Cell Processes: Traffic across cells: Epithelial transport of glucose

Question 1

What are epithelial tissues made of?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

What separates epithelial cells?

Answer 3

lateral intercellular space

Question 4

What holds the luminal edges of epithelial cells together?

Answer 4

tight junctions

Question 5

What do tight junctions consist of?

Answer 5

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

Question 6

What do tight junctions appear to be in freeze fracture

Answer 6

interlocking network of ridges in the plasma membrane

Question 7

What do increased ridges in cells mean?

Answer 7

the cells are more tightly packed

Question 8

What is the barrier function of tight junctions

Answer 8

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

Question 9

What is the barrier function of tight junctions in the SKIN

Answer 9

they prevent microbes from entering the body

Question 10

What is the fence function of tight junctions?

Answer 10

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

Question 11

What do tight junctions separate in epithelial cells

Answer 11

they separate the cell into two distinct membrane domains

Question 12

What is the apical membrane

Answer 12

membrane that faces the lumen of the organ or body cavity

Question 13

other names for the apical membrane

Answer 13

luminal or mucosal

Question 14

What is the basolateral membrane

Answer 14

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

Question 15

What does a cell having distinct membrane domains mean

Answer 15

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

Question 16

What two pathways can transport occur

Answer 16

paracellular or transcellular pathway or via both

Question 17

What is the transcellular pathway?

Answer 17

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

Question 18

What is the paracellular pathway?

Answer 18

crossing the lateral intercellular (paracellular) space

Question 19

What governs Paracellular transport

Answer 19

the laws of diffusion and the tightness of the junctions

Question 20

What is NOT involved in paracellular transport?

Answer 20

transport protein

Question 21

What is measured in tight junctions?

Answer 21

electrical resistance to ion flow through tight junctions can be measured

Question 22

What does a higher electrical resistance mean?

Answer 22

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

Question 23

What does more strands in a tight junction do

Answer 23

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

Question 24

What is leaky epithelium?

Answer 24

epithelial tissue where paracellular transport dominates

Question 25

What pathway does leaky epithelial tissue allow?

Answer 25

Ability to move molecules through paracellular pathway

Question 26

What is tight epithelium?

Answer 26

epithelial tissue where transcellular transport dominates

Question 27

Does tight epithelium allow paracellular transport?

Answer 27

No

Question 28

Examples of 'leaky' epithelium location

Answer 28

Duodenum, proximal tubule

Question 29

Examples of 'tight' epithelium

Answer 29

Colon, collect duct

Question 30

What type of epithelium is proximal?

Answer 30

Leaky epithelium

Question 31

What electrical resistance is proximal?

Answer 31

low

Question 32

What number of strands is proximal

Answer 32

low

Question 33

What type of transport is proximal

Answer 33

bulk transport (paracellular)

Question 34

What type of epithelium is distal?

Answer 34

tight epithelium

Question 35

What electrical resistance is distal?

Answer 35

high

Question 36

What number of strands is distal

Answer 36

high

Question 37

What type of transport is distal?

Answer 37

hormonally controlled (transcellular)

Question 38

What type of transport is absorption

Answer 38

transport from lumen to blood

Question 39

What type of transport is secretion

Answer 39

transport from blood to lumen

Question 40

What is transcellular transport?

Answer 40

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

Question 41

Rules of transepithelial transport (4)

Answer 41

entry and exit steps, electrochemical gradient, electroneutrality, osmosis

Question 42

What are is the entry step for absorption and secretion

Answer 42

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

Question 43

What is the electrochemical gradient for transepithelial transport

Answer 43

is the entry or exit step passive or active

Question 44

What is electroneutrality in transepithelial transport

Answer 44

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

Question 45

What is osmosis in transepithelial transport

Answer 45

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

Question 46

What is osmosis

Answer 46

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

Question 47

What are the 3 properties of permeability through lipid bilayer

Answer 47

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

Question 48

Formula for permeability to water

Answer 48

Pw= Pd + Pf

Question 49

What does Pd mean

Answer 49

through lipid bilayer

Question 50

What does Pf mean

Answer 50

through water channel

Question 51

Is Pd or Pf bigger

Answer 51

Pf > Pd

Question 52

What are the 3 properties of permeability through water channel

Answer 52

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

Question 53

What is osmotic pressure?

Answer 53

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

Question 54

What regulates the movement of water (Pf)

Answer 54

aquaporins

Question 55

What are aquaporins

Answer 55

proteins that allow only water to flow through, 9 isoforms

Question 56

Why do cells have different Pw

Answer 56

Cells have different Pw because they express different aquaporin isoforms

Question 57

What does sodium glucose symporter (SGLT) do

Answer 57

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

Question 58

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

Answer 58

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

Question 59

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

Answer 59

2K+ in and 3Na+ out

Question 60

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

Answer 60

mediates glucose exit across basolateral membrane via passive diffusion down gradient

Question 61

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

Answer 61

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

Question 62

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

Answer 62

induces paracellular Cl and water influxes

Question 63

What is oral rehydration therapy

Answer 63

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

Question 64

What does oral rehydration therapy use?

Answer 64

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

Question 65

What is Glucose-galactose malabsorption syndrome

Answer 65

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

Question 66

Treatment for glucose-galactose malabsorption syndrome

Answer 66

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

Question 67

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

Answer 67

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

Question 68

What is GLUT5

Answer 68

Fructose transporter

Question 69

What is the Renal threshold

Answer 69

200 mg/dl

Question 70

What happens if glucose isn't reabsorbed in the kidney

Answer 70

it appears in the urine

Question 71

How much glucose is in the kidney

Answer 71

5 mmol

Question 72

What energy does Glucose reabsorption in the kidney | use

Answer 72

Using energy from sodium ATPase

Question 73

What is blood sugar level in diabetes

Answer 73

over 200mg/mL

Question 74

What is Glucosuria

Answer 74

glucose in the urine

Question 75

What happens to the glucose sympoter in diabetes?

Answer 75

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

Question 76

When does glucose appear in the urine

Answer 76

When renal threshold is reached

Question 77

What does the renal threshold reflect?

Answer 77

the transport maximum of SGLT