1st Lecture on the Histology of Skin by Dr. Roomi

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.

1st Lecture on the Histology of Skin by Dr. Roomi

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