What Is the Hepatic System?
The hepatic system, or hepatobiliary system, includes:
- the liver,
- the gallbladder,
- the cystic duct connecting the liver to the gallbladder,
- the common bile duct formed by the union of the lobar ducts and the cystic duct and opening into the duodenum, the first portion of the small intestine,*
- as well as the various vessels running through it, such as the hepatic artery and its branches, and the portal vein.
The Liver Wears Many Hats
The liver, known in Ancient Greek as ἧπαρ (*hēpar*), is an organ described as accessory to the digestive system. Located in the cranial portion of the abdomen, it lies against the diaphragm and is partially shielded by the ribs. This gland, the largest in the body, consists of 6 lobes.
The liver is indeed a multi-functional organ, with over 300 roles attributed to it.
It plays a role in digestion by secreting bile, which consists of both waste products and secretion products—such as bile salts, for example. This yellowish digestive fluid is essential for lipid digestion and the absorption of vitamins A, D, E, and K.
It detoxifies the body by breaking down numerous toxic molecules into non-toxic or less harmful byproducts that can be more easily eliminated. For instance, ammonia—toxic to nerve cells—is converted into non-toxic urea, which is readily excreted by the kidneys. Medications can also be broken down in the liver, even though the primary route of elimination is renal.
It is within the hepatic cells that vitamins A, B, and D, along with certain minerals—such as zinc, iron, and copper—are stored. The liver also serves as an energy reserve, as it can store carbohydrates in the form of glycogen, which, when needed, is converted back into molecules directly usable by the body’s cells. The same applies to lipids, stored as triglycerides.
Finally, the liver can synthesize blood proteins—such as globulins, albumin, and clotting factors, among others. It also plays a key role in vitamin D activation.
What About the Gallbladder?
This small pouch, nestled in the "gallbladder fossa," has the sole purpose of storing bile produced by the liver. It’s thanks to the signal triggered during meals that the gallbladder contracts, sending bile to the small intestine.
*Cats have an anatomical peculiarity. While in dogs, the bile duct and the pancreatic duct each open separately into the duodenum, in cats, these two ducts merge at the same papilla—the major duodenal papilla. This characteristic makes this species prone to "feline tetrad."
