7. Diarrhoea. Causes, pathophysiological forms, consequences

Normal water content stool?

< 200mL/day

Frequency of defecation during diarrhea?

Frequency is commonly increased during diarrhea, but it is not decisive for the definition.

- The definition of diarrhea is stool exceeding 200mL of water/day

What is the result of increased water content in stool?

The quantity and consistence of the feces is altered

- Peristaltic movement are enhanced

Reabsorption capacity of the intestines?

8L of digestive juice daily

3 types of diarrhea?

Osmotic diarrhea

• water content is increased due to presence of osmotically active molecules in the feces

Secretory diarrhea

• Increased secretion/decreased reabsorption

Motor diarrhea

• Motility of the intestines is increased primarily

Osmotic diarrhea?

There is a disorder of digestion and/or absorption

- Unabsorbed nutrients may be osmotically active themselves

OR

- They can be digested by bacteria which convert them into osmotically active substances

The substances hold on to water & draws water from the intestinal wall by osmosis

= preventing the intestines from reabsorbing water

When does osmotically active diarrhea stop?

When feeding is stopped

Common causes of osmotic diarrhea?

- Lactose intolerance: Lactose is not broken down -> metabolized by bacteria turning into osmotically active substances

- Chronic pancreatitis: Undigested nutrients are broken down by bacteria into osmotically active substances

- Osmotic laxatives

- Any malabsorption

- Too much fibre-rich food

- Chewing disorders

- Post-gastrectomy

Secretory diarrhea?

Excessive mucosal secretion of fluid and electrolytes produces large-volume diarrhea

If the daily secretion exceeds 8 liters, will the intestines be unable to reabsorb the excess secretions

- Secretory diarrhea is not related to food intake (will therefore persist despite feeding restriction)

Common causes of secretory diarrhea?

• Inflammation of the intestinal wall

• Poor intestinal perfusion

• Overproduction if secretory GI hormones like VIP and gastrin, due to hormone-producing cancers

• Carcinoid (NET) tumors

• Infections

  • Enterotoxic pathogens - they stimulate secretions (cholera, E.coli)

  • Enteropathogenic pathogens - pathogens damage mucosa

  • Enteroinvasive pathogens - pathogens enter the mucosa

• Translocation-inducing pathogens

• Short bowel syndrome - bile acids in the colon stimulate colonic secretions

Treatment - secretory diarrhea?

Fluid replacement

- Should contain electrolytes and glucose

Glucose: enhances the intestinal absorption capacity

Motor diarrhea?

When peristaltic movement of the intestines is increased

• Intestines will have less time to reabsorb fluid → reducing the reabsorption capacity

Primary causes for increased GI motility? (Motor diarrhea)

- Stress (emotional factors)

- Parasympathetic overactivation - mushroom poisoning, organophosphate poisoning

- Hyperthyroidism

- Irritable bowel syndrome

- Secondarily due to other types of diarrhea

Consequences of diarrhea?

• Salt and water loss → hypovolemia

• Metabolic acidosis occurs due to bicarbonate loss

• Potassium is lost

  • due to secondary hyperaldosteronism due to the initial hypovolemia

  • also because GI mucosal cells (containing potassium) detach and are lost with the diarrhea

• Calorie-loss