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nuero > ions vit and minearals > Flashcards

ions vit and minearals Flashcards

1
Q

what is diffusion

A

The process whereby atoms or molecules intermingle because of their random thermal motion.

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2
Q

osmosis

A

diffusion of water from a hypotonic to hypertonic thru a medium

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3
Q

How can molecules cross the epithelium to enter the bloodstream?

A

Paracellular Transport

through tight junctions and lateral intercellular spaces.

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4
Q

or

A

Transcellular Transport through the epithelial cells

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5
Q

how can solute cross cell membrane

A

simple diffusion

  • facilitated transport
  • active transport
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6
Q

how are they transported

A

Channel proteins

- Carrier proteins

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7
Q

what is a channel protien

A

form aqueous pores allowing specific solutes to pass across the membrane.

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8
Q

what are carrier protiens

A

bind to the solute and undergo a conformational change to transport it
across the membrane.

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9
Q

whats faster

A

Channel proteins allow much faster transport than carrier proteins.

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10
Q

Types of carrier-mediated transport

A

uniport
symport (symp and anti are coupled transport)
antiport

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11
Q

what is primary AT

A

transport is linked directly to cellular metabolism (uses ATP to power the transport).

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12
Q

what is secondary AT

A

derives energy from the concentration gradient of another substance that is actively transported.

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13
Q

what is Facilitated transport /facilitated diffusion

A

Enhances the rate a substance can flow down its concentration gradient. This tends to equilibrate the substance across the membrane and does not require energy.

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14
Q

are channel mediated transport active or passive

A

passive always

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15
Q

and carrier

A

passive or active

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16
Q

Examples of Primary active transporters already covered in the course?

A

Na+/K+ ATPase (Pancreatic HCO3- Secretion)

H+/K+ ATPase (Stomach – Parietal Cell)

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17
Q

Examples of Secondary active transporters already covered in the course?

A

SGLT-1 co-transport (Small bowel absorption of monosaccharides)

HCO3-/Cl- counter transport (Pancreatic HCO3- Secretion)

Na+/H+ counter transport (Pancreatic HCO3- Secretion)

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18
Q

Examples of Facilitated transport /facilitated diffusion transporters already covered in the course?

A

GLUT-5, GLUT-2 (Small bowel absorption of monosaccharides)

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19
Q

how are glucose and galactose absorbed

A

is by 2o active transport (carrier protein & electrochemical gradient).

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20
Q

what carrier protien

A

Carrier protein = SGLT-1 on apical membrane

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21
Q

why sglt 1

A

SGLT1 can transport glucose uphill against its concentration gradient (so effective when glucose at levels in the lumen are below those in the enterocyte).

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22
Q

fructose absorption

A

Absorption of fructose is by facilitated diffusion.

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23
Q

what protien

A

Carrier protein = GLUT-5 on apical membrane.

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24
Q

why is it effective

A

Effective at relatively low concentrations of fructose in the lumen as tissue and plasma levels are low.

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25
Q

Exit of glucose at the basolateral membrane is by

A

facilitated diffusion.

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26
Q

what protien

A

Carrier protein = GLUT-2, a high-capacity, low-affinity facilitative transporter.

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27
Q

where is most water absorbed

A

The greatest amount of water is absorbed in the small intestine, esp the jejunum.

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28
Q

what 2 ions are not completely absorbed

A

Calcium and iron are incompletely absorbed, and this absorption is regulated.

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29
Q

how is water absorbed

A

through standing gradient osmosis

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30
Q

what is it driven by

A

Na+

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31
Q

how is the transport of na+ from the lumen to the enterocyte in the proximal bowel

A

Counter-transport in exchange for H+ (proximal bowel)

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32
Q

jejunum

A

Co-transport with amino acids, monosaccharides (jejunum)

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33
Q

ileum

A

Co-transport with Cl- (ileum)

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34
Q

colon

A

Restricted movement through ion channels (colon)

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35
Q

how is cl- co transported with na+ in iluem

A

Cl- co-transported with Na+ in ileum

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36
Q

colon

A

exchanged with HCO3- (colon) into enterocytes

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37
Q

what are both above example sof

A

Both secondary active transport

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38
Q

how does k+ diffuse in colon

A

in via paracellular pathways in small intestine, leaks out between cells in colon.

