L5 Histology of endocrine pancreas - Islets of Langerhans

Question 1

What are the secretory parts of the pancreas ?

Answer 1

1. Exocrine :
   - secrete different hormones that help in digestion
2. Endocrine :
   - islets of langerhan
   - secretes hormones to the circulation

Question 2

Where you find the islets ?

Answer 2

Everywhere but more in the tail

Question 3

What are the parts of the pancreas ?

Answer 3

1. Head - attached to the c curve of duodenum ( can’t be separated )
2. Neck
3. Body
4. Tail - near the spleen

It is a retropretoinum organ

Question 4

What are the ducts of pancreas ? What is there organization ?

Answer 4

1. Main duct of wirsung
2. 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

Question 5

What are the histological features of the pancreas?

Answer 5

1. Surrounded by CT capsule
2. The capsule gives many septa that divides the pancreas to lobules
3. The darkly stained lobules are the exocrine ( made of tubuolacinar secretory units )
4. The lightly stained areas are the endocrine ( islets of langerhans ) which are in the mid or periphery of the lobule

Question 6

What does the secretory units ( acini ) in exocrine produce ?

Answer 6

The acini secrete proenzymes, which are involved in digestion
It will go the second part of the duodenum

Question 7

What are the different cells in the exocrine part ?

Answer 7

1. Tubuloacinar/ acinus
   - pyramidal shape cells
   - contain zymogen granules at the apex contain proenzymes
2. Centroacinar / serous acinar cells
   - they are the first part of duct system
   - pinkish in color and stain with eosin
   - the secrete HCO3 and Na

Question 8

What is the function bicarbonate ?

Answer 8

Neutralizing the pH in duodenum so it can work

Question 9

What is the duct system in the pancreas ?

Answer 9

1. the serous acini
2. intercalated ducts
3. intralobular ducts
4. interlobular ducts
5. main duct

Question 10

What is the structure of islets ?

Answer 10

1. Surrounded by thin fibrous capsule
2. Surrounded by fenestrated capillaries
3. cells are arranged in cords

Question 11

Why the islet cells are lighter ?

Answer 11

Due to less RER

exocrine normally have more RER

Question 12

What is the significance of the veins ?

Answer 12

1. The veins are more important than the arteries as they are the main structures to carry the hormones

Question 13

What is the Development of islets of Langerhans ?

Answer 13

• They develop from the endoderm in the third month

- Insulin is the first hormone to be secreted in fifth month ( other hormones later )

Question 14

What are the genes that are important for Development of islets of Langerhans ?

Answer 14

Paired homeobox genes ( PAX 4 and PAX 6 )

If both&raquo_space; alpha / beta / gamma

If only PAX 6&raquo_space; only alpha

Question 15

What is the inter-species differences in regard to islets of Langerhans ?

Answer 15

In all species, beta cells are more

1. Mice:
   - beta in the centre
   - few alpha and gamma in the periphery
2. Human and monkey
   - they are dispersed
   - more beta in centre ( but still have both )
   - more alpha in the periphery ( but still have both )
3. Pigs
   Beta is mainly in collections ( clusters ) so it can be used to transplant islets to humans

Question 16

What are the Cell types in the islets of Langerhans and their functions-humans ?

Answer 16

1. Alpha
2. Beta
3. Gamma
   4 . F cells ( PP )
4. D1 cells
5. Epsilon
6. Enterochromaffin ( EC )

Question 17

What is Zollinger – Ellison syndrome ?

Answer 17

pancreatic islet tumors secrete gastrin hormone

Question 18

What is the BV organization ?

Answer 18

1. The enter the islets
2. They branch into fenestrated capillaries
3. They get out of the islets but they form a capillaries around the acinus

Question 19

Why secretions of the islets have regulatory effects on acinar cells ?

Answer 19

As When the capillaries leave the islets, they branch into a capillary network that surround the acini of exocrine pancreas

Question 20

Which islets hormones that stimulate and inhibit exocrine secretion ?

Answer 20

ACTIVE :

1. insulin ( as it is produced when you eat, so you really needs digestive enzymes 💡 )
2. CCK
3. VIP

INHIBIT :

• glucagon
• PP
• somatostatin

Question 21

What are the main regions of islets ?

Answer 21

1. Mantle region ( outer )
2. Core region ( inner )&raquo_space; more beta cells
3. Vascular region ( inner most )

Question 22

What will happen to the regions in diabetic patient?

Answer 22

Beta cells will decrease ( so less core region )
But
Also both mantle and vascular regions will regress

So the ratio will remain the same

Question 23

What is the arrangement of cells in the islets ?

Answer 23

• 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

Question 24

What is the function of cytoplasmic processes ?

Answer 24

Sensing blood glucose

Question 25

What will control the islet secretion ?

Answer 25

1. Blood biochemistry

2. Autonomic nervous system

Question 26

What is the function of ANS on the islets ?

Answer 26

10% of the cells have a direct contact with the fibers

Para&raquo_space; stimulate insulin and glucagon
Sym&raquo_space; stimulate glucagon / inhibit insulin

Question 27

Why sympathetic nervous system stimulate glucagon only ?

Answer 27

As you require more glucose