L31 Flashcards
where is CCK secreted from and what are its functions
released from I-cells in the duodenum due to fat and protein digestive products
inhibits gastrin secretion in the antrum
increases protein secretion in the pancreatic acini
where is Secretin released from and what is its function
released from S-cells in the small intestine due to acidification of the duodenum increases fluid secretion in the pancreatic duct
what is the exo and endocrine parts of the pancreas
endocrine is the insulin and glucagon part (islet cells)
exocrine is the asein and the duct cells
what is the exo and endocrine parts of the pancreas
endocrine is the insulin and glucagon part (islet cells)
exocrine is the asein and the duct cells
describe the structure of the exocrine pancreas
there are 3 main parts, the lobules, ducts and secretory units
lobules
acini
ducts
intercalated
common bile
secretory units
acini
intercalated ducts
describe the structure of the exocrine pancreas
there are 3 main parts, the lobules, ducts and secretory units
lobules
acini
ducts
intercalated
common bile
secretory units
acini
intercalated ducts
the pancreas has 2 major ducts. where do these come together
the sphincter of oddi
the acini are the primary site for what??
fluid secretion
how many acinus per lobule
15-20 cells
what do acinus cells synthesise and secrete
synthesis and secretion of
proteins
secrete isotonic NaCl solution
what is the finction of intercalated ducts
modify primary secretion by
secretion of HCO3-
rich fluid
Very different to salivary gland eg in the salivary gland the epithelium is tight but here it is leaky. Also here most of the fluid comes from the ducts
what is the finction of intercalated ducts
modify primary secretion by
secretion of HCO3-
rich fluid
Very different to salivary gland eg in the salivary gland the epithelium is tight but here it is leaky. Also here most of the fluid comes from the ducts
what is the finction of intercalated ducts
modify primary secretion by
secretion of HCO3-
rich fluid
Very different to salivary gland eg in the salivary gland the epithelium is tight but here it is leaky. Also here most of the fluid comes from the ducts
what is the differnt between the duct cells in the salivary gland compeared to in the pancras
Very different to salivary gland eg in the salivary gland the epithelium is tight but here it is leaky. Also here most of the fluid comes from the ducts
what is the differnt between the duct cells in the salivary gland compeared to in the pancras
Very different to salivary gland eg in the salivary gland the epithelium is tight but here it is leaky. Also here most of the fluid comes from the ducts
what is the differnt between the duct cells in the salivary gland compeared to in the pancras
Very different to salivary gland eg in the salivary gland the epithelium is tight but here it is leaky. Also here most of the fluid comes from the ducts
what is the differnt between the duct cells in the salivary gland compeared to in the pancras
Very different to salivary gland eg in the salivary gland the epithelium is tight but here it is leaky. Also here most of the fluid comes from the ducts
what volume of fluid does the pancreas secrete per day
1.5 L
what is the osmolarity of the pancreatic secretions
300mOsmol
what is the pH of the pancreatic secretions
7.8
slightly alkaline
what is the concentrations of ions in the pancreatic secretions
Na = 140 K = 10 Cl = 70 HCO3 = 80 mmol/L
the stomach secretes bicarbonate into the blood (mostly) there is some into the lumen of the stomach
The pancreas and the liver also secrete bicarbonate into the lumen
This all comes together in a loop as in the stomach you make acid anhydrase and then in the intestine you nutrolise H+ by creating it back from bicarbonate
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Volume and compositon of secretions
1-1.5 L of alkaline fluid and 5 -15 g protein secreted per day
where does the protein come from
proteins - acinar cells
how many different proteins are secreted from the acinar cells
20 different proteins secreted - mainly digestive enzymes
what are zymogens
what are some examples
zymogens - inactive precursors of digestive enzymes
trypsinogen, chymotrypsinogen, procarboxypeptidase
other digestive enzymes (not zymogens) amylase, lipase, colipase
there is an enzymes for all major nutrient groups
where does the alkaline fluid come from in pancreatic secretion
alkaline fluid - intercalated duct cells
essentially isosmotic NaHCO3
solution
what is the role of the alkaline fluid secreted from the pancreas
neutralises acidic chyme from the stomach
this is because the These enzymes needed for digestion dont work in acidic environment that is provided by the stomach therefore it needs to be neutralised
what stimulates pancreatic secretion
in absence of food
low basal secretion
during the cephalic and gastric phase
limited secretion
during intestinal phase - arrival of food in intestine
largest volume of secretion
cholecystokinin (CCK) and secretin
also get minor regulation via vagus
acetylcholine
what is the stimulus for CCK
fat, products of protein digestion in duodenal lumen
what is the stimulus for secretin
acidic chyme in duodenal lumen
CCK and Secretin have different effects
what are these
Secretin is important for increasing bicarbonate and decreasing CL whereas CCK has not effect
CCK effects acini
Secretin acts on the duct cells which is where 75% of the pancreatic secretion comes from
