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Large & small bowel function Flashcards

1
Q

Fluid absorption

A

9L of fluid emptied into s intestine (2L oral + 7L secretions)
D&J: 5.5L (but very little net fluid absorption due to secretion in duodenum)
I: ~2L
1.5L to colon (1.3 absorbed)
can increase capacity to compensate

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2
Q

Villi

A

projections into the lumen covered with mature, absorptive enterocytes
occasional mucus-secreting goblet cells
lifespan ~days

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3
Q

Crypts

A

tubular invaginations of the epithelium around the villi, lined largely with younger epithelial cells, primarily involved in secretion

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4
Q

Na+ absorption

A

along the entire intestine
proximal SI: Na/H exchanger, Na/solute co-transporter (glucose, galactose, aa)
Ileum/colon: coupled NaCl pathway
Distal colon/rectum: Na channels

Driving force - Na/K ATPase

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5
Q

Na/solute co-transport

A

most important means of Na absorption
Transporter on luminal surface binds both Na and organic molecule
Electrogenic

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6
Q

Na/H exchange

A

Located on apical membrane of proximal SI
Major mode of non-nutrient mediated Na absorption in proximal SI
stimulated by high HCO3-
Protons generated by cell metabolism

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7
Q

Coupled NaCl absorption

A

ileum and colon
Na/H exchange coupled to anion transport via Cl/HCO3 exchanger
electroneutral
most important during interdigestive period

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8
Q

Na channels

A

minor in SI but important in distal colon and rectum
coupled to Na/K ATPase
stimulated by aldosterone

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9
Q

Cl absorption

A

SI: nutrient-coupled Na transport, Cl- follows
distal SI, proximal colon: coupled NaCl
Ileum, colon: Cl/HCO3 exchange alone as well
During interdigestive period - Coupled NaCl absorption

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10
Q

Water absorption

A

Major: paracellular diffusion
Simple diffusion across the lipid bilayer - water drag
Aquaporins - aquaporin 10 highly expressed in enterocytes in ileum
Na-dependent transporters (very high molar ratio of water absorbed)

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11
Q

Function of fluid secretion

A

propel substance out of crypts
maintain fluidity of the intraluminal contents
maintain osmotic equilibrium
dilution of potentially injurious substances

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12
Q

Crypt cell secretion pathway

A

K driven into cell via Na/K ATPase, then moves out through basal K channels
Cl enters cell via NKCC
Cl secreted via CFTR - regultaed by secretagogues
Na moves down gradient paracellularly

Stimulation occurs due to secretagogues: VIP, ACh, 5-HT (serotonin)

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13
Q

Diarrhea definition

A

> 200 g/day, 70-90% water

notable changes in bowel movements including consistency and frequency, usually >3 times/day

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14
Q

Heat-stable enterotoxin mediated infectious enteritis

A

Toxin activates guanyl cyclase
Phosphorylation of intracellular proteins that influence ion transport
Primarily inhibits NaCl absorption

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15
Q

Congenital chloridorrhea

A

absence/defective apical surface Cl/HCO3 antiporter

inability to absorb Cl- –> watery diarrhea

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16
Q

Lactose malabsorption

A

Lactose, osmotically active
Osmotic diarrhea
Colonic bacteria - can metabolize some lactose to produce H2, CO2, other gasses, short-chain FAs

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17
Q

Osmotic laxatives (magnesium hydroxides)

A

similar to lactose malabsorption

attract and retain water in intestinal lumen

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18
Q

IBS

A

functional disorder
abd pain, bloating, marked flatulence, excessive rectal mucus production, alteration of bowel habits, absence of organic cause
patients have motor dysfuncitons
stress-induced uncoordinated contractions of bowels

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19
Q

Bacterial enterocolitis pathophys

A
  1. Cholera enterotoxin binds GM1 ganglioside receptors –> endocytosis
  2. Subunit dissociates –> enters cytoplasm, ribocylates G protein, inhibiting GTPase
  3. continuous actiation of AC –> cAMP –> hyperstimulation of NaCl transport from serosa to mucosa, cause diarrhea

NaCl absorption inhibited
nutrient-coupled Na absorption remains normal: give rice/glucose solution with Na for oral rehydration

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20
Q

Carcinoid syndrome

A

EC cell products cause diarrhea
serotonin, bradykinin, substance P, neurotensin - increase intracellular Ca
PG - stimulate cAMP production

