tissues - Tissues 4 types of tissues: 1. epithelial covers...

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Tissues 4 types of tissues: 1. epithelial – covers exposed surfaces, lines passages, forms glands 2. connective – fills spaces, provides structural support, transports materials, stores energy 3. muscle – contraction – muscles, organs, heart 4. nervous – carries information in the form of electrical impulses epithelial tissues cover surfaces, form glands – which produce fluid secretions. Epithelia cover every exposed surface of the body – respiratory, digestive, reproductive Also internally, surfaces not exposed to outside world, so don’t have to be as durable. Characteristics: Cellularity – bound together by junctions – tight sheets Polarity – cells have distinct “sides” – one facing out and one going in to adjacent tissue. This polarity extends to location of cell organelles, etc. Attachment – bound to basal lamina or basement membrane Avascularity – don’t have blood vessels of their own, thus must rely on diffusion for nutrients and O2 – some epithelia are dead however and don’t require any nutrients Regeneration – continuously replaced – more quickly than most cells (think of burning the roof of your mouth) Functions: 1. physical protection from abrasions, dehydration, other damage. 2. control permeability – some are very permeable, some impermeable, some selectively permeable. This can be regulated and changed. 3. provide sensation – many sensory nerve endings since many are exposed to outside, this is a good way to sense environment 4. secretion – most epithelia have some glands – some are almost all glands – glandular epithelium Epithelial repair and maintenance: it’s not easy being epithelial! Have to replace and renew constantly because they are always getting messed up – abrasion, etc. germinative stem cells, near basal lamina (basement membrane), continually sending up new cells. Classification of epithelium – can be done with 2 categories: Shape – squamous, cuboidal, or columnar Number of layers – simple or stratified Simple – one cell layer – thin, also fragile. Needed where excretion/absorption take place. But can only have on inside lining of cavities, not in places open to outside world. Stratified – multiple cell layers – takes abrasion better.
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Cell types: Squamous – flat, scale/plate shape. - simple squamous – alveoli, lining of blood vessels. Most delicate epithelium. - Stratified squamous – where lots of mechanical stress occurs. Can remove sheets of cells and still be ok. Skin – lining of mouth, esophagus, etc. Skin is keratinized – protein which makes it tough and water resistant. Cuboidal – box shaped.
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This note was uploaded on 04/17/2008 for the course BIO 121 taught by Professor Short during the Fall '07 term at Finger Lakes Community College.

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tissues - Tissues 4 types of tissues: 1. epithelial covers...

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