Stage 1: Hemostasis
Hemostasis or haemostasis occurs immediately after the
injury. When our skin breaks our body’s first response is vasoconstriction.
Vasoconstriction is when our blood vessels constrict to decrease the amount of
blood leaving. This happens because of direct injury to smooth muscles,
chemicals released by endothelial cells and platelets and by reflexes initiated
by nearby pain receptors. Platelets flow in our blood and have 2 main receptors: glycoprotein1b(GP1b) and
glycoprotein2b3a(GP2b3a). There is another glycoprotein found in our blood
called the von Willebrand factor(VWF). When this binds to the GP1b receptor and
the subendothelial collagen the platelet is activated. In platelets there are 2 granules called dense
granule and alpha granule. In these granules there are different
substances called fibrinogen, VWF, serotonin, adenosine diphosphate (ADP), and
calcium. These substances are released into the blood through degranulation.
When combined with thromboxaneA2 they lead to more platelets aggregating which
creates a platelet plug. Finally fibrinogen found in our blood changes to
fibrin through the coagulation cascade. Fibrin creates a mesh on top of the
platelet plug making it stronger.
Figure 1: Hemostasis http://physiologyplus.com/describe-the-three-steps-of-hemostasis
Stage 2: Inflammation
When the skin is injured our body sends out chemokines,
chemical messengers, into the interstitial fluid which is located under our
skin but above the endothelial cells. The chemokines, a type of cytokine, tell
the body something is happening. The bacterium surrounding our cut comes into
the body and may send out its own byproducts into the bloodstream. These
byproducts or the chemokines can activate the mast cells in our skin. The mast
cells when activated will release histamine, an inflammatory mediator.
Histamine goes to the endothelial cells and cause vasodilation in the
capillaries. The capillaries are now filling up with fluid. When this happens
the endothelial cells move apart letting the blood flow through. The bacteria
byproducts as well as the chemokines enter into the blood vessel. Neutrophils,
a type of white blood cell, are attracted to these chemicals. They want to get
close to them which they achieve by margination and extravasation. Margination
is when the neutrophils adhere to the endothelial cells. Extravasation or
diapedesis is when the neutrophils start to leave the blood vessel through the
gaps between the endothelial cells. The whole point of this is so that the neutrophils
can get to the pathogens and go through phagocytosis. Phagocytosis will enable
them to ‘eat’ up the bacteria, the debris and any damaged cells. Dendritic
cells, another cell in our skin, B-cells, T-cells, macrophages and other
phagocytes help get rid of the bacteria just like the neutrophils.
Through this process our body gives off heat, becomes red,
starts to swell and hurt which are called inflammatory responses. Redness
occurs because the capillaries are filled up with more fluid than normal.
Swelling happens because of the increase in fluid. More blood comes to the area
because of vasodilation which makes our skin hot. The cut often gives us pain
because the body releases chemicals that fuel nerve endings making the area
Inflammation process https://www.slideshare.net/pramodkuamarpamu/acute-inflammation-40385817
Stage 3: Proliferation
The proliferation or granulation stage is when the wound
closes and can from 4 to 24 days. Fibroblasts and myofibroblasts proliferate in
the wound and end up making the extracellular matrix. Then the myofibroblasts
attach to the fibronectin and collagen in the extracellular matrix and start to
pull which contracts the wound by bringing the sides of the wound closer. Any
redundant fibroblasts are taken away through apoptosis, in other words a
planned cell death. Collagen is made from fibroblast and is especially
important in this stage as well as maturation. Blood vessels need an optimal
supply of oxygen and nutrients for the granulation tissue to be made. The
granulation tissue is made of extracellular matrix and collagen which lets the
granulation tissue to develop a new web of blood vessels to take over for the
damaged ones. This process I called angiogenesis. The colour of the granulation
tissue can tell us if the process is going smoothly. If it is pink or red that
means the tissue is healthy but if it is dark it could mean there is an
infection, a poor delivery of blood also known as perfusion or a stoppage of
blood which is known as ischemia. The body changes damaged mesenchymal cells
into fibroblasts to help cells move around. They secrete collagen and liquids
which helps to strengthen the wound. The wound continues to grow stronger as
the fibroblasts help in the formation of new tissue and accelerate the healing
process. The epithelial cells come to surface of the wound and close the wound.
