chapter 39: tissue and wound healing

The human body has the ability to heal itself after suffering a wound or injury, what is a wound?

a wound is an injury that disrupts the normal structure and function of a tissue or organ

its healing process can continue for several months from the initial injury through repair

wounds are classified in two different ways

acute and chronic, what are they?

An acute wound occurs suddenly or over a brief period of time and is usually caused by physical trauma or medical interventions, it typically heals in an organized and timely manner, upon healing structural and functional integrity are restored, healing occurs in 4-6 weeks

A chronic wound occurs over a relatively long period of time and does not heal properly and is in a prolonged state of inflammation, it does not heal in an organized and timely manner, and results in some degree of structural and functional impairment

There is also something known as partial or full thickness wounds, what are they?

A partital thickness wound is a wound in which damage extends through the epidermis while all or a portion of rheumatoid arthritis dermis remains intact and is primarily repaired by epithelial cells that migrate to the area and replicate by mitosis (reepithelialization) 

A full thickness wound is a wound in which damage extends through the epidermis and the entire thickness of the dermis with possible extensions into subcutaneous tissue, muscle, and bone. Repair would be complex and results in considerable scar formation 

Wound healing (tissue repair) is a dynamic, complex, and predictable process which occurs in 4 sequential, overlapping phases; what are they

1) hemostasis

2) inflammation

3) proliferation/granulation

4) remodeling/maturation

the phases of wound healing are directed by cells that release chemical mediators to regulate the healing process, what are these different chemical mediators

1) neutrophils

2) macrophages

3)lymphocytes

4) platlets

5) keratinocytes

6) fibroblasts

7) endothelial cells

chemical mediators include growth factors and cytokines, what are cytokines

cytokines are substances secreted by cells that help cells communicate with each other and coordinate the healing process, the cell types and meditators at an injury site change as the healing process

what are local and systemic factors that can impede wound healing (7)

1) lifestyle risk factors 

2) environmental risk factors 

3) nutritional deficits 

4) inadequate hydration 

5) immobility 

6) chronic disease 

7) inadequate perfusion to distal extremities 

wounds can lead to a lack of skin integrity that puts the individual at risk of infection 

The skin is the largest organ of the Body, how much does it realty measure?

1.2-2.2 square meters

4-5 kg (9-11 pounds)

7% of total body weight

what is the function of the skin

the skin serves as a waterproof barrier and the first line of defense against environmental stressors (toxins, radiation, and dirt), it minimizes excessive water loss, it maintains effective thermoregulation, it contains somatic sense receptors for touch, pain, and temperature, and it helps metabolize and activate vitamin D when exposed to ultraviolet light

the skin in different body areas varies in thickness, pigment, and distribution; what are the characteristics of this 

its normal thickness varies from 1.5-4.0 mmm difference is based on function of specific skin region, for example skin is thick in high friction areas like the soles of the feet

The skin has two layers separated by the basement membrane what are they

the epidermis and the dermis

characteristics of the epidermis 

the epidermis is the visible upper layer of the skin, it is composed of multiple layers of keratinocytes 

Keratinocytes: stratified squamous epithelial cells that are deep in the epidermis and are columnar or cuboidal, their cells flatten as they progress toward the skin surface 

Other cells are found in the epidermis in much lower numbers, what are they? (4)

1) melanocytes

2) T lymphocytes

3) Dendritic (lagerhans cells)

4) Tactile (Merkel) cells; these cells have specialized functions that contribute to homeostasis and repair of the epidermis

The epidermis is avascular and contains no lymphatic vessels, why is it?

this is because they are sustained by nutrients from the blood vessels of the dermis and nutrients diffuse through the basement membrane

As keratinocytes migrate from the basal layer to the skin surface they synthesize large amounts of keratin which is a water insoluble protein, what are the steps to which this is done

1) when cells reach the surface their cytoplasm has been replaced by keratin

2) the cells are dry, scaly, and dead

3) this process is called keratinization and takes 3-5 weeks

4) keratinization gives the outer epidermis a tough, horny quality that protects the basal layer

the epidermis itself is made of 3-5 layers cha

characteristics of the dermis 

the dermis is the layer of skin just below the epidermis which is much thicker than the epidermis, its depth varies with age and anatomical location

the function of the dermis is that it provides most of the skins strength, it contains blood vessels that provide nutrients and oxygen to the dermis AND epidermis, and it stores water and electrolytes 

which skin appendages are present in the dermis (4)

