The main mechanism by which blood clots are formed, involving a complex series of reactions in the blood plasma (see blood clotting).
The blood pressure is biphasic, being greatest (systolic pressure) at each heartbeat and falling (diastolic pressure) between beats. The average systolic pressure is around 100 mm Hg in children and 120 mm Hg in young adults, generally rising with age as the arteries get thicker and harder. Diastolic pressure in a healthy young adult is about 80 mm Hg, and a rise in diastolic pressure is often a surer indicator of HYPERTENSION than is a rise in systolic pressure; the latter is more sensitive to changes of body position and emotional mood. Hypertension has various causes, the most important of which are kidney disease (see KIDNEYS, DISEASES OF), genetic predisposition and, to some extent, mental stress. Systolic pressure may well be over 200 mm Hg. Abnormal hypertension is often accompanied by arterial disease (see ARTERIES, DISEASES OF) with an increased risk of STROKE, heart attack and heart failure (see HEART, DISEASES OF). Various ANTIHYPERTENSIVE DRUGS are available; these should be carefully evaluated, considering the patient’s full clinical history, before use.
HYPOTENSION may result from super?cial vasodilation (for example, after a bath, in fevers or as a side-e?ect of medication, particularly that prescribed for high blood pressure) and occur in weakening diseases or heart failure. The blood pressure generally falls on standing, leading to temporary postural hypotension – a particular danger in elderly people.... blood pressure
Composition The cellular components are red cells or corpuscles (ERYTHROCYTES), white cells (LEUCOCYTES and lymphocytes – see LYMPHOCYTE), and platelets.
The red cells are biconcave discs with a diameter of 7.5µm. They contain haemoglobin
– an iron-containing porphyrin compound, which takes up oxygen in the lungs and releases it to the tissue.
The white cells are of various types, named according to their appearance. They can leave the circulation to wander through the tissues. They are involved in combating infection, wound healing, and rejection of foreign bodies. Pus consists of the bodies of dead white cells.
Platelets are the smallest cellular components and play an important role in blood clotting (see COAGULATION).
Erythrocytes are produced by the bone marrow in adults and have a life span of about 120 days. White cells are produced by the bone
marrow and lymphoid tissue. Plasma consists of water, ELECTROLYTES and plasma proteins; it comprises 48–58 per cent of blood volume. Plasma proteins are produced mainly by the liver and by certain types of white cells. Blood volume and electrolyte composition are closely regulated by complex mechanisms involving the KIDNEYS, ADRENAL GLANDS and HYPOTHALAMUS.... blood
In blood transfusion, the person giving and the person receiving the blood must belong to the same blood group, or a dangerous reaction will take place from the agglutination that occurs when blood of a di?erent group is present. One exception is that group O Rhesus-negative blood can be used in an emergency for anybody.
| Agglutinogens | Agglutinins | Frequency | |
| in the | in the | in Great | |
| Group | erythrocytes | plasma | Britain |
| AB | A and B | None | 2 per cent |
| A | A | Anti-B | 46 per cent |
| B | B | Anti-A | 8 per cent |
| O | Neither | Anti-A and | 44 per cent |
| A nor B | Anti-B | ||
Rhesus factor In addition to the A and B agglutinogens (or antigens), there is another one known as the Rhesus (or Rh) factor – so named because there is a similar antigen in the red blood corpuscles of the Rhesus monkey. About 84 per cent of the population have this Rh factor in their blood and are therefore known as ‘Rh-positive’. The remaining 16 per cent who do not possess the factor are known as ‘Rh-negative’.
The practical importance of the Rh factor is that, unlike the A and B agglutinogens, there are no naturally occurring Rh antibodies. However, such antibodies may develop in a Rh-negative person if the Rh antigen is introduced into his or her circulation. This can occur (a) if a Rh-negative person is given a transfusion of Rh-positive blood, and (b) if a Rh-negative mother married to a Rh-positive husband becomes pregnant and the fetus is Rh-positive. If the latter happens, the mother develops Rh antibodies which can pass into the fetal circulation, where they react with the baby’s Rh antigen and cause HAEMOLYTIC DISEASE of the fetus and newborn. This means that, untreated, the child may be stillborn or become jaundiced shortly after birth.
