Sticky Situations

Platelets are irregularly-shaped, colorless bodies that are present in blood. Their sticky surface lets them, along with other substances, form clots to stop bleeding.

When bleeding from a wound suddenly occurs, the platelets gather at the wound and attempt to block the blood flow. The mineral calcium, vitamin K, and a protein called fibrinogen help the platelets form a clot.

A clot begins to form when the blood is exposed to air. The platelets sense the presence of air and begin to break apart. They react with the fibrinogen to begin forming fibrin, which resembles tiny threads. The fibrin threads then begin to form a web-like mesh that traps the blood cells within it. This mesh of blood cells hardens as it dries, forming a clot, or "scab."

Calcium and vitamin K must be present in blood to support the formation of clots. If your blood is lacking these nutrients, it will take longer than normal for your blood to clot. If these nutrients are missing, you could bleed to death. A healthy diet provides most people with enough vitamins and minerals, but vitamin supplements are sometimes needed.

A scab is an external blood clot that we can easily see, but there are also internal blood clots. A bruise, or black-and-blue mark, is the result of a blood clot. Both scabs and bruises are clots that lead to healing. Some clots can be extremely dangerous. A blood clot that forms inside of a blood vessel can be deadly because it blocks the flow of blood, cutting off the supply of oxygen. A stroke is the result of a clot in an artery of the brain. Without a steady supply of oxygen, the brain cannot function normally. If the oxygen flow is broken, paralysis, brain damage, loss of sensory perceptions, or even death may occur.

Sticky Blood

Hemostasis - prevention of blood loss from broken vessel

1 - Vascular spasm - vasoconstriction of injured vessel due to contraction of smooth muscle in the wall of the vessel. This 'spasm' may reduce blood flow & blood loss but will not stop blood loss.

2 - Formation of a platelet plug - platelets aggregate at the point where a vessel ruptures. This occurs because platelets are exposed to collagen (a protein found in the connective tissure located just outside the blood vessel). Upon exposure to collagen, platelets release ADP (adenosine diphosphate) & thromboxane. These substances cause the surfaces of nearby platelets to become sticky and, as 'sticky' platelets accumulate, a 'plug' forms.

3 - Blood coagulation (clotting):

The result of all of this is a clot - formed primarily of fibrin threads (or polymers), but also including blood cells & platelets.

Blood clots in the right places prevent the loss of blood from ruptured vessels, but in the wrong place can cause problems such as a stroke (see below under inappropriate clotting).

Clot retraction:

• "tightening" of clot
• contraction of platelets trapped within clot shrinks fibrin meshwork, pulling edges of damaged vessel closer together

Over time (with the amount of time depending on the amount of damage), the clot is dissolved and replaced with normal tissue.

Fibrinolysis:

• dissolution of clot
• mechanism = plasminogen (a plasma protein) is activated by many factors & becomes PLASMIN. Plasmin then breaks down fibrin meshwork & phagocytic WBCs remove products of clot dissolution

Inappropriate clotting:

• thrombus - clot formed in an intact vessel, possibly due to:
  • roughened vessel walls (atherosclerosis; see normal & occluded coronary arteries below)
  • slow-moving blood (e.g., in varicose veins) = small quantities of fibrin form & accumulate

• embolus - 'moving' clot

'Sticky blood', 'Hughes Syndrome' or 'Anti-Phospholipid Syndrome' is a disorder of the clotting cells and the effect is to create inappropriate clotting within blood vessels. This inappropriate clotting can be extremely dangerous. A blood clot that forms inside of a blood vessel can be deadly because it blocks the flow of blood, cutting off the supply of oxygen. A stroke is the result of a clot in an artery of the brain. Without a steady supply of oxygen, the brain cannot function normally. If the oxygen flow is broken, paralysis, brain damage, loss of sensory perceptions, or even death may occur.

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