WikiVet English - User contributions [en]

Skin - Anatomy & Physiology

2008-08-28T17:39:16Z

Lwyanrr: /* Cells of the Epidermis */

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|linkpage =Integumentary - Anatomy & Physiology
|linktext =INTEGUMENTARY SYSTEM
|maplink = Integumentary System (Content Map) - Anatomy & Physiology
|pagetype =Anatomy
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==Development==

===Origin of the epidermis===

Following neurulation, the precursor of the epidermis is formed from the cells covering the embryo - the '''ectoderm'''. This then becomes 2 layers, the outer forming the '''periderm''' and the inner forming the '''basal layer''' or ''stratum basale''. A further layer is formed from the basal layer called the '''spinous layer''' or ''stratum spinosum''. The basal and spinous layers are termed the ''Malphigian layer'', the cells of which then divide to produce the '''granular layer''' or ''stratum granulosum''. As the cells of the granular layer differentiate and keratinise, they form the outer '''cornified layer''' or ''stratum corneum''.

==Structure and Function==

===Epidermis===

[[image: Section of Monkey Skin.jpg|thumb|250px|right|Monkey epidermis showing the layers present. ©RVC2008]]

The epidermis is a stratified squamous epithelium and is composed of 4 cell layers anchored to a basal lamina of connective tissue. Keratinocytes migrate through the epidermis from the basal layer. This migration begins in the stratum basale, then moves up through the stratum spinosum, stratum granulosum and the stratum corneum.

*'''Stratum basale'''
The deepest layer of the epidermis is the ''stratum basale''. It consists of a single layer of columnar epithelium which is adhered to the basal lamina. Nutrition is supplied from the underlying capillaries of the dermis. Migration of cells towards the surface begins here.

*'''Stratum spinosum'''
Above the stratum basale is the ''stratum spinosum''. Spinous cells are large polygonal cells with prominent '''desmosomal intercellular filaments''', which act like bridges between the cells. When cells move into this layer, they shrink and move apart. Keratinisation begins in the stratum spinosum and continues in the stratum granulosum.

*'''Stratum Granulosum'''
External to the stratum spinosum, lies the ''stratum granulosum''. Granular cells are thin, flattened keratinocytes with variably prominent keratohyaline granules. At its outer surface, the stratum granulosum secretes oragnelles called '''lamellar bodies''', which are composed of lipid and enzymes which fuse with the plasma membrane and help to form the water concentration gradient that leads to transepidermal water loss.

*'''Stratum Corneum'''
The outer layer, ''stratum corneum'', consists of anucleate, thin cells filled with keratin filaments and proteins that form a cell envelope resistant to solvents and enzymes; there is also a permeability barrier to water and ions. The cells of the stratum corneum are embedded in a lipid-rich matrix which helps to hold the cells together, while the '''desmosomes''' that were present in lower layers have disappeared. For the stratum corneum to maintain a constant thickness, there is a constant turnover of exfoliated corneocytes, being replaced by new corneocytes. Enzymes in the lamellar bodies from the '''stratum granulosum''' help to break down the intercellular lipid 'glue' that holds the cells in place and there is also some degradation of desmosomes.

====Cells of the Epidermis====

*'''Langerhans' cells'''
These are dentritic cells derived from [[Bone Marrow - Anatomy & Physiology|bone marrow]]. They act as [[Peyer's Patches - Anatomy & Physiology#M cells|antigen presenting cells]] in the epidermis as part of the mononuclear phagocyte immune system. Langerhans' cells express MHC I and II molecules and immunoglubulin Fc receptors and are a key feature of '''delayed hypersensitivity responses.'''

*'''Melanocytes'''
These are also dentritic cells and are derived from the neural crest. They are immersed in the epidermis where they form close contact with a defined number of keratinocytes - an '''epidermal-melanin unit'''. '''Melanin''' is composed of 2 types: ''eumelanin'' which is black-brown and ''phaeomelanin'' which is reddish-brown. Melanocytes produce pigment in melanosome structures which are membrane-bound structures involved in the transfer of pigment to keratinocytes. An important function of melanin is UV protection and absence of pigment confers increased sensitivity to UV damage.

*'''Merkel cells'''
These are part of the sensory apparatus of the skin and are located within the '''stratum basale''' of the epidermis where they act as slow-adapting mechanoreceptors. They are usually closely associated with the afferent myelinated nerve fibres, arranged in a plate-like structure with the base of the Merkel cell, together forming a '''''Merkel's corpuscle'''''.

