Small Intestine Part 1 Flashcards
Embryology
The duodenum arises from the
Junction of the foregut and midgut
Embryology
The jejunum and upper part of the ileum develop from
Proximal limb of the midgut loop
Embryology
The distal ileum develops from the
Caudal limb of the midgut loop
Microscopic anatomy
Mucosa
Epithelium
Muscularis mucosa
Lamina propia
Microscopic anatomy
Submucosa
Blood vessels
Lymphatics
Myenteric meissners plexus
Microscopic anatomy
Produce an alkaline secretion to protect against acidic gastric chyme
Duodenal brunners gland
Microscopic anatomy
Lymph node aggregates called___________ are most prevalent in the ileum
Peyers patches
Layers of the small intestine
Muscularis
Inner - circular
Outer - longitudinal layers
Between - myenteric auerbach’s plexus
Layers of the small intestine
Single layer of mesoepithelial cells lining the exterior of the SI
Serosa
Layers of the small intestine
Mucosa
Epithelium
Lamina propria
Muscularis mucosa
Layers of the small intestine
Sub mucosa
Meissners plexus
Layers of the small intestine
Muscularis propria
Circular muscle
Auerbach’s plexus
Longitudinal muscle
Layers of the small intestine
The strongest layer of the small intestine
This should be included when performing intestinal anastomoses
Submucosa
Specific cells
Arise from pluripotential cells in the crypts of Liberkuhn and migrate to the tips of villi
Enterocytes
About 95% of the epithelial cells are enterocytes and it is specialized for
Digestion and absorption of dietary nutrients
Specific cells
Found at the base of the crypts of lieberkuhn
Function include, phagocytosis
Mucosal defense
Regulation of intestinal flora
Secretion of variety antimicrobial peptides
Paneth cells
Specific cells
Located above the peyers patches
Specialized for antigen presentation
Microfold M cells
Specific cells
Specialized for mucous secretion
Goblet cells
Specific cells
Specialized to produce and secrete hormones
Entero endocrine cells
Properties of small intestine
Mucosal folds visible upon gross inspection
Also visible radio graphically and help in the distinction from the colon, which not contain them.
More prominent in the proximal intestine than in the distal small intestine.
Plicae circulares or valvulae conniventes
Properties of small intestine
Seen on gross examination of the small intestinal mucosa follicles.
Located in the ileum, are the most prominent and designated peyers patches
Aggregates of lymphoid follicles
Helpful both upon gross inspection in the OR and on abdominal x rays, to differentiate between the small and large bowel
Plicae circulares
Colon doesn’t have
Describe jejunum
Larger diameter Thicker wall More prominent plicae circulares Few arcade 1-2 Long vasa recta
Describe ileum
Many aracades
Short vasa recta
Fatty messentery
Innervation
Para sympathetic innervation
Vagus
Innervation
Sympathetic innervation
Splanchnic nerves
Innervation
Provides enteric nervous system innervation
Meissners and Auerbach plexuses
The entire small bowel is supplied by branches of the SMA except the
Proximal duodenum
Supplied by celiac trunk
Small bowel obstruction
Foreign bodies
Gallstones
Meconium
Intraluminal
Small bowel obstruction
Tumors
Chronhs
Intramural
Small bowel obstruction
Adhesion
Hernias
Carcinomatosis
Extrinsic
Small bowel obstruction
The most common causes of small bowel obstruction are
Hernia Adhesions Volvolus Intussusception Crohns Gallstone ileus SMA syndrome Neoplasm
Small bowel obstruction
Related to prior abdominal surgery account for up to 75% of the cases of small bowel obstruction
Intra abdominal adhesion
Small bowel obstruction
Commonly due to extrinsic or invasion by advanced malignancies arising in organs other than the small bowel.
