SKINSKIN Group : Nurul Ikhsani Umar Ridha Anggriani R Gina Salsabila T Fadillah Justika A Idelia L Pandin Ainayah Al Fatiha
The human skin is the outer covering of the body. In humans, it isthe largest organ of the integumentary system. The skin has multiple layers of ectodermal tissue and guards the underlying muscles, bones, ligaments and internal organs. Human skin is similar to that of most other mammals, except that it is not protected by a pelt. Though nearly all human skin is covered with hair follicles, it appears hairless. There are two general types of skin, hairy and glabrous skin. The adjective cutaneous literally means "of the skin".
In humans, skin pigmentation varies among populations, and skin type Severely damaged skin can range from dry to oily.will try to heal by forming Such skin variety provides ascar tissue. This is often rich and diverse habitat for discolored and bacteria which number depigmented. roughly at 1000 species from 19 phyla.
Skin has mesodermal cells,pigmentation, or melanin providedby melanocytes, which absorbsome of the potentially dangerous One form predominantlyultraviolet radiation (UV) in produced by UV light,sunlight. It also contains DNA- malignant melanoma, isrepair enzymes that help reverse particularly invasive, causingUV damage, and people who lack it to spread quickly, and canthe genes for these enzymes often be deadly. Human skinsuffer high rates of skin cancer. pigmentation varies among populations in a striking manner. This has led to the classification of people(s) on the basis of skin color.
The skin is the largest 2–3 mm (0.10 inch) organ in the human thick. The averagebody. For the average square inch (6.5 cm²)adult human, the skin of skin holds 650has a surface area of sweat glands, 20 between 1.5-2.0 blood vessels, 60,000square metres (16.1- melanocytes, and21.5 sq ft.), most of it more than 1,000 is between nerve endings.
Skin performs the following functions : 1. Protection : an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense; Langerhans cells in the skin are part of the adaptive immune system.2. Sensation : contains a variety of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury.
4. Control of evaporation : the skin provides a relatively dry and semi-impermeable barrier to fluid loss. Loss of this function contributes to the massive fluid loss in burns. 5. Aesthetics and communication : others see our skin and can assess our mood, physical state and attractiveness.
7. Excretion: sweatcontains urea, howeverits concentration is1/130th that of urine,hence excretion bysweating is at most asecondary function totemperature regulation.
9. Water resistance : The skinacts as a water resistant barrierso essential nutrients arentwashed out of the body.
Melanin : It is brown in color and present in the germinative zone of the There are at epidermis. least five Melanoid : It resembles melanin different but is present diffusely throughoutpigments that the epidermis.determine the Keratin : This pigment is yellow to orange color of the in color. It is present in the stratum skin. These corneum and fat cells of dermis and pigments are superficial fascia. Hemoglobin (haemoglobin): It is found present at in blood and is not a pigment of the skindifferent levels but develops a purple color. and places. Oxyhemoglobin : It is also found in blood and is not a pigment of the skin. It develops a red color.
Skin is composed of three primary layers: the epidermis , which provides waterproofing and serves as a barrier to infection; the dermis , which serves as a location for the appendages of skin; and the hypodermis , which useful as the subcutaneous adipose layer.
Epidermis, "epi" coming from the Greek meaning"over" or "upon", is the outermost layer of the skin. Itforms the waterproof, protective wrap over the bodyssurface and is made up of stratified squamousepithelium with an underlying basal lamina. The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis. The main type of cells which make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells also present. The epidermis can be further subdivided into the following strata (beginning with the outermost layer): corneum, lucidum (only in palms of hands and bottoms of feet), granulosum, spinosum, basale.
This keratinized layer ofThey eventually reach the skin is responsible forcorneum and slough off keeping water in the(desquamation). This body and keeping otherprocess is called harmful chemicals andkeratinization and takes pathogens out, makingplace within about 27 skin a natural barrier todays. infection.
The epidermis containsno blood vessels, and is Epidermis is divided into several nourished by diffusion layers where cells are formed from the dermis. The through mitosis at the innermostmain type of cells which layers. They move up the strata make up the epidermis changing shape and composition are keratinocytes, as they differentiate and become melanocytes, filled with keratin. They eventually Langerhans cells and reach the top layer called stratum Merkels cells. The corneum and are sloughed off, orepidermis helps the skin desquamated. This process is to regulate body called keratinization and takes temperature. place within weeks. The outermost layer of the epidermis consists of 25 to 30 layers of dead cells.
1. Stratum corneum The stratum corneum (Latin for horned layer) is the outermost layer of the epidermis, consisting of dead cells (corneocytes) that lack nuclei and organelles. The purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress. Desquamation, the process of cell shedding from the surface of the stratum corneum, balances proliferating keratinocytes that form in the stratum basale. These cells migrate through the epidermis towards the surface in a journey that takes approximately fourteen days.
