Lecture 4 Notes - The Liver Structure and Function PDF

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Dr Carol Rea...

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Human Anatomy and Physiology with Clinical Correlations 2 Lecture 4: The Digestive System – Liver Digestive System  Two groups of organs o Alimentary canal (gastrointestinal or GI tract)  Mouth to anus  Digests food and absorbs fragments  Mouth, pharynx, oesophagus, stomach, small intestine and large intestine o Accessory digestive organs  Teeth, tongue, gallbladder  Digestive glands  Salivary glands  Liver o Pancreas Blood Supply: Splanchnic Circulation  Branches of aorta serving digestive organs o Hepatic, splenic, and left gastric arteries o Inferior and superior mesenteric arteries  Hepatic portal circulation o Drains nutrient-rich blood from digestive organs o Delivers it to the liver for processing Duodenum  Curves around head of pancreas; shortest part – 25cm  Bile duct (from liver) and main pancreatic duct (from pancreas) o Join at hepatopancreatic ampulla o Enter duodenum at major duodenal papilla o Entry controlled by hepatopancreatic sphincter The Liver and Gallbladder  Accessory organs  Liver o Many functions; only digestive function  bile production  Bile – fat emulsifier  Gallbladder o Chief function  bile storage Liver 

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Falciform ligament o Separates larger right and smaller left lobes o Suspends liver from diaphragm and anterior abdominal wall Round ligament (ligamentum teres) o Remnant of foetal umbilical vein along free edge of falciform ligament

Liver: Associated Structures  Lesser omentum anchors liver to stomach  Hepatic artery and vein enter at porta hepatis  Bile ducts o Common hepatic duct leaves liver o Cystic duct connects to gallbladder

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Bile duct formed by union of common hepatic and cystic ducts

Liver: Microscopic Anatomy  Liver lobules o Hexagonal structural and functional units o Composed of plates of hepatocytes (liver cells)  Filter and process nutrient-rich blood o Central vein in longitudinal axis  Portal triad at each corner of lobule o Branch of hepatic artery supplies oxygen o Branch of hepatic portal vein brings nutrient-rich blood o Bile duct receives bile from bile canaliculi  Liver sinusoids – leaky capillaries between hepatic plates  Stellate macrophages (hepatic macrophages or Kupffer cells) in liver sinusoids remove debris and old RBCs  Hepatocytes – increased rough and smooth ER, Golgi, peroxisomes, mitochondria  Hepatocyte functions o Process bloodborne nutrients o Store fat-soluble vitamins o Perform detoxification o Produce ~900 ml bile per day Liver 

Regenerative capacity o Restores full size in 6-12 months after 80% removal o Injury  hepatocytes  growth factors  endothelial cell proliferation

Homeostatic Imbalance  Hepatitis o Usually viral infection, drug toxicity, wild mushroom poisoning  Cirrhosis o Progressive, chronic inflammation from chronic hepatitis or alcoholism o Liver  fatty, fibrous  portal hypertension  Liver transplants successful, but livers scarce Bile 

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Yellow-green, alkaline solution containing o Bile salts – cholesterol derivatives that function in fat emulsification and absorption o Bilirubin – pigment formed from heme  Bacteria break down in intestine to stercobilin  brown colour of faeces o Cholesterol, triglycerides, phospholipids, and electrolytes Enterohepatic circulation o Recycles bile salts o Bile salts  duodenum reabsorbed from ileum  hepatic portal blood  liver  secreted into bile

The Gallbladder  Thin-walled muscular sac on ventral surface of liver  Stores and concentrates bile by absorbing water and ions  Muscular contractions release bile via cystic duct, which flows into bile duct  High cholesterol; too few bile salts  gallstones (biliary calculi)

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Obstruct flow of bile from gallbladder  May cause obstructive jaundice Gallbladder contracts against sharp crystals  pain Treated with drugs, ultrasound vibrations (lithotripsy), laser vaporisation, surgery

Metabolic Role of the Liver  Hepatocytes o ~500 metabolic functions o Process nearly every class of nutrient o Play major role in regulating plasma cholesterol levels o Store vitamins and minerals o Metabolise alcohol, drugs, hormones and bilirubin Functions of the Liver  Protein carbohydrate and lipid homeostasis  Reticuloendothelial system – breakdown of red cell  Metabolism, detoxification and excretion of endogenous and exogenous compounds  Excretion of water soluble end-products from the metabolism of nutrients and toxins and of digestive aids such as bile acids into the biliary tree  Synthesis of plasma proteins including serum albumin and many of the clotting factors and natural anticoagulants Biochemical Functions  Hepatic Excretory Function  Bilirubin  Bile acids – facilitate the hepatic excretion of cholesterol and solubilisation of lipids for intestinal absorption  Reabsorption occurs in the terminal ileum – referred to as enterohepatic circulation  Primary bile acids are those produced by the liver, secondary bile acids are formed by the action of bacteria in the gut upon these Metabolism of Haem  Red blood cells and haem from other sources are engulfed by cells of te reticuloendothelial system  Globin is recycled or converted into amino acids  Haem is oxidised, with the harm ring being opened by haem oxygenase  Produced biliverdin, Fe3+ and CO  Biliverdin reductase produce bilirubin Bilirubin Metabolism  In hepatocytes, UDP glucuronyl transferase adds 2 equivalents of glucuronic acid to bilirubin to produce the more water soluble, bilirubin diglucuronide derivative  Facilitates its excretion with the remainder of the bole as the bile pigments  Intestinal bilirubin is acted on by bacteria to produce urobilinogens and urobilins, that are found in the faeces  Some urobilinogen and urobilin is reabsorbed and excreted in urine Jaundice  Yellow discolouration of the skin or sclera of the eye  Due to increased bilirubin in plasma .40umol/l (normally...