Lecture 9: Microanatomy of GI Glands Flashcards
list the accessory organs of the GIT
pancreas, gallbladder, salivary glands, liver
what type of tissue is present in the liver
mostly epithelial, very little CT
what vessels deliver blood to liver
how do these vessels enter the liver
hepatic artery (30%) - O2 rich hepatic portal vein (70%) - nutrient rich
vessels enter at Porta Hepatis (hilum), divide into smaller branches, and end in portal areas
what vessel drains the liver and how
hepatic vein empties deoxy nutrient rich blood into IVC
what are the 5 main functions of the liver
- exocrine - prod of bile
- endocrine - prod of plasma proteins
- process and store nutrients absorbed in GIT
- degrades toxins, drugs, alcohol etc
- destroys worn out RBC
what two ways liver morphology can be interpreted
- lobule - based on histology
2. acinus - based on function
name the 4 main features of a liver lobule
- peripheral portal areas
- vascular sinusoids
- hepatocytes
- central vein
what is the function of vascular sinusoids
- drains blood entering at portal area
- fenestrated so nutrients/solutes/toxins can diffuse into hepatocytes as blood flows through
- blood drains into central vein
- all central vv. drain into hepatic v. then into IVC
describe the function of hepatocytes
- make bile
- process and store diffused material from blood
how are hepatocytes arranged
- polygonal aggregation of cells
- hepatocytes arranged in irregular radial cords
- radiate out from central vein
what structures are present in the portal area
- small branch of hepatic artery
- small branch of hepatic portal vein
- bile duct
- lymphatic vessel
how is bile drained from hepatocytes
bile moves from cell to cell through specialised channels called bile canaliculi, then drains into bile duct in portal area
in histology how would you differentiate between a bile duct and branch of septic artery within the portal area
bile duct - simple cuboidal epithelium
hepatic a. - simple squamous epithelium
describe the arrangement of a liver acinus
- spread over two adjoining lobules
- hepatocytes divided into zones
- hepatocytes have diff. metabolic activity depending on zone
- zone 1 closest to portal area and zone 3 closest to terminal hepatic venule (central vein)
describe the difference in metabolic activity of hepatocytes for each zone of an acinus
zone 1
- receive O2 and nutrient rich blood
- cells able to actively synthesise glycogen and plasma proteins
zone 2 - intermediate region that receive second class blood
zone 3
- blood low in O2 and nutrients
- major site of alcohol and drug detoxification
- most susceptible to hypoxia and toxic damage
describe the hepatocyte-sinusoid boundary (what features are present)
- Kupffer cells –> macrophages on inner wall of sinusoid
- space of Disse –> plasma filters here to make intimate contact with microvilli of hepatocytes
- bile canaliculus –> intercellular channels sealed by tight junctions
how is the pancreas divided
divided into lobules by CT septa with both endocrine and exocrine function
what is the exocrine function of the pancreas
- serous acini and branched ducts
- prod. enzymes for digestion of food (trypsinogen, lipase, amylase)
- produced in inactive form to avoid self digestion
- small ducts lead to main pancreatic duct that enters duodenum
what is the endocrine function of the pancreas
- islets of Langerhans and blood caps
- islet cells prod. hormones (insulin, glucagon, somatostatin, pancreatic polypeptide)
what histological feature differentiates pancreas from parotid gland
- islet of Langerhans
describe an Islet of Langerhans
compact mass of epi cells pervaded by complex network of capillaries
name the 4 principal cell types present in each islet and the hormone they secrete
- alpha cells - glucagon
- beta cells - insulin
- delta cells - somatostatin
- f cells - pancreatic polypeptide
describe the function of somatostatin secreted by delta cells in pancreas
inhibits insulin and glucagon secretion at local islet level
describe the function of pancreatic polypeptide secreted by f cells in the pancreas
- inhibits enzyme secretion from pancreatic exocrine glands
- reduce secretion of bile from gallbladder
describe the direction of flow of blood and bile within and liver lobule
- blood from rim to centre through vascular sinusoids
- bile from centre to rim through canaliculi