If there is a scab in the way then this process will take much longer than it
Figure 3: Collagen and fibroblast at the wound in the
proliferation stage https://tbtri2dc00482337.wordpress.com/about/
Stage 4: Maturation
Maturation or remodeling is the last stage in
the healing process and transpires after the wound is closed. This stage can
last months even years. It is responsible for the formation of new epithelium
and scar tissue. In this stage the new granulation tissue made in the
proliferative stage becomes stronger and flexible. The collagen fibers reorganize
whereas the tissue remodels and matures. Any cells left that are of no use
anymore are removed by apoptosis. The amount of blood vessels in the injured
area decreases as they leave the area. In the proliferative stage the collagen
is all over the place and disorganized. In this stage collagen type III, the
main material in granulation tissue, is replaced with collagen type I, the main
component in the dermis. The collagen now aligns itself with the tension lines
and water is absorbed which lets the collagen fibers lie next to each other and
cross link. The intramolecular and intermolecular cross links of collagen
results in an increased wound bursting strength. Wound bursting strength is the
amount of pressure needed to break the wound. The final scar reaches only 80%
of its original tensile strength.
happens when bacteria, viruses, or other microbes enter our body and star to
multiply. Disease happens when the cells in our body are damaged and signs of
an illness appear. A lot of the symptoms we suffer through when we are infected
are caused by our immune system fighting off the infection. White blood cells,
antibodies and other microbes get rid of the pathogen. The immune system may
cause the following symptoms in order to help fight off the infection: fever,
headache, rash or malaise.
Viruses have nucleic acid in them, DNA or RNA, which is
surrounded by a protein shells and sometimes lipids. They cannot reproduce on
their own so when it enters a host cell it uses the host’s metabolic system to
make copies of itself. These copies can come out of infected cells or a cell
membrane. They make us sick by killing cells and disrupting their cell
function. Most of the time our body will respond with a fever; a fever
inactivates viruses. The body will also secrete interferon, a chemical that
stops viruses from reproducing. Another way our body might stop a virus is by
sending all the antibodies to the pathogen.
Bacteria are single celled organisms that can either help us
or hurt us. They carry DNA which programs the genes needed to reproduce and
other functions. Sometimes they also have plasmids which encode for specialized
functions like antibiotic resistance. Bacteria can only carry one set of
chromosomes. They reproduce by splitting into two cells through binary fission.
The offspring are clones with the same genetic material. If a mistake were to
occur during replication a mutation can happen. It would create variety in the
population that could lead to the ability to adapt in a changing environment.
Bacteria can evolve rapidly and suddenly when they take genetic material from
other bacteria, viruses, plants and even yeast. Bacteria have learned how to
adhere to cells, make toxins that hurt other cells, avoid or restrain our
defenses and resist not only drugs but our immune system’s antibodies. Some
bacteria reproduce so quickly that they crowd our tissues and interrupt normal
functions. They can kill cells and tissues. The toxins they create can paralyze,
destroy a cells metabolic system, or form an immune reaction that is toic.
