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Appendix > Small Bowel > Flashcards

Small Bowel Flashcards

1
Q

Except for the duodenum which is a foregut structure, the rest of the small intestine is derived from?

A

midgut

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2
Q

What are the four main cell types in the small intestine?

A

absorptive enterocytes (make up 95% of all cell types)

Paneth cells

goblet cells

enteroendocrine cells

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3
Q

During fifth week of embryological development, when intestine is rapidly growing, herniation occurs via the umbilicus around what artery?

A

SMA

this herniation continues until up to 10 weeks

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4
Q

Entire small bowel extends from where to where?

A

pylorus to cecum

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5
Q

What’s the entire length of small bowel?

A

approx. 300 cm

duodenum–> 20 cm

jejunum–> 100 cm

ileum–> 150 cm

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6
Q

What divides the duodenum from the jejunum?

A

ligament of Treitz

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7
Q

Where does the jejunum begin?

A

ligament of Treitz

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8
Q

How do we separate the jejunum from ileum?

A

no actual demarcation

jejunum makes up proximal 2/5
ileum makes up remaining 3/5

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9
Q

How do we distinguish jejunum from ileum on gross inspection?

A

jejunum has;

larger circumference

is thicker

has only 1 or 2 arcades sending long vasa recta thru the mesentery

(ileum has 4 or 5 arcades with shorter vasa recta)

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10
Q

What are the tranverse folds of small bowel, commonly seen in distal duodenum and jejunum called?

A

plicae circulares

valvulae conniventes

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11
Q

What is the blood supply of the small intestine?

A

jejunum + Ileum and distal duodenum–> SMA

proximal duodenum–> celiac axis

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12
Q

Anatomic location of SMA in relation to the pancreas and duodenum?

A

the SMA is anterior to uncicate process of pancrease

the SMA is anterior to 3rd part of duodenum

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13
Q

What is the venous drainage of the small bowel?

A

SMV–> drains into the splenic vein behind the neck of pancreas–> portal vein

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14
Q

In this part of the small bowel the circumference is smaller and the walls are thinner, there are multiple vascular arcades with short vasa recta;

A

ileum

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15
Q

This part of intestine is relatively thick, with prominent plicae circulares, and you see only one or two arcades with long vasa recta;

A

jejunum

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16
Q

What’s the innervation of the small bowel?

A

PSNS–> Vagus

SNS–> from splanchnic ganglia

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17
Q

Where do we find the lymphatics of the small bowel?

A

Peyer’s patches of distal small bowel

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18
Q

Lymphatic drainage of small bowel is carried via?

A

cysterna chyli —> thoracic duct—> neck

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19
Q

What are the four layers of the small bowel?

A

mucosa

submucosa

muscularis propria

serosa

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20
Q

What is the outermost layer of the small intestine consisting of a single layer of flattened mesoepithelial cells?

A

serosa

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21
Q

What are the two muscle types found in the muscularis propria layer of the small bowel?

A

thin outer longitudinal muscle layer

thick inner circular muscle layer

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22
Q

Where do we find the myenteric Auerbach’s plexus in the small bowel wall?

A

in the muscularis propria layer between the thin longitudinal outer layer and thick inner circular layer

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23
Q

What’s the strongest layer of the small intestinal wall?

A

submucosa

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24
Q

This is the strongest layer of the small intestinal wall and needs to be incorporated during anastomotic sutures;

A

submucosa

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25
Q

In what part of the small bowel wall do we find blood vessels and nerves?

A

submucosa (strongest part of wall)

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26
Q

This part of the small bowel wall contains lymphatics, arterioles, venules, and an extensive network of nerve fibers:

A

submucosa

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27
Q

Where do we find Meissner’s plexus in the small bowel wall?

A

submucosa

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28
Q

What are the four main cell types of the small intestine and where do we find them in the small bowel lumen?

A

Goblet cells–> make mucus

Paneth cells–> lysozyme, TNF, leukocyte defensins

absorptive enterocytes (most abundant type)

enteroendrocrine cells–> make GI hormones

** all found in mucosal layer

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29
Q

Microscopically, the mucosa of the small intestine is designed for what?

