abdominal viscera

key to understanding abdominal viscera

  • There are three unpaired arteries that arise from the abdominal aorta

  • These three arteries supply derivatives of the foregut, midgut, and hindgut

  • Celiac trunk – Foregut : Arises at the level of the T12/L1

  • Superior mesenteric - Midgut : Arises at the level of the lower border of L1

  • Inferior mesenteric – Hindgut: Arises at the level of L3

foregut derivatives are supplied by branches of celiac trunk

  • Lower esophagus

    Stomach

    Proximal duodenum

    Pancreas

    Liver

    Gallbladder

esophagus

  • 25 cm long muscular tube

  • Passes through the diaphragm at level of T10 vertebra

  • Esophageal hiatus is within the right crus of the diaphragm

  • Terminates at cardiac orifice at level of T11

normal (anatomic) constrictions of esophagus

  • Three constrictions:

    1. Cervical caused by the cricopharyngeus muscle. (not shown)

    2. Broncho-aortic is a compound constriction caused by the aorta and then, left main bronchus.

    3. Diaphragmatic at the esophageal hiatus.

clinical note: pyrosis & GERD

  • GERD

    Gastroesophageal reflux disorder is when an incompetent esophageal valve allows acid to rise into the esophagus causing pyrosis (heartburn).

    In chronic cases, the lining of the esophagus can change or worse, become eroded.

clinical note: barret esophagus

  • Barrett esophagus is a metaplastic change of the esophageal epithelium from stratified squamous to simple columnar epithelium, like that of the intestines, secondary to gastroesophageal reflux.

  • The majority of people with Barrett esophagus are smokers and drinkers.

clinical note: esophageal varices

  • The esophageal veins are a site where the caval venous

    drainage anastomoses with the portal venous drainage.

  • Portal hypertension cause dilation of the esophageal veins. These

    dilated and weakened varices are prone to hemorrhage and is a

    common cause of death in persons with portal hypertension.

    The esophageal veins are a site where the caval venous drainage, azygos vein, anastomoses with the portal venous drainage, left gastric vein.

    Portal hypertension cause dilation of the esophageal veins. These dilated and weakened varices are prone to hemorrhage and are a common cause of death in persons with portal hypertension.

clinical note: hiatal hernia

  • more common in women over 50.

  • may mimic heart pain

stomach

duodenum

  • Name duodenum derived from Latin, duodenum digitorum, meaning 12 finger breadths.

  • About 20-25cm long.

  • Mostly, secondarily retroperitoneal.

    Has 4 parts:

    1. From pylorus of stomach to neck of gallbladder at the level of the L1 vertebra.

    Duodenal cap or ampulla is the site of duodenal ulcers.

    1. Descending part, passes from the neck of the gallbladder inferiorly to the level of L3.

    Lies over the hilum of the right kidney.

    1. Crosses the IVC, aorta and the vertebral column.

    The SMA, which arise at L1, and SMV pass anteriorly over the 3rd part.

    1. Ascending part passes superiorly up to the level of L2 and joins the jejumum.

clinical note: duodenal ulcers

  • Usually occur in the superior part of the duodenum.

    65% occur within the posterior wall within 3cm of the pylorus.

    Most patients have impaired duodenal bicarbonate secretion.

    Believed related to H pylori.

    Posteriorly eroding ulcers can affect the gastroduodenal artery causing severe hemorrhage into the peritoneal cavity.

    Image shows endoscopy of posterior erosion with an exposed branch of gastroduodenal artery.

pancreas

  • mostly posterior to the stomach in the posterior wall of the omental bursa.

  • Head is cradled by the C-shaped duodenum.

  • Neck lies anterior to the SMV and SMA.

  • Body is elongated.

  • Tail passes between the layer of the lienorenal (splenorenal) ligament to the hilum of spleen.

  • Uncinate process lies posterior to SMV and SMA.

blood supply to pancreas

  • Note anterior and posterior pancreaticoduodenal arcades. These vessels provide anastomoses between the celiac trunk via the gastroduodenal artery and the SMA.

  • The major duodenal papilla marks the junction between foregut and midgut derived structures.

clinical note: Obstructive Jaundice Due to Pancreatic Carcinoma

  • Jaundice results from retention of bile.

    Bile pigments stain tissues such as the sclera (whites) of the eyes (icterus)

    Cancer of the head of the pancreas can often compress the bile duct or the hepatopancreatic ampulla (ampulla of Vater).

    Associated with severe back pain.

    Large gallstone can also cause obstructive jaundice and so one must consider this as a possibility in the differential.

spleen

  • note derived from foregut

  • immune organ

  • highly vascular: filters blood

  • located on L sd within greater sac

  • It lies against the 9th-11th ribs

  • Clinical note: Trauma to these ribs can rupture the spleen causing profuse internal bleeding

liver

  • Largest, most vascular organ of abdominal cavity

    Two surfaces

    Diaphragmatic

    Visceral

    Bare area in direct contact with diaphragm

change from fetal to newborn circulation

biliary tree

clinical note: gallstones

  • Gallstones common in Western society

    Twice as likely in female than male

    Americans have extraordinary rate of gallstones

    Can remain asymptomatic

    But, can cause severe epigastric or right upper quadrant pain

    Pain can be referred to right shoulder

    Some authors (your book) say that the right phrenic nerve provides sensory innervation to the gallbladder and that explains referred pain to the right shoulder

    Others (your book in Blue Box) say that irritation of diaphragm explains referred pain

    Large gallstones can cause obstructive jaundice

Magnetic Resonance Cholangiopancreatography (MRCP)

cholelithasis: cholesterol stones

  • Cholesterol gallstones are common in US

    20% of men over 75yo

    35% of women over 75yo

    During reproductive years, women 3x more likely to develop cholesterol gallstones than men

cholelithiaisis: brpown pigment gallstones

  • Brown pigment stones almost always associated with bacterial cholangitis

    Related to increased concentration of unconjugated bilirubin in bile

clinical note: gallbladder syndrome

  • Also known as 5F Syndrome

    Fair – white with a light complexion

    Fat – BMI>30

    Female - XY

    Fertile – one or more children

    Forty or older

    Right shoulder pain with dyspeptic flatulence is the best indicator.

clinical note: referred pain to R shoulder

  • Pain associated with visceral disease and inflammation is often referred to the body wall. This is because visceral afferents enter the spinal cord with somatic afferents.

