Path of Small & Large Intestine

Question 1

Causes of Gastro-Intestinal Obstruction

Answer 1

4 main causes:
 - Hernias, internal or external
 - Volvulus
 - Intussusception
 - Tumors
Sympts:
 - Pain
 - Distension
 - Vomiting 
 - Constipation

Question 2

Intussusception

Answer 2

Most common cause of intestinal obstruction in children < 2 yo
- infants and children-usually no underlying anatomic defect…viral infection…? lymphoid hyperplasia….lead point for telescoping
- older children and adults-usually an intraluminal mass or tumor (remember Meckel’s as the leader!)
Most frequent type one in which the ileum enters the cecum

Question 3

Intussusception - Clinical

Answer 3

Dance’s sign
Ultrasound is considered imaging modality of choice.
A target-like mass, usually around 3cm in diameter, confirms the diagnosis.
Can be treated with either a barium or water-soluble contrast enema or an air-contrast enema

Question 4

Hernia

Answer 4

60% right sided
Much more common in males
A hernia that can manually be pushed back into the abdominal cavity can be “reduced”
If the hernia cannot be reduced, it is “incarcerated”
- With prolonged incarceration, get ischemia and obstruction; danger of perforation
Direct hernias occur medial to the inferior epigastric vessels
Indirect hernias occur when abdominal contents protrude through the deep inguinal ring, lateral to the inferior epigastric vessels; this may be caused by failure of embryonic closure of the processus vaginalis.

Question 5

Volvulus

Answer 5

Twisting of bowel leads to obstruction and infarction.
#1-sigmoid colon….followed by the cecum, small bowel, stomach, large bowel
“Bent inner tube” or “coffee bean” sign
Gastrografin instead of barium enema if perforation of bowel is suspected

Question 6

Adhesions

Answer 6

Most common cause of obstruction in the US.
Post-op adhesions, inflammation, endometriosis.
Fibrous bridges create closed loops through which other loops can slide through and become entrapped…”internal hernia”
Most patients do improve with conservative care in 2–5 days

Question 7

Ischemic Bowel Disease - Etiology

Answer 7

Arterial embolism (60%): cardiac vegetation, angiography procedure, aortic atheroembolism…superior mesenteric most common
Arterial thrombosis (20%)…superior mesenteric
Venous thrombosis
Non-occlusive ischemia (20%): cardiac failure, shock, dehydration, vasoconstrictive drugs (cocaine), CMV infection

Question 8

Mesenteric ischemia

Answer 8

Inflammation and injury of the small intestine result from inadequate blood supply.
Hyper active stage occurs first, in which the primary symptoms are severe abdominal pain and the passage of bloody stools. Many patients get better and do not progress beyond this phase
Paralytic phase can follow if ischemia continues; the abdominal pain becomes more widespread, belly becomes more tender touch, and bowel motility decreases, resulting in abdominal bloating, no further bloody stools, and absent bowel sounds on exam.
Shock phase can develop as fluids start to leak through the damaged colon lining.

Question 9

Ischemic colitis

Answer 9

inflammation and injury of the large intestine result from inadequate blood supply.
The most common form of bowel ischemia.
In its mildest form, mucosal and submucosal hemorrhage and edema are seen, possibly with mild necrosis or ulceration.
In the most severe cases, transmural infarction with resulting perforation may be seen; after recovery, the muscularis propria may be replaced by fibrous tissue, resulting in a stricture.
Endoscopy to dx

Question 10

Colonic blood supply

Answer 10

(SMA) and its branches: middle colic, right colic, ileocolic arteries
(IMA) and its branches: left colic, sigmoid, superior rectal artery.
Watershed areas are most vulnerable to ischemia when blood flow decreases, as they have the fewest vascular collaterals

Question 11

Angiodysplasia

Answer 11

Non-neoplastic vascular lesion.
Usually cecum or prox. rt colon
Pathogenesis unknown
Tortuous dilatation of malformed submucosal and mucosal blood vessels (veins, venules,capillaries)
~1% of adult population, 60+ yr old
Accounts for 20% of significant lower intestinal bleeding
Intestinal hemorrhage may be acute, chronic or intermittent; minimal or massive
Classic association is Heyde’s syndrome (coincidence of aortic valve stenosis and bleeding from angiodysplasia). In this disorder, von Willebrand factor (vWF) is proteolysed due to high shear stress in the highly turbulent blood flow around the aortic valve

