Integument SKIN By Dr Abdullah Aldahmash The single

Integument (SKIN) By Dr. Abdullah Aldahmash

The single largest organ. About 16% of the human body weight. Its about 1. 2 - 2. 3 m 2. Has two layers 1. epidermis : epithelial tissue 2. dermis: connective tissue Two types 1. thick skin (glabrous): Palms and soles (400 -600µm, 0. 8 -1. 4 mm)- dermatoglyphs 2. thin skin: the hairy: every where (75 -150µm , 0. 07 -0. 12 mm) hypodermis (subcutaneous tissue) as a pad for the skin (the superficial fascia of gross anatomy), helps the skin to slide over underlying organs. – Panniculus adiposus

Dermis epidermis junction - irregular - dermis and epidermis interdigitate though 1. dermis projection into the epidermis {papillae (P) papilla (s)}. 2. epidermis evaginations - basement membrane

Epidermis - consist MAINLY of a stratified sequamous keratinized epithelium. 0. 07 to 0. 12 mm in thickness Epidermal layers 1. stratum basale (stratum germinativum). 2. stratum spinosum 3. 4. stratum granulosum stratum lucidum 5. stratum corneum

stratum basale Mitotically active Cuboidal /low columnar Large nucleus stratum Spinosum Thickest layer Mitotically active (less!!) Has more tonofilaments

Stratum granulosum 3 -4 layer The most superficial layer with nucleated cells Has keratohyalin granules Membrane-coating granules Stratum Lucidum Only in thick skin No nuclei and organelles Stratum Corneum Flattened cells. Has two layers – squames or horny – desquamated

Epidermal specialized cells - melanocyte - Lengerhans - melanin producing cells 1. 2. 3. star-shape cells bone marrow derivative play important role in skin immunology Merkel’s 1. present mainly in thick skin most abundant in the fingertips 2. serve as mechanoreceptors

melanocytes Located under or within the basal layer (stratum basale) Produce melanin Derived from neural crest cells Attached to basement membrane by hemidesmosomes

Developmental stages of mature melanin granule Tyrosine is synathesized in the RER then accumulated in vesicles (melanosomes) by Golgi Tryrosine; (inside melanosomes), activated by UV and after series of activation, will be converted into melanin Melanosomes (containing melanin only) travel through melanocyte projections to be deposited (Cytocrine secretion)

Dermis 1 - Development regulator (mesodermal derivative). 2 - Has two layer with indistinct boundaries: 1 - papillary layer 2 - reticular layer

- papillary layer • mainly of loss connective tissue, fibroblasts and other connective tissue cells (Mast, macrophages and leukocytes). • collagen, elastic and Anchoring fibrils • Mechanoreceptors (Meissner corpuscles & Krause end bulb) - reticular layer • dense connective tissue • more fibers and less cells • thick elastic fibers. • Type I collagen fibers. • Some smooth muscles. • Mechanoreceptors (pacinian corpuscles & Ruffini corpuscles )

Vessels &skin sensorial receptors Two arterial plexuses, located between - papillary and reticular layer - dermis and subcutaneous three veins plexuses, located between - two in the same location as the arterial - the 3 rd in the middle of the dermis Extensive sensory receptors are found in the skin: - free nerve ending (touch-pressure) - encapsulated: Vater-Pacini, Meissner and Krause corpuscles - expanded: include Ruffini endings

Skin appendages or derivatives Hair Nails Gland 1. Sebaceous glands 2. Sweet glands 3. Mammary glands

Sweat gland Eccrine: 1 - Simple 2 - Embedded in the dermis 3 - two cell types in the secretory part: -dark (pyramidal) lining the lumen & they have secretory granules in their apical surface. -clear devoid of secretory granules and accumulate glycogen. 4 - surrounded by myoepithelial Apocrine 1 - present in axillary, areolar and anal region. 2 - hair associate. 3 - their product is initially odorless.

• Acinar glands, i. e. have several acini opening into a short duct. • holocrine gland. • in some regions they open directly into the epidermal surfaces, e. g lips, penis and clitoridis. • secret sebum • Controlled by testosterone in men and by ovarian and adrenal androgens in women. Sebaceous glands