Pancreas and Liver Physiology Flashcards
GI Physiology
What does a pancreatic islet contain?
Alpha cells
Beta cells and Exocrine acinus
What are the two endocrine functions of the pancreas?
Produces hormones e.g. insulin and glucagon
Hormones secreted directly into bloostream
What are the three exocrine functions of the pancreas?
Pancreatic juice
Site of action is the small intestine
Duct mediated secretion similar to salivary secretion
What is the microscopic structure of the pancreas similar to?
salivary glands - secretory
what do the pancreatic secretions move through, into what?
they move through intercalated ducts into one large duct - and then secretes into duodenum
in most species, where does the pancreatic duct secrete directly into?
directly into the duodenum
In goats and sheep, where does the pancreatic duct join the common bile duct?
joins BEFORE the entrance into the duodenum
what enters the duodenum from the pancreas?
A mixture of bile and pancreatic juice enters the duodenum
what does a lower concentration of HCO3- and Cl- determine about the secretion rate?
the lower the conc = the faster the secretion rate
what enzymes are found in the pancreatic juice?
lipase, amylase and proteases
what does lipase do?
it breaks down fat, glycerol and fatty acids
what does amylase do?
it breaks down starch, glucose and maltose
what do proteases do?
they break down peptides and amino acids
what form are all enzymes secreted in?
all secreted in their inactive form
what are inactive precursors?
the inactive forms of enzymes
what does trypsin do?
it activates all enzymes
what enzyme is an autocatalyst?
trypsin
what is autocatalysis?
the process where the reaction product is also the catalyst for the reaction
what does trypsin inhibitor do?
it can limit innapropriately activated trypsins
what is trypsin secreted as?
secreted as trypsinogen
where is trypsin formed and what forms it?
it is formed in the duodenum and it is formed by enteropeptidase
which cells secrete trypsin inhibitor?
gland cells
what is produced in large volumes?
pancreatic juice
describe the pH of pancreatic juice?
alkaline
why is pancreatic juice alkaline?
due to the HCO3- ions
Point of the pancreatic juice being alkaline?
it neutralises ingesta/chyme that is entering the duodenum from the stomach
Why is it good that the pancreatic juice is alkaline?
it prevents injury to mucosa
it provides the optimal pH for enzymatic activity
how many phases of juice secretion are there?
3 phrases
what are the three phases of pancreatic juice secretion?
cephalic phase
gastric phase
intestinal phase
what occurs during the cephalic phase of pancreatic juice secretion?
changes that occur before food enters the stomach - prehension, mastication and deglutition
what occurs during the gastric phase of pancreatic juice secretion?
changes in digestive tract motility initiated in the stomach - peristalsis and churning of food as a trigger
what does feeding result in for most species? what’s different for pigs and horses?
increases enzyme production in most species - increase in secretion of pancreatic juice HOWEVER pigs and horses there are also increases in water and ion secretion
what occurs during the intestinal phase of pancreatic juice secretion?
chyme entering the duodenum causes increases in pancreatic secretion - this is regulated by CCK and secretin
What feedback system is secretin involved in?
it is involved in the negative feedback system
when and where is secretin released from?
it is released from duodenum upon increased acidity
what is secretin?
it is a neuroendocrine peptide hormone
what does secretin have action on?
many organ systems
where is secretin secreted from?
secrteed by the S cells of the duodenum
what does the release of secretin stimulate?
stimulates HCO3- secretion - neutralisation function
when does secretin production reduce?
once acid in the duodenum decreases
what does CCK stand for?
Cholecystokinin
what is CCK?
it is a peptide hormone secreted by the duodenum
when is CCK released?
when FAs and peptides/amino acids increase in duodenum
what does CCK stimulate?
it stimulates the pancreas to increase enzyme secretior and increases bile secretion
what effect does CCK have on enzymes?
it results in increased enzymes = increased ingesta degradation
overall, CCK results in?
increased products of digestion
what feedback system is CCK involved in?
positive feedback system
rate of secretion of pancreatic juice comparison between ruminants, horses and cats&dogs?
ruminants - constant rate of secretion and chyme transport
horses - increase in rate of rate of secretion within a few minutes of feeding starting –> low levels of enzymes due to microbial degradation
Cats&Dogs - great increase in amount of juice produced after feeding
little production when small intestine is empty
How many roles of the liver are there?
9
Role one of the liver:
The liver handles nutrients absorbed from the intestine and regulates their release into the blood
Role two of the liver:
Inactivating substances (toxins and drugs)
Role three of the liver?
Conversion of lipid soluble substances to water-soluble metabolites
Role four of the liver:
excretion of substances
role five of the liver?
production of plasma proteins
role six of the liver?
production of blood coagulation factors
role seven of the liver?
excretion of bile pigments
role eight of the liver?
production of cholesterol
role nine of the liver?
bile production BY hepatocytes
what is bile made from?
made from cholesterol
what type of processes are involved in bile production?
active processes - active transport
what are bile salts transported into?
transported from the hepatocytes into bile canaliculi
What is the journey for bile from bile canaliculi?