===Dermis===

The epidermis interfaces with the underlying dermis at the '''basement membrane zone (BMZ)'''. The binding includes anchoring junctions called ''hemidesmosomes'' and ''focal adhesions''. The former comprise extra cellular matrix (ECM) proteins such as '''laminin-5''' and '''collagen type IV''' molecules, which form the lamina densa part of the BMZ, while the lamina lucida is composed of '''Collagen type V'''. '''Collagen type VII''' is important in forming anchoring fibrils between the dermis and the basal lamina.

Rete ridges are epidermal projections into the dermis in areas of mechanical loading such as the nasal planum and footpads.

The '''dermis''' consists of dense fibrous tissue composed of '''collagen type I, III and V''', with some elastin fibres and provides a supporting mattress for the carriage of blood vessels, lymphatic vessels, nerves and sensory receptors, '''hair follicles''', sebaceous and sweat glands, with circulating white cells.

===Glands===

[[image: Skin.jpg|thumb|250px|right|A diagram of a section through typical skin]]

*'''Sweat glands'''
Sweat is considered to be the product of [[General Pathology - Necrosis#Apoptosis|apoptosis]] releasing cell contents into the gland lumen, together with secretion where exocytosis, microapocrine blebbing, transcellular and perhaps paracellular processes involved in varying degrees. Sweat is composed of secretions and cellular debris and includes inorganic ions, water, immunoglobulins, amino acids and waste products including urea and lactic acid. Equine sweat is rich in proteins including glycoproteins, albumin and gammaglobulins, which cause the sweat to froth and the horse is said to "lather up".

Sweat is degraded by bacteria leading to odour. Dogs and cats produce very little sweat and use panting to lower body temperature.

*[[Lactation - The Mammary Gland - Anatomy & Physiology|'''Mammary glands''']]
These are greatly modified, enlarged sweat glands and are present in both male and female animals. Depending on species, they extend from the axillae to the groin, associated with teats and a complex array of sinuses and ducts. Age, pregnancy and [[Endocrine System - Anatomy & Physiology|endocrine]] factors have an important role in determining glandular activity.

*'''Sebaceous glands'''
One or more sebaceous glands surround each '''hair follicle''' at a point about 1/3 of its length beneath the skin's surface. Each gland is composed of numerous ''acini'' attached to a common '''excretory duct''' through which they discharge their secretions ('''sebum''') onto the hair shaft and epidermis. In the skin and eyelids such glands release the cell contents together with secretory products with holocrine secretion. This secretion involves [[General Pathology - Necrosis#Apoptosis|apoptosis]] in which the secretory products and cell debris are released into the gland lumen. The secretory products vary from species to species and include various fatty acids, diglycerides, cholesterol, diesters, wax esters and giant-ring lactones.

The function of sebum is that of an emolient of the hair and skin, preventing excessive dryness. It may combine with '''sweat''' to form an emulsion within the stratum corneum and a form of cement around the hair pores preventing bacterial invasion of the epidermis. Sebum is also released from the glands during piloerection, as the action of the [[Hair - Anatomy & Physiology#Hair Types|arrector pili]] muscle squeezes the gland as it raises the hair.

In sheep, sebum is often referred to as "'''lanolin'''". This is the cause of many skin allergies in humans.

*'''Circumanal and supracaudal tail glands'''
Hepatoid sebaceous glands restricted to the perineum, dorsal tail and prepuce, they may have an endocrine and/or pheromone function. They empty into special sweat glands.

*'''Submental and circumoral glands'''
Large glands in the [[Lips - Anatomy & Physiology|lip]] region of cats and some rodents; presumed to have a territory marking role. Circumoral glands are enlarged integumentary glands bordering on the mucocutaneous junctions of the mouth or oral margins associated with greeting and related behaviours, especially in scuiriomorph rodents.

*'''Inguinal glands'''
Sexually-related scent glands prominent in ungulates and lagomorphs. They are located at the base of the udders to allow offspring to locate the teats of their mother.

*[[Anus - Anatomy & Physiology#Species Differences|'''Anal sacs''']]
Sebaceous (and modified apocrine in the dog) glands lie within the wall of the anal sacs, with a duct carrying material to the anal opening. The foul smelling secretion may act as a territorial marker. Secretions are expressed on defecation. The secretions are composed of fatty and serous materials with cellular debris.