CCK and Secretin have different effects
what are these
Secretin is important for increasing bicarbonate and decreasing CL whereas CCK has not effect
CCK effects acini
Secretin acts on the duct cells which is where 75% of the pancreatic secretion comes from
what % of pancreatic secretion comes from the duct cells
Secretin acts on the duct cells which is where 75% of the pancreatic secretion comes from
what stimulates acinar cells
CCK and vagus (ACh)
what do acinar cells secrete
secrete small volumes of isotonic NaCl and digestive enzymes
what % of secretion are acinar cells responsible for
primary fluid secretion (25% of total pancreatic solution)
what acts on duct cells
secretin
what do duct cells secrete
secrete larger volumes of isosmotic NaHCO3
primary secretion modified by further secretion
Pancreatic secretion
A. is hypotonic due to high Na+ re-absorption in pancreatic ducts.
B. is stimulated by somatostatin.
C. contains trypsinogen released from zymogen granules.
D. is elevated during the gastric phase.
A. Iso because it is leaky therefore there is not Na reabsorption, you actually secrete it
B. CCK and secretin
D. there is limited secretion during the gastric phase it is largest during the intestinal phase
C is correct
zymogen graduals in the acinar cells are responsible for the protein secretion
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CCK and ACh stimulate an increase in acinar cell secretion via….
increase in Ca
Acinar cells secrete isotonic NaCl solution by electrogenic Cl- secretion
what channels are needed for this
Na/K ATPase
K channel
NKCC1
Cl channel in apical membrane
Cl creates an electrical gradient, Na follows Cl (paracellular pathway) and water follows salt (paracellular pathway) because leaky epithelium
summery of acinar cells
fluid secretion is driven by electrogenic Clsecretion
CCK and acetylcholine stimulate increase in [Ca2+]i activates a Ca2+ -dependent apical Cl- channel increase in intracellular Ca2+ also stimulates the secretion of enzymes
results = the secretion of a small volume of isotonic NaCl solution containing
a high concentration of digestive enzymes
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duct cells secrete large volumes of HCO3- rich solution
what is the effect of this
hydrates proteins secreted by acinar cells
alkalinises the solution bathing proteins
flushes protein out of ducts into small
intestine
neutralises gastric acid
Helps to flush into the small intestine but the main function is to neutralise the acid as the digestive enzymes wont work at the low pH
what is the secretion in duct cells stimulated by
stimulated by..
secretin (main stimulus) which acts through cAMP
also ACh
what is the driver of secretion in duct cells
secretory epithelia
secrete Cl ions not HCO3-
saw an exception to that with HCl secretion
in duct cells HCO3- drives
secretion
Under resting conditions we don’t have any release during the cephalic and gastric phase
Under stimulated condition you have additional support of CFTR
There is leaky epithelium and the electrical greident the Cl crates an electrical gradient. Bicarbonate adds to this therefore causes lots of water secretion
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what channels are in an activated duct cell
basolateral
Na/K ATPase
K channel
Na/HCO3 cotransporter
Na/H exchanger
apical
Cl/HCO3 exchanger
when secretin binds (basolateral) it increases cAMP which causes CFTR to be inserted into the membrane which creates an electrical greident
what happens in the duct cell when CFTR gets inserted into the membrane
it causes secretion of HCO3 (via Cl/HCO3 exchanger)
the Cl electrical gradient causes Na and water to move through the paracellular pathway
what happens in the duct cell when CFTR gets inserted into the membrane
it causes secretion of HCO3 (via Cl/HCO3 exchanger)
the Cl electrical gradient causes Na and water to move through the paracellular pathway
what happens in cystic fibrosis at the level of the pancreas
Cystic fibrosis = mutation in CFTR therefore if the CFTR is not working then you cant secrete the bicarbonate rich fluid which means that they cant get the enzymes from the pancreas to the intestine therefore
they are mellabsorbed because they cant further digest food for absorption
Worst cases is they gat stuck in the pancreas and the pancreas starts digesting itself
Salivary vs pancreatic duct cell secretion
tight (s) vs leaky epithelium (p)
chloride secreted to drive bicarbonate
secretion (boosted by secretin in pancreas)
NO change in sodium content (pancreas). no ENaC because Na can move through the paracellular pathway
major site of fluid secretion in pancreas
summery of duct cell
dependent on apical Cl-/HCO3- exchanger
at rest this is inactive as very little Cl- in duct lumen
this is controlled indirectly via a cAMP-dependent Cl- channel (CFTR) activated by secretin
increase in cAMP = activation of apical Cl- channel (cAMP-activated)
Cl- diffuses into the lumen of the duct providing luminal Cl for apical Cl-/HCO3- exchanger
luminal Cl- exchanged for HCO3- which results in HCO3- secretion
Na+ diffuses across paracellular pathway due to potential set
up by Cl- movement
water follows because of osmotic gradient
secretion of NaHCO3
,
The secretion of a bicarbonate-rich solution by pancreatic
duct cells is driven by CCK,
BECAUSE
bicarbonate secretion in stimulated pancreatic duct cells is facilitated by CFTR.
