Cyclic Amp & Platelet Functions

• Platelets form the clots that stop wounds from bleeding.hand with blood image by Ivonne Wierink from Fotolia.com
  
  Most folks know what platelets do: they form clots to stop bleeding. Fewer know what platelets are or how they work.
  
  Cyclic adenosine monophosphate, abbreviated as cyclic AMP or cAMP, is a common chemical in cells that serves as a secondary messenger. Once a cell membrane has detected a signal outside the cell, secondary messengers amplify the signal and relay it to sites inside the cell.
  
  Cyclic AMP helps regulate the activity of platelets.
  
  

What Are Platelets?

• In bone marrow, huge cells called megakaryotes release fragments of themselves. These free bags of cytoplasm never have a nucleus and therefore are not true cells. The pieces leak into the blood as thrombocytes, or platelets.
  
  

How Platelets Work

• Platelets remain inert until they encounter damaged tissue. The platelets stick to the damaged tissue and to each other. They change shape from disks to octopus-like balls with many long arms. The platelets undergo physiological changes, too. They release signal chemicals to activate other platelets and other products to promote a series of reactions that help convert fibrinogen in the blood into fibrin, a tough, sticky protein that forms the skeleton of blood clots.
  
  The sticky mesh of platelets, fibrin, and a few other cells and products covers the wound and prevents further loss of blood. If this stuff is exposed to air, it dries and hardens into a scab.
  
  

Cyclic AMP in Platelets

• The cAMP in a platelet regulates and prevents inappropriate activity. Cyclic AMP plays little or no role in a platelet's change of shape but is a major factor in its physiological reaction.
  
  Research indicates that cAMP plays a number of roles inside a platelet. For one, it regulates the fibrinogen receptor on the platelet membrane. If cAMP levels are high, the platelet will not promote the production of fibrin from fibrinogen.
  
  Cyclic AMP also regulates the concentration of calcium ions inside the platelet. As cAMP levels drop, calcium ions enter the platelet and initiate reactions that ultimately result in the release of proteins and chemicals that promote clotting.
  
  Most importantly, however, cAMP controls a platelet's "stickiness." If cAMP levels of a platelet are artificially kept at pre-clotting levels during a clotting event, the platelet will not stick to the wound site or aggregate with other platelets despite its change of shape.
  
  Cyclic AMP basically keeps a platelet inert, which is good because you don't want random clots forming in your bloodstream. Torn tissue produces chemicals that signal the platelet to suppress its level of cAMP, thereby enabling it to participate in and promote clotting when required.