pancreatic and billary Flashcards
(21 cards)
2 main secretions of the stomach overall
Gastrin (Gastrin, secreted during a meal, stimulates pancreatic acinar cells to release more enzymes)
Pepsinogen to pepsin
How does the duodenum inhibit gastric emptying?
Keeps pylorus closed, chyme churns longer to aid digestion
Why does the duodenum inhibit acid secretion, and neutralise acid?
Acid is effective and useful in the stomach.
* Duodenum needs to bring pH to netrual in order to:
* Inactivation pepsin
* Prevent acid damage
* Make fatty acids more soluble
* Optimise enzymes
I cells
- purpose on apical vs basolateral surface
Apical surface: Sample
partially digested fats (fatty
acids) and proteins (amino
acids) in duodenal content
Basolateral surface: secrete CCK (cholecystokinin)
CCK is a key gut hormone
* Slows motility (speed of peristalsis) by inhibiting gastric emptying
* Influences satiety (feeling of fullness)
* Bile squirted out from the gallbladder
S cells
- located
- purpose
-detect
Apical surface: sense the pH.
When pH <4…
Basolateral surface: releases secretin into the capillaries
* Secretin – sticks to receptors on pancreas ductal cells, releasing
bicarbonate
* Inhibits gastric acid production
Enterochromaffin Cells
-purpose on apical vs basolateral
Apical surface:
senses foods
and irritants
- Serotonin: stimulates gut motility
- Too much serotonin: activates the medulla leading to vomiting
- 90% of serotonin is made by the gut
Not to be confused with enterochromaffin-like cells in the stomach that make
histamine
Delta Cells
- secrete what
- purpose
Somatostatin: Paracrine & Endocrine. Hypothalamus, pylorus, duodenum & pancreas
* Reduces acid secretion
* Increases gastrin and histamine to slow digestion – slows the stomach and reduces peristalsis
* Suppresses pancreatic & GI hormones
* Reduces GH, TSH, PL
Pancreas roles:
2 functions
cells in each function and what they do
Endocrine function
- Islet of Langerhan cells
Insulin, glucagon,
Exocrine function
- Ductal cells
Bicarbonate ions to neutralise stomach acid and
regulate enzymes
- Acinar cells
Secrete zymogens: granular precursors to digestive
enzymes
More enzyme activation at the brush border
3 ways the gut can make bicarbonate
1 - Pancreatic production
* pH < 4
* secretin made by S
cells
* Secretin sticks on
its receptor
* cAMP increased
* CFTR transporter
activated
* HCO3 pumped into
the lumen
2 - Direct vagal stimulation
Mediated by ACh –
low level HCO3 for
meal readiness
3 – Duodenal production
- Brunner’s glands make
HCO3
How does the body know when to release acinar granules
CCK stimualtes vagus afferent
This goes to vagus nerve then to vagus efferent to pancreas acinar cells to release zymogens
Gastrin: made in a meal stimulates acinar
production too
Release amylase and lipase (ready to go) and pro-enzymes
Where do protesases get activated? and the flow of activation
The duodenal brush border:
where the proteases get
activated.
Enterokinase enzymes at the
brush border cleave
Trypsinogen (from zymogen
granules) into Trypsin
* Trypsin cleaves more
Trypsinogen (auto-catalysis)
* Trypsin also cleaves
Chymotrypsinogen to other
proenzymes
What does pancreatic lipase and proteases and amylase do?
Pancreatic lipase converts triglycerdies into monoglycerdies and FFA
Amylase: Converts starch into sugars
Protease: Digest proteins
Negative feedback to turn off production esp. from Acinar cells and Ductal cells
- Glucagon, somatostatin and
Pancreatic polypeptide inhibit
pancreatic enzyme and HCO3
secretion - Pancreatic polypeptide acts on
brainstem – vagal efferents - Peptide YY – made from ileum and
colon in response to free fatty acts
how is bile formed
- Hepatocytes make: bile acids, BR, fats
(cholesterol), organic molecules and salts - Ductal epithelial cells: add water and Bicarb
The Bile Acid Recycling
System
Secreted bile salts consist of 95% old, recycles bile salts and 5% newly made bile salts
95% bile salts are reabsorbed by SI
Resorbed bile salts are recycled by enterohepatic circualuation
5% bile salts lost in faeces
What stimulates bile release
- Fat in duodenum Stimulates CCK from I cells and sphincter of oddi relaxes. On way, bile
mixes with pancreatic
enzymes + HCO3
CCK and Secretion summary role
- Fats and proteins in duodenum stimulate I cells to make CCK
CCK stimulates pancreatic acinar cells to make digestive enzymes via 2 pathways:
1. enters blood stream to get to acinar cells of pancreas to stimulate release of pan enzymes
2. Send message via afferent fibres - VG - Vagnus efferent to to pancreas to stim pan enzymes
CCK stimulates bile production, GB contraction and Sphnicter releaction of oddi allowing delievery of bile
HCI in duodenum stimulates S cells to release secretin. Secretin stimulates pancreatic ductal cells to make secretions rich in HCO3
to neutralise stomach HCl
CF and pancreas relationship
Secretions: low in Cl, low in HCO3,
hyperviscous & salty
* Cells negatively charged: drawing Na
then H2O from ductal lumen into cells
Exocrine and endocrine pancreatic production reduced. Pancreatic ducts blocked by thick
mucous. Autodigestion of the
pancreas/pancreatitis + fibrosis.mLifelong replacement of pancreatic
enzymes needed
Raised Amylase and lipase means?
Decreased feaccel elastase means
Pancreatitis
Exocrine pancreatic
deficiency
Generally how does jaundice happen
Bile flow can get blocked:
* Large ducts - stones, tumour, strictures, worms, auto- immune (PSC)
* Small ducts - above + toxins, auto immune (PBC)
Pressure builds in the biliary tracts + liver.
tight junctions rupture, bile leaks into the circulation with BR
* Causes the clinical scenario of jaundice
common symptoms with jaundice
- Yellow sclera – BR in sclera and skin
- Pale poo – BR not in the poo
- Itch – bile salts in skin
- Painful or painless – depending on cause
