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Gastroenterology > Ions, Vitamins and Minerals > Flashcards

Ions, Vitamins and Minerals Flashcards

1
Q

How does water move down a concentration gradient

A
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2
Q

How can molecules cross the epithelium to enter the bloodstream

A

Paracellular transport through tight junctions and lateral intercellular spaces

Transcellular transport through epithelial cells

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3
Q

What are channel protein

A
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4
Q

What are carrier proteins

A
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5
Q

What are the two types of co-transported ion

A
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6
Q

What is the difference between primary active transport and secondary active transport

A

Primary - linked with ATP

Secondary - derives energy from concentration gradient of another substance that is actively transported

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7
Q

Example of primary active transport

A
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8
Q

Example of secondary active tranport

A

SGLT-1 co transport in small bowel absoprtion

HCO3/Cl in pancreatic HCO3 secretion

Na/H counter transport in pancreatic HCO3 secretion

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9
Q

Example of facilitated transport

A
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10
Q

How are glucose and galactose absorbed

A
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11
Q

How is fructose absobred

A

Facilitated diffusion

GLUT-5 on apical membrane

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12
Q

How does glucose exit the basolateral membrane

A

Facilitated diffusion

Glut-2 high capacity low affinity

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13
Q

Where is water being absorbed coming from

A
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14
Q

How is water absorbed

A

Driven by Na

Counter transport in exchange for H (proximal bowel)

Co transport with amino acids, monosaccharides (jejunum)

Co transport with Cl (ileum)

Restricted movement through ion channels (colon)

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15
Q

How is Cl absorbed

A
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16
Q

How is K absorbed

A

Diffuses via paracellular pathways in small intestine

Passive transport

17
Q

What happens to Na after being used for secondary active transport

A

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

18
Q

What happens when Na moves into intercellular space

A

Intercellular spaces causes fluid to be hypertonic

Osmotic flow of water from gut lumen via adjacent cells, tight junctions into the intercellular space

Water distends the intercellular channels and causes increased hydrostatic pressure

19
Q

What stimulates calcium absorption

A
20
Q

How is calcium carried across apical membrane

A
21
Q

What are teh implications for Ca transport transport across the cell

A

Need to transport Ca while maintaing low intracellular concetrations

Binds to calbindin in cytosol

22
Q

How is Ca pumped across basolateral membrane by plasma membrane

A

PMCA has a high affinity for Ca but low capacity

Ca (ATPase)

Also pumped by Na/Ca which has low affinity but high capacity ( requires larger concentrations)

23
Q

What is the rold of 1,25-dihydroxy d3

A

Enhances transport of Ca

Increases levels of calbindin

Increase rate of extrusion across basolateral membrane by increasing Ca ATPase

24
Q

What is iron essnetial for

A

Oxygen transport

Oxidative phosphrylation

25
Q

How is iron presented in the diet

A
26
Q

Facts about iron

A
27
Q

How is heme absorbed

A

Heme carrier protein 1 (HCP-1) and via receptor-mediated endocytosis

Fe liberated by Heme oxygenase

28
Q

How is iron uptook

A

Duodenal cytochrome B catalyzes the reduction of Fe3 to Fe2 in the process of iron absorption

Fe2 transported via divalent metal transporter (DMT-1) , H coupled cotransporter

Fe2 binds to unkown factors carried to basolateral membrane via ferroportin ion channel

Hephaestin is a transmembrane copper-dependent ferroxidase converts 2 to 3

Fe3 binds to apotransferrin, travels in blood as transferrin

29
Q

Facts about ferritin

A

Binds to apoferritin in cytosol to form ferritin micelle

Ferritin molecule can store up to 4000 iron

In excess diertary iron absorption, porduce more ferritin

Globular portein complex

Fe crystallises within protein shell

30
Q

What happens to ferritin stored in enterocytes

A

Prevents absorption of too much iron

31
Q

How are fat soluble vitamins (A,D,E,K) transported

A

K taken up by active transprot

Others transported to brush border

32
Q

What happens during impaired absorption of vit B12

A

Retards the maturation of RBC - pernicious anaemia

Most b12 bound to proteins

33
Q

How is denaturation of B12 in stomach avoided

A

Binds to R portein (haptocorrin) released in saliva and from parietal cells

R proteins digested in duodenum

34
Q

What is the intrinsic factor

A

Vit B12 binding glycoprotein secreted by parietal cells

Resistatnt to digestion

Vit B12/IF binds to cubilin receptors, taken up in distal ileum

35
Q

What happens to B12 once in cell

A

Vit B12/IF complex broken

B12 binds to protein transcobalamin II (TCII)

Travels to liver bound to TCII

TCII receptors on cells allow them to uptake complex

Proteolysis breaks down TCII inside cell

36
Q

Where is the greatest amount of water absorbed

A

Small bowel, jejunum

37
Q

How much iron is absorbed

A

5% inorganic iron

20% of heme iron

Gastroenterology (9 decks)

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