B&B: GI Anatomy

mesenteric ischemia diagnosis

-PE: pain out of proportion to exam findings -mild tenderness -no rebound tenderness -occult blood in stool -elevated WBC, lactate and acidosis

arteries supplying blood to stomach

-all from celiac trunk -left gastric: contributes to right gastric and gastroduodenal -common hepatic: branches to proper hepatic and gastroduodenal -right gastric comes off proper hepatic -left gastroepiploic comes from splenic -right gastroepiploic off gastroduodenal -short gastric off the splenic

retroperitoneal structures

-aorta -IVC -head and body of pancreas -kidneys -2nd and 3rd portions of duodenum -ascending, descending colon -part of rectum

arcades and vasa recta

-arcades: anastamoses of ileal/jejunal arteries -vasa recta: arteries extending from arcardes

watershed areas of colon

-areas of colon located between major vessels -at risk for ischemia in shock/hypoperfusion -often ischemic in ICU patients due to hypotension and pressors -splenic flexure: small branches -rectosigmoid junction: supplied by narrow branches of IMA

retroperitoneal bleeding

-blood visible on CT scan -many causes -often a complication of surgical procedures

SMA syndrome

-bowel obstruction -SMA courses over distal 1/3 of duodenum -mesenteric fat keeps SMA away from duodenum -if pressed downwards obstruction of SMA happens -occurs in patients with recent massive weight loss due to shrunken fat pads

ulcers and erosions of GI tract

-breakdown of GI tract lining -dyspepsia, bleeding -erosions include mucosa only -ulcers include submucosa and muscularis mucosa

abdominal collateral circulation

-celiac trunk and SMA: superior and inferior pancreaticoduodenal arteries -SMA-IMA: marginal artery of drummond branches from middle colic (SMA) and left colic (IMA) arteries -IMA-iliac: occurs in rectum, superior rectal (IMA) merges with middle rectal (iliac) -dual circulation means rectal ischemia from occlusion is rare

abdominal aorta branches

-celoac trunk -SMA -renal arteries -testicular/ovarian -IMA -splits into common iliacs that split into internal and external

pringle's maneuver

-clamp on hepatoduodenal ligament -used to control liver bleeding -if bleeding continues its from IVC or hepatic vein

main branches of celiac trunk

-common hepatic: rightmost -splenic: leftmost -left gastric: gives off esophageal branch

GI submucosa

-connective tissue -contains Meissner's plexus (submucosal plexus) -correlated with Hirschsprung's disease

hepatoduodenal ligament

-connects liver to duodenum -found on free border of lesser omentum -contents -proper hepatic artery -portal vein -common bile duct

intraperitoneal structures

-covered by mesentery/visceral peritoneum -stomach -appendix -liver -tail of pancreas -spleen -1st part of duodenum, jejunum, ileum -transverse and sigmoid colon -part of rectum

pectinate line

-dentate/anocutaneous line -part of anal canal -above line: hindgut derived columnar epithelium similar to digestive tract -below line: stratified squamous epithelium similar to skin derived from protoectoderm

causes of mesenteric ischemia

-embolism (most common) -often cardiac origin: LV thrombus, LV appendage thrombus -affects jejunum via SMA -arterial thrombosis: atherosclerotic site -venous thrombosis: venous clot causes resistance to flow out of mesentery -occurs with hypercoaguable states or malignancy -non-occlusive ischemia: under perfusion from shock -usually affects watershed areas of colon -often causes ischemic colitis too

GI mucosa

-epithelium absorbs nutrients -lamina propria for support and gastric glands in stomach -muscularis mucosa for motility

short gastric arteries

-five to seven small vessels -branches of splenic artery from celiac trunk -supply fundus and upper cardiac portions of stomach -vulnerable to ischemia if splenic artery is occluded because no dual blood supply -contrast with gastrric and gastroepiploic arteries which are supplied by dual sources

perforated ulcers

-gastric ulcers common lesser curvature -rupture of these causes bleeding from left gastric artery -posterior duodenal ulcers rupture and bleed from gastroduodenal artery

