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DIG > Absorption of Ions and Water > Flashcards

Absorption of Ions and Water Flashcards

1
Q

What is the surface area of the small intestine increased by?

A
  • Macroscopic folds of Kerckring (plicae circulares)
  • Villi + microvilli
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2
Q

What ions does absorption of water depend on primarily?

A
  • Na+
  • Cl-
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3
Q

Mechanism of water absorption

A
  • Transport of Na+, Cl- and HCO3- into lateral intercellular spaces
  • High NaCl near apical end of spaces means it is hypertonic
  • Osmotic flow of water from lumen into spaces
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4
Q

4 different transport routes of entry for Na+

A
  • Na+/glucose transport (or Na+/amino acid)
  • Na+/H+ exchanger
  • Parallel Na+/H+ and Cl-/HCO3- exchange
  • Epithelial Na+ channels
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5
Q

Mechanism of parallel Na+/H+ and Cl-/HCO3- exchange

A
  • Water + CO2 brought in from blood
  • Via carbonic anhydrase, these are turned into H+ and HCO3-
  • These are transported into lumen separately, bringing in Na+ and Cl- respectively
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6
Q

Which substances regulate parallel Na+/H+ and Cl-/HCO3- exchange, and what happens if their levels increase?

A
  • cAMP
  • cGMP
  • Intracellular Ca2+
  • Increase in any decreases NaCl absorption
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7
Q

How do mineralocorticoids increase Na+ absorption?

A
  • Increase opening of apical channels
  • Insertion of preformed channels from sub-apical epithelial vesicle pools into apical membrane
  • Increase synthesis of apical channels + Na+/K+ pumps
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8
Q

What effect do absorptagogues have on intestinal electrolyte transport?

A

Promote absorption

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9
Q

What effect do secretagogues have on intestinal electrolyte transport?

A

Promote secretion-diarrhoea

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10
Q

What are examples of absorptagogues?

A
  • Angiotensin
  • Aldosterone
  • Somatostatin
  • Enkephalins
  • Noradrenaline
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11
Q

How does angiotensin increase Na+ absorption?

A
  • Dehydration + drop in effective circulating volume stimulates RAAS
  • Angiotensin levels increase
  • Enhances NaCl absorption by upregulating apical membrane Na+/H+ exchange
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12
Q

How does aldosterone increase Na+ absorption?

A
  • Dehydration + drop in effective circulating volume stimulates RAAS
  • Aldosterone levels increase
  • Stimulates Na+ absorption through epithelial Na+ channels
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13
Q

4 categories of secretagogues

A
  • Bacterial enterotoxins
  • Hormones + neurotransmitters
  • Products of cells of immune system
  • Laxatives
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14
Q

How does the bacterial cholera toxin (enterotoxin) cause secretory diarrhoea?

A
  • Enterotoxin induces intracellular cAMP concentrations
  • This increase Cl- and K+ secretion + inhibits parallel Na+/H+ and Cl-/HCO3- exchange
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15
Q

Net uptake of Ca2+ in a day (using amounts absorbed and secreted)

A
  • Absorbed = 500mg/day
  • Secreted = 325mg/day
  • Net = 175mg/day uptake
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16
Q

Active and passive movements of Ca2+ in the small intestine

A
  • P = passive absorption of Ca2+ via paracellular pathway (not under control of VDR)
  • A = active, trans-cellular uptake by epithelial cells of duodenum (under control of VDR)
17
Q

What form must iron be in to be absorbed, and how does it get to this state?

A
  • Fe2+
  • Fe3+ reduced in stomach acid or by the ferrireductase enzyme duodenal cytochrome B (Dcytb)
18
Q

Which protein absorbs Fe2+?

A

DMT1

19
Q

3 fates of Fe2+ after being absorbed into the cell

A
  • Used within cell
  • Stored in protein ferritin
  • Effluxed into blood via ferroportin (FPN), re-oxidised to Fe3+ and bound to transferrin
20
Q

If iron is contained in haem, how is it absorbed and how is iron released?

A
  • Haem-Fe absorbed via haem carrier protein 1 (HCP1)
  • Haem oxygenase 1 (HO1) deconstructs inside cell to release Fe2+
21
Q

How is iron transported into non-enterocytes?

A
  • Fe-transferrin captured by receptors on cells requiring iron
  • Transported in and iron released
22
Q

Where are the major stores of iron?

A
  • Liver
  • Spleen
  • Bone marrow
23
Q

What do iron stores use to communicate with the small bowel to regulate iron absorption?

A

Hepcidin

24
Q

How is hepcidin used to regulate iron absorption?

A
  • Binds to ferroportin
  • Prevents transport of Fe2+ out of enterocytes
25
Q

How does inflammation/infection cause anaemia?

A
  • Hepcidin levels elevated
  • Causes reticulo-endothelial sequestration of iron
  • Anaemia despite adequate body iron levels
26
Q

What is haemochromatosis?

A

Hereditary disease characterised by improper dietary iron metabolism which causes the accumulation of iron in a number of body tissues

27
Q

What does accumulation of iron in body tissues from haemochromatosis cause?

A
  • End organ damage
  • Most importantly in liver + pancreas
  • Manifests as liver failure + DM respectively
28
Q

2 Fenton reactions

A
  • Fe2+ + H2O2 –> Fe3+ + OH. + OH-
  • Fe3+ + H2O2 –> Fe2+ + OOH. + H+
29
Q

What does production of free radicals by Fenton reactions cause?

A
  • Oxidative stress
  • Cellular damage
  • Cell death via apoptotic signalling
30
Q

How does coeliac disease work?

A
  • Autoimmune reaction caused by gliadin (gluten protein found in wheat)
  • Upon exposure, enzyme tissue transglutaminase modifies the protein
  • Immune system cross-reacts with bowel tissues, causing inflammatory response
  • Causes villous atrophy
31
Q

Symptoms of coeliac disease

A
  • Iron deficiency anaemia (IDA)
  • Diarrhoea
  • Weight loss (or stunted growth in kids)
  • Fatigue
32
Q

Treatment of coeliac disease

A

Lifelong gluten-free diet

33
Q

Test for coeliac disease

A

Anti-tissue transglutaminase test followed by small bowel biopsy

DIG (19 decks)

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