lecture 23 - traffic across cells: general properties of epithelial cells

Question 1

epithelial cells sit on the?

Answer 1

basement layer

Question 2

2 things that epithelial tissues form a barrier between

Answer 2

• between body and external environment - between organs

Question 3

burn victims are fucked because?

Answer 3

easily get infections and loose water because they have lost the epithelial tissue barrier between body and external environment (skin)

Question 4

why is it necessary for epithelial tissues to undergo constant and rapid repair?

Answer 4

because they are subject to physical breakdown and injury

Question 5

reasons epithelial tissues are important

Answer 5

• protection - filtration - secretion - absorption - excretion - neuroendocrine functions

Question 6

2 types of epithelial tissue and their features

Answer 6

• covering and lining epithelium: skin epidermis, lining of blood vessels, lining of respiratory, urinary and GI tract - glandular epithelium: secretory portion of glands (thyroid, adrenal, sweat)

Question 7

simple = ? important for?

Answer 7

1 cell layer thick, important for absorption and secretion

Question 8

stratified =?

Answer 8

many cell layers thick

Question 9

pseudostratified = ?

Answer 9

1 cell layer thick, however not all cells reach the apical surface

Question 10

squamous = ?

Answer 10

flat

Question 11

cuboidal = ?

Answer 11

cube shaped

Question 12

columnar = ?

Answer 12

tall column

Question 13

transitional = ?

Answer 13

shape varies with tissue streching

Question 14

how do glandular epithelium form?

Answer 14

epithelial cells sink below the surface during development

Question 15

two types of glands

Answer 15

1. exocrine - secretion onto free surface of epithelium 2. endocrine - secretion of hormones into blood

Question 16

end pieces of glands consist of ______ cells, while the openings of glands are comprised of ________ cells. These two cell types have different ________ properties.

Answer 16

end pieces of exocrine glands consist of _acinar (secretory)_ cells, while the openings of glands are comprised of _duct_ cells. These two cell types have different _transport_ properties.

Question 17

acinar cells function

Answer 17

a primary sercretion rich in organic molecules (enzymes, regulatory molecules)

Question 18

duct cells function

Answer 18

modify the composition of the primary secretion by either absorbing or secreting specific ions (HCO3-, Cl-, K+, Na+)

Question 19

what separates neighbouring epithelial cells?

Answer 19

paracellular space or lateral intercellular space

Question 20

proteins of tight junctions

Answer 20

occludins, claudins

Question 21

tight junctions location

Answer 21

most apical cell junction

Question 22

how do tight junctions do their thang?

Answer 22

thin bands encircle the cell and interlock with thin bands from adjacent cells. The more bands, the tighter the junction.

Question 23

2 functions of tight junctions:

Answer 23

1. a barrier to restrict movement of substance between paracellular space 2. a fence to prevent proteins from diffusing in the plane of the lipid bilayer. 2 distinct domains with different transport proteins.

Question 24

2 distinct membrane domains set up by tight junctions

Answer 24

1. apical (or luminal or mucosal) membrane face lumen or of organ/cavity 2. basolateral membrane adheres to basement membrane and interfaces with the blood (includes paracellular space part)

Question 25

amount of paracellular transport depends on…

Answer 25

how tight the tight junction is i.e the number of bands

Question 26

band numbers vs. ion flow resistance

Answer 26

the more bands, the higher the resistance to ion flow

Question 27

dominant transport in leaky epithelial tissues

Answer 27

paracellular

Question 28

dominant transport in tight epithelial tissues

Answer 28

transcellular

Question 29

direction of paracellular transport governed by…

Answer 29

laws of diffusion

Question 30

tight junction resistance increases in a _________ to _________ direction in the __ tract and ______.

Answer 30

tight junction resistance increases in a _proximal_ to _distal_ direction in the _GI_ tract and _Kidneys_.

Question 31

tight junction resistance in proximal end (duodenum, proximal tubule)

Answer 31

leaky

Question 32

tight junction resistance in distal end (colon, collecting duct)

Answer 32

tight

Question 33

in transcellular transport, how do substances move across membrane

Answer 33

active (primary and secondary) and passive (through ion channels) trasport

Question 34

from lumen to blood =

Answer 34

absorption

Question 35

from blood to lumen =

Answer 35

secretion e.g. sweat

Question 36

entry step for absorption

Answer 36

apical membrane

Question 37

entry step for secretion

Answer 37

basolateral membrane

Question 38

electroneutrality refers to?

Answer 38

movement of ions through selectively permeable membrane will attract a counter ion

Question 39

under EM, tight junctions appear? in freeze fracture, tight junctions appear?

Answer 39

In EM tight junctions appear as though the membranes have fused. In freeze fracture, it appears as interlocking network of ridges.