Hsf: Epithelium

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4 Basic Tissues

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-Epithelium
-Connective Tissue
-Muscle
-Nerve

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What are epithelia?

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-Continuous sheets of cells that are tightly joined to each other with little intervening substance

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General Functions of Epithelia (3)

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-Cover most surfaces
-Line all body cavities
-Form the parenchyma of glands

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Specializations of Epithelia (6)

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-Protection (and barriers)
-Transport
-Absorption
-Secretion
-Distension
-Receptor Functions

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Epithelia form _____, ______ and ______, defining and maintaining most microenvironments within the body

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-Lumena
-Compartments
-Surfaces

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3 Germ Layers that Give Rise to Epithelia

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-Ectoderm
-Mesoderm
-Endoderm

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Ectoderm (Epithelia Derivation)

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-Skins and its Appendages
-Neural Tissue and Related Structures

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Mesoderm (Epithelia Derivation)

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-Lining of Serous Cavities (endothelium of blood vessels, mesothelium of peritoneal cavity)
-Epithelium of Urogenital tracts

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Endoderm (Epithelia Derivation)

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-Lining of GI tract
-Respiratory passages
-Many Glands

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Common Characteristics of Epithelia (3)

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-Cellularity
-Polarity
-Connectivity

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Cellularity (Epithelia)

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-Epithelia arranged in sheets of closely packed cells with little extracellular material b/w them
-May be more than one cell type in epithelia

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Polarity (Epithelia)

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-Apical Surface=interface
-Lateral Surface (separated from apical by intercellular junctions)
-Basal Surface (rests on basal membrane)

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Connectivity (Epithelia)

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-Epithelial cells are tightly connected to each other by means of intracellular junctions and junctional complexes

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Tight Junctions (zonula occludens)

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-Act as continuous "seal" b/w the apical end of each cell and is neighboring cells
-Restrict movement of membrane proteins b/w apical and basolateral surface=separate membrane domain

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Tightness of Tight Junctions

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-Varies
~Some prevent passage of substances between cells (Capillaries)
~Relatively permeable, allowing small molecules between cells through occluding junction

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Some _____, _____ and _____ can affect the tightness of the tight junctions, making them more permeable.

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-toxins
-cytokines
-pathogens

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Adhering Junctions (def and ex)

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-type of junctions that reinforce the mechanical bond between adjacent cells
-Ex: Zonula adherens and Desmosomes

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Hemidesmosomes (def)

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-Reinforce attachment of the basal surface of the cell to the underlying basal lamina by providing zone for attachment of intermediate filaments

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Focal Adhesions (def)

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-attaches basal surface to the extracellular matrix
-anchor actin filaments of the cytoskeleton to the basal lamina using adhesion molecules called integrins

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Integrins

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-type of adhesion molecule used by focal adhesions

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Communicating Junctions

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-aka Gap Junctions
-form hydrophilic pores between cells, through which molecules (e.g. ions, cAMP) can pass

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Avascular

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-Epithelia contains no blood vessels
-Supplied by capillaries in the underlying connective tissue

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Epithelia: Continuously Renwed

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-Renewed after wear and tear
-Stable cell population capable of significant renewal if damaged

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Basal lamina

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-Extracellular structure formed by the epithelial cells

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Composition of basal lamina

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-Type IV Collagen (primarily)
-Proteoglycans (largely heparin sulfate)
-Glycoprotein (laminin)

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Divisions of Basal Lamina

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-lamina rara
-lamina densa

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Basement Membrane

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-Basal lamina + associated reticular fibers

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Type _____ collagen attach the basal lamina to underlying reticular fibers (Type __ collagen) of the connective Tissue

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-VII
-III

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Basal Lamina Functions

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-Attachment of epithelium to the underlying connective tissue using integrins
-Orientation of the epithelium
-Selective barrier
-Regeneration

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Apical Surface Examples

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-Microvilli (absorption=increases surface area)
-Stereocilia (absorption=increases surgace area)
-Cilia (9+2 microtubles)
-Flagella
-Specialized receptors

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Lateral Surface

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-characterized by junctional complexes
-may be extensive lateral folds present
-space b/w cells may vary with transport into the lateral or basal-lateral space

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Basal Surface

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-attached to the basal lamina

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______ _______ are indicative of transport across the plasma membrane, but usually it is ion transport.

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Basal infoldings

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Irritation from smoking can cause the _______ _________ epithelium of the trachea to change into a more protective ______ _______ epithelium.

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-Pseudostratified columnar
-Stratified Squamous

CALLED SQUAMOUS METAPLASIA

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Squamous Metaplasia

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-Process by which one differentiated normal tissue is changed to another type of normal, differentiated tissue called metaplasia

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Benign epithelial tumors are usually _______ or ______.

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-Polyps
-Papilloma

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Malignant neoplasias of epithelial origin are called ______.

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Carcinomas

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Neoplasias of glandular origin are ________.

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Adenomas

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Malignant neoplasias are ________.

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Adenocarcinomas