Gastrointestinal: BLOCK 1 Flashcards: The Exocrine Pancreas

describe the basic anatomy of the pancreas (4)

• retroperitoneal

• originates from the foregut

• pancreas is split into the tail, body, head and Uncinate Process

• has exocrine and endocrine portions

Describe the anatomy of the Exocrine Pancreas

• exocrine pancreas has a bile duct which travels from the liver and runs through the pancreas

• the pancreas has an auxiliary duct which empties into the duodenum

• made up of Acinar Units

What units make up the endocrine pancreas?

• islets of langerhans

Describe the innervation of the Pancreas:

• has autonomic (sympathetic + parasympathetic) and visceral sensory fibers

Which nerve is responsible for parasympathetic innervation of the pancreas?

• vagus nerve (these fibers reach the pancreas via the celiac plexus

What function does Parasympathetic Innervation have on the pancreas?

• stimulates exocrine secretion (digestive enzymes)

• promotes endocrine activity (insulin and glucagon release)

What nerves are responsible for sympathetic innervation of the pancreas?

• nerve fibers originate from T5-T9 → travel via greater splanchnic nerves → synapse in celiac ganglia → postganglionic fibres supply pancreas through celiac plexus

What function does sympathetic innervation of the pancreas have?

• inhibits pancreatic secretion

• causes vasoconstriction of pancreatic blood vessels

What visceral innervation does the pancreas have?

• pain fibers travel with sympathetic pathways back to spinal cord levels T5-T9

• this explains referred pain from the pancreas to the epigastric region and sometimes the back

describe the celiac plexus

• innervates the pancreas

• integrates sympathetic and parasympathetic fibers

list the 7 lymph nodes found in the pancreas

1. superior mesenteric lymph node

2. splenic lymph node

3. pyloric lymph node

4. posterior pancreaticoduodenal lymph node

5. anterior pancreaticoduodenal lymph node

6. celiac

7. hepatic

What arteries supply the pancreas?

• hepatic artery

• splenic artery

• superior pancreticoduodenal artery

• inferior pancreaticoduodenal artery

describe the pathway of the superior pancreaticoduodenal arteries:

celiac trunk → gastroduodenal artery → superior pancreaticoduodenal arteries

where do the inferior pancreaticoduodenal arteries originate from?

branches of the superior mesenteric artery

which veins drain the pancreas?

• splenic vein

• hepatic portal vein

• superior and inferior pancreatioduodenal veins

• superior mesenteric vein

where do the Endocrine cells (islets of langerhans) of the pancreas originate from?

• bud cells of the ‘trunk’ domain

• endoderm

• pancreatic epithelium → differentiation → islets cell clusters → islets of langerhans

where do the exocrine cells (acinar cells) originate from?

• multipotent progenitor cells at the ‘tip’ domain

Describe the embryology of the pancreas:

1. arises from foregut (endodermal lining of duodenum) - around week 4-5

2. two buds form; dorsal develops first, then ventral

3. ventral bud rotates posteriorly around the duodenum and fuses with dorsal bud ~ week 7

4. duct systems also fuse

What structures arise from dorsal pancreatic bud?

• upper part of head of pancreas

• neck of pancreas

• body

• tail

What structures arise from ventral pancreatic bud/

• associated with common bile duct

• forms inferior part of pancreatic head

• uncinate process

describe how Acinar cells are arranged in the exocrine pancreas:

• acinar cells are arranged in grape-like clusters called acini

List 2 functions of ductal cells

• ductal cells produce bicarbonate-rich fluid that neutralises stomach acid in the duodenum

• they also deliver enzymes from acinar cells to the duodenum

where are ductal cells located?

• lining the network of ducts within the exocrine pancreas

What receptors do Acinar cells have and why?

• Acinar cells have CCK receptors

• when CCK binds to these receptors → release of enzyme zymogens into small intestine

• helps with digestion

What receptors do ductal cells have and why?

• ductal cells have receptors for secretin

• when secretin binds to receptors → increase in cAMP → activates protein kinases → pKA acts on Cl- channels

• Cl- channels transport chloride out of cell

• this gradient is used by another transporter → release of bicarbonate and water

What is the name for the chloride channels within ductal cells?

• Cystic fibrosis transmembrane conductance regulator proteins

What function do CFTR proteins have in the pancreas?

• regulate water balance and fluid secretion

• ensures thin, non-viscous mucus

List 3 diseases of the exocrine pancreas:

1. chronic pancreatitis

2. acute pancreatitis

3. pancreatic cancer

What is Chronic Pancreatitis?

• long-standing inflammatory disease of pancreas

• irreversible structural damage; fibrosis and scarring

• loss of exocrine and endocrine function

what is acute pancreatitis?

• extreme inflammation of pancreatic cells → causes necrosis

• endocrine failure → diabetes

• exocrine failure → malabsorption of food

what is pancreatic cancer?

• malignant tumor arising from the cells of the pancreas

• most commonly from the exocrine ductal epithelium (at head of pancreas)

What causes pancreatitis on a cellular level?

• Activation of trypsinogen into trypsin within the pancreas → caused by spike of calcium within Acinar cell

• This causes cell damage, cytokine release, inflammation and necrosis → causes further trypsinogen proenzyme activation → active trypsin

explain exactly what happens when trypsinogen is activated to trypsin:

• Release of calcium causes cathepsin B vesicles to join with the trypsinogen vesicles → activates trypsinogen to become trypsin → acute pancreatitis 

What normally happens when this loop occurs in the pancreas in a healthy pancreas?

• Body releases pancreatic enzyme inhibitors SPINK1/PSTI

• This is a form of auto-regulation and inhibits trypsinogen from becoming activated and prevents the active trypsin from functioning.

I GET SMASHED:

I = idiopathic and hereditary

G = gallstones is the most common cause 

E = ethanol (alcohol abuse)

T = trauma

S = steroids

M = mumps 

A = autoimmune

S = scorpion stings

H = hyper - calcaemia, lippidaemia, thermia

E = ERCP

D = drugs 

What happens in the exocrine pancreas in a patient with acute pancreatitis? (11)

• increased CCK release

• increased trypsinogen

• decreased SPINK1

• Acinar cell damage

• decreased bicarbonate

• decreased water

• decreased pH

• decreased flow

• increased viscosity

• proteolytic cleavage

• protein plugs

What is the main cause of chronic pancreatitis?

• alcohol

In what 2 ways can alcohol be metabolised and which one causes a calcium spike in Acinar cells?

1. oxidative metabolism

2. non oxidative metabolism; carboxylesterase converts alcohol to fatty acid ether esters → causes calcium spikes in pancreatic cells

what was the mortality rate of pancreatic cancer in 2000?

• 100%