Chapter 12, part 2 Flashcards by Deborah Karp

Purpose of the colon

Extracts water, sodium, short-chain fatty acids (SCFAs), and some vitamins from the stool
Excretes potassium

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What percentage of water and sodium is recovered by the colon?

90% of each

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How much water can the colon absorb a day?

Where does most of this absorption occur?

6 L/day

Most occurs on the right side

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What is the primary energy source of the colon?

SCFAs
-Butyrate
-Propionate
-Acetate
Also creates osmotic gradient, driving solute absorption

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Bacterial population of the colon

Bacteroides (anaerobe): MC bacteria overall

E. coli is the MC aerobe

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What are the three patterns of colonic motility?

Retrograde
Segmental
Mass movements

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Retrograde colonic motility

Anti-peristaltic that starts near the hepatic flexure and moves toward the cecum
Results in slowing of colonic transit and increasing fecal mixing

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Where does segmental motility occur?

What does it do?

Transverse and left colon

Propels stool forward over small distances (increasing stool mixing)

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What do mass movements do?

Progress along the length of the colon and can move a column of stool up to 1/3 the length of the bowel
During these, pressure is the highest in the sigmoid colon

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What supplies extrinsic control of the colon to stimulate and inhibit motility?

Parasympathetic and sympathetic neurons

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What are the two plexuses of the intrinsic neurons?

Myenteric (Auerbach)

Submucosal (Meissner)

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Where is the myenteric (Auerbach) plexus?

At junction between longitudinal and circular layers of muscularis propria

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How is the submucosal (Meissner) plexus formed?

In the submucosa from nerve fibers that perforate the circular muscle layer

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Gastrocolic reflex

Ingestion of a meal results in increased colonic tone

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How does nl defecation occur?

Initial trigger leads to rectal distention, which leads to internal sphincter relaxation
Puborectalis relaxes, which leads to strengthening of anorectal junction
External anal sphincter relaxes and intra-abdominal pressure increases
Rectal contents evacuated

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What is the purpose of the rectum?

Reservoir for stool

Filling of this leads to the urge to defecate as the internal sphincter relaxes

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Appendicitis

Inflammation of inner lining that can be d/t obstruction of the lumen by a fecalith or d/t infection

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Sx of appendicitis

Periumbilical pain migrating toward RLQ
Nausea
Anorexia

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Labs of appendicitis

LFTs

Pancreatic enzymes

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Rads of appendicitis

CT of abdomen and pelvis

U/s- for peds or pregnant pts (non-compressible tubular structure)

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Tx of appendicitis

Appendectomy
If small abscess or phlegm: do IV abx initially followed by interval appendectomy after 4-6 wks
Large abscess- drainage catheter in addition to abx therapy

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Diverticular dz

Outpouchings of the colonic wall
Most commonly d/t high intraluminal pressure in areas of anatomic weakness where small arterioles traverse the colon wall

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What is the MC site for diverticular dz?

Sigmoid colon

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Diverticulosis

Usually asymptomatic

Common cause of lower GI bleeding

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Diverticulitis

Infection and inflammation resulting from perforation of a diverticulum

S/sx of diverticulitis

``` Localized abd pain (at sigmoid, MC) Change in bowel habits Anorexia Nausea Fever/chills Urinary urgency ```

Labs/rads of diverticulitis

Leukocytosis | Do CT scan of the abdomen

Tx of uncomplicated diverticulitis

Bowel rest, analgesia prn, and abx -Can be outpatient if pt is afebrile and stable vital signs -Must be able to tolerate oral intake If they don't meet these criteria: admit for bowel rest, IV abx and serial evaluations -Abx for 10-14 days Need colonoscopy 6 wks after resolution of sx

What is considered complicated diverticulitis?

Presence of abscess, fistula, obstruction, or free perforation

Tx of complicated diverticulitis

Greater than or equal to 4 cm pericolonic abscess: percutaneous drainage Smaller abscesses: abx and observation Once resolved, should consider elective colectomy

What can abscesses in diverticulitis lead to?

Erode adjacent organ | Fistula

What is the most common fistula in diverticulitis? | How is this confirmed?

``` Colovesical fistulas (pneumaturia and recurrent UTIs) Confirm with CT (air in the bladder without previous cath= colovesical fistula) ```

Tx of abscess in diverticulitis

Broad spectrum abx until inflammation resolves then elective resection

Hinchey classification

Stratify severity of diverticular dz complicated by perforation

Hinchey classification I

Small, confined pericolonic or mesenteric abscess

Hinchey classification II

Larger, walled-off pelvic abscess

Hinchey classification III

Generalized purulent peritonitis

Hinchey classification IV

Generalized fecal peritonitis

Tx for Hinchey classification I-II

Abx and percutaneous drainage | Then elective colectomy and anastamosis

Tx for Hinchey classification III-IV

Surgical emergencies that require immediate exploration Hartmann's procedure: segmental resection, proximal end colostomy, and closure of the rectal stump Could also do laparoscopic lavage- treats diverticulitis with purulent peritonitis

Cause of large bowel obstruction

Typically caused by neoplasms

Sx of large bowel obstruction

``` Similar sx to SBO Abd pain Distention Obstipation N/V ```

What is the MCC of nonmechanical colonic obstruction?

``` Colonic pseudo-obstruction Can cause a closed-loop obstruction btwn the valve and point obstruction Leads to progressive distention Leads to vascular compromise Leads to possible perforation ```

When would you need prompt surgical exploration in a large bowel obstruction?

If s/sx of sepsis or peritonitis

Imaging for large bowel obstruction

Plain abdominal XR and upright CXR adequate to show free intra-abdominal air Profound dilation of cecum (10-12 cm) indicates impending perforation Can do CT- if not obvious dx, can do water soluble contrast enema

Volvulus- what is it? What area is most common in the rest of the world? What area is most common in the US?

Twisting loop of colon around the axis of its mesentary Causes closed loop obstruction Sigmoid area Cecum: rotation of the cecum and terminal ileum around the mesentery

Sx of volvulus

Acute or chronic abdominal pain Distention Vomiting

Initial tx of volvulus

Prompt IV resuscitation followed by detrosion of the sigmoid

When will a rigid protoscopy or flexible endoscope be successful for a volvulus?

Rush of gas and stool from dilated proximal colon

Cecal bascule

Variant of cecal volvulus that occurs when floppy cecum flips anteriorly and superiorly, becoming fixed

S/sx of cecal volvulus

Abdominal pain Distention N/V

Rads of cecal volvulus

X-ray | Coffee bean sign

Tx of cecal volvulus

Surgical resection with right colectomy

Most pts with ______ will present with obstruction

Colon CA

What is the mainstay of tx for malignancies causing obstruction?

Surgery

What is the tx for proximal lesions in malignant obstructions?

Right colectomy

Tx for distal lesions in malignant obstructions

Proximal diversion with loop colostomy Other option: Hartmann's procedure (resection of colonic segment and creation of an end proximal colostomy) Can also do endoluminal stenting for palliative care

Sx of colonic pseudo-obstruction (Ogilvie's syndrome)

Similar sx to LBO, but characterized by large dilation proximal to the colon WITHOUT mechanical obstruction

Dx of colonic pseudo-obstruction

Water soluble enema to r/o mechanical etiology

Tx of colonic pseudo-obstruction

Initial tx- NG tube decompression, NPO, IVF, cessation of narcotics and anticholinergics, and correct electrolyte abnormalities If it doesn't resolve, neostigmine and endoscopic decompression