SN5 SHORT NOTE 5M ★ High-yield

Describe the extrahepatic biliary apparatus. Add a note on Calot's triangle and gallstones.

Anatomy · 1st Professional — Pre-Clinical

The Biliary Apparatus

The extrahepatic biliary apparatus comprises the right and left hepatic ducts, the common hepatic duct, the gall bladder and cystic duct, and the bile duct.

The Gall Bladder

Feature	Detail
Capacity	30–50 mL
Parts	Fundus, body, neck; the neck bears Hartmann's pouch, where stones lodge
Surface marking of the fundus	Tip of the right 9th costal cartilage, where the lateral border of rectus abdominis crosses the costal margin
Function	Concentrates bile 5 to 10 times by absorbing water; stores and expels it
Blood supply	Cystic artery, usually from the right hepatic artery
Mucosa	Honeycomb appearance; Rokitansky–Aschoff sinuses are outpouchings

Calot’s Triangle

Boundary	Structure
Superior	Inferior surface of the liver
Medial	Common hepatic duct
Inferior (lateral)	Cystic duct

Contents — the cystic artery, the right hepatic artery, and the cystic lymph node (of Lund)
The cystic artery must be identified within this triangle before it is divided in cholecystectomy

Bile Duct — Parts and Relations

Part	Position	Relations
Supraduodenal	In the free margin of the lesser omentum	In front of the portal vein, to the right of the hepatic artery
Retroduodenal	Behind the first part of the duodenum	In front of the portal vein; the gastroduodenal artery is on its left
Infraduodenal (pancreatic)	In a groove on the back of the head of the pancreas	Compressed by carcinoma of the head of the pancreas
Intraduodenal	Pierces the duodenal wall obliquely	Sphincter of Oddi

Applied Aspects

Gallstones — the five Fs: female, fat, forty, fertile, fair. Cholesterol stones are commonest in the West, pigment stones in India, where haemolysis and infection are common
Murphy's sign — the patient catches their breath on deep inspiration while the right hypochondrium is palpated, as the inflamed gall bladder meets the examining hand
Courvoisier's law — in obstructive jaundice, a palpable gall bladder is unlikely to be due to stones; a chronically inflamed gall bladder is fibrosed and cannot distend, so a palpable one suggests carcinoma of the head of the pancreas
Referred pain to the right shoulder tip occurs when the inflamed gall bladder irritates the diaphragm (C4 via the phrenic nerve)
Obstructive jaundice gives pale stools, dark urine, pruritus, and a prothrombin time correctable by vitamin K
Anatomical variation of the cystic artery and ducts is very common — the reason a systematic dissection of Calot's triangle matters more than memorising a "normal" pattern

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