Wounds Hemostasis Normal Blood Flow To have normal
Wounds & Hemostasis
Normal Blood Flow • To have normal blood flow, blood must be kept at an exact viscosity (thickness) – Too thin, and the smallest cuts would cause a pet to bleed to death – Too thick, and the blood would not flow • Anticoagulants keep the blood thin and allow it flow under normal circumstances • Injury changes the situation – Blood must not be allowed to flow freely everywhere or the wound would never heal
4 Types of Open Wound • Abrasions-injuries destroying only surface layers of the skin. • Incisions- wounds produced by sharp instruments – these types of cuts usually have smooth edges. • Puncture Wounds- penetrations of the superficial (surface-layer) tissue. • Lacerations- cuts with irregularly torn edges. » Slide courtesy of Texas A&M
Hemostasis • The series of chemical reactions needed to stop bleeding is called hemostasis • Hemostasis has three steps – Step 0: Injury – Step 1: Vasoconstriction – blood vessels constrict (or “shrink”) to slow blood flow at the site of injury – Step 2: Platelet Plug formation – the wound is “corked”, or covered with sticky platelets – Step 3: Formation of a fibrin blood clot – a more sturdy solution is created
Step 1: Vasoconstriction • In vasoconstriction, the walls of the blood vessels “shrink” to reduce the size of the area that blood can flow through. • The muscles surrounding the vessel will contract, shrinking the vessel
Step 2. Platelet Plug Formation • At the site of injury, collagen will help platelets to stick to the site of the injury • Collagen is sort of like branches that the platelets can grab onto as they pass in the bloodstream
Platelets • Platelets are formed in the bone marrow and live in your body’s circulatory system for roughly a week – Platelets aren’t really cells – they do not have a nucleus and cannot divide – Platelets do have a coat made of a particular protein that prevents a platelet from sticking to anything other than injured tissue • Platelets contain contractile proteins (like those in your muscle cells) – These proteins enable a platelet to expand contract • Inside the platelet are special chemicals that aid in the formation of the platelet plug (explanation on next slide).
Clot Contraction & Repair • About 30 -60 minutes after a blood clot has formed, the platelets within the clot contract – Like muscle cells, platelet cells can shrink due to actin and myosin contractile proteins • This contraction pulls on the wound from the inside; bringing the edges of the wound closer together • The blood clot is temporary – at the same time of contraction, the tissue surrounding the damaged site begin to divide and repair via mitosis.
WBC RBC Platelet
Degranulation: A Feed Forward Mechanism • The platelets release granules that enable more platelets to get stuck. • The more platelets that get stuck, the more granules are released the promote more platelets to get stuck. • This is a “feed-forward” mechanism…the process becomes stronger as it happens more.
Step 3: Coagulation • The platelet plug will become reinforced with a fibrin “mesh net” • This fibrin net also traps red and white blood cells in order to from a blood clot over the site of the injury – The red blood cells will form a solid “plug” – The white blood cells will aid in fighting infectious agents that are able to make it inside the body.
Review: 3 Steps of Hemostasis • 1. Vasoconstriction – the muscles of the damaged blood vessel contract to reduce the amount of blood flowing through it by reducing the size of the blood vessel • 2. Platelet Plug Formation – collagen fibers protruding from the site of the injury ‘catch’ platelets and form a plug. Platelets contract and “shrink” the wound • 3. Formation of a Blood Clot – a fibrin “mesh” catches red and white blood cells to form a clot and prevent infection. » http: //www. mhhe. com/biosci/esp/2002_general/Esp/folder_struct ure/tr/m 1/s 7/trm 1 s 7_3. htm
Prevention of Infection • Once bleeding has been controlled, the next step is stopping infection • The blood vessels that were constricted now dilate (open up) to bring white blood cells rushing to the scene. – The process in which the wound swells and becomes inflamed is called inflammation.
White Blood Cells • White blood cells engulf and destroy any germs that may have gotten into the body through the open wound. • This process of destroying germs creates heat – This causes the trademark symptoms of serious wounds – swelling, redness, tenderness, and heat. • The worse the infection, the greater the inflammation and heat.
Fibrinolysis • 2 days after clotting the fibrin mesh that holds the clot together is dissolved – This process is called Fibrinolysis Source: thrombosisadviser. com
Stuff You Should Know: Warfarin • Warfarin (or Coumadin) is a blood thinner. • It was originally a rat poison, and is still widely used for this method – Rats that eat food laced with Warfarin die from blood loss because their blood is unable to coagulate • Warfarin, in much lower doses is one of the most widely prescribed medications in the world. – Warfarin can help dangerous clots from forming in heart attack and stroke victims • Warfarin is named for WARF, or the Wisconsin Alumni Research Foundation. – This is the agency that funds all research at the University of Wisconsin.
Review • • • What is necessary for normal blood flow? What is an anticoagulant? What are the four types of open wounds? What is hemostasis? What are the 3 steps of hemostasis? What is vasoconstriction and how does it happen? What is a platelet and how does it help a wound heal? How do they know where to go when there is an injury? How is a platelet different from other kinds of cells? What is a fibrin blood clot made from? (i. e. what is a scab? ) How does it form? How does an open wound close? Why do open wounds sometimes swell, become hot, and look red? What is fibrinolysis? How does a wound “know” how to heal? What is Warfarin and what does it do?
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