1-2 Hemostasis Physiology

Publish in



Please download to get full document.

View again

of 48
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
  Blood Physiology   Hemostasis and Blood Coagulation    Events in Hemostasis  The term  hemostasis   means prevention of blood loss  Whenever a vessel is cut or ruptured, hemostasis is achieved by several mechanisms: (1)Vascular constriction (2)Formation of a platelet plug (3)Formation of a blood clot as a result of blood coagulation (4)Growth of fibrous tissue into the blood clot to close the hole in the vessel permanently  1- Vascular Constriction  Immediately after a blood vessel has been cut or ruptured, the smooth muscle in the wall contract  The contraction results from: (1) Local myogenic spasm : vasoconstriction probably results from local myogenic contraction   of the blood vessels initiated by direct damage to the vascular wall,the platelets are responsible for much of the vasoconstriction by releasing a vasoconstrictor substance, thromboxane A 2.   (2) Local autacoid factors: from the traumatized tissues and blood platelets - augmented by the local secretion of factors such as Endothelin (3) Nervous reflexes: the nervous reflexes are initiated by pain nerve   Events in Hemostasis  2- Formation of the Platelet Plug (Primary Hemostasis) If the cut in the blood vessel is very small-indeed, the cut is often sealed by a  platelet plug ,   rather than by a blood clot. Physical and Chemical Characteristics of Platelets  Platelets ( thrombocytes  ) are minute discs 1 to 4 micrometers in diameter.  The megakaryocytes fragment into the minute platelets either in the bone marrow or soon after entering the blood, especially as they squeeze through capillaries.  The normal concentration of platelets in the blood is between 150,000 and 450,000 per microliter   It has a half-life in the blood of 8 to 12 days  It is eliminated from the circulation mainly by the tissue macrophage system. More than one half of the platelets are removed by macrophages in the spleen Events in Hemostasis
Related Search

Next Document


We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks