Wounds & Healing

1. Wounds & Healing By C. Kohn, Waterford WI

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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 and contract • Inside the platelet are special chemicals that aid in the formation of the platelet plug (explanation on next slide).

8. 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.

9. WBC RBC Platelet

10. 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.

11. 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.

12. 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_structure/tr/m1/s7/trm1s7_3.htm

13. 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.

14. 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.

15. Fibrinolysis • 2 days after clotting the fibrin mesh that holds the clot together is dissolved • This process is called Fibrinolysis Source: thrombosisadviser.com

16. 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 WisconsinAlumni Research Foundation. • This is the agency that funds all research at the University of Wisconsin.

17. 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?