Abdominal Viscera and Anatomy

Introduction to Abdomen

  • Lecture presented by David J. Wright, Ph.D. from University of Dayton

Abdominal Viscera Overview

  • Focus on the structure and functions of various abdominal organs.

The Liver

  • Definition and Significance:

    • Largest visceral organ of the body (approximately 3 lbs)

    • Skin is technically the largest organ

  • Structure:

    • Soft and fragile

    • Located under the dome of the diaphragm and protected by the thoracic wall (right side only)

  • Cell Composition:

    • Predominantly made up of hepatocytes

    • Hepatocytes are arranged in hexagonal cylinders

  • Blood Supply:

    • Blood is carried directly from the intestines via the hepatic portal vein

    • Functions include nutrient processing and blood detoxification

  • Key Functions:

    • Remove bilirubin (green breakdown product of hemoglobin) and secrete it as bile

      • Bile emulsifies fats for digestion

      • Bacteria modify bilirubin to become brown

  • Liver Surfaces:

    • Two main surfaces:

      • Diaphragmatic (superior) – smooth and dome-shaped, shaped by diaphragm

      • Visceral (inferior) – indented, pressed against nearby organs (esophagus, stomach, duodenum, gallbladder, colon, right kidney)

  • Peritoneum:

    • Covers most of the liver except where reflected

    • Results in some "bare" areas and recesses

    • Reflections act as ligaments

  • Ligaments Associated with the Liver:

    • Falciform ligament (remains of ventral mesentery)

    • Hepatogastric ligament

    • Hepatoduodenal ligament

    • Other smaller ligaments

Liver Lobes

  • Divided by the falciform ligament into:

    • Right lobe

    • Left lobe

    • Two smaller lobes on the right side:

      • Quadrate lobe

      • Caudate lobe

  • Functional Segmentation:

    • Lobes are functionally distinct, which is advantageous in case of trauma/pathology

  • Arterial Supply:

    • Supplied by left and right hepatic arteries

      • Both branches of the hepatic artery proper

      • Branches from the common hepatic artery, itself from the celiac artery

Gallbladder

  • Description:

    • Pear-shaped sac located on the visceral surface of the liver (right lobe)

    • Three parts:

      • Rounded fundus

      • Large body

      • Narrow neck with internal spiral ridges

  • Function:

    • Stores, concentrates, and releases bile

  • Arterial Supply:

    • Cystic artery, a branch of the right hepatic artery

Pancreas

  • Unique Characteristics:

    • Serves as both an exocrine gland (releases digestive juices) and an endocrine gland (releases insulin and glucagon)

    • Posterior to the stomach, primarily retroperitoneal

    • J-shaped with:

      • Head within the “C” of the duodenum

      • Small uncinate process behind the superior mesenteric artery

      • Neck, body, and tail elongated in front of the superior mesenteric artery

  • Duct Systems:

    • Two sets of ducts drain pancreatic juices into the duodenum:

      • Pancreatic duct (large) from neck/body/tail, joining with the bile duct

      • Accessory pancreatic duct (small) from uncinate process

    • Drain into the duodenum at:

      • Major duodenal papilla

      • Minor duodenal papilla

    • Smooth muscle sphincters control the flow

Pancreatic Arterial Supply

  • Comprises the following arteries:

    • Gastroduodenal

    • Dorsal pancreatic

    • Greater pancreatic

    • Pancreaticoduodenal arteries:

      • Anterior superior

      • Posterior superior

      • Anterior inferior

      • Posterior inferior

Pancreatic Cancer

  • Originates mostly from pancreatic exocrine glandular tissues (and their ducts)

  • Symptoms typically appear late, often after cancer has spread (considered a "silent killer")

  • Statistics on pancreatic cancer:

    • Approximately 46,000 people diagnosed per year

    • Approximately 40,000 die per year

  • Symptoms include:

    • Abdominal and back pain

    • Jaundice if the bile duct is obstructed

Biliary Pathway

  • Bile Duct System:

    • Progressively larger ducts merge within the liver into right and left hepatic ducts

    • These merge to form the common hepatic duct

    • Connects with the cystic duct (to/from gallbladder) to form bile duct

    • Travels through the lesser omentum before emptying into the duodenum with the pancreatic duct

  • Gallstones:

    • Affect approximately 10% of the population:

      • Formed from precipitated cholesterol and bile salts (with or without calcium)

      • May lead to deterioration of the gallbladder

      • Symptoms include pain (referred to right shoulder via phrenic nerve) and jaundice if a gallstone blocks the bile duct

Spleen

  • Description and Function:

    • A single rounded/oval organ (approximately 12 cm) flattened against the diaphragm

    • Functions as a lymphoid organ (similar to a giant lymph node) filled with lymphocytes

    • Filters blood of pathogens and old/dying cells (like old red blood cells)

    • Highly vascularized and fragile

    • Positioned in the mesentery between the stomach and posterior abdominal wall, connected by:

      • Gastrosplenic ligament

      • Splenorenal ligament

Abdominal Aorta

  • Overview:

    • Extends from aortic hiatus of diaphragm to vertebrae LIV, dividing into two common iliac arteries

  • Branches of the Abdominal Aorta:

    • Anterior branches:

      • Celiac trunk (supplying the foregut)

      • Superior mesenteric artery (supplying the midgut; central axis of gut rotation)

      • Inferior mesenteric artery (supplying the hindgut)

      • Testicular or ovarian arteries

    • Lateral branches:

      • Renal arteries

      • Middle suprarenal arteries

      • Inferior phrenic arteries

    • Posterior branches:

      • Lumbar arteries

      • Median sacral artery

Gastrointestinal Tract Blood Supply

  • Hepatic Portal System:

    • Blood from the gastrointestinal tract does not return to the heart directly; instead, it goes to the liver via the hepatic portal vein

    • This process allows the liver to detoxify and store nutrients

    • Main tributaries include:

      • Splenic vein

      • Superior mesenteric vein

      • Inferior mesenteric vein

Lymphatic Drainage of the Gastrointestinal Tract

  • Extensive network of lymphatic vessels drains into three main sets of pre-aortic lymph nodes:

    • Celiac nodes

    • Superior mesenteric nodes

    • Inferior mesenteric nodes