Physiology for MRCEM Primary

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Gastro-intestinal physiology


[box type=”download”]  Constituents of a portal triad  Origin and constituents of hepatic bile  Pathway of enterohepatic circulation [/box]

Largest organ of the body, (~1 kg in the adult).
The functions of the liver can be divided into two broad categories.
First, it is involved with the processing of absorbed substances, both nutrient and toxic (metabolism).
Second (exocrine function) :
–(i) the production of bile acids used in the digestion and absorption of fats ;
–(ii) the production of alkaline fluids for the neutralization of gastric acid in the intestines;
–(iii) the breakdown and production of waste products following digestion;
–(iv) the detoxification of noxious substances;
–(v) the excretion of waste products and the detoxification of substances in bile.

The majority of waste metabolites and detoxified substances are excreted from the body in the bile, from the GI tract, or via secretions from the liver into the bloodstream for subsequent excretion by the kidney.
The liver consists of four lobes, with each made of thousands of hexagonal lobules (functional unit).
Each lobule consists of a central vein that eventually becomes part of the hepatic vein.
Surrounding the central vein are single columns of liver cells (hepatocytes) radiating outwards; between the hepatocytes are small canaliculi which drain into the bile duct on the periphery of the lobule.
At each of the six corners of the lobules lies a ‘portal triad’ comprising branches of the hepatic artery, the portal vein and the bile duct.
The bile ducts eventually drain into the terminal bile duct.