ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

General Considerations And Physiological Importance Of Normal Hemostasis To Man

Updated on February 3, 2014

Hemostasis Cascade


A General Overview

Normal hemostasis can be considered under two headings, the vascular platelet mechanisms and the coagulation mechanism, which are closely interconnected in several ways. When injured, the blood vessel contracts and retracts in an attempt to close the wound. This is brought about by the intrinsic contractile elements in the vessel wall. The platelets adhere to and aggregate at the site of endothelial injury. Simultaneously, the coagulation proteins are sequentially activated to generate thrombin which converts fibrinogen into fibrin. Fibrin forms a mesh in which platelets and other formed elements of blood are entangled to form a clot which arrests blood loss. The platelets contract and the fibrin plus is drawn together more tightly to the vessels wall. Once the optimum amount of clot has been formed, further extension is arrested by the antithrombic substances and the fibrinolytic enzyme plasmin, which is generated locally. Plasmin helps in removing excess of fibrin by converting it into soluble fibrin degradation products (FDP).

Thus, it will be seen that normal hemostasis is a well balanced system brought about by the close interaction of the vascular platelet factor, coagulation and fibrinolysis. This can be achieved only in the presence of normal vessel walls, adequate number of functioning platelets, sufficient quantities of functional coagulation proteins, and a normal fibrinolytic mechanism.

The endothelium which lines the blood vessels synthesizes factor VIII-related von willebrand factor (VWF). Following endothelium, platelets bind to factor VIII-vWF polymers and collagen, and adhere to the surface to initiate the hemostatic process. The normal vascular endothelium also produces a prostaglandin PGI2 (Prostacyclin, epoprostenol) which has the opposite effect, i.e vasodilation, prevention of platelet aggregation, and inhibition of adenosine diphosphate (ADP) release.

Thrombocytes- Platelets

The white cell in the midsts of the Red blood cells here is a platelet cell.
The white cell in the midsts of the Red blood cells here is a platelet cell. | Source


Normal count is 150- 300,000/cmm. They are disc-shaped, non-nucleated from the megakaryocytes in the bone marrow under the influence of thrombopoietin, a controlling factor. Platelets have a lifespan of about 10 days. The megakaryocytes remain extravascularly on the sinusoids and liberate the platelets into the vessels. The platelets contain several substances held in the different organelles (surface membrane, tubules, granules and vacuoles). These take part in the platelet adhesion, aggregation, release reaction and they interact with coagulation factors.

Functions of platelets

Platelets adhere to exposed subendothelial structures. The adhesion takes place between the platelets and subendothelial factor VIII-vWF polymers and collagen. This leads to change of shape from discs to spiny spheres and release of their granules locally and into blood. Adenosine disphosphate which is a strong platelet aggregating agent released from dense granules causes more platelets to aggregate and join the platelet plug already formed. Thrombin, formed as a result of coagulation reaction, causes further aggregation of platelets, so also does the stress hormone epinephrine, which also constricts the arteries and arterioles. Adhesion to vessel wall and aggregation of platelets result in change in their membrane structure. Platelet fatty acid cyclo-oxygenase, which is an enzyme, converts arachidoni acid into the endoperoxides. A prostaglandin derivative thromboxane A2 is produced which potentiates the release of the contents of the granules. It also leads to further platelet aggregation and local vasoconstriction. Thromboxane A2 is hydrolysed non-enzymically into thromboxane B2 which is an inactive product.

In addition to these intrinsic mechanisms, platelets adsorb various coagulation factors on their surface and provide a surface for them to be activated.

© 2014 Funom Theophilus Makama


    0 of 8192 characters used
    Post Comment

    No comments yet.


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)