Blood’s Amazing Self-Sealing System

YOU are busy using a knife to prepare your family meal. Ouch! The knife slips and you are cut. While such external cuts happen only occasionally, did you know that hundreds of tiny, internal tears occur each day? Yet we do not bleed to death. Why? Blood has a marvelous means of sealing off such breaks.

Minor Repair by Plugs

Flowing in the blood are all the substances needed for repair. But they are kept inactive until a crisis develops. When this occurs, pain triggers nervous reflexes that contract the blood vessel. This is a signal for the tiny platelets in the blood to go into action. They rush to the scene of the emergency and attach themselves to the exposed fiber at the tear. Chemical signals from the platelets cause more platelets to converge on the spot, and a loose plug is formed. This is usually sufficient to seal minor tears.

Major Repair by Clots

In larger cuts, a stronger, more permanent patch is needed. A platelet plug is still formed, but it must be covered with a clot. However, forming the clot is a complicated task involving several dozen substances and an intricate sequence of chemical reactions.

Briefly, here is what takes place: In response to the emergency, the blood-vessel walls or the clotting factors in the blood release a chemical into the bloodstream. This causes fibrinogen, an inert protein found in blood plasma, to be converted into fibrin. The fibrin molecule is unique in its ability to link together, forming long threads that wrap around the platelet plug. The threads act much like a spiderweb, catching more platelets, red blood cells, and other substances to form a clot. The newly formed, jellylike clot is about 99 percent water. So two proteins are released by the platelets, causing the clot to contract and squeeze out the fluid. A solid clot has now formed. On the skin surface, where the clot has been exposed to air, it is commonly called a scab.

Once begun, the process must be stopped so that the clot does not become so big that it blocks the vessel and cuts off blood circulation. How is it stopped? After the mending work is done, blood flow rapidly returns to normal and disperses the clotting factors. There are also several anticoagulants in the blood that prevent excessive clotting and keep platelets from collecting together when there is no emergency.

Removing the Clot

After the wound is healed, another chemical reaction is triggered to break down the fibrin threads and dissolve the clot. Fragments of the clot that break free in the bloodstream are either devoured by white blood cells or filtered out in the liver, spleen, and bone marrow.

Helping the Blood Do Its Job

There are certain things that we can do to help the blood do this intricate job better. Exercise, such as brisk walking and swimming, keeps the blood circulating freely. Eating lecithin-rich foods, such as whole-grain breads, and fish high in fatty acid both make platelets less sticky and help keep the blood from forming abnormal clots. Also, leafy green vegetables, tomatoes, and vegetable oils supplement our vitamin K supply, which helps keep the clotting mechanism in good order.

Truly, blood’s amazing self-sealing system helps us to appreciate more fully the truth of what Moses wrote: “The life of every living thing is in the blood.”​—Leviticus 17:11, Today’s English Version.

[Diagram on page 26]

(For fully formatted text, see publication)

Red cells

Platelets

Normal blood vessel

Platelets repair minor tears

Platelets, red cells, and fibrin threads repair larger injuries

Fibrin threads holding a red cell