Foregut Anatomy Notes

Viscera

Foregut Overview

• Viscera 1 lecture focuses on the foregut.

• Viscera 2 lecture covers the midgut and hindgut.

• Foregut starts at the distal esophagus and includes:

  • Distal esophagus

  • Stomach

  • Proximal part of the duodenum

  • Liver

  • Gallbladder

  • Pancreas

• Spleen is grouped with the foregut for this class due to its blood supply association, though it's not technically part of it.

• Main blood supply for foregut organs: Celiac artery.

Celiac Trunk

• One of the three main anterior branches of the abdominal aorta.

• Arises anteriorly from the abdominal aorta, right underneath the diaphragm (around the level of T12 for reference).

• Splits into three main branches almost immediately after arising from the aorta.

• Three main branches of the celiac trunk:

  • Left gastric artery

  • Splenic artery

  • Common hepatic artery

Branches of Celiac Trunk – Detailed

Left Gastric Artery

• Travels to the left side of the body.

• Supplies the stomach.

• Travels in the lesser curvature of the stomach.

• Meets up with the right gastric artery in the lesser curvature.

• The smallest branch of the celiac trunk goes to the lesser curve of the stomach.

Splenic Artery

• The largest branch of the celiac trunk.

• Travels to the left side of the body.

• It is tortuous in appearance.

• Travels superior to the pancreas.

• Gives off several branches as it travels:

  • Short gastric arteries: supply the fundus of the stomach.

  • Left gastro-omental artery: supplies the stomach and greater omentum. Travels on the left side of the greater curvature of the stomach, embedded in the greater omentum.

Common Hepatic Artery

• Travels to the right side of the body.

• Goes to the liver.

• Splits into two terminal branches:

  • Proper hepatic artery

  • Gastroduodenal artery

Proper Hepatic Artery

• Continues to go to the liver.

• Branches of the proper hepatic artery:

  • Supraduodenal artery: supplies the top part of the duodenum. Can be disregarded for the exam according to the instructor.

  • Right gastric artery: travels in the lesser curvature of the stomach to meet up and anastomose with the left gastric artery.

  • After giving off the supraduodenal and right gastric arteries, the proper hepatic continues up to the liver and splits into:

    • Left hepatic artery: supplies the left lobe of the liver.

    • Right hepatic artery: supplies the right lobe of the liver.

      • Cystic artery: a small branch that goes to the gallbladder. Usually comes off the right hepatic artery but sometimes comes off the left.

Gastroduodenal Artery

• Goes to part of the stomach and part of the duodenum.

• Splits into two arteries:

  • Posterior superior pancreaticoduodenal artery

  • Anterior superior pancreaticoduodenal artery

• Both supply the superior part of the pancreas and the duodenum. One is traveling anterior to it, and one is traveling posterior to it.

• Another branch coming off the gastroduodenal artery is the right gastro-omental artery, which travels along the greater curvature of the stomach.

Key Summary of Arterial Supply

• Fundus of the stomach supplied by the short gastric arteries.

• Left lobe of the liver supplied by the left hepatic artery.

Venous Drainage

• Generally, the naming of the veins matches the arteries.

• The flow is different because veins drain to the portal system instead of the inferior vena cava.

• Splenic vein drains the spleen.

  • Landmark: Splenic artery is curly and travels superior to the pancreas. The splenic vein travels on the posterior surface of the pancreas.

• Tributaries to the splenic vein:

  • Short gastric and left gastro-omental veins

  • Pancreatic veins: drain the pancreas.

  • Inferior mesenteric vein: drains into the splenic vein.

• The superior mesenteric vein drains the midgut.

Additional Vein Tributaries to Foregut

• Left and right gastric veins (drain stomach)

• Cystic veins (drain gallbladder)

• Paraumbilical veins (drain abdominal wall)

Formation of Hepatic Portal Vein

• The superior mesenteric vein joins with the splenic vein behind the neck of the pancreas to physically form the hepatic portal vein.

• Supramesenteric vein here joins with splenic vein here to actually physically form the hepatic portal vein right behind the neck of the pancreas.

Lymphatic Drainage

• Foregut structures drain to the celiac lymph nodes.

• Examples: The stomach drains to the celiac lymph nodes.

Innervation of the Foregut

• Autonomic innervation (parasympathetic and sympathetic)

• A plexus of nerves around the celiac trunk and celiac ganglia.

