Case 3- Pancreatitis Flashcards
What ducts lead into the main pancreatic duct?
Intralobular ducts
i.e., Acini within the exocrine pancreas are connected by intercalated ducts. These ducts unit with lobules to form intralobular ducts, which then flow into the main pancreatic duct
What cell types are present in the pancreas and what do they secrete?
Alpha cells - glucagon
Beta cells - insulin and amylin
Delta cells - somatostatin
Gamma cells - pancreatic polypeptide
Epsilon cells - ghrelin
What is the role of:
- Amylin
- Pancreatic polypeptide
- Ghrelin
Amylin = slows gastric emptying to prevent a spike in blood glucose
PP= Gi function
Ghrelin = increases appetite
What does release of glucagon lead to?
- Increased glycogenolysis
- Decreased glycogenesis
- Increased gluconeogenesis
- Increased ketogenesis
Where are digestive enzymes stored in the pancreas?
Within zymogen granules in acinar cells
What enzymes does the pancreas secrete and what do they digest?
- Proteases = chymotripsinogen and trypsinogen, digests proteins and peptides into AAs
- Pancreatic lipase = digests triglycerides, monoglycerides and free FA
- Amylase= digests starch and maltose (dissacharides)
How is bicarbonate secreted?
- H2O and CO2 combine in pancreatic ductal cells to form carbonic acid, which dissociates to HCO3- and H+
- H+ is exchanged into the blood for Na+ (via antiporter), then Na+ goes back into the blood via Na+/K+ ATPase
- HCO3- is exchanged for Cl- and enters into lumen of intercalated ducts of pancreas
- HCO3-, Na+ and H2O move through intercalated ducts and enter main pancreatic duct
What increases pancreatic juice secretion?
- Vagal innervation (PNS): i.e. sight, smell, taste of food or stretched stomach
- CCK: released by I cells in response to FA and protein content within chyme in the duodenum (also causes bile secretion via gall bladder contraction)
What stimulates bicarbonate secretion?
Secretion - acidic chyme in duodenum stimulates S cells to release secretin, which causes ductile cells to secrete HCO3-, lowers bile secretion and inhibits gut motility
What does the ileum absorb?
Vitamin B12, bile salts and K+
What does the colon absorb?
Na+, some water, and short-chain fatty acids
What are 2 important features of the small intestine?
- Expansion of absorptive surface: achieved by foldings in the wall, villi and microvilli
- Polarised expression of transport proteins, i.e. different ones on different sides of the cell
What is secondary active transport?
Transport against a concentration gradient, with energy derived from Na+ gradient from the Na+/K+ ATPase (primary active transport)
What transporter is present on the apical membrane of the gut lumen for glucose or galactose absorption?
SGLT1: an Na+ dependent (secondary active) transporter; brings in one Na+ with glucose
What does SGLT1 transporter rely on?
Na+/K+ ATPase pump on the basolateral side
What transporter is present for fructose absorption?
GLUT5 transporter on the apical membrane
What transporter is responsible for glucose/ fructose absorption into the intracellular fluid?
GLUT2 (on basolateral side) via facilitated diffusion
What is glucose-galactose malabsorption syndrome? What would this lead to?
Genetic condition where SLGT1 is mutated, so there is no absorption of glucose or galactose. Leads to severe and potentially fatal diarrhoea in infants
Which transporter absorbs 50% of amino acids as di and tri peptides?
PepT1 transporter, uses a proton gradient (i.e. absorbed peptides with H+)
How does pancreatic lipase digest fat?
Breaks down triglycerol into monoacylglycerole and 2 free fatty acids (reversible)
Fat digestion is dependent on bile salts - what is the role of bile salts?
- Emulsification of large fat droplets, i.e. breaks them down to increase SA for action of lipase
- Formation of mixed micelles, which stabilise products of triglyceride hydrolysis while they are ‘translocated’ to the apical memrbane
What is the consequence of not having bile? i.e. in liver disease
Steatorrhea (fatty diarrhoea)
What is the pKa of free FA? What does this mean?
pKa = 4.9
This means that at pH of 4.9, 50% of fatty acids will be in the dissociated form and simple diffusion is possible.