the first statment is false and the second is true
to be true the first statement should say srecretin not CCK
what is the liver responsible for
The liver is responsible for digesting fat
what is the function of the liver
- processing of absorbed nutrients and control of metabolism
- secretion and excretion (exocrine function)
how does the liver process absorbed nutrients and control of metabolism
gluconeogenesis, glucose buffering, fatty acid oxidation, synthesis of plasma proteins (e.g., albumin)
how does the liver have a role in secretion and excretion (exocrine function)
provision of bile acids and alkaline fluid to:
aid digestion and absorption of fats
neutralise gastric acid
also causes…
degradation and conjugation of waste products of metabolism
detoxification of poisonous substances
excretion of waste metabolites and detoxified substance in bile
The liver either release’s or stores glucose
Albumin is the oncotic pressure in the kidney
The liver is a duct secreting organ as well
We are secreting metabolites as well as drugs and secretes a slightly alkaline fluid
k
If you take an aspirin then it first goes to the liver. The liver is the gate keeper for our system. why is this is a problem for pharmaceutical reasons
if it does not pass through the liver then the drug will go straight back into the intestine and be excreted
It can convert medications to nonfunctional metabolites (therefore they wont have an effect)
describe the anatomy of the liver
hepatic artery = blood supply
portal vein and central vein.
bile canaliculi and bile duct
hepatocytes line canaliculi
ducts secrete bicarbonate rich fluid
what is the volume of pancreatic secretions
0.5L per day
what is the composition of bile secreations
excretory products
bile pigments - waste products
cholesterol - excreted by liver
steroids, heavy metal, drugs
products associated with digestion
HCO3- rich fluid - secreted by duct cells
bile salts (Emulsify the fat to get it digested)
why are bile salts amphipathic compounds
because they have a hydrophillic and hydrophobic
surface
therefore they are able to emulsify FFA, and cholesterol
what is the primary bile acid
cholic acid
there are 2 sources of bile salts. what are they
newly synthesized
enterohepatic circulation (recycling)
what is the enterohepatic circulation
it is a mechanism in the small intestine that causes limited passive absorption of bile salts and active absorption in ileum
the colon also plays a limited role
it is about the reabsorption of bile salts
what % of bile salts are absorbed
95%
the 5% that we lose is resynthesized
control of biliary secretion has 3 mechanisms. what are they
nervous, hormonal and bile salts
biliary secretion mainly happens in the intestinal phase. what causes this
hormonal
secretin stimulates production of HCO3- rich solution by ducts
CCK stimulates contraction of gallbladder
bile salts
arrival of bile salts in portal venous blood stimulates absorption by liver and subsequent secretion
The liver produces a bicarbonate-rich bile,
BECAUSE
bile acids are required to reabsorb protein in the
intestine.
the first statment is true and the second is false
second statement should say fat to be correct
Functions of the liver
gluconeogenesis, glucose buffering, fatty acid oxidation, synthesis of
plasma proteins (e.g., albumin), detoxification;
Biliary secretion (stimulation: intestinal phase, CCK and secretin)
liver produces a bicarbonate-rich bile including bile acids, drugs and metabolites;
bile acids are used to reabsorb fat;
bile acids are recycled;
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