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39
Q

what is that an example of

A

Passive transport.

40
Q

what happens to intracellular sodium

A

Active transport of Na+ into the lateral intercellular spaces by Na+K+ATPase transport in the lateral plasma membrane

41
Q

what strcutures absorb ca2+

A

Duodenum and Ileum

42
Q

what affect does calcium have on gut ability to absorb

A

Ca2+ deficient diet increases gut’s ability to absorb.

43
Q

what factors can stimulate absoprtion of ca2+

A

Vit D and parathyroid hormone stimulate absorption.

44
Q

how can calcium enter our cells from the small bowel

A

cia paracellular junction

45
Q

another way

A 
through calcium channels 
binds to calbindin 
prevents the prescence of high concentration in our cells  
so either goes through another channel 
or swapped for na+
46
Q

what can vit d do in the cell

A

enhances absorption and movement of calcium through the cell

47
Q

what are the 2 ways that ca2+ can be carried across the apical membrane

A

Intestinal calcium-binding protein (IMcal)- facilitated diffusion.

Ion channel

48
Q

what are the implications for transport of Ca2+ into the cell from the lumen?

A

Ca2+ acts as an intracellular signalling molecule.

49
Q

What are the implications for Ca2+ transport across the cell?

A

Need to transport Ca2+ while maintaining low intracellular concentrations.

Binds to calbindin in cytosol, preventing its action as an intracellular signal.

50
Q

how can calcium be trasnported out of the basolateral membrane (and what type of movememnt)

A

Ca2+ pumped across basolateral membrane by plasma membrane Ca2+ ATPase (PMCA) against concentration gradient.

51
Q

what is the affinity of PMCA for ca2+ and capacity

A

PMCA has a high affinity for Ca2+ (but low capacity).

52
Q

what is an alternate method for ca to be transported through teh basolateral membrane

A

Ca2+ pumped across basolateral membrane by plasma membrane Na+/Ca2+ exchanger against concentration gradient.

53
Q

describe the affinity of the na/ca exchanger for ca and capacity

A

The Na+/Ca2+ exchanger has a low affinity for Ca2+ but a high capacity. Requires larger concentrations of Ca2+ to be effective.

54
Q

what can 1, 25-dihydroxy D3 when taken up by enterocytes

A

Enhances the transport of Ca2+ through the cytosol
Increases the levels of calbindin
Increases rate of extrusion across basolateral membrane by increasing the level
of Ca2+ ATPase in the membrane.

55
Q

is iron an electron donor or acceptor

A

Iron can act as an electron donor and an electron acceptor

56
Q

What processes in the body is iron critical for?

A

Oxygen transport (red blood cells)

Oxidative phosphorylation
mitochondrial transport chain

57
Q

what are the 2 forms of ions that can be absorbed in oir bodies

A

heam

non haem

58
Q

what happens to haem irion

A

absorbed directly through a transporter and goes to intracellular region

59
Q

non haem aka

A

ferrous

60
Q

problem

A

ferrous not very absorbable so changed to a ferric

61
Q

how

A

by duodenal cytrocrome b agent

62
Q

then

A

absorbed via channel to intraceelular area

63
Q

then

A

stored as ferritin or absorbed across basolateral membrane through ferroportin channels

64
Q

how is iron transported

A

first convert ferric to ferrous by transferin to liver or bone marrow

65
Q

what happens if there is enough ferritin in the liver

A

hepcidin is produced

reduces production of ferroportin

66
Q

how is Iron present in the diet as:

A

inorganic iron (Fe3+ ferric, Fe2+ ferrous)

as part of heme (haem) group (haemoglobin, myoglobin and cytochromes).

