both cause clumping, the blood group is AB, and if it is not clumped by either, it is identified as group O.
occult blood that present in such small amounts as to be detectable only by chemical tests or by spectroscopic or microscopic examination.
peripheral blood that obtained from acral areas, or from the circulation remote from the heart; the blood in the systemic circulation.
blood poisoning popular term for septicemia.
blood pressure
1. the pressure of the blood against the walls of any blood vessel.
2. the term usually refers to the pressure of the blood within the arteries, or arterial blood pressure. This pressure is determined by several interrelated factors, including the pumping action of the heart, the resistance to the flow of blood in the arterioles, the elasticity of the walls of the main arteries, the blood volume and extracellular fluid volume, and the blood's viscosity, or thickness.

The pumping action of the heart refers to how hard the heart pumps the blood (force of heartbeat), how much blood it pumps (the cardiac output), and how efficiently it does the job. Contraction of the heart, which forces blood through the arteries, is the phase known as systole. Relaxation of the heart between contractions is called diastole.

The main arteries leading from the heart have walls with strong elastic fibers capable of expanding and absorbing the pulsations generated by the heart. At each pulsation the arteries expand and absorb the momentary increase in blood pressure. As the heart relaxes in preparation for another beat, the aortic valves close to prevent blood from flowing back to the heart chambers, and the artery walls spring back, forcing the blood through the body between contractions. In this way the arteries act as dampers on the pulsations and thus provide a steady flow of blood through the blood vessels. Because of this, there are actually two blood pressures within the blood vessels during one complete beat of the heart: a higher blood pressure during systole (the contraction phase) and a lower blood pressure during diastole (the relaxation phase). These two blood pressures are known as the systolic pressure and the diastolic pressure, respectively.

It is generally agreed that a reading of 120 mm Hg systolic and 80 mm Hg diastolic are the norms for a blood pressure reading; that is, it represents the average blood pressure obtained from a large sampling of healthy adults. In general, a blood pressure of 95 mm Hg systolic and 60 mm Hg diastolic indicates hypotension. However, a reading equal to or below this level must be interpreted in the light of each patient's “normal” reading as determined by baseline data.

On the basis of validated research on the long-term effects of an elevated blood pressure, it is generally agreed that some degree of risk for major cardiovascular disease exists when the systolic pressure is greater than or equal to 140 mm Hg, and the diastolic pressure is greater than or equal to 90 mm Hg. Life expectancy is reduced at all ages and in both males and females when the diastolic pressure is above 90 mm Hg. (See accompanying table.)
Measurement of the Blood Pressure. The blood pressure is usually measured in the artery of the upper arm, with a sphygmomanometer.
Measurement of blood pressure. From Applegate, 2000.
This consists of a rubber cuff and a gauge or column of mercury for measuring pressure. The rubber cuff is wrapped about the patient's arm, and then air is pumped into the cuff by means of a rubber bulb. As the pressure inside the rubber cuff increases, the flow of blood through the artery is momentarily checked.

A stethoscope is placed over the artery at the elbow and the air pressure within the cuff is slowly released. As soon as blood begins to flow through the artery again, Korotkoff sounds are heard. The first sounds heard are tapping sounds that gradually increase in intensity. The initial tapping sound that is heard for at least two consecutive beats is recorded as the systolic blood pressure.

The first phase of the sounds may be followed by a momentary disappearance of sounds that can last from 30 to 40 mm Hg as the gauge needle (or mercury column) descends. It is important that this auscultatory gap not be missed; otherwise, either an erroneously low systolic pressure or high diastolic pressure will be obtained.

During the second phase following the temporary absence of sound there are murmuring or swishing sounds. As deflation of the cuff continues, the sounds become sharper and louder. These sounds represent phase three. During phase four the sounds become muffled rather abruptly and then are followed by silence, which represents phase five.