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21
Q

VIPoma

A

islet cell pancreatic tumor, produces VIP

Increases fluid secretion by stimulating cAMP –> increase Cl- secretion and decrease NaCl absorption

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22
Q

Gastrinoma

A

Tumor in pancreas/duodenal mucosa that secretes gastrin
Stimulates acid secretion –> ulcer formation
DIarrhea due to increased volume of fluid entering SI, + increased duodenal secretions
Steatorrhea due to inactivation of lipase, ppt of bile salts, damage to absorptive mucosa

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23
Q

Ulcerative colitis pathophys

A

starts in rectum, spreads proximally
advanced disease - may extend 2-3 cm into terminal ielum
Continuous disease
mucosallybased, no transmural spread (except in fulminant colitis)
Can form muscular strictures, but more uncommon; due to hypertrophy and spasm of muscularis mucosa (not fibrosis)
Granulation leads to bleeding

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24
Q

Ulcerative colitis histo

A

Crypt abscesses involving the crypts of Lieberkuhn

PMNs accumulate in abscesses - frank necrossi of surrounding crypt epithelium

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25
Q

Crohn’s disease pathophys

A

anywhere in GI tract, but most commonly terminal ileum
Patchy, discontinuous
Transmural inflammation
Fibrous strictures (permanent), adhesions and fistulas

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26
Q

Crohn’s disease pathophys

A

hyperplasia of perilymphatic histiocytes
diffuse granulomatous infiltration
discrete noncaseating granulomas in submucosa & lamina propria
edema and lymphatic dilation of all layers of the gut
monocytic infiltration within lymph nodules and Peyer’s patches

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27
Q

Adenomatous polyps

A

gland formation
Premalignant cnodition
>2cm - 50% incidence of cancer
can be anywhere, but more seen in L colon

28
Q

Colon cancer genetics

A

APC 9low-grade adenoma) –> K-ras (high-grade adenoma) –> p53 (carcinoma)

29
Q

IBD epidemiology

A

more common in females
teens/20s, then 50-60
more common in Caucasians, Ashkenazi Jews

30
Q

Crohn’s S/S

A 
recurrent mild diarrhea, abd pain, fever
20% RLQ pain, fever, bloody diarrhea
fistulas, fissures, abscesses common
slowly progressing
constant pain, not relieved by bowel movement
stool often not bloody
31
Q

UC S/S

A

bloody diarrhea with stringy, mucoid material
Lower abd pain/cramps
Temporarily relieved by bowel movement
Systemic symptoms: fever, anorexia, weight loss, fatigue

32
Q

Dx of IBD

A

Rule out other causes
Leukocytes, CRP may be elevated
Imaging
Colonoscopy/sigmoidoscopy and biopsy, unless active flare of UC

33
Q

Tx of mild/moderate IBD

A

1) 5-ASA: mesalamine, balsalazide, sulfasalazine
2) Corticosteroids if cond’n does not improve with 5-ASA
3) Immunomodulating agents
4) biologics

34
Q

Tx of severe UC

A

If no improvement with corticosteroids (started immediately):
anti-TNF therapy
cyclosporine
surgery

35
Q

UC: surgical indications

A

severe hemorrhage
perforation
carcinoma
fulminent colitis/toxic megacolon that does not improve within 48-72 hours
refractory disease requiring long-term corticosteroids

36
Q

UC surgical procedure

A

Colectomy + IPAA (ileal pouch anal anastomosis)
5-7 loose bowel movements per day without incontinence
pouchitis in >40%

37
Q

Crohn’s surgery

A

75% require surgery within 20 years
Indications: intractibility to medical therapy, abscess, massive bleed, obstruction, fistulas
Ileotomy, stricturectomy

38
Q

Celiac disease Dx

A

serology:
IgA endomysial Ab & IGA tTG Ab
then mucosal biopsy of distal duodenum/proximal jejunum

39
Q

Celiac disease S/S

A

infants: malabsorption
older: chronic diarrhea, dyspepsia, flatulence, extraintestinal manifestations

40
Q

Diverticulosis

A

herniation of colonic mucosa

41
Q

Diverticulitis

A

infection/inflammation of diverticulum

42
Q

Diverticulitis pathophys

A

increased luminal pressure –> hypertrophic muscle with weakness at site of BV penetration –> herniation
often at sigmoid colon
debris compresses/erodes BV
many microperforations –> inflammation

