Integumentary system
- "Integument" redirects here; in botany, an integument refers to an outer membrane of an ovule, which later develops into a seed coat.
| Integumentary system | |
|---|---|
| Details | |
| Identifiers | |
| Latin | integumentum commune |
| MeSH | D034582 |
| TA98 | A16.0.00.001 |
| TA2 | 7040 |
| TH | H3.12.00.0.00001 |
| FMA | 72979 |
| Anatomical terminology | |
The integumentary system (From Latin integumentum, from integere 'to cover'; from in- + tegere 'to cover'[1]) is the organ system that protects the body from damage, comprising the skin and its appendages[2][3] (including hair, scales, feathers, and nails). The integumentary system has a variety of functions; it may serve to waterproof, cushion, and protect the deeper tissues, excrete wastes, and regulate temperature, and is the attachment site for sensory receptors to detect pain, sensation, pressure, and temperature. In humans the integumentary system also provides vitamin D synthesis.
The integumentary system is the largest organ system. In humans, this system accounts for about 16 percent of total body weight and covers 1.5-2m2 of surface area.[4] It distinguishes, separates, protects and informs the animal with regard to its surroundings. Small-bodied invertebrates of aquatic or continually moist habitats respire using the outer layer (integument). This gas exchange system, where gases simply diffuse into and out of the interstitial fluid, is called integumentary exchange.
Epidermis
The human skin (integumentary) is composed of a maximum of 3 major layers of tissue. theynsbsabhjfsab is the Epidermis, which is includes 6 layers of tissue. Deep to the Epidermis are the Dermis and Hypodermis. The Dermis is comprised of two sections, the Papillary and Reticular layers; they contain connective tissues, vessels, glands, follicles, hair roots, sensory nerve endings, and muscular tissue[5]. The third layer of the skin is the Hypodermis and it generally contains areolar and adipose tissue.
The superficial layer of the Epidermis is called the Stratum Corneum; it contains up to 30 layers of dead Keratinocites and bumps up into friction ridges providing its host with grip. The keratinocyte is pushed up from the Stratum Basale to the Corneum by dividing cells where it will eventually exfoliate. Mechanical stresses expedite the process of keratinocyte replication. These keratinized cells are water proofed by 3 proteins: lamellar bodies, eleidin, and keratin. One layer deeper to the keratinized skin is the skin is the Stratum Lucidum. This layer is only found in layers of the thickest skin, such as the palmar regions of the hands and the plantar regions of the feet. This is the area of the skin in which the keratinocytes are densely packed with a protein called Eleidin. When they reach Stratum Lucidum the cells are dead and can be distinguish from other tissue layers by their lack of nuclei.
Deep to Stratum Lucidum is a section called the Stratum Granulosum. It consists of 2-5 layers of flat keratinocytes, depending on the thickness of the skin. It is composed of keratinocytes containing keratohyalin granules which contain a protein called lamellar bodies (granules). These lamellar bodies are a membrane-coating-vesicle which is released into the intercellular space between the keratinocyte membranes to form an impermeable lipid-containing sheet which helps to form a water tight barrier. Do to the waterproof coating these cells are cut off from their nutrient supply and quickly die.
Deep to the Granulosum is the Spinosum, the deepest cells of this layer undergo mitosis, which contributes to the replacement of epidermal cells. As these cells are pushed closer to the surface of the skin they cease division and produce more keratin filaments, this is the third water proofing protein and it causes the cells to flatten. When the keratinocytes are flattened they begin to pull away from each other but remain attached to each other through junctions called Desmosomes. A Desmosome is a junction that binds against mechanical stresses to the skin. The spiny appearance of the cell is due to these junctions, which are also for what this layer of tissue is named. The Stratum Spinosum and Granulosum both contain macrophages called dendritic (Langerhans) cells but migrate to the Stratified Squamous Epithelia of the epidermis. They help to protect the body against pathogens and foreign matter.
Deep to the Stratum Spinosum is the Stratum Basale, this layer is composed of 3 types of cells: Keratinocytes, melanocytes and tactile (merkel) cells. Keratinocytes are what compose the majority of the cells in this tissue and as mentioned earlier they are responsible for Epidermal cell Keratinization + Replacement. The Melanocytes continually shed melanin containing fragments from their tips among the basal keratinocytes. The keratinocytes will phagocytize these fragments forming them into granules along the superficial side of the Nucleus, this pigment shields the DNA from UV-Rad.. Lastly there are Tactile (Merkel) cells. These are few in number across the skin and they are responsible for touch sensations. The Basal layer concludes this basic description of the epidermis.