Although there is disagreement as to which of the latter phases should represent the diastolic pressure, it is usually recommended that phase five, the point at which sounds disappear, be used as the diastolic pressure for adults, and phase four be used for children. The reason for this is that children, having a high cardiac output, often will continue to produce sounds when the gauge is at a very low reading or even at zero. In some adult patients whose arterioles have lost their elasticity, the fifth phase is also extremely low or nonexistent. In these cases, it is recommended that three readings be recorded: phase one and phases four and five. For example, the blood pressure would be written as 140/96/0. On most occasions, however, the blood pressure is written as a fraction. The systolic pressure is written as the top number, a line is drawn, and the diastolic pressure is written as the bottom number.

Errors in blood pressure measurement can result from failure of the cuff to reach and compress the artery. The cuff diameter should be 20 per cent greater than the diameter of the limb, the bladder of the cuff must be centered over the artery, and the cuff must be wrapped smoothly and snugly to ensure proper inflation. When a mercury gauge is used, the meniscus should be at eye level to avoid a false reading.
Direct Measurement of Blood Pressure. Critically ill patients who require continuous monitoring of the blood pressure may have a catheter inserted into an artery and attached to a catheter-monitor-transducer system. The blood pressure is displayed on an oscilloscope at the bedside so that the patient's pressure can be determined at a glance. This intra-arterial technique of blood pressure monitoring provides accurate, objective, and continuous data on the patient's status.
blood pressure, mean arterial MAP; the average pressure within an artery over a complete cycle of one heartbeat; in the brachial artery, calculated to be the diastolic pressure plus 1/3 of the difference between the systolic and diastolic pressures.
blood stream bloodstream.
blood urea nitrogen see urea nitrogen.
blood volume
1. the total quantity of blood in the body; the plasma volume added to the red cell volume.
2. a laboratory test performed to determine this. The indicators used to determine these measurements are 125I-labeled human serum albumin for plasma volume and 51Cr-labeled erythrocytes for red cell volume. The regulation of blood volume in the circulatory system is affected by the intrinsic mechanism for fluid exchange at the capillary membranes and by hormonal influences and nervous reflexes that affect the excretion of fluids by the kidneys. A rapid decrease in the blood volume, as in hemorrhage, greatly reduces the cardiac output and creates a condition called shock or circulatory shock. Conversely, an increase in blood volume, as when there is retention of water and salt in the body because of renal failure, results in an increase in cardiac output. The eventual outcome of this situation is increased arterial blood pressure.

The blood volume in the pulmonary circulation is approximately 12 per cent of the total blood volume. Such conditions as left-sided heart failure and mitral stenosis can greatly increase the pulmonary blood volume while decreasing the systemic volume. As would be expected, right-sided heart failure has the opposite effect. The latter condition has less serious effects because the volume of the systemic circulation is about seven times that of the pulmonary circulation and it is therefore better able to accommodate a change in fluid volume.
Tests. Clinical assessment of blood volume can be accomplished in a number of ways, for example, by measuring the patient's blood pressure while he is lying down, sitting, and standing. The quality and volume of peripheral pulses will give information about blood volume, as does determining the ease and speed with which a compressed vein will refill after pressure is released. Neck veins that are engorged indicate hypervolemia; the collapse of these veins indicates hypovolemia. A more accurate assessment can be done through the use of intravascular catheters such as the central venous pressure catheter, which measures pressure in the right atrium, and the swan-ganz catheter, which measures pressure on both sides of the heart.

Measurement of blood volume is accomplished by using substances that combine with red blood cells, for example, iron, chromium, and phosphate, or substances that combine with plasma proteins. In either case the measurement of the blood volume is based on the “dilution” principle. That is, the volume of any fluid compartment can be measured if a given amount of a substance is dispersed evenly in the fluid within the compartment, and then the extent of dilution of the substance is measured.

