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Tissues - Austin Community College

By Annette Wagner,2014-01-29 07:28
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Tissues - Austin Community CollegeTissue

BIOL 2304 Tissues

    Tissues

    Cells work together in functionally related groups called tissuesTissue - A group of closely associated cells that perform related functions and are similar in structure

    Four primary types:

    Epithelium

    Connective tissue

    Nervous tissue

    Muscle

    Epithelial Tissue

    Covers a body surface or lines a body cavity

    Forms parts of most glands

    Functions of epithelium

    Protection

    Absorption, secretion, and ion transport

    Filtration

    Forms slippery surfaces

    Special Characteristics of Epithelia

    Cellularity - cells separated by minimal extra cellular materialSpecialized contacts - cells joined by special junctionsPolarity - cell regions of the apical surface differ from the basal surfaceSupport by connective tissue

    Avascular but innervated - epithelia receive nutrients from underlying connective tissue via diffusion

    Regeneration - lost cells are quickly replaced by cell division

    1

    Classifications of Epithelia

    First name of tissue indicates number of cell layers

    Simple – one layer of cells

    Stratified – more than one layer of cells

    Classifications of Epithelia

    Last name of tissue describes shape of cells

    Squamous – cells are wider than tall (plate-like)

    Cuboidal – cells are as wide as tall, like cubes

    Columnar – cells are taller than they are wide, like columns

    Simple Squamous Epithelium

    Description – single layer – flat cells with disc-shaped nucleiSpecialized types

    Endothelium (inner covering) – slick lining of hollow organs

    Lines inside of vessels and hollow tubes

    Mesothelium (middle covering)

    Lines peritoneal, pleural, pericardial cavities

    Covers visceral organs of those cavitiesFunction

    Passage of materials by passive diffusion and filtration

    Secretes lubricating substances in serosaeLocation

    Renal corpuscles

    Alveoli of lungs

    Lining of heart, blood and lymphatic vessels

    Lining of ventral body cavity (serosae)

    2

    Simple Cuboidal Epithelium

    Description

    single layer of cube-like cells with large, spherical central nucleiFunction

    secretion and absorption

    Location

    kidney tubules, secretory portions of small glands, ovary surface

    3

    Simple Columnar Epithelium

    Description

    Single layer of column-shaped (rectangular) cells with oval nuclei

    Some bear cilia at their apical surface

    May contain goblet cells

    Function

    Absorption; secretion of mucus, enzymes, and other substances

    Ciliated type propels mucus or reproductive cells by ciliary actionLocation

    Nonciliated form - lines digestive tract, gallbladder, ducts of some glands

    Ciliated form - lines small bronchi, uterine tubes, and uterus

    Pseudostratified Columnar Epithelium

    Description

    All cells originate at basement membrane, but only tall cells reach the apical surface

    May contain goblet cells and bear cilia

    Nuclei lie at varying heights within cells, giving false impression of stratification

    Function –

    secretion of mucus; propulsion of mucus by cilia

    Locations

    Nonciliated - ducts of male reproductive tubes, ducts of large glands

    Ciliated - lines trachea and most of upper respiratory tract

    4

    Stratified Epithelia

    Properties

    Contain two or more layers of cells

    Regenerate from below (basal layer)

    Major role is protection

    Named according to shape of cells at apical layer

    Description

    Many layers of cells – squamous in shape

    Deeper layers of cells appear cuboidal or columnar

    Thickest epithelial tissue, adapted for protection from abrasionTwo types

    Keratinized – forms epidermis, surface cells are dead and full of keratin, a protective protein,

    waterproof

    Nonkeratinized - forms moist lining of body openings

    Stratified Squamous Epithelium

    Description

    Several lays of cells

    Basal cells are cuboidal or columnar

    Surface cells are flattened (squamous)

    If keratinized, cells lose nucleus and are full of keratin

    Function

    Protects underlying tissues in areas subject to abrasionLocation

    Keratinized – epidermis

    Nonkeratinized – esophagus, mouth, anus, vagina, urethra

    5

    Stratified Cuboidal Epithelium

    Description – generally two layers of cube-shaped cellsFunction – protection

    Location

    Forms ducts of

    Mammary glands

    Salivary glands

    Largest sweat glands

    6

Stratified Columnar Epithelium

    Description – several layers; basal cells usually cuboidal; superficial cells elongated

    Function – protection and secretion

    Location - rare tissue type, found in male urethra and large ducts of some glandsTransitional Epithelium

    Description

    Basal cells usually cuboidal or columnar

    Superficial cells dome-shaped or squamous

    Function – stretches and permits distension of urinary bladder

    7

Location – lines ureters, urinary bladder, and proximal urethra

    Glandular Epithelium

    Endocrine glands

    Ductless glands

    Secrete substances directly into bloodstream

    Produce molecules called hormones

    Exocrine Glands

    Ducts carry products of exocrine glands to epithelial surface

    Include the following diverse glands

    Mucus-secreting glands

    Sweat and oil glands

    Salivary glands

    Liver and pancreas

    Unicellular Exocrine Glands: Goblet CellsGoblet cells - unicellular exocrine glands that produce mucin

    mucin + water ; mucus

    Protects and lubricates many internal body surfaces

    Goblet Cell

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Multicellular Exocrine Glands

    Have two basic parts

    epithelium-walled duct

    secretory unit

    Classified by structure of duct

    Simple

    Compound

    Categorized by secretory unit (where secretory cells are located)

    Tubular

    Alveolar (acinar)

    Tubuloalveolar

    Lateral Surface Features: Cell Junctions

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    Factors holding epithelial cells together

    Adhesion proteins link plasma membranes of adjacent cells

    Contours of adjacent cell membranes (Like puzzle pieces)

    Special cell junctions

    10

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