THE SKIN By P.D.Sanaa El-Sherbiny Mansoura University
Function of theskinand protects the body. Covers 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.
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
The epidermal cells:1-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
:Langerhans cells -3 Found in upper layers of st.spinosum Have branched shape ¢ral 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
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
Meissner‘s )Tactile( Corpuscle Located in the dermlpapillae Receptor for light touch 28
Reticular layer -2 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
sweat glands Two 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: Apocrine glands: Allover the body Axilla,groin,pubic Secretory cells 2types region Clear cells cubical rich in Secretory part similar glycogen granules. To mero. With wider Dark with narrow basal part with apical Lumen Glycoprotein granules Their ducts are lined Myoepithelialt cells With 2 layers of cubical cells Ducts lined by 2layers of but open into hair follicles cubical cells Secretion stim.by sex hormons
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