• These branches anterior to the aorta are called the prevertebral plexus.

• Paravertebral ganglia chain (sympathetic chain) is on the sides of the vertebrae.

• Splanchnic nerves connect the paravertebral plexus to the prevertebral plexus.

• Types of Splanchnic Nerves:

  • Thoracic: Greater, lesser, and least splanchnic nerves (sympathetic).

  • Lumbar splanchnic nerves (sympathetic).

  • Sacral splanchnic nerves (sympathetic).

  • Pelvic splanchnic nerves (parasympathetic) - Remember PNP (Pelvic Parasympathetic).

• Sympathetic fibers from the paravertebral sympathetic chain reach the celiac ganglia (foregut) or superior/inferior mesenteric ganglia (mid/hindgut) via splanchnic nerves.

• For the foregut, sympathetic fibers come from the greater splanchnic nerve (T5-T9 levels) to the celiac ganglia.

• Sympathetic stimulation decreases digestion.

• Parasympathetic innervation is via branches from the vagus nerve, which travel through the esophageal hiatus in the diaphragm.

Organ-Specific Details

Abdominal Esophagus

• The very end of the esophagus after passing through the diaphragm and before connecting to the stomach.

• Typically only a couple of centimeters long.

• Passes through the diaphragm at the level of T10 (

Viscera

Foregut Overview

• Viscera 1 lecture focuses on the foregut organs, which are derived from the embryonic foregut.

• Viscera 2 lecture covers the midgut and hindgut, derived from their respective embryonic segments.

• The foregut extends from the distal esophagus to the major duodenal papilla (which marks the transition point to the midgut). It includes:

  • Distal esophagus

  • Stomach

  • Proximal part of the duodenum (first and second parts, up to the major duodenal papilla)

  • Liver

  • Gallbladder

  • Pancreas (head, body, and tail)

• The Spleen is functionally grouped with the foregut in this class due to its blood supply originating from the celiac artery, although embryologically it develops from mesenchymal tissue in the dorsal mesogastrium and is not part of the gut tube.

• The main arterial blood supply for all foregut organs is the Celiac artery.

Celiac Trunk

• The celiac trunk is the first major unpaired anterior branch of the abdominal aorta.

• It arises anteriorly from the abdominal aorta, typically just inferior to the aortic hiatus of the diaphragm, at the level of the upper border of the first lumbar vertebra ($L1$) or the intervertebral disc between $T12$ and $L1$.

• It is a short, thick trunk that immediately branches into its three main arteries, forming a 'tripod' or 'trivium' shape.

• The three main branches of the celiac trunk are:

  • Left gastric artery

  • Splenic artery

  • Common hepatic artery

Each of these branches supplies a specific set of foregut organs and further subdivides.

Branches of Celiac Trunk – Detailed

Left Gastric Artery

• The smallest branch of the celiac trunk.

• It ascends to the left to supply the esophagus and then descends along the lesser curvature of the stomach.

• Supplies the inferior esophagus, the superior part of the lesser curvature, and portions of the anterior and posterior walls of the stomach.

• It travels within the lesser omentum (specifically, the hepatogastric ligament portion).

• It anastomoses with the right gastric artery, which is a branch of the proper hepatic artery, along the lesser curvature of the stomach.

Splenic Artery

• The largest and most tortuous (winding) branch of the celiac trunk.

• It travels horizontally to the left, along the superior border of the pancreas, usually embedded within the splenorenal ligament as it approaches the spleen.

• Gives off several significant branches as it travels:

  • Pancreatic branches: numerous small branches that supply the body and tail of the pancreas.

  • Short gastric arteries: Typically 5-7 small branches that arise near the hilum of the spleen, penetrate the gastrosplenic ligament, and supply the fundus and upper greater curvature of the stomach. They have limited anastomosis, making the fundus vulnerable to ischemia if the splenic artery is ligated proximally.

  • Left gastro-omental (gastroepiploic) artery: Travels along the greater curvature of the stomach, between the layers of the greater omentum. It supplies the greater curvature and greater omentum, anastomosing with the right gastro-omental artery (a branch of the gastroduodenal artery).

Common Hepatic Artery

• Travels to the right side of the body, heading towards the liver.

• It typically passes along the superior border of the head of the pancreas and then anterior to the portal vein.

• It splits into two terminal branches:

  • Proper hepatic artery

  • Gastroduodenal artery

Proper Hepatic Artery

• This artery ascends towards the liver within the hepatoduodenal ligament (part of the lesser omentum), anterior to the portal vein and to the left of the bile duct.

