| Revision as of 20:38, 28 November 2012 edit198.236.17.23 (talk) →Layers of the skin← Previous edit |
Revision as of 20:39, 28 November 2012 edit undo198.236.17.23 (talk) →Layers of the skinTag: section blankingNext edit → |
| Line 26: |
Line 26: |
|
| page=142 |
|
| page=142 |
|
}}</ref> (including ], ], ], ]s, and ]). The integumentary system has a variety of functions; it may serve to waterproof, cushion, and protect the deeper tissues, excrete wastes, and regulate ], and is the attachment site for ]s to detect pain, sensation, pressure, and temperature. In most terrestrial vertebrates with significant exposure to sunlight, the integumentary system also provides for ] synthesis. |
|
}}</ref> (including ], ], ], ]s, and ]). The integumentary system has a variety of functions; it may serve to waterproof, cushion, and protect the deeper tissues, excrete wastes, and regulate ], and is the attachment site for ]s to detect pain, sensation, pressure, and temperature. In most terrestrial vertebrates with significant exposure to sunlight, the integumentary system also provides for ] synthesis. |
|
|
|
|
==Layers of the skin== |
|
|
The integumentary system is the largest of the body's ]. In humans, this system accounts for about 12 to 15 percent of total body weight and covers 1.5-2m<sup>2</sup> of surface area.<ref>Martini & Nath: "Fundamentals of Anatomy & Physiology" 8th Edition, pp.158,Pearson Education, 2009</ref> It distinguishes, separates, and protects the organism from its surroundings. Small-bodied invertebrates of aquatic or continually moist habitats ] using the outer layer (integument). This gas exchange system, where gases simply diffuse into and out of the ], is called '''integumentary exchange'''. |
|
|
|
|
|
The human skin (integument) is composed of a minimum of 3 major layers of tissue: the ]; ]; and ]. The epidermis forms the outermost layer, providing the initial barrier to the external environment. Beneath this, the dermis comprises two sections, the papillary and reticular layers, and contains connective tissues, vessels, glands, follicles, hair roots, sensory nerve endings, and muscular tissue.<ref name="ageing skin"></ref> T this subject sucks pohe deepest layer is the hypodermis, which is primarily made up of ]. Substantial collagen bundles anchor the dermis to the hypodermis in a way that permits most areas of the skin to move freely over the deeper tissue layers.<ref>{{cite web|last=Pratt|first=Rebecca|title=Integument|url=http://www.anatomyone.com/a/integument/|work=AnatomyOne|publisher=Amirsys, Inc|accessdate=2012-09-28}}</ref> |
|
|
|
|
|
===Epidermis=== |
|
|
{{Main|Epidermis (skin)}} |
|
|
This is the top layer of skin made up of ]. It does not contain blood vessels. Its main function is protection, absorption of nutrients, and homeostasis. In structure, it consists of a keratinized stratified ] comprising four types of cells: ], ], ], and ]. The major cell of the epidermis is the keratinocyte, which produces keratin. ] is a fibrous protein that aids in protection. Keratin is also a water-proofing protein. Millions of dead keratinocytes rub off daily. The majority of the skin on the body is keratinized, meaning ]. 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 protein keratin stiffens epidermal tissue to form ]s. Nails grow from thin area called the ]; growth of nails is 1 mm per week on average. The ] is the crescent-shape area at the base of the nail, this is a lighter color as it mixes with the matrix cells. |
|
|
|
|
|
===Dermis=== |
|
|
{{Main|Dermis}} |
|
|
The dermis is the middle layer of skin, composed of dense irregular connective tissue and ] such as collagen with ] arranged in a diffusely bundled and woven pattern. The dermis has two layers. The Papillary layer which is the superficial layer and consists of the areolar connective tissue and the Reticular layer which is the deep layer of the dermis and consists of the dense irregular connective tissue. These layers serve to give elasticity to the integument, allowing stretching and conferring flexibility, while also resisting distortions, wrinkling, and sagging.<ref name="ageing skin"/> The dermal layer provides a site for the endings of blood vessels and nerves. Many ] are also stored in this layer, as are the bases of integumental structures such as ], ], and ]. |
|
|
|
|
|
===Hypodermis=== |
|
|
{{Main|hypodermis}} |
|
|
Also called the hypoderm, subcutaneous tissue, or superficial fascia and the bottom layer of the integumentary system in vertebrates (hypoderm and subcutaneous are from Greek and Latin words, respectively, for "beneath the skin"). Types of cells that are found in the hypodermis are fibroblasts, adipose cells, and macrophages. It is derived from the mesoderm, but unlike the dermis, it is not derived from the dermatome region of the mesoderm. In arthropods, the hypodermis is an epidermal layer of cells that secretes the chitinous cuticle. |
|
|
|
|
|
|
==Functions== |
|
==Functions== |