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7/31/2019 1st Lecture on the Histology of Skin by Dr. Roomi
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Histology of Integumentary
System
By
Dr. Mudassar Ali Roomi (MBBS, M.Phil.)
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SKIN
It is the largest organ, about16 % of the total bodyweight.
It is composed of twolayers: epidermis anddermis.
Skin also contains severalappendages (sweat glands,hair follicles, sebaceousglands and nails).
The skin and its appendagesare collectively called asintegument.
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Functions of the Skin
1. Protection of body from invasion of pathogens; prevention oftissue damage by toxic chemicals and ultraviolet light
2. Prevention of dehydration and loss of body fluids (impermeableto water)
3. Regulation of body temperature (production and excretion of
sweat, vascular shunts)4. Sensation of touch, pain, temperature, pressure, and vibration;
important for communication, dexterity, and injury prevention
5. Immunological function of Langerhans cells (antigen-presentingcells) present antigens to lymphocytes in the immune responses
6. Production of vitamin D from precursors under the effects ofsunlight (UV rays)
7. Absorption of creams and ointments
8. Secretion of sebum
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LAYERS OF EPIDERMIS
It consists of following 5
strata (layers):
1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum
5. Stratum corneum
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The basal layer (stratum basale)
Also called as st. germinativum.
It is a single layer ofbasophiliclow columnar cells.
It rests on basal lamina at thedermal-epidermal junction .
Hemidesmosomes bind thesecells to the basal lamina anddesmosomes bind the cells of thislayer together in their lateral andupper surfaces.
This layer has got intense mitoticactivity . ***
All keratinocytes in the st. basalecontain intermediate filaments(keratins).
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The spinous layer (stratum spinosum)
It is normally the thickest epidermal layer It consists of irregular polyhedral cells having
central nuclei with nucleoli and cytoplasm
actively synthesizing keratin filaments.
Just above the st. basale some cells may still
divide in st. spinosum
Stratum Malpighii = st. basale+ st.spinosum
The keratin filaments form microscopically
visible bundles called tonofibrils which
converge and terminate at the numerous
desmosomes, by which the cells are joined
together strongly to resist friction.
False spiny appearance of these cells is
produced during the preparation of thetissue for microscopy
The epidermis of soles of the feet and palms
of hand has a thicker st. spinosum with more
abundant tonofibrils and desmosomes.
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MEDICAL APPLICATION
In adults, one third of all cancers are of the skin.
Most of these derive from cells of the basal or spinous layers, producing,respectively, basal cell carcinomas (BCC) and squamous cell carcinomas
(SCC).
Fortunately both types of tumors can be diagnosed and excised early and
consequently are rarely lethal.
Skin cancer shows an increased incidence in fair-skinned individualsresiding in regions with high amounts of solar radiation.
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The granular layer
(stratum granulosum)
This layer consists of 35 layers of flattened
polygonal cells.
Nuclei of the cell show degeneration.
Cell organelles are lost by autophagy.
Their cytoplasm is filled with intensely
basophilic masses called keratohyaline
granules. These structures are notmembrane-bound and consist of dense
masses offilaggrin and other proteins that
associate with the keratins , linking them into
large cytoplasmic structures in the process of
keratinization.
These cells also contain membrane-coated
lamellar granules, small ovoid structures
containing many lamellae composed of
various lipids. Lamellar granules undergo
exocytosis, discharging their contents into
the intercellular spaces of the stratum
granulosum. The layer of lipid is a major
component of epidermal barrier against the
loss of water from skin.
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The stratum lucidum
The stratum lucidum is onlyseen in thick skin, where itconsists of a thin, translucentlayer of extremely flattenedand eosinophilic cells.
The nuclei and organelles havebeen lost
the cytoplasm consists almostonly of densely packed keratinfilaments embedded in anelectron-dense matrix called
eleidin which is a derivative ofkeratohyaline.
Desmosomes are still evidentbetween adjacent cells.
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The stratum corneum
This layer consists of 15
20 layersof flattened, non-nucleatedkeratinized cells whose cytoplasmis filled with filamentous keratins.
These cells are devoid of nucleiand organelles.
After keratinization, the cellscontain only fibrillar andamorphous proteins withthickened plasma membranesand are called squames or horny,cornified cells (corneocytes).
These cells are continuously shedat the surface of the st. corneum.
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MEDICAL APPLICATION
In psoriasis, a common skindisease, there is an increasein the number ofproliferating cells in the st.basale and the st. spinosum
as well as a decrease in thecycle time of these cells.
This results in greaterepidermal thickness andmore rapid renewal of
epidermis, but also canproduce abnormalkeratinization with adefective skin barrier.