1) sweat glands 

2) sebaceous glands 

3) hair follicles 

4) nail roots 

these appendages are present in the dermis but derived from the epidermis, what is their purpose?

these appendages contain keratinocyte stem cells, they have the potential to regenerate, and they play a role in the reepithelialization of partial thickness wounds

the dermis contains sensory receptors for pain, touch, and temperature as well as smooth and skeletal muscle cells

the dermis is made of two layers, what are they?

1) Papillary layer (superficial)

2) Reticular layer (deep)

What are the characteristics of the dermal-epidermal junction(DEJ)? 

The dermal epidermal junction is the boundary between the epidermis and rheumatoid arthritis dermis and is known as a basement membrane zone

it underlies the basal layer of keratinocytes 

it separates the epidermis from the dermis by binding the layers together and minimizing slippage and separation 

it also acts as a barrier against chemicals and pathogens coming into the body and against water and electrolytes leaving the body 

it lately provides a framework on which regenerating cells can migrate and restore tissue architecture 

what are the characteristics of the extracellular matrix?

The extracellular matrix (ECM) is a combination of substances that are essential for tissue growth and wound healing, its a ground substance

it is primarily secreted by fibroblasts

its framework promotes the structural integrity of the body by helping the body withstand compressive forces and acts as a scaffold for cell adhesion and migration

most dermal cells attach to the ECM and are speed over it to proliferate and survive 

it also adds tensile strength, elasticity, and compressibility to the skin 

the extracellular matrix provides a medium for rapid diffusion of various substances between blood and tissues cells, what are they? (4)

1) nutrients

2)Metabolites

3)Chemical mediators

4)Hormones th

there are three classes of substances that make up the ECM, what are they?

1) fibrous structural proteins (collagen and elastin)

2) Adhesive glycoproteins (laminin, fibronectin, vitronectin)

3) Polysaccharide chains (glycosaminoglycans [GAGs]

What are the characteristics of collagen in relation to the ECM

collagen is the most abundant protein In the human body and in the ECM, there are about 16 different types 

the matrix is composed of three types of collagen 

• Type I 

• type III

• type V 

the cross linking collagen chains provide strength and stability

the hydration in the dermis is maintained by collagens water binding capabilities 

what are the characteristics of elastinin relation to the ECM

elastin is the primary structural component of elastic fibers in connective tissue of the skin, lungs, and blood vessels 

the steps to which this is done are 

1) molecules sythesize by fibroblasts and smooth muscle cells of blood vessels 

2) they loosely arrange in all directions 

3) they can coil and recoil like a spring 

4) the elastic fibers will calcify with age, causing elasticity of skin to deteriorate 

5) the elastic fibers are absent from scar tissue and fibrotic tissue 

What are glycosaminoglycans (GAGS) in relation to the ECM

glycoaminoglycans are polysaccharides that are highly polar and attract water to the ECM, they influx water to determine dermal volume and compressibility 

what is hyaluronan (Hyluronic acid) in terms of the ECM

hyluronan is a type of GAG abundant in the ECM which is produced in large amounts during wound healing

think when used for skincare, its purpose is to hydrate and heal

What is cell-matrix and cell-cell interactions?

Tissues have a complex system for enabling cell-cell communication and cell-ECM communication

their communication is essential for cells to respond to internal and external environmental changes

Integrins are a prominent family of receptors involved in the cell-cell and cell-ECM communication network

cytokines and growth factors are also essential components in cell-cell and cell-ECM communication, this enables epidermal cells to influence location and structure of the ECM and also enables ECM to influence keratinocyte growth, mitosis, proliferation, and apoptosis

there are three types of uncomplicated wound healing, what are they?