Greater and lesser peritoneal sacs

-greater: entire width of abdomen, from diaphragm to pelvic floor -lesser sac: closed space behind liver stomach and lesser omentum -epiploic/omental/winslow's foramen: opening between two sacs

imperforate anus

-hindgut and ectoderm meet to form anus, failure to do so causes absence of anal opening -commonly associated with GU malformations like renal agenesis and bladder exstrophy -presents with failure to pass meconium or meconium passage via urethra or vagina via fistula

Peyer's patches

-in the duodenum the lymph cells are found in lamina propria -in ilieum they aggregate to form Peyer's patches which are in muscularis mucosa and submucosa

clinical features below pectinate line

-inferior rectal artery off internal pudendal and iliac artery -venous drainage to IVC via inferior rectal vein to internal pudendal to internal iliac -lymph drainage via superficial inguinal nodes -somatic innervation: painful -external hemorrhoids -squamous cell carcinoma more common here (also generally more common than anal adenocarcinoma)

chronic mesenteric ischemia

-intestinal angina -usually in older patients with other vascular disease (PAD risk factors common) -recurrent abdominal pain after eating -fear of eating causes weight loss -sudden worsening on top of history of recurrent pain may suggest acute thrombosis

ischemic colitis

-ischemia of colon -may spontaneously resolve -more dual circulation

mesenteric ischemia

-ischemia of the intestines -ischemia of small intestine most severe -often life threatening

GI muscular layer

-layers of smooth muscle -inner circular, outer longitudinal -between layers lies Auerbach's plexus which is abnormal in achalasia

IMA branches

-left colic -sigmoid -superior rectal

lacteal

-lymphatic channels within villi -important for absorption of fats

digestive tract layers

-mucosa -submucosa -muscle -serosa

Brunner's Glands

-only in duodenum -found in submucosa -produces alkaline fluid which protects from acidic stomach fluid and chyme -increased thickness in peptic ulcer disease

GI slow waves

-oscillating membrane potential of GI smooth muscle -originates in interstitial cells of Cajal -membrane potential slowly rise near threshold -when near threshold action potentials occur -sets maximum number of contraction per unit of time -characteristic for each part of GI -stomach: 3/min -duodenum: 12/min -ileum: 8/min

haustra

-pouches on colon -can be seen on imaging to identify large bowel obstructions

colon histological features

-produces lots of mucous -absorbs fluid and electrolytes -crypts without villi -loss of goblet cells

stomach mucosa

-simple columnar epithelium -gastric pits -gastric glands in lamina propria made of parietal, chief, mucous neck, and G cells

Goblet cells

-small and large intestine -produce mucinogen which is converted to mucus -increase in number from duodenum to ileum where they are most plentiful -not usually found in stomach unless gastritis is present causing intestinal metaplasia

esophagus epithelium

-stratified squamous epithelium -non-keratinized

enteric nervous system

-submucosal plexus: Meissner's, controls secretion and blood flow -Myenteric/Auerbach's plexus: controls motility

clinical features above the pectinate line

-superior rectal artery off IMA -superior rectal vein drains to inferior mesenteric which goes to portal system (swelling during portal hypertension) -lymph drainage to internal iliac nodes -visceral innervation so not painful -internal hemorrhoids -adenocarcinoma most common here

celiac trunk

-supplies foregut -esophagus, stomach, liver, gallbladder, spleen -part of duodenum and pancreas

superior mesenteric artery

-supplies midgut structures -distal duodenum, jejunum, ileum, cecum, appendix -ascending colon, first 2/3 of transverse -descends across pancreas head and duodenum -branches -right colic -ileocolic -ileal and jejunal arteries -middle colic

GI serosa

-surrounds GI tract -layer of surface epithelial cells: mesothelium -secretes lubricating fluid -called the adventitia in retroperitoneal structures, loose connective tissue without lubrication

plicae circulares

-valves of Kerckring/Kerckring folds -valvulae conniventes -folds of mucosa and submucosa -most abundant in jejunum -increase surface area for absorption

small intestine histological features

-villi: mucosa extensions into lumen to increase absorptive surface area -crypts of Lieberkuhn: goblet cell containing pits -microvilli: epithelial cell membrane extensions (teeny tiny)