==Cutaneous Appendages==
===Footpads===

[[image: Section of Dog Footpad.jpg|thumb|250px|right|Thickened skin of the canine footpad. ©RVC2008]]

Cats and Dogs have a digitigrade stance with digital, metacarpal and metatarsal pads in contact with the ground. A carpal pad is also present, but seems to be superfluous.

Pads are covered with a very thickened epidermis with no hair follicles. They are hyperpigmented and have atrichial sweat glands opening to the surface under the influence of epinephrine.

There is little dermis and the hypodermis is composed of collagenous and elastic fibres mixed with adipose tissue to form a digital cushion that provides protection from mechanical impact.

===The Nose===
The covering of the nose is very thickened with rete ridges providing anchoring. The surface has a cobblestone appearance in dogs and cats. Hair and sebaceous glands are absent, atrichial glands are present.
[[image: The nose of a Dog.jpg|thumb|200px|left|The cobblestone appearance of the nose of the Dog. Courtesy of Piotr Grzywocz]]

===Claws===
Claws have a variety of functions including locomotion, climbing, fighting and hunting. They are composed of a coronary band, lateral compressed walls and a flaky ventral sole. The hard keratinised epidermis is formed from the nail matrix that is an extension of the hirsute skin, with an underlying vascular dermis.

Cats can unsheath their claws by muscle action and retract them with an elastic ligament on the dorsal aspect of the middle and distal phalanges.

Depending on the pigmentation of the claw, the dermis may or may not be visible. Care must be taken when clipping claws to avoid laceration of the 'quick' and subsequent haemorrhage.

The claws of the accessory first digits on the medial aspect of the foot of dogs is often termed the '''dew claw'''.

===Eyelids===
The palpebral margin is thicker than the remainder of the eyelid and cilia grow from the margin. There are various glands in the region, including '''Moll's glands''' that are modified sweat glands, associated with the cilia. '''Meibomian glands, Zeis glands''' associated with the cilia and the '''lacrimal glands''' together produce the tear film.

==Immunology==
The immune system is involved in several diseases of the skin, with different types of hypersensitivity reactions occuring.

See also [[Skin Immunologic - Pathology|Skin Immunology]]

==Species Differences==
As the integument of avians, reptiles and amphibians is markedly different to that of mammals, it is covered on another page.

[[The Integument of Exotic Species|The Integument Exotic Species]]

Endocrine & Nutritional Influences on the Skin

2008-08-28T17:31:25Z

Lwyanrr: /* Vitamins */

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|linkpage =Integumentary - Anatomy & Physiology
|linktext =INTEGUMENTARY SYSTEM
|maplink = Integumentary System (Content Map) - Anatomy & Physiology
|pagetype =Anatomy
}}
<br>

==Endocrinology of the Skin==
There are various hormones that may influence the structure of the [[Skin - Anatomy & Physiology|skin]]. These influences may be made apparent by the repeated long-term administration of various glucocorticoids or their analogues. Endogenous imbalances are generally seen in adult mature animals although congenital forms have been seen, especially with [[Endocrine System - Thyroid Gland - Anatomy & Physiology#Problems associated with the Thyroid Gland|hypothyroidism]]. The hormones implicated as important for maintaining skin structure are '''thyroxine, cortisol''' and '''estradiol'''. Deficiencies or excessive production may result from abberations in the function of the [[Endocrine System - Adrenal Glands - Anatomy & Physiology|hypothalamic-adrenal axis]], the '''adrenal gland, thyroid gland''' or the '''gonads'''.

Cutaneous changes may include [[Skin Glossary - Pathology|alopecia]], epidermal and dermal thinning, atrophy of [[Skin - Anatomy & Physiology#Glands|sebaceous glands]] and the [[Hair - Anatomy & Physiology#Hair Types|arrector pili]] muscles. There may also be an increased risk of [[Bacterial skin infections - Pathology|microbial infection]] due to poor immune surveillance and delayed wound healing. There are significant differences between species in the manifestation of symptoms.

==Nutrition and the Skin==
Most animals are fed balanced diets and are therefore unlikely to exhibit symptoms. There are some systemic conditions that can reflect deficiency as a result of [[Liver General Pathology - Pathology|hepatic]] or [[Small and Large Intestines - Pathology|intestinal]] diseases for example.

Malnutrition whether due to a deficiency of protein or other nutrients or secondary to a debilitating condition may lead to a dull, brittle and thin [[Hair - Anatomy & Physiology|haircoat]] and to dry, scaly [[Skin - Anatomy & Physiology|skin]]. This in part reflects the high requirement for dietary amino acids to supply requisite building blocks for epidermal turnover and hair growth. Sulfur-containing amino acids are common in the skin and therefore sulfur supplementation is popular for dealing with skin conditions.

