blood(redirected from blood urea nitrogen (BUN))
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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.
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.
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.
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.)
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.
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.
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:
See also: arterial blood, venous blood.
bloodHematology 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.
See also: arterial blood, venous blood
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 bloodSee: coagulation, blood
formed elements of blood
occult bloodSee: occult
predonation of bloodautologous blood transfusion.
unit of blood
bloodA 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).
blooda 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:
See also: arterial blood, venous blood
Patient discussion about blood
Q. does serratrol thin your blood?
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
hope i helped :)
Q. how can i reduce my blood pressure?