Chapter 17 part 5--Small Intestine Flashcards
Disease processes common to the small intestine and colon
-bc of their roles in nutrient and water transport and their interface with diverse food and microbial Ags, the intestines are involved by processes like malabsorption, infectious, inflammatory and neoplastic processes
What are the most common causes of intestinal obstruction?
- Tumors, infarctions and strictures (due to for ex: CD) account for 10-15% of obstructions
- 80% are attributable to 4 entities: Hernias, Adhesions, Volvulus and Intussusception
Hernias–hernia sac
- Peritoneal wall defects permit peritoneal sac protrusion in which bowel segments can be trapped (external herniation!!!)
- subsequent vascular stasis and edema lead to incarceration!
- vascular compromise leads to STRANGULATION
Locations of hernias
-femoral and inguinal canals, umbilicus, and surgical scars
Most common cause of intestinal obstruction worldwide
Hernias!!
-also the 3rd most common cause in US
Adhesions are
- residua of localized peritoneal inflammation (peritonitis) following surgery, infection, endometriosis, or radiation
- healing leads to fibrous bridging bw viscera
- congenital adhesions also rarely occur
Most common cause of intestinal obstruction in the US??
-Adehesions!!
Complications of adhesions
-internal herniation (within peritoneal cavity), obstruction and strangulation
4 major causes of intestinal obstruction
1) herniation of a segment in the umbilical or inguinal regions
2) adhesion between loops of intestine
3) volvulus
4) intussusception
Volvulus
- complete twisting of a bowel loop about its mesenteric vascular base leading to vascular and lumina obstruction with infarction
- occurs most often in redundant loops of sigmoid colon followed by cecum and small bowel
Intussusception
- occurs when an intestinal segment (usually small bowel) telescopes into the immediately distal segment
- Peristalsis propels the invaginated segment along with its attached mesentery, resulting in obstruction, vessel compression, and infarction
Intussusception in children vs adults–causes
- infants and children: spontaneous or ROTAVIRUS infxn
- adults: point of traction is usually a tumor!!
- in children under 2 years, intussusception is the most common cause of intestinal obstruction!!!
Ischemic Bowel Disease
- abundant collateral supply throughout GI tract allows bowel to usually tolerate slowly progressive loss of blood supply
- BUT abrupt compromise of any major vessel can cause infarction of severe meters in intestine
Watershed zones
-between major branches (e.g., splenic flexure bw superior and inferior mesenteric artery circulations) are most vulnerable for infarction
Infarction damage ranges; what cells are more susceptible to infarction??
- ranges from mucosal infarction to transmural infarction
- bc they are at the end of the capillary network, the epithelial cells at the tips of villi are more susceptible to ischemia than crypt epithelial cells!!
Important causes of ischemia of bowel=
- Atherosclerosis
- Aortic aneurysm
- Hypercoagulable states
- Embolization
- Vasculitis
Hypoperfusion also associated with?
- cardiac failure, shock, dehydration, vasoconstrictive drugs
- Mesenteric venous obstruction or thrombosis due to hypercoagulability, masses or cirrhosis can also cause ischemic disease
Pathogenesis of ischemic bowel disease
- An initial hypoxic injury occurs at onset of vascular compromise (although intestinal epithelium is relatively resistant to transient hypoxia)
- subsequent repercussion leads to an influx of inflammatory cells and mediators causing majority of damage
Ischemic bowel disease morphology–Mucosal infarction
-Patchy mucosal hemorrhage but with normal serosa
Ischemic bowel disease morphology–Mural infarction
- Complete mucosal necrosis, with variable necrosis of submucosa and muscularis propria
- Distribution is typically segmental without serositis!!
Ischemic bowel disease morphology–Transmural infarction
- involved segments are hemorrhagic and has associated serositis
- Coagulative necrosis of muscular propria with perforation develops within 1-4 days
Microscopic morphology of Ischemic bowel disease
- atrophy and sloughing of surface epithelium but preserved crypts can be hyper proliferative
- Extent of inflammation and edema depends on duration of injury
- Superimposed bacterial infection can induce pseudomembrane formation
Chronic vascular insufficiency in Ischemic Bowel disease results in what?
-fibrosis of lamina propria and occasionally structure formation
Clinical features of Ischemic Bowel Disease–in who? what are the symptoms?
- typically occurs in older individuals with coexisting cardiac or vascular disease
- ischemic bowel presents with severe abdominal pain, bloody diarrhea or gross melon, abdominal rigidity, nausea and vomiting
- Right sided colonic disease has more severe course and coexisting COPD is a poor prognostic indicator
Treatment of Ischemic bowel disease and prognosis
- Surgery is indicated in unto 10% of cases
- with appropriate management, 30-day mortality is 10-20%
Aangiodysplasia lesions–what are they
- tortuous, ecstatic dilations of mucosal or submucosal veins occurring in 1% of population
- most common in the cecum or ascending colon, after age 60
- accounts for 20% of major episodes of lower GI bleeding
Causes for Angiodysplasia
- partial, intermittent venous occlusion
- cecal or right colonic predilection derives from the greater wall tension in those owing to larger diameter
What is malabsorption?
-defective absorption of fats, fat and water-soluble vitamins, proteins, carbs, electrolytes, minerals and water
Symptoms of malabsorption
- diarrhea, flatus, abdominal pain, and muscle wasting
- classic hallmark=steatorrhea!!=excessive fecal fat and greasy, malodorous stools
Clinical consequences of malabsorption (due to various deficiencies)
- Anemia and mucositis (pyridoxine, folate or vitamin B12)
- Bleeding (vitamin K)
- Osteopenia and tetany (calcium, magnesium, vitamin D)
- peripheral neuropathy (vitamins A or B12)
Most common causes of malabsorption in the US
- celiac disease
- pancreatic insufficiency
- CD
Pathogenesis of malabsorption
- Intraluminal digestion
- Terminal digestion
- Transepitheial transport
- Lymphatic transport
Intraluminal digestion
-Emulsification and initial enzymatic breakdown
Terminal digestion
-Hydrolysis within enterocyte brush border
Transepithelial transport
-through enterocytes
Lymphatic transport
-of absorbed lipids
What is diarrhea?
- increased stool mass, frequency, or fluidity usually exceeding 200g/day
- severe cases can exceed 14 L/day and be fatal without fluid restoration
Dysentery
-Painful, bloody, small-volume diarrhea
Categories of diarrhea
- Secretory
- Osmotic
- Malabsorptive
- Exudative
Secretory diarrhea
-isotonic with plasma and persists during fasting
Osmotic diarrhea
- Unabsorbed luminal solutes (e.g., due to lactase deficiency) increase osmotic pull of fluid
- stool is more than 50 most hyperosmolar relative to plasma and abates with fasting
Malabsorptive diarrhea
- abates on fasting
Exudative diarrhea
- due to inflammatory disease
- purulent, bloody stools persist during fasting
Cystic fibrosis
- due to absence of the epithelial cystic fibrosis transmembrane conductance regulator (CFTR)
- causes defective bicarb, sodium and water secretion resulting in defective luminal hydration
Results of cystic fibrosis
-ocassionally causes intestinal obstruction but more commonly (80% of cases) results in formation of pancreatic intraductal concretions and causes pancreatic duct obstruction, low grade chronic auto digestion of pancreas with eventual exocrine pancreatic insufficiency
Tx for failure of nutrient absorption in CF
-oral enzyme supplementation