Question 12

Hemorrhoids

Answer 12

Develop because of persistent elevation in venous pressure within the hemorrhoidal venous plexus
Affect pregnant females (venous stasis of pregnancy)
Unusual under age 30 years; common after 50 yrs
Cirrhosis (portal hypertension)
Most common cause: simply straining at stool

Question 13

Secretory diarrhea

Answer 13

> 500 ml of isotonic fluid stool/d
persists during fasting
usually infectious; viral or enterotoxin

Question 14

Osmotic diarrhea

Answer 14

> 500mL of hypertonic fluid stool/d
abates with fasting
classically lactase deficiency

Question 15

Exudative diarrhea

Answer 15

mucosal damage -> purulent, bloody stools
persists during fasting
usually bacterial or IBD

Question 16

Deranged motility

Answer 16

improper gut neuromuscular function
variable during fasting
can be neural, hormonal, surgical

Question 17

Malabsorption

Answer 17

improper absorption -> bulky stool with excess fat (steatorrhea)
abates with fasting
classically celiac disease, Giardia, also Cystic Fibrosis, chronic pancreatitis
72 hour stool for fat is considered the standard test

Question 18

Infectious Enterocolitis

Answer 18

Viral— Norovirus, Rotavirus, & Adenovirus most common
Bacterial—3 main mechanisms
Other—parasites, etc
Can present with a broad range of symptoms including diarrhea, abdominal pain, urgency, perianal discomfort, incontinence, and hemorrhage.

Question 19

Rotavirus

Answer 19

The most common cause of severe diarrhea among infants and young children
dsRNA virus
60% of childhood viral enterocolitis
Toxic rotavirus protein NSP4

Question 20

Bacterial EnterocolitisMechanisms

Answer 20

Ingestion of preformed toxin [rapid onset]:
Staph food poisoning, Vibrio, C. perfringens, C. botulinum

Infection by toxigenic organisms [incubation period, then diarrhea]:
Traveler’s diarrhea; et E coli, V. cholerae, Campylobacter

Infection by enteroinvasive organisms [invade/destroy mucosa cells]:
Shigella, Salmonella, Campylobacter, enteroinvasive E coli

Question 21

Enterotoxigenic E. Coli.

Answer 21

ETEC organisms are the principal cause of traveler’s diarrhea and spread via contaminated food or water.
(LT) and (ST) both induce chloride and water secretion while inhibiting intestinal fluid absorption.
LT toxin is similar to cholera toxin and activates adenylate cyclase, resulting in increased intracellular cAMP.
ST toxins bind to guanylate cyclase and increase intracellular cGMP

Question 22

Enterohemorrhagic E. Coli.

Answer 22

O157:H7 and non-O157:H7 serotypes produce Shiga-like toxins, and the morphology and clinical symptoms are thus similar to S. dysenteriae.
O157:H7 strains of EHEC are more likely than non-O157:H7 serotypes to cause large outbreaks, bloody diarrhea, and hemolytic-uremic syndrome.

Question 23

Enteroinvasive E. Coli.

Answer 23

Invade epithelial cells and cause nonspecific features of acute self-limited colitis.

Question 24

Enteroaggregative E. Coli.

Answer 24

Unique pattern of adherence to epithelial cells.
Adherence fimbriae and are aided by dispersin
Nonbloody diarrhea that may be prolonged in individuals with the acquired immunodeficiency syndrom

Question 25

Salmonella

Answer 25

The causative agent of typhoid fever.
Invasion, translocation, lymphoid inflammation, dissemination
SX: Fever, pain, diarrhea or dysentery, bacterial extraintestinal infx.
The risk of severe illness and complications is increased in patients with malignancies, immunosuppression, alcoholism, cardiovascular dysfunction, sickle cell disease, and hemolytic anemia.

Question 26

Typhoid Fever

Answer 26

S. typhi are able to survive in gastric acid and, once in the small intestine, are taken up by and invade M cells.
Infection causes Peyer’s patches in the terminal ileum to enlarge.
Mucosal shedding creates oval ulcers, oriented along the axis of the ileum, that may perforate.
Typhoid nodules are macrophage aggregates in liver parynchema w/necrosis
Pts experience anorexia, abdominal pain, bloating, nausea, vomiting, and bloody diarrhea followed by a short asymptomatic phase that gives way to bacteremia and fever with flu-like symptoms.

