Epithelial Tissues

Question 1

How are epithelial cell classified? give examples

Answer 1

shape - squamous (flat), cuboidal, columnar

layering - single, multilayered

Question 2

Give examples of different epithelial cell types

Answer 2

simple squamous e.g. lung alveolar, blood vessel endothelium
simple cuboidal e.g. enterocytes, absorptive and secretive cells
stratified squamous keratinising e.g. epidermis
stratified squamous non-keratinising e.g. mouth, cervix, uterus, anus, oesophagus lining
pseudostratified e.g. airway epithelium, urinary duct

Question 3

Why do epithelia have polarity?

Answer 3

gives unidirectionality to functions such as secretion and absorption

Question 4

How is polarity established?

Answer 4

junctions separate the membrane into 2 biochemically (lipid/protein composition) and functionally different domain

Question 5

Whys is polarity important for transport?

Answer 5

ion pumps and channels have polarisation to restrict activity to certain parts and maintain concentration gradient e.g. pump present on one membrane

Question 6

How is polarity important for secretion?

Answer 6

so secretions are delivered to correct tissue compartment

Question 7

How are tight junctions involved in polarity?

Answer 7

separate the apical and basolateral compartments and seal the paracellular pathway

Question 8

What is a key characteristic of cell junctions?

Answer 8

they are dynamic so can be reassembled and disassembled rapidly

Question 9

How may an epithelial cell be specialised for transporting, such as absorptive or fluid/ion transport?

Answer 9

simple columnar
more ion transporters on membrane
mitchochondria associated with basal membrane infolding to provide E for active transport
SA increased by length, foldings and microvilli

Question 10

What is exocrine secretion?

Answer 10

secretes into a duct or lumen

Question 11

What is endocrine secretion?

Answer 11

secretes into the blood

Question 12

How may an epithelial cell be specialised for protection such as skin epidermis?

Answer 12

stratified squamous
keratinised = no nuclei visible, dry upper layers and cells die
non-keratinised = nuclei visible, wet upper layer as cells alive

Question 13

What do cytokeratin or cell junction defects cause?

Answer 13

blistering disease due to fragile skin

Question 14

What need to be balanced for epithelial cells?

Answer 14

proliferation and death so steady tissue mass

Question 15

What is the rate of cell turnover in gut lining, fat/heart/bone and neuronal cells

Answer 15

gut = 3-10 days
fat = 8-10 days
neuronal = not replaced