1)Primary intention

2)secondary intention

3)tertiary intention

the type of intention that occurs in regards to wound healing will depend on several factors, what are they? (4)

1)Type of injury

2)extent of tissue loss

3)presence of infection,necrosis, or secondary tissue breakdown

4)type of cells involved

The healing process is similar in all three intentions but varies in three ways, what are these ways 

1) amount of granulation tissues 

2)length of healing time

3) amount of scar formation 

characteristics of primary healing with wound healing

healing by primary intention (primary closure) usually occurs after surgical closure of a wound but also can occur in non surgical scenarios such as

1) wounds with minimal tissue loss

2)wounds without infection or contamination

3) wounds with edges that can be approximated or closed

A wound closure can be achieved in several ways, what are they? (4)

1) suture

2)staple

3) butterfly closure

4)fibrin glue (superglue for the skin)

there are two principal events that are involved with primary closure, what are they

1) repair which is the formation of new ECM to replace lost ECM

2) Regeneration which is reepithelialization

When tissue damage is minimal, what is the result?

1) Little granulation is needed to fill dead space

2) Mitosis and regeneration of epidermal cells is rapid

3) Epithelium migrates over suture line

4) scarring is minimal

5)Normal tissue estruture and function are restored

the process is complete in 5-21 days

Characteristics of secondary intention

Healing by secondary intention (spontaneous closure) occurs when a full thickness wound heals without a closure attempt

The wounds are left open to heal because of their size of the margins of the injury to prevent approximation of wound edges, a large amount of exudate Is present, and the wound is infected,necrotic, or contaminated

a large amount of granulation tissue is generated during healing, the primary mechanism is wound contraction by myofibroblasts interacting with the ECM

More connective tissue is needed to fill the wound than in primary intention because healing is longer and the scar is larger

natural regeneration of the epidermis is possible but grafts may be required with severe tissue loss, because of this the risk for infection is greater than in primary intention

Characteristics of tertiary intention

healing by terry intention (delayed primary closure) occurs when would closure is delayed

tertiary intention is a combination of primary intention and secondary intention because

• contaminated wound is cleaned and left open for several days

• drainage of exudate is observed for signs of infection

• center of wound gifts with granulation tissue

• would edges are approximated

the scarring is greater in primary intention but less than in secondary intention

the healing process involves a complex, overlapping progression of events where these events overlap in both time and activity , they are broken down into 4 phases, what are these phases

1) hemostasis

2) Inflammatory

3)Proliferative

4)remodeling

the extent and duration of phases will vary by wound type and nature

Communication between the ECM and surrounding cells is essential for effective wound healing

these are facilitated by chemical mediators that directly or indirectly regular each step, what are these steps? (7)

1) Cytokines

2) Growth factors

3)proteases

4)Amines

5)Structural adhesion proteins

6)GAGS

7)Proteoglycans

Some mediators are derived from inflammatory and resident cells, what are these cells?(7)

1) neutrophils

2)macrophages

3)lymphocytes

4)platlets

5)keratinocytes

6)fibroblasts

7)endothelial cells

some mediators are substances found in plasma, what are these mediators? (2)

1) Fibrinogen

2)Thrombin

cytokines and growth factors are the most important classes of mediators in the wound healing process, what are these different classes (3)

1) almost every type of cell in skin participates in cytokine and growth factor production

2) Cytokines are small proteins secreted by immune cells

3)Growth factors are proteins that stimulate the growth, division, or differentiate of other cells

• secreted by a variety of cells in a wound

• named for their cell of origin or the target cell

• grouped into families with similar structures and functions

• control activities of other cells by regulating intercellular communication

Nitric oxide is also a mediator which is critical for wound healing, why is this

because it is a reactive oxygen species or free radical and it may be directly or indirectly involved in wound healing

the profile of chemical mediators at the injury site during each phase is critical to successful wound closure, why is this?

this is because the profile changes as the healing progresses and the timing/concentration of cytokines and growth factors and their relationship to other mediators is complex

Clinical mediators that are associated with wound healing are included in several tables, what are these tables? (2)

1) scarring is minimal

2) normal tissue structure and function are restored

process is complete in 5-21 days

what are the characteristics of secondary intention?

healing by secondary intention (spontaneous closure) occurs when a full thickness wound heals without a closure attempt

A large amount of granulation tissue is generated during healing

the primary mechanism is wound contraction by myofibroblasts interacting with the ECM

