64 - GI Fluid and Electrolytes

Question 1

What part of the GI tract participates in electrolyte and water absorption and secretion?

Answer 1

BOTH the small and large intestine participate in electrolyte/water absorption and secretion

Question 2

How is water and electrolyte absorption and secretion accomplished?

Answer 2

• Specific channels
• Pumps
• Transporters located at specific sites

Question 3

What is the net goal of absorption and secretion of water and electrolytes in the small intestine

Answer 3

• Net absorption of sodium, chloride, potassium, and water

- Net secretion of bicarbonate

Question 4

What is the net goal of absorption and secretion of water and electrolytes in the large intestine

Answer 4

• Net absorption of sodium, chloride, and water

- Net secretion of potassium and bicarbonate

Question 5

What the secretion of chloride mediated by?

Answer 5

CFTR: cystic fibrosis transmembrane conductance regulator

Question 6

What regulates the opening of this channel?

Answer 6

• Opening

of this channel is regulated by several second messenger signals which include cAMP and Ca++

Question 7

What happens when the CFTR channel is activated?

Answer 7

Activation of this channel promotes the secretion of chloride ions. As a result of chloride secretion, sodium will passively follow chloride secretion

Question 8

What is the sodium-hydrogen ion exchanger?

Answer 8

There is a sodium-hydrogen ion exchanger in the jejunum, ileum, and proximal colon; which functions in sodium uptake during the interdigestive period

Question 9

Describe ways in which the CFTR and sodium-hydrogen ion exchanges are both regulated

Answer 9

Both CFTR and the sodium-hydrogen ion exchanger are regulated by the second messengers cAMP, cGMP, and calcium.

Question 10

What happens when these second messengers accumulate in the intracellular space?

Answer 10

• Intracellular accumulation of these second messengers will inhibit the sodium-hydrogen ion exchanger and open CFTR
• As a result sodium absorption is inhibited and chloride
  secretion is stimulated allowing for the accumulation of NaCl in the lumen

Question 11

How do bacterial toxins affect the CFTR channel and the sodium-hydrogen ion exchanger?

Answer 11

Bacterial toxins

• Stimulate CFTR
• Inhibit Na+/H+ exchanger

Question 12

How do immune cells secretions such as prostaglandins and histamine affect the CFTR channel and the sodium-hydrogen ion exchanger?

Answer 12

Prostaglandins and histamin

• Stimulate CFTR
• Inhibit Na+/H+ exchanger

Question 13

How do neurotransmitters such as ACh, Serotonin and VIP affect the CFTR channel and the sodium-hydrogen ion exchanger?

Answer 13

VIP, ACh and Serotonin

• Stimulate CFTR
• Inhibit Na+/H+ exchanger

Question 14

What is osmotic diarrhea

Answer 14

An increase in the number of bowel movements or a decrease in stool consistency that results from a shift in osmotic pressure in the lumen of the intestines causing a decrease in the absorption of water.

Question 15

What causes osmotic diarrhea?

Answer 15

The presence of a nonabsorbable nutrient such as methocellulose or, for some people lactose, can lead to the retention of fluid in the lumen and thus cause osmotic diarrhea.

Question 16

What is secretory diarrhea?

Answer 16

An increase in the number of bowel movements or a decrease in stool consistency that is caused by intestinal secretion of fluid and electrolytes

Question 17

What causes secretory diarrhea?

Answer 17

Some toxins secreted by infectious organisms or hormone secreting tumors will stimulate the secretion of water and electrolytes and cause secretory diarrhea

Question 18

What is constipation?

Answer 18

Constipation can be defined as infrequent evacuation of the feces

Question 19

What causes constipation?

Answer 19

Multiple causes of constipation

• Physiological changes such as hormone secreting tumors that decrease motility
• Presence of toxins
• Various disease states
• Muscle weakness
• Sedentary life-style

Other causes are more subjective…

• A person’s perception of what is a normal frequency for bowel movements
• Psychological stress
• Depression
• Diet

Pharmacological agents

• Opiates
• Anticholinergics
• Antacids

In many cases constipation is relieved by simply increasing water/fiber intake and exercise

Question 20

Onto case #8…

Answer 20

Go read case #8…

Question 21

What is the causative agent giving rise to the patient’s presentation?

Answer 21

C-diff infection

Question 22

What critical host defense mechanism has been breached in this case?

Answer 22

• Colonization of microbes

- Antimicrobial agents have given the this opportunity

Question 23

What is the significance of the patient taking cephalosporins?

Answer 23

MAIN CONTRIBUTOR

- Antibiotics

Question 24

What is the significance of the patient taking proton pump inhibitors?

Answer 24

• Decrease acid secretion, make it easier for bugs to live in GI tract
• pH is increased (not so harsh of a condition)
• This plays a role and is a risk factor

Question 25

What is the significance of the patient taking narcotics?

Answer 25

• Delayed motility is another risk factor

- Fast moving motility in GI tract can defend against bugs as well

Question 26

What is the significance of the patient taking anti-diarrheal agents?

Answer 26

Instead of flushing the bacteria out by bacteria it remains in GI tract and is less diluted by water in lumen

Question 27

What is the pathophysiological cause of the patient’s diarrhea? Is this presentation most consistent with osmotic diarrhea, secretory diarrhea, or both?

Answer 27

BOTH processes are going on

Also note that the pseudo membrane that we are seeing here is NOT a biofilm (coats/protects bacteria) here we are seeing white plaques that have bacteria, debris and immune cells (NOT a biofilm)