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18 Cards in this Set

  • Front
  • Back
Epithelium- General Features
- always contiguous
- cell-cell junctions create impermeable barrier
General Function and Locations of Epithelium
Function: cover exterior body surfaces and line internal cavities and tubes; form secretory portion of glands and ducts (important in secretion)

- General Locations: free surfaces of body exterior; outer surface of internal organs; lining of body cavities, tubes and ducts; ex: pleural, pericardial, peritoneal)
Three principle characteristics of epithelium
1. Cell junctions

2. Defined cell polarity
a) Apical domain (facing outside)
b) Lateral domain (sides)
c) Basal domain
(each domain has specific functions and proteins associated with it)

3. Basement membrane
Epitheloid Tissue
- specialized epithelial tissue
- no free surface (doesn't have the outer layer)
- basement membrane and cell junctions
- found in most endocrine glands (secretion)
- ex: Leydig cells, Langerhans
Classification- based on no of cell layers and shape of surface layer
1. Cell Layers:
a) Simple- one cell layer thick (every cell touches basement membrane)
b) Stratified- two or more layers thick

2. Cell Shape (based on outermost layer):
a) Squamous- cell width> height(flat)
b) Cuboidal- cell width= height (square)
c) Columnar- cell width< cell height

* Subclasses: (specialized)
1. Endothelium- line blood vessels of body
2. Mesothelium- epithelium lining your body cavities
Simple Squamous- locations
typical locations:
a) Lining of vessels (endothelium)= exchange
b) Body cavities (mesothelium) = exchange and lubricate
c) Bowman's capsule in the kidney = a selective barrier
d) Respiration = exchange

- large nucleus, flat cytoplasm
Simple Cuboidal- locations
typical locations:
a) small duct of exocrine = absorption
b) ovary (germinal epithelium) = barrier
c) kidney tubules = absorption and secretion

- can be flat or form tubes
Simple Columnar- locations
typical locations:
a) small intestine and colon = absorption and secretion
b) stomach lining and gastric glands = secretion
c) gallbladder = absorption

- have a distinct polarity
Psuedostratified- structure and locations
- appears stratified (but it's not)
- contact basement membrane- simple
- limited distribution
- ID difficult, based more on location

typical locations:
a) trachea and bronchial tree- secretion, conduit
b) ductus deferens- secretion, conduit
c) epididymis- absorption, conduit

- the giveaway is nuclei at different heights (stratified are at the same heights)
- every cell touches basement membrane
Stratified Squamous- locations
typical locations:
a) epidermis- barrier and protection
b) oral cavity and esophagus- barrier and protection
c) vagina- barrier and protection

- designed to handle a rough environment
Stratified Cuboidal and Columnar- locations
stratified cuboidal typical locations:
a) sweat glands- barrier and conduit
b) large ducts of exocrine glands- barrier and conduit

stratified columnal typical locations:
a) largest ducts of exocrine glands- barrier and conduit
Transitional Epithelium- locations
location: renal calyces to urethra- barrier and distensible property (able to spread out)

- bubble shaped cells; stratified
- found in urinary tract
General Trends in Function
- secretion and absorption = simple or pseudostratified (few)
- simple squamous = high level transepithelial transport (capillaries, blood vessels)
- stratification = low transepithelial transport

- height of cells indicate the level of activity
- the larger and taller the cells are, the more metabolically active
Cell Polarity:
1. Apical domain
2. Lateral domain
3. Basal domain
1. Apical domain- directed toward external or lumen of cavity or tube

2. Lateral domain- communicates with adjacent cells; characterized by special attachment areas

3. Basal domain- rests on basal lamina; anchors cells to underlying CT
Apical Domain

1. Enzymes
2. Ion channels
3. Carrier proteins
4. Structural modifications:
a) Microvilli
b) Stereocilia
c) Cilia

- receptors can also be found in apical domain
Apical Domain: structural modifications- microvilli
- vary in appearance
- appearance varies with function- usually involved in increased surface area if they are taller cells
- microvilli borders

- shorter microvilli are usually involved in transport
Microvillar structure
- core made up of actin that forms microfilaments

- villin is a capping protein on the end

- fimbrin and fascin- involved in cross-links

- terminal web- anchors microvilli
Apical Domain: structural modifications- stereocilia
1. Limited distribution (not as common)
2. Facilitates absorption
3. Unique features:
- apical cell protrusion
- thick stem
- long microvilli

- have actin filaments present
- have cytoplasmic bridges that connect some