Natural regeneration of the epidermis is possible but grafts may be required with severe tissue loss

risk for infection is greater than in primary intention

wounds are left open to heal for specific reasons, what are these reasons?(3)

1) the size or margins of the injury prevent approximation of wound edges

2) A large amount of exudate is present

3)The wound is infected, necrotic, or contaminated

More connective tissue is needed to fill the wound than in primary intention, why is this? (2)

1) it is healing longer

2) the scar is larger

characteristics of tertiary intention

healing by tertiary intention ( delayed primary closure) occurs when wound closure is delayed

scarring is greater than in primary intention but less than in secondary intention

tertiary intention is combination of primary intention and secondary intention, what are the characteristics that make up the combination? (4)

1) Contaminated wound is cleaned and left open for several days

2) daring of exudate is observed for signs of infection

3)center of wound fills with granulation tissue

4)wound edges are approximated

characteristics of the phases of wound healing

the healing process involves a complex, overlapping progression of events; these events overlap in both time and activity

the extent and duration of phases varies by wound type and nature

there are 4 phases of wound healing, what are they?

1) hemostasis

2)inflammatory

3) proliferative

4) remodeling

Communication between the ECM and surrounding cells is essential for effective wound healing, these are facilitated by chemical mediators that directly or indirectly regulate each step, what are these steps (7)

1) cytokines

2) growth factors

3) proteases

4)amines

5)structural adhesion proteins

6) GAGS

Characteristics of hemostasis

1) the first step of the inflammatory phase

2)controls hemorrhage and maintains vascular integrity

3)uses two physiologic processes

• formation of a platelet plug

• generation of a fibrin-based clot

brief, intense period of injury site vasoconstriction occurs immediately following an injury

• reduces vessel diameter

• slows blood loss

narrowing vessel lumen brings endothelial surfaces into contact with each other

• increases stickiness of surfaces

• causes severed vessel ends to adhere to each other

characteristic of inflammatory phase

acute inflammation is the first phase of wound healing, the goal of this phase is to

• minimize tissue damage

• prevent additional injury

• prepare the wound for healing and regeneration

the functions of this phase is to

-stop bleeding

-break down damaged extracellular matrix

-recruit phagocytic cells

-remove injurious agent and debris from wound bed

platelet ahdesion, platelet activation, and the platelet plug is when the endothelial lining is disrupted and blood contacts collagen in the ECM so platelets release clotting factors

• platelets are activated

• promote platelets adherence to site of injury

platelet activation also leads to devlopment of platelet plug at the injury site by

-temporarily stoping leaks

-fibrin clots eventually develop to take its place

platelets store chemical mediators that are released at the injury site, those chemical mediators are

• vasoactive substances

• cytokines

• growth facotrs

• adhesion molecules

• digestive enzymes

what is the fibrin clot in regards to the inflammatory phase

the fibrin clot are activated platelets that initiate a series of events leading to the coagulation cascade

recruitment of phagocyte cells and wound debridement requires 3 steps, what are these steps

1) after the hemostasis is achieved and the inflammatory process begins

2)dictated by the activities and secretion of cells are

• platlets

• mast cells

• neutrophils

• macrophages

3)macrophages are the most important product of cytokines and growth factor

what are the characteristics of the proliferative phase

the proliferative phase guides the wound toward tissue repair, because of this several cells are responsible for this phase; these cells include

• fibroblasts

• endothelial cells

• keratinocytes

the events of the proliferative phase depend heavily on cell migration, these include

• collagen deposition

• angiogenesis

• reepitheliaization

cell migration is the dynamic process of coordinated changes in the cell cytoskeleton, this process includes? (3)

1) allows detachment from basement membrane,neigboring cells, and ECM components

2) allows adhesion to components of the ECM

3)Allows forward movement through the ECM

what is granulation tissue?

granulation tissue is a mass of new connective tissue that forms on the surface of a healing wound

it serves as a foundation for the collagen based matrix that eventually replaced the provisional matrix, the amount of granulation tissue generated depends on the extent of the injury

1) wounds healed by primary intension have minimal tissue loss so have little granulation tissue

