Lecture 12: Epithelial Tissue PDF

Quiz 2 Monday October 7 Lecture 7 Thursday September 19 Lecture 8 Monday September 23 Lecture 9 Monday September 23 Lecture 10 Thursday September 26 Lecture 11 Monday September 26 Lecture 12: Epithelial Tissue Lecture 12: Epi...

Quiz 2 Monday October 7 Lecture 7 Thursday September 19 Lecture 8 Monday September 23 Lecture 9 Monday September 23 Lecture 10 Thursday September 26 Lecture 11 Monday September 26 Lecture 12: Epithelial Tissue Lecture 12: Epithelial Tissue Define tissue. Classify major body tissues. Identify characteristics of epithelial tissue. Compare cell shape and layering arrangements of epithelial tissue. Describe cell adhesion molecules and basal lamina. Define a gland. Distinguish between exocrine and endocrine glands.  Tissues Histology is study of tissues  Tissues Group of structurally and functionally related cells and their external environment that perform a common function.  Tissues Share 2 basic components: 1. Group of structurally and functionally related cells. 2. Extracellular matrix (ECM). Overview of Types of Tissues Epithelial, connective, muscle and nervous  Epithelial Tissues Sheets of cells with no visible ECM. Covers all body surfaces and cavities. Specialized cells form glands.  Connective Tissues Connects other tissues to one another. Most have large ECM with cells scattered throughout it. Binds, supports, protects and transports substances.  Muscle Tissues Contracts and generates force. Very little ECM. Include smooth, cardiac and skeletal muscle.  Nervous Tissue Unique ECM. Cells generate, send and receive messages. Includes other cells that support its functions. Extracellular Matrix (ECM) Substances surrounding cells  Functions of ECM 1. Provides strength to resist tensile and compressive forces. 2. Directs cells to proper place in a tissue. 3. Regulates development, mitotic activity and survival of cells. 4. Holds cells in proper positions.  Components of ECM 1. Ground substance. 2. Protein fibers.  Ground Substance Contains extracellular (interstitial) fluid consisting of H2O, solutes and macromolecules  Ground Substance 3 families of macromolecules. 1. Glycosaminoglycans (GAGs). 2. Proteoglycans. 3. Glycoproteins.  1. Glycosaminoglycans (GAGs) Polysaccharide chains with negative charges to attract cations to draw H2O out of cells and blood vessels.  2. Proteoglycans Form aggregates such as hyaluronic acid. Makes tissues more solid and resistant to compression.  3. Glycoproteins Also called cell adhesion molecules that glues cells to each other. Binds cell surface proteins, protein fibers and proteoglycans. Maintains architecture of tissue.  Protein Fibers 2nd part of extracellular matrix and includes collagen, elastic and reticular fibers  1. Collagen Fibers 20-25% protein in body. Appears like entwined steel cables. Resistant to tension and pressure.  2. Elastic Fibers Stretches without breaking (extensibility). Returns to original length (elasticity). Formed with protein elastin.  3. Reticular Fibers A type of collagen that is thinner and shorter. Forms meshwork to support cells and ground substance. “Webs” trap foreign cells.  Cell Junctions Anchors neighboring cells by integral proteins  Cell Junctions 3 types. 1. Tight junctions. 2. Desmosomes. 3. Gap junctions.  1. Tight Junctions Hold cells tightly like a zipper. Some are “leakier” than others.  2. Desmosome Extracellular fluid can pass between cells. Increases strength of tissues. Integral “linker” proteins attach to intermediate filaments of  3. Gap Junctions Protein channels in adjacent plasma membranes. Allow substances to pass from one cell to another cell.  Epithelial Tissues Found on all body surfaces This figure is not in your text. Based on this figure what can you say about epithelial tissues?  Functions of Epithelial Tissues 1. Protection. 2. Immune defenses. 3. Secretion. 4. Transport. 5. Sensation.  1. Protection From mechanical and thermal injury. Keratin in skin is hard protein making more resistant to injury. Skin is subject to damage but has high mitotic rate.  2. Immune Defenses Barrier against invading microorganisms. Immune cells scattered throughout epithelial tissues.  3. Secretion Form glands that produce substances (such as oils or hormones). Substances secreted through a duct or into bloodstream.  4. Transport into Other Tissues Epithelium selectively permeable. Substances cross by passive or active transport. Critical in areas such as small intestine.  5. Sensation Most epithelia are innervated. Nerves detect changes in internal and external environments.  