GI secretions Flashcards
In the duct of salivary glands, what are the main things secreted (2) and the main things reabsorbed (2)?
Secreted: bicarb, potassium
Absorbed: sodium, chloride
Salivary secretion is always secreted isotonic in the acinus but then as it proceeds thru the ducts and out into the GI tract it is hypotonic. How does the flow rate of saliva affect tonicity?
Faster flow rates lead to less hypotonic saliva and slower flow rates lead to more hypotonic saliva. This is because the reabsorption and secretion is given more time during slow flow rate and the Na/K pump reabsorbs 3 sodium and secretes 2 potassium leading to less osmolarity in saliva overall.
Name the two major chemical mediators that increase saliva secretion.
- VIP (major)
- ACh
parasympathetics
How does bradykinin lead to increased salivary production?
Vasodilation of blood vessels allows more fluid to surround the acinar cells that can be used for salivary secretion.
What is the major function of the bicarb secreted in saliva?
Neutralize acid that may reflux from the stomach in the distal esophagus.
Name the 3 gastric endocrine cells and what each secretes.
- G-cells: gastrin
- Enterochromaffin-Like (ECL) cells: histamine
- D-cells: somatostatin
What do gastric parietal cells secrete?
- HCl
2. Intrinsic Factor
What is the Alkaline Tide?
Carbon dioxide diffuses into gastric parietal cells where carbonic anhydrase combines it with water to form carbonic acid. The acid dissociates to form a proton and bicarbonate. The bicarbonate is transported thru a bicarb/Cl- antiport back into the blood resulting in alkaline blood stream by the stomach.
How do protons in the parietal cells exit into the stomach lumen?
Thru a H+/K+ antiport
What are the 3 activators of acid secretion?
- Histamine (major)
- Gastrin
- ACh
Name two major inhibitors of acid production.
- Somatostatin
2. Prostaglandins
Name 5 hormones that signal D cells to secrete somatostatin.
- VIP
- Secretin
- Low pH
- GIP
- Glucagon
How does acid damage the mucosa layer?
The protons enter the mucosal layer and stimulate mast cells with release immune mediators that signal the immune system to release damaging inflammatory mediators.
It also activates pepsinogen which breaks down proteins.
What is a general mechanism that leads to stress ulcers?
Trauma, burns, ventilators lead to an increase in sympathetic activity. This constricts blood vessels around the GI tract. The mucosa in the stomach and duodenum need the blood supply for nutrients so that they can produce the protective mucous. Without the blood supply the mucous is not produced.
What supplies the bicarb to neutralize acid that enters the duodenum?
Pancreatic exocrine duct cells
Zymogen released by the pancreas that activates all the other enzymes released by the pancreas.
Trypsinogen: activated by enterokinase located on the duodenal lumen wall
(if a blockage occurs in the exocrine ducts, trypsinogen can “self-activate” and lead to pancreatitis)
Name the 2 major stimulators of zymogen secