D. Hildbrand

Introductory text about blood clotting:

Mr and Mrs Bean are the parents of a 12-year-old son and 2 younger daughters. They do not worry too much about their daughters but when they have to go to the dentist with their son, they get terribly afraid and even fear for their son's life. Why? When their son once had a tooth pulled the bleeding went on and on and it took a very long time until it could be stopped.

Mr Davidson, a 60-year-old manager, on the other hand has to take a tablet every morning to prevent unwanted blood clots in his blood vessels. This was found out four months ago when he suddenly got a terrible pain in the chest and had to be taken to hospital immediately.

BLOOD CLOTTING

(BLOOD COAGULATION)

Bleeding is useful because it carries germs away from the wound, but it must not go on for too long. To prevent serious loss of blood and the entry of more germs, the wound is naturally plugged by the blood clotting. The production of a blood clot is complicated.

First the nearest blood capillaries start dilating ( = increasing in diameter) and become leaky. The blood flow to the area increases for about 2 - 6 minutes (bleeding time) so that an increasing number of special white blood cells called phagocytes are transported to the wound. These pass into the tissues around the wound and destroy the germs. Pus, the yellow substance that collects at wounds, is a mixture of these phagocytes tissue fluid and the germs.

At the same time a clot is forming: The blood thickens or clots and then a scab forms to seal off the wound. The clot is a mass of threads or filaments in which blood cells are caught. There are several components within the blood that are needed in order for blood to clot. These components are the platelets, prothrombin and fibrinogen.

The clotting process seems unusually complex with so many steps. This is an advantage to the human body because it prevents the formation of dangerous blood clots in our blood vessels: The blood contains a natural anti-coagulant called heparin which inactivates the thrombin, thus preventing such blood clots.

If unwanted blood clots do form in the body we have very serious problems. For example, if there is "hardening of the arteries" (atherosclerosis), a blood clot (called a thrombus) may form on the inner surface of a blood vessel. If this clot breaks free and circulates in the blood it is known as an embolus. A thrombus or an embolus can result in a blocked blood vessel and no blood getting through to some important organ such as the heart (coronary thrombosis-->heart attack) or the brain (cerebral thrombosis -->stroke).

There are some people (mainly males) who have difficulty in clotting blood. The disorder is a genetic condition called haemophilia. These individuals bleed easily from the gums, nose, and skin. They have a deficiency in one of the many plasma proteins (clotting factors) that are required in small quantities for correct blood coagulation.

Words given

blood clotting = blood coagulation - Blutgerinnung; l. 1 germs - Bakterien etc.; l. 3 to plug up - verstopfen, verschließen; l. 5 leaky - löcherig; l. 7 tissues - Gewebe; l. 7 pus - Eiter; l.10 scab - Wundschorf; l. 11 threads - Fäden; l. 12 components - Bestandteile; l. 15 to release - to set free (freisetzen); l. 16 bruise - Bluterguß; l. 18 to catalyse - katalysieren, herbeiführen; l. 19 conversion = change - Umwandlung; l. 22 soluble - löslich (opp.: insoluble); to be trapped - to be caught; l. 27 to prevent - verhindern; l. 28 blood vessel - Blutgefäß; l. 34 coronary - of the heart; l. 35 cerebral - of the brain; stroke - here: Schlaganfall; l. 37 haemophilia - Bluterkrankheit; l. 38 deficiency - Mangel, Defekt.