A

maximum absorptive capacity

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30
Q

How is the mucosa of the small intestine designed for maximum absorptive potential?

A

villi protrude into the luminal cavity

** increase absorptive capacity 30-fold

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31
Q

Main role of small intestine?

A

absorption of dietary carbs, proteins fats, vitamins, ions, H2O

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32
Q

How much daily carbs consumed by avg human in western diet?

A

300-350 g/day (50% starch, 30% sucrose)

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33
Q

In what form are carbs absorbed from small intestine?

A

monosacharides via active transporters; SGLT1, GLUT2, GLUT5

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34
Q

Where does protein digestion begin?

A

stomach via stomach acid (denatures protein)

continued in small intestine where protein comes in contact with pancreatic proteases

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35
Q

Pancreatic protease trypsinogen is secreted by pancreas in the inactive form, but it’s activated by what brush border enzyme in the duodenum?

A

enterokinase

** once trypsin activated, it activates other pancreatic enzymes in the protelytic pathway

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36
Q

In what part of the small intestine is digestion and absorption of proteins 80-90% completed?

A

jejunum

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37
Q

What part of intestine do we see majority of digestion and absorption of proteins (80-90%)?

A

jejunum

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38
Q

Most adults consume how much fat/day?

A

60-100 g

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39
Q

Essentially all fat digestion occurs in small intestine, where first step is what?

A

fat globules broken down into smaller molecules, process call emulsification (increase surface area for further digestion)

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40
Q

How does the gallbladder help emulsify dietary fats?

A

bile secretions contain bile salts and lecithin

incorporate into fat globules and help aggregate them and increase their surface area for digestion

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41
Q

What is the most important enzyme in the digestion of dietary fats?

A

pancreatic lipase

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42
Q

How is majority of fat absorbed in small intestine (80-90%)?

A

chylomicrons pass from epithelial cells to lacteals

pass thru lymphatics into venous system via thoracic duct

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43
Q

How much water enters the small bowel daily and how much leaves it for colon?

A

8-10 L /day

500 cc makes it to the colon

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44
Q

Where is Fe absorbed in the small intestine?

A

proximal duodenum

deposited within the cell as ferritin or transferred to plasma bound to transferrin

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45
Q

How are fat soluble ADEK vitamins absorbed?

A

incorporated into chylomicrons

absorbed via lacteals, thoracic duct, venous circulation

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46
Q

Where is vitamin B12 absorbed?

A

terminal ileum

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47
Q

How is vitamin B12 absorbed?

A

b12 derived from cobalamin (free in duodenum by pancreatic proteases)

cobalamin binds to IF secreted by stomach

receptors in terminal ileum pick up cobalamin-IF complex

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48
Q

Small bowel secretes what immunoglobulin?

A

IgA

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49
Q

Produced by plasma cells in lamina propria, and secreted into intestine, prevents adherence of bacteria to epithelial cells:

A

IgA

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50
Q

I cells of duodenum make what hormone?

A

CCK

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51
Q

What does CCK do?

A

stimulates pancreatic secretions

stimulates GB contraction

relaxes sphincter of oddi

inhibits gastric emptying

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52
Q

Antigens in the gut come in contact with what cells in Peyer’s patches which then process the antigen and present it to the immune system;

A

M cells

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53
Q

Most common causes of SBO?

A
  1. adhesions (60%)
  2. tumors (20%)
  3. hernias (10%)
  4. Crohn’s (5%)
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54
Q

These are responsible for 60% of all cases of SBO:

A

adhesions from previous abdominal surgeries

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55
Q

Malignant tumors account for what % of SBO?

A

20%

usually tumors from other abdominal sources, primary SB tumors very rare

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56
Q

Third leading cause of SBO?

A

hernias (10%)

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57
Q

How does Crohn’s dx cause SBO?

A

often from acute inflammation + edema

pts with chronic Crohn’s get strictures

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58
Q

Misc. causes of SBO?

