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Lecture 5

Week 5 Integumery System (1).docx

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Department
Biology
Course
BLG 10A/B
Professor
Emily Agard
Semester
Fall

Description
Week 5: The Integumentary System The skin and its derivatives (sweat and oil glands, hairs, and nails) make up a complex set of organs. These organs form the Integumentary system. The Skin • composed of 2 regions: epidermis & dermis • Epidermis is composed of epithelial cells & is the outmost part of the body • The dermis makes up the bulk of the skin (tough, leathery, fibrous connective tissue) • Nutrients reach epidermis by diffusing through tissue fluid blood vessels in dermis • The subcutaneous tissue is the hypodermis; not part of the skin, but shares functions • Also called supercial fascia consists of adipose tissue o Stores fat, anchors skin to underlying structures (mostly muscles) but loosely enough that the skin can slide relatively freely over those structures o Acts as a shock absorber and insulator that reduces heat loss o Thickens when a person gains weight Epidermis Cells • Keratinocytes o Tightly connected by desmosomes, they arise in the deepest part of the epidermis from a layer called the stratum basale o Undergo continuous mitosis o As they are pushed forward by the new cells beneath them, they make keratim o By the time they reach the surface of the skin, they are dead • Persistant friction causes a thickening of the epidermis called a callus • Melanocytes – spider shaped epithelial cells that make melanin o In deepest layer of the epidermis o Melanin accumulates in membrane bound granules, melanosomes that are moved by motor proteins to the ends of the melanocytes (spider arms) o Taken up by nearby keratinocytes. They accumulate on the superficial side of the keratinocyte nucleus, forming a pigment shield that protects the nucleus from damaging effects of UV radiation • Epidermal Dendritic Cells/Langerhans Cells o Arise from bone marrow & migrate to epidermis o Ingest foreign substances and are key activators of the immune system • Tactile (Merkel) cells – present at the epidermal-dermal junction o Each tactile cell is associated with a sensory nerve ending o The combination, tactile or merkel disc, is a sensory receptor for touch Layers of the Epidermis In thick skin, the epidermis has 5 layers/strata; From deep to superficial: Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. Stratum Basale (Stratum germinativum) - Deepest epidermal layer, attached to underlying dermis along wavy borderline Stratum Spinosum - Several cell layers thick; Contain web-like intermediate filaments of pre-keratin filaments, which span their cytosol to attach to desmosomes Stratum Granulosum - Thin layer consists of 3-5 cell layers; Keratinocyte appearance changes Stratum Lucidum (Clear) - Appears as a thin translucent band; 3-4 Layers of clear, fat, dead keratinocytes - Gummy substance of keratohyaline granules clings to keratin filaments in the cells, causing them to aggregate in large, cable-like, parallel arrays Stratum Corneum - Broad zone 20 to 30 cell layers; ¾ of epidermal thickness - Keratin and thickened PM protect skin against abrasion and penetratin - Glycolipids = waterproofs this layer - Shingle-like ell remnants are cornifield or horney cells – dandruff Dermis • Flexible connective tissue • Fibroblasts, macrophages, and occasional mas cells & WBC’s • Semifluid matrix embedded with fibres, binds entire body together • Richly supplied with nerve fibers, blood vessels and lymphatic vessels • Two layers: papillary and reticular • Superficial papillary layer – areolar connective tissue in which fine interlacing collagen and elastic fibers form a loose mat with many small blood vessels • Deeper reticular layer is coarse, irregulary arranged, dense fibrous connective tissue • Collagen fiber of dermis gives skin strength and resiliciency preventing jabs/scrapes o Binds ater, helping keep skin hydrated • Flexure lines -- dermal folds that occur at/near joints, where dermis is tightly secured to deeper structures o Since skin cannot slide easily to accommodate joint movement, dermis folds and deep skin creases form Skin Colour - Melanin, carotene and hemoglobin contribute to skin colour - Melanin: polymer made of tyrosineAA; Two forms range in color from yellow to tan to reddish-brown to black o Synthesis depends on tyrosinase; passes from melanocytes to basal keratinocytes - Melanosomes broken down by lysosomes, so melanin only in deep
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