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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 ¢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
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
28
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