Bacteria can be in our body without causing an infection but
the chance of infection increases when there is a break in the skin. A common
example of a bacterial skin infection would be cellulitis. Cellulitis can cause
skin to swell, turn red and become warm; three out of the four inflammatory
responses. It can happen anywhere on your body and forms deep in our skin. Its
symptoms range from fever, numbness, infection near our eyes or ears to
swelling, bruising, and a sense of coldness. Cellulitis is typically caused by
either Streptococcus pyogenes (strep) or Staphylococcus aureus (staph). It can
appear by itself or a result from an infected wound. The only way cellulitis
can spread is if the infected person comes in contact with another person and
the bacteria enter through a cut in their skin. Another bacterial skin
infection that is easy to catch due to its symptoms is impetigo. Impetigo
starts off as red spots and progresses to itchy blisters, normally around the
nose or mouth. Impetigo is easily given to another person by skin contact or
contact with anything the infected person touched. It can be caused by
staphylococcus or streptococcus.
Wounds only start the healing process if they reach the
dermis. The dermis is underneath the epidermis. The epidermis consists of
hardened cells called keratinocytes and melanocytes. Melanocytes make melanin
which gives us the colour in our skin. Our skin colour varies not because dark
skinned people have more melanocytes but because they have more activated
melanin. The epidermis is constantly losing dead skin cells and making new ones
making it easy to repair. The epidermis is the body’s first shield.
The dermis is also known as the corium. It consists of living
tissue and connective tissue. Living tissue refers to blood and lymph vessels,
nerve fibers as well as oil and sweat glands. Connective tissue alludes to
fibroblasts, histocytes and mast cells. Fibroblast cells help repair injuries
to the skin. Histocytes protect the body by surrounding foreign substances.
Mast cells contain histamine, a substance that can also be released in
allergies which leads to itching. Fibers in the dermis are made of collagen.
Collagen means glue and it tough but flexible. It is a fibrous protein
substance found in the bone, cartilage, tendons and ligaments. Collagen fibers
support and protect the blood and nerves in the dermis. The nerve endings in
the dermis can sense hot, cold, pain, pressure and touch. Overall the dermis
helps control infection and gives us sensation.
Often times when people get cut they reach for rubbing
alcohol or hydrogen peroxide to clean the wound but what they don’t realize is
that they are doing more damage than helping our skin. Disinfectants like
rubbing alcohol, hydrogen peroxide, iodine and sodium hypochlorite do clean the
wound but also kill off many healthy cells. In addition to killing off cells
these disinfectants often burn when in contact with our injury. They don’t actually
burn you but the chemicals in them activate a cell called vanilloid
receptor-1(VR1 or TRPV1). VR1 is a nerve receptor that tells us when something
is hot. When exposed to alcohol the alcohol molecules actually lower the
temperature needed to send the signal to the brain. Studies show that ethanol
reduces the threshold temperature by 10 degrees. There are 2 theories as to why
our wound still burns if the alcohol lowers the temperature threshold but
neither is confirmed. Either the heat made from our cells through the
inflammatory response causes the burning or our own body temperature activates
the VR1. Because of this our cut now hurts and feels like it’s on fire. A
spokesperson from American Association of Dermatology, Robert Kirsner, told
Reader’s Digest that these disinfectants kill off healthy cells and clean the
wound. He also stated “The most effective way to get rid of debris and bacteria
without damaging healthy tissue is flushing the wound out with water.” Most
people who don’t have any disinfectants will clean the wound with water and
soap. The addition of soap isn’t as great as people think. You don’t know how
our body will react with the chemicals in the soap. They might help, they might
not. It’s better to stick with just water.
Many factors can affect the healing process. Temperature
controls the rate of chemical and enzymatic process happening in the injury. It
also controls the metabolism of cells and tissue working in the process.
Changing the wounds many times or cleaning the wound with room temperature
solutions decreases the temperature of the wound. It takes hours to recover to
the needed physiological levels. Therefore, wound dressings giving a “cooling”
effect are not really helping. If the wound is on a bony prominence, areas of
less vascularity and in areas with thicker skin usually take longer to heal.
Linear wounds heal faster than square or rectangle ones and circular wounds
take the longest to heal. If the wound is too dry a scab forms which gets in
way of epithelialization. If the wound is to wet it becomes macerated.
