2.5 The Spleen, Esophagus & Stomach

The Spleen

The spleen is the largest lymphoid organ, lying in the left upper quadrant of the abdomen beneath ribs 9–11. Its long axis follows the 10th rib. A normal spleen is not palpable below the costal margin; palpable splenomegaly suggests enlargement at least twice normal.

Surfaces and Relations

The spleen has a diaphragmatic surface (convex, smooth, related to the costal diaphragm and the 9th–11th ribs) and a visceral surface (concave, with impressions for neighboring organs):

• Gastric impression (anterior) — contacts the posterior wall of the stomach (fundus).
• Renal impression (posterior) — contacts the left kidney.
• Colic impression (inferior) — contacts the splenic flexure of the colon.
• Pancreatic impression (near the hilum) — the tail of the pancreas touches the splenic hilum.

The splenic hilum transmits the splenic artery and splenic vein, plus lymphatics and nerves. The spleen is suspended by gastrosplenic (carrying short gastric and left gastroepiploic vessels) and splenorenal (carrying splenic vessels and the tail of the pancreas) ligaments.

Vascular Supply

The splenic artery is the largest branch of the celiac trunk. It runs a characteristically tortuous course along the superior border of the pancreas (this tortuosity is a useful identifier on angiography), giving off:

• Dorsal pancreatic artery and pancreatic branches (to the body and tail of the pancreas).
• Short gastric arteries (to the fundus of the stomach).
• Left gastroepiploic artery (along the greater curvature).

It then enters the splenic hilum and divides into segmental branches. The spleen is segmentally supplied, which permits partial splenectomy.

The splenic vein runs below the artery, along the posterior surface of the pancreas, and joins the superior mesenteric vein behind the neck of the pancreas to form the portal vein. Because the splenic vein drains into the portal system, portal hypertension causes splenomegaly and splenic vein thrombosis can cause isolated gastric varices.

Clinical Correlates

• Splenic rupture — blunt left-upper-quadrant trauma (e.g., rib fractures 9–11) can tear the splenic capsule; the spleen's rich blood supply makes hemorrhage rapid. Kehr's sign (referred pain to the left shoulder via diaphragmatic irritation) is classic.
• Splenic vein thrombosis — often from pancreatitis or pancreatic cancer; isolated gastric varices without esophageal varices is the hallmark.
• Accessory spleens (splenunculi) — present in ~10% of people, usually near the hilum; they must be removed during splenectomy for hematologic disease or recurrence may occur.

The Esophagus

The esophagus is a muscular tube ~25 cm long extending from the pharynx (at the level of C6, the cricoid cartilage) to the stomach (the cardiac orifice at the level of T10). It has cervical, thoracic, and abdominal parts.

Course and Constrictions

The esophagus has three classic constrictions where foreign bodies or tumors lodge:

1. At its origin — where the cricopharyngeus (upper esophageal sphincter) constricts it (level of C6).
2. At the aortic and left main bronchus crossing — T4/T5 level.
3. At the diaphragmatic hiatus — the lower esophageal sphincter region (T10).

Sphincters

• Upper esophageal sphincter (UES) — the cricopharyngeus part of the inferior pharyngeal constrictor; skeletal muscle; prevents air entry into the esophagus during breathing.
• Lower esophageal sphincter (LES) — smooth muscle of the distal esophagus, functionally reinforced by the right crus of the diaphragm as it sweeps around the esophageal hiatus. The phrenoesophageal ligament anchors the esophagus to the diaphragm.

LES relaxation is mediated by inhibitory nonadrenergic noncholinergic neurons (nitric oxide and VIP). Failure of LES relaxation is achalasia (loss of inhibitory neurons in Auerbach's plexus); persistent LES incompetence produces gastroesophageal reflux.

The abdominal esophagus is only ~2 cm long. It enters the stomach at the cardiac orifice, where the Z-line marks the squamocolumnar junction. The angle of His (the acute angle between the esophagus and the fundus) acts as a flap valve that limits reflux.

Vascular Supply

• Cervical esophagus — inferior thyroid artery (from the thyrocervical trunk).
• Thoracic esophagus — esophageal branches from the thoracic aorta and the bronchial arteries.
• Abdominal esophagus — left gastric artery (from the celiac trunk) and the left phrenic (inferior phrenic) artery.

Venous drainage connects the left gastric (coronary) vein (portal system) to the esophageal veins (systemic via the azygos), forming the esophageal variceal anastomosis that dilates in portal hypertension and can bleed massively.

The Stomach

The stomach is a J-shaped organ in the left upper quadrant and epigastrium. It has four regions, two curvatures, two surfaces (anterior and posterior), and two orifices.

Regions and Curvatures

• Cardia — surrounds the cardiac orifice where the esophagus enters.
• Fundus — the dome above the cardia, typically gas-filled; visible on an upright x-ray as the gastric bubble.
• Body — the largest portion, between the fundus and the antrum.
• Pylorus — divided into the antrum and the pyloric canal, ending at the pyloric sphincter (thickened circular smooth muscle) that regulates gastric emptying into the duodenum.

The lesser curvature forms the right (superior) border and gives attachment to the lesser omentum (hepatogastric ligament). The greater curvature forms the left (inferior) border and gives attachment to the greater omentum and the gastrosplenic ligament. The cardiac notch (incisura cardiaca) is the angle between the esophagus and the fundus.

Vascular Supply

The stomach's rich dual blood supply along both curvatures makes ischemic infarction rare. The arteries are all branches of the celiac trunk:

The right and left gastric arteries anastomose along the lesser curvature; the right and left gastroepiploic arteries anastomose along the greater curvature. Venous drainage parallels the arteries: the left gastric (coronary) vein drains into the portal vein, providing the principal route for esophageal varices in portal hypertension.

Posterior Relations and the PA-CAT Ulcer Item

The posterior surface of the stomach is related (across the lesser sac) to:

• The pancreas (body and neck),
• The left kidney and left adrenal gland,
• The splenic artery running along the superior border of the pancreas,
• The transverse colon and its mesocolon.

This relation is the anatomical basis for the classic PA-CAT Bulletin of Information, rev. 20240815 Anatomy sample item: a posterior penetrating gastric (peptic) ulcer can erode through the posterior stomach wall into the pancreas (producing pancreatitis with elevated amylase/lipase and mid-back pain), or into the splenic artery (producing sudden, massive upper gastrointestinal hemorrhage), or into the left gastric artery (also producing hemorrhage). The choice among these complications depends on which posterior relation the ulcer reaches — a question that tests knowledge of stomach relations, not just stomach regions.

Anterior penetrating ulcers, by contrast, can perforate into the lesser sac or the greater sac, producing peritonitis and free air under the diaphragm.

Innervation

The stomach receives parasympathetic input from the anterior (left) and posterior (right) vagal trunks (from the esophageal plexus) along the lesser curvature, which give the hepatic, celiac, and gastric branches. The vagus drives acid secretion (via parietal-cell muscarinic and gastrin-mediated pathways) and motor function. Highly selective vagotomy (parietal-cell vagotomy) divides only the gastric branches to the body and fundus, sparing the "crow's foot" branches to the antrum to preserve gastric emptying.

Sympathetic fibers travel with the arteries from the celiac plexus (T6–T9); they mediate visceral pain, which is referred to the epigastrium.

This section ties three organs together through their shared celiac arterial supply and the posterior relations that make posterior ulcers dangerous — exactly the integrative reasoning the PA-CAT samples.