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Equine Integumentary System - Horse Anatomy (view source)
Revision as of 15:11, 19 November 2012
, 15:11, 19 November 2012→Epidermis
====Stratum Corneum====
====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.
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===
===Dermis===