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BRS (RF) > Ions and minerals > Flashcards

Ions and minerals Flashcards

1
Q

What is diffusion?

A

The net random movement of molecules from a region of high concentration to low concentration. Multicellular organisms evolve circulatory system to provide cells within their diffusion range.

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2
Q

What cellular structure behaves as a diffusion barrier?

A

Cell membrane

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3
Q

Which molecules can pass through the phospholipid bilayer?

A

Lipid soluble (Non-polar) molecules can diffuse passively with minimal resistance in comparison to water soluble (Polar molecules); phospholipid bilayer consist of hydrophobic tails repelling polar molecules.

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4
Q

What is osmosis?

A

Osmosis concerns the net movement of water across a partially permeable membrane from a region of high water potential (Hypotonic), to a region with low water potential (hypertonic).
Within isotonic solutions there is no net movement of water.

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5
Q

What is paracellular transport?

A

Molecules can pass the epithelial layer through tight junctions, and lateral intercellular spaces.

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6
Q

What is transcellular transport?

A

Transcellular transport: Transport of solutes through a cell.

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7
Q

What are the three membrane transport mechanisms?

A

Simple diffusion
Facilitated transport
Active transport

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8
Q

What are channel proteins?

A

Form aqueous pores enabling specific solute to pass cross the membrane
Faster method of transportation than carrier proteins
Channel proteins are linked with an internal hydrophilic surface in order to shield solutes from the hydrophobic fatty acid tails

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9
Q

What are carrier proteins?

A

Binds to solute and undergo conformational change to transport solute across the phospholipid bilayer into intracellular cytoplasmic space.

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10
Q

What are the three types of gated ion channels?

A

Voltage gated
Ligand gated
Mechanically gated

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11
Q

What is a uniporter?

A

A uniporter is an integral membrane protein that transports a single type of substrate species across a cell membrane

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12
Q

What are symporters?

A

Symporters are secondary active transporters that move two substances in the same direction. Example: Sodium-glucose symporter passively diffuses into the cell, resulting in the cooperative movement of glucose into the cell (Glucose has higher intracellular concentrations), as energy is supplied through passive sodium transport.
Secondary active

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13
Q

What is an anti-porter?

A

Sodium-hydrogen anti porter users energy from inward movement of sodium to move hydrogen ions extracellular (Used to maintain internal pH)

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14
Q

What are the two main examples of coupled transport?

A

Antiporters

Sympoters

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15
Q

What are the three main transport mechanisms?

A

Primary ative transporter
Secondary active transport
Facilitated transport

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16
Q

What is primary active transport?

A

Linked directly to cellular metabolism (Uses ATP to power the transporter of substrates)

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17
Q

What is secondary active transport?

A

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

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18
Q

What is facilitated transport?

A

Enhances the rate of a substance can flow its concentration gradient, there is a tendency to equilibrate the substance across membrane

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19
Q

What are the two main examples of secondary active co transporters?

A

SGLT-1 co transporter (Monosaccaride absorption)

HCO3/Cl- counter transporter

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20
Q

How are glucose and galactose molecules absorbed within enterocytes?

A

Secondary active transport, through SGLT-1 on enterocyte apical membrane and electrochemical gradient

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21
Q

What is SGLT-1?

A

Has the ability to transport glucose against concentration gradient, therefore effective when extracellular luminal concentrations are comparatively less than that in enterocytes

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22
Q

What type of transport enables fructose absorption into enterocytes?

A

Facilitated diffusion

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23
Q

Which carrier protein is involved in the fructose absorption on the apical membrane of enterocytes?

A

GLUT-5 glucose co-transporters

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24
Q

Which transporters are involved in the exist of carbohydrates from enterocytes?

A

GLUT-2

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25
Q

What is the affinity and capacity of GLUT-2?

A

High capacity

Low affinity

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26
Q

Where is the majority of water absorbed within the GI tract?

A

Absorbed predominantly within the jejunum

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27
Q

Which two hormones regulates the GI absorption of calcium?

A

Calcitriol

Parathyroid hormone

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28
Q

Which hormone regulates enterocyte absorption of iron?

