BIOL 221: Liver Location, Organization, and Blood Supply

• BIOL 221 covers the digestive system, focusing on the liver.
• Cristofre Martin is from the Department of Biochemistry at St. George's University.

Liver Location and Organization

• The liver is inferior to the diaphragm and divided into a large right lobe and a smaller left lobe.
• The liver is a major "processing plant" for the body, prioritizing nutrient delivery from the small intestine.

Blood Supply

• The liver receives a "double" blood supply, meaning it has more than one source of blood.
• The hepatic artery delivers oxygenated blood and nutrients.
• The hepatic portal vein delivers nutrients for processing.
• The standard blood path is: heart, arteries, capillaries, veins, then back the heart.
• The portal system's path is: heart, arteries, capillaries, vein, capillaries, vein, then back the heart.
• The hepatic portal vein carries blood from the small and large intestines to the liver.
• This blood is deoxygenated and contains nutrients and toxins.
• The hepatic artery carries oxygenated blood from the heart to the liver

Liver Organization

• Hepatocytes are the liver's basic cells, organized into strands bordering specialized capillaries called sinusoids.
• Blood coming from the portal vein and hepatic artery enters these sinusoids.
• The liver comprises lobules organized around central veins.
• Liver lobules happen to be hexagonal.
• At the corners of the hexagon are portal triads containing a portal vein, hepatic artery, and bile duct.

Sinusoids

• Sinusoids are capillaries with notable large lumens.
• They have endothelial cells that contain large windows and intercellular spaces.
• The basal lamina that is present is discontinuous.
• The conditions of Sinusoids facilitate easy movement into hepatocytes.
• Macrophages, also known as Kupffer cells, are involved in RBC breakdown and phagocytosis of bacteria and foreign bodies, residing around the sinusoids in the liver.

Blood and Bile Flow

• Blood flows from the hepatic artery and portal vein into sinusoids, draining into the central vein.
• Bile, formed in hepatocytes, moves towards bile ducts via intercellular canaliculi, in the opposite direction as the blood.
• Hydatid cysts in the liver can be caused by ingesting eggs from the tapeworm Echinococcus granulosus and can be fatal if untreated.

Liver Functions

• The liver stores glycogen, iron, and vitamins A, D, and B12.
• It maintains blood glucose concentration and functions in lipid metabolism.
• The liver deaminates amino acids to form urea, allowing the remainder to enter glycolysis and the Krebs cycle.
• It synthesizes blood proteins, destroys damaged RBCs and foreign materials, and detoxifies toxic materials like alcohol.
• The liver functions as a blood reservoir, storing approximately 300ml of blood.

Bile Production and Function

• About 800 ml of bile are secreted daily by the liver.
• Bile salts help emulsify fats in the small intestine.
• Bile disperses large fat globules into small, uniform particles to hasten triglyceride digestion by pancreatic lipase.
• Important for the absorption of fat, cholesterol, and fat-soluble vitamins (A, D, E, K).
• Waste products, including bilirubin (from heme breakdown), are eliminated via bile and feces.

Bile Pathway

• Bile starts in the Hepatic duct (A), then the hepatic duct merges with the cystic duct (B) from the gall bladder to form the common bile duct (C), followed by the pancreatic duct (D)to become the hepato-pancreatic ampulla (E).

Gallbladder

• Bile emerges from the liver in the hepatic duct (A).
• The hepatic duct meshes with the cystic duct (B) on its way to the gall bladder to form the common bile duct.
• The common bile duct merges with the pancreatic duct (D) to become the hepato-pancreatic ampulla (E).
• Bile is emptied into the duodenum with bile salts that are reabsorbed by the ileum.

Other info on the Gallbladder

• It is located on the visceral surface of the liver.
• It concentrates and stores bile, which backs up there behind the Sphincter of Oddi (band of muscle around beginning of hepato-pancreatic ampulla).

Bile Secretion

• Bile is a process primarily controlled by two entric hormones, secretin and cholecystokinin (CCK).
• Secretin is produced by cells in the duodenum in response to low pH (digested food and HCl from the stomach).
• Secretin stimulates biliary duct cells to secrete bicarbonate and water, expanding bile volume and increasing its flow into the intestine.
• It also stimulates pepsin release in the stomach to increase food digestion.
• CCK is produced primarily in response to fat entering the small intestine.
• CCK causes the release of digestive enzymes and bile from the pancreas and gallbladder.
• It increases bile production, stimulates gallbladder contraction, and relaxes the Sphincter of Oddi to release bile into the duodenum.
• CCK also inhibits the stomach, slowing gastric emptying for better fat digestion.
• Gastrin stimulates the release of HCl in the stomach.
• Secretin stimulates bile production in the liver.
• CCK stimulates bile release from the gallbladder.
• Secretin and CCK inhibit and slow digestion in the stomach.

Gallstones

• Gallstones are usually by crystallization of cholesterol in the bile.
• As gallstones grow, their passage along the ducts grows more painful.
• Surgery used to be the only source of relief to remedy symptoms.
• Gallstone dissolving drugs can be and Lithotrypsy (shock wave therapy) can break up stones.
• New surgical techniques are less invasive.