Digestive System - Alimentary Glands Flashcards
What are the 3 salivary glands?
Parotid - exclusively serous, largest, only contributes 25% to saliva
Submandibular - mostly serous, contributes 70% to saliva
Sublingual - mostly mucous, serous demilunes present providing 5% saliva
What are the functions of the liver?
Functions;
Production of bile (exocrine) and plasma proteins (endocrine)
Modifies the action of hormones produced in other parts of the body (endocrine-like function)
Breakdown of harmful toxins and substances
Nutrients absorbed in digestive tract are stored in liver.
Describe the organisation of the liver.
Classic hepatic lobule - drains blood from portal vein and hepatic artery to hepatic or central vein
Portal lobule - drains bile from hepatocytes to the bile duct
Hepatic acinus - supplies oxygenated blood to hepatocytes.
What is the liver lobule?
Central vein
Hepatocytes - arranged in plates or cords radiating outward from the central vein
Sinusoids - capillary-like located between the hepatocyte plates. They receive oxygen-rich blood from branches of the hepatic artery and portal vein
Portal triad - supply the liver with oxygen, nutrients, and hormones from the bloodstream and drain bile produced by hepatocytes into the bile ducts
Functions;
Metabolism - detoxifying harmful substances
Bile production - Hepatocytes produce bile
Blood filtration - Sinusoids filter blood coming from the hepatic artery and portal vein
What is the portal lobule?
Portal triad - consists of portal vein, hepatic artery and bile duct
Emphasises the hepatocytes’ exocrine function
Bile produced by hepatocytes is collected by bile canaliculi and ultimately drains into bile ducts within the portal triad, where it is transported out of the liver and into the bile duct system
Blood from the portal vein and hepatic artery enters the liver through the portal triad and is distributed throughout the hepatic sinusoids
What is the acinus?
Spread over 2 adjoining classic lobules
Hepatocytes have different zones depending on distance from portal areas
Zone 1 - hepatocytes closest to portal area, receive blood rich in nutrients + oxygen, cells able to actively synthesise glycogen and plasma proteins
Zone 2 - intermediate region
Zone 3 - furthest from portal area, major site of detoxification, low oxygen + nutrients so susceptible to hypoxia.
Describe blood and bile flow.
Blood and bile flow through sinusoids in opposite directions
Blood flows from portal areas to central vein
Bile flows towards the triads.
Describe the structure and function of the gall bladder.
Function;
Bile storage - diverted into the gallbladder via the cystic duct
Bile concentration - water and electrolytes are reabsorbed, concentrating the bile and increasing its potency
Bile release - when fats enters the duodenum cholecystokinin triggers the gallbladder to contract and release stored bile into the cystic duct.
Bile then flows through the common bile duct into the duodenum, where it aids in the emulsification and digestion of fats
Structure;
Pear-shaped sac located in depression on liver’s postero-inferior surface
Sphincter of Oddi guards entry of bile and pancreatic secretions
What is bile?
Bile is a digestive fluid produced by the liver and stored in the gallbladder
Liquid secreted by hepatocytes containing bile salts, water, electrolytes, cholesterol
Only bile salts have a digestive function emulsification of fats
Bile pigments are breakdown products of haemoglobin from red blood cells and are excreted in bile.
Describe the exocrine function of the pancreas.
Serous acini surrounding small duct lumen
Produce digestive enzymes and release them via ducts into duodenum
Secretin and cholecystokinin - hormone that control release of pancreatic secretions.
Describe the endocrine function of the pancreas.
Islets of Langerhans
Secrete a range of hormones regulating blood sugar levels
Alpha cells – Glucagon
Beta cells – Insulin
Delta cells – Somatostatin
Gamma (PP) cells - Pancreatic polypeptide.
Describe the hepatocyte-sinusoid boundary.
Sinusoids lined with specialized endothelial cells that have large gaps or fenestrations between them.
Hepatocytes are the primary functional cells of the liver and are arranged in plates or cords around the sinusoids.
Space of disse - space between the endothelial lining of the sinusoids and the hepatocytes, allows exchange of substances.
the hepatocyte-sinusoid boundary is a dynamic interface crucial for the exchange of substances and interactions between blood and liver cells
