Diseases of the small intestine

1. Common adult diseases of small
and colon(diarrhea and
malabsorption)
Dr Lombe

2. Brief physiology
• approximately 10 L of fluid passes into the proximal small
• intestine (2 L from diet; 8 L from endogenous secretions)
• The small bowel absorbs most of the fluid 9 L
• colon absorbs about 90% of the remaining 1 L
• about 1% of the original fluid entering the small intestine is excreted in the
stool.
• A normal stool is 75% water and 25% solids,
• with a normal fecal water output of 60 mL daily.
• An increase in fecal water output of only 100mL is enough to cause
increased stool fluidity or decreased stool consistency

3. • the gut has reserve absorptive capacity
• with the small intestine having a maximal absorptive capacity of 12 L
daily
• and the colon, 6 L daily
• HELPS WITH SMALL CHANGES IN AMOUNT IN INSTESTINES TO AVOID
DIARRHEOA

4. Diarrhea
• Diarrhea is a symptom or a sign, not a disease
• it can manifest as 1 or more of the following:
 a decrease in consistency,
an increasein fluidity
increase in number volume of stools.
• As a sign diarrhea is an increase in stool weight or volume of more
than 200 g or 200 mL per 24 hours for a person eating a Western diet.

5. Mechanisms of Diarrhea
• Osmotic diarrhea occurs when a poorly absorbed substance remains
in the intestinal lumen
• causes water retention that maintains an intraluminal osmolality
equal to that of body fluids (approximately 290 mOsm/kg)
• Stool volume is less than 1 L daily, and the stool osmotic gap (SOG)
SOG = 290 mOsm/kg 2 − × ( [ Stool Na ] [ + Stool K])
• A normal stool osmotic gap is less than 50 mOsm/ kg
• a gap (typically >100 mOsm/kg)
• Stops with fasting

6. • Clinical causes of osmotic diarrhea include
carbohydrate malabsorption
lactase deficiency
sorbitol-sweetened foods
saline cathartic
magnesium-based antacids

7. • secretory diarrhea indicate disordered intestinal epithelial electrolyte
transport (ie, the intestine secretes electrolytes and fluid rather than
absorbing them)
• even though secretory diarrhea is more commonly caused by reduced
absorption than by net secretion
• Stool volume is more than 1 L daily.
• no stool osmotic gap.
• Secretory diarrhea persists despite fasting.

8. • Causes of secretory diarrhea include
 bacterial toxins
neuroendocrine tumors
bile acid diarrhea
fatty acid diarrhea.

9. • motility disorders both rapid transit (inadequate time for chyme to
contact the absorbing surface) and delayed transit (bacterial
overgrowth) can cause diarrhea.
• Rapid transit occurs after gastrectomy or intestinal resection and with
hyperthyroidism or carcinoid syndrome.
• Delayed transit occurs with structural defects (strictures, blind loops,
and small-bowel diverticula) or with underlying illnesses that cause
visceral neuropathy (diabetes mellitus) or myopathy
• (scleroderma), resulting in pseudo-obstruction.

10. exudative diarrhea
• abnormal membrane permeability allows serum proteins blood, or
mucus to be exuded into the bowel from sites of inflammation,
ulceration, or infiltration.
• The volume of feces is small and the stools may be bloody.
• Examples include invasive bacterial pathogens (eg, Shigella and
Salmonella) and inflammatory bowel disease.

11. Clinical Approach to Diarrhea
• distinguishing between diarrhea arising from the small bowel or
ascending colon (“right-sided diarrhea”) and diarrhea arising from the
distal colon (“left-sided diarrhea”)

12. Acute Diarrhea
• Acute diarrhea is abrupt in onset and usually resolves in 3 to 10 days.
It is self-limited, and the cause (often viral)
• No evaluation is necessary invasive infection is suspected (eg, bloody
stools, fever,
• travel history, or a common source outbreak).

13. Chronic Diarrhea
• is defined as diarrhea lasting longer than 4 weeks. The most common
cause of chronic diarrhea is
• irritable bowel syndrome, but lactase deficiency should always be
considered
• HIV GIOI in immucompromised pts

14. Physiology of Nutrient Absorption
• The sites of nutrient, vitamin, and mineral absorption are the
following:
The duodenum absorbs iron, calcium, folate, water-soluble vitamins,
and monosaccharides.
The jejunum absorbs fatty acids, amino acids, monosaccharides, and
water-soluble vitamins.
The ileum absorbs monosaccharides, fatty acids, amino acids, fat-
soluble vitamins (A, D, E, and K), vitamin B12, and conjugated bile
salts

15. • Fat absorption is the most complex process.
• Dietary fat consists mostly of long-chain triglycerides that must be digested
by pancreatic lipase, which cleaves 2 of the 3 long-chain fatty acids from
the glycerol backbone.
• The resultant free fatty acids and monoglycerides are solubilized by
micelles for absorption.
• The fatty acids and monoglycerides are reesterified by intestinal epithelial
cells into chylomicrons that are absorbed into the circulation via lymphatic
vessels.
• medium-chain triglycerides are absorbed directly into the portal venous
system and do not require micellar solubilization

16. • Malabsorption should be suspected if
the medical history suggests steatorrhea or
if diarrhea occurs with weight loss (especially if intake is adequate)
chronic diarrhea of indeterminate nature
nutritionaldeficiency

17. Diseases Causing Diarrhea
• Noninvasive (Toxicogenic) Bacterial Diarrhea
Toxicogenic bacterial diarrhea,
characterized by watery stools without fecal leukocytes, is caused by
several organisms
Staphylococcus aureus
Clostridium perfringens
Escherichia coli
Vibrio cholera
Bacillus cereus
Clostridium botulinum
Clostridium difficile

18. Causes of Invasive Bacterial Diarrhea
• Shigella
• Salmonella
• Vibrio parahaemolyticus
• Escherichia coli
• Staphylococcus aureus (enterocolitis)
• Yersinia enterocolitica
• Campylobacter jejuni
• Vibrio vulnificus

19. Malabsorption Due to Diseases
of the Small Intestine
• Celiac Disease
• Tropical Sprue
• Whipple Disease
• Eosinophilic Gastroenteritis
• Intestinal Lymphangiectasia