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Epithelial Tissue

Epithelial Tissue. I. Features. A. cover or line surfaces B. tightly packed cells C. Anchored to underlying tissues by basement membrane D. Avascular—no blood vessels. Cells get nutrients by diffusion from underlying tissue. II. Functions. A. Protection—prevents damage and dehydration

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Epithelial Tissue

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  1. Epithelial Tissue

  2. I. Features • A. cover or line surfaces • B. tightly packed cells • C. Anchored to underlying tissues by basement membrane • D. Avascular—no blood vessels. Cells get nutrients by diffusion from underlying tissue

  3. II. Functions • A. Protection—prevents damage and dehydration • B. Regulation of material passage—food, oxygen, water • C. Secretion—eg. Sweat, bile

  4. III. Connections • A. To basement membrane (protein fibers) 1. cells are held in place by proteins • B. Cell to cell 1. Tight junction—membranes are fused together by interlocking proteins—creates impermeable seal. Eg. Digestive tract 2. Gap junction—channel proteins hold cells together. Allows cell to cell passage

  5. 3. Desmosome—cells are held together by cement and protein filaments • Very strong connection • Eg. Skin cells

  6. IV. Renewal • A. epithelial cells are constantly replaced by stem cells near the basement membrane

  7. V. Classification • A. By layer 1. simple—one layer 2. stratified—multiple layers • B. By shape 1. squamus—flat 2. cuboidal—square 3. columnar--rectangular

  8. VI. Epithelial tissue types • A. Simple squamus—single layer of flat cells 1. line mouth, blood vessels, body cavities and lungs 2. important in absorption and diffusion of gasses to and from underlying cells • B. Simple cuboidal-single layer of square-ish cells 1. found in glands and ducts eg. Salivary, thyroid 2. sturdy, can withstand damage from passage of materials through ducts

  9. C. Simple Columnar—single layer of tall closely packed cells 1. Line digestive tract 2. protect, absorb • D. Stratified squamus—several layers of cells, flat at the top 1. provides protection against physical damage, microbes and chemicals 2. cells become hardened as they reach the surface 3. makes up surface of skin, mouth, rectum, anus

  10. E. Stratified Transitional 1. found in urinary bladder 2. allow for distension • F. Pseudostratified columnar—looks like two layers, but is only one 1. line much of respiratory tract 2. protect, secrete, move substances • G. Stratified cuboidal and columnar 1. Not common—line some ducts

  11. VII. Glandular Epithelia • A. Produce secretions • B. Two types: 1. Endocrine—secrete chemical messengers called hormones into the blood 2. Exocrine—discharge secretions through a duct or tube to a free surface • C. classified two ways

  12. VIII. Classification by mode of secretion • A. Merocrine—product is released through exocytosis • B. Apocrine—portion of cytoplasm is released with product • C. Holocrine—the entire cell bursts to release product

  13. IX. Classification by type of Secretion • A. Serous—secrete a watery solution containing enzyme. eg. Parotid salivary gland • B. Mucous—secrete a thick and slippery substance. eg. Sublingual salivary gland • C. Mixed—have both serous and mucous secreting cells. eg. Submandibular salivary gland

  14. X. Surface features of epithelia • A. microvilli—finger-like extensions of the cell membrane that increase surface area • B. cilia—longer extensions of the cell membrane that contains microtubules which allow them to move

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