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BIOSCI 107 Part Two > Cell Processes: Traffic across cells: Epithelial transport of glucose > Flashcards

Cell Processes: Traffic across cells: Epithelial transport of glucose Flashcards

1
Q

What are epithelial tissues made of?

A

cells arranged in continuous sheets in either single of multiple layers on top of the basement membrane

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2
Q

What do epithelial tissues form and what are they subject too?

A

the boundary between the body’s organs or between the body and the external environment
are subject to physical breakdown and injury – therefore undergo constant and rapid renewal process

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3
Q

What separates epithelial cells?

A

lateral intercellular space

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4
Q

What holds the luminal edges of epithelial cells together?

A

tight junctions

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5
Q

What do tight junctions consist of?

A

thin bands of proteins that encircle the cell and make contact with thin bands from adjacent cells

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6
Q

What do tight junctions appear to be in freeze fracture

A

interlocking network of ridges in the plasma membrane

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7
Q

What do increased ridges in cells mean?

A

the cells are more tightly packed

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8
Q

What is the barrier function of tight junctions

A

they restrict the movement of substances through the intercellular space between cells

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9
Q

What is the barrier function of tight junctions in the SKIN

A

they prevent microbes from entering the body

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10
Q

What is the fence function of tight junctions?

A

they prevent membrane proteins from diffusing in the plane of the lipid bilayer

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11
Q

What do tight junctions separate in epithelial cells

A

they separate the cell into two distinct membrane domains

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12
Q

What is the apical membrane

A

membrane that faces the lumen of the organ or body cavity

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13
Q

other names for the apical membrane

A

luminal or mucosal

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14
Q

What is the basolateral membrane

A

membrane that adheres to the adjacent basement membrane and interfaces with the blood

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15
Q

What does a cell having distinct membrane domains mean

A

transport proteins can be inserted into either the apical or basolateral membrane

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16
Q

What two pathways can transport occur

A

paracellular or transcellular pathway or via both

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17
Q

What is the transcellular pathway?

A

crossing 2 membranes (create across epithelial by electrochemical or osmotic gradients which pulls the movement of molecules by paracellular pathway)

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18
Q

What is the paracellular pathway?

A

crossing the lateral intercellular (paracellular) space

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19
Q

What governs Paracellular transport

A

the laws of diffusion and the tightness of the junctions

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20
Q

What is NOT involved in paracellular transport?

A

transport protein

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21
Q

What is measured in tight junctions?

A

electrical resistance to ion flow through tight junctions can be measured

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22
Q

What does a higher electrical resistance mean?

A

the greater the number of tight junction strands holding the cell together

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23
Q

What does more strands in a tight junction do

A

More strands = tighter tight junctions = higher electrical resistance = lower current flow

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24
Q

What is leaky epithelium?

A

epithelial tissue where paracellular transport dominates

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25
Q

What pathway does leaky epithelial tissue allow?

A

Ability to move molecules through paracellular pathway

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26
Q

What is tight epithelium?

A

epithelial tissue where transcellular transport dominates

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27
Q

Does tight epithelium allow paracellular transport?

A

No

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28
Q

Examples of ‘leaky’ epithelium location

A

Duodenum, proximal tubule

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29
Q

Examples of ‘tight’ epithelium

A

Colon, collect duct

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30
Q

What type of epithelium is proximal?

A

Leaky epithelium

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31
Q

What electrical resistance is proximal?

A

low

32
Q

What number of strands is proximal

A

low

33
Q

What type of transport is proximal

A

bulk transport (paracellular)

34
Q

What type of epithelium is distal?

A

tight epithelium

35
Q

What electrical resistance is distal?

A

high

36
Q

What number of strands is distal

A

high

37
Q

What type of transport is distal?

A

hormonally controlled (transcellular)

38
Q

What type of transport is absorption

A

transport from lumen to blood

39
Q

What type of transport is secretion

A

transport from blood to lumen

40
Q

What is transcellular transport?

A

Epithelial cells using primary and secondary active transport in combination with passive diffusion through ion channels to produce transport across the epithelial tissues

41
Q

Rules of transepithelial transport (4)

A

entry and exit steps, electrochemical gradient, electroneutrality, osmosis

42
Q

What are is the entry step for absorption and secretion

A

the entry step for absorption is the apical but for secretion is the basolateral membrane

43
Q

What is the electrochemical gradient for transepithelial transport

A

is the entry or exit step passive or active

44
Q

What is electroneutrality in transepithelial transport

A

movement of a positive or negative ion will attract a counter ion

45
Q

What is osmosis in transepithelial transport

A

net movement of ions will establish a difference in osmolarity that will cause water to flow by osmosis

46
Q

What is osmosis

A

Net movement of water through a selectively permeable membrane from an area of high water concentration to an area of lower water concentration

47
Q

What are the 3 properties of permeability through lipid bilayer

A

Small (not a lot of water flow through)
Mercury insensitive
Temp dependent (lipid fluidity)- high temp higher fluidity

48
Q

Formula for permeability to water

A

Pw= Pd + Pf

49
Q

What does Pd mean

A

through lipid bilayer

50
Q

What does Pf mean

A

through water channel

51
Q

Is Pd or Pf bigger

A

Pf > Pd

52
Q

What are the 3 properties of permeability through water channel

A

Large
Mercury sensitive (you can block the channel)
Temp independent

53
Q

What is osmotic pressure?

A

The pressure applied by a solution to prevent the inward flow of water across a semi-permeable membrane

54
Q

What regulates the movement of water (Pf)

A

aquaporins

55
Q

What are aquaporins

A

proteins that allow only water to flow through, 9 isoforms

56
Q

Why do cells have different Pw

A

Cells have different Pw because they express different aquaporin isoforms

57
Q

What does sodium glucose symporter (SGLT) do

A

Uses the energy of the sodium gradient to actively accumulate glucose above its concentration gradient

58
Q

What sets up the ion gradient in glucose absorption in the small intestine

A

Na-pump sets up ion gradients by carrier mediated transport (primary active transport)

59
Q

What ions are brought into and out of a cell by Na pump in glucose absorption in the small intestine

A

2K+ in and 3Na+ out

60
Q

What does Facilitative glucose transporter (GLUT) do in glucose absorption in the small intestine

A

mediates glucose exit across basolateral membrane via passive diffusion down gradient

61
Q

Why does Na that was taken up move out of cell via the basolateral Na-pump in glucose absorption in the small intestine

A

to maintain Na at low levels. sodium is maintained at low level in cell creating positive charge on blood side which attracts Cl- and H20

62
Q

What does the movement of Na and glucose out of the cell do in glucose absorption in the small intestine?

A

induces paracellular Cl and water influxes

63
Q

What is oral rehydration therapy

A

A simple sugar solution when given to dehydrated babies suffering from diarrhea is responsible for saving millions of lives per year

64
Q

What does oral rehydration therapy use?

A

The ability of glucose to enhance the absorption of Na+ and hence Cl- and water

65
Q

What is Glucose-galactose malabsorption syndrome

A

A mutation to the glucose symporter (SGLT - glucose absorption entry step) in the small intestine means that sugar is retained in the intestine lumen

66
Q

Treatment for glucose-galactose malabsorption syndrome

A

Removing glucose and galactose from the diet, using fructose as a source of carbohydrate

67
Q

What does glucose not being taken up do in Glucose-galactose malabsorption syndrome

A

Osmolarity of lumen increases (low H2O as glucose isn’t being absorbed/high solute conc) so Water moves from blood into small intestine to balance out osmolality. The associated increase in lumen osmolarity induces a water influx. The increased water flow produces a pronounced diarrhoea

68
Q

What is GLUT5

A

Fructose transporter

69
Q

What is the Renal threshold

A

200 mg/dl

70
Q

What happens if glucose isn’t reabsorbed in the kidney

A

it appears in the urine

71
Q

How much glucose is in the kidney

A

5 mmol

72
Q

What energy does Glucose reabsorption in the kidney

use

A

Using energy from sodium ATPase

73
Q

What is blood sugar level in diabetes

A

over 200mg/mL

74
Q

What is Glucosuria

A

glucose in the urine

75
Q

What happens to the glucose sympoter in diabetes?

A

can not absorb glucose fast enough and glucose appears in the urine

76
Q

When does glucose appear in the urine

A

When renal threshold is reached

77
Q

What does the renal threshold reflect?

A

the transport maximum of SGLT

BIOSCI 107 Part Two (17 decks)

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