Stimate

Definition

Platelets are elements within the bloodstream that recognize and cling to damaged areas inside blood vessels. When they do this, the platelets trigger a series of chemical changes that result in the formation of a blood clot. There are certain hereditary disorders that affect platelet function and impair their ability to start the process of blood clot formation. One result is the possibility of excessive bleeding from minor injuries or menstrual flow.

Description

Platelets are formed in the bone marrow--a spongy tissue located inside the long bones of the body--as fragments of a large precursor cell (a megakaryocyte). These fragments circulate in the bloodstream and form the first line of defense against blood escaping from injured blood vessels.

Damaged blood vessels release a chemical signal that increases the stickiness of platelets in the area of the injury. The sticky platelets adhere to the damaged area and gradually form a platelet plug. At the same time, the platelets release a series of chemical signals that prompt other factors in the blood to reinforce the platelet plug. Between the platelet and its reinforcements, a sturdy clot is created that acts as a patch while the damaged area heals.

There are several hereditary disorders characterized by some impairment of the platelet's action. Examples include von Willebrand's disease, Glanzmann's thrombasthenia, and Wiskott-Aldrich syndrome. Vulnerable aspects of platelet function include errors in the production of the platelets themselves or errors in the formation, storage, or release of their chemical signals. These defects can prevent platelets from responding to injuries or from prompting the action of other factors involved in clot formation.

Causes & symptoms

Platelet function disorders can be inherited, but they may also occur as a symptom of acquired diseases or as a side effect of certain drugs, including aspirin. Common symptoms of platelet function disorders include bleeding from the nose, mouth, vagina, or anus; pinpoint bruises and purplish patches on the skin; and abnormally heavy menstrual bleeding.

Diagnosis

In diagnosing platelet function disorders, specific tests are needed to determine whether the problem is caused by low numbers of platelets or impaired platelet function. A blood platelet count and bleeding time are common screening tests. If these tests confirm that the symptoms are due to impaired platelet function, further tests are done-- such as platelet aggregation or an analysis of the platelet proteins-- that pinpoint the exact nature of the defect.

Treatment

Treatment is intended to prevent bleeding and stop it quickly when it occurs. For example, patients are advised to be careful when they brush their teeth to reduce damage to the gums. They are also warned against taking medications that interfere with platelet function. Some patients may require iron and folate supplements to counteract potential anemia. Platelet transfusions may be necessary to prevent life-threatening hemorrhaging in some cases. Bone marrow transplantation can cure certain disorders but also carries some serious risks. Hormone therapy is useful in treating heavy menstrual bleeding. Von Willebrand's disease can be treated with desmopressin (DDAVP, Stimate).

Prognosis

The outcome depends on the specific disorder and the severity of its symptoms. Platelet function disorders range from life-threatening conditions to easily treated or little-noticed problems.

Prevention

Inherited platelet function disorders cannot be prevented except by genetic counseling; however, some acquired function disorders may be guarded against by avoiding substances that trigger the disorder.

Key Terms

Anemia

A condition in which inadequate quantities of hemoglobin and red blood cells are produced.

Bone marrow

A spongy tissue located within the body's flat bones-- including the hip and breast bones and the skull. Marrow contains stem cells, the precursors to platelets and red and white blood cells.

Hemoglobin

The substance inside red blood cells that enables them to carry oxygen.

Megakaryocyte

A large bone marrow cell with a lobed nucleus that is the precursor cell of blood platelets.

Platelets

Fragments of a large precursor cell (a megakaryocyte) found in the bone marrow. These fragments adhere to areas of blood vessel damage and release chemical signals that direct the formation of a blood clot.

Further Reading

For Your Information

Books

• Ware, J. Anthony, and Barry S. Coller. "Platelet Morphology, Biochemistry, and Function." In Williams Hematology, edited by Ernest Beutler et al. New York: McGraw-Hill, Inc., 1995.
• Williams, William J. "Classification and Clinical Manifestations of Disorders of Hemostasis." In Williams Hematology, edited by Ernest Beutler et al. New York: McGraw-Hill, Inc., 1995.

  Periodicals

• Liesner, R. J., and S. J. Machin. "Platelet Disorders." British Medical Journal 314, no. 7083 (1997): 809.

Gale Encyclopedia of Medicine. Gale Research, 1999.