• Before reaching the liver hilum, it typically gives off:

  • Right gastric artery: Travels inferiorly to the lesser curvature of the stomach, where it anastomoses with the left gastric artery, supplying the inferior part of the lesser curvature.

  • Supraduodenal artery: A small, inconsistent branch that may supply the superior portion of the duodenum. Its significance for clinical purposes is often considered negligible for basic anatomy exams.

• After giving off these branches, the proper hepatic artery continues to the porta hepatis and splits into its final functional branches for the liver lobes:

  • Left hepatic artery: Supplies the left functional lobe of the liver (segments $II, III, IV$).

  • Right hepatic artery: Supplies the right functional lobe of the liver (segments $V, VI, VII, VIII$).

  • Cystic artery: A small but clinically important branch that typically arises from the right hepatic artery in the triangle of Calot (cystohepatic triangle). It supplies the gallbladder, and its origin can vary (sometimes from the left hepatic artery or common hepatic artery).

Gastroduodenal Artery

• Descends posterior to the first part of the duodenum before splitting into its terminal branches.

• It supplies parts of the stomach, duodenum, and pancreas.

• Splits into two primary arteries supplying the pancreas and duodenum:

  • Posterior superior pancreaticoduodenal artery: Travels posterior to the head of the pancreas.

  • Anterior superior pancreaticoduodenal artery: Travels anterior to the head of the pancreas.

• Both these arteries supply the superior part of the head of the pancreas and the C-shaped curve of the duodenum, forming anastomoses with their inferior counterparts from the superior mesenteric artery supply.

• Another significant branch coming off the gastroduodenal artery is the Right gastro-omental (gastroepiploic) artery, which travels along the greater curvature of the stomach from right to left, embedded within the greater omentum. It supplies the greater curvature of the stomach and the greater omentum, anastomosing with the left gastro-omental artery.

Key Summary of Arterial Supply for Specific Regions

• Fundus of the stomach is primarily supplied by the short gastric arteries (from the splenic artery).

• The lesser curvature of the stomach is supplied by the left and right gastric arteries.

• The greater curvature of the stomach is supplied by the left and right gastro-omental arteries.

• The left lobe of the liver is supplied by the left hepatic artery.

• The right lobe of the liver is supplied by the right hepatic artery.

• The proximal duodenum and head of the pancreas receive blood from the superior pancreaticoduodenal arteries (from gastroduodenal artery).

Venous Drainage

• Generally, the naming of the veins draining foregut organs matches their corresponding arteries, but their flow differs significantly as they drain into the hepatic portal system, not directly into the inferior vena cava.

• The hepatic portal vein carries nutrient-rich, deoxygenated blood from the gastrointestinal tract, spleen, and pancreas to the liver for processing before it enters the systemic circulation.

Major Veins of Foregut Drainage

• Splenic vein: Drains the spleen. Its landmark feature is its travel along the posterior surface of the pancreas, typically inferior to the splenic artery.

• Tributaries to the splenic vein:

  • Short gastric veins and left gastro-omental vein: Drain parts of the stomach and greater omentum.

  • Pancreatic veins: Drain the pancreas.

  • Inferior mesenteric vein (IMV): Drains the hindgut. It typically drains into the splenic vein (though sometimes it drains into the superior mesenteric vein or at the confluence of the splenic and superior mesenteric veins).

• The superior mesenteric vein (SMV) drains the midgut but is crucial for portal vein formation.

• Left and right gastric veins: Drain the lesser curvature of the stomach directly into the hepatic portal vein.

• Cystic veins: Drain the gallbladder, usually into the right branch of the hepatic portal vein itself or directly into the liver sinusoids.

• Paraumbilical veins: Drain the abdominal wall around the umbilicus and can connect to the portal system, providing a potential portosystemic anastomosis pathway.

Formation of Hepatic Portal Vein

• The hepatic portal vein is formed by the confluence of the superior mesenteric vein and the splenic vein.

• This critical anatomical junction occurs posterior to the neck of the pancreas.

• The portal vein then ascends anterior to the inferior vena cava and posterior to the neck of the pancreas, entering the porta hepatis of the liver.

Lymphatic Drainage

• Lymphatic vessels typically follow the arterial supply.

• Lymph from all foregut structures drains primarily to the celiac lymph nodes.