    Many texts say that the inflamed gallbladder can irritate the underside of the diaphragm, the patient may feel pain in their right shoulder.

    Note: Your book says that the right phrenic nerve directly innervates the gallbladder. There may be some evidence supporting this proposition.

blood supply to foregut derivatives: celiac trunk

  • The pancreaticoduodenal arteries are anatomoses between the celiac trunk and the SMA.

foregut innervation

  • Receives sympathetic innervation from spinal cord segments T6-T9 via the greater splanchnic nerve that contains preganglionic sympathetic axons that synapse predominantly in the celiac ganglion.

    Pain afferents run with the sympathetics.

    Other afferents, such as stretch and distension, run with the parasympathetics (vagus).

midgut derivatives

  • Supplied by branches of the superior mesenteric artery

    Distal duodenum

    Jejunum

    Ileum

    Cecum and appendix

    Ascending colon

    Proximal 2/3rds of transverse colon

  • Relationship of superior mesenteric vein and artery to the uncinate process of the pancreas is an important one.

development

small intestine

  • Small intestine is 7 meters long

    Duodenum, described above, is the initial portion of small intestine

    Jejunum is the upper 2/5ths of the remainder

    Mostly located in left upper quadrant

    Ileum is lower (more distal) 3/5ths

    Mostly in right lower quadrant

    Suspended in abdominal cavity by mesentery (mesentery proper)

jejunum

  • Prominent plicae circulares, intestinal folds

  • blood supply: Less prominent arterial arcades and long vasa recta are a feature of the jejunum

ileum

  • Less prominent plicae circulares, intestinal folds. Has antimesenteric Peyers patches (arrow).

  • blood supply Compared to the jejunum (A), the ileum (B) has more arterial arcades and shorter vasa recta.

blood supply to midgut

  • SMA arises at the level of the lower border of L1.

large intestine or colon

  • 1.5 meters long

    Made up of 7 parts

    Midgut derivatives

    Cecum

    Dilated saccular pouch in right iliac fossa

    Appendix attached about 2cm below ileocecal junction

    Ascending colon

    Proximal 2/3rds of transverse colon

    Hindgut derivatives

    Distal 1/3rd of transverse colon

    Descending colon

    Rectum

    Anal canal

  • Teniae coli (TC): Three distinct bands of longitudinal muscle

  • Haustra coli (HC): Sacculations evident between teniae

  • Omental appendages (OA): Tabs of fat

  • The rectosigmoid junction is at the S3 vertebral level.

midgut innervation

  • Receives sympathetic innervation from spinal cord segments T8-T12 via preganglionic sympathetic axons in the greater, lesser and least splanchnic nerves that synapse in the celiac, aorticorenal, superior and inferior mesenteric ganglia. The postganglionic sympathetic axons follow the arteries to their targets.

    Pain afferents run with the sympathetics.

    Other afferents, such as stretch or distension, run with the parasympathetics (vagus).

hindgut derivatives

  • Supplied by branches of the inferior mesenteric artery

    Distal 1/3rd of the transverse colon

    Descending colon

    Sigmoid colon (rectosigmoid junction at S3)

    Rectum

    Upper part of anal canal

blood supply of hindgut

  • arises at L3

  • At the left colic flexure, there is an anastomosis between the SMA and IMA.

blood supply to rectum & anal canal

  • Superiorly is the terminal branch of the inferior mesenteric artery, the superior rectal.

    The middle portion is supplied by the middle rectal off the internal iliac.

    Inferior portion is supplied by the inferior rectal off the internal pudendal artery.

hindgut innervation

  • Receives sympathetic innervation from spinal cord segments T12-L2 via preganglionic axons in the lesser and lumbar splanchnics that synapse in the inferior mesenteric ganglion. From there, postganglionic sympathetics follow the branches of the inferior mesenteric artery.

    Above a line passing through the middle of the sigmoid colon, pain afferents run with the sympathetics.

    Below a line passing through the middle of the sigmoid colon, all afferents, including pain afferents, travel with parasympathetics to S2-S4.

  • parasympathetic innervation to the descending colon, sigmoid colon, rectum and upper part of anal canal is via the pelvic splanchnics (S2-S4).

portal vein

  • Formed when the splenic and superior mesenteric vein join posterior to the neck of the pancreas at the level of the L2 vertebra. It receives all the blood from the GI tract and spleen.

    The blood from the kidneys does not drain into the portal vein.

clinical note: portal-caval anastomoses

  • The anastomoses of the portal venous drainage with the somatic (caval) venous drainage has important clinical significance.

    There are 4 sites of anastomosis:

    1. Esophageal veins

    Veins of anal canals

    1. Paraumbilical veins

    Paracolic

    • The first and third are often associated with alcohol abuse and cirrhosis.

lymphatic drainage

clinical noteL recto-anal watershed

  • In this region of multiple vascular supply, the lymphatics follow the arteries.

  • The upper portion of the rectum drains along the route of the inferior mesenteric A.

  • The middle And lower portions drains back toward the internal iliac arteries.

  • Below the pectinate line, drainage is to the superficial inguinal nodes.

segmental innervation of GI tract