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Lecture 4a. Epithelial Tissue. Epithelial Tissue. Overview: Characteristics and functions of epithelia Cell junctions Classification of epithelia Exocrine glands. Four types of tissues in the body. Groups of cells similar in structure and function The four types: Epithelial Connective

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lecture 4a

Lecture 4a

Epithelial Tissue

epithelial tissue
Epithelial Tissue
  • Overview:
    • Characteristics and functions of epithelia
    • Cell junctions
    • Classification of epithelia
    • Exocrine glands
four types of tissues in the body
Four types of tissues in the body
  • Groups of cells similar in structure and function
  • The four types:
    • Epithelial
    • Connective
    • Muscle
    • Nerve
what is an epithelium
What is an Epithelium?
  • Epi = “on” or “around”
  • Thele = “nipple”
  • Covers the external body surface (epidermis), lines cavities and tubules, and generally marks off our insides from our outsides
  • Other examples?
epithelial tissues two types
Epithelial Tissues – two types
  • Epithelia:
    • layers of cells covering internal or external surfaces
  • Glands:
    • structures that produce secretions
characteristics of epithelia
Characteristics of Epithelia
  • Cellularity: composed of cells bound by cell junctions
  • Polarity: apical and basal surfaces
  • Attachment: via basal lamina to underlying connective tissue
  • Avascularity: no blood vessels (but richly innervated)
  • Regeneration: germinative cell division
free surface and attached surface
Free Surface and Attached Surface
  • Polarity:
    • apical and basolateral surfaces

Figure 4–1

repairing and replacing epithelia
Repairing and Replacing Epithelia
  • Epithelia are replaced by division of germinative cells (stem cells)
  • Near basal lamina
functions of epithelial tissue
Functions of Epithelial Tissue
  • Provide physical protection
  • Control permeability
  • Move fluids over the surface
  • Provide sensation (e.g. neuroepithelia)
  • Produce specialized secretions (glandular epithelium)
specializations
Specializations
  • Microvilli increase absorption or secretion
  • Cilia (ciliated epithelium) move fluids
effective barriers
Effective Barriers
  • Physical integrity is maintained by:
    • intercellular connections
    • attachment to basal lamina
    • maintenance and repair
cell junctions
Cell junctions
  • Tight Junctions – surround cells, waterproof
    • Isolates wastes in the lumen
  • Gap junctions – allow rapid communication
  • Desmosomes – tie cells together with great strength (like rivets)
    • Hemidesmosomes attach

Figure 4–2b

desmosomes
Desmosomes
  • CAMs, dense areas, and intercellular cement

Figure 4–2d

attachment to basal lamina
Attachment to Basal Lamina
  • Hemidesmosomes

Figure 4–2e

classification of epithelia
Classification of epithelia
  • Cell shape
    • Squamous: flat
    • Cuboidal: square
    • Columnar: tall
  • Layers of cells
    • Simple: one layer of cells (what is a function?)
    • Stratified: many layers of cells (what is a function?)
classes of epithelia
Classes of Epithelia
  • Based on shape and layers

Table 4–1

classification of epithelia19
Classification of Epithelia
  • Simple or stratified

Figure 4.1a

classification of epithelia20
Classification of Epithelia
  • Squamous, cuboidal, or columnar

Figure 4.1b

simple squamous epithelia
Simple Squamous Epithelia
  • Single layer of flattened cells with disc-shaped nuclei and sparse cytoplasm

Look like a fried egg from the top

  • most delicate
  • Diffusion, friction reduction
  • Special names

Mesothelium:

      • lines body cavities (e.g. peritoneum, pleura)

Endothelium:

      • lines heart and blood vessels
epithelia simple cuboidal
Epithelia: Simple Cuboidal
  • Single layer of cube-like cells with large, spherical central nuclei
  • Function in secretion and absorption
  • Present in kidney tubules, ducts and secretory portions of small glands, and ovary surface
simple cuboidal epithelium
Simple Cuboidal Epithelium
  • Kidney tubules

Figure 4–4a

epithelia simple columnar
Epithelia: Simple Columnar
  • Single layer of tall cells with oval nuclei
  • May contain microvilli
  • Goblet cells are often found in this layer
  • Function in absorption and secretion
  • Line digestive tract and gallbladder, small bronchi, uterine tubes, and some regions of the uterus
epithelia pseudostratified columnar
Epithelia: Pseudostratified Columnar
  • Single layer of cells with different heights; all touch the basal lamina but some do not reach the free surface
  • Nuclei are seen at different layers
  • Function in secretion and propulsion of mucus
  • Present in the male sperm-carrying ducts (nonciliated) and trachea (ciliated)
epithelia transitional
Epithelia: Transitional
  • Several cell layers, basal cells are cuboidal, surface cells are dome shaped (or flat)
  • Stretches to permit the distension of the urinary bladder
  • Lines the urinary bladder, ureters, and part of the urethra
epithelia transitional35
Epithelia: Transitional
  • Urinary bladder

Figure 4.2f

epithelia stratified squamous
Epithelia: Stratified Squamous
  • Thick membrane composed of several layers of cells (the only one with more than 2 or 3 true layers)
  • Functions in protection of underlying areas subjected to abrasion
  • Forms the external part of the skin’s epidermis (keratinized cells), and linings of the esophagus, mouth, and vagina (nonkeratinized cells)
epithelia stratified cuboidal
Epithelia: Stratified Cuboidal
  • Quite rare in the body
  • Found in some sweat and mammary glands
  • Typically two cell layers thick
  • Only top layer is cuboidal
stratified cuboidal epithelium
Stratified Cuboidal Epithelium
  • Sweat gland ducts

Figure 4–4b

epithelia stratified columnar
Epithelia: Stratified Columnar
  • Limited distribution in the body
  • Found in the pharynx, male urethra, and lining some glandular ducts
  • Also occurs at transition areas between two other types of epithelia
stratified columnar epithelium
Stratified Columnar Epithelium
  • Rare
  • Salivary gland duct

Figure 4–5c

epithelia glandular
Epithelia: Glandular
  • A gland is one or more cells that makes and secretes an aqueous fluid
  • Classified by:
    • Site of product release – endocrine or exocrine
    • Relative number of cells forming the gland – unicellular or multicellular
glandular epithelia
Glandular Epithelia
  • Endocrine and exocrine glands

Figure 4–6

glands
Glands
  • Endocrine
    • Ductless glands that produce hormones
    • Secretions include amino acids, proteins, glycoproteins, and steroids
  • Exocrine
  • More numerous than endocrine glands
  • Secrete their products onto body surfaces (skin) or into body cavities via ducts
  • Examples include mucous, sweat, oil, digestive, and salivary glands
  • The only important unicellular gland is the goblet cel
  • EXAMPLES?
goblet cell
Goblet Cell

Figure 4.3b

modes of secretion
Modes of Secretion
  • Merocrine – products are secreted by exocytosis (e.g., pancreas, sweat, and salivary glands)
  • Holocrine – products are secreted by the rupture of gland cells (e.g., sebaceous glands)
  • Apocrine – products acumulate in the top of the cell and then it breaks down
summary
Summary
  • Epithelial tissue structures and functions
  • Cell junctions
  • Classification by cell shape and layers
  • Glands