Term
| What is the basic anatomy and blood supply of the small intestine? |
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Definition
Entire small bowel supplied by superior mesenteric arteries at level of hepatic flexure.
1) Duodenum is retroperitoneal (superior, descending, horizontal and ascending portions)
2) Jejunum (first 1/3) and Ileum (remainder down to cecum) are peritoneal |
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Term
| What is the basic histological organization of the small bowel? |
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Definition
1) Mucosa (villi and crypts)
- Villi epithelium has goblet cells, endocrine cells, paneth cells and columnar epithelium with microvilli (brush border)
- Lamina propria (loose connective tissue, vessels, lymphatics, lymphocytes)
- Muscularis mucosa (large vessels and lymphatics)
2) Submucosa
- Bruners' glands in duodenum
- Terminal ileum has Peyer's patches
3) Muscularis propria
- circular and longitudinal with myenteric plexus in between.
4) Sub-serosa and serosa |
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Term
| What happens when the vitelline duct fails to involute during development? |
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Definition
Meckel's diverticulum, with a blind pouch located on the anti-mesenteric side of the bowel, following "rule of twos"
- Can cause pain, bleeding and other problems. |
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Term
| What functional properties of the intestine make it succesptible to certain disease processes? |
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Definition
1) Maldigestion means malnutrition
2) Microorganisms that come with the food may find a port of entry, too
3) High turnover and exquisite vasculature mean susceptibility to toxins and ischemia
4) High proliferation rate opens the door to dysplasia, and possibly cancer |
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Term
| What is meant by "intussusception" and "volvulis" in small intestine pathology? |
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Definition
1) Intussusception
- Protrusion of a segment of bowel into the lumen of the more distal segment
- Usually begins at a nidus of some sort (like a Meckel’s)
Peristalsis pulls the segment along
2) Volvulus
- Twisting of a segment of bowel on its mesentery |
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Term
What are the most important causes of invasive bacteira diarrheal illness (Enterocolitis)?
How do you distinguish between the causes clinically? |
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Definition
Small volume of bloody diarrhea is termed "dysentery" and inflammatory conditions that produce diarrhea are called Enterocolitis.
1) Yersinia (gram negative coccobacillus)
- Involves lleum, colon and appendix
- causes "right lower quadrant pain"
- can involve PP, causing granuloma infection
2) Salmonella (gram-negative invasive)
- Invade lymphoid tissue and causes ulcerations like 1
- "crypt abscess" on histology
3) C. jejuni
- more common, found in unpasteurized milk, contaminated water, uncooked chicken
- dysentery; proliferation in lamina propria and lymphoid tissue leads to enteric fever
- Villous blunting, ulcers, purulent exudate
Can mimic ulcerative colitis, with crypt abscesses and ulcers (more later) |
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Term
| What are the important parasitic causes of enterocolitis? |
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Definition
1) Nematodes (roundworms)
- Ascaris lumbricoides, Strongyloides stercoralis, hookworms (Necator and Ancylostoma spp.)
2) Cestodes (flatworms)
- Diphyllobothrium latum, Taenia solium, Hymenolepsis nana
3) Protozoa
Giardia lamblia
Entamoeba histolytica
Cryptosporidium parvum |
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Term
| What protozoan infections can cause enterocolitis and how? |
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Definition
1) Giardia lamblia (most common infection in humans)
- drinking contaminated water (cyst form ingested, excysted trophozoites (“trophs”) proliferate in small bowel)
- Severe diarrhea with steatorhea
- Trophs seen on biopsies (binucleate, pear-shaped)
2) Entamoeba histolytica
- Quadrinucleate cyst forms in the distal ileum, releasing trophozoites that invade through epithelium and spread out on the muscularis mucosa.