A

2-4 %

intussussception
foreign bodies
gallstones
phytobezoars

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59
Q

Describe the pathophyiology of SBO:

A

early on–> intestinal contractility increases to overcome the obstruction

increased peristalsis occurs proximal and distal to obstruction—> see diarrhea early on

later on–> intestine gets fatigued, dilates, contractions less severe, less intense

bowel dilates–> accumulates water and electrolytes intraluminally and in bowel wall–> this third spacing causes hypovolemia, dehydration

60
Q

With a more proximal obstruction with resultant vomiting, what metabolic derangements do we see?

A

hypochloremia
hypokalemia
metabolic alkalosis

61
Q

How does SBO compromise ventilation?

A

get increased intra-abdominal pressures
decreased venous return
elevation of diaphragm

62
Q

As the intraluminal pressure increases inside the bowel, a decrease in mucosal blood flow can occur, causing;

A

ischemia, perforation

63
Q

This type of SB obstruction, commonly caused by a twist in the bowel, can progress to ischemia and perforation rapidly if not corrected quickly;

A

closed loop obstruction

64
Q

In the abscence of obstruction, the jejunum and ileum are almost sterile, with obstruction we see change in bacterial flora;

A

most commonly e.coli, streptococcus, klebsiella

65
Q

Cardinal symptoms of SBO?

A

colicky abdominal pain, N/V
abdominal distention
obstipation (not passing flatus/feces)

66
Q

Failure to pass flatus/feces is known as?

A

obstipation

67
Q

Early on in course of SBO, pts may report a hx of diarrhea, how is this possible?

A

early on we see increased contractions and peristalsis as the body tries to overwhelm the obstruction

68
Q

As a SBO progresses, and more bacteria accumulate, the vomitus becomes?

A

more feculent indicating a late established obstruction

69
Q

Tachycardia and hypotension are signs of what in someone suspected of SBO?

A

dehydration

70
Q

Accuracy of diagnosis of SBO on plain abdominal xray?

A

60%

71
Q

What do we see on xray of suspected SBO?

A

dilated loops of SB without colonic distention

multiple air fluid levels

72
Q

What are some late signs seen on CT scan of irreversible ischemia due to SBO?

A

pneumatosis intestinalis

portal venous gas

73
Q

Pre-operatively how can we tell if bowel is ischemia or strangulated in cases of SBO? What parameters or labs can we use?

A

no definitive test or lab value shown to be useful

74
Q

What % of pts with partial SBO improve with conservative medical management and tube decompression?

A

60-85%

75
Q

How can we ensure that a questionable area of small bowel is viable or not?

A

place area of questionable bowel in warm saline sponge for 15-20 mins–> reassess

second look laparotomy

76
Q

Indications for laparoscopic exploration for suspected SBO?

A

mild abd distention
proximal obstruction
partial obstruction
anticipated single band obstruction

77
Q

Most effective means of reducing post-op adhesions is?

A

good surgical technique

78
Q

In the early post-operative period, SBO presents a challenge, bc it’s a question of is it SBO vs ileus, with >90% of post-op obstructions being partial and;

A

spontaneously resolve with conservative management

79
Q

This describes intestinal distention and the slowing or abscence of passage of luminal contents without a mechanical obstruction;

A

ileus

80
Q

What are some metabolic causes of ileus?

A

hypokalemia
hypomagnesemia
hyponatremia

81
Q

Which age distribution does Crohn’s disease affect?

A

young adults 20-30s

smaller peak in 6th decade of life

82
Q

What is the association between Crohn’s dx and smoking?

A

risk of getting Crohn’s is twice as likely in smokers

83
Q

Genetic component of Crohn’s?

A

67% concordance in monozygotic twins

84
Q

Cause of Crohn’s?

A

likely combo of immunologic, genetic, environmental

85
Q

What is the single strongest risk factor for developing Crohn’s dx?

A

having a first degree relative with Crohn’s

86
Q

Most common sites of Crohn’s dx are?

A

colon + small intestine

87
Q

Crohn’s is discontinuous and segmental, and in pts with colonic involvement, this is characteristic, distinguishing it from UC:

A

rectal sparing

88
Q

What are skip areas commonly seen with Crohn’s dx?

A

areas of diseased bowel separated by areas of grossly normal appearing bowel

89
Q

What is fat wrapping?

A

circumferential growth of mesenteric fat around the bowel wall

pathognomonic for Crohn’s

90
Q

What’s the earliest lesion we see in Crohn’s on gross inspection of lumen?

