Epithelial Tissues
1. Identify the two major subdivisions of epithelium (epithelium and glands) and their
embryological origin.
a. Epithelium is divided to either epithelium, the layer of cells that covers the body’s
surfaces, and glands
b. Epithelial tissue can be derived from all three germ layers (endoderm, mesoderm,
and ectoderm).
2. Be able to define the tissue epithelium, list it’s various functions and common structural
characteristics
a. Epithelium are layers of tissue that covers the body’s surfaces
b. Epithelium are predominately cellular, forming contiguous sheets of cells in a
layer or membrane
i. Numerous intercellular junctions
ii. Polar cells with basolateral and apical regions
iii. Free surface
iv. Sits on basement membrane of connective tissue
v. Avascular, receiving nutrients from the connective tissue
c. Epithelium serves several functions
i. Selectively permeable barriers
ii. Protection against mechanical, dehydration, and chemical damage
iii. Secretion of materials
iv. Absorption (e.g. G.I. tract)
v. Transport (e.g. endothelium, lung)
vi. Function as a sensory surface
vii. Can regenerate and repair itself
3. Be able to describe and classify the various types of epithelium by cell and number of cell
layers
a. Epithelium are categorized by the number of layers of cells and the shape of the
cell
i. Number of Layers
1. Unilaminar or Single – One layer of cells
2. Multilaminar or Stratified – Several layers of cells
3. Pseudostratified – Looks like stratified but really a single layer of
cells, only some don’t reach all the way to the surface
ii. Shape of Cell
1. Squamous – Thin, flattened cells
2. Cuboidal – Cells in a cube
3. Columnar – tall narrow cells
4. Translational – Looks to be cuboidal translating towards squamous
but really not; found in uroepithelium in distended and undistended
forms
5. Keratinized – upper layers are killed with increasing amounts of
keratin, leaving no nuclei on surface layers
6. Non-keratinized – just like keratinized only surface cells have
nuclei and are still alive
iii. Specialized
1. Gustatory – covers tongue and has taste buds
2. Olfactory – covering part of nasal passage
3. Stato-acustic – covering inner ear, sensing sound and
proprioception
4. Germinal – lines seminiferous tubule of testis; produce
reproductive cells
4. Be able to describe the polarity of the epithelial membrane and how it’s specializations
contribute to it’s polarity and function. Be able to related other structural specializations
to epithelial functions
a. Epithelium contains apical and basolateral sides.
i. Apical
1. Contains carrier proteins, glycoprotiens, carbohydrates attached to
proteins (glycocalyx), hydrolytic enzymes, aquaporins, etc.
2. Capable of endocytosis, exocytosis, and transcytosis
3. Can have special specializations such as microvilli for absorption,
cilia and flagella for motility
ii. Basolateral
1. Specialized cell junctions, hormone receptors, Na+/K+ ATPase, ion
channels
2. Three types of structural and functional junctions
a. Zonula Occludens
i. Tight Junctions
ii. Creates impermeable barrier
iii. Reinforced by cadherins
b. Zonula Adherens
i. Adhesion Belt
ii. Mechanical attachment to adjucant cells
c. Macula Adherens
i. Desmosomes
ii. Spot weld mechanical attachment of adjacent cells
iii. Phemphigus vulgaris
3. Gap junctions
a. Intercellular communication
b. Composed of connexons
i. Made of 6 conexin subunits in a barrel
iii. Basal
1. Basal Lamina
a. Dense layer located outside cell just below basal membrane
holds epithelium to connective tissue
2. Membrane Enfoldings
a. Increases surface area for fluid passage (tessellation)
3. Hemidesmosomes
a. Appears as a half desmosome on cytoplasmic side
b. Integrin transmembraneprotein binds cell membrane to
basal lamina
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5. Describe and differentiate between an exocrine and endocrine gland.
a. Exocrine glands have ducts; endocrine glands are ductless
i. Exocrine glands deliver secretion directly to the epithelial surface
ii. Endocrine glands secrete directly into the surrounding extracellular matrix
and blood
6. Be able to describe the common components of an exocrine gland and classify exocrine
glands by morphology, mode of secretion, and secretory product.
a. Exocrine glands maintain a connection to the epithelial surface
b. Can be classified by structure, secretion mode, and secretion type
i. Structure
1. Unicellular – consist of single cells embedded in epithelial layer
2. Multicellular – divided into duct and secretory portions
a. Named after duct branching and secretory shape
i. Duct
1. Simple – have a single duct
2. Compound – have branced ducts
ii. Secretory
1. Tubular – long tube
2. Acinar/Alveolar – like grapes
3. Tubuloalveolar – like grapes with long tube
extensions
ii. Secretion Mode
1. Merocrine – secrete by exocytosis
2. Apocrine – secrete by pinching off a part of a living cell
3. Holocrine – cell fills up with secretion, dies and is secreted as a
whole dead cell
4. Cytocrine – whole living cell secreted
iii. Secretion Type
1. Mucus – thick viscous secretion
2. Serous – watery secretion
3. Mixed – combination of mucus and serous
4. Sebum – oily secretion
5. Ceruminous – waxy secretion
7. Be able to define and describe the different levels of organization in the body.
a. Cells organized into Tissues
b. Tissues organized into Organs
c. Organs organized into Systems
8. Be able to list and describe the four basic tissue types of the body
a. Epithelium
i. Layer of cells covering body surfaces
b. Muscle
i. Group of cells that change shape, specialized for contraction
c. Nerve
i. Group of cells characterized by excitability and ability to receive stimuli
and transform into an electrical impulse
d. Connective Tissue
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i. Group of cells that connects the other tissues together both metabolically
and structurally.
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