For example, a small amount of radioactive chromium (51Cr), which is widely used to determine blood volume, is mixed with a sample of blood drawn from the patient. After about 30 minutes the 51Cr will have entered the red blood cells. The sample with the tagged red blood cells is then returned by injection into the patient's bloodstream. About 10 minutes later a sample is removed from the patient's circulating blood and the radioactivity level of this sample is measured. The total blood volume is calculated according to this formula:
When volume is used to arrive at the total blood volume, a dye (usually T-1824, also known as Evans blue) is injected into the circulating blood. The dye immediately combines with the blood proteins and within 10 minutes is dispersed throughout the circulatory system. A sample of blood is then drawn and the exact quantity of dye is measured. Using the information about plasma volume obtained by applying the above formula, the total blood volume can be calculated, provided the hematocrit is also known. The formula for this calculation is:
whole blood that from which none of the elements has been removed, sometimes specifically that drawn from a selected donor under aseptic conditions, containing citrate ion or heparin, and used as a blood replenisher.


The "circulating tissue" of the body; the fluid and its suspended formed elements that are circulated through the heart, arteries, capillaries, and veins; blood is the means by which 1) oxygen and nutritive materials are transported to the tissues, and 2) carbon dioxide and various metabolic products are removed for excretion. Blood consists of a pale yellow or gray-yellow fluid, plasma, in which are suspended red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.
See also: arterial blood, venous blood.
Synonym(s): haema [TA]
[A.S. blōd]




(blud) the fluid circulating through the heart, arteries, capillaries, and veins, carrying nutriment and oxygen to body cells, and removing waste products and carbon dioxide. It consists of the liquid portion (the plasma) and the formed elements (erythrocytes, leukocytes, and platelets).
arterial blood  oxygenated blood, found in the pulmonary veins, the left chambers of the heart, and the systemic arteries.
citrated blood  blood treated with sodium citrate or citric acid to prevent its coagulation.
cord blood  that contained in umbilical vessels at time of delivery of the infant.
occult blood  that present in such small quantities that it is detectible only by chemical tests or by spectroscopic or microscopic examination.
predonated autologous blood  blood donated prior to surgery or other invasive procedure for use in a possible autotransfusion.
venous blood  blood that has given up its oxygen to the tissues and is carrying carbon dioxide back through the systemic veins for gas exchange in the lungs.
whole blood  that from which none of the elements has been removed, sometimes specifically that drawn from a selected donor under aseptic conditions, containing citrate ion or heparin, and used as a blood replenisher.


a. The fluid consisting of plasma, blood cells, and platelets that is circulated by the heart through the vertebrate vascular system, carrying oxygen and nutrients to and waste materials away from all body tissues.
b. A similar fluid in animals other than vertebrates.
c. The juice or sap of certain plants.
2. A vital or animating force; lifeblood.
3. One of the four humors of ancient and medieval physiology, identified with the blood found in blood vessels, and thought to cause cheerfulness.
4. Temperament or disposition: a person of hot blood and fiery temper.
a. Descent from a common ancestor; parental lineage.
b. Family relationship; kinship.
c. Descent from noble or royal lineage: a princess of the blood.
d. Recorded descent from purebred stock.
e. National or racial ancestry.


Etymology: AS, blod
the liquid pumped by the heart through all the arteries, veins, and capillaries. The blood is composed of a clear yellow fluid, called plasma, and the formed elements, which are red cells, white cells, and platelets. The major function of the blood is to transport oxygen and nutrients to the cells and to remove carbon dioxide and other waste products. Adults normally have a total blood volume of 7% to 8% of body weight, or 70 mL/kg of body weight for men and about 65 mL/kg for women. Compare lymph. See also blood cell, erythrocyte, leukocyte, plasma, platelets.
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Hematology A circulating tissue composed of a fluid portion–plasma, suspended formed elements–RBCs, WBCs, platelets, and other components, including CO2, O2, proteins, glucose, cholesterol and other fats, which circulates in a closed system–the heart, arteries, capillaries and veins, and is charged with transporting O2 and nutrients to cells, and removing CO2 and waste products to the appropriate sites. See Artificial blood, Bad blood, Deoxygenated blood, Euroblood, Fecal occult blood, Frozen blood, Leukocyte-poor blood, Occult blood, Safe blood, Strawberry cream blood, Umbilical cord blood, Whole blood, Yellow blood. Cf Snake blood.


