GI Tract: Liver, Gallbladder, Pancreas, Spleen – Anatomy Notes

Liver, Gallbladder, Pancreas, Spleen – Anatomy Review (GI Tract)

• Overview

  • The liver is part of the digestive system and serves as one of the two main accessory organs to the GI tract (the other being the pancreas).
  • In specimens, expect to see liver lobing and landmarks used to orient left vs right and caudal-oriented features.

• Orientation and landmarks for the liver

  • Lobes and fissures resemble subdividing “crepts” similar to lung lobes but do not extend completely through the liver.
  • Determine left vs right by how the liver sits in the body; tips of the lobes face caudal.
  • Vena cava is a large blue vessel that sits dorsally; in the cat model it is clearly labeled as the vena cava.
  • On the cat, left and right lobes are distinguishable: left side contains a larger left lateral lobe and a left medial lobe; right side contains a large right medial lobe and a right lateral lobe.
  • The quadrate lobe is located between the left medial lobe and the gallbladder (between the quads and the gallbladder).
  • The gallbladder appears as a shriveled green-like structure.
  • Caudate lobe is on the caudal surface, closest to the GI tract, and is deep within the liver.
  • The caudate lobe forms a bow-tie configuration with the lesser omentum passing between its two parts.
  • Renal (kidney) impression: a depression on the caudate lobe where the right kidney sits against the liver.
  • In plastinated dog liver models, the same general arrangement is visible, helping with size comparison between species.

• Gallbladder presence across species

  • Most species have a gallbladder, but large animals (e.g., horses) do not.
  • Some pocket pets (e.g., rats) also lack a gallbladder.
  • The gallbladder location is typically between the left medial lobe and the quadrate lobe in small animals.

• Pancreas and pancreatic ducts

  • The pancreas is another key GI accessory organ; its enzymes must reach the small intestine (duodenum) for digestion.
  • In small animals, the pancreas has a boomerang shape with a characteristic right-angle orientation.
  • Right lobe of the pancreas lies along the duodenum.
  • Left lobe of the pancreas lies along the backside of the greater curvature after reflecting the greater omentum.
  • The two lobes of the pancreas run along ducts that merge with the biliary ducts to empty into the duodenum.
  • The pancreatic ducts and bile ducts join and empty into the duodenum at a common entry point.
  • The duodenum is the first part of the small intestine and is located on the right body wall just after the stomach (pylorus).
  • The ducts drain into the duodenum in close proximity to where the stomach empties into the small intestine.
  • The pylorus is the distal end of the stomach and opens into the duodenum.

• Digestive tract context and functional flow

  • From the stomach, chyme enters the duodenum via the pylorus.
  • The duodenum is the site where protein digestion and carbohydrate digestion begin (via pancreatic enzymes and bile).
  • Bile ducts (from the liver via the gallbladder) and pancreatic ducts empty into the duodenum, sharing a short distal segment before entering the lumen.
  • The liver’s and pancreas’ secretions act together to emulsify fats, digest proteins and carbohydrates, and optimize nutrient absorption.

• Falciform ligament and abdominal landmarks

  • The falciform ligament is the membrane seen on the cranial edge of the liver, running from the diaphragm to the liver and extending down toward the umbilicus (belly button).
  • When the ribs are reflected or the diaphragm is peeled back, the falciform ligament becomes visible and helps orient the liver within the abdominal cavity.

• Greater omentum, spleen, and pancreas relationships

  • The greater omentum is reflected to access underlying organs and serves as a landmark for locating the pancreas.
  • The spleen lies embedded on the left side within the greater omentum.
  • Reflection of the greater omentum helps locate the left lobe of the pancreas and provides context for the liver’s left side anatomy.
  • The spleen’s position and relation to the greater curvature of the stomach contribute to identifying the pancreas and surrounding structures.

• Species-specific notes and exam relevance

  • In both small animals and dogs, the liver organization follows a consistent left/right pattern, with distinct lobes named as left lateral, left medial, quadrate, caudate, right medial, and right lateral.
  • The caudate lobe commonly shows a renal impression on its surface due to proximity to the right kidney.
  • Plastinated specimens are used to demonstrate size differences and to practice identifying lobes and landmarks in a controlled context.

• Quick reference of key terms

  • Vena cava: the large dorsal vessel carrying venous blood to the heart.
  • Gallbladder: stores bile; absent in horses and some pocket pets (e.g., rats).
  • Quadrate lobe: liver section between left medial lobe and gallbladder.
  • Caudate lobe: caudal liver lobe with a bow-tie appearance between lobes and commonly near the kidney.
  • Falciform ligament: liver-to-diaphragm/umbilicus connection.
  • Greater omentum: apron-like fold of peritoneum that helps locate the spleen and pancreas.
  • Duodenum: first section of the small intestine where digestion begins and where ducts enter.
  • Pylorus: distal stomach region that empties into the duodenum.
  • Pancreatic ducts: carry pancreatic enzymes to the duodenum and often join bile ducts.
  • Bile ducts: carry bile from the liver/gallbladder to the duodenum.
  • Renal impression: indentation on the liver where the kidney sits.