The SKIN

Dr. Samar Asker

The largest organ in the body

ProtectionRegulation

ExcretionSynthesis

Receive sensation

Medico legal

functions

Diagnose some diseases as : Measles anemia Jaundice chicken pox.

Types of the skin Thick skin Palm, sole, tips of

Fingers& toes

Thin skinAll over the body

Thick skinFormed ofepidermis & dermis.

The epidermis keratiniezed str.sq.epith formed of. Keratinocytes & non Keratinocytes

The Keratinocytes::85% of cells of epidermis form keratin 5 layers .

1

2

345

•Basal layer together with Spinous layer are called malpighian layer

Basal cell layer or Germinal l .LM:

• Single layer of columnar cells resting on clear wavy basement membrane . Have basal oval nucleus & basophilic Cytoplasm.

• The nuclei show mitotic figures for renewal which take place every 2-4 weeks mostly at night

.

EM: • Cells are joined together

by “desmosomes” • to the basement

membrane by “hemidesmosomes”.

• Rich in ribosomes and polysomes

•Melanocytes & Merkels cells are present in this layer.

Spinous layer or Prickle cell l. LM:• 4-8 layers of polyhedral cells with

central and rounded nuclei.• They have spine-like processes

indicating sites of desmosomes as cells shrink during preparation.

EM:•The cells are joined by “desmosomes” & have interdegitating cell membrane.

•The superficial cells contain membrane bound (coated) lamellar granules.

•Langerhans cells are present in this layer

Granular layer LM: •Formed of 2-4 layers of spindle shaped cells with flat nuclei & basophilic granules .

EM:2 types of granules -coated lamellar granules oval or rod shaped covered by membrane contain lamellar discs = lipid bilayer. They discharge their content to the intercellular spaces to form lipid sheets to act as cement & act as Barrier againest bacteria.

Keratohyaline granules: large not covered by membrane form matrix which bind tonofilaments to form bundles

Clear layer LM:1 layer of flattened cells with no nuclei “scales” which contain {eleidin granules} Keratohyaline eleidin granules).EM:No nucleus or organelles. Cells are joined by remnant of desmosomes contain packed filaments of eleidin = immature keratin imbedded in the matrix formed by the keratohyaline granules.

Horny layer

LM : Many acidophilic layers or scales Of keratinized dead cellsEM: dead cells with no nuclei or organelles joined by remnant of desmosomes Filled with mature keratin filaments imbedded in the matrix

Non Keratinocytes

Melanocytes:Origin: ectodermalLM:• have pale rounded nuclei.

• long processes to transport their melanin to the adjacent cells .

• Give Dopa +ve reaction.

EM: euchromatic nucleus

with prominant nucleolus

Character of protein forming cell i.e. many mito. rER & well developed GA

No desmosomes () keratinocytes but hemidesmosomes.

Function:Form tyrosinase enzyme

to form melanin which give the color of the skin

melanin granules protect the DNA from ultraviolet rays.

Merkel’s cells:Origin: ectodermal

LM:Modified basal cells but slightly largerNaked sensory nerve fiber end in a disc like expansion under these cells

EM:attached to the neighboring cells by desmosomes.Cytoplasm contains electron dense granules so may belong to ABUD cellsFunction:1. Mechanoreceptors for touch

& preasure.2. The content of the granules

is responsible for paracrine regulation of epidermal cells

Langerhans Cells:Site:In the upper layer of stratum spinosum, representing 3-8% of the epidermal cells.Origin:MesodermalLM:• Branched cells between

cells of spinous layer.• Dark nucleus & pale

cytoplasm.

EM:No desmosomes & no junction with keratinocytes.

1ry & 2ry lysosomesBirbeck granules= tennis racquet-shaped which contain hydrolytic enzymes.

Function:1. Phagocytic cells of the

skin2. Antigen presenting

cells

The dermis

Reticular layer Papillary layer

thicker & deeper thinner & superficial

dense fibrous C. T. loose C. T.Less cellular & vascular more cellular & vascular Krause and bulbs.Ruffini &Paciniancorpuscles.

Receptors: Meissner’s corpuscle

Thin skin Thick skin The rest of the body Palm, sole, tips of

Fingers& toessite

ThinnerThinner

Thinner=1 AbsentThinner

ThickThickerThicker 2-4 LsPresentThick

EpidermisMalpighian L. Granular LClear layer

Horny layer

Few irregular Regular , numerous, high Dermal papillae

Less numerous

present.

Sweat glands: more numerous.Hair follicles:Sebaceous glands: abcent Arrector pili muscle:.

Appendages

Mitotic figures are common in the cells of :

 a. Basal cell layer.

b. Spinous layer.

c. Horny layer.

d. Clear layer.

e. None of the above.

The cells of granular layer contain :

 a. Melanin pigments.

b. Carotene pigments.

c. Eleidin granules.

d. Basophilic keratohyaline granules.

e. Acidophilic keratohyaline granules.

Berbick granules are present in : a. Melanophores.

b. Merkel's cells.

c. Langerhans cells.

d. Stratum lucidum.

e. Meissner's corpuscles

1.Granular layer.

2.Horny layer.

3. Spinous layer.

4.Clear layer.

a. Squames condensed in

linear manner.

b. Wavy clear acidophilic

line.

c. Diamond-shaped cells.

d. Polyhedral cells.