Hemostasis

• Hemostasis is the arrest of bleeding, a physiological response that stops bleeding
• Hemostasis is maintained by hemorrhagic responses and thrombosis
• Components of Hemostasis:

  • Vascular System
  • Platelets/Thrombocytes
  • Blood Coagulation Factors
  • Fibrinolysis
• Other Components involved in Hemostasis:

  • Complement System
  • Kinin System
  • Serine Protease Inhibitors
• Blood Vasculature consists of:

  • Arteries and Veins
  • Arteries have the thickest wall of the vascular system
  • Veins are larger and have a more irregular lumen than arteries
• Blood Vasculature is composed of three layers:

  • Tunica intima: single layer of endothelium cells thickened by sub-endothelial connective tissue layer, contains elastic fibers
  • Tunica media: thickest coat, composed of smooth muscle and elastic fibers
  • Tunica adventitia / Tunica Externa: consists of fibrous connective tissue with nerve endings, small networks of blood vessels, supplies nutrients to the tissues of the wall
• Arterioles and Venules are smaller blood vessels:

  • Arterioles are microscopic continuations of arteries giving off metarterioles joining capillaries
  • Venules are microscopic veins connecting to capillaries
• Capillaries are responsible for microcirculation linking between arterial and venous circulation:

  • Thinnest walled and most numerous of blood vessels composed of a basement membrane tightly anchored with collagen that offers support for the microvascular unit
  • Sinusoids are found in bone marrow, spleen, and liver
• Thrombocytes/Platelets are cells involved in thrombopoiesis

  • Thrombopoietin is a hormone that stimulates the production and maturation of megakaryocytes