- Look for “flask-shaped” ulcers that look like macrophages with RBCs in them on biopsy
3) Cryptosporidium parvum (problem in immunocompromised)
- Intestinal parasite (affects small intestine and colon) via fecal-oral
- Very tiny (2-4um); cysts attach to enterocyte surface; merozoites end up in the apical cytoplasm
- Look for merozoits in ovocysts on EM. |
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Term
Which parasitic enterocolitis is described histologically by each of the following?
1) Trophs seen on biopsies (binucleate, pear-shaped)
2) “flask-shaped” ulcers that look like macrophages with RBCs
3) Tiny cysts and merozoits withinin ovocysts on EM. |
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Definition
1) Giardia (water-born)
2) Entemoeba histolytica
3) Crypto (problem in immunocompromised) |
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Term
Infant presents with bloody stools, shock and gangrene.
What would you see on biopsy? |
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Definition
Acute ischemic necrotizing inflammation from Necrotizing Enterocolitis.
Would probably see necrotic small bowel with adhesions. |
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Term
| What is the most common cause of drug-induced enterocolitis? |
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Definition
NSAID use, leading to mucosal ulcerations
Rapid turnover of mucosa also leaves it open to chemotherapy-mediated damage. |
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Term
| What are the classic features of a biopsy taken from a patient with radiation-induced enterocolitis? |
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Definition
1) Regenerative appearance to epithelial cells
2) Amorphous, pink (“hyalinized”) lamina propria
3) Thick-walled blood vessels
4) Atypical (possibly bizarre) stromal cells/fibroblasts/endothelial cells |
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Term
| What are the 3 primary components of digestion that might be disrupted in malabsorption syndrome? |
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Definition
Common causes are Celiac, infection, pancreatic insufficiency and IBD
1) Intraluminal digestion
- large molecules broken down into smaller parts
- Saliva, gastric acid, pancreatic enzymes
2) Terminal digestion
- hydrolysis of CHO and peptides by enzymes on SI brush border
3) Transepithelial transport
- nutrients, fluid, ions absorbed by the mucosa and delivered to the bloodstream |
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Term
Why is megaloblastic anemia more commonly encountered in tropical sprue than in celiac disease?
How can you distinguish the two on biopsy? |
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Definition
TS tends to occur in distal small bowel (where B12 is absorbed).
They are indistinguishable on biopsy! |
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Term
| What malabsorptive, diarrheal disease involves lymphatic obstruction with dilation of the superficial lymphatics and inclusions within mucosal macrophages that are bright pink on PAS stain? |
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Definition
Whipple's disease from gram positive Tropheryma whillplei infection.
Actually a systemic disease with extra-GI sites (joints, LN, CNS) |
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Term
| What are the 2 primary forms of IBD? |
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Definition
Maybe CD4+ T cell mediated?
1) Ulcerative colitis (UC)
- Primarily affects the colon, as the name suggests
- Continuous distribution
- Primarily affects mucosa
2) Crohn’s disease (CD)
- Affects the GI tract anywhere along its length, mouth to anus
- "Skip lesions"
- Involves full thickness of intestinal wall
- Most often affects the distal ileum and right colon |
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Term
| What are the classic gross and histological findings associated with the form of IBD that can affect the GI tract anywhere from mouth to anus? |
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Definition
Crohn's Disease
1) Gross
- Inflammatory "skip lesions"
- Transmural inflammation (ulcers and "fat wrapping" common)
- Thick-walled intestine
2) Histology
- Early-on, PMNs in surface epithelium over lymphoid aggregates (aphthous ulcers)
- Later, PMNs may fill and destroy crypts (“crypt abscesses”)
- Increased acute and chronic inflammation in lamina propria |
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Term
| What is the most common neoplasm found in the small bowel? |
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Definition
| Metastasis from from breast of lung. |
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Term
| What kinds of primary small bowel tumors are found? |
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Definition
1) Adenoma/carcinoma
2) Endocrine (carcinoid)- well differentiated
3) Mesenchymal (soft tissue) |
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