Anatomy and Physiology of the Pancreas

Overview

• The pancreas is a vital organ with dual functions: exocrine and endocrine.
• It is located centrally in the body, surrounded by key anatomical landmarks, making it difficult to image via ultrasound.

Anatomy

Development

• Begins forming around week 4 of embryonic development and starts functioning by week 10.
• Arises from two buds off the duodenal embryonic tube:
  • Dorsal bud: Neck, body, tail
  • Ventral bud: Head and uncinate process

Structure

• Divided into five parts:
  1. Uncinate Process: Wrapped between IVC (posterior) and SMV (anterior).
  2. Head: Surrounded by C-loop of the duodenum. Home to common bile duct groove and gastroduodenal artery.
  3. Neck: Small region between head and body; lies anterior to the portal confluence.
  4. Body: Largest portion, difficult to image due to stomach overlay; lies over the aorta and other structures.
  5. Tail: Extends towards the spleen and is posterior to the kidney.

Ducts

• Duct of Wirsung (Main pancreatic duct): Runs from tail to head, joining with common bile duct.
• Duct of Santorini (Accessory duct): Branches off the main duct, enters duodenum separately.

Vasculature

• Highly vascularized but most vessels are non-visual on ultrasound.
• Gastroduodenal artery: Supplies the head.
• Splenic and superior mesenteric arteries: Supply body and tail.

Variants

• Annular pancreas: Pancreatic tissue forms a ring around the duodenum.
• Ectopic pancreas: Small bits of pancreatic tissue scattered, no ductal connection.
• Agenesis: Partial or complete absence of the pancreas.
• Pancreas divisum: Dorsal and ventral parts do not fuse.

Microanatomy

• Comprised of exocrine (acini cells) and endocrine (Islets of Langerhans) components.
• Acini cells: Produce digestive enzymes.
• Islets of Langerhans: Produce hormones like insulin, glucagon.

Physiology

Exocrine Function

• Acini cells: Produce amylase, lipase, proteases, and bicarbonate.
• Ductal system: Transports enzymes to the duodenum.

Endocrine Function

• Hormones produced: Insulin (lowers blood glucose), glucagon (raises blood glucose), and others.
• Beta cells: Produce insulin; Alpha cells: Produce glucagon.

Ultrasound Appearance

• More echogenic than the liver; should appear homogeneous and smooth.
• Challenges include obscuration by gas or other organs.
• Landmarks: IVC, SMV, portal confluence, aorta, and splenic vein help identify pancreas.

Pancreatic Protocols

• Part of routine abdominal ultrasound; includes measurement and evaluation for tumors, duct obstruction, and pancreatitis.
• Endoscopic ultrasound: More detailed imaging, performed by specialists.
• Patient preparation involves fasting (NPO) for better image clarity.

Tips

• Use the liver as an acoustic window for better visualization.
• Apply pressure to displace bowel gas for clearer images.
• Understand and practice using anatomical landmarks for accurate imaging.