Spleen and pancreas

Spleen - The Body's Bouncer

• Anatomy: Intraperitoneal organ in LUQ, protected by ribs 9-11. Supplied by splenic artery (from celiac trunk), drains via splenic vein.
• Function: Filters blood and mounts immune responses.
  • Red Pulp: Cords of Billroth with macrophages; removes old RBCs and platelets.
  • White Pulp: Periarteriolar lymphoid sheaths (PALS) and follicles; key for immune surveillance.

• Clinical Correlates:
  • Asplenia: ↑ susceptibility to encapsulated bacteria. 📌 Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis (SHiN).

⭐ Howell-Jolly bodies (nuclear remnants in RBCs) are classic peripheral smear findings in asplenic patients.

Pancreas (Exocrine) - Digestive Juice Factory

• Primary Role: Produces digestive enzymes (as zymogens) and alkaline fluid ($HCO_3^−$) to neutralize stomach acid and aid digestion.
• Anatomy & Ducts:
  • Acinar cells: Secrete enzyme precursors.
  • Ductal cells: Secrete bicarbonate-rich fluid.
  • Main pancreatic duct (Wirsung): Joins common bile duct at the ampulla of Vater.
  • Accessory duct (Santorini): Variable, may open separately into the duodenum.
• Activation Cascade:
  • Duodenal enteropeptidase converts trypsinogen to trypsin.
  • Trypsin then activates other zymogens (e.g., chymotrypsinogen, procarboxypeptidase).
• Hormonal Control:
  • Secretin: Stimulates ductal cells to release $HCO_3^−$.
  • Cholecystokinin (CCK): Stimulates acinar cells to release zymogens.

⭐ In cystic fibrosis, inspissated secretions block pancreatic ducts, causing exocrine insufficiency, malabsorption (steatorrhea), and vitamin A, D, E, K deficiencies.

Pancreas (Endocrine) - Sugar-Control Central

• Islets of Langerhans: Clusters of endocrine cells scattered throughout the pancreas.
  • α cells: Secrete Glucagon (↑ blood glucose). Acts primarily on the liver.
  • β cells: Secrete Insulin (↓ blood glucose) and Amylin. Insulin facilitates glucose uptake into muscle and adipose tissue.
  • δ cells: Secrete Somatostatin, which inhibits both insulin and glucagon release.

• Insulin Synthesis: Preproinsulin → Proinsulin → Insulin + C-peptide.

⭐ C-peptide is secreted in equimolar amounts with endogenous insulin. Its presence can distinguish endogenous insulin production from exogenous insulin administration in cases of hypoglycemia.

Clinical Correlates - When Spleen & Pancreas Go Rogue

• Spleen Issues

  • Splenomegaly: Enlargement from portal hypertension, infections (e.g., EBV), or hematologic disorders. Massive splenomegaly common in myelofibrosis.
  • Splenic Rupture: Most commonly due to trauma. Can occur spontaneously with severe splenomegaly. Presents with shock, peritonitis.
  • Kehr's Sign: Referred pain to the left shoulder (C3-C5 dermatomes) from diaphragmatic irritation after splenic rupture.

• Pancreatic Pathologies

  • Acute Pancreatitis: Autodigestion by prematurely activated enzymes. Causes: 📌 I GET SMASHED. Presents with epigastric pain radiating to the back, ↑ serum lipase & amylase (>3x ULN).
  • Pancreatic Adenocarcinoma: Typically at the pancreatic head, causing obstructive jaundice.

⭐ Courvoisier's Law: A palpable, non-tender gallbladder in a jaundiced patient suggests malignant obstruction (e.g., pancreatic cancer), not gallstones.

High‑Yield Points - ⚡ Biggest Takeaways

• The spleen is an intraperitoneal organ in the LUQ, supplied by the splenic artery from the celiac trunk.
• It functions to filter blood, remove old red blood cells, and is a key site of immune response.
• The pancreas is primarily retroperitoneal, with its head in the C-loop of the duodenum.
• The tail of the pancreas is intraperitoneal and can be injured during splenectomy.
• The celiac trunk and SMA form critical anastomoses to supply the pancreas.