THE SKIN By

P.D.Sanaa El-Sherbiny Mansoura University

Function of the skin Covers and protects the body. Control internal temperature. Produces vitamin D. Receptors to detect environmental

stimuli. Regulates the movement of

substances into and out of the body Forms the largest organ of the body forms 16%of body weight

Bio 130 Human Biology

Skin structure Epidermis: is outermost layer. Stratified squamous keratinized

epithelium. Keratinization production of a waterproof protein. Pigments.

Dermis: living portion of skin mostly dense connective tissue. Contains :C.T fibers &cells ,vessels,

sweat glands, sebaceous glands, hairs.

Hypodermis :Adipose tissue Contains receptors

Bio 130 Human Biology

Types:1-THICK SKIN EPIDERMIS IS THICK:0.8mm in

palm ,1.4 mm in sole. Contains 4 types of cells: 1-keratinocytes (85% of cells) 2-Melanocytes 3-Langerhans cells 4-Merkel cells ِ<Arranged in five layers.

Epidermis and dermis

Epidermis (purple)

Dermis

•Superficial papillary layer contains loose connective tissue, blood vessels, nerves, and lymphatics

•Deeper reticular layer has dense fibrous irregularly arranged connective tissue

Dermal papillae

Layers of epidermis are

Stratum basale (germinativum)

Stratum spinosum Stratum

granulosum Stratum lucidum

(may not be present) Stratum corneum

Layers of epidermis

Stratum basale (germinativum) Single layer of cells on

basal lamina Stem cells which give

rise to keratinocytes Contain melanin

transferred from melanocytes

May see mitotic figures

Desmosomes and hemidesmomes

Layers of epidermis Stratum spinosum

Several cells thick Have cytoplasmic

processes (spines) Desmosomes

Layers of epidermis Stratum

granulosum 1 to 3 layers of

fusiform shaped basophilic cells

Keratohyalin granules contain cystine-rich and histidine-rich proteins that associate with keratin filaments

Layers of epidermis

Stratum lucidum Present only in thick skin

Cells in which keratinization is advanced

Layers of epidermis Stratum corneum Superifical keratinized

layer Cells

Almost filled with keratin

Flattened, non nucleate

Coated with extra-cellular lipids that form water barrier of skin

Layer that varies most in thickness

TYPES OF EPIDERMAL CELLS

The epidermal cells1-keratinocytes: They are

responsible For keratin

formation Formed of many

layers that continuously shed

And regenerate every 2-4 weeks

They are arranged In many layers.

Melanocytes: Found inbetween cells of the basal

layer & At the basal part of the hair follicles. Branched cells with centeral nuclei By EM contains organells for protein

synthesizes (rER, Golgi, mitochondria &melanosomes).

They form melanin by tyrosinase from tyrosine amino acid

By converting it to dioxyphenyl alanine DOPA

3 -Langerhans cells: Found in upper layers of st.spinosum

Have branched shape &central nuclei Represent 3-8%of epid. Cells Mesodermal in origin. EM not connected to keratinocytes &

contain Birbeck granules Stained with silver & vital stains Phagocytic & antigen presenting

cells

Langerhans cells

4-Merkels cells Found in basal cell layer Are modified epidermal cells Sensory nerve fibers

form terminal disk under

Merkels cells Function as

touch receptors

THIN SKIN ALLOVER THE BODY EXCEPT SOLE & PALMS. EPIDERMIS

ISTHINNER,ST.spinosum,2-4LAYERS,ST.GRA.ONE INCOMPLETE

LAYER:NO ST LUCI. ,ST,COR.THINNER NUMEROUS SWEAT

GLANDS. *CONTAIN HAIRE,

SEBACEOUS GLANDS*AND ERECTOR PILLI MUSCLE

THIN SKIN

The dermis 1-Papillary layer : Forms dermal papillae Loose C.T rich in collagen type 111 Elastic fibers,C.T cells and rich in

blood capillaries Contain meisssners corpuscles

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Meissner’s (Tactile) Corpuscle

Located in the dermlpapillae Receptor for light touch

2 -Reticular layer The thicker deep layer Formed of dense c.T rich in

interlacing wavy collage fibers It is less cellular &less vascular Contain many nerve receptors: Krause end bulbs Ruffini corpuscles Pacinian corpuscles

Glands and skin appendages:

Sebaceous glands Clumps of epithelial tissue distributed within

dermis Secrete “sebum”—oily, fat-based substance that

is also anti-bacterial Located all over body

Sweat glands Microscopic clumps of epithelial tissue

distributed within dermis, duct extends out through dermis to pore their secretion.

More than 2.5 million glands per person Eccrine sweat glands, concentrated on hands and

soles of feet and forehead, secrete sweat to cool body, also at conditions of fear and emotion.

Apocrine glands, concentrated in armpits and groin, analogous with sexual scent glands of other animals, odor comes from bacteria that concentrate here.

Ceruminous glands: modified sweat glands in ear canal produce ear wax

Mammary glands: modified sweat glands in female breast produce mother’s milk

sweat glandsTwo types of sweat glands

Eccrine Not associated with hair

follicle Duct segment

less coiled, leads to epidermis

Stratified cuboidal epithelium

Secretory segment in deep dermis or

hypodermis Secretory cells Myoepithelial cells lie

between secretory cells, contraction expels sweat

Apocrine Found in limited areas Empty into hair follicle

SWEAT GLANDS Merocrine

glands: Allover the body Secretory cells

2types Clear cells cubical rich

in glycogen granules. Dark with narrow

basal part with apical Glycoprotein granules Myoepithelialt cells Ducts lined by 2layers

of cubical cells

Apocrine glands: Axilla,groin,pubic

region Secretory part

similar To mero. With wider Lumen Their ducts are lined With 2 layers of cubical

cells but open into hair follicles

Secretion stim.by sex

hormons