A

Hepcidin

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29
Q

How much water is absorbed in the small bowel?

A

8L

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30
Q

How much water is absorbed in the large bowel?

A

1.4l

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31
Q

What is standing gradient osmosis?

A

Transport of sodium ions from lumen into enterocyte
Counter-transport (antiporter), hydrogen ion exchange within the duodenum
Co-transport with amino acids and monosaccarides
Co-transprot with chloride ions

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32
Q

Which ion are chloride ions exchanged with into the enterocytes?

A

bicarbonate ions

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33
Q

What role is performed by the basolateral enterocyte Na/K ATPae in terms of ion transport?

A

Chloride ion co-transported with Na+ within ileum, exchanged with HCO3- (Colon) into enterocytes. Co-transporter executed through secondary active transport on apical membrane. Symporter occurs due to active transport of Na+ into lateral intercellular spaces by Na+/K+ATPase on enterocyte basolateral membrane into lateral plasma space.
Potassium diffuse in via paracellular pathways in small intestine

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34
Q

Which uptake protein is responsible for the facilitated diffusion of calcium ions int the enterocyte through the apical membrane?

A

TRPV6 (IMcal)

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35
Q

How is calcium cytoplasmically transported to the basolateral membrane of enterocytes from the apical membrane?

A

Cytoplasmic calcium biding protein, calbindin-D permits the movement of calcium

36
Q

Why is calcium intracellularly transported by calbindin-D proteins?

A

Prevents the action as an intracellular signal

37
Q

What are the two methods of calcium absorption?

A

Facilitated diffusion model using IMcal

Paracellular ion channels

38
Q

How are calcium ions removed from enterocyte through the basolateral membrane?

A

Calcium extrusion from enterocytes performed by two proteins: PMCA1 and NCXI, calcium ions are pumped across the basolateral membrane against concentration gradient into circulation

39
Q

What are the two protein transporters in the basolateral membrane that enables calcium enterocyte exist?

A

PMCA1 & NCX1

40
Q

Why does PMCA1 have a high affinity to calcium?

A

To maintain low intracellular concentrations

41
Q

Which calcium exit transporter has a low affinity, but high capacity?

A

NCX1 exchanger

42
Q

What would be the effect for a high intracellular concentration of calcium?

A

Result in activation of signalling cascade (Ca2+ is a signalling molecule)

43
Q

What is the average intracellular concentration of calcium?

A

100nM

44
Q

What is the average extracellular concentration of calcium?

A

1-3mM

45
Q

What effect does calcitriol exhibit in terms of calcium gut absorption?

A

Potentiates the transcription of Calbindin-D , PMCA, andTRPV6 transports to increase calcium enterocyte absorption from lumen into circulation

46
Q

Which promoter regions does Calctriol act upon?

A

Promoter regions VDRs -> Increases transcription

47
Q

How does calcitriol increase the rate of extrusion across basolateral membrane?

A

Increases PMCA transporters

48
Q

What are the effects of vitamin D deficiency?

A

Rickets

Osteporosis

49
Q

Which oxidative iron state is used to form haem?

A

Ferrous Fe2+

50
Q

What is the role of ferrous iron in haem?

A

Prophetic group with porphyrin ring of haemoglobin, facilitated oxygen transport

51
Q

Which cytochrome does haem form within the electron transport chain?

A

Complex 2

52
Q

What are the 3 main functions of iron?

A

Ferrous forms haem prophetic group within the porphyrin ring of haemoglobin - oxygen transport
Exhibits electron donor and electron acceptor properties
Essential for oxidative phosphorylation within the inner mitochondria membrane as cytochromes

53
Q

How is haem iron absorbed into the enterocyte?

A

Absorbed into he apical membrane through haem transporter

54
Q

What is the fate of ferrous iron within enterocytes?

A

Directly stored as mucosal ferritin (protective mechanism for overload)
Transported through the basolateral membrane via ferroportin into circulation

55
Q

What happens to ferritin within enterocytes?

A

Shed across epithelial cells

56
Q

How is ferrous iron converted into ferric iron?