The fluid and its suspended formedelements that are circulated through the heart, arteries, capillaries, and veins; the means by which oxygen and nutritive materials are transported to the tissues, and carbon dioxide and various metabolic products are removed for excretion. The blood consists of a pale yellow or gray-yellow fluid, plasma, in which red blood cells (erythrocytes), white blood cells (leukocytes), and platelets are suspended.
See also: arterial blood, venous blood
[A.S. blōd]


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BLOOD COMPOSITION: Components of blood and relationship to other body tissues
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BLOOD COMPOSITION: Cell types found in smears of peripheral blood from normal individuals.
The cell-containing fluid that circulates through the heart, arteries, veins, and capillaries, carrying nourishment, electrolytes, hormones, vitamins, antibodies, heat, and oxygen to the tissues and taking away waste matter and carbon dioxide. See: erythropoietin


Blood has a distinctive, somewhat metallic, odor. Arterial blood is bright red or scarlet and usually pulsates if the artery has been cut. Venous blood is dark red or crimson and flows steadily from a cut vein.


Human blood is about 52% to 62% plasma and 38% to 48% cells. The plasma is mostly water, ions, proteins, hormones, and lipids. The cellular components are the erythrocytes (red blood cells [RBCs]), leukocytes (white blood cells [WBCs]), and thrombocytes (platelets). The leukocytes comprise neutrophils, eosinophils, basophils, lymphocytes, and monocytes. See: illustration; buffy coat; plasma; serum

An adult weighing 70 kg has a blood volume of about 5 L or 70 ml/kg of body weight. Blood constitutes about 7% to 8% of the body weight. The pH of the blood is from 7.35 to 7.45. The specific gravity of blood varies from 1.048 to 1.066, the cells being heavier and plasma lighter than this. Blood is of slightly higher specific gravity in men than in women. Specific gravity is higher after exercise and at night. See: blood count; cell; erythrocyte; leukocyte; plasma; platelet


In passing through the lungs, the blood gives up carbon dioxide and absorbs oxygen; after leaving the heart, it is carried to the tissues as arterial blood and then returned to the heart in the venous system. It moves in the aorta at an average speed of 30 cm/sec, and it makes the circuit of the vascular system in about 60 seconds. RBCs carry oxygen; WBCs participate in the immune response to infection; platelets are important in blood clotting. The plasma transports nutrients, waste products, hormones, carbon dioxide, and other substances, and contributes to fluid-electrolyte balance and thermal regulation.


RBCs are produced in the red bone marrow at the rate of about 2,400,000/sec, and each RBC lives for about 120 days. In healthy individuals, the concentration of RBCs in the blood remains stable over time. Platelets and WBCs are also produced in the red bone marrow, and agranular WBCs are produced in lymphatic tissue.

clotting of blood

See: coagulation, blood

cord blood

The blood present in the umbilical vessels connecting the placenta to the fetus. Because cord blood is immunologically immature, it is esp. useful in transfusion therapy and hematological transplantation.

defibrinated blood

Whole blood from which fibrin has been removed. It does not clot.

formed elements of blood

Blood cells, as opposed to blood proteins or other chemical constituents of blood.

fresh blood

Blood that has been collected less than 48 hours prior to its use in a transfusion.

occult blood

See: occult

oxygenated blood

Blood that has been exposed to oxygen in the lung; sometimes referred to as arteriolized blood.

predonation of blood

autologous blood transfusion.

reconstituted blood

A blood product used in transfusion therapy composed of components of blood (packed red blood cells plus plasma), which have been recombined after their separation and storage.

sludged blood

Hemagglutinated blood.

unit of blood

Approx. 1 pint (473 ml) of blood, the usual amount used in adult transfusion.


