L5 Histology of endocrine pancreas - Islets of Langerhans Flashcards
What are the secretory parts of the pancreas ?
- Exocrine :
- secrete different hormones that help in digestion - Endocrine :
- islets of langerhan
- secretes hormones to the circulation
Where you find the islets ?
Everywhere but more in the tail
What are the parts of the pancreas ?
- Head - attached to the c curve of duodenum ( can’t be separated )
- Neck
- Body
- Tail - near the spleen
It is a retropretoinum organ
What are the ducts of pancreas ? What is there organization ?
- Main duct of wirsung
- Accessory duct of santorini
Accessory mainly drain the head of pancreas to the main duct
The main duct join the bile duct and secrete their contents in the second part of duodenum
What are the histological features of the pancreas?
- Surrounded by CT capsule
- The capsule gives many septa that divides the pancreas to lobules
- The darkly stained lobules are the exocrine ( made of tubuolacinar secretory units )
- The lightly stained areas are the endocrine ( islets of langerhans ) which are in the mid or periphery of the lobule
What does the secretory units ( acini ) in exocrine produce ?
The acini secrete proenzymes, which are involved in digestion
It will go the second part of the duodenum
What are the different cells in the exocrine part ?
- Tubuloacinar/ acinus
- pyramidal shape cells
- contain zymogen granules at the apex contain proenzymes - Centroacinar / serous acinar cells
- they are the first part of duct system
- pinkish in color and stain with eosin
- the secrete HCO3 and Na
What is the function bicarbonate ?
Neutralizing the pH in duodenum so it can work
What is the duct system in the pancreas ?
- the serous acini
- intercalated ducts
- intralobular ducts
- interlobular ducts
- main duct
What is the structure of islets ?
- Surrounded by thin fibrous capsule
- Surrounded by fenestrated capillaries
- cells are arranged in cords
Why the islet cells are lighter ?
Due to less RER
exocrine normally have more RER
What is the significance of the veins ?
- The veins are more important than the arteries as they are the main structures to carry the hormones
What is the Development of islets of Langerhans ?
- They develop from the endoderm in the third month
- Insulin is the first hormone to be secreted in fifth month ( other hormones later )
What are the genes that are important for Development of islets of Langerhans ?
Paired homeobox genes ( PAX 4 and PAX 6 )
If both»_space; alpha / beta / gamma
If only PAX 6»_space; only alpha
What is the inter-species differences in regard to islets of Langerhans ?
In all species, beta cells are more
- Mice:
- beta in the centre
- few alpha and gamma in the periphery - Human and monkey
- they are dispersed
- more beta in centre ( but still have both )
- more alpha in the periphery ( but still have both ) - Pigs
Beta is mainly in collections ( clusters ) so it can be used to transplant islets to humans
What are the Cell types in the islets of Langerhans and their functions-humans ?
- Alpha
- Beta
- Gamma
4 . F cells ( PP ) - D1 cells
- Epsilon
- Enterochromaffin ( EC )
What is Zollinger – Ellison syndrome ?
pancreatic islet tumors secrete gastrin hormone
What is the BV organization ?
- The enter the islets
- They branch into fenestrated capillaries
- They get out of the islets but they form a capillaries around the acinus
Why secretions of the islets have regulatory effects on acinar cells ?
As When the capillaries leave the islets, they branch into a capillary network that surround the acini of exocrine pancreas
Which islets hormones that stimulate and inhibit exocrine secretion ?
ACTIVE :
- insulin ( as it is produced when you eat, so you really needs digestive enzymes 💡 )
- CCK
- VIP
INHIBIT :
- glucagon
- PP
- somatostatin
What are the main regions of islets ?
- Mantle region ( outer )
- Core region ( inner )»_space; more beta cells
- Vascular region ( inner most )
What will happen to the regions in diabetic patient?
Beta cells will decrease ( so less core region )
But
Also both mantle and vascular regions will regress
So the ratio will remain the same
What is the arrangement of cells in the islets ?
- The islet cells are organized into a continuous folded epithelial plate-like structure (trilaminar)
- The central part of the plate is occupied by the β cells which are lined on either side by α and other cells
- the beta cells has cytoplasmic processes
What is the function of cytoplasmic processes ?
Sensing blood glucose
What will control the islet secretion ?
- Blood biochemistry
2. Autonomic nervous system
What is the function of ANS on the islets ?
10% of the cells have a direct contact with the fibers
Para»_space; stimulate insulin and glucagon
Sym»_space; stimulate glucagon / inhibit insulin
Why sympathetic nervous system stimulate glucagon only ?
As you require more glucose
