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Small_Intestine

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					                                                        Small Intestine

Congenital anomalies:
    Atresia- no opening
    Stenosis- narrowing after development
    Diverticula- in mesenteric border at sites of penetration of blood vessels where musculature is a little weak
       Can cause bacterial overgrowth, malabsorption, ulceration and bleeding. Obstruction can cause it.
       Food in divertucula becomes stagnant infection
    Meckel‟s Diverticulum- persistent vitelline duct, in about 2% of general population, occur in ileum about 12 inches from
       ileocecal valve.
       Heterotopic gastric mucosa present, acid secretion peptic ulceration with bleeding, occasionally other heterotopic tissue
       present, it can be solid like a cord or open to the abdominal wall, can cause intestinal obstruction and PU
    Heterotopic pancreatic tissue- small masses of pancreatic tissue, anywhere in small intestine, confused with tumor

Tumors of small intestine:

Benign- rare, e.g. leiomyoma, neurofibroma, adenoma
Peutz-Jeghers syndrome- hereditary GI polyposis assoc with excessive melanin pigmentation, can be sm and lg intestine,
autosomal dominant, intessuception can occur, as well as, intestinal obstruction

Malignant-
Carcinoid tumor, lymphoma, adenocarcinoma, leiomyosarcoma in descending order of frequency

Carcinoid tumor:
     Arise from neuroendocrine cells of GIT; malignant tumor but of low malignancy
     Assoc with bronchial carcinoid tumor
     Produce enzymes, hormones and proteins such as gastrin, ACTH, bradykinin, histamine, prostaglandins
     May cause Cushing‟s syndrome (ACTH) or Z-E syndrome (gastrin)
     Morphology: seen in appendix and terminal ileum (75%), rectum, stomach, esophagus or duodenum
     All locally invasive. Carcinoids of ileum, colon, and stomach frequently metastasize to liver and elsewhere
     Carcinoid syndrome: excessive production of seratonin
     Diarrhea, wheezing, flushing
     Major chemical mediator is seratonin
     Seratonin (=5HT=5 hydroxytryptamine) decarboxylated in liver to 5-HIAA (5-hydroxy-indole-acetic-acid)
        excreted in urine (used for dx)
     Right side of heart affected- pulm and tricuspid valves, not left side

Adenocarcinoma of the small intestine and lymphomas:
Rare, cause obstruction

Malabsorption syndromes:
    Impaired intestinal absorption w/ consequent fecal excretion of fat (steatorrhea), proteins, carbohydrates, fat soluble
       vitamins, minerals and water
    Impairment of digestion, absorption, and transport of absorbed nutrients occur

Common clinical features of malabsorption-
    Bulky, frothy, greasy, foul-smelling stools, fatty, and yellow
    Weight loss, anorexia, edema due to protein deficiency, ecchymosis
    Osteoporosis, bleeding, anemia due to deficiency of vitamins, minerals, folate and iron
    Bacterial infection and glossitis
    Excessive diarrhea
    Sudan stain- see fat globules in stool

Celiac sprue (important):
     Aka Celiac disease, Gluten-sensitive enteropathy, nontropical sprue
     Malabsorption due to villous atrophy of jejunal mucosa, improvement following withdrawal of food containing gluten
         (wheat, barley, rye), villi are short
     Immune reaction to gliadin (a glycoprotein in gluten) results in damage to epithelial cells of villi of intestine, cell
         mediated, Tc cells against gliadin “bystander” destruction
        Morphology: jejunal mucosa flattened; villous atrophy
        Celiac disease is the most common cause of “flat biopsy” in U.S.

Whipple‟s disease:
    Aka intestinal lipodystrophy
    Multisystem disorder CNS, joints, heart, blood vessels, skin, kidneys, lungs, lymph nodes
    Bacterial infection caused by Tropheryma whippelii detected in macrophages, neutrophils
    Chronic inflammation rxn, with regional lymph nodes involved
    Small intestinal villi are distended by numerous foamy macrophages laden with granules
    Clinical: malabsoption, diarrhea, steatorrhea, weight loss, anemia

Disaccharidase deficiency: disaccharides cannot be digested because of absence of enzyme, e.g. lactose

Bacterial overgrowth syndrome:
     Colonization by abnormally large population of bacteria in jejunum inflammation and malabsorption
     Mainly due to intestinal luminal stasis fistulas, diverticular blind loops, postoperative states

Abetalipoproteinemia:
     Familial form of malabsorption- an inborn error of metabolism
     Absorbed lipoproteins cannot be transported (because of absence of apoprotein)
     Failure to absorb essential fatty acids cause defective lipid membrane of RBC‟s RBC‟s show „burr cell‟ appearance

Intestinal obstruction- most are mechanical but you can get physiologic obstruction
Major causes:
    1. Hernias
    2. Adhesions
    3. Intussusception
    4. Volvulus
** #1-4= 80%

Hernia- most common
     Protusion of organ or tisse through an abnormal opening, through an area of weakness or defect in the abdominal wall
     Sites: inguinal, femoral, umbilicus, surgical scars
     Intestine may become obstructed due to incarceration
     It may impair venous drainage and later arterial supply of trapped viscus strangulation (strangulated hernia) leads to
        infarction or gangrene of trapped organ (surgical condition)

Intestinal adhesions (didn‟t say anything about it)

Intussusception-
      Invagination of proximal portion of intestine into the lumen of the immediately distal segment (telescoping)
      Peristalsis propels the telescoped segment further into the distal bowel
      Most common in children

Volvulus-
     Twisting of a loop of bowel about its mesenteric base
     Commonly in sigmoid colon due to long mesenteries
     Can cause infarction

Paralytic ileus-
     Obstruction without mechanical blockage (physiologic obstruction)
     Absence of peristalsis due to neuromuscular dysfunction, often post-op
     Severe abdominal trauma
     Generalized peritonitis

Ischemic bowel disease:
     Not enough blood getting to intestines
     Hypotension and shock lead to generalized ischemia
     Remember the arterial supply of intestines- CT, SMA, IMA, collaterals form arches
       Hypotension Ischemia Infarction of bowel
       Acute ischemia involving SMA and IMA infarction often in splenic flexure of colon, watershed area between SMA
        and IMA
       Pathogenesis: Mesenteric venous thrombosis, Ischemia secondary to intestinal obstruction: intraabdominal
        herniation causing strangulation and torsion, intestinal adhesions trap or kink bowel segments, intussusception,
        volvulus
       Clinical- S/S of “acute abdomen”, tx quickly
       Intestinal angina- abdominal pain soon after eating

Inflammatory bowel disease (IBD) (very important):
Small and large intestine inflammation, diarrhea usually results (main clinical sx)
Etiology (just know general):
     1. infectious diseases
     2. noninfectious diseases
     3. idiopathic IBD- Crohn’s disease (CD), Ulcerative colitis (UC)- common diseases
***Diagnosis of idiopathic IBD requires exclusion of (1) and (2)***

General considerations of idioapathic IBD:
    10-20% of patients cannot be classified as either CD or UC, even after histologic examination indeterminate colitis
    Pathogenesis: unknown, maybe virus, immunologic, genetic, psychosomatic
    Incidence on the increase in U.S.
    Most common age 20-30
    Females are affected more than males
    Disease of the industrialized world
    Whites five times more than non whites and Jews 5X more than non Jews
    Overall UC (more dangerous) more than CD, hard to differentiate

Crohn’s disease (CD):
    Chronic recurrent ulcero-inflammatory lesion of GIT extending from mouth to anus, although most common in terminal
       ileum
    Regional Ileitis and colon and esophagus an be affected
    Characterized by discontinous lesions
    Mac: segmental or discontinous lesions with intervening normal mucosa called skip areas
    Bowel wall markedly thickened with inflammation creeping fat
    Marked narrowing of gut lumen with mucosal edema fibrous stricture and string sign in X-ray
    Elongated ulcers forming deep fissures fistulas (perforate into peritoneum, adjacent viscera or skin)
    See polymorphs
    Mic: transmural chronic inflammation with noncaseating epithelial granulomas (not always present and not required for
       diagnosis)
    Lymphocytes and plasma cells, mucosal edema, submucosal fibrosis, cryptitis and crypt abscesses
    Clinical: malnutrition, fistulas and obstruction, ananl and perianal disease more common, malabsorption, migratory
       polyarthritis, ankylosing spondylitis, uveitis, erythema nodusum, extraintestinal manifestation in both CD and UC,
       perianal abscesses and fistulas

Ulcerative colitis (UC):
     Chronic recurrent ulcero-inflammatory disease mainly of colon and rectum, occasionally entire large bowel, has
        continuous lesions
     Backwash ileitis- involvement of terminal ileum in 10%
     Edematorus mucosa protrude as inflammatory polyps (pseudopolyps)
     Recurrent bouts of bloody mucoid diarrhea and tenesmus, pain in passing stool
     Sever chronic ulceration colonic dilatation and systemic shock Toxic megacolon
     Complications: development of carcinoma, dysplastic lesions
                              Differential diagnosis of CD and UC
                     CD                                       UC
Rectal bleeding      uncommon                                 common
Weight loss          common                                   unusual
Internal fistulas    common                                   rare
Risk of carcinoma    less common                              greater

Type of lesions      discontinuous                           continuous
                     “skip lesions”
Ileal involvement    usual                                   rare
Inflammation         transmural                              mucosal & submuc
Bowel lesion         deep fissures                           no fissures
                     granulomas                              no granulomas
Pseudopolyps         unusual                                 common
Fibrous strictures   very common                             very rare