A complex fluid vital to life and circulated by the pumping action of the heart. The average blood volume is 5 litres. It is a transport medium, especially for oxygen, which it carries in the red blood cells linked to the HAEMOGLOBIN with which they are filled. It also transports dissolved sugars, dissolved proteins such as ALBUMIN and GLOBULIN, protein constituents (AMINO ACIDS), fat-protein combinations (LIPOPROTEINS), emulsified fats (TRIGLYCERIDES), vitamins, minerals and hormones. Blood also carries waste products such as carbon dioxide, urea, lactic acid, and innumerable other substances. In addition to the countless red cells the blood carries enormous numbers of uncoloured cells most of which are concerned in the defence of the individual against infection and cancer. It also contains large numbers of small non-nucleated bodies called PLATELETS which are concerned with BLOOD CLOTTING (coagulation).
Bloodclick for a larger image
Fig. 71 Blood . The constituents of blood.


a connective tissue with a liquid matrix called BLOOD PLASMA. Suspended in the plasma are three types of cell which form about 45% of total blood volume:
  1. red blood cells or ERYTHROCYTES,
  2. white blood cells or LEUCOCYTES and
  3. cell fragments or PLATELETS.


fluid circulating in the vascular system - the heart and blood vessels. The total volume is typically ∼5 litres in a man weighing 70 kg. The fluid plasma, carrying a great variety of substances, from simple inorganic ions to complex protein molecules, accounts for a little over half the blood volume and the cells ('formed elements') for the rest. See also body fluids, electrolytes, erythrocytes, extracellular fluids, leucocytes.


connective tissue, consisting of fluid plasma in which is suspended cells (e.g. erythrocytes, leukocytes, platelets), soluble proteins (e.g. immunoglobulins, enzymes) and salts (e.g. calcium ions) circulating the body through arteries, capillaries and veins, transporting oxygen, nutrients and drugs to tissues and removing carbon dioxide and metabolic byproducts from the tissues for excretion


The "circulating tissue" of the body; the fluid and its suspended formed elements that are circulated through the heart, arteries, capillaries, and veins; blood is the means by which: 1) oxygen and nutritive materials are transported to the tissues, and 2) carbon dioxide and various metabolic products are removed for excretion. Blood consists of a pale yellow or gray-yellow fluid, plasma, in which are suspended red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.
See also: arterial blood, venous blood
[A.S. blōd]


n the fluid circulating through the heart, arteries, capillaries, and veins; carries nutrients and oxygen to body tissues.
blood alcohol concentration (BAC),
n the amount of ingested alcohol absorbed into the body's cells and intercellular fluid; measured by a percentage based on milligrams of alcohol per deciliter of blood. The higher the BAC, the greater the physical and mental impairment. Most states have a legal limit of 0.10% (100 mg/dL) or lower for intoxication.
blood, arterial,
n oxygen-rich blood taken away from the heart through the arteries and used as nourishment for the tissues of the body.


the red fluid that circulates through the heart, arteries, capillaries and veins carrying nutrients and oxygen to the body tissues and metabolites away from them. It consists of a yellow, protein-rich fluid, the plasma, and the cellular elements including leukocytes, erythrocytes and platelets. It has a high viscosity and osmotic tension and clots on exposure to air and to damaged tissue. It has an essential role in the maintenance of fluid balance.
In an emergency, blood cells and antibodies carried in the blood are brought to a point of infection, or blood-clotting substances are carried to a break in a blood vessel. The blood carries hormones from the endocrine glands to the organs they influence. And it helps in the regulation of body temperature by carrying excess heat from the interior of the body to the surface layers of the skin, where the heat is dissipated to the surrounding air. See also bloody.