This is the top layer of skin made up of epithelial cells. It does not contain blood vessels. Its main function is protection, absorption of nutrients, and homeostasis. In structure, it consists of a keratinized stratified squamous epithelium comprising four types of cells: keratinocytes, melanocytes, Merkel cells, and Langerhans' cells. The major cell of the epidermis is the keratinocyte, which produces keratin. Keratin is a fibrous protein that aids in protection. Millions of dead keratinocytes rub off daily. The majority of the skin on the body is keratinized, meaning waterproofed. The only skin on the body that is non-keratinized is the lining of skin on the inside of the mouth. Non-keratinized cells allow water to "stay" atop the structure.
The epidermis contains different types of cells: The most common are squamous cells, which are flat, scaly cells on the surface of the skin; basal cells, which are round cells; and melanocytes, which give the skin its color. The epidermis also contains Langerhan's cells, which are formed in the bone marrow and then migrate to the epidermis. They work in conjunction with other cells to fight foreign bodies as part of the body's immune defense system. Granstein cells play a similar role. Melanocytes create melanin, the substance that gives skin its color. These cells are found deep in the epidermis layer. Accumulations of melanin are packaged in melanosomes(membrane-bound granules). These granules form a pigment shield against UV radiation for the keratinocyte nuclei.
The epidermis itself is made up of four to five layers. From the lower to upper epidermis, the layers are named: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (the extra layer that occurs in places such as palms and soles of the feet), and the stratum corneum.
The stratum basale is the only layer capable of cell division, pushing up cells to replenish the outer layer in a process called terminal differentiation. The stratum corneum is the most superficial layer and is made up of dead cells, proteins, and glycolipids.
The protein keratin stiffens epidermal tissue to form fingernails. Nails grow from thin area called the nail matrix; growth of nails is 1 mm per week on average. The lunula is the crescent-shape area at the base of the nail, this is a lighter colour as it mixes with the matrix cells.
Dermis
The dermis is the middle layer of skin, composed of dense irregular connective tissues such as collagen with elastin arranged in a diffusely bundled and woven pattern. These layers serve to give elasticity to the integument, allowing stretching and conferring flexibility, while also resisting distortions, wrinkling, and sagging[5]. The dermal layer provides a site for the endings of blood vessels and nerves. Many chromatophores are also stored in this layer, as are the bases of integumental structures such as hair, feathers, and glands.
Subdermis (aka subcutaneous layer, hypodermis, or superficial fascia)
Although technically not part of the integumentary system, the subdermis is the layer of tissue directly underneath the dermis. It is composed mainly of connective and adipose tissue or fatty tissue. Its physiological functions include insulation, the storage of energy, and aiding in the anchoring of the skin.
Functions
The integumentary system has multiple roles in homeostasis. All body systems work in an interconnected manner to maintain the internal conditions essential to the function of the body. The skin has an important job of protecting the body and acts as the body’s first line of defense against infection, temperature change, and other challenges to homeostasis. Functions include:
- Protect the body’s internal living tissues and organs
- Protect against invasion by infectious organisms
- Protect the body from dehydration
- Protect the body against abrupt changes in temperature, maintain homeostasis
- Help excrete waste materials through perspiration
- Act as a receptor for touch, pressure, pain, heat, and cold (see Somatosensory system)
- Protect the body against sunburns
- Generate vitamin D through exposure to ultraviolet light
- Store water, fat, glucose, and vitamin D
Diseases and injuries
Possible diseases and injuries to the human integumentary system include:
References
- ^ Merriam+Webster+Dictionary at the U.S. National Library of Medicine Medical Subject Headings (MeSH)}
- ^ Integumentary+System at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- ^ Marieb, Elaine (2007). Human Anatomy & Physiology (7th ed.). Pearson Benjamin Cummings. p. 142.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Martini & Nath: "Fundamentals of Anatomy & Physiology" 8th Edition, pp.158,Pearson Education, 2009
- ^ a b The Ageing Skin - Structure of Skin