2)wounds healed by secondary and tertiary intention involve greater tissue loss so have more granulation tissue

synthesis of granulation tissue begins 3-5 days after injury and overlaps inflammatory phase

provisional matrix is replaced by addition of new collagen and elastin fibers and proteoglycans

rapid cell proliferation and matrix generation require oxygen and nutrients to cause angiogenesis ti being, endothelial cells to migrate to their wound bed, new and leaky capillaries are formed (capillaries are responsible for red, knobby, and moist appearance of granulation tissue

what is the difference between fibroblasts and myofibroblasts

fibroblasts produce collagen and adhesive proteins for new ECM, they are one of the last cell types at a wound as they arrive 48-72 hours after the injury, the 1st fibroblasts will differentiate INTO myofibroblasts

myofibroblasts are fibroblasts with the characteristics of smooth muscle cells by intermingling with collagen bundles and growth factors to promote wound contraction and disappearing from the wound bed via apoptosis at the end of the proliferative phase

collagen production becomes significant one week after injury

characteristics of endothelial cells

endothelial cells are responsible for new vessel growth in the wound bed

angiogenesis is the formation of new blood vessels within a tissue which is referred to as neovasculariation

when does new capillary growth typically occur

when capillary buds arise from preexisting venues adjacent to wound

new vessels are critical for provision of oxygen and nutrients of granulation tissue

know that

progression of angiogenesis is proportional to the amount of perfusion and the oxygen tension in the wound

growth factors and other molecules stimulate and regulate angiogenesis VEGF

know that too

what is reepitheliaization

the process of regenerating keratinocytes that provide a protective barrier for the wound bed underneath the scab, it will begin within hours of injury and overlaps with the inflammatory phase , it requires keratinocyte stem cells from the stratum basal at the wound edges, it occurs more quickly when basement membrane is intact

minimal repithelizaition is needed in primary intuition healing because wound edges as placed against each other

extent of damage determines amount of reepithelization in secondary or tertiary intention healing

when the wound size exceeds keratinocyte ability to regenerate over surface of wound, another wound covering or graft must be used

what is the remodeling phase

remodeling is the final phase of wound healing; it overlaps with the proliferative phase , its goal is to restore structural and functional integrity of the skin

when the dermal matrix is mended not regenerated like the epidermal matrix, what happens

granulation tissue in provisional matrix is slowly replaced with more stable collagen based matrix and collagen deposition started in proliferative phase continues in remodeling phase

the outcome of the remodeling phase is a scar or fibrotic tissue, why is this

collagen in scar tissue has a different structural organization than in uninjured tissue, normal tissue has a netlike collagen arrangement, and scar tissue has a parallel orientation of collagen fibers along stress lines

wound contraction is mechanical force exerted by cells that causes a reduction in wound size, what does this lead to

leads to closure, begins 4-5 days after injury in early proliferative phase, continues for about two weeks, mediated in part by contractile myofibroblasts as myofibroblats adhere to one another and to the wound edges, when they contract the entire wound bed contracts, and wound contraction continues after reepithlization

continuous collagen turnover occurs in the matrix, how is this done

collagen production initially exceeds destruction, about 3 weeks after injury collagen content is maximal, net production of collagen then declines and degradation increases, and synthesis and breakdown continues to occur and there is no net increase in collagen content

the type of collagen fibers changes, what does this mean for them

initially type II collagen is produced in large amounts, fibers are laid down randomly and provides a large amount of collagen but little tensile strength

during remodeling type III is replaced by type I

the ratio of type I to type III becomes similar to that of intact connective tissue

type I collagen fibrils rearrange to increase cross linking of molecules, what are the steps of this

1) maximizes tensile strength against stress and shear forced on the skin

2)three weeks after the injury, collagen content is maximal and wound has 20-25% of tensile strength on uninjured skin

3) six months after injury collagen has achieved 75-80 % of tensile strength

scar changes as it matures, what are the steps of this

1) capillary density decreases, changing scars from pink to white

2) cellular content declines

3)collagen production declines

4)fibroblasts in ECM decrease

mature scar has no appendages (hair follicles, sweat gland, sebaceous glands)

maturation of scar tissue continues for at least 1 year after injury

characteristics of blood flow and hypoxia

blood flow to the injury site is one of the of the most important factor in healing, hypoxia can delay or stop the wound healing process, early hypoxia of the wound bed is excepted due to initial disruption of the vascular and ischemic associated with injuries, hypoxia is greatest at the center, diminishing toward the edges,

hypoxia is the leading cause of wound infection, why is this

1) oxygen is needed for optimal phagocyte function in the inflammatory phase

2)oxygen in the wound improves host immune defenses against microbial infection

3) because inflammatory cells consume a lot of oxygen, hypoxia can be amplified by infection

hypoxia inhibits fibroblast activity and collagen deposition in the matrix, why is this

