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BIOB33 - Lecture 2.doc

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Biological Sciences
Connie Soros

1 BIOB33 – Lecture 2 Prof’s Speech - Purple 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. 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 • Stops flow of materials • Waterproofing • Closer to apical surface • Ensures nothing gets in between the cells 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 - Whole “zone” is connected, terminal web – thread is sewn through all 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. - More individual snap than cell adhesion molecule - Connect the epithelia to basal lamina or connective tissue beneath • Lock cells together • Cell adhesion molecules – occur in between the cell walls; where two cells connect together – like a thread being used to sew the cells together - Like a snap or a button 2. 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. • Allows material to flow from one cell to another • Free diffusion of ions and small molecules between two cells • Little pores that allow ions, glucose, acids, small regulatory molecules to pass to other cells 2 Introduction – Integumentary System Riddle: What organ weighs about 5 kg and measures 1-2 m (large surface area and same weight as your head) - skin The integumentary system is composed of: • Skin • Hair • Nails • Sweat glands • Oil glands • Mammary glands • Integument = skin, uses 2 types of tissue: 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, warmth from the blood dissipates as sweat as sweat gland release fluid onto the skin surface - When cold vessels constrict, there is less flow of blood, maintain more heat at the core of the body • Excretion of products – sweat, waste • Synthesis of products – keratin, vitamin D • Sensation - sensory receptors for touch, vibration, pressure, tickle, pain, hot/cold thermosensation - There is one sensory receptor in the epidermis, and several in the dermis • Absorption – certain drugs (smoking/birth control/etc patch, DMSO absorbed transdermally) skin is selectively permeable - The skin is slowly permeable, thus the slow absorption • 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 - Avascular • Dermis – deep to epidermis - Papillary layer (with papilla) - Reticular layer – “netted”, unorganized pattern - vascular • Hypodermis (subcutaneous layer) is deep to the dermis - Lots of blood vessels, nerves and tissues - Fat cells, fibres, arteries, veins in this area • Accessory structures -Hair, nails, exocrine glands 3 - Hair follicles – actually formed by epidermal tissue, surrounded by thin layer of dermal tissue, found in dermal layer The Epidermis • Region that deals with friction (1-2 dimes thick), thickest on soles of feet and palms 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/basal (deepest) layer is most important • Layers of the Epidermis: • Basal lamina – attach to the dermis, under stratum basale • Stratum basale (stratum germinativum) – figure 4.3, pg. 93 o 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  Everyone has roughly the same number of melanosomes (which are filled with melanin), but the amount of melanin varies  Melanocytes produce melanosomes  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 layers in fair skinned individuals and more superficially in darker skinned individuals  Moles (nevus) are harmless localized overgrowths of melanin-forming cells, most people have at least a few of these  Melanin pigments act like umbrellas; 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  Too much sun = cell damage to cell producing cells and then future cells will also be damaged  Melanin pigments help to shade dividing cells 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  Touch receptor – very sensitive to light touch  Present in deepest layer of epidermis – stratum basale o In the stratum basale, cells divide by mitosis, 2 identical daughter cells are produced 4  One daughter cells stays in the basale, and the other migrates upwards  Never will both of the daughter cells move upwards  Once one dividing cell is damaged, all cells will be damaged afterwards • 750 million skin cells are shed per day • Stratum spinosum – once cell division occurs in the stratum basale, one daughter cell remains in the stratum basale, while the other daughter cell is pushed up into the next more superficial layer, the stratum spinosum (spiny layer), where the new cell will begin to differentiate into a keratinocyte, o all keratinocytes in the stratum spinosum are tied together by a network of interlocked macula adherens (desmosomes) and tonofibrils (bundles of protein filaments) o Langerhans cells (dendritic/immune cells) are common in this layer o Langerhans cells play an important role in initiating an immune response against pathogens that have penetrated the superficial layers of the epidermis and epidermal cancer cells o Location of recently divided daughter cells o Melanosomes move upwards and
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