চামড়া: সংশোধিত সংস্করণের মধ্যে পার্থক্য

 

== মানুষ এবং স্তন্যপায়ীদের ক্ষেত্রে গঠন ==

{{anchor|Skin layers|Layers|Layer}}

<!-- This section is linked from redirect "[[Skin layers]]"; please adjust when changing section title -->

 

===Epidermis===

বহিস্ত্বক ত্বকের দূরতম স্তর নিয়ে গঠিত হয়। এটা শরীরের পৃষ্ঠের উপর একটি প্রতিরক্ষামূলক বাধা তৈরী করে, যা শরীরে জলধারণ করা এবং প্যাথোজেনের প্রতিরোধ করার জন্য দায়ী। এটি একটি স্তরীভূত স্কোয়ামাসসেল এপিথেলিয়াম<ref name="Rooks">{{cite book|last1=McGrath|first1=J.A.|last2=Eady|first2=R.A.|last3=Pope|first3=F.M.|title=Rook's Textbook of Dermatology|year=2004|edition=7th|publisher=Blackwell Publishing|isbn=978-0-632-06429-8|pages=3.1–3.6}}</ref>, যা মূলত প্রলিফারাটিং বেসাল (proliferating basal) এবং পৃথকীকৃত সুপ্রবাসল কেরাটিনোসাইটস (suprabasal keratinocytes) দ্বারা গঠিত।

 

 

===Basement membrane===

The [[epidermis (skin)|epidermis]] and [[dermis]] are separated by a thin sheet of [[fibers]] called the [[basement membrane]], and is made through the action of both [[tissue (biology)|tissues]].

The [[basement membrane]] controls the traffic of the [[cell (biology)|cells]] and [[molecules]] between the [[dermis]] and [[epidermis (skin)|epidermis]] but also serves, through the binding of a variety of [[cytokine]]s and [[growth factors]], as a reservoir for their controlled release during [[physiological]] remodeling or [[repair]] processes.<ref>{{cite journal | pmid=16064139 | year=2005 | last1=Iozzo | first1=RV | title=Basement membrane proteoglycans: From cellar to ceiling | volume=6 | issue=8 | pages=646–56 | doi=10.1038/nrm1702 | journal=Nature reviews. Molecular cell biology}}</ref>

 

===Dermis===

The '''dermis''' is the layer of skin beneath the [[epidermis (skin)|epidermis]] that consists of [[connective tissue]] and cushions the body from [[stress (biology)|stress]] and strain.

The [[dermis]] provides tensile [[strength of materials|strength]] and [[elasticity (physics)|elasticity]] to the skin through an [[extracellular matrix]] composed of [[collagen fibrils]], [[microfibrils]], and [[elastic fibers]], embedded in [[hyaluronan]] and [[proteoglycans]].<ref name="Pmid" /> Skin proteoglycans are varied and have very specific locations.<ref>{{cite journal | vauthors = Smith MM, Melrose J | title = Proteoglycans in normal and healing skin | journal = Adv. Wound Care | volume = 4 | issue = 3 | pages = 152–73 | year = 2015 | pmid = 25785238 | doi = 10.1089/wound.2013.0464 | pmc=4352701}}</ref> For example, [[hyaluronan]], [[versican]] and [[decorin]] are present throughout the [[dermis]] and [[epidermis]] [[extracellular matrix]], whereas [[biglycan]] and [[perlecan]] are only found in the [[epidermis]].

 

===Hypodermis===

The [[hypodermis]] is not part of the skin, and lies below the [[dermis]]. Its purpose is to attach the skin to underlying [[bone]] and [[muscle]] as well as supplying it with [[blood vessels]] and [[nerves]]. It consists of loose [[connective tissue]] and [[elastin]]. The main [[cell (biology)|cell]] types are [[fibroblast]]s, [[macrophage]]s and [[adipocyte]]s (the [[hypodermis]] contains 50% of [[body fat]]). [[Fat]] serves as padding and insulation for the body. Another name for the [[hypodermis]] is the [[subcutaneous tissue]].

 

 

===Fish and amphibians===

The epidermis of [[fish]] and of most [[amphibian]]s consists entirely of live [[cell (biology)|cells]], with only minimal quantities of [[keratin]] in the [[cell (biology)|cells]] of the superficial layer. It is generally permeable, and in the case of many [[amphibians]], may actually be a major respiratory organ. The [[dermis]] of [[bony fish]] typically contains relatively little of the [[connective tissue]] found in [[tetrapod]]s. Instead, in most species, it is largely replaced by solid, protective bony [[scale (zoology)|scale]]s. Apart from some particularly large dermal bones that form parts of the [[skull]], these [[scale (zoology)|scale]]s are lost in [[tetrapods]], although many [[reptile]]s do have [[scale (zoology)|scale]]s of a different kind, as do [[pangolin]]s. [[Cartilaginous fish]] have numerous tooth-like [[Dermal denticle|denticle]]s embedded in their skin, in place of true [[scale (zoology)|scale]]s.

 

 

===Birds and reptiles===

The [[epidermis (skin)|epidermis]] of [[bird]]s and [[reptile]]s is closer to that of [[mammals]], with a layer of dead keratin-filled [[cell (biology)|cells]] at the surface, to help reduce [[water]] loss. A similar pattern is also seen in some of the more terrestrial [[amphibians]] such as [[toad]]s. However, in all of these [[animals]] there is no clear [[cell differentiation|differentiation]] of the [[epidermis (skin)|epidermis]] into distinct layers, as occurs in [[humans]], with the change in [[cell (biology)|cell]] type being relatively gradual. The [[mammalian]] [[epidermis (skin)|epidermis]] always possesses at least a [[stratum germinativum]] and [[stratum corneum]], but the other intermediate layers found in [[humans]] are not always distinguishable.

[[Hair]] is a distinctive feature of [[mammalian]] skin, while [[feather]]s are (at least among living species) similarly unique to [[birds]].<ref name=VB>{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA|pages= 129–145|isbn= 0-03-910284-X}}</ref>