Bile canaliculi gradually feed into larger canals and then into the common bile duct
What part of the bile salts is produced from cholesterol?
BILE ACIDS
What are conjugated bile acids?
they are bile acids that are bound to amino acids
what do conjugated bile acids do?
they attract sodium to become bile salts
what do bile salts do?
they digest fat in the intestine
what do the hepatocytes in bile secrete?
phospholipids and cholesterol
function of phospholipids in liver?
aid with fat digestion
function of cholesterol in liver?
waste product
what is happening at the gall bladder?
site of storage for bile when no digestion is occurring
what is extending from the common bile duct?
a side duct to the gall bladder
contraction of gall bladder is controlled by what?
CCK
What is the sphincter of Oddi?
band of smooth muscle cells between the bile duct and duodenum
Solubility of bile salts? meaning…
they are not soluble meaning they are not absorbed by diffusion from the small intestine
what is enterohepatic circulation?
when bile salt molecules are returned to the liver
where do bile salts function and where do they get absorbed?
they function throughout the entire length of the small intestine before being absorbed at its end
what type of organ is the pancreas?
a secretory organ
pancreatic duct joins with bile duct and then into the duodenum?
sheep, rodents, humans etc.
chyme pH?
really acidic
point of bicarbonate?
instantly neutralises the acidic chyme
what animals don’t have amylase in their saliva?
dogs
ogen? e.g. pepsinogen
this enzyme is an inactive precursor
which is the master regulator that activates all other enzymes?
trypsin - release as trypsinogen
importance of inhibitors?
if none, there might be not enough food components for trypsin to break up so instead it gets ‘bored’ and starts breaking down small intestines
alkaline carbonates function?
break down connective tissue in ‘meaty’ meals
how many phases of pancreatic juice secretion are there?
3
when we are eating, tasting, smelling the food what messages are sent to brain by what nerve?
by vagus nerve
in which stage of pancreatic juice secretion do enzyme rich secretions occur?
gastric phase
what does chyme entering the duodenum result in?
an increase in pancreatic secretions
when is secretin released
when pH drops below 4.5
where is secretin secreted?
mucosa in duodenum
2 hormones that stimulate intrinsic phase?
secretin and CCK
CCK is going to be released as long as…
we’re receiving products from the stomach
apetite suppressant?
CCK - males are less susceptible to CCK
Ruminants - how much pancreatic juice made in 24 hours?
4-5L
horses - level of pancreatic enzymes in juice?
low levels
how much pancreatic juice does a horse produce in 24 hours?
30-35L
how much pancreatic juice will a 20kg dog produce?
2-3 ml/min
why does liver convert lipid soluble substances to water soluble substances?
so that they can be excreted
portal triad, what is it made up of?
arterioles of hepatic artery, portal venule and bile duct
bile canulili?
form between tight junctions of cells
caniliculi?
increases surface area
two most common bile acids
coalic acid, keodnocoalic acid
what makes bile acids attracted to sodium in order to become bile salts?
when the bile acids bind to amino acids
other lipids found in bile?
phospholipid
cholesterolb
bile is 95%?
water
bile leaving bile duct controlled by?
sphincter of Oddi
5% of bile salts?
excreted in faeces
return to liver?
hepatic… circulation route
regulation of bile secretion stimulated by?
by increased parasympathetic activity mediated via vagal nerves and secretin
what is the most important factor determning the volume of bile?
the amount of bile salts in the bile canaliculi
what happens when the conc of bile salts in the portal blood rises?
the amount of bile released from the hepatocytes increases
between meals, where is bile stored?
in gall bladder
when is bile production the greatest?
when bile salts recirculate after a meal
when does blood concentration of bile salts and therefore excretion of bile salts remain low?
in between meals
how does secretin regulate bile secretion?
release stimulated by acidic duodenal content
causes increase of HCO3- from pancreas
Causes increase of bile production
when will the sphincter of Oddi be closed and the gall bladder relaxed?
when there is no food in the small intestine
what happens to bile in the gall bladder?
bile gets concentrated in the gall bladder - ions get actively transported out of the bile - water follows by osmosis as a water potential gradient is formed
which species do not have a gall bladder?
horses, trickle feeders, constantly eating
after a meal, what happens to the gall bladder and sphincter of Oddi?
the gall bladder contracts and the sphincter of Oddi opens
after a meal, what happens in response to CCK?
fat and peptides in the duodenum cause CCK release
ensuring pancreatic and hepatic secretions coincide
what happens when fat digestion is complete?
the stimulus for CCK release is removed and bile is stored in the gall bladder
describe fat digestion in dogs and cats?
fat digestion is intermittent therefore bile is not present in the intestine all the time - very useful to have a gall bladder
describe the gall bladder of a ruminant?
gallbladder has a short retention time - poorly developed concentrating mechanism