1) the collagen production rate is directly related to oxygen tension in the wound

2)fibroblasts cannot produce collagen without mature blood vessels to deliver oxygen

3)new blood vessels fail to mature without a strong collagen matrix

In the proliferative phase, hypoxia acts as a stimulus for angioengeis in the wound bed, how is this?

1) if hypoxia persists despite new vessel growth, necrosis and impaired wound healing will result

2)protracted hypoxia due to a prolonged decrease in blood flow to the wound can lead to chronic, non healing wound

hypoxia impedes reepiethlizaiton of the wound, why is this

it can only occur when the wound is covered with granulation tissue , granulation tissue requires production of collagen and angiogenesis in the wound

both of these processes are oxygen dependent

what are the characteristics of wound infection and contamination

infection limits the ability of neutrophils to phagocytize bacteria and its the most common cause of delayed healing

most wounds are contaminated at the time of injury, how do they over this problem

host defensives are responsible for containing infection, badly contaminated wounds may overwhelm host defenses, may occur in the presence of several types of foreign bodies including dirt, glass, wood, metal

technical aspects of surgical wound handling and closure can affect the occurrence of wound infection, why is this

innaproroprate suture material increases likelihood of foreign body reaction leading to infection, other risk factors leading to infection of surgical wounds could include break in asepsis, duration of surgery,spill of intestinal contents into peritoneum, failure to properly prepare skin preoperatively ht

the presence of infection stimulates complement activation and exaggerates and prolongs the inflammatory process, what does this create

this creates substances that interfere with preparation of wound bed for collagen deposition, reepithelization, and contraction including excessive exudate, inflammatory cells, necrotic tissue, and microorganisms, leads to failure to heal

Tissue damage from infection and be extensive if allowed to proceed for prolonged period because why

microorganisms compete with uninjured cells for oxygen and nutrients

any necrotic or foreign material remaining in a wound delays healing, why is this

necrotic tissue acts as a mechanical barrier to reepitehlization and deposition of granulation tissue by providing a breeding place for infection and prolongs the inflammatory phase, releasing endotoxins that may inhibit fibroblast and keratinocyte migration, impairing reepitrhalization and collagen formation and it must derided to speed wound healing

forgiven or exogenous materials enter the would from the environment by acting as continuing stimulus for inflammation and infection, can act as a mechanical barrier to fibroblasts, endothelial cells, and keratinocytes trying to enter the wound matrix, results in impairment of reeptierhlization and granulation tissue formation

wound healing may also be impaired by contamination with endogenous substances produced within the body for example contamination of peritoneal cavity for intestinal fluids

what are esstential for cellular respiration in healing wounds

carbs and fats a

a negative nitrogen balacne affects wound healing in many ways, what are these ways

• blunt b- and t-lymphcyte immune response

• depresses inflammatory response

• reduces effect of bacterial phagocytosis and killing

• increases probability of delayed wound healing and infection

• diminishes angiogenesis

• decreases collagen synthesis and cross linking

• lessens tensile strength and stability

• reduces matrix formation and remodeling

many vitamins and minerals are required for wound healing, what are they

• vitamin and minerals deficency are commonly associated with chronic and non healing wounds

• vitamin deficiency affect wound healing directly

• mineral deficency affect introcellular activities need for healing to occur

explain a vitamin a deficency

it negatively affects reepithelization, impairs deposition of collagen and fibronection

