64 - GI Fluid and Electrolytes Flashcards
What part of the GI tract participates in electrolyte and water absorption and secretion?
BOTH the small and large intestine participate in electrolyte/water absorption and secretion
How is water and electrolyte absorption and secretion accomplished?
- Specific channels
- Pumps
- Transporters located at specific sites
What is the net goal of absorption and secretion of water and electrolytes in the small intestine
- Net absorption of sodium, chloride, potassium, and water
- Net secretion of bicarbonate
What is the net goal of absorption and secretion of water and electrolytes in the large intestine
- Net absorption of sodium, chloride, and water
- Net secretion of potassium and bicarbonate
What the secretion of chloride mediated by?
CFTR: cystic fibrosis transmembrane conductance regulator
What regulates the opening of this channel?
- Opening
of this channel is regulated by several second messenger signals which include cAMP and Ca++
What happens when the CFTR channel is activated?
Activation of this channel promotes the secretion of chloride ions. As a result of chloride secretion, sodium will passively follow chloride secretion
What is the sodium-hydrogen ion exchanger?
There is a sodium-hydrogen ion exchanger in the jejunum, ileum, and proximal colon; which functions in sodium uptake during the interdigestive period
Describe ways in which the CFTR and sodium-hydrogen ion exchanges are both regulated
Both CFTR and the sodium-hydrogen ion exchanger are regulated by the second messengers cAMP, cGMP, and calcium.
What happens when these second messengers accumulate in the intracellular space?
- 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
How do bacterial toxins affect the CFTR channel and the sodium-hydrogen ion exchanger?
Bacterial toxins
- Stimulate CFTR
- Inhibit Na+/H+ exchanger
How do immune cells secretions such as prostaglandins and histamine affect the CFTR channel and the sodium-hydrogen ion exchanger?
Prostaglandins and histamin
- Stimulate CFTR
- Inhibit Na+/H+ exchanger
How do neurotransmitters such as ACh, Serotonin and VIP affect the CFTR channel and the sodium-hydrogen ion exchanger?
VIP, ACh and Serotonin
- Stimulate CFTR
- Inhibit Na+/H+ exchanger
What is osmotic diarrhea
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.
What causes osmotic diarrhea?
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.
What is secretory diarrhea?
An increase in the number of bowel movements or a decrease in stool consistency that is caused by intestinal secretion of fluid and electrolytes
What causes secretory diarrhea?
Some toxins secreted by infectious organisms or hormone secreting tumors will stimulate the secretion of water and electrolytes and cause secretory diarrhea
What is constipation?
Constipation can be defined as infrequent evacuation of the feces
What causes constipation?
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
Onto case #8…
Go read case #8…
What is the causative agent giving rise to the patient’s presentation?
C-diff infection
What critical host defense mechanism has been breached in this case?
- Colonization of microbes
- Antimicrobial agents have given the this opportunity
What is the significance of the patient taking cephalosporins?
MAIN CONTRIBUTOR
- Antibiotics
What is the significance of the patient taking proton pump inhibitors?
- 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
What is the significance of the patient taking narcotics?
- Delayed motility is another risk factor
- Fast moving motility in GI tract can defend against bugs as well
What is the significance of the patient taking anti-diarrheal agents?
Instead of flushing the bacteria out by bacteria it remains in GI tract and is less diluted by water in lumen
What is the pathophysiological cause of the patient’s diarrhea? Is this presentation most consistent with osmotic diarrhea, secretory diarrhea, or both?
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)
