Histology of the Pancreas Flashcards
Where is the pancreas located?
What is it attached to?
located in the retroperitoneal space
attached to the duodenum and spleen
at level of ~2nd lumbar vertebra
oblique, transverse in position
What is the origin of the pancreas?
endodermal in origin
develops from ventral & dorsal pancreatic buds
What defines the border of the head and neck of the pancreas?
gastroduodenal artery defines border with neck
yields superior pancreaticoduodenal artery (SPDA)
- divides into anterior & posterior SPDA
- branches to duodenum and rt border of head.
What touches the anterior, posterior and inferior surface of the pancreas?
anterior surface separated from stomach by lesser sac
posterior surface related to:
aorta, lt. adrenal, lt. renal vessels, and upper 1/3rd of lt. kidney
splenic vein embedded in posterior surface
inferior surface is covered by tranverse mesocolon
Where does the pancreatic tail lie?
Where does the tail terminate?
When may it be injured?
short, narrow segment
lies at level of 12th thoracic vertebra
terminates at splenic hilum, within splenophrenic lig.
anteriorly, related to splenic flexure of colon
may be injured during splenectomy (fistula)
What is the main pancreatic duct?
Where does it run? Where does it drain (landmark)? How does it stop backflow?
What does the accessory duct drain?
main duct (duct of Wirsung)
runs length of pancreas, merges with common bile duct at ampulla of Vater
2–4mm diameter, ~20 secondary branches
ductal pressure is higher than in common bile duct to prevent backflow, damage
accessory duct (duct of Santorini)
drains superior portion of head & empties separately into duodenum
What are the arterial sources of the pancreas?
arterial sources
superior pancreaticoduodenal artery (from gastroduodenal artery)
inferior pancreaticoduodenal artery (from sup. mesenteric artery)
ant. & post. branches of each anastomose
dorsal pancreatic artery (from splenic artery)
great pancreatic artery (from splenic artery)
caudal pancreatic artery (from splenic artery)
numerous other small, un-named branches supply body & tail
What is the venous drainage of the pancreas?
generally follows arterial supply
ant. and post. arcades drain head & body
drain to SMV and/or to portal vein
splenic vein drains body & tail
ultimately, all drain into hepatic portal vein - significance?
What are the components of pancreatic exocrine microanatomy?
secretory acini and ducts
constitute ~98% of pancreatic mass
acini
20-40 secretory cells coalesce into a sac-like unit
cells secrete digestive enzymes
duct system
tubular network delivers exocrine secretions to duodenum
What do acinar cells secrete? Talk about the product.
acinar cells
secrete digestive enzymes
packaged in zymogen granules, released into acinar lumen
- includes amylase, lipase, and trypsinogen
What do ductal cells secrete? What do centroacinar and intercalated duct cells secrete? Where is mucin secreted?
ductal cells
secrete water and electrolytes
centroacinar & intercalated duct cells
secrete bicarbonate
- in larger ducts, some cells secrete mucins
Describe the final digestive juice. Why does it have the pH that it has?
final digestive juice - alkaline fluid
- colorless, odorless, isosmotic
- 500-800ml secreted per day
Enzymes activated in duodenum by acidic environment
pH neutralizes gastric acid & buffers intestinal pH
What are the 4 major cell types in the endocrine pancreas?
What does each one produce?
What are the percentages of cell types present?
4 major cell types
a (alpha) cells
25-35% of islet cells
produce glucagon
b (beta) cells
55-65% of islet cells
produce insulin, amylin
d (delta) cells
5-15% of islet cells
produce somatostatin
PP cells
<2% of islet cells
produce pancreatic polypeptide
3 minor cell types of the endocrine pancreas?
3 minor cell types
d-1 (delta-1) cells 1% of islet cells produce VIP also found in: exocrine acini ductal epithelium
EC (beta) cells
1% of islet cells produce: secretin, motilin, substance P also found in: exocrine acini ductal epithelium
e (epsilon) cells
1% of islet cells produce ghrelin
What is the primary islet function?
Primary hormones released?
What are they released in response to?
What do they promote?
Stimulatory Inputs?
Inhibitory Inputs?
Primary islet hormones:
Insulin
released in response to glucose
promotes uptake of glucose into target tissues
(primarily liver, muscle and fat)
Glucagon
secreted in response to low blood glucose
counter-regulatory hormone
promotes production of glucose from
liver glycogen
glucose precursors
Stimulatory inputs:
glucose, amino acids, glucagon, GIP, CCK, sulfonylurea compounds, b-sympathetic fibers
Inhibitory inputs:
somatostatin, amylin, pancreastatin, α-sympathetic fibers (significance?) ONLY DR KETCHUM KNOWS.
What is the function of pancreatic polypeptide?
Vasoactive intestinal peptide (VIP)
Secretin?
Motilin?
Substance P
Ghrelin?
Pancreatic polypeptide (regulatory peptide)
stimulates gastric chief cells
inhibits bile secretion and intestinal motility
inhibits pancreatic enzymes and HC03- secretion
Vasoactive Intestinal Peptide (VIP)
similar to action of glucagon (hyperglycemic & glycogenolytic)
also affects secretory activity & motility in gut
stimulates pancreatic exocrine secretion
Secretin
acts locally
stimulates HC03- secretion (in pancreatic juice)
stimulates pancreatic enzyme secretion
Motilin
increases gastric and intestinal motility
Substance P
has neurotransmitter properties
Ghrelin
stimulates appetite - from Greek, “to eat”
What is the organization of islets? How does intercellular communication happen? What is the innervation?
Animal islets considered “mantle” islets
precise relationship among cells types
generally: b-cells form medulla
a-, d-, & PP-cells form thin cortex (mantle)
Human islets now viewed differently:
- precise relationship among cells types
- all cells “randomly” distributed but arrayed along vessels such that all cells see blood
Intercellular communication occurs via:
blood supply
paracrine relationships
junctional communications (gap junctions)
Innervation: sympathetics & parasympathetics
- islet-acinar axis (islet acinar portal system)
What does insulin regulate in addition to metabolism? What does insulin trigger the release of?
Islets of Langerhans within the exocrine pancreas have a specific purpose
- insulin regulates both metabolism and secretion of pancreatic acinar nutrients in the gastrointestinal tract
Will stimulate insulin secretion via nervous and hormonal pathways
- insulin released will not only regulate blood glucose, but will also potentiate exocrine pancreatic secretion
- insulin also stimulates other acinar cell functions, such as transport of amino acids or glucose, as well as protein and enzyme synthesis
- insulin directly regulates the acinar pancreas
- endogenous insulin potentiates zymogen release
- insulin has both short-term and long-term effects on the exocrine pancreas
A suppressive role of the islet-acinar axis via endogenous somatostatin and/or pancreatic polypeptide is suggested
What is the first sign of pancreatic dysfunction?
Appearance of fat in the stool.
What do delta-1 cells stimulate in the body?
vasodilation, increase arterial BP, heart contractility increases, increased glycogenolysis
What percentage of the pancreas is taken up by endocrine cells? Where are these cells?
Endocrine pancreas
<2% of total cell mass is taken up by endocrine cells
cells sequestered in Islets of Langerhans