===Trace Elements===
Trace elements such as '''copper''' are rarely deficient in farm animals, although deficiency can be associated with poor fertility, ill-thrift and leukotrichia - leading to perioccular 'spectacles'. This reflects the role of copper in the formation of [[Skin - Anatomy & Physiology#Cells of the Epidermis|melanin]].

Excessive exposure to trace elements can also have harmful effects and again, although rare, examples may include [[Skin Nutritional - Pathology|selenosis]] which is usually seen as [[Skin Glossary - Pathology|alopecia]] in geographical areas with high '''selenium''' soil content for grazing animals.

===Vitamins===
*'''Vitamin A''' has a variety of roles that may influence skin and coat condition. Some conditions may respond to supplementation with vitamin A or zinc, but this may not necessarily reflect a deficiency in the diet.

*'''Vitamin C''' deficiency may be associated with [[Skin Nutritional - Pathology|scurvy]] in guinea pigs. The impact of various disease processes that influence feed intake may lead to poor quality coat and skin condition.

*'''Vitamin D''' is processed in part in the skin.

Naomi Ragsdell

2008-06-28T11:24:56Z

Lwyanrr:

===Naomi===

Naomi Ragsdell
[[Image:Lamb.jpg|thumb|Lamb]]

== Contact details ==
* email [[lwyanrr@nottingham.ac.uk]]

== About me ==
I have just passed my second year exams and so I am entering the third year.

==What I hope to get out of this project ==
*Something to do over the summer
*Hope to improve resources available to vet students to help with exam revision

== My best learning experience in the past ==
When we had a guide dogs for the blind demonstration at the vet school and we got to experience what it would be like to be guided by a guide dog round an obstacle course whilst blindfolded.

== Curriculum area that interests me ==
*Endocrinology

== Topics that are difficult ==
*Remembering anatomy

==Day one thoughts==
*There are many different ways you can put information on Wiki e.g flash cards and case studies

===What (three things) I learn't today===

*How to do bullets
*''How to do bullets and italics''
*'''''How to do bullet, italics and bold'''''

===What I still need to learn===
*Lots

===How I feel about what has happened today===
*Good, I've enjoyed it

==Three weeks into the wikivet project (or thereabouts)==

===Sections I've been working on===

* [[Pancreas]]
*

===What I feel I've gained so far from being involved in the project===
*

===Problems or issues that I've had or can forsee===
* T

===My suggestions for improving the way the project works for the future===
*

===What involvement (if any!) I would like to have with the project in the future===
*

File:Lamb.jpg

2008-06-28T11:19:39Z

Lwyanrr: Lamb

Lamb

Naomi Ragsdell

2008-06-28T11:18:04Z

Lwyanrr: New page: ===Naomi=== Naomi Ragsdell 125px == Contact details == * email lwyanrr@nottingham.ac.uk == About me == I have just passed my se...

===Naomi===

Naomi Ragsdell
[[Image:Cattle fibrinopurulent arthritis.jpg|thumb|125px]]

== Contact details ==
* email [[lwyanrr@nottingham.ac.uk]]

== About me ==
I have just passed my second year exams and so I am entering the third year.

==What I hope to get out of this project ==
*Something to do over the summer
*Hope to improve resources available to vet students to help with exam revision

== My best learning experience in the past ==
When we had a guide dogs for the blind demonstration at the vet school and we got to experience what it would be like to be guided by a guid dog round an obstacle course whilst blindfolded.

== Curriculum area that interests me ==
*Endocrinology

== Topics that are difficult ==
*Remembering anatomy

==Day one thoughts==
*There are many different ways you can put information on Wiki e.g flash cards and case studies

===What (three things) I learn't today===

*How to do bullets
*''How to do bullets and italics''
*'''''How to do bullet, italics and bold'''''

===What I still need to learn===
*Lots

===How I feel about what has happened today===
*Good, I've enjoyed it

==Three weeks into the wikivet project (or thereabouts)==

===Sections I've been working on===

* [[Pancreas]]
*

===What I feel I've gained so far from being involved in the project===
*

===Problems or issues that I've had or can forsee===
* T

===My suggestions for improving the way the project works for the future===
*

===What involvement (if any!) I would like to have with the project in the future===
*