T1 L6: Secretions of the intestine, liver, gall bladder, and pancreas Flashcards
Where is vitamin B12 absorbed in the intestine?
In the ilium (Payers patches)
What is secretin?
Secreted by S cells and it stimulates pancreatic and biliary bicarbonate secretion to produce high volume HCO3- rich pancreatic juice
What is Cholecystokinin (CCK)?
Its secreted by I cells and it stimulates pancreatic and gall bladder secretion
What is glucose dependent insulinotrophic peptide (GIP)?
Secreted by K cells and it inhibits acid secretion and insulin release is stimulated
What do goblet cells secrete?
Mucus
What do enteroendocrine cells secrete?
Secretin, cholecystokinin, or GIP
What do Paneth cells secrete?
Lysozyme capable of phagocytosis
Which secretory cells are found on villi?
absorptive enterocytes and goblet cells
Which secretory cells are found in intestinal glands?
Enterocytes secreting isotonic fluid, entero-endocrine cells, Paneth cells
Where are Brunner’s glands found?
Only in the duodenum
What do Brunner’s glands secrete?
Mucus and HCO3-
Where are stem cells found in the intestines?
In the base of crypts
What is the turnover rate in the intestines?
3-6 days
What is exocrine pancreatic juice made up of?
Bicarbonate and digestive enzymes
What is produced in the alpha islets of Langerhans in the pancreas?
Glucagon
What is produced in the beta islets of Langerhans in the pancreas?
Insulin
What is produced in the delta islets of Langerhans in the pancreas?
Somatostatin
What is produced in the F-cells in the islets of Langerhans in the pancreas?
Pancreatic polypeptide
What does Somatostatin do?
It inhibits many digestive processes
What does pancreatic polypeptide do?
It regulates pancreatic secretions
What % of the pancreas is made up of exocrine acinar clusters secreting pancreatic juice?
99%
What stimulates the production of ACh in acinar clusters of the pancreas?
Parasympathetic vagus nerve stimulation
What makes up the pancreatic juice secreted by exocrine acinar clusters in the pancreas?
Water, electrolytes, sodium bicarbonate and pro-enzymes
What stimulates the production of CCK in acinar clusters of the pancreas?
Chyme containing fat and proteins
What stimulates the production of secretin in ductal cells of the pancreas?
H+ in chyme
What is the function of trypsin inhibitor?
It prevents activation of trypsin to prevent pancreatic digestion
Why are proteolytic enzymes secreted in inactive form?
To prevent autodigestion within the pancreas. They’re activated in the brush border of the small intestine
What do nucleases digest?
RNA and DNA into nucleic acids
What are zymogens?
The inactive form of proteolytic enzymes
What does trypsin do?
A type of proteolytic enzyme that goes on to activate other proteolytic enzymes
How is trypsin activated?
The enzyme enterokinase cleaved hexapeptide to form active trypsin from trypsinogen in the brush border of the small intestine
What is the brush border of the small intestine?
The border of the small intestine. The epithelium lining it
What is the CFTR transporter for and what controls it?
For recycling of Cl-. Its under the stimulation of secretin
Which nerve supplies the submandibular and sublingual glands?
Super salivary nucleus (CN7 - the facial nerve)
Which nerve supplies the parotid gland?
The inferior salivary gland (CN9 - the glossopharyngeal nerve). Has to go through the Ottic ganglia to get to the gland
What do enteroendocrine G-celldo?
They respond to partially digested proteins and therefore the [H+] in the stomach, and then they will secrete gastrin in response
What does gastrin do?
It stimulates parietal cells to release HCl and chief cells to release pepsinogen
What do chief cells do?
They secrete pepsinogen that under a specific pH will turn into pepsin in the stomach
Why do partially digested proteins result in a pH change?
H+ will bind to proteins so having a lot of proteins increases pH into more alkali
What is somatostatin stimulated by?
Low pH
What do parietal cells do?
They have carbonic anhydrase to produce HCl in the stomach
What do ECL cells do?
Secrete histamine
What do D-cells do?
Produce somatostatin
Which nervous system control motility?
The enteric NS
How does omeprazole work?
Inhibits H+/K+ ATPase
How does Atropine work?
It inhibits muscarinic receptors and vagal stimulation of acid secretion
What is the mechanism behind cholera?
The permanent activation of adenylyl cyclase so Cl- are constantly being pushed out and water will follow leading to dehydration
What is the ionic composition of unstimulated secretion?
Low secretion rate and its similar in composition as plasma
What is the ionic composition of stimulated secretion?
High secretion rate high in HCO3- and low in Cl-
What is the mechanism behind cystic fibrosis?
The CFTR transporter is defective leading to the ducts being blocked with enzymes and mucus that will lead to fibrosis of the pancreas
Which cells secrete intrinsic factor needed for vitamin B12 digestion?
Parietal cells
What oral medication is given to those with the CFTR Cl- transporter?
Oral pancreatic enzyme supplements with each meal
What is pancreatitis?
An inflammatory disease where pancreatic enzymes are activated within the pancreas leading to autodigestion. Most common causes are gall stones and alcohol abuse
Which organ concentrates bile and how?
The gallbladder by reabsorbing water and electrolytes across the gall bladder mucosa
What do Kupffer cells do?
They digest old RBC’s
What is Hepatocellular (congenital) jaundice?
The hepatocytes have altered function that prevents conjugation of bilirubin (making hydrophilic) so it can’t be transported by albumin. Caused by Crigler-Najjar syndrome
What is pre-hepatic jaundice?
Excessive RBC breakdown causing build up of bilirubin because the body can’t keep up. Can happen with haemolytic anaemia
What is Hepatocellular (congenital) jaundice?
The hepatocytes have altered function
What is post-hepatic jaundice?
Obstruction of the bile duct. Caused by gall stones
How is bile secretion regulated (3 ways)?
CCK causes gall bladder contraction. Secretin is released in response to acidic chyme and it causes ductal secretion of HCO3-. Vagal and ACh stimulation causes bile flow and gall bladder contraction
What is enterohepatic circulation for?
Recycling of bile salts
What are the common causes of glass stones?
Excessive water and bile salt reabsorption, excessive cholesterol, inflammation
What is Cholelithiasis?
Gall stones