67
Q

can you absorb fe3+

A

Cannot absorb Fe3+, only Fe2+.

68
Q

what reduces fe3+ to fe2+

A

Vit C reduces Fe3+ to Fe2+

69
Q

what happens to heam once it is absorbed

A

Heme is absorbed intact into the enterocyte.

Evidence that this occurs via heme carrier protein 1 (HCP-1), and via receptor-mediated endocystosis.

70
Q

what liberates the fe2+

A

Fe2+ liberated by Heme oxygenase.

71
Q

what enzyme is responsible for
catalyzes the reduction of Fe3+ to Fe2+ in the process of iron absorption in the duodenum of mammals
Duodenal cytochrome B (Dcytb)

A

Duodenal cytochrome B (Dcytb)

72
Q

how is fe2+ transported into the cell

A

Fe2+ transported via divalent metal transporter 1 (DMT-1), a H+-coupled co-transporter.
Fe2+ binds to unknown factors, carried to basolateral membrane, moves via ferroportin ion channel into blood.

73
Q

how does fe2+ move across basolateeral membrane

A

ferroportin

74
Q

what converts fe2+ to fe3+

A

Hephaestin is a transmembrane copper-dependent ferroxidase that converts Fe2+ to Fe3+.

75
Q

how does fe3+ travel in blood

what does it bind to

A

Fe3+ binds to apotransferrin, travels in blood as transferrin.

76
Q

hepcidin function

A

(Hepcidin, the major iron regulating protein, suppresses ferroportin function to decreases iron absorption).

77
Q

what is an alternative method for fe2+ transport

A

Binds to apoferritin in cytosol to form ferritin micelle.

78
Q

how is it oxidised

A

Ferritin is globular protein complex. Fe2+ is oxidised to Fe3+ which crystallises within protein shell.

79
Q

What happens to this ferritin stored in enterocytes?

A

Prevents absorption of too much iron (toxic)

80
Q

what is the binding of iron to ferritin like

A

Irreversible binding of iron to ferritin in the epithelial cells.

81
Q

how is ferritn lost

A

Iron/Ferritin is lost in the intestinal lumen and excreted in the faeces.

82
Q

what happens when iron sythesis increases

A

Increase in iron concentration in the cytosol increases ferritin synthesis.

83
Q

how is vit k taken up

A

active tr

84
Q

where is vit b stored

A

Liver contains a large store (2-5mg).

85
Q

how is vit b12 freed

A

In the stomach, low pH and the digestion of proteins by pepsin releases free vit B12.
But B12 is easily denatured by HCl.

86
Q

How is the denaturation of B12 in the stomach avoided?

A

Binds to R protein (haptocorrin) released in saliva and from parietal cells.
R proteins digested in duodenum.

87
Q

what is intrisic factor/Vit B12 binding glycoprotein secreated by

A

parietal cells.

88
Q

what is special about Vit B12/IF

A

it is resistant to digestion.

89
Q

No IF then

A

then no absorption of vit B12

90
Q

where do the Vit B12/IF complex go

A

binds to cubilin receptor, taken up in distal ileum (mechanism unknown, but thought to involve receptor-mediated endocytosis

91
Q

what happens once in a cell

A

Once in cell, Vit B12/IF complex broken- possibly in mitchondria

92
Q

how does it cross to basolateral membrane

A

B12 binds to protein transcobalamin II (TCII), crosses basolateral membrane by unknown mechanism

93
Q

then it travels to

A

Travels to liver bound to TCII.

94
Q

function of TCII

A

TCII receptors on cells allow them to uptake complex.

95
Q

how is TCII removed

A

Proteolysis then breaks down TCII inside the cell.

96
Q

In the epithelial cells, majority of iron is bound to ferritin and is unavailable for absorption.

A

In the epithelial cells, majority of iron is bound to ferritin and is unavailable for absorption.

nuero (36 decks)

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