43
Q

Diverticulitis S/S

A

> 80% asymptomatic

fever, LLQ pain, tenderness, nausea/vomiting, altered bowel habits

44
Q

Diverticulitis Tx

A

simple - high fiber diet
bowel rest (liquid diet)
broad-spectrum antibiotics: cipro/metronidazole
drain abscess if necessary

45
Q

Types of adenomas

A

Pedunculate (attached by a stalk)
sessile (little/no stalk)
Tubular: complex network of branching glands
Villous: extends straight down, long/finger-like
Tubulovillous - combination

46
Q

Mesalazine MOA/PD

A

bowel-specific, metabolized in the gut
blocks COX/PG formation?
topical effect

47
Q

Azathioprine MOA

A

antagonize purine metabolism - inhibit DNA/RNA/protein synthesis
inhibit proliferation of leukocytes and lymphocytes
incorporated into DNA structure

48
Q

Azathioprine SE

A

bone marrow suppression

hepatoxicity with regards to 6-MMP

49
Q

Infliximab MOA

A

TNA-alpha mab

lysis of TNF-producing macrophages and T-cells

50
Q

Infliximab SE’s

A

serious infections

hepatosplenic T-cell lymphoma

51
Q

Loperamide MOA

A

binds to opiate receptor in the gut wall
inhibits ACh/PG release - inhibit propulsive peristalsis, increase intestinal transit time, enhance resorption
increases anal sphincter tone

52
Q

Loperamide indication

A

adjunct to rehydration therapy for symptomatic control of acute, nonspecific diarrhea

53
Q

Most common cause of lower GI bleeding

A
  1. Diverticular disease
  2. Colitis
  3. Adenomatous polyps
  4. Malignancies
54
Q

Tight junctions in s. intestine

A

Formed by extracellular domains of transmembrane “claudins”
Connected to actin cytoskeleton via intracellular scaffold proteins –> gives jxn physical integrity + ability to be contracted (by myosin)

55
Q

Paracellular vs transcellular absorption

A

paracellular mostly proximal SI

transcellular entirety of small and large intestines

56
Q

Celiac disease pathophys

A

1) decreased brush border hydrolase resulting in unabsorbed osmols
2) villous atrophy - malabsorption
3) Crypt hyperplasia
4) inflammation-induced hyper-secretion by crypt enterocytes

57
Q

Extracolonic manifestations of IBD

A 
Conjunctivitis/iritis
Growth retardation
Aphthous ulcers/moniliasis
Skin eruptions
Ankylosing spondylitis
Sacroilitis
Clubbing
Venous thrombosis
Erythema nodosum
Pyoderma gangrenosum
Obstructive hydronephrosis
Nephrolithiasis
Hepatobiliary disorders
58
Q

R-sided colorectal tumour symptoms

A

fatigue, Fe-deficiency anemia

change in bowel habit - diarrhea

59
Q

L-sided colorectal tumour symptoms

A

rectal bleeding
crampy pain, anemia
change in bowel habit often constipation

60
Q

Colorectal cancer stages

A

1: doesn’t penetrate muscle
2: penetrates muscle into fat
3: penetrates fat into lymph nodes

61
Q

Hereditary hemorrhagic telangectasia

A

Autosomal dominant
telangectasia of the skin, mucous membranes, GI, arteriovenous malformations of the lungs, liver
most commonly present as recurrent epistaxis or iron deficiency anemia due to GI blood loss
>50% patients manifest by age 10

62
Q

Double duct sign

A

simultaneous dilation of common bile duct and pancreatic duct, most commonly due to a tumour in the head of the pancreas

63
Q

Radiation proctitis

A

Radiation injury for treatment of cancers of the rectum/cervix/uterus/prostate/bladder/testes
Acute - first few weeks
Chronic - several months, years
Symptoms - diarrhea, rectal bleeding, painful defecation, bowel obstruction
Tx: sucralfate, hyperbaric oxygen, corticosteroids, metronidazole and argon plasma coagulation

64
Q

Non-neoplastic polyps

A

hyperplastic
hamartomas
inflammatory

65
Q

Colonoscopy guidelines

A

50 for high-risk (1st degree relative with colon cancer), or 10 years before the first relative if their diagnosis was <50
Otherwise FIT at age 50, followup with colonoscopy if positive

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