Question 27

Cholera

Answer 27

Vibrio cholerae are comma-shaped, Gram-negative bacteria. non-invasive.
In those with severe disease there is an abrupt onset of watery diarrhea and vomiting following an incubation period of 1 to 5 days. The voluminous stools resemble rice water and are sometimes described as having a fishy odor

Question 28

Cholera patho

Answer 28

After retrograde toxin transport to the endoplasmic reticulum (ER), the A subunit is released by the action of protein disulfide isomerase (PDI) and is then able to access the epithelial cell cytoplasm. In concert with an ADP-ribosylation factor (ARF), the A subunit then ADP-ribosylates Gsα, which locks it in the active, GTP-bound state. This leads to adenylate cyclase (AC) activation, and the cAMP produced opens CFTR to drive chloride secretion and diarrhea.

Question 29

Campylobacter enterocolitis

Answer 29

The most common bacterial enteritis in the world
Chicken , milk, water
Small infective dose  
Adhere, toxin, invasive
Gram neg. motile
C. jejuni  most common
Watert diarrhea w/flu-like prodrome
Arthritis, IBS
Erythema nodosum
Guillain-Barré Syndrome
Many neutrophils, crypt abscess

Question 30

Shigella enterocolitis

Answer 30

Classic enteroinvasive or ‘dysenteric’ organism
Humans are the only reservoir
Small infective dose
Gram neg. unencapsulated Non-motile
Taken up by M cells
Bloody diarrhea
Left colon (less commonly, ileum)
Self-limited disease characterized by about 6 days of diarrhea, fever, and abdominal pain.
Reiter syndrome complicates: a triad of sterile arthritis, urethritis, and conjunctivitis that preferentially affects HLA-B27-positive men

Question 31

Pseudomembranous Colitis

Answer 31

Acute colitis characterized by formation of an adherent layer of inflammatory cells and debris overlying sites of mucosal injury, a so-called “pseudomembrane”
Two major toxins produced by Clostridia difficile, A & B
Occurs primarily in adults as an acute diarrheal illness, can have chronic phase
Diagnosis by detecting C difficile cytotoxin in stool
Plaques of yellow fibrin and inflammatory debris adherent to a reddened colonic mucosa.

Question 32

Antibiotic-Associated Colitis

Answer 32

nearly all antibiotic agents have been associated, but 3rd generation cephalosporins most common
hospitalization and immunosuppression
C. difficile overgrowth and toxin production following normal flora loss

Question 33

C. diff clinical

Answer 33

Individuals with C. difficile–associated colitis present with fever, leukocytosis, abdominal pain, cramps, hypoalbuminemia, watery diarrhea, and dehydration

Question 34

Whipple Disease

Answer 34

Chronic, relapsing multisystem illness involving the GI tract (diarrhea, steatorrhea, malabsorption) and distant sites (arthritis, lymphadenopathy)
Disease characterized by weight loss, diarrhea, and polyarthritis; occur together at presentation in 75% of cases
Infection of the small intestinal mucosa by the bacillus Tropheryma whipplei
Whites in 4th-5th decade of life with 10:1 male predominance
Many cases from rural areas
treat successfully with antibiotics

Question 35

Whipple Disease morpho

Answer 35

Distended, foamy macrophages in the small intestinal lamina propria.
Villous expansion.
bacteria-laden macrophages bacteria-laden macrophages Can accumulate within mesenteric lymph nodes, synovial membranes of affected joints, cardiac valves, the brain, and other sites

Question 36

Cryptosporidium spp.

Answer 36

C. parvum was considered a very rare pathogen of immunodeficient individuals.
At least three strains of C. parvum, as well as C. hominis, infect human beings and animals
Now recognized as an important cause of diarrhea worldwide, inc. traveler’s diarrhea
Source: contaminated drinking water
Most concentrated in terminal ileum and right colon.
Intracellular at brush border
Sodium malabsorption, chloride secretion, and increased tight junction permeability are responsible for the nonbloody, watery diarrhea that ensues.
villous atrophy, crypt hyperplasia, and variable inflammatory infiltrates

Question 37

Amebiasis

Answer 37

Infection by Entamoeba histolytica occurs by ingestion of mature cysts in fecally contaminated food, water, or on hands.
In some patients the trophozoites invade the intestinal mucosa (intestinal disease), or, through the bloodstream, extend to extraintestinal sites such as the liver, brain, and lungs (extraintestinal disease), with resultant pathologic manifestations such as amoebic liver abscesses.

Question 38

Giardia

Answer 38

Most common pathogenic parasitic infection

In the small intestine occurring in three clinical forms:
- Asymptomatic carrier w/or w/o history clinical disease
- Acute diarrhea
- Chronic gastrointestinal disease manifested as :
MalabsorptionRecurrent diarrhea
With or without abdominal discomfort/pain