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Lecture #2 Notes - Epithelium and Connective Tissue Proper.doc

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Queen's University
Anatomy and Cell Biology
ANAT 101
Richard Oko

Anatomy Lecture #2 Tissues • collections of cells that perform specific, limited functions histology: the study of tissues • 4 types of tissues 1) Epithelial 2) Connective 3) Muscle 4) Neural Epithelial Tissue -includes 1) Epithelia -layers of cells that cover internal/external surfaces 2) Glands -composed of secreting cells derived from epithelia Characteristics of Epithelia • cells are bound closely together • free (apical) surface exposed to environment • attachment to underlying connective tissue by basement membrane • avascularity: absence of blood vessels (obtain nutrients from connective tissues) • continual regeneration of cells that are damaged/lost at exposed surface Functions of Epithelia • provide physical protection (ex. skin protects from scrapes) • control permeability (ex. any substance that enters/leaves body must cross epithelium) • provide sensation (detect changes in environment, relay info to nervous system) • produce specialized secretions (glandular epithelium) -exocrine: secretions discharged onto surface of epithelium (ex. perspiration) -endocrine: secretions released into surrounding tissue fluid and blood (ex. hormones) Intercellular Connections *to be effective, epithelial cells must be firmly attached to basement membrane *if damaged, it is no longer an effective barrier cell adhesion molecules (CAMs): transmembrane proteins that connect large areas of opposing plasma membranes proteoglycans: thin layer that binds membranes together 3 Common Cell Junctions 1)Tight Junctions: keep cells attached, good permeability barrier (made of lipids) 2)Gap Junctions: form pores between cels for communication Anatomy Lecture #2 connexons: allow small molecules and ions to pass through 3)Desmosomes: form bonds with other cells, like adhesion belts, but just spots -spot desmosome: form a small disc -hemidesmosomes: half a spot desmosome Epithelial Surface apical surface: exposed to internal/external environment -many have microvilli for absorption and secretion (ex. digestive, urinary tracts) Anatomy Lecture #2 -cell with microvilli have 20x more surface area -↑ surface area↑transport proteins exposed to extracellular environment Basement Membrane *epithelial cells not only adhere to one another, but remain firmly connected to rest of the body basement membrane: lies between epithelium and underlying connective tissues basal surface is connected to deeper connective tissue with basement membrane Epithelial Renewal and Repair -replaced by division of stem cells (germinative cells) -occurs near basement membrane Classification of Epithelia 1) Number of layers -simple ~ single layer of cells (thin, fragile -> ex. blood vessels, heart chambers) -stratified ~ several layers (more protection -> ex. surface of skin, linings of mouth) 2) Cell shape -squamous ~ thins and flat Anatomy Lecture #2 -cuboidal ~ square shaped -columnar ~ tall and slender rectangles pseudostratified ~ appears layered/stratified all cells are actually in contact with basement membrane transitional epithelium ~ stratified epithelium that tolerates many cycles of stretching/recoiling “transitional” -> unstretched to stretched state *when there are many types of cells, go by the type of cell on the surface! Glandular Epithelia endocrine glands: release hormones -into interstitial fluid and plasma -no
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