Lower Gastrointestinal Tract Flashcards
Most common and the most clinically significant congenital anomaly of the small intestine.
Two thirds pts < 2 yrs old
Outpouching of the gut on the antimesenteric border of the ileum, caused by persistence of the vitelline duct. Mostly asymptomatic.
Potential complications:
Bleeding, perforation, obstruction, diverticulitis
Merkel Diverticulum
Complete occlusion of the intestinal lumen
atresia (neonatal intestinal obstruction)
Narrowing, but do not complete occlusion, of the lumen
stenosis (neonatal intestinal obstruction)
diagnosed on the basis of persistent vomiting within the first day of life. Surgical correction is usually successful.
stenosis and atresia
The abdominal musculature fails to form, leading to birth of an infant with herniation of abdominal contents into a ventral membranous sac
omphalocele
A portion of the abdominal wall fails to form altogether, causing extrusion of the intestines.
gastroschisis
Caused by bacterial colonization of the surface epithelium with toxigenic strains of Escherichia coli and Vibrio cholerae
High mortality rate in infants from underdeveloped countries
Increased intestinal secretion stimulated by bacterial toxins and enteric hormones cause watery diarrhea and dehydration
Damage to the intestine is minimal
bacterial (toxigenic) diarhhea
Common cause of infantile diarrhea
~50% of acute diarrhea in hospitalized kids < 2 yrs old
Associated with injury to surface epithelium
rotavirus viral gastroenteritis
~30% of the epidemics of viral gastroenteritis in the USA
Patchy mucosal lesions (duodenum) and malabsorption
Symptoms resolve within 2 days
Norwalk viral gastroenteritis
Triggered by decreased intestinal flow
ischemic bowel disease
Most common type of ischemic bowel disease
acute intestinal ischemia
Associated with atherosclerotic narrowing of major splanchnic arteries
Intermittent abdominal pain (intestinal angina)
Pain starts within 30 min after eating and last for a few hrs
May promote fibrosis and stricture formation, leading to intestinal obstruction
chronic intestinal ischemia
A general term describing a number of clinical conditions that prevent the appropriate absorption of important nutrients by the GI tract.
malabsorption
The most common clinical presentation is chronic diarrhea, and the hallmark of _____ is steatorrhea (excessive fecal fat content).
malabsorption
Occur within lumen of small bowel.
Pancreatic enzymes and bile acids must be normally secreted into duodenal lumen. Prepares various nutrients to be taken up by small-bowel absorptive cells (i.e., adequate pH).
luminal phase of normal intestinal absorption
Includes processes that occur in the cells and transport channels of the intestinal wall.
intestinal phase of normal intestinal absorption
Reflects secretory insufficiency of pancreatic enzymes and bile acid
luminal phase of malabsorption
Impaired mucosal function
intestinal phase of malabsorption
Two types of clinical features of malabsorption
Specific: identifiable molecular defect causing malabsorption of a single nutrient (i.e., Disaccharidase deficiency, mainly lactase deficiency).
Generalized: a condition where absorption of several nutrient classes is impaired.
characterized by
intolerance for their corresponding disaccharide
lactase deficiency
Chronic disease, in which there is a characteristic
mucosal lesion of the small intestine and impaired
generalized nutrient absorption
celiac disease
Damage to epithelial cells: flat mucosa, blunting of villi
Increased number of intraepithelial T cells
Increased plasma cells in lamina propria
Often duodenum and proximal jejunum
celiac disease
Diarrhea, flatulence, abdominal pain, weight loss, and mucositis resulting from vitamin deficiencies
alimentary tract malabsorption
Anemia from iron, pyridoxine, folate, and/or vitamin B12 deficiency
Bleeding from vitamin K deficiency
hematopoietic system malabsorption
Osteopenia and tetany from calcium, magnesium, and vitamin D deficiency
musculoskeletal system malabsorption
Amenorrhea, impotence, and infertility from generalized malnutrition
Hyperparathyroidism from protracted calcium and vitamin D deficiency
endocrine system malabsorption
Purpura and petechiae from vitamin K deficiency
Edema from protein deficiency
Dermatitis and hyperkeratosis from deficiencies of vitamin A, zinc, essential fatty acids and niacin
epidermis malabsorption
Peripheral neuropathy from vitamin A and B12 deficiencies
nervous system malabsorption
Intraluminal obstruction
A segment of bowel protudes distally into a surrounding outer portion. Often in infants or young children.
May impair blood supply: infarction
intussusception
Segment of gut twists on its mesentery, kinking the bowel and usually interrupting blood supply.
volvulus
Fibrous scars caused by previous surgery or peritonitis may cause obstruction
adhesions
Loops of small bowel may be incarcerated in an inguinal or femoral hernia. Vascular supply may be compromised
hernias
Intestinal hamartomatous polyps
Mucocutaneous melanin pigmentation: perioral region, buccal mucosa, hands, feet, perianal, and genital areas.
Symptoms of bowel obstruction. However in ~25% pts diagnosis is based on hyperpigmentation.
Mutation in LKB1 tumor suppressor gene (encodes a serine threonine kinase)
Increased risk for cancers of breast, pancreas, testis, and ovary
Peutz-Jeghers Syndrome
Arise from lymphoid tissue in mucosa/submucosa. Associated with celiac disease.
Persistent activation of T lymphocytes in the bowel may predispose to develop T-cell lymphomas
Intestinal Lymphoma
Intestinal Lymphoma types
Mediterranean type:
Young men in underdeveloped countries
Most common sites: Duodenum and jejunum
Associated with a-heavy chain disease: proliferative disorder of intestinal B lymphocytes, which secrete the heavy chain of IgA without light chains.
Western type:
Children under 10 yrs of age and adults older than 40 yrs old
Most common site: Ileum
Intestinal obstruction, perforation, ocult bleeding.
When distal mets are present, 5-yr survival is <10%
Submucosal nodules covered by intact mucosa. Larger tumors invade muscular layer and may cause fibrosis.
neuroendocrine tumors
Most common cause of congenital intestinal obstruction
Dilation of colon due to the absence of ganglion cells and ganglia in the muscle wall and submucosa of the affected segment. Similar etiology as achalasia (esophageal motor disorder)
Usually in the wall of the rectum (diagnosis by biopsy)
Congenital Megacolon (Hirschsprung disease)
Generic term for an inflammatory disease of the colon: exudative plaques on the mucosa
Associated with antibiotic therapy (alteration of fecal flora): Clostridium difficile. Produces toxins that damage the colonic mucosa
pseudomembranous colitis
Acquired herniation of the mucosa and submucosa through the muscular layer of the colon. In reality, it is a false diverticulum.
diverticulosis
Inflammation at the base of the diverticulum. Presumably from irritation caused by retained fecal material. 10-20% pts with diverticulosis at some point develop diverticulitis.
Most common symptoms: persistent abdominal pain and fever. Leukocytosis is the rule.
diverticulitis
Chronic, segmental, transmural inflammation of the intestine
Mainly in the distal small intestine (ileum and cecum ~50% cases) but may involve any part of the GI tract. Only colon in ~20% cases.
Crohn Disease
involvement of the intestine is discontinuous. Some segments are affected, some are normal.
sharply delimited lesions
All layers of the bowel are typically involved with an inflammatory process (edema and fibrosis) with mucosal damage. Ulceration is the usual outcome of severe active disease.
transmural inflammatory disease
mostly in the submucosa
presence of noncaseating granulomas
Chronic superficial inflammation of the colon and rectum
Cause is unknown.
ulcerative colitis
Three major features of ulcerative colitis
Diffuse disease: extends from the most distal part of the rectum to variable proximal distances.
Inflammation is generally limited to colon and rectum
Essentially a mucosal disease: no involvement of deeper layers of intestine.
A phenotypic variant of FAP is ______ and include colonic and extracolonic lesions such as:
G.I. polyposis, stomach at ampulla of vater: polyps progress to colon cancer
Osteomas of jaws and long bones
Soft tissue tumors of skin
Garner Syndrome