2. Stratum lucidum The stratum lucidum (Latin for "clear layer") is a thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope. It is readily visible by light microscopy only in areas of thick skin, which are found on the palms of the hands and the soles of the feet. Located between the stratum granulosum and stratum corneum layers, it is composed of three to five layers of dead, flattened keratinocytes. The keratinocytes of the stratum lucidum do not feature distinct boundaries and are filled with eleidin, an intermediate form of keratin.The thickness of the lucidum is controlled by the rate ofmitosis (division) of the epidermal cells. In addition,melanocytes determine the darkness of the stratum lucidum.The cells of the stratum lucidum are flattened. They aresurrounded by an oily substance that is the result of theexocytosis of lamellar bodies accumulated while thekeratinocytes are moving through the stratum spinosum andstratum granulosum.
3. Stratum granulosum The stratum granulosum At the transition between this (or granular layer) is a layer and the stratum corneum, thin layer of cells in the cells secrete lamellar bodies epidermis. Keratinocytes (containing lipids and proteins) migrating from the into the extracellular space. underlying stratum This results in the formation of spinosum become the hydrophobic lipid envelope known as granular cells responsible for the skins in this layer. These cells barrier properties. contain keratohyalin Concomitantly, cells lose their granules, protein nuclei and organelles causing structures that promote the granular cells to become hydration and non-viable corneocytes in the crosslinking of keratin. stratum corneum.
This layer is composed of polyhedral keratinocytes, they have large pale staining nuclei as they are active in synthesizingfibrilar proteins, known as cytokeratin, which build up within thecells aggregating together forming tonofibrils. The tonofibrils goon to form the desmosomes allowing strong connections to form between adjacent keratinocytes.
They divide to form theThe stratum basalt is a keratinocytes of the stratumcontinuous layer of cells. It is spinosum, which migrateoften described as one cell superficially. Other types of cellsthick, though it may in fact be found within the stratum basale aretwo to three cells thick in melanocytes (pigment-producingglabrous (hairless) skin and cells), Langerhans cells (immunehyperproliferative epidermis cells), and Merkel cells (touch(from a skin disease). The receptors). Blood capillaries arestratum basale is primarily found beneath the epidermis, andmade up of basal are linked to an arteriole and akeratinocyte cells, which can venule. Arterial shunt vessels maybe considered the stem cells bypass the network in ears, theof the epidermis. nose and fingertips.
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 It contains the hair follicles, basement membrane. It also sweat glands, sebaceous harbors many glands, apocrine glands, Mechanoreceptor/nerve endings lymphatic vessels and blood that provide the sense of touchvessels. The blood vessels in and heat. the dermis provide nourishment and wasteremoval from its own cells as well as from the Stratum basale of the epidermis.
Also located within theThe reticular region lies deep in reticular region are thethe papillary region and is roots of the hair,usually much thicker. It is sebaceous glands,composed of dense irregular sweat glands,connective tissue, and receives receptors, nails, andits name from the dense blood vessels.concentration of collagenous,elastic, and reticular fibers thatweave throughout it. These Tattoo ink is held in theprotein fibers give the dermis dermis. Stretch marks fromits properties of strength, pregnancy are also locatedextensibility, and elasticity. in the dermis.
In the palms, fingers, soles,The papillary region is and toes, the influence of thecomposed of loose areolar papillae projecting into theconnective tissue. It is named epidermis forms contours infor its fingerlike projections the skins surface. These arecalled papillae, that extend called friction ridges, becausetoward the epidermis. The they help the hand or foot topapillae provide the dermis grasp by increasing friction.with a "bumpy" surface that Friction ridges occur ininterdigitates with the patterns that are geneticallyepidermis, strengthening the and epigenetically determinedconnection between the two and are therefore unique to thelayers of skin. individual, making it possible to use fingerprints or footprints as a means of identification.
The hypodermis is not partof the skin, and lies belowthe dermis. Its purpose is to It consists of looseattach the skin to underlying connective tissue andbone and muscle as well as elastin. The main cell typessupplying it with blood are fibroblasts,vessels and nerves. macrophages and adipocytes (the hypodermis contains 50% of body fat). Fat serves as padding and insulation for the body.
Macrophages : Macrophagesfibroblast : A fibroblast are cells produced by the is a type of cell that differentiation of monocytes in synthesizes the tissues. Macrophages were discovered by Ilya Mechnikov, aextracellular matrix and Russian bacteriologist, in 1884. collagen, the structural Human macrophages are aboutframework (stroma) for 21 micrometres (0.00083 in) in animal tissues, and diameter. Monocytes and plays a critical role in macrophages are phagocytes. wound healing. Macrophages function in bothFibroblasts are the most non-specific defense (innate common cells of immunity) as well as help connective tissue in initiate specific defense animals. mechanisms (adaptive immunity) of vertebrate animals.
Their role is to phagocytose, or engulf and then digest, cellular debris and pathogens, either as stationary or as mobile cells. They also stimulate lymphocytes and other immune cells to respond to pathogens. They are specialized phagocytic cells that attack foreign substances, infectious microbes and cancer cells through destruction and ingestion. They move by action of amoeboid movement. Adipocytes : Adipocytes, also known as lipocytes andfat cells, are the cells that primarily compose adiposetissue, specialized in storing energy as fat. There are twotypes of adipose tissue, white adipose tissue (WAT) andbrown adipose tissue (BAT), which are also known aswhite fat and brown fat, respectively, and comprise twotypes of fat cells.