• decreases formation of granulation tissue

• adversely affects tensile strength and stability of healing wound

It impedes inflammatory process and impairs white blood cell function by

• impairs debridement of the wound bed

• reduces antimicrobial activity

• decreases secretion of cytokines and growth factors

it also impedes development of new capillaries in the wound

there is also a vitamin c, vitamin e, and vitamin k, zinc, magnesium, copper, and iron deficency

she doesn’t elaborate on these just know what they are

medications in terms of wound healing

medications can affect wound and tissue healing, immunosuppressants and corticocorteriods, greatly influence immunologic mechanism involved in tissue repair

medications affecting blood flow may also influence wound healing by altering perfusion of the wound bed

corticosteroids in terms of wound healing

corticosteroids are hormones given for many diseases including asthma, rheumatoid arthritis, allergies, and shock

they promote breakdown of carbohydrates and proteins by breaking down impairs anabolic processes need for cell growth and proliferation during wound healing

they exert powerful anti inflammatory action by impeding inflammatory phase of wound healing and the normally only affect wound healing when taken in high doses for prolonged period

the negative effects are phagocytosis are reduced, reduction in fibroblast proliferation and collagen synthesis, and decreased angiogenesis

the impact on wound healing was prolonged wound hypoxia, increased suscpetibilty to wound infection, reduced granulation tissue formation, decreased wound tensile strength and stability, increased incidence of dehiscence, and reduced wound contraction

antineoplastic drugs in terms of wound healing

antinoplastic drugs are used to treat cancer, can be toxic to human cells by interrupt to mitrotic cycles of rapidly proliferating cells in wound healing

may be potent immunosurpresents by diminish production of leukocyte, erythrocytes, and platelets, and impair recepithelization, granulation tissue formation, and angiogenesis

malignancies being treated with antineoplastic drug can also inhibit wound healing

everything we already know about diabetes mellitus

just know the basics

scarless fetal wound healing

cutaneous wounds in a fetus younger than 24 weeks gestation heal with little or no scarring, healing is multifactorial in nature

what affects scarless healing is gestational age and wound size

gestational age positively correlates to the extent of the scarring, as gestational age increases scarring becomes more visible

would size has different degrees of wounding at the same gestational age may or may not result in a scar , as wound size increases scarring increases even at a young gestational age

there are 4 important factors in scarless wound healing

1)increasing inflammatory response

• scarless fetal wounds heal with minimal inflammation

• lack of inflammation is related to diminished function of fetal neutrophils, macrophages, and platelets

• as the immune system matures and the inflammatory response strengthens, scar formation increases

2) collagenous structure of the ecm

• collagenous architecture in scarless fetal healing contains less collagen and more hylauonan than adult

• as gestational age increases the collagen profile becomes more like that of an adult increasing scar formation

3) myofibroblasts

• myofibroblasts are not present early in gestation

• when myofibroblasts appear scar formation increases

4) cytokines and growth factors

• scarless fetal wounds manifest a different cytokine and growth factor profile than adult scar forming wounds

• as gestational age increases profile becomes more like heat of an adult increasing scar formation

abnormal wound healing

scarring is a result of the body’s effort to repair epithelial skin loss, large variations exist in the degree and quality of scar formation, excessive healing involves abnormally high connective tissue despositon that results in altered tissue structure and function

fibrosis

the replacement of normal tissue elements with excessive nonfunctional collagen or scar tissue

• results in the destruction of normal tissue architecture and composition

• excessive accumulation of collagen at the wound site involves excess synthesis or delayed degradation where etiology is likely mulifactoral and involves process at all stages of wound healing

clinical problems can be due to

• keloids

• hypertrophic scars

• adhesions

• strictures

• liver cirrhosis

keloids

lesions characterized by excess of dermal sac or fibrotic tissue that extends beyond the boundary of the original Injury

• typically occurs in individuals under 30 with darker pigmented skin

• more likely to defvlopem from trauma, burn, and tension injuries

• raises above the level of the surrounding skin

• scar is larger than the original wound

• usually appears 6 months to 1 year after injury

• tend to grow over time and do not regress spontaneously

• almost always recur after simple excision

hypertrophic scars

characterized by an excess of fibrotic tissue that grows within the boundaries of the original tissue

• associated with trauma or burn wounds

• raised above surrounding skin

• develop 1st month after injury

• appearance is related to the inflammatory phase

• often located in wounds on the trunk and wounds that cross flexor surfaces of the extremtiires

• often regress spontaneously

• may be pruritic and edematous but less painful than keloids