29 - Diseases of the Colon and Rectum Flashcards Preview

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Flashcards in 29 - Diseases of the Colon and Rectum Deck (154)
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1

Colon & Rectum - Development

First trimester of gestation
Distal midgut (Cecum to splenic flexure) & hindgut (splenic flexure to rectum)

2

Colon & rectum - Size

1m long
2L capacity

3

Colon & Rectum - Regions

Cecum
Ascending Colon
Transverse Colon
Descending Colon
Sigmoid Colon
Rectum

4

Colon - 5 layers

Mucosa
Submucosa
Circular muscle
Longitudinal muscle
Serosa

5

Colon - Haustra

Tonic contractions of rings of circular muscle (plicae semilunares coli)

6

Colon - Circular muscle layer control

Thin layer of cells, interstitial cells of Cajal on submucosal surface of smooth muscle layer

7

Colon & Rectum - Histo

Mucosa:
Columnar cells
Goblet cells
Enteroendocrine cells (mainly located in the crypts)

No Villi

Epithelial cells proliferate in lower parts of crypts, migrate toward surface

8

Blood supply: Cecum, Ascending Colon, Transverse Colon

SMA

9

Blood Supply: Transverse Colon, Descending Colon, Sigmoid Colon, Rectum

IMA

10

Venous drainage

Analogous to arterial supply

11

Colon - Neuronal supply

Intrinsic and extrinsic neurons

Extrinsic - Autonomic

Parasympathetic innervation supplied by vagal fibers (midgut derivatives) or the nerves of the pelvic plexus from sacral spinal cord (hindgut derivatives)

12

Colon & Rectum purpose

Maintain fluid & electrolyte balance
Salvage products of intra-colonic fermentation
Store waste materials
Recover 1.5L fluid per day (mostly in proximal colon)
1 - 2 bowel movements/day
Can absorb sodium against high electrochemical gradient!

13

Colon & Rectum - Pharmacology

Most drugs already absorbed by that point

EXCEPT Sulfasalazine (used to treat UC)

14

Sulfasalazine

Composed of sulfapyridine (sulfonamide antibacterial) linked by a diazo bond with 5-Aminosalicylic acid (5-ASA, or mesalamine)

15

5-ASA

The active therapeutic moiety of sulfasalazine.

The sulfapyridine just prevents 5-ASA from being absorbed earlier. The diazo bond is broken by bacterial action.

5-ASA decreases inflammation in the colon.

16

Microbiome

10^10 organisms/mL

Represent a pool of metabolic enzymes

Anaerobes, can thrive in low-oxygen tension

Modify oxygen tension, pH, mucopolysaccharide composition & hydration capacity of stool solids.

Normal flora protects against pathogenic bacterial proliferation. Homeostasis between types of bacteria.

17

Colon & Rectum - Vascular Diseases

Ischemic colitis
Diverticular bleeding
Hemorrhoidal bleeding

18

Colon & Rectum - Neoplastic Diseases

Colon polyps
Colorectal cancer

19

Colon & Rectum - Infectious Diseases

Appendecitis
Bacerial/Viral Colitis
Clostridium Difficile
Diverticulitis

20

Colon & Rectum - Mechanical Diseases

Volvulus
Large bowel obstruction

21

Colon & Rectum - Immunologic Diseases

IBD
Collageneous/Microscopic Colitis
Ileus

22

Colon & Rectum - Motility Diseases

Ileus
IBD

23

Ischemic Colitis - Presentation

Crampy, mild LLQ abdominal pain

Urge to defecate

Pass bright red (or maroon) blood mixed with stool

24

Ischemic Colitis - Morphologic Changes

Vary with duration & severity of injury

25

Ischemic Colitis - Watershed Areas

Splenic Flexure
Rectosigmoid

Due to limited collateral flow

26

Ischemic Colitis - Mildest injuries

Reversible

Mucosal & submucosal hemorrhage & edema

with or without partial necrosis of the mucosa

27

Ischemic Colitis - Unresorbed Hemorrhage

Overlying mucosa sloughs off, forming an ulcer.

28

Ischemic Colitis - Prolonged Severe Ischemia

Muscularis propria is damaged, replaced with fibrous tissue.

Stricture.

29

Ischemic Colitis - Most Severe

Trans-mural infarction
Gangrene
Perforation

30

Diverticulae

Herniations of colonic mucosa through defects in the muscularis layer, resulting in formation of pseudodiverticulae (wall is only made of mucosa and serosa)

Common. Found in 50% of individuals over age 60 on western diet, and 2/3 of patients over 80

Cause unknown