Liver: structure and function.

Question 1

Functions of the liver?

Answer 1

-Metabolism:
1.) Carbohydrates.
2.) Fats.
3.) Protein.
4.) Vitamins.
-Detoxification of drugs and toxins.
-Synthesis of bile, cholesterol, and plasma proteins (e.g., albumin, globulin, clotting factors, acute phase proteins, complement proteins, and serum binding/ transport proteins).
-Processing and activation of enzymes.
-Storage of glycogens, fats, copper, iron, and vitamins.
-Removal of bacteria and spent erythrocytes (immunological function).

Question 2

Fat metabolism?

Answer 2

-Oxidising triglycerides to produce energy.
-Synthesis of plasma lipoproteins.
-Synthesis of cholesterol and phospholipid.

Question 3

Carbohydrate metabolism?

Answer 3

-Converting carbohydrates and proteins into fatty acids and triglycerides.
-Regulation of blood glucose concentration by glycogenesis, glycogenolysis, and gluconeogenesis.

Question 4

Protein metabolism?

Answer 4

-Synthesis of plasma proteins, including albumin and clotting factors.
-Synthesis of non-essential amino acids.
-Detoxification of metabolic waste products (e.g., deamination of amino acids and production of urea).

Question 5

Liver?

Answer 5

-Location:
1.) Cranial abdomen between the diaphragm cranially and the stomach and intestines caudally.
2.) Extends across the median plane; the bulk of it is located on the right.
Exception: in ruminants, it is located entirely on the right, because of the rumen.
-Colour: Usually brownish-red.
-Consistency: Fresh liver is soft and friable.
1.) Covered in a fibrous capsule and then visceral peritoneum.

Question 6

Gross Anatomy: Canine and Feline Liver?

Answer 6

-The liver is divided into lobes by fissures that extend inward from the ventral margin.
Left Lobe:
1.) Left lateral lobe.
2.) Left medial lobe.
Right Lobe:
1.) Right lateral lobe.
2.) Right medial lobe.
-Quadrate lobe.
-Caudate lobe (has a caudate process and papillary process).
-The lobes are largely fused in ruminants.
-The papillary process is absent in the pig and the horse.

Question 7

Canine?

Answer 7

-Almost entirely intrathoracic.
-Caudate process contacts the right kidney.

Question 8

Pig?

Answer 8

-Resembles a dog in position and lobation.
-Does not contact the right kidney.

Question 9

Horse?

Answer 9

-No gall bladder.
-Bile is constantly secreted.
-Right lobe contacts the right kidney.

Question 10

Cow?

Answer 10

-Located entirely on the right in an adult.
-The caudate lobe contacts the right kidney.
-Fused lobes.

Question 11

Ligaments of the liver?

Answer 11

-The liver has various ligaments attaching it to the abdomen:
1.) Coronary ligament: Remnants of the ventral portion of the ventral mesogastrium.
2.) Left and right triangular ligament: Remnants of the ventral portion of the ventral mesogastrium.
3.) Falciform ligament: Remnants of the ventral portion of the ventral mesogastrium.
4.) Roung ligament: Remnant of the umbilical vein in the free edge of the falciform ligament.
-The liver is attached to the diaphragm by the coronary ligament which gives rise to:
1.) Left and right triangular ligament: from the diaphragm to the left and right lateral liver lobes, respectively.
2.) Falciform ligament: extends between the liver and the diaphragm and the ventral body wall to the umbilicus.

Question 12

Liver vasculature?

Answer 12

-Hepatic artery (branch of coeliac artery):
1.) Bring nutrients and oxygen for the liver’s consumption.
-Hepatic portal vein (venous supply):
1.) Brings the nutrient-rich blood from the GIT for metabolism in the liver.
-Hepatic veins (venous drainage):
1.) Drain the metabolised nutrients into the caudal vena cava.

Question 13

Portal vein?

Answer 13

-Portal vein collects blood from the stomach, pancreas, intestines, and spleen, and transports ‘functional blood’ to the liver.
-In dogs, the portal vein has four main contributors:
1.) Splenic.
2.) Gastroduodenal.
3.) Cranial Mesenteric vein.
4.) Caudal Mesenteric vein.
-The contributing veins of the portal vein are connected with the veins of the cardio-oesophageal region and of the rectoanal region.
-These constitute alternative routes the blood can take when intrahepatic circulation is impaired (e.g., in the case of liver cirrhosis).

Question 14

Liver histology?

Answer 14

-The liver surface is covered with a fibrous capsule and visceral peritoneum.
-A functional cell of the liver is an epithelial cell called ‘Hepatocyte’, organised in the form of hexagonal hepatic lobules.
-Each lobule has a central hepatic venule at its centre, and portal triad/ tracts at the periphery.
-Each portal triad comprises a hepatic arteriole, a portal hepatic venule, and a bile duct(ule).
-Hepatocytes within a lobule are arranged in thin plates, separated by vascular sinusoids. This allows for absorption of nutrients and secretion of products.

Question 15

Hepatic stellate cells and Kupffer cells?

Answer 15

-Kupffer cells:
1.) Star-shaped macrophages are attached to the inner surface of the hepatic sinusoids.
2.) Important in the defence against bacteria that have penetrated the barrier of the digestive tract.
-Stellate cells:
1.) Pericytes between the hepatic cells and sinusoids.
2.) Store Vitamin A when in quiescent form.
3.) Take up the repair function when the liver is damaged.

Question 16

Gall bladder and bile?

Answer 16

-Gallbladder:
1.) A pear-shaped organ attached to the visceral aspect of the liver.
2.) Stores and concentrates the bile.
-Bile:
1.) Formed by the hepatocytes.
2.) Drains into the hepatic ducts.
3.) Common hepatic duct (the liver) and the cystic duct (from the gallbladder) join to form the bile duct.
4.) Bile duct opens in the duodenum at the major duodenal papilla.

Question 17

Hepatobiliary duct system and Pancreatic ducts?

Answer 17

-In most animals, the bile duct joins the main pancreatic duct before opening into the duodenum (common bile duct).
-The pancreatic duct opens into the duodenum differently for the different species:
1.) Dog, Horse, and Human: separate openings of the common bile duct and (accessory) pancreatic duct.
2.) Cats, Sheep, and Goats: pancreatic and bile ducts share the common opening into the duodenum.
3.) Cattle and Pig: pancreatic ducts fuse to give one pancreatic duct, which remains separate from the bile duct.

Question 18

Bile?

Answer 18

-Bile aids in digestion and lubrication of food as it enters the duodenum.
-Bile contains bile salts, phospholipids, cholesterol, and other lipid-soluble organic substances such as bile pigments (bilrubin).
-Bile acids are produced from cholesterol.
-Primary bile acids get converted to bile salts.
-Bile salts emulsify lipids and are essential for digestion and absorbing dietary fats.

Question 19

Enterohepatic circulation?

Answer 19

-About 95% of the excreted bile salts are reabsorbed in the ileum and returned to the liver via the hepatic portal vein.
-This recycling of bile salts happens many times throughout the day and is called ‘The Enterohepatic circulation’.