Skin repair
Encyclopedia
Protection from mechanical injury, chemical hazard
s, and bacterial invasion is provided by the skin
because the epidermis is relatively thick and covered with keratin
. Secretion
s from sebaceous glands and sweat glands also benefit this protective barrier. In the event of an injury that damages the skin's protective barrier, the body triggers a response called wound healing
. After hemostasis
, inflammation
white blood cells, including phagocytic macrophages arrive at the injury site. Once the invading microorganisms have been brought under control, the skin proceeds to heal
itself. The ability of the skin to heal even after considerable damage has occurred is due to the presence of stem cells in the dermis
and cells
in the stratum basale of the epidermis, all of which can generate new tissue
.
When an injury extends through the epidermis into the dermis, bleeding occurs and the inflammatory response begins. Clotting mechanisms in the blood are soon activated, and a clot of scab is formed within several hours. The scab temporarily restores the integrity of the epidermis and restricts the entry of microorganisms. After the scab is formed, cells of the stratum basale begin to divide by mitosis
and migrate to the edges of the scab. A week after the injury, the edges of the wound are pulled together by contraction. Contraction is an important part of the healing process when damage has been extensive, and involves shrinking in size of underlying contractile connective tissue, which brings the wound margins toward one another. In a major injury, if epithelial
cell migration
and tissue contraction cannot cover the wound, suturing the edges of the injured skin together, or even replacement of lost skin with skin grafts
, may be required to restore the skin.
As epithelial cells continue to migrate around the scab, the dermis
is repaired by the activity of stem cells. These active cells produce collagen
ous fibers and ground substance
. Blood vessels soon grow into the dermis, restoring circulation. If the injury is very minor, the epithelial cells eventually restore the epidermis once the dermis has been regenerated.
In major injuries, the repair mechanisms are unable to restore the skin to its original condition. The repaired region contains an abnormally large number of collagenous fibers, and relatively few blood vessels. Damaged sweat
and sebaceous glands, hair follicle
s, muscle
cells, and nerve
s are seldom repaired. They are usually replaced by the fibrous tissue. The result is the formation of an inflexible, fibrous scar
tissue.
Chemical hazard
A chemical hazard arises from contamination of an area with harmful or potentially harmful chemicals. Possible sources of chemical hazards include the burning of fossils, materials and chemicals used in construction and industry, pollution of the environment and water supply, chemical spillages,...
s, and bacterial invasion is provided by the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
because the epidermis is relatively thick and covered with keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
. Secretion
Secretion
Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
s from sebaceous glands and sweat glands also benefit this protective barrier. In the event of an injury that damages the skin's protective barrier, the body triggers a response called wound healing
Wound healing
Wound healing, or cicatrisation, is an intricate process in which the skin repairs itself after injury. In normal skin, the epidermis and dermis exists in a steady-state equilibrium, forming a protective barrier against the external environment...
. After hemostasis
Hemostasis
Hemostasis or haemostasis is a process which causes bleeding to stop, meaning to keep blood within a damaged blood vessel . Most of the time this includes blood changing from a liquid to a solid state. Intact blood vessels are central to moderating blood's tendency to clot...
, inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
white blood cells, including phagocytic macrophages arrive at the injury site. Once the invading microorganisms have been brought under control, the skin proceeds to heal
Healing
Physiological healing is the restoration of damaged living tissue, organs and biological system to normal function. It is the process by which the cells in the body regenerate and repair to reduce the size of a damaged or necrotic area....
itself. The ability of the skin to heal even after considerable damage has occurred is due to the presence of stem cells in the dermis
Dermis
The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
and cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
in the stratum basale of the epidermis, all of which can generate new tissue
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
.
When an injury extends through the epidermis into the dermis, bleeding occurs and the inflammatory response begins. Clotting mechanisms in the blood are soon activated, and a clot of scab is formed within several hours. The scab temporarily restores the integrity of the epidermis and restricts the entry of microorganisms. After the scab is formed, cells of the stratum basale begin to divide by mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
and migrate to the edges of the scab. A week after the injury, the edges of the wound are pulled together by contraction. Contraction is an important part of the healing process when damage has been extensive, and involves shrinking in size of underlying contractile connective tissue, which brings the wound margins toward one another. In a major injury, if epithelial
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
cell migration
Cell migration
Cell migration is a central process in the development and maintenance of multicellular organisms. Tissue formation during embryonic development, wound healing and immune responses all require the orchestrated movement of cells in particular directions to specific locations...
and tissue contraction cannot cover the wound, suturing the edges of the injured skin together, or even replacement of lost skin with skin grafts
Skin grafting
Skin grafting is a type of graft surgery involving the transplantation of skin. The transplanted tissue is called a skin graft.Skin grafting is often used to treat:*Extensive wounding or trauma*Burns...
, may be required to restore the skin.
As epithelial cells continue to migrate around the scab, the dermis
Dermis
The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
is repaired by the activity of stem cells. These active cells produce collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
ous fibers and ground substance
Ground substance
Ground substance is a term for the non-cellular components of extracellular matrix which contain the fibers.It is usually not visible on slides, because it is removed during the preparation process....
. Blood vessels soon grow into the dermis, restoring circulation. If the injury is very minor, the epithelial cells eventually restore the epidermis once the dermis has been regenerated.
In major injuries, the repair mechanisms are unable to restore the skin to its original condition. The repaired region contains an abnormally large number of collagenous fibers, and relatively few blood vessels. Damaged sweat
Sweat gland
Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:...
and sebaceous glands, hair follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
s, muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
cells, and nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s are seldom repaired. They are usually replaced by the fibrous tissue. The result is the formation of an inflexible, fibrous scar
Scar
Scars are areas of fibrous tissue that replace normal skin after injury. A scar results from the biological process of wound repair in the skin and other tissues of the body. Thus, scarring is a natural part of the healing process. With the exception of very minor lesions, every wound results in...
tissue.