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GI Week 3 > Electrolytes and Motility Physiology > Flashcards

Electrolytes and Motility Physiology Flashcards

1
Q

What is Anismus?

A

Anal sphincter dyssynerigia

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2
Q

What are Haustra?

A

One of the pouches of the colon, produced by adaptation of its length to the taenia coli

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3
Q

What is Haematochezia?

A

Blood in the stool

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4
Q

What is Ileus?

A

Failure of forward movement of intestinal contents

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5
Q

What is purgative?

A

Substance that promotes bowel loosening and movement; cathartic, laxative

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6
Q

What is Tenesmus?

A

Feeling that you need to pass stool even when bowels are empty

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7
Q

What are three transmembrane ion transporter processes in the large bowel?

A
  1. Pumps
  2. Channels (pores)
  3. Carriers
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8
Q

How do Pumps work?

A

Active transport, Na+/K+ ATPase and H+/K+ ATPase.

  • Uphill transport against an electrochemical gradient
  • Effective at low concentrations
  • Demonstrate saturable kinetics
  • Require cellular energy
  • Demonstrate high ionic specificity
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9
Q

How do channels work?

A

(Pores) Na+, CFTR, K+

-Passive movement along the prevailing electrochemical gradient

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10
Q

How do carriers work?

A

Movement of ion or substance against electrochemical/concentration gradient by coupling it to movement of another ion moving with electrochemical gradient (secondary active transport)

  • Exchangers - substances move in opposite directions (antiporter) - NHE Na+/H+ and Cl-/HCO3-
  • Cotransporters - substances move in same direction (symporter) - 2 Na+/glucose, bile salts, amino acids, Pept1 H+/peptide, 2Cl-/Na+/K+ found on basolateral import Cl- into cell
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11
Q

What amount of water is moved through the GI tract?

A

~9 liters of fluid enters the gut/day
~8.9 liters of fluid is absorbed/day by the small and large intestines
~0.1 liter is excreted by the gut/day

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12
Q

How fluid does the colon absorb of the fluid presented to it?

A

90%

If the colon is removed, the body will compensate by increasing fluid and electrolyte intake.

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13
Q

What does absorbed fluid replenish?

A

Fluid losses in sweat, urine, and lungs

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14
Q

How do properties of the epithelium control fluid movement?

A
  • Water can move through cells (transcellular rout) or between cells (paracellular route)
  • Tight junction permeability is regulated by cytokines, bacterial toxins, and hormones which modify claudins.
  • Water movement follows osmotic gradients
  • Driven by electrogenic or electroneutral ion transport processes
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15
Q

What are the seven main Net Ion movements in the Small Intestine?

A
  1. Electroneutral NaCl absorption
  2. Bicarbonate secretion
  3. Sodium-coupled nutrient absorption
  4. Proton-coupled nutrient absorption
  5. Chloride Secretion
  6. Sodium-coupled bile acid absorption
  7. Calcium and iron absorption (not a major determinant of fluid transport)
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16
Q

How does fluid absorption and excretion occur simultaneously in the small intestine?

A
  • Cells at tips of the villi absorb fluid
  • Cells in crypts secrete fluid by chloride ion secretion
  • Huge surface area created by folded mucosa allows for high capacity for absorption
17
Q

How does Electroneutral NaCl absorption mediate fluid uptake?

A
  • Coupled activity of sodium/hydrogen exchanger (NHE) and chloride/bicarbonate exchanger in the apical membrane
  • Water follows to maintain osmotic balance
18
Q

How does Electrogenic uptake of Na+ and glucose (amino acids, bile salts) drive fluid absorption in the small intestine?

A

-No active transport of a counterion. Instead, anions (largely chloride) and water follow passively via the tight junctions

19
Q

What do Oral Rehydration Salts contain to help facilitate fluid uptake in small intestine?

A

Contain NaCl and glucose to exploit these transport processes and promote water uptake.

20
Q

How is Chloride Secretion in the Crypts of Lieberkuhns in the Small Intestine a major mechanism promoting fluid entry into the intestinal lumen?

A
  • Chloride is actively taken up by the 1Na+, 2Cl- symporter (NKCC1) at the basolateral membrane
  • Chloride leaves the luminal side of the cell via CFTR
  • Postassium leaves basilar side via a Ca++ activated K+ channel
21
Q

What mediates the opening of CFTR channels?

A

cAMP

22
Q

Where does calcium get absorbed and how is it ingested?

A

Ingested mostly in dairy and 30 percent is absorbed predominantly in duodenum.

23
Q

How is Calcium absorbed?

A

30 percent is absorbed predominantly in duodenum through paracellular and transcellular routes.

  • Ca++ channel on brush border membrane inwardly driven by the electrochemical gradient.
  • Intracellular calcium is bound to calbindin
  • Basolateral Ca++-ATPase pumps, calcium exchanged with sodium, or calcium is exocytosed.
  • Vitamin D enhances expression of Ca++ channels.
24
Q

Where does iron get absorbed and how is it ingested?

A

3-6 percent of ingested iron mostly from meat is absorbed - primarily in duodenum.

25
Q

What does excess iron absorption lead to?

A

Hemochromatosis and a decrease in number of DMT1 transporters (iron transporters).

26
Q

What is a frequent complication of partial gastrectomy?

A

Iron deficiency anemia

27
Q

What is the function of gastric secretions in iron absorption?

A

Gastric secretions dissolve the iron and aid its reduction to the Fe2+ form. So individuals deficient in acid secretion absorb less.

28
Q

What things regulate ion absorption and secretion?

A
  • Active transport of solutes, especially Na+, requires energy therefore blood flow increases during a meal to increase oxygen and glucose.
  • ACh/VIP stimulate chloride secretion (long reflex)
  • Stroking the mucosa releases 5-hydroxytryptamine (serotonin) from local enterochromaffin cells (short reflex)
  • Mucus secretion lubricates the GI tract, binds bacteria, and traps immunoglobulins
29
Q

What can VIP and cholera toxin do to secretions in the small and large intestines?

A

VIP and cholera toxin are agonists that elevate cAMP and promote opening of the CFTR channel resulting in copious secretion in small and large intestine.

30
Q

What can a VIP stimulating tumor induce?

A

Secretory diarrhea

31
Q

What is Guanylin and what secretes it?

A

Gastrointestinal polypeptides secreted by goblet and ECL cells.

32
Q

What does Guanylin do?

A

Binds GC-C recpetor on epithelial cells to promote secretion.
-Binding raises concentration of intracellular cGMP increasing Cl- secretion through CFTR into the lumen

33
Q

What is Linaclotide?

A

A drug that acts similarly to Guanylin. It activates guanylate cyclase type C receptors and is used to treat constipation.

34
Q

What toxin also induces diarrhea in the same manner as Linaclotide/Guanylin?

A

Heat-stable toxin produced by pathogenic E. coli induces diarrhea in the same manner.

35
Q

In a healthy adult, the volume of fluid presented to the intestine on a daily basis is approximately 8 liters. Assuming a normal diet, reabsorption of the bulk of this fluid is driven primarily by which of the following?

A

Nutrient-coupled electrogenic sodium absorption (SGLT1 - is the transporter for glucose and Na+)

36
Q

What five processes mediate the Net Movement of Ions in the Colon (lack of nutrients)?

A
  1. Electrogenic sodium absorption
  2. Electroneutral NaCl absorption
  3. Short chain fatty acids absorption
  4. Chloride absorption/secretion
  5. Potassium absorption/secretion (not a major determinate of fluid transport)

GI Week 3 (10 decks)

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