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| | ==Species Differences== | | ==Species Differences== |
| | As the integument of avians, reptiles and amphibians is markedly different to that of mammals, it is covered on another page: | | As the integument of avians, reptiles and amphibians is markedly different to that of mammals, it is covered on another page: |
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| − | ===Avian Skin===
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| − | The general make-up of the avian skin is similar to that of mammals, having an ''epidermis'' a ''dermis'' and a ''subcutaneous layer''. In comparison, however, it is much thinner, effectively glandless and contains [Feather - Anatomy & Physiology|feathers]]. Generally, the skin is thin enough to be transparent, aiding examination of superficial internal organs including the liver.
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| − | The '''epidermis''' consists of 3 layers:
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| − | * The basal (germinative) layer
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| − | * Intermediate layer
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| − | * Outer (cornified) layer
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| − | Striated muscles in the epidermis move the skin.
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| − | The '''dermis''' is divided into:
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| − | * A superficial layer which varies in thickness depending on position on the body and age of the bird. This layer contains loosely arranged layers of collagen in interwoven bundles.
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| − | * A deep layer containing fat, [Feather - Anatomy & Physiology|feather follicles]], smooth muscles that control the movement of the feathers, blood vessels and nerves that supply the dermis and epidermis.
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| − | The '''subcutaneous layer''' is formed mainly by loose connective tissue. It also contains fat, both as a layer, and in discrete fat bodies. These are readily observed as yellow deposits beneath the skin.
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| − | Areas of fat deposition vary from species to species (high in aquatic birds) and the time of year (pre-migration deposition).
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| − | Common areas of fat deposition are lateral to the pectoral muscles, in the cloacal region and on the dorsum.
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| − | ====Skin of the legs and feet====
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| − | *'''Podotheca''' - the non-feathered areas of the legs and feet. Scales are formed from raised, heavily keratinised epidermis separated by folds of less keratinised tissue overlying a proliferative germinal layer, giving it a 'pimpled' architecture.
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| − | ====Glandular tissue====
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| − | The avian skin is effectively glandless, lacking sebaceous and sweat glands and most of the skin is thin, dry and inelastic. The exceptions are:
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| − | * Uropygial gland
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| − | * Glands of the ear canal
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| − | * Pericloacal glands
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| − | * ''Keratinocytes''
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| − | The '''Uropygial gland''' is also known as the ''preen gland''. It is a bilobed gland located dorsal to the cloaca at the end of the pygostyle. It opens through a caudally directed nipple.
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| − | This ''holocrine'' gland is NOT present in all species of bird. It is well developed in some parrots (African Greys) but absent in others (Amazons). It is also present in most finches but only some ''columbiformes''.
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| − | The uropygial gland is involved in maintaining feather condition and secretions spread by preening. It serves a waterproofing function. The secretions contain a pro-vitamin D, converted by UV light to active vitamin D. The secretions are also believed to suppress the growth of micro-organisms, serving an anti-bacterial function.
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| − | '''Keratinocytes''' are important in birds without a uropygial gland. Developing dermal cells (keratinocytes) undergo metamorphosis from cuboidal or squamous nature, lose organelles, produce lipids and fibrous proteins ('''keratin''') and dehydrate and lyse.
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| − | This function is unique to birds and it is suggested that the lipid production by the keratinocytes makes the entire skin an 'oil-producing' gland.
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| − | Given that birds do not have sweat or odour producing glands, it is noted that when stressed (e.g. during handling), some parrot species emit a musty odour. This appears to arise from volatile fats emitted directly onto the skin by rapidly lysing keratinocytes.
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| | ==Links== | | ==Links== |
| | http://en.wikipedia.org/wiki/Feathers | | http://en.wikipedia.org/wiki/Feathers |