Cancer related SBO
Small bowel obstruction
Should not be forgotten when considering the differential diagnosis of adult patients with acute or chronic symptoms of small Boswell obstruction, especially those without a history of prior abdominal surgery
Intestinal Malrotation
Midgut volvulus
Small bowel obstruction
Rare etiology of obstruction
Compression of third portion of duodenum by the superior mesenteric artery
Considered in young asthenic individuals who have chronic symptoms suggestive of proximal small bowel obstruction
Superior messenteric artery syndrome
Small bowel obstruction
Pathophysiology
Onset of obstruction
Gas and fluid accumulate
Intestinal activity increases
Pathophysiology of SBO
Most of the gas that accumulates originates from
Swallowed air
Pathophysiology of SBO
The fluid consist of
Swallowed liquids
GI secretions
Pathophysiology of SBO
Gas and fluid accumulate in lumen Intaluminal and intramural pressure rise Decrease intestinal motility Changes in luminal flora and small bowel Translocation of bacteria Impaired microvascular perfusion Intestinal ischemia Necrosis Strangulated obstruction
Small bowel obstruction
Only portion of intestinal lumen is occluded
Strangulation is less likely
Partial SBO
Small bowel obstruction
Dangerous form of bowel obstruction
Obstructed both proximal and distal (volvolus)
Rapid progression to strangulation
Closed loop obstruction
Clinical presentation of SBO
More prominent symptom with proximal obstructions than distal
Vomiting
More feculent more establish obstruction
Clinical presentation of SBO
Continue passage of flatus and or stool beyond 6-12 hours after onset of symptoms
Obstipation
More on partial than complete obstruction
Clinical presentation of SBO
Abdominal distention most pronounced if the site of obstruction is in the
Distal ileum
Clinical presentation of SBO
Abdominal distention
May be absent if the site of obstruction is in the
Proximal small intestine
Clinical presentation of SBO
Bowel sound may be
Hyper active initially
But minimal bowel sounds in late
Clinical presentation of SBO
Laboratory findings
Reflect intravascular volume depletion
Hemocencentration
Electrolyte abnormalities
Mild leukocytes is is common
Features associated with strangulated SBO include
Tenderness Tachycardia Fever Elevated WBC Acidosis
Diagnosis of SBO
Goals
Mechanical vs ileus
Etiology
Partial vs comple
Simple vs strangulated
Symptoms of small bowel obstructions are
Colicky abdominal pain
Nausea
Vomiting
Obstipation
Diagnosis of SBO
Important elements to obtain on history
Prior abdominal operations
Presence of abdominal disorders
Diagnosis of SBO
PE
Search for
Hernias
Abdominal scars
Diagnosis of SBO
LABS
Full labs
Normal at initial stage
Progression
Leukocytosis
Hemocencentration
Electrolyte abnormalities
Diagnosis of SBO
The stool should be checked for gross or occult blood
Presence of strangulation
Diagnosis of SBO
Confirmed by
Radiographic examination
Diagnosis of SBO
Abdominal series of Radiographic evaluation
Abdomen - supine
Abdomen - upright
Chest - upright
Diagnosis of SBO
Radiographic
Triad
Dilated stool bowel loos >3 cm
Air fluid levels
Paucity of air
Diagnosis of SBO
Radiographic
Sensitivity range from
70-80%
Diagnosis of SBO
Radiographic
Specificity is low because
Mimic small bowel obstruction
Diagnosis of SBO
CT scan
Sensitivity and specificity
Sensitive - 80-90%
Specific - 70-90%
Diagnosis of SBO
CT scan
Findings
Discrete transition zone, dilation of bowel proipximally, decompression distally
Intra luminal contrast that dose not pass beyond transition zone
Colon containing little gas or fluid
Closed loop obstruction
CT scan
Is suggested by the presence of
U shaped or C shaped dilated bowel loop
Closed loop obstruction
CT scan
Depend on 2 things
Length of bowel segment
Orientation of the loop
Closed loop obstruction
CT scan
If we have a short closed loop oriented with the plane of imaging, we will see a
U or C shaped loop of bowel
Strangulated obstruction
CT scan
The cause of this radiologic finding was intestinal ischemia
Patient was taken emergently to the operating room
Intestinal pneumatosis
Limitation of CT scan
Detection of grade or partial small bowel obstruction
Low sensitivity
Other limitation of CT scan
Subtle transition zone may be difficult to identify in the
Axial images obtained during CT scan
Standard small bowel series
Although barium can be used water soluble contrast agents, such as _____________ should be used if the possibility of intestinal perforation exists.
Gastrografin
An x ray examination of the small intestine that looks at how the liquid contrast material moves through the small intestine
Enteroclysis
Enteroclysis
Double contrast technique used for better assessment of
Mucosal surface and detection of small lesions
Enteroclysis
200 - 250 ml of barium followed by 1-2 L of a solution of ___________ in water is instilled into the proximal jejeunum via a___________
Methylcellulose
Long nasoenteric catheter
Treatment of SBO
Trial of non operative mangy
NPO
Isotonic fluid
NGT
Foley catheter
Treatment of SBO
May be necessary to assist with fluid management, particularly in patients with underlying cardiac disease.
Central venous or pulmonary artery catheter monitoring
Treatment of SBO
Given by some because of concerns that bacterial translocation may occur in the setting of small bowel obstruction;
Broad spectrum antibiotics
Treatment of SBO
Standard therapy for complete SBO has been
Surgery
Treatment of SBO
The goal is
Operate before the onset of irreversible ischemia