• These nodes are located around the origin of the celiac artery (preaortic lymph nodes).

• From the celiac lymph nodes, lymph then drains into the cisterna chyli and ultimately into the thoracic duct.

• Examples: Lymph from the stomach, liver, spleen, and pancreas drains to the celiac lymph nodes.

Innervation of the Foregut

• The foregut receives dual autonomic innervation: parasympathetic and sympathetic.

• These nerves form a complex network known as the celiac plexus (or solar plexus), which surrounds the celiac trunk and its branches.

• The celiac plexus contains the celiac ganglia, which are large paired sympathetic ganglia.

• Prevertebral plexus: This refers to the network of nerves and ganglia located anterior to the abdominal aorta (e.g., celiac, superior and inferior mesenteric plexuses).

• Paravertebral ganglia (sympathetic chain): These are chains of sympathetic ganglia located on either side of the vertebral column.

• Splanchnic nerves: These are nerves that carry autonomic fibers (both preganglionic sympathetic and visceral afferent fibers) from the sympathetic chain or vagus nerve to the prevertebral plexuses and ultimately to the viscera.

Types of Splanchnic Nerves

• Thoracic Splanchnic Nerves (Sympathetic preganglionic):

  • Greater splanchnic nerve: Arises from $T5-T9$ or $T10$ spinal cord levels. Carries preganglionic sympathetic fibers that synapse in the celiac ganglia, innervating foregut structures.

  • Lesser splanchnic nerve: Arises from $T10-T11$ spinal cord levels. Synapses in the superior mesenteric ganglia (innervates midgut).

  • Least splanchnic nerve: Arises from $T12$ spinal cord level. Synapses in the renal plexus (innervates kidneys).

• Lumbar splanchnic nerves (Sympathetic preganglionic): Arise from $L1-L2$ spinal cord levels. Synapse in the superior/inferior mesenteric ganglia.

• Sacral splanchnic nerves (Sympathetic postganglionic): Originate from the sacral sympathetic trunk and contribute to pelvic plexuses.

• Pelvic splanchnic nerves (Parasympathetic preganglionic): Arise from $S2-S4$ spinal cord levels. Crucial for parasympathetic innervation of the hindgut and pelvic organs. A helpful mnemonic is "PNP" (Pelvic = Parasympathetic).

Sympathetic Innervation of the Foregut

• Preganglionic sympathetic fibers for the foregut originate from cell bodies in the intermediolateral cell column of the spinal cord (T5-T9/T10 levels).

• These fibers exit via ventral roots, enter sympathetic trunks, and then pass through without synapsing to form the greater splanchnic nerve.

• The greater splanchnic nerve travels inferiorly to synapse on postganglionic neurons located within the celiac ganglia (prevertebral ganglia).

• Postganglionic fibers then travel along arterial branches to innervate the foregut organs.

• Effect of sympathetic stimulation: Generally inhibitory to digestion – causes vasoconstriction, decreases glandular secretion, and reduces gastrointestinal motility. It prepares the body for “fight or flight” responses, diverting blood away from the digestive tract.

Parasympathetic Innervation of the Foregut

• Preganglionic parasympathetic fibers for the foregut are primarily carried by the vagus nerve (cranial nerve X).

• The vagus nerve descends through the thorax and passes into the abdomen via the esophageal hiatus of the diaphragm (at approximately T10 level) as the anterior and posterior vagal trunks.

• These preganglionic fibers travel to the various foregut organs and synapse directly on postganglionic neurons located within or very close to the walls of the target organs (intramural ganglia).

• Effect of parasympathetic stimulation: Generally stimulatory to digestion – promotes glandular secretion, increases gastrointestinal motility, and enhances blood flow to the digestive organs, facilitating "rest and digest" functions.

Organ-Specific Details

Abdominal Esophagus

• The very distal portion of the esophagus, after it passes through the esophageal hiatus of the diaphragm and before it connects to the stomach.

• It is typically only a couple of centimeters long.

• Passes through the diaphragm at the level of T10 (T10T10).

• Blood Supply: Receives arterial supply from esophageal branches of the left gastric artery (from the celiac trunk) and the inferior phrenic arteries.

• Venous Drainage: Drains into the left gastric vein (part of the portal system) and also into the azygos vein (systemic system), forming a clinically important portosystemic anastomosis.

• Lymphatic Drainage: Follows arterial supply to celiac lymph nodes.