Maceration can make the wound bigger and increase the risk of infection. Debris, necrotic tissue and foreign bodies
increase the risk of infection which is why they need to be taken out in the
inflammatory stage. Too much pressure on the wound can compromise the blood
flow and the healing process cannot happen. Anti-inflammatory medication gets
in the way of the inflammation process. Infection also slows the healing
process. Oxygen is needed for better healing.
Moist Wound Healing
In 1962 Dr. George D. Winter from the University of London
did an experiment that changed wound healing for the better. He wondered
whether letting the wound dry out was the best method of repairing it. He
created many wound on the backs of pigs. He left some of the wounds to dry out
and covered the others with polymer film. The wounds covered with polymer film
epithelialized 2 times faster than the wounds left on their own. Winter
hypothesized that epithelial cells in dry wounds had to find a way to get past
the scab which wasted time and energy while in the moist wounds they move
easily across a moist, vascular wound surface. His hypothesis is supported by
many studies. Most of our body is made of water and the natural environment of
a cell is moist which means that if a cell were to dry up it would be a dead
cell. Moist wound healing decreases dehydration, cell death and pain. It
increases angiogenesis and re-epithelialization. It has a lower chance of
infection and less scarring. Moist wound healing allows epithelial cells to
migrate through the wound exudates to close the wound.
A dressing has direct contact with the wound whereas a bandage holds a
bandage in place. Dressings help the wound heal, prevent infections, stop
bleeding, absorb excess blood, plasma or any other liquids, and begin the
healing process. There is a variety of dressings each with their unique
Hydrocolloid dressings are used on pressure and venous ulcers, burns,
necrotic wounds and under compression wraps. They are self-adhesive,
non-breathable, provide thermal insulation and create moist condition which
triggers moist wound healing. A hydrocolloid surface is coated with
polysaccharides and other polymers which absorb water and form a gel, protect
the wound from infection, keep it clean and help heal the wound faster. They
are impermeable to bacteria making them effective in defending the wound from
infection. Hydrocolloids are easy to use, last long and are environmental.
Hydrogel can be used on an assortment of wounds that are leaking a small
amount of fluid or no fluid, are painful or necrotic wounds, pressure ulcers,
donor sites, second degree burns and infected wounds. They are designed to
comfort the patient and reduce their pain while still aiding in the healing
process and fighting infection. The cooling gel in them is what makes them
successful at decreasing pain and speeding up the process. Hydrogels are mainly
water or glycerin based dressings available in sheets, gels or gauzes. Hydrogels
aren’t effective bacteria shields since they let gas and water pass through.
Hydrogels like hydrocolloids provide a moist environment for the wound to
Alginates dressings need to be changed every 2 days because of the
amount of liquid they absorb and the nature of the wound. If you change the
dressings a lot it can result in dryness which can lead to bacteria penetrating
the wound. They should only be used for wounds with a lot of liquid drainage
otherwise they can damage healing by drying the wounds too quickly. They are
made from sodium and seaweed fibers which allow them to absorb high amounts of
liquid and they are biodegradable after use.
Foam dressings absorb exudates which creates an environment that helps
speed up the healing process. They let water vapor to enter which keeps the
injury moist but prevent bacteria from entering. These dressing can be adhesive
and non-adhesive. Foam dressings are foamed polymer solutions with small
‘pockets’ that can hold fluids. They can be layered in a mixture with other
materials. They are used for partial and complete thickness wounds.
Collagen act as a crutch for new cells to grow and can be really
successful when it comes to healing. They help remove dead tissue, help in the
proliferation stage, and speed up the process. As you can see wound dressings
can be a great help to our body.
Our body works hard to finish the healing process as best as they can.
They have many obstacles in their way that may be caused by us or pathogens
that have entered. Add to the fact that not many people know the right way to
clean a wound, it makes our bodies’ work much harder than it has to be.
Learning how the healing process works, the right way to clean a wound, which
dressing to use and why, and what infections could be in our body can make a