Epithelium: Characteristics And Classification

Front 1

Tissue

Back 1

an aggregate of cells and intercellular substances specialized to perform a particular function

Front 2

Basic Tissues

Back 2

connective
muscle
nervous
epithelium

organs consist of various arrangements of four basic tissues

Front 3

Epithelium

Back 3

a group of closely apposing cells of similar morphology with very little intercellular space having one free(apical) and another attached (basal) surface
-subdivisions:
surface epithelium:sheets of aggregated cells of similar type that cover/line all external and internal surface of the body
glands (epitheloid): secretory cells of endocrine and exocrine glands, proliferation of surface epithelium into underlying connective tissue

Front 4

epithelial characteristics

Back 4

-basal and apical surface
-little intercellular substances
-derived from all 3 embryonic tissues
-polar
-contacts basement membrane
-acascular
-mitosis
Table 2.2

Front 5

Functions

Back 5

Protection
Absorption
Secretion
Excretion
Selective Permeability/barrier

Front 6

Basement Membrane

Back 6

-present wherever any tissue comes in contact with connective tissue
-acts like glue

Front 7

layers of basement membrane

Back 7

lamina lucida:
electron micrograph is light layer(low density), hemidesmososmes, anchoring filaments
basal lamina/lamina densa/lamina basalis:
collagen, don't make dark filaments
sub-basal lamina:
reticular fibers (produced by fibroblasts), connects lamina densa to subepithelial connective tissue

first two produced by epithelium
Functions: Ultrafiltration and selective barrier

Front 8

Classification
based on number of cell layers

Back 8

- Based on number of cell layers:
- Simple (one layer of cells)
- Stratified (2 or more layers of cells)
- Pseudostratified (appears to have more than one layer)

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based on shape of surface cells

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- Squamous
- Cuboidal
- Columnar

In real life you will encounter forms in the middle

Front 10

simple squamous epithelium

Back 10

- Single layer of thin flat cells with spherical,oval, flattened nucleus
- Scale-like cells with serrated borders (in surface view)
-location:
blood vessels, alveoli, pleura, peritoneum (want it where materials can need to pass through quickly)
fxns:
diffusion

Front 11

simple cuboidal epithelium

Back 11

- Single layer of hexagonal cells with equal height and width
- Appears square in cross section
- Low and tall cuboidal epithelia
-location: ducts where secretion takes place, collecting ducts of the kidney
-fxns: where material passes with little processing

Front 12

Simple columnar epithelium

Back 12

- Tall & narrow cells
- Oval and basally located nuclei
-location:
intestines, where absorption/secretion occurs, gallbladder, bulbourethral gland
fxns:
perform processing of material

Front 13

Pseudostratified epithelium

Back 13

- Single layer of cells but appears multi-layered, nuclei at
different levels, all cells rest on basement membrane
- Cell types:
- Basal cells
- Ciliated cells
- Non-ciliated cells
- Goblet cells
-location:
lining of bronchioles, trachea, uterus, nasal cavity
-fxns:
present where you need rapid turnover of cells

Front 14

Stratified squamous epithelium

Back 14

-surface cells are squamous
2 types:
- Stratified Squamous Keratinized Epithelium: surface cells lose nuclei, filled with keratin (a water resistant
protein) so forms protective barrier
- Stratified Squamous Non-keratinized Epithelium: surface cells retain nuclei
-location:
skin
3 layers=non-keratinized
4-5=keratinized

Front 15

layers BSGLC

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Stratum:
Basale
Spinosum
Granulosum
Lucidum
Corneum

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basale

Back 16

deepest layer w/ mitotically dividing cells (cuboidal to columnar)

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Spinosum

Back 17

- Polyhedral cells forming varying number of layers; contain numerous desmosomes; “spiny processes” contain intermediate filaments, for strength

Front 18

Granulosum
ABSENT in non-keratinized and hard keratin tissues

Back 18

contain keratohyalin and lamellar granules

Front 19

Lucidum
ABSENT in hairy skin

Back 19

translucent appearance due to eleidin protein

Front 20

Corneum or station superfiale(in non-keratinized)

Back 20

contain keratinized cells w/ no/pyknotic nuclei or organelles

Front 21

stratified cuboidal epithelium

Back 21

- Two or more layers of cells
- Surface layer is typical cuboidal
- Mostly occur as 2-layered epithelium
-location:
excretory ducts of glands

Front 22

stratified columnar epithelium

Back 22

- Several layers of cells
- Surface layer is columnar (often prismatic)
- Deeper cells are small & polyhedral
-location:
urethre, mandibular ducts, parotid ducts

Front 23

transitional epithelium

Back 23

- Pseudostratified type of epithelium
- Wide variety of appearances
- Basement membrane: thin & folded
-location:
lines hollow organs w/ considerable capacity for distension, urinary system
-shape of cells depends on stretching