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Digestive MBChB 2 > Lecture 25; Intestinal fluid and electrolyte balance > Flashcards

Lecture 25; Intestinal fluid and electrolyte balance Flashcards

1
Q

What increases the SA of the SI?

A
  • Folds of kerchring a.k.a plicae circularis
  • Microvilli and crypts of lieberkuhn
  • Submicroscopic microvilli
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2
Q

What increases the SA of the LI?

A
  • Semilunar folds
  • Crypts, but NO VILLI
  • Microvilli
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3
Q

What are the primary secretions of the small intestine?

A
  • Pancreatic secretions
  • Bile secretions
  • HCO3

NOT POTASSIUM

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4
Q

What does the SI absorb?

A
  • Water
  • Na (Glucose, Protein)
  • K
  • Cl

6.5L

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5
Q

What does the LI secrete?

A
  • Potassium

- HCO3

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6
Q

What does the LI absorb?

A
  • Na
  • Cl
  • Water

NOT NUTRIENTS

(~2.0L)

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7
Q

What happens with increased secretion in the SI and LI?

A

Secretory diarrhoea

SI = far worse
LI = not as bad (because less fluid at this point)
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8
Q

Why do they need to give HCO3 in solutions to people who have secretory diarrhoea?

A

Both SI+LI secrete lots of HCO3 (Not pulled with electrolytes)

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9
Q

What is notable about epithelium?

A

They are polarised (Concentration gradient b/w lumen and apical surface)

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10
Q

What are the transporters present in the intestinal epithelium?

A
  • Na/K ATPase

This creates a Na and K gradients, (electro chemical) which facilitates diffusion from the lumen into the cell.

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11
Q

What are the ways solutes can move across the epithelium?

A
  • Either absorptive or secretory

Transcellular: (Crossing one membrane therefore requires active transport)

OR

Paracellular: (Passive movement between tight junctions)

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12
Q

How does water move across the epithelium?

A
  • Osmosis

Transcellular and paracellular (predominantly)

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13
Q

Where does majority of water absorption occur?

A

Jejunum

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14
Q

What is the huge water movement responsible for?

A

Solvent drag, i.e osmosis is coupled with movement of Na and urea in the jejunum

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15
Q

Where does Na absorption occur in relation to mucosal structures in the SI and LI?

A

SI = Villus epithelial cells

LI = Surface epithelial cells

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16
Q

What are the sodium transporters of the epithelium?

A
  • Na/glucose or Na/AA co-transporters
  • Na/H exchanger
  • Parallel Na/H and Cl/HCO3 exchangers
  • Epithelial Na channels

Na/K ATPase for Na transport across the apical membrane

17
Q

What follows Na movement?

A

Cl-

18
Q

How does Cl move?

A
  • Passive Cl absoprtion
  • Cl-HCO3 exchanger
  • Parallel Na-H and Cl-HCO3 exchangers
19
Q

What is the channel for Cl secretion?

A

CFTR (cystic fibrosis)

20
Q

What can increase CFTR insertion?

A

Inflammation / microbes etc cause an increase of intracellular Ca or cAMP

= insertion of CFTR into lumen membrane (from subapical vesicles)

21
Q

Whats the other ion to consider? not too important…

A

Potassium

  • Passive K absorption and secretion
  • Active K absorption and secretion
22
Q

What changes the absorption and secretion of the gut?

A
  • ENS = ACh
  • Endocrine = Aldosterone
  • Paracrine system = 5HT
23
Q

Summarise the net movement of ions in the SI and LI;

A

SI

  • Net absorber of Water, Na, Cl and K
  • Net secretor of HCO3

LI

  • Net absorber of Na and Cl
  • Net secretor of K and HCO3
24
Q

Describe the potential origins of diarrhoea and implications?

A 
SI = Voluminous
LI = Small volume
25
Q

Describe osmotic and secretory diarrhoea;

A

Osmotic = Disturbance of absorbance

Secretory = Disturbance in secretion

26
Q

Give examples of osmotic diarrhoea;

A
  • Lactose intolerance

- Coeliac disease

27
Q

What can cause secretory diarrhoea?

A

Increased active secretion

Microbial endotoxins cause increased intracellular cAMP or Ca = increased CFTR insertion. = Luminal Cl, THUS Na is carried with it

28
Q

In secretory diarrhoea what happens because of increased Cl secretion?

A

Na goes with it to maintain charge. Draws water also.

29
Q

Explain; Gloria, severe diarrhoea. BP 60/40, HR 120bpm. explain; Cholera was found.

A
  • Decreased BV, MAP, = baroreflex and high HR.

Cholera = toxins = Secretory diarrhoea

30
Q

In secretory diarrhoea where does the fluid come from?

A

Fluid is from ECF because theres no change in osmolarity, thus not from intracellular.

31
Q

What is oral rehydration therapy?

A
  • Na
  • K
  • Glucose
  • HCO3 (to replace the net secretion of bicarb lost in the gut)
32
Q

What is the purpose of oral rehydration therapy?

A
  • Correct loss of electrolytes from body
  • Restore fluids
  • Restore Na balance across membrane and maintain transport
  • Aid osmotic reabsorption

Digestive MBChB 2 (31 decks)

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