A

superficial apthous ulcer noted in mucosa

as dx progresses, ulcer becomes pronounced and transmural inflammation occurs

91
Q

What gives characteristic cobblestone appearance in Crohn’s dx?

A

apthous ulcers are linear, they covalesce to form sinuses with islands of normal tissue in between

92
Q

What are two characteristic histological lesions seen in Crohn’s?

A

non-caseating granulomas w/Langerhan’s giant cells

appear later in disease course (seen in 60-70% of pt)

93
Q

Most common sxs of Crohn’s?

A

lower colicky abdominal pain

diarrhea second most common sxs

94
Q

Compare BMs of UC vs Crohn’s dx;

A

Crohn’s dx–> have less BMs than UC

BMs rarely have mucus, pus, blood

95
Q

Common intestinal complications of Crohns?

A

obstruction + perforation

96
Q

These are two autoantibodies associated with IBD:

A

pANCA

anti-saccharomyces cervisiae

97
Q

Perianal involvement and racto-vaginal fistulas are more common UC or Crohn’s?

A

Crohn’s

98
Q

Most commonly prescribed drug for Crohn’s?

A

sulfasalazine (an aminosalycilate)

mesalamine is a new sulfasalazine like drug that’s used as first line for Crohn’s

99
Q

What’s an altrernative medication used in pts with active Crohn’s flare?

A

budesonide (steroid)

not used for long-term remission maintenance because of side effects

100
Q

What antibiotic commonly used in Crohn’s?

A

metronidazole

may be useful in treating perianal disease, fistulas, etc

101
Q

What are the two immunosuppressive agents used in Crohn’s pts?

A

azathioprine

6-MP

102
Q

Side effects of azathioprine and 6-MP?

A

pancreatitis
hepatitis
fever
rash

103
Q

Most concerning side effects of azathioprine and 6-MP?

A

bone marrow suppression

malignancy potential

104
Q

This other immunosuppressive agent used in Crohn’s for pts with fistula, with MOA of blocking production of IL-2 by helper T-cells:

A

tacrolimus

105
Q

This is a monoclonal antibody to TNF-a and has shown promise in tx of moderate to severe Crohn’s dx:

A

infliximab

106
Q

MOA of infliximab?

A

monoclonal antibody to TNF-a

107
Q

Side effects of infliximab?

A

TB reactivation
fungal and other opportunisitc infexns
reactivation of laten MS
CHF exacerbation

108
Q

What extra-intestinal manifestations of Crohn’s dx do not resolve after surgery?

A

ankylosing spondylitis

hepatic complications

109
Q

Principle of surgery when operating on pt with Crohn’s?

A

only resect the segment causing the problem/complication

do not resect anything you don’t have to, even if it looks diseased

frozen sections during OR are unreliable to determine disease involvement

110
Q

What is acute ileitis?

A

pts have RLQ abdominal pain, confused with appendicitis

appendix normal–> but should be removed to prevent future confusion

acute ileitis is a self-limited dx–> no resection needed

111
Q

What is the most common indication for surgical intervention in pts with Crohn’s dx?

A

intestinal obstruction (often partial)

112
Q

What is the treatment of choice for pts with intestinal obstruction due to Crohn’s?

A

for complete obstruction and partial non-responsive to conservative tx–> segmental resection w/ anastomosis

113
Q

If a segment or multiple segments of bowel are involved with strictures, what can we do beside resect bowel and re-anastomose?

A

perform a stricturoplasty of involved segment

114
Q

How is a stricturoplasty performed?

A

longitudinal incision is made thru narrowed area

followed by closure in a tranverse fashion

115
Q

What is a Heineke-Mikulicz pyloroplasty?

A

make a longitudinal incision on stricture bowel segment

pull the open area superior and inferiorly, and run a suture in a tranverse manner (up and down)

116
Q

For shorter strictured segments, what kind of stricturoplasty do we perform?

A

Heineke-Mikulicz pyloroplasty

117
Q

For strictured segments > 10 cm what kind of stricturoplasty do we perform?

A

Finney pyloroplasty

118
Q

What is a Finney pyloroplasty?