As about one in six expectant mothers is Rh-negative, a blood-group examination is now considered an essential part of the antenatal examination of a pregnant woman. All such Rh-negative expectant mothers are now given a ‘Rhesus card’ showing that they belong to the rhesus-negative blood group. This card should always be carried with them. Rh-positive blood should never be transfused to a Rh-negative girl or woman.... blood groups
Habitat: Widely distributed throughout North America.
Features ? Root reddish-brown, wrinkled lengthwise, about half-inch thick. Fracture short. Section whitish, with many small, red resin cells which sometimes suffuse the whole. Heavy odour, bitter and harsh to the taste.Part used ? Root.Action: Stimulant, tonic, expectorant.
Pulmonary complaints and bronchitis. Should be administered in whooping-cough and croup until emesis occurs. The powdered root is used as a snuff in nasal catarrh, and externally in ringworm and other skin eruptions. The American Thomsonians use it in the treatment of adenoids. Dose, 10 to 20 grains of the powdered root.... blood rootThe three-stage process of coagulation is complex, involving many di?erent substances. There are two cascading pathways of biochemical reactions for activating coagulation of blood. The extrinsic pathway is the main physiological mechanism, which is triggered when blood vessels are damaged, usually by trauma or surgery. The intrinsic pathway is activated by internal disruption of the wall of a blood vessel. The basic pattern is broadly the same for both and is summarised simply as follows:
prothrombin + calcium + thromboplastin
thrombin + ?brinogen
?brin
Prothrombin and calcium are normally present in the blood. Thromboplastin is an enzyme which is normally found in the blood platelets and in tissue cells. When bleeding occurs from a blood vessel, there is always some damage to tissue cells and to the blood platelets. As a result of this damage, thromboplastin is released and comes into contact with the prothrombin and calcium in the blood. In the presence of thromboplastin and calcium, prothrombin is converted into thrombin, which in turn interacts with ?brinogen – a protein always present in the blood – to form ?brin. Fibrin consists of needle-shaped crystals which, with the assistance of the blood platelets, form a ?ne network in which the blood corpuscles become enmeshed. This meshwork, or CLOT as it is known, gradually retracts until it forms a tight mass which, unless the tissue injury is very severe or a major artery has been damaged, prevents any further bleeding. It will thus be seen that clotting, or coagulation, does not occur in the healthy blood vessel because there is no thromboplastin present. There is now evidence suggesting that there is an anti-thrombin substance present in the blood in small amounts, and that this substance antagonises any small amounts of thrombin that may be formed as a result of small amounts of thromboplastin being released.
The clotting or coagulation time is the time taken for blood to clot and can be measured under controlled conditions to ensure that it is normal (3–8 minutes). In certain diseases – HAEMOPHILIA, for example – clotting time is greatly extended and the danger of serious haemorrhage enhanced.... coagulation
When a blood vessel is damaged, it constricts immediately to reduce blood flow to the area. The damage sets off a series of chemical reactions that lead to the formation of a clot to seal the injury. First, platelets around the injury site are activated, becoming sticky and adhering to the blood-vessel wall. Then, the activated platelets release chemicals, which, in turn, activate blood clotting factors. These factors, together with vitamin K, act on fibrinogen and convert it to fibrin. Strands of fibrin form a meshwork, which traps red blood cells to form a clot.
There are several anticlotting mechanisms to prevent the formation of unwanted clots. These include prostacyclin (a prostaglandin), which prevents platelet aggregation, and plasmin, which breaks down fibrin (see fibrinolysis). Blood flow washes away active coagulation factors; and the liver deactivates excess coagulation factors.
Defects in blood clotting may result in bleeding disorders.
Excessive clotting (thrombosis) may be due to an inherited increase or defect in a coagulation factor (see factor V), the use of oral contraceptives, a decrease in the level of enzymes that inhibit coagulation, or sluggish blood flow through a particular area.
Treatment is usually with anticoagulant drugs such as heparin or warfarin.... blood clotting
Toxins. In conditions such as chronic glomerulonephritis (see KIDNEYS, DISEASES OF) and URAEMIA there is a severe anaemia due to the e?ect of the disease upon blood formation.
Drugs. Certain drugs, such as aspirin and the non-steroidal anti-in?ammatory drugs, may cause occult gastrointestinal bleeding.... defective blood formation
In one part of the body there is a further complication. The veins coming from the bowels, charged with food material and other products, split up, and their blood undergoes a second capillary circulation through the liver. Here it is relieved of some food material and puri?ed, and then passes into the inferior vena cava, and so to the right atrium. This is known as the portal circulation.
The circle is maintained always in one direction by four valves, situated one at the outlet from each cavity of the heart.
The blood in the arteries going to the body generally is bright red, that in the veins dull red in colour, owing to the former being charged with oxygen and the latter with carbon dioxide (see RESPIRATION). For the same reason the blood in the pulmonary artery is dark, that in the pulmonary veins is bright. There is no direct communication between the right and left sides of the heart, the blood passing from the right ventricle to the left atrium through the lungs.
In the embryo, before birth, the course of circulation is somewhat di?erent, owing to the fact that no nourishment comes from the bowels nor air into the lungs. Accordingly, two large arteries pass out of the navel, and convey blood to be changed by contact with maternal blood (see PLACENTA), while a large vein brings this blood back again. There are also communications between the right and left atria, and between pulmonary artery and aorta. The latter is known as the ductus arteriosus. At birth all these extra vessels and connections close and rapidly shrivel up.... circulatory system of the blood
Menstruation. The regular monthly loss of blood which women sustain as a result of menstruation always puts a strain on the blood-forming organs. If this loss is excessive, then over a period of time it may lead to quite severe anaemia.
Childbirth. A considerable amount of blood is always lost at childbirth; if this is severe, or if the woman was anaemic during pregnancy, a severe degree of anaemia may develop.
Bleeding from the gastrointestinal tract. The best example here is anaemia due to ‘bleeding piles’ (see HAEMORRHOIDS). Such bleeding, even though slight, is a common cause of anaemia in both men and women if maintained over a long period of time. The haemorrhage may be more acute and occur from a DUODENAL ULCER or gastric ulcer (see STOMACH, DISEASES OF), when it is known as haematemesis.
Certain blood diseases, such as PURPURA and HAEMOPHILIA, which are characterised by bleeding.... loss of blood
Blood tonic. Decoction, tablets, tinctures or fluid extracts:– Echinacea 3; Burdock 2; Goldenseal 1. See also: ALTERATIVES. ... blood purifiers
Red blood cells (also known as RBCs, red blood corpuscles, or erythrocytes) transport oxygen from the lungs to the tissues (see respiration). Each is packed with haemoglobin, enzymes, minerals, and sugars. Abnormalities can occur in the rate at which RBCs are either produced or destroyed, in their numbers, and in their shape, size, and haemoglobin content, causing forms of
anaemia and polycythaemia (see blood, disorders of).
White blood cells (also called WBCs, white blood corpuscles, or leukocytes) protect the body against infection and fight infection when it occurs. The 3 main types of are granulocytes (also called polymorphonuclear leukocytes), monocytes, and lymphocytes. Granulocytes are further classified as neutrophils, eosinophils, or basophils, and each type of granulocyte has a role in either fighting infection or in inflammatory or allergic reactions. Monocytes and lymphocytes also play an important part in the immune system. Lymphocytes are usually formed in the lymph nodes. One type, a T-lymphocyte, is responsible for the delayed hypersensitivity reactions
White (see allergy) and Red blood blood cell is also involved in cell (neutrophil) protection against cancer. T-lymphocytes manufacture chemicals, known as lymphokines, which affect the function of other cells. In addition, the T-cells moderate the activity of B-lymphocytes, which form the antibodies that can prevent a second attack of certain infectious diseases. Platelets (also known as thrombocytes), are the smallest blood cells and are important in blood clotting.
The numbers, shapes, and appearance of the various types of blood cell are of great value in the diagnosis of disease (see blood count; blood film).... blood cells
Occasionally, there is an underlying cause (such as an infection or, very rarely, cancer) that requires treatment.