A

Hephaestin action

57
Q

Why is ferrous iron concerted into ferric iron after release from enterocyte?

A

In order to be associated with plasma transferrin and circulated towards liver or bone marrow

58
Q

What effect does ferric iron through the liver have on hepcidin?

A

Increases hepcidin secretion

59
Q

What effect does Hepcidin have on enterocytes?

A

Reduces ferrorportin integration into basolateral membrane in order to reduce systemic overload

60
Q

Which cytochrome converts ferric sulphate iron into ferrous iron for entry into enterocytes?

A

Duodenal cytochrome B

61
Q

How does ferrous iron enters into enterocytes?

A

Through DMT-1

62
Q

Why is iron toxic in excess?

A

They body has no removal mechanism of actively excreting iron,
Free radicals

63
Q

Which vitamin reduces Ferric iron to ferrous?

A

Vitamin C

64
Q

What are the main insoluble ferric salts?

A

Hydroxide, phosphate, bicarbonate

65
Q

What % of dietary iron is absorbed?

A

20%

66
Q

Which protein potentates the absorption of haem into the apical duodenum membrane, through receptor-mediated endocytosis?

A

Haem carrier protein 1 (HCP1)

67
Q

Which enzyme cleaves ferrous iron from erythrocytes to liberate ferrous iron?

A

haem oxygenate

68
Q

What is the purpose of cytochrome B?

A

Catalyses the reduction of ferric iron to ferrous iron, in the process o iron absorption within the duodenal enterocytes
Ferrous transported into the enterocyte from divalent metal transporter H coupled co transporter

69
Q

Which iron transporters enable iron exit from enterocytes?

A

Ferroportin ion channel

70
Q

Which hormone regulates ferroportin transcription?

A

Hepcidin

71
Q

What is Hephaestin?

A

Fe2+ is oxidised by transmembrane copper-dependent ferroxidase (Hephaestin)  Ferric Fe3+  Bound to apotransferrin  transferrin.

72
Q

Which plasma protein enables the transport of ferric iron?

A

Transferrin

73
Q

How is ferrous iron stored within enterocytes?

A

Fe2+ alternatively binds to cytoplasmic apoferritin forming ferritin micelle  Globular protein complex (Fe2+ oxidised to Fe3+)  Crystallises within protein shell. Single ferritin = 4000 iron ions. Increased dietary ion absorption  Ferritin.

74
Q

What is ferritin?

A

Ferritin: Irreversible binding of iron to ferritin in epithelial cells  not available for transport into plasma. Loss in intestinal lumen and excreted into faeces  Increases in cytoplasmic iron  Increased ferritin synthesis.

75
Q

What are the four main fat soluble vitamins?

A

A, D, E, and K

76
Q

How are the fat soluble vitamins transported to the brush border?

A

As micelles

77
Q

A B12 deficiency results in which type of anaemia?

A

Pernicious anaemia

78
Q

How is B12 released within the stomach?

A

HCl

79
Q

Which protein does B12 combiner with within the stomach?

A

Haptocorrin

80
Q

Which factor is B12 bound to?

A

Intrinsic factor

81
Q

Which cells synthesise intrinsic factor?

A

Gastric parietal cells

82
Q

Which protein does B12 bind with within enterocytes?

A

Transcobalamin-11

83
Q

Where is b12-transcobalamin-II stored?

A

Liver, and transported to tissues

84
Q

What is intrinsic factor?

A

Intrinsic factor: Vit B12 binding protein secreted by parietal cells. Complex resistant do digestion  Binds to cubilin receptor in distal ileum (receptor mediated endocytosis)

85
Q

Which receptor does the IF-B12 complex bind onto within enterocytes?

A

Cubillin receptor

86
Q

What are the four main causes of vitamin b12 deficiency?

A

Inadequate intake of sources containing the compound (Veganism)
Inadequate secretion of intrinsic factor: pernicious anaemia (an autoimmune disorder)- autoantibodies interfere.
Lack of stomach acid (achlorhydria) – after partial gastrectomy surgery.
Malabsorption- diseases in the ileum reduces B12 absorption.

BRS (RF) (38 decks)

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