Wounds, Bleeding, and Healing
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Transcript Wounds, Bleeding, and Healing
Wounds & Hemostasis
By C. Kohn, Waterford WI
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.
o 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 and 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.
o http://www.mhhe.com/biosci/esp/2002_general/Esp/folder_structu
re/tr/m1/s7/trm1s7_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?