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LSS : Alimentary system > ions vitamins and minerals > Flashcards

ions vitamins and minerals Flashcards

1
Q

what are the two main types of transport?

A
  • para cellular

- transcellular

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2
Q

what are the methods via transcellular transport?

what do these also involve?

A
  • facilitated diffusion
  • simple diffusion
  • active transport

carrier proteins

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3
Q

what is paracellular transport?

A

when things don’t go through the cells they travel around the cells

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4
Q

what are the two types of channel proteins?

A

Channel proteins :
channel proteins form aqueous pores allowing specific solutes to pass across the membrane
(much faster)

Carrier proteins:
carrier proteins bind to the solute and undergo an conformational change to transport it across the membrane

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5
Q

what are the two ways of active transport?

A
  • primary
    linked directly to cellular metabolism
  • secondary
    derives energy from concentration gradient of another substance actively transported
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6
Q

example of secondary active transport?

A
  • enterocytes absorb GLUCOSE & GALACTOSE via 2nd active transport
  • glucose transporter
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7
Q

example of facilitated diffusion?

A

Exit of glucose then via facilitated diffusion (GLUT-2)

absorption of fructose

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8
Q

example of primary active transport?

A

sodium potassium ATPase

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9
Q

where does water absorption happen ?

how much water is absorbed?

A

99% of water is absorbed by GI tract
- Most water is absorbed in the small intestine
mainly jejunem

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10
Q

how are ions absorbed?

A
  • Many ions absorbed slowly by passive diffusion
  • Ca2+
    and iron are incompletely absorbed
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11
Q

how much water does the small intestine absorb?

A

8 litres

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12
Q

how much water does the colon absorb?

A

1.4 litres

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13
Q

where does the water come from?

A 
Ingestion (2L)
 saliva (1.2L).
 Gastric secretions (2L) 
 bile (0.7L).
 The pancreas (1.2L) 
 intestine (2.4L).
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14
Q

what is the name of the process by which the water is absorbed?

A
  • standing gradient osmosis

- is driven by absorption of the sodium ion

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15
Q

how does sodium get into cells in different placed enterocytes?

A
  • proximal bowel - counter transport of Na+ for H+
  • jejunum - co-transport with amino acid, monosaccharides
  • ileum - co transport with Cl-
  • colon - restricted movement through the ion channels
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16
Q

how are chloride ions moved?

A

Cl- is co-transported with Na+
in the ILEUM and
exchanged with HCO3- in the COLON.

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17
Q

how is potassium chlorides transported?

A

Cl- is co-transported with Na+
in the ILEUM and
exchanged with HCO3-in the COLON.

so we get potassium in faeces

18
Q

what happens with high sodium in the cell?

A
  • sodium is pumped into lateral intracellular spaces by Na/K ATPase
  • this increases the electrochemical gradient to positive
  • so negative ions move Cl- and HCO3
  • the solution is hypertonic
  • so this drives the absorbtion of water
19
Q

where is the calcium absorbed?

A

Most absorption of calcium occurs in the duodenum and ileum.

20
Q

what stimulates the absorption of calcium?

A
  • calcium deficiency increases the absorbtion

- Vitamin D and parathormone stimulate the absorption of calcium

21
Q

how much calcium do we ingest

how much calcium do we absorb?

A

1-6g of calcium a day

we only absorb 0.7g of it

22
Q

by which transporters is the calcium carried across by?

A
  • intestinal calcium binding protein (IMcal)

- ion channel

23
Q

what is the issue with absorbing calcium

A

calcium acts as a secondary transporter

- we need to keep it inactive so we bind it to calbindin to make it inactive

24
Q

how do we ship the calcium across the cell into the blood stream ?

A

actively transport it

  • using Ca2+ATPase (PMCA).
  • HIGH affinity but LOW capacity.

Na+/Ca2+ exchanger.
low affinity but high capacity

25
Q

so what happens just after the calcium is in the cell?

A
  • calbindin is unbound
  • high Ca2+ conc
  • The Na+/Ca2+ exchanger will effectively reduce the large calcium concentration
  • PMCA will then lower the
    calcium concentration even further
26
Q

why do we need vit D?

A 
Essential for normal Ca2+
 absorption
- increases level of calbindin 
- Enhance transport of Ca2+ through cytosol.
- Increase number of Ca2+ATPase
27
Q

why is iron important?

A

Iron is vital for oxygen transport (in haem) and oxidative phosphorylation (ETC)

28
Q

what happens to iron in excess

and what do we need to do?

A
  • toxic
  • must be regulated
    so we absorb 15- 20mg/day
  • but we only absorb 0.5-1.5mg/day
29
Q

how do we absorb iron?

method 1 ?

A
  • inorganic iron
    – Fe2+ (ferric) or Fe3+ (ferrous)
  • We CANNOT absorb Fe3+ directly
    so we absorb it as Fe3+ + insoluble salt binding
  • or we reduce it to Fe2+ using vit C
30
Q

how do we absorb iron?

method 2?

A

as part of haem
- absorb this intact into the enterocyte via haem carrier protein 1 (HCP-1) which endocytoses via receptor mediated endocytosis.

Fe2+ is then liberated by haem oxygenases.

31
Q

how is iron uptaken?

method 1

A
  • haem can bind to haem carrier protein 1 and then is absorbed by receptor mediated endocytosis
  • Haem Oxygenase
    (HO) then liberates Fe2+
32
Q

how is iron uptaken ?

method 2

A

Duodenal Cytochrome B (Dcytb – this enzyme can reduce
Fe3+ → Fe2+
which then passes into cytosol via Divalent Metal Transporter 1 (DMT-1) with H+ ions.

33
Q

how is iron excreted into the blood?

A
  • Ferric enters the blood via ferroportin (FP).
  • Hephaestin (HP) is a copper dependant
    ferroxidase that converts Fe2+ → Fe3+
  • Fe3+ binds to apotransferrin and travels in
    blood as transferrin (TF).
    -
34
Q

what suppresses ferroportin?

A

Hepcidin

35
Q

how is iron excreted?

A
  • Ferric binds to apoferratin to form ferritin micelle
  • Fe2+ then oxidises to Fe3+ which creates a protein shell.
  • The micelle is lost when the enterocytes
    are shunted off the tip of the villi.
  • Increase of iron conc. in cytosol increases
    ferritin synthesis.
36
Q

how are most vitamins transported?

A
  • Vitamins are predominantly absorbed by passive diffusion.
37
Q

how are fat soluble vitamins ADEK transported?

A
  • K is actively taken up.

- ADE transported to the brush border by micelles

38
Q

where is vit B12 stored?

A

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

39
Q

what happens when there is impaired absorbtion of B12?

A

pernicious anaemia.

40
Q

how is B12 released from food in stomach?

what is the problem and what happens?

A

most B12 is bound to protein in the food

  • the stomach low PH and pepsin releases the B12 from the food
  • B12 is easily denatured by HCl
  • B12 therefore binds to R protein (haptocorrin) which is released by parietal cells and in saliva.

the R protein is then digested in the duodenum

  • then the B12 binds to the intrinsic factor
    the intrinsic factor is not digested
  • B12/IF complex binds to cubulin (cub) receptor in distal ileum and is endocytosed
  • then within the mitochondria the complex is broken down
    and B12 binds to transcobalamin II (TCII) and travels to liver in the blood.
  • TCII receptors on the Liver allow uptake of complex.
  • Proteolysis then breaks down the TCII inside the cell.

LSS : Alimentary system (13 decks)

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