Platelet Plug Formation

Platelets will not adhere to the endothelium (inner lining) of undamaged blood vessels. The endothelium is normally very smooth and coated with prostacyclin, a platelet repellent. When a vessel is broken, however, collagen

Platelets Plug Formation

Figure 18.20 Hemostasis. (a) Vasoconstriction of a broken vessel reduces bleeding. (b) A platelet plug forms as platelets adhere to exposed collagen fibers of the vessel wall. The platelet plug temporarily seals the break. (c) A blood clot forms as platelets and erythrocytes become enmeshed in fibrin threads. This forms a longer-lasting seal and gives the vessel a chance to repair itself. How does a clot differ from a platelet plug?

Figure 18.20 Hemostasis. (a) Vasoconstriction of a broken vessel reduces bleeding. (b) A platelet plug forms as platelets adhere to exposed collagen fibers of the vessel wall. The platelet plug temporarily seals the break. (c) A blood clot forms as platelets and erythrocytes become enmeshed in fibrin threads. This forms a longer-lasting seal and gives the vessel a chance to repair itself. How does a clot differ from a platelet plug?

Saladin: Anatomy & I 18. The Circulatory System: I Text I © The McGraw-Hill

Physiology: The Unity of Blood Companies, 2003 Form and Function, Third Edition

704 Part Four Regulation and Maintenance fibers of its wall are exposed to the blood. Upon contact with collagen or other rough surfaces, platelets put out long spiny pseudopods that adhere to the vessel and to other platelets; the pseudopods then contract and draw the walls of the vessel together. The mass of platelets thus formed, called a platelet plug, may reduce or stop minor bleeding.

As platelets aggregate, they undergo degranulation— the exocytosis of their cytoplasmic granules and release of factors that promote hemostasis. Among these are serotonin, a vasoconstrictor; adenosine diphosphate (ADP), which attracts more platelets to the area and stimulates their degranulation; and thromboxane A2, an eicosanoid that promotes platelet aggregation, degranulation, and vasoconstriction. Thus, a positive feedback cycle is activated that can quickly seal a small break in a blood vessel.

Essentials of Human Physiology

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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • daniela
    Can platelets adhere to exposed collagen?
    4 years ago
  • charles davis
    What stimulates clot formation or platelet plug?
    4 years ago
  • Alesha
    How does a clot differ from a platelet plug ?
    3 years ago

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