A

side-to-side iso-peristaltic stricturoplasty

119
Q

Advantages of stricturoplasty?

A

preserve intestinal length

similar outcomes/complications compare to resection and anastomosis pts

120
Q

Given the high concern for carcinoma developing at stricture sites, what needs to be done when performing stricuturoplasty?

A

full thickness biopsy of stricture needed

121
Q

Most common urologic complication assc with Crohn’s dx?

A

ureteral obstruction

due to ileo-colic dx with retroperitoneal abscess

122
Q

Why do pts with Crohn’s dx who are found to have cancer have a worse prognosis than pts without Crohns?

A

usually dx is delayed in Crohn’s pt

123
Q

Crohns dx of duodenum seen in 2-4% of cases, and primary indication for surgery in these pts is duodenal obstruction, what’s the procedure of choice?

A

we don’t resect

we bypass obstruction with a gastro-jejunostomy

124
Q

Leading cause of disease related death in pts with Crohn’s

A

GI cancer

125
Q

Small bowel neoplasms are rare, with mean age at onset?

A

60

126
Q

Most common benign tumors of small bowel?

A

leiomyomas

adenomas

127
Q

What is the most malignant neoplasm of the small bowel?

A

adenocarcinoma vs carcinoid

128
Q

Risk factors or conditions that predispose to small bowel neoplasms?

A

hereditary conditions like; FAP, HNPCC, peutz-jeghers, Crohn’s, celiac sprue,

smoking, heavy etoh use, consuming red meat

129
Q

What are the most common benign tumors of the small bowel?

A

GISTs
adenomas
lipomas

130
Q

These are benign small bowel tumors of smooth muscle origin:

A

GISTs

** MC symptomatic benign tumors of small bowel

131
Q

What causes GISTs?

A

arise from interstitial cells of Cajal (intestinal pacemaker of mesodermal origin)

132
Q

Most GISTs are benign, (3-4 x more common than malignant GISTs), and most GISTs, >90%, express what tumor marker?

A

CD117

it’s a c-kit proto-oncogene protein

133
Q

These small bowel neoplasm expressed CD117 and CD 34;

A

GISTs

134
Q

What neoplasm of small bowel expressed CD 117, a c-kit proto-oncogene protein?

A

GISTs

135
Q

When are GISTs most commonly diagonsed age wise?

A

5th decade

equally seen in men/women

136
Q

What is the most common reason for surgery in pts with benign GISTs?

A

these tumors sometimes outgrow their blood supply and cause bleeding

137
Q

This small bowel tumor looks firm, grayish-white, with a whorled appearance, with well differentiated smooth muscle cells:

A

GIST

138
Q

These make up 15% of benign small bowel tumors:

A

adenomas

20%–> duo
30%–>Jej
50–> ileum

139
Q

How do we manage villous adenomas of small bowel?

A

depend on location (have malignant potential of 35-55%)

jejunum + ileum–> resect
duodenum –> endoscopic polypectomy, if invasive or recurs–> pancreaticoduodenectomy

140
Q

What is a Brunner gland adenoma of small bowel?

A

benign hyperplastic lesions found in Brunner gland of proximal duodenum

produce sxs similar to PUD

Tx–> simple excision, no malignant potential, no need to radical surgery

141
Q

These benign small bowel lesions commonly seen in ileum, and present as single intramural lesions found in submucosa of lumen;

A

lipomas

142
Q

Hamartomas of the small bowel occur as a result of this entity;

A

Peutz-Jeghers syndrome

143
Q

This is an AD inherited syndrome of mucocutaneous melanotic pigmentation and gastrointestinal polyps;

A

Peutz-Jeghers syndrome

144
Q

These are developmental malformations consisting of submucosal proliferation of blood vessels;

A

hemagiomas

145
Q

Hemangiomas commonly seen in what small bowel segment?

A

jejunum

make up 5% of benign small bowel neoplasms

146
Q

Hemangiomas of small bowel may occur as part of a syndrome called;

A

Osler-Weber-Rendu dx

147
Q

Most common symptom of small bowel hemangiomas is bleeding, what studies do we get?

A

CTA

red-blood cell tagged study

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