Blood in the semen may also occur after a prostate biopsy.... semen, blood in the
Donated blood is tested for a range of infectious agents such as hepatitis B and hepatitis C and antibodies to HIV. After being classified into blood groups, the blood is stored in a blood bank, either whole or separated into its different components (see blood products). Apheresis is a type of blood donation in which only a specific blood component, such as plasma, platelets, or white cells, is withdrawn from the donor. blood film A test that involves smearing a drop of blood on to a glass slide for examination under a microscope. The blood film is stained with dyes to make the blood cells show up clearly.
The test allows the shape and appearance of blood cells to be checked for any abnormality, such as the sickleshaped red blood cells characteristic of sickle cell anaemia.
The relative proportions of the different types of white blood cells can also be counted.
This examination, called a differential white cell count, may be helpful in diagnosing infection or leukaemia.
Blood films are also used in diagnosing infections, such as malaria, in which the parasites can be seen inside the red blood cells.
Blood films are usually carried out together with a full blood count.... blood donation
Platelets may be given in transfusions for people with blood-clotting disorders. Patients who have life-threatening infections may be treated with granulocytes, a type of white blood cell. Fresh frozen plasma is used to correct many types of bleeding disorder because it contains all the clotting factors. Albumin, prepared from the plasma of whole blood, is used mainly to treat shock resulting from severe blood loss until compatible whole blood becomes available. Purified albumin preparations are used to treat nephrotic syndrome and chronic liver disease.
Concentrates of blood clotting factors and are used in the treatment of haemophilia and Christmas disease.
Immunoglobulins (also called antibodies), which are extracted from blood plasma, can be given by injection (see immunoglobulin injection) to protect people who are unable to produce their own antibodies or have already been exposed to an infectious agent, or to provide short-term protection against hepatitis A.
Immunoglobulins are given in large doses to treat certain autoimmune disorders.... blood products
in septicaemia. Microbiology also looks for antibodies in the blood, which may confirm immunity to an infection. blood transfusion The infusion of large volumes of blood or blood products directly into the bloodstream to remedy severe blood loss or to correct chronic anaemia. In an exchange transfusion, nearly all of the recipient’s blood is replaced by donor blood. Before a transfusion, a sample of the recipient’s blood is taken to identify the blood groups, and it is matched with suitable donor blood. The donor blood is transfused into an arm vein through a plastic cannula. Usually, each unit (about 500 ml) of blood is given over 1–4 hours; in an emergency, 500 ml may be given in a couple of minutes. The blood pressure, temperature, and pulse are monitored during the procedure.
If mismatched blood is accidentally introduced into the circulation, antibodies in the recipient’s blood may cause donor cells to burst, leading to shock or kidney failure. Less severe reactions can produce fever, chills, or a rash. Reactions can also occur as a result of an allergy to transfused blood components. All
blood used for transfusion is carefully screened for a number of infectious agents, including HIV (the AIDS virus) and hepatitis B and hepatitis C.
In elderly or severely anaemic patients, transfusion can overload the circulation, leading to heart failure.
In patients with chronic anaemia who need regular transfusion over many years, excess iron may accumulate (haemosiderosis) and damage organs such as the heart, liver, and pancreas.
Treatment with desferrioxamine to remove excess iron may be needed.... blood tests
Investigations into coughing up blood include chest X-ray, and, in some cases, bronchoscopy. In about a 3rd of cases, no underlying cause is found. Treatment depends on the cause.... coughing up blood
The cause of vomiting blood is investigated by endoscopy of the oesophagus and stomach, or by barium X-ray examinations. If blood loss is severe, blood transfusion, and possibly surgery to stop the bleeding, may be required.... vomiting blood
There are more than 30 blood group systems, one of the most important of which is the ABO system. This system is based on the presence or absence of antigens A and B: blood of groups A and B contains antigens A and B, respectively; group AB contains both antigens and group O neither. Blood of group A contains antibodies to antigen B; group B blood contains anti-A antibodies or *isoagglutinins; group AB has neither antibody and group O has both. A person whose blood contains either (or both) of these antibodies cannot receive a transfusion of blood containing the corresponding antigens. The table illustrates which blood groups can be used in transfusion for each of the four groups.
Blood group... blood group
NHS Blood and Transplant website... nhs blood and transplant
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