Features of Epithelia Epithelia tissues are avascular  Features of Epithelia No ECM between epithelial cells. ECM present below cells as a basement membrane.  Basement Membrane Upper basal lamina and lower reticular lamina. Basal lamina contains ECM synthesized by epithelial cells. Consists of collagen fibers and ground substance.  Basement Membrane Reticular lamina made by deeper connective tissue. Consists of reticular fibers and ground substance.  Apical and Basal Surfaces Free apical surface. Basal surface is attached to basal lamina. Classification of Epithelia No. of cell layers and shape of cell Classification by Cell Layers 1. Simple epithelia. Consists of a single layer of cells. 2. Stratified epithelia. Consists of more than one cell layer. Classification by Cell Shape Cell Shape Name Description 1. Squamous cells. Flattened cells. 2. Cuboidal cells. Short cells. 3. Columnar cells. Tall cells. Most Classified By Cell Layers and Cell Shape Example: Simple Squamous Epithelium  Simple Epithelia Simple squamous epithelium Simple cuboidal epithelium Simple columnar epithelium  Simple Squamous Epithelium Single layer of flat cells. O2, CO2, fluids and ions to diffuse across quickly. Examples are in lungs, kidney tubules and lining blood vessels. Simple Cuboidal Epithelium Single layer of short square shaped cells. Substances diffuse across rapidly. Found in kidney tubules, respiratory passages, ducts of glands and thyroid gland. Simple Columnar Epithelium Single layer of tall rectangular cells. Often with microvilli as in small intestine and kidney tubules. Often with cilia as in uterine tubes and some respiratory passages. Specialized Epithelia Pseudostratified Columnar Epithelium  Pseudostratified Columnar Epithelium Simple All cells rest on epithelium that basal lamina. appears Ciliated in upper stratified. respiratory Some cells passages and shorter than nasal cavity. others. Thickness Nuclei at provides different heights. protective Transport Across Simple Epithelia Paracellular or transcellular transport  Paracellular Transport Substances leak between cells of epithelial membrane. Most epithelial cells have tight junctions making them impermeable.  Transcellular Transport Transport by most epithelial cells. 1. Substance enters cell through phospholipid bilayer. 2. Substance diffuses through cytosol. 3. Exits through other surface of cell. Summary of Simple Epithelia Stratified Epithelia Thicker and more effective protection barrier  Stratified Squamous Epithelium Keratinized or non-keratinized.  Keratinized Stratified Squamous Epithelium Apical layers anucleated and dead. Filled with protein keratin. Makes epithelium tough and resistant to friction. Forms outer layer of skin.  Non-Keratinized Stratified Squamous Epithelium Apical cells are nucleated and living. Found in organs requiring protection from abrasion but need to retain a moist surface. Examples are mouth, throat, esophagus, anus and vagina.  Stratified Cuboidal Epithelium Rarer in the human body. Consists of 2 layers of cuboidal cells. Lines ducts of sweat glands.  Stratified Columnar Epithelium Relatively rare in human body. Appear columnar in apical layers and cuboidal in basal layers. Lines ducts of salivary glands, part of male urethra and the cornea. Unique Stratified Epithelia Transitional epithelia named due to belief that cells transitioned between cuboidal and squamous cells  Transitional Epithelia Only in urinary system. Lines interior of kidney, ureters, urinary bladder and urethra. Basal layers dome-shaped when relaxed and flattened if stretched. Summary of Stratified Epithelia Glandular Epithelia Forms and secretes substances  Glandular Epithelia Grows inward into underlying connective tissue. Secretory cells synthesize and release products.  Classification of Glands 1. How they release their products. 2. Their shape. How Glands Release their Products 2 ways: Endocrine and exocrine glands  How Glands Release their Products Exocrine Endocrine Ducts. No ducts. Releases product Secretes to exterior of hormones body or into directly into hollow organ. blood.  1. Unicellular Glands One cell. Goblet cell most common and found in digestive and respiratory tracts. Secretes mucus protecting epithelium. a  2. Multicellular Glands Divided into: 1. Simple (non-branching). 2. Compound (branching) glands. Exocrine Gland Secretion 2 types: merocrine and holocrine  Merocrine Secretion Most common. Salivary and sweat glands. Packages product into secretory vesicles and released by exocytosis.  Holocrine Secretion Cells accumulate products and released when cell ruptures. Cells shed with products and replaced by new cells. Example are