Secretions of the small intestine, liver, gall bladder, and pancreas Flashcards
Where does the majority of chemical digestion and absorption of nutrients, electrolytes and water take place in the GIT?
- small intestines
What are ther 3 parts of the small intestines called from top to bottom?
1 - duodenum
2 - jejunum
3 - ileum
What is the name of the spincter that facilitates movement from the stomach into the duodenum
- pyloric sphincter
What are the 3 main secretions into the duodenum of the small intestines?
- intestinal juice (mucus/HCO3-)
- pancreatic juice (digestive enzymes)
- bile (fat emulsifier)
In addition to pancreatic juice, bile salts and intestinal juice, hormones can be secreted into the duodenum. What are the endocrine enzymes that are secreted that we need to know about?
- secretin
- cholecystokinin [CCK]
- glucose dependent insulinotrophic peptide [GIP]
The secretion of endrocrine secretions secretin, cholecystokinin [CCK] and glucose dependent insulinotrophic peptide [GIP] have an important functions in the duodenum. What 2 main secretions do they regulate in the duodenum?
- regulate bile and pancreatic secretions
Secretin is secreted by endocrine cells in the small intestines, which cells in the duodenum secrete it and what is the role of this hormone?
- peptide hormone secreted by S cells in duodenum
- regulates water homeostasis and pH
- regulates pH by secretions in the stomach, pancreas, and liver
Is secretin secreted into the lumen of the small intestines or into the blood stream?
- can be both
What is cholecystokinin and what is its main function?
- a peptide hormone
- secreted by enteroendocrine cells of te duodenum
- stimulates digestive enzymes and bile to be released
- can also act as a hunger supressant
What cells secrete glucose dependent insulinotrophic peptide (GIP) and what is the function for GIP?
- K cells in duodenum (hormone)
- trophic means to secrete and insulin tells you what
- inhibits gastric acid secretion
Cells at the tip of the microvilli are called enterocytes, what are they primarily involved in?
- absorption
What are goblet cells?
- cells in small intestines that secrete mucous
What are enteroendocrine cells?
- specialized cells found within the GIT stomach and pancreas
- able to secrete hormones when stimulated
Enteroendocrine cells are able to secrete hormones. They can secrete locally or systematicall, how do they do this and what are the different effects?
- local secretion = local messenger
- blood secretion = systemic effects
What are paneth cells that can be found in the epithelium of the small intestines?
- highly specialized secretory epithelial cells
- produce dense granules containing antimicrobial peptides and immunomodulating proteins
- main role immunotherpay
What are Brunners glands and where is the only place they can be found?
- glands are located in the submucosa of the duodenum
Brunners glands can only be found in the duodenum, what is their purpoose?
- secrete HCO3- and mucus
- increase pH and protect mucus
What cell in the walls of the GIT differentiate into different epithelial cells and drive shedding of epithelail cells?
- stem cells
Epithelial cells of the GIT have a high turnover, how often do they generally shed?
- 3-6 days
As the epithelial cells have a high regenerative capacity, what are they susceptible to in relation to a specific type of treatment?
- cancer treatment
- X-rays
- chemotherapy
Do paneth cells come from stem cells?
- no
- they come from daughter cells
- migrate downwards instead of upwards
What is intestinal juice, and what is it made up of?
- solution that facilitates digestion in the small intestines
- enterocytes secrete water containing electrolytes
- paneth cells secrete lysozyme to degrade bacteria
- goblet cells secrete mucus
- brunners glands secrete alkaline mucus
What is the main role of bile in the small intestines?
- fat emulsification
What is pancreatic juice?
- composed of digestive enzymes and bicarbonate
- eznymes are screted by acinar cells in pancrease
- bicarbonate is secreted from the epithelial cells lining small pancreatic ducts
The pancreas is classed as both exocrine and endocrine, why is this?
- exocrine = digestive enzymes
- endocrine = insulin and glucagon
Typically, what is the pH of the pancreatic juice secreted by the pancreas?
- pH 8
- crucial for neutrilising the acid contents from the stomach
Which large nerve provides parasympathetic control in stiumlating the pancreas?
- vagal nerve (cranial nerve X or 10)
In addition to neural innervation of the pancreas, there is hormonal control, which 3 hormones influence pancreatic secretions?
1 - cholecystokinin
2 - secretin
3 - gastrin
The pancreas is composed of exocrine and endocrine epithelial clusters. What are the 2 types of clusters, and which makes up the majority of these clusters?
- acinar clusters (exocrine) and islets of langerhans (endocrine)
- 99% are acinar clusters
- secrete pancreatic juice (water, electrolytes, sodium bicarbonate and pro-enzymes)
The pancreas is composed of glandular epithelial clusters. What makes up a small but very important proportion of these clusters?
- 1%- endocrine pancreatic islets (Islets of Langerhans)
The pancreas is composed of glandular epithelial clusters. 1% of these clusters are endocrine clusters, of which there are 4 types, what are they?
1 - alpha cells (glucagon)
2 - beta cells (insulin)
3 - delta cells (somatostatin)
4 - F cells (pancreatic polypeptide)
What does acinar relate to?
- berry
- group of cells resembling a berry
Contentc of the pancreatic juice are created in the acinar cells of the pancreas. What is the flow of the exocrine secretions from the acinar cells into the main pancreatic duct?
- acinar cells in lobules secretions enter the intercalated ducts
- intercalated ducts merge into interlobular ducts
- interlobular ducts merge with the main duct of the pancreas
In addition to the acinar cells secretions, the ducts of the pancreas are also able to secrete fluids that make up the pancreatic juice. When looking at the image of the pancreatic duct from acinar seretions to the duodenum, what are the concentrations of key electrolytes?
- both ends of the ducts have high Na+ and low K+
- acinar end of ducts = high Cl- and low HCO3-
- ductal end of ducts = low Cl- and high HCO3-
- H2O follows Na+ into the duct but then cannot leave
Acinar cells secret sodium bicarbonate (NaHCO3-) due to the high Na+ and HCO3- concentrations and ductal secretions are NaCl due to the high Na+ and Cl- concentrations. What is the importance of the different secretions from the acinar and ductal secretions?
- provides optimal enviorment for enzymatic actions
The GIT is able to sense the differing contents of food and drink entering the GIT, and therefore secrete different contents based on this. For example how are the acinar cells stimulated and what do they secrete in response?
- parasympathetic innervation via vagus nerve
- CCK released when fat and protein sensed in duodenum
- lower over all volume of pancreatic juice
- concentrated enzyme rich pancreatic juice
The GIT is able to sense the differing contents of food and drink entering the GIT, and therefore secrete different contents based on this. For example how are the ducts stimulated and what do they secrete in response?
- secretin in released when pH is low, able to sense H+ from stomach
- high volume HCO3- rich pancreatic juice
- low enzyme concentration pancreatic juice
Are all enzymes that are secreted by the pancreas in the active or inactive form?
- can be both
- inactive forms ensures no self digestion
The pancreas secretes enzynes that have a high proteolytic activity (able to digest proteins). But to ensure they do not digest the pancreas when they are secreted by acinar cells, they are secreted in their inactive form. How are these enzymes activated?
- enzymes present in the brush border of the duodenum activate the enzymes
The pancreas secretes enzymes that have a high proteolytic activity (able to digest proteins) in their inactive forms. What are the names of the 2 main enzymes?
1 - trypsinogen
2 - proteolastase
The pancreas secretes amylase, what do they digest and what is the name of this enzyme?
- hydrolysis of starch, glycogen, and other carbohydrates to form di/trisaccharides
- alpha amylase is main enzyme
The pancreas secretes lipases, what do they digest and what are the names of the 3 main enzymes?
- lipases hydrolyse fat into fatty acids and monoglycerides
- lipase
- pancreatic lipase
- phospholipase A2
The pancreas secretes nucleases, what do they digest and what are the names of the 2 main enzymes?
- digest RNA and DNA to nucleic acids
- RNAse
- DNAse
What are zymogens?
- precursors for active enzymes
- these are the inactive forms of the enzymes
In the small intestinal brush border there is a kinase called enterokinase, what is the function of this kinase?
- cleaves hexapeptide (6 amino acid sequence) from trypsinogen
- forms the active trypsin
- this process stops self digestion of the pancreas
In the small intestinal brush border the kinase called enterokinase is able to cleave a 6 amino acid sequence, called a hexapeptide from trypsinogen to form the active trypsin. What is the physiological importance of activating trypsin?
- entero = digestive tract
- kinase = adding phosphate
- trypsin activates other proteolytic enzymes
What are the suffix that are given to inactive proteolytic enzymes secreted by the pancreas?
- pro at the start of the name
- ogen at the end of the name
In order for ductal secretions of pancreatic juice containing high volume of liquid containing high amounts of HCO3-, but low enzyme concentration, what hormone is required to initiate ductal secretions?
- secretin secreted when pH is below 4
- secreted by S cells which is a enteroendocrine cell in duodenum
Once secretin has been secreted by enteroendocrine cells in the duodenum in response to a low pH, they stimulate the ductal cells of the pancreas, which then triggers the release of pancreatic juice that is low enzymatic concentration, but high HCO3- concentration. In the ductal cells the enzyme carbonic anhydrase is present. What does this enzyme create in ductal cells?
- combines H2O and CO2 into carbonic acid
- carbonic acid dissociates into HCO3- and H+
- H+ pumped into blood inexchange for Na+
- HCO3- is pumped into the ducts in exchange for Cl-
In order for HCO3- to be pumped from the ductal cells into the ducts, what exchanger must be present?
- Cl- / HCO3- exchanger
- Cl- enters ductal cell
- HCO3- enters the ducts
- cystic fibrosis transmembrane conductance regulator (CFTR) is important in the ductal cells
Once HCO3- and Cl- have exchanged places there may be a build of of Cl- within the ductal cells. What transmembrane transporter that is activated by secretin is responsible for ensuring that Cl- is recycled back into the ducts of the pancreas?
- cystic fibrosis transmembrane conductance regulator [CFTR]
- Cl− channel under secretin stimulation, via cAMP
- in CF this is where secretions are problematic
Na+ is transported into ductal cells from the blood through the Na+ / H+ exchanger. H+ is created by what enzyme, which also creates HCO3-?
- carbonic anhydrase
Once Na+ has been transported into ductal cells from the blood through the Na+ / H+ exchanger, there will be an increased Na+ concentration. Where will the Na+ then move into and what will follow this?
- Na+ moves down concentration gradient into ducts
- H2O follows Na+ due to osmosis
- this creates NaHCO3- in ducts
What are the 3 phases of pancreatic secretion?
1 - cephalic
2 - gastric
3 - intestinal
In the cephalic phase of pancreatic secretion, what stimulates pancreatic secretion and how does this trigger pancreatic secretions?
- senses (smell, sight) detect food and signal the brain
- efferent signals are sent down the vagus nerve
- vagus nerve stimulates acinar cells in the pancrease
In the cephalic phase of pancreatic secretion, in addition to vagul nerve stimulation, there is also the release of vasoactive intestinal peptide (VIP). What is VIP and what is its main role?
- a peptide hormone that is vasoactive in the intestine
- stimulates pancreatic secretions
- inhibits the release of gastrin and the secretion of acid in stomach
What % of total secretions does the cephalic phase account for?
- 20%
The gastric phase is when food enters the stomach. Once food enters the stomach what happens?
- mechanoreceptors in the stomach are stretched
- afferent signals are sent to the brain
- efferent signals are transmitted to via vagus nerve to pancreas
- pancreas secretions increase
In the gastric phase of pancreatic secretion, there is a vago-vagal activation, what is this?
- afferent signals sent to brain
- efferent signals are sent out to the body
How much of total pancreatic secretion does the gastric phase account for?
- 10%
In the gastric phase, in addition to the vaso-vagal reflex the vagus nerve also stimulates the secretion of something in the antrum of the stomach, what is this?
- G cells in antrum secrete gastrin
- gastrin stimulates HCl secretion and stomach motility
In the intestinal phase of pancreatic secretion, the chyme enters the duodenum from the stomach. The chyme contains 2 important stimuli what are these 2 stimuli in the duodenum?
1 - chyme containing fatty acids and protein in duodenum
2 - low pH of the chyme
In the intestinal phase of pancreatic secretion, chyme enters the duodenum which contains fatty acids and proteins. What cells in the duodenum are able to sense these components of chyme and what do these cells secrete in response?
- I cells
- cholecystokinin (CCK)
In the intestinal phase of pancreatic secretion, chyme enters the duodenum which contains fatty acids and proteins. In response the I cells of the duodenum secrete cholecystokinin (CCK). What is the role of CCK in pancreatic secretion?
- CCK binds to acinar cells in pancreas
- acinar cells secrete pancreatic juice with high enzymes concentration
- also contribute to pancreatic juice with high HCO3- from ductal cells
In the intestinal phase of pancreatic secretion, chyme enters the duodenum which contains fatty acids and proteins. In response the I cells of the duodenum secrete cholecystokinin (CCK). in addition to the chyme, there will be an acid solution from the stomach, which will have a high concentration of H+. What does this trigger the secretion of?
- secretin from S cells
- secretin triggers the release of pancreatic juice high in HCO3-
In patients with cystic fibrosis (CF) the pancreas can be affected. How does CF cause problems with the pancreas?
- CF patients have a dysfunctional Cl- transporter
- Cl- is not able to be recyled between the ductal cells and ducts
- results in low Na+ and H2O in ducts and blocks them
- endocrine and exocrine functions are impaired
Patients with cystic fibrosis (CF) have an inability to recycle Cl- in the pancreatic ducts. This can result in a lack of Na+ and H2O, which results in thick pancreatic juice that is unable to travel to the duodenum. These patients often have a failure to thrive. What is the most common treatment CF patients have to treat this part of their disease?
- enzymes to replace those from the pancreas
- most common is creon
What is pancreatitis?
- pathologic inflammation of the pancreas
- enzymes are activated within pancreas and it digests itself
What are some common causes of pancreatitis?
- alcohol dependance
- drug misuse
- gall stones
- all block the pancreatic ducts
What is bile?
- combination of mucus, cholesterol and bile salts
- secreted by gall bladder
- emulsify fats and allow digestion forming micelles
In addition to allowing fat digestion, bile also has another important function, what is this function?
- remove waste products from the body
- biliruben from haem in degraded RBCs
- cholesterol removal
- drug removal
Which organ synthesises bile?
- liver
The liver synthesises bile, specifically which part of the liver?
- hepatocytes lining sinusoidal blood vessels in the liver acinus
The liver synthesises bile in the hepatocytes lining the sinusoidal blood vessels in the liver acinus. How does bile makes its way from the sinusoidal blood vessels to the gall bladder?
- drains into the canniculi of the sinusoidals
- drains into left and right hepatic bile ducts
- into the common hepatic duct and into the cystic duct
Bile is stored in the gall bladder. When it needs to be secreted what pathway does it take from the gall bladder?
- leaves cystic duct and merges with common bile duct
- common bile duct and pancreatic duct merge
- pass through the hepatopancreatic sphincter
- they enter the duodenum at the ampulla
Cholecystokinin (CCK) secreted by I cells in the duodenum in response to amino and fatty acids being recognised in the duodenum stiumlate pancreatic juice to be secreted from the pancreas. CCK also has another important function involving fat digestion, what is this?
- CCK stimulates gall bladder contraction
- sphincter of hepatopancreatic ampulla (Sphincter of Oddi) relaxes
What does enterohepatic circulation refer to?
- the secretions of the gall bladder into the small intestines
- they are recycled and re-absorbed back into the liver
- processed and make their way back to the gall bladder
- includes bile, biliruben
How much bile salts is recycled normally and where does the re-absorption of bile take place?
- around 94% is re-absorbed
- re-absorbed in the ileum, travel along portal vein into liver
What are the 2 main things that can go wrong in gall bladder disease?
- insufficient synthesis
- blocked bile ducts
One of the main causes of gall bladder disease, is gall stones. What are the 3 main things that can cause gall stones?
- excessive water and bile salt reabsorption from bile
- excessive cholesterol in bile causing precipitation
- inflammation of epithelium
- essentially an imbalance of the normal make up of bile