How does pH influence the state of FA?
- Decreasing pH <4.9 = more dissociative form
- Increasing pH > 4.9 = less dissociated form
What are the proposed transporters for free fatty acids?
FAT and CD36
What happens after monoacyglycerol and FA are absorbed?
Triglyceride re-synthesis in the ER, packaged into chylomicrons. They leave the enterocyte via chylomicrons, and are transported in the lymphatic system (lacteals) to the liver (enter the blood via thoracic duct)
Where is cholesterol absorbed and what is it dependent on?
Duodenum
Dependent on NPC1L1 protein - which allows for receptor-mediated endocytosis
What drug targets the NPC1L1 protein?
Ezetimibe - inhibits endocytosis to reduce plasma cholesterol
Give some examples of short chain fatty acids
Butyrate, propionate, acetate
What transporter is responsible for absorption of short-chain fatty acids in the colon?
SMCT1
What is osmotic load and what can it lead to?
Incomplete digestion and absorption of food, leads to increased fluid in the colon and thus in the faeces (= diarrhoea)
Give some examples of how lack of enzymes/ transporters can lead to osmotic load, and how this alters stool consistency
- Congenital causes: watery = glucose-galactose malabsorption (SGLT1) or lactase deficiency
- Disease of pancreas and biliary systems: leads to steatorrhoea, i.e. pancreatitis, CF, hepatitis, gall stones
Give examples of what can damage mucosal cells, leading to osmotic load
- Autoimmune/ immune diseases: coealic disease, Crohns
- Infections: bacteria, i.e. shigella (destroys intestinal wall)
- Salmonella: inflammation of intestinal wall
What is recommended to treat individuals suffering from cholera and why?
Oral rehydration therapy: the toxins inhibit Na+ absorption but not the SGLT1, therefore give individuals water with salt and glucose - enhances water transport into the body with the gluocse
How are fat-soluble vitamins absorbed?
Vitamins A, D, E and K
- At very low concentrations they require facilitated diffusion and/or endocytosis
- Required optimal fat digestion
How are water-soluble vitamins absorbed?
Vitamins B and C
- Specific transporters; facilitated diffusion and secondary active transporter
- Exception = B12 is via endocytosis (uses intrinsic factor)
Describe the transcellular route of calcium absorption
1: calcium enters via TRPV6 channel, down its electrochemical gradient
2: Ca2+ is sequestered to calbindin to prevent damage to the cell and enable movement to the basolaterla membrane
3: Calcium is removed by active transport via Ca2+ ATPase (PMCA) - expends Ca2+ out of the cell
Describe the parcellular route of calcium absorption
Crosses the epithelium down the concentration gradient
What does absorption of Ca2+ depend on and why?
Vitamin D (1,25-dihydroxy-vitamin-D) = transcription of mRNA which encodes for PMCA, calbindin and TRPV6
What route is iron absorbed down and where does this occur in the GI tract?
In the duodenum via transceullar routes
How can iron enter over the apical membrane?
- Via DMT: transports ferrous form (reduced) Fe2+ across with the transport of H+
- Via Heme
How does heme transport iron into the cell?
- Heme = protein bound to Fe2+
- Inside the cell it is oxidised to release Fe2+ = ferric irons
- Then reduced again = ferrous irons
- Ferrous iron binds to mobilferrin as it is toxic, and moves it to the basolateral membrane
- Iron leaves the cell via FP1
What happens after ferrous iron leaves the cell via FP1?
Ferrous irons are re-oxidised to ferric irons (Fe3+), and bind to transferrin
What catalyses the oxidation of iron?
hephaestin
After oxidation of heme releases Fe2+, what does the remainder of the heme proteins produce?
biliverdin, a precursor of bilirubin
(excreted in bile)
What regulates iron absorption? How?
Hepcidin, produced by the liver when you have enough iron. It is secreted into the blood and results in internalisation of FP1 = inhibit step of iron exiting the cell. this means iron is stored in enterocytes, bound to mobilferin (then lost by faeces)
How is gastric pain vs pancreatic pain differentiated?
Pancreatic pain radiates to the back, gastric pain tends to stay localised to the epigastrium