Diseases of the Blood - Hemorrhagic or clotting-deficiency diseases



The blood has the ability to change from a fluid to a solid and back to a fluid again. The change to a solid is called clotting . There are mechanisms not only for sealing off breaks in the circulatory system when serious blood loss is threatened, but also for breaking down the seals, or clots, once the damage has been repaired and the danger of blood loss is eliminated. Both mechanisms are in continuous, dynamic equilibrium, a delicate balance between tissue repair and clot dissolution to keep us from bleeding or literally clogging to death.

Clotting involves a very complex chain of chemical events. The key is the conversion of an inactive blood protein, fibrinogen , into a threadlike sealant known as fibrin . Stimulus for this conversion is an enzyme called thrombin , which normally also circulates in an inactive state as prothrombin (formed from vitamin K in the daily diet).

For a clot to form, however, inactive prothrombin must undergo a chemical transformation into thrombin, a step requiring still another chemical— thromboplastin . This agent comes into play only when a tissue or vessel has been injured so as to require clot protection. There are two ways for thromboplastin to enter the bloodstream to spark the chain of events. One involves the release by the injured tissue of a substance that reacts with plasma proteins to produce thromboplastin. The other requires the presence of blood platelets (small particles that travel in the blood) and several plasma proteins, including the so-called antihemophilic factor. Platelets tend to clump at the site of vessel injury, where they disintegrate and ultimately release thromboplastin, which, in the presence of blood calcium, triggers the prothrombinthrombin conversion.

The clot-destroying sequence is very similar to that involved in clot formation, with the key enzyme, ftbrinolysin , existing normally in an inactive state ( profibrinolysin ). There are also other agents (e.g., heparin ) in the blood ready to retard or prevent the clotting sequence, so that it does not spread to other parts of the body.

Naturally, grave dangers arise should these complex mechanisms fail. For the moment, we shall concern ourselves with hemorrhagic disorders arising from a failure of the blood to clot properly. Disorders stemming from excessive clotting are discussed below under “Diseases of the Blood Vessels” because they are likely to happen as a consequence of preexisting problems in the vessel walls.

Hemophilia

Hemophilia is probably the best known (although relatively rare) of the hemorrhagic disorders, because of its prevalence among the royal families of Europe. In hemophilia the blood does not clot properly and bleeding persists. Those who have this condition are called hemophiliacs or bleeders. The disease is inherited, and is transmitted by the mother, but except in very rare cases only the male offspring are affected. Hemophilia stems from a lack of one of the plasma proteins associated with clotting, antihemophilic factor ( AHF ).

The presence of hemophilia is generally discovered during early childhood. It is readily recognized by the fact that even small wounds bleed profusely and can trigger an emergency. Laboratory tests for clotting speed are used to confirm the diagnosis. Further investigation may occasionally turn up the condition in other members of the family.

In advanced stages, hemophilia may lead to anemia as a result of excessive and continuous blood loss. Bleeding in the joints causes painful swelling, which over a long period of time can lead to permanent deformity and hemophilic arthritis. Hemophiliacs must be under constant medical care in order to receive quick treatment in case of emergencies.

The Circulatory System

Treating bleeding episodes may involve the administration of AHF alone so as to speed up the clotting sequence. If too much blood is lost a complete transfusion may be necessary. Thanks to modern blood bank techniques, large quantities of whole blood can be made readily available. Bed rest and hospitalization may also be required. For bleeding in the joints, an ice pack is usually applied.

Proper dental hygiene is a must for all hemophiliacs. Every effort should be made to prevent tooth decay. Parents of children with the disease should inform the dentist so that all necessary precautions can be taken. Even the most common procedures, such as an extraction, can pose a serious hazard. Only absolutely essential surgery should be performed on hemophiliacs, with the assurance that large amounts of plasma are on hand.

Purpura

Purpura refers to spontaneous hemorrhaging over large areas of the skin and in mucous membranes. It results from a deficiency in blood platelets, elements essential to clotting. Purpura is usually triggered by other conditions: certain anemias, leukemia, sensitivity to drugs, or exposure to ionizing radiation. In newborns it may be linked to the prenatal transfer from the maternal circulation of substances that depress platelet levels. Symptoms of purpura include the presence of blood in the urine, bleeding from the mucous membranes of the mouth, nose, intestines, and uterus. Some forms of the disease cause arthritic changes in joints, abdominal pains, diarrhea and vomiting—and even gangrene of the skin, when certain infectious organisms become involved.

To treat purpura in newborns, physicians may exchange the infant's blood with platelet-packed blood. Sometimes drug therapy with steroids (i.e., cortisone) is prescribed. In adults with chronic purpura it may be necessary to remove the spleen, which plays an important role in eliminating worn-out blood components, including platelets, from the circulation. Most physicians prescribe large doses of steroids coupled with blood transfusions. Purpura associated with infection and gangrene also requires appropriate antibiotic therapy.



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