16 - Pancreas and Liver Microanatomy Flashcards
Describe the endocrine aspect of the pancreas
- islets of langerhan
- only make up 3% of the pancreas
- big and pale staining
- release hormones
Describe the exocrine aspect of the pancreas
- pancreatic acini
- are spherical, smaller, dark staining due to zymogen granules
- release pre-enzymes
- need to be inactive until reach SI/target to avoid pancreatic degradation
- ductal cells also release HCO3-
- fluids and electrolytes
What do the ductal cells of the pancreas release?
Bicarbonate
How is the structure of the salivary glands similar to the pancreas?
The pancreas on histology also as lobules and a CT interlobular septa
Describe the structure of the exocrine pancreas cells?
A tubulo-acinar gland with highly branched ducts (similar to the parotid gland - serous)
Describe the acini of the pancreas?
- the acini contain 5-8 pyramid shaped cells surrounding a lumen
The acinar cells have … nuclei in a … position and …. arranged … to the basal surface
Spherical nuclei in a basal position (like serous acinar cells) and mitochondria arranged perpendicular to the basal surface (i.e. energy to make enzymes)
How are the digestive pancreatic enzymes made in the acinar cells?
The protein secretory products are synthesised in the basal rER, packaged at the golgi and accumulate as zymogen granules at the apical cytoplasm towards the lumen - the acini produce a small amount of enzyme-rich fluid
How do the ducts of the acini begin (i.e. which are the smallest?)
Intercalated ducts insert into the acini.
What do the duct cells of the intercalated ducts produce?
HCO3- and a lagre volume of alkaline fluid (a litre a day)
Describe the order of convergence of the pancreatic cells ducts
Intercalated ducts > intraLOBULAR ducts > interlobular ducts > pancreatic duct > hepatopancreatic ampulla of vater (with common bile duct) > duodenum
What kind of organ is the liver?
Gland - exo and endocrine
What does the liver do to the blood from the gastric and intestinal capillary networks?
Detoxifies and modifies it appropriately. There is a close relationship between the blood and hepatic cells
What is the structural problem of the hepatocytes?
To get blood to and then away from them and tp transport bile away form them into the duodenal lumen
How are the heptocytes arranged?
In columns radiating away from the centre
What is the anatomical/structural division/organisation of the liver?
Hexagonal lobules with a portal area with a portal triad at each corner
Is the liver vascularised?
Yes very
What is livers function?
forming clotting factors/proteins
makes bile acids
detoxifies bloods
What separates the hexagonal lobules of the liver?
CT septa
What runs in the CT septa?
Collagen, nervous tissue etc
What is at the junctions of the CT/corners and what is it filled with?
Portal area (not space as not empty - filled with CT that binds the components of the portal triad
What separates the radiating columns of hepatocytes?
Space filled with BVs (sinusoids)
Hepatic lobule?
Classical anatomical division/unit
- doesn’t reflect functional divisons
What is in the portal area
CT which surrounds and connects the portal triad
What are the 3 structures of the portal triad?
Branches of the …
Portal Vein
Hepatic Artery Proper
Common Bile Duct
How can you tell vein?
- less smooth muscle/thin muscular wall compared to large lumen
- weaker as experience less pressure
- de-oxygenated nutrient rich blood
How can you tell artery?
Thick muscular wall compared to smaller lumen suggesting under higher pressure (systemic)
Oxygenated (i.e. needs to sustain metabolic function as well as filter)
What does the portal vein branch into?
Distributing veins > feed into inlet venules > feed into sinusoids
What else is in the sinusoids?
Hepatic artery feeds straight into sinusoids = mixing of nutrient venous rich and o2 rich blood, drained away from hepatocytes and into central vein
Where does the sinusoid blood drain into?
The central vein in the centre of the hepatic (hexagonal) lobule
How do the sinusoids feed into the IVC?
Sinusoid > intercalated veins > collecting vein > hepatic vein > IVC
What is a liver/hepatic acinus?
It is the functional division of the liver. It forms a diamond shape between two portal triads and 2 central veins
How is a liver acinus formed?
As the nutrient rich blood and the O2 rich blood travels from the portal triad to the central vein, both O2 and nutrients are given off to the hepatocytes as it passes through the sinusoids due to their leakiness. Because of this as the blood moves away from the triad to the central vein both the nutrient and O2 composition/profile of the blood changes and the hepatocytes closest to the vein have differential access to nutrients compared to the hepatocytes at the triad. This forms 3 zones
What are the zones and how are they formed?
The zones are determined by a hepatocytes access to nutrients and O2 i.e. their distance from the central vein or triad. The hepatocytes at the different zones will therefore have different enzyme profiles, different functions, and different sensitivity to disease and pathogens
Diff zones…
- Dif enzyme profile
- Functions
- Sensitivities to pathogens and diseases
What is the sinusoid lined with?
Endothelium/endothelial cells that are fenestrated/holey and has intercellular openings (wide gap between adjacent endothelial cells)
Also are much WIDER and can hold more than 1 RBC
What do the special features of sinusoids achieve?
Fenstrated, intercellular openings, wide
= help to maximise transfer/access to materials from bloodstream to the hepatocytes
Considering the function of hepatocytes, what would you expect the basement membrane between the hepatocyte and endothelial cells to be like?
Not thick CT layer. In the region between the endo cells and adjacent hepatocytes the only structural support we have are RETICULAR fibres. Thinner rather than thick collagen. Structure but not enough to obstruct diffusion
What lies between the hepatocytes and endothelial cells?
Reticular fibres - thinner than collagen so provide structure to sinusoid but don’t obstruct diffusion
What are kuffer cells?
- Macrophage like cells that eat luminal obstructions so there is no obstruction of both blood flow and diffusion
- Keep lumen of sinusoid clean
- anti-bacterial-
- Limit barriers to access to nutrients
What cells keep the lumen of sinusoids clean and free of obstructions?
Kuffer cells
Are the ends/sides of the hepatocytes straight?
No. They have microvillus extensions/microvili to increase the SA for proteins to be studded in the membrane to increase transport of nutrients
What lies between the microvilli and endothelial cells?
- reticular fibres
- the lymphatic SPACE is called the SPACE OF DISSE
- this space contains stellate cells
What is the space of disse and what does it contain?
Lymphatic space between the microvili of the edges of the hepatocyte and the endothelial cells. Contain stellate cells
What are stellate cells?
Found in the space of Disse
Are fat storing cells
Have a role in vitamin A metabolism
Become activated in disease states as they have a role in fibrosis (make more collagen). Means that the normally and specialised thin barrier is thickened and this can obstruct normal liver function
Is the liver cell renewal rate low or high?
High cell turnover rate/division/renewal because it has an important function so actively replacing. Often see bi-nucleate/polyploid hepatocytes under microscope
When do the organelles of the hepatocyte differ?
Depending on if they are in zone 1,2,3 as have different functions, needs and profiles.
How is bile transported?
Through membranous distensions that create spaces called cannuliculi. Sealed off from adjacent areas through occluding junctions (stops bile leaking between hepatocytes)
Where are canuliculi located?
Course around outside of hepatocytes. Found between adjacent hepatocytes of the same column
Describe the passage of bile?
Through the cannuliculi which converge > bile ductiles > bile duct (of portal triad)
Where do blood and bile flow?
Blood - triad to central vein to form liver acini
Bile - from central vein to triad forming a portal lobule
What is a portal lobule?
Formed by the movement of bile from the central vein to the bile duct at the portal triad trough the bile canuliculi and bile ductiles.
How can you tell the bile duct?
NOT lined with simple squamous endothelial cells but cuboidal epithelial cells