arterial blood
oxygenated blood in the arterial side of the circulation between the cardiac ventricles and the capillaries.
blood buffers
substances which enable the blood to absorb much acidity without significant change in pH. The principal ones are the bicarbonate and hemoglobin buffers.
central blood
blood from the pulmonary venous system; sometimes applied to splanchnic blood, or blood obtained from chambers of the heart or from bone marrow.
central venous blood
unoxygenated blood collected centrally from the right atrium or venae cavae.
citrated blood
blood treated with sodium citrate to prevent its coagulation.
blood clotting cascade
see coagulation cascade.
cord blood
that contained in the umbilical vessels at the time of delivery of the fetus.
defibrinated blood
whole blood from which fibrin has been separated during the clotting process.
extracorporeal blood flow
see extracorporeal circulation.
blood in feces
see melena.
blood islet
aggregates of splanchnic mesoderm on the surface of the yolk sac and allantois; the first blood cells in the embryo.
blood lactate
this estimation has good predictive value in a number of diseases, e.g. intestinal obstruction in horses.
blood in milk
appears as clots or as diffuse red tint. Common only in recently calved cows or after trauma. Of no disease significance but renders the milk unsuitable for sale.
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Blood clots in pink milk. By permission from Blowey RW, Weaver AD, Diseases and Disorders of Cattle, Mosby, 1997
occult blood
that present in such small amounts as to be detectable only by chemical tests or by spectroscopic or microscopic examination. See also occult blood test.
blood osmolality
see serum osmolality.
peripheral blood
that obtained from the circulation remote from the heart; the blood in the systemic circulation.
selective blood agar
see blood agar.
shunted blood
blood which is not oxygenated in the lung because it passes through unaerated tissue.
sludged blood
blood in which the red cells have become aggregated into clumps and is most marked where the flow rate is slowest, i.e. in the capillaries.
blood solutes
see individual elements, metabolic products, hormones and the like.
stiff blood agar
see blood agar.
blood substitutes
synthetic substances that may be used in place of blood or its components include dextran, hydroxyethyl starch, polyvinylpyrrolidone, gelatin and perfluorocarbon.
blood urea nitrogen (BUN)
see urea nitrogen.
blood urea test
see urea nitrogen.
blood in urine
venous blood
blood which has passed through the capillaries and discharged its oxygen load to tissues and relieved the tissue load of carbon dioxide by absorbing it, and is on its way to the lungs to reverse these processes; is dark red in color due to the high concentration of reduced hemoglobin.
blood volume expanders
are used in the treatment of shock to restore tissue perfusion. Various fluids including whole blood, plasma, crystalloids and colloids may be used.
blood in vomitus
whole blood
that from which none of the elements has been removed, especially that drawn from a selected donor under aseptic conditions, containing citrate ion or heparin, and used as a blood replenisher.

Patient discussion about blood

Q. does serratrol thin your blood?

A. i don't know about blood thinning but i do know that when i looked for information about it (i looked for an alternative medicine for my mother) i found out this review about it:

according to this after reviewing 34 researches done on serratrol - they found no evidence supporting the claim it helps.

Q. what are Blood thiners what pilles are blood thinners

A. anticoagulants, given in order to avoid blood clots in your systems. some heard conditions (for example) like damaged valves can cause blood to clot on them and then there's a big risk that it'll detach itself and move around your body until it'll get stuck and block the blood vessel. can be blood vessels to the leg, hand,lungs or even brain. the most well known anticoagulants are Warfarin and Low Molecular Heparin (which is given in a shot not per os like WArfarin).
hope i helped :)

Q. how can i reduce my blood pressure?

A. The main steps in lowering high blood pressure is to take some very important changes in lifestyle- consuming much less salt in food, losing weight and exercising regulary. If this doesn't help (and usually it doesn't help mainly when people don't try hard enought and make an effort), medications can be added to control the blood pressure.

More discussions about blood
References in periodicals archive ?
Individuals with this condition lack sufficient quantities of thrombocytes (platelets) to initiate the normal clotting of blood.
TTP/HUS involves a combination of symptoms, including abnormal clotting of blood in small blood vessels.
Thrombophlebitis (inflammation and clotting of blood in veins) or deep vein thrombosis (clotting of blood in the deeper veins) may sometimes be associated with varicose veins.
The new treatment, called Xyntha Antihemophilic Factor (Recombinant) Plasma/Albumin Free, is a genetically engineered version of factor VIII, a protein essential for the clotting of blood.