Hey all AIPMT Biology Aspirants, learn about structure and function of Liver And Gall Bladder in the given notes.

Liver

• Largest gland in the body and largest internal organ of the body. In an adult human, the liver weighs about 1.5 kg and is the size of a football.
• Located in the upper right section of the abdominal cavity, below the diaphragm.
• It is almost completely covered by visceral peritoneum.
• Divided into two principal lobes—a large right lobe and a smaller left lobe—by the falciform ligament; left lobe is further divided into quadrate lobe and a caudate lobe.
• Structural and functional unit of liver are Hepatic lobules, i.e. lobes of the liver are made up of lobules.

Hepatic Lobule- Structural unit of Liver

• Each lobule contains Hepatocytes (liver cells), Hepatic sinusoids, Stellate reticuloendothelial cells (Kupffer cells), and a central vein.
• Each lobule is covered by a thin connective tissue sheath called the Glisson’s capsule.

• Hepatocytes produce bile that is collected by small ducts called Bile canaliculi. From bile canaliculi, bile passes into bile ductules and then bile ducts. The bile ducts merge and eventually form the right and left hepatic ducts, which unite and exit the liver as the Common Hepatic duct. The common hepatic duct joins the Cystic duct from the gallbladder to form the Common bile duct. From here, bile enters the duodenum of the small intestine to participate in digestion.
• Liver produces bile, which is stored and concentrated in the gallbladder.

• Hepatic sinusoids are highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from branches of the hepatic artery and nutrient-rich deoxygenated blood from branches of the hepatic portal vein. Hepatic sinusoids converge and deliver blood into a central vein.

• Kupffer Cells or Stellate reticuloendothelial cells (or Hepatic macrophages) are fixed phagocytes in hepatic sinusoids, which destroy old white and red blood cells, bacteria, and other foreign matter in the venous blood draining from the gastrointestinal tract.

• Together a bile duct, branch of the hepatic artery, and branch of the hepatic portal vein are referred to as a Portal triad.
• Portal Triads are  located between the lobules, consist of a bile duct, which takes bile away from the liver; a branch of the hepatic artery, which brings O2-rich blood to the liver; and a branch of the hepatic portal vein, which transports nutrients from the intestines.

Gallbladder

• Gall bladder is a pear-shaped muscular sac that is attached to the posterior surface of the liver.
• It stores and concentrates bile by reabsorbing water so that bile becomes a thick, mucus-like material. When needed, bile leaves the gallbladder and proceeds to the duodenum via the common bile duct.
• Bile contribution to digestion in the emulsification of dietary lipids.
• Duct from gall bladder is called Cystic duct, which joins common hepatic duct from liver to form Common bile duct.

Structure of Liver, Gall Bladder and Pancreas with their respective ducts

NOTE: Bile has a yellowish green or olive green color because it contains the bile pigment bilirubin.

• Bile has pH of 7.6–8.6 and consists mostly of water, bile salts, cholesterol, phospholipids (lecithin), bile pigments (bilirubin and biliverdin), and several ions but no enzymes.Principal bile pigment is bilirubin. 
• Bile pigments do not participate in digestion.These are the waste products resulting from the destruction of old RBCs in liver and are ultimately eliminated with the faeces. Bilirubin is derived from heme portion of haemoglobin.
• Stercobilin (breakdown product of bilirubin) gives faeces their normal brown color.
• If the excretion of bile pigments by the liver is blocked, the pigments can accumulate in the blood and cause a yellow staining of the tissues known as jaundice.
• Neonatal jaundice occurs in newborn babies because the liver of a newborn functions poorly for the first few weeks, that disappears as the liver matures. Usually, it is treated by exposing the infant to blue light, which converts bilirubin into substances that kidneys can excrete.