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Lecture 2

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Biological Sciences
Connie Soros

1 Lecture 3 The Integumentary System (based on chapters 2 and 4) Intercellular Attachment Cells are joined by cell junctions, which prevent unwanted movement through the epithelium 1. Communicating Junction (Gap Junction) – in the middle between base and apex of the cell, have channels (gaps) made of structures called connexions consisting of 6 transmembrane proteins arranged in a circle to form a tiny fluid filled tunnel or pore so that cells can communicate with each other. Ions, glucose, amino acids, regulatory molecules and other small solutes pass through. Common in epithelial cells where they help coordinate the beating of cilia and in muscles where they coordinate muscle contraction. 2. Adhering Junction – attach cells to one another a. Tight Junction (Occluding Junction) – at apex, keeps cells tight and really close together, completely encircles cells bringing plasmalemmae of adjacent cells together (like a ziploc bag) with interlocking membrane proteins. Seals intercellular space and forces materials to move through (via an energy-requiring process) rather than between epithelial cells, eg. Small intestine – prevents digestive enzymes that degrade molecules from moving between epithelial cells and connective tissue b. Anchoring Junction – either mechanically link two adjacent cells at their lateral surfaces or link epidermal cell to basal lamina. These are very strong linkages and they can resist stretching and twisting. Linkages occur via cell adhesion molecules (CAMS) which bind to each other and to other extracellular materials and proteoglycans that link the opposing membranes and form a junction with the cytoskeleton within the adjoining cells. Neighbouring cells are separated by a small space spanned by a fine web of protein filaments which anchor to a thickened protein plaque (dense area) at the internal surface of the plasma membrane, on the cytoplasm side, intermediate filaments of cytoskeleton penetrate the plaque to extend throughout the cell for support and strength • Zonae adherens (adhesion belt) – a sheet-like anchoring junction that stabilizes non-epithelial cells • Macula adherens (desmosome) – provides small localized spot-like anchoring junctions that stabilize adjacent epidermal cells, like a button or snap, with each cell contributing half of the snap. Introduction – Integumentary System 2 Riddle: What organ weighs about 54 kg and measures 1-2 m (large surface area and same wt as head) The integumentary system is composed of: Skin Hair Nails Sweat glands Oil glands Mammary glands Integument = skin, uses 2 types of tissue: © 2012 Pearson Education, Inc. 2 Epithelial – on surface, protects underlying body layers or lines body cavities, composed of one or more layers of closely packed cells, little or no extracellular matrix cells and no blood vessels within Connective – is most diverse, abundant and widely distributed and is designed to support, protect and bind organs; under epithelium, contains blood vessels that provide nutrients Functions include: Physical protection – against external environment (rain, viruses), physical injury, chemicals, toxins, microbes Regulation of body temperature (thermoregulation) – blood vessels increase in diameter (vasodilation), more blood flow, warm form the blood dissipates as sweat as sweat gland release fluid onto the skin surface Excretion of products – sweat, waste Synthesis of products – keratin, vitamin D Sensation - sensory receptors for touch, vibration, pressure, tickle, pain, hot/cold thermosensation Absorption – certain drugs (smoking/birth control/etc patch, DMSO absorbed transdermally) skin is selectively permeable Immune defense – phagocytic cells against pathogens and epidermal cancer cells – epidermal dendritic (Langerhans) cells Integumentary Structure and Function Skin (cutaneous membrane) is made of two divisions Epidermis – most superficial Dermis – deep to epidermis Hypodermis (subcutaneous layer) is deep to the dermis Accessory structures -Hair, nails, exocrine glands The Epidermis • Region that deals with friction (1-2 dimes thick), thickest on soles of feet and thinnest behind ears and eyelids • Like a deck of cards, each card is flexible but the entire deck is tough and hard to tear • Epidermis is derived from ECTODERM germinal layer (next lecture) • Bottom (deepest) layer is most important: Layers of the Epidermis: Stratum basale (stratum germinativum) Deepest layer, single layer of cuboidal cells which divide rapidly to produce the cell layers above (germinal (epidermal stem cell) layer o Cells produced in this layer move superficially toward skin surface o Location of melanocytes – produce pigment MELANIN – brown/black pigment, amount produced is variable  When exposed to the sun, melanocytes become more active and produce more melanin, giving a tanned, darker look  Everyone has about the same number of melanocytes but melanocyte activity and colour of the melanin produced by these cells varies among individuals and races resulting in different skin tones  The melanin forms in vesicles called melanosomes which eventually are destroyed by lysosomes, the melanosomes are destroyed and release melanin in deeper © 2012 Pearson Education, Inc. 3 layers in fair skinned individuals and more superficially in darker skinned individuals  Melanin pigments help prevent skin damage by absorbing ultraviolet (UV) radiation in sunlight. A small amount of UV is necessary because the skin requires it to convert a cholesterol-related steroid precursor into Vitamin D hormones. Vitamin D is required for normal calcium and phosphorus absorption by the small intestine; too much UV absorption can damage the skin however o Stratum basal is also the location of Merkel cells  Specialized epithelial cells that are sensitive to touch and release chemicals that stimulate sensory nerve endings known as tactile discs (Merkel’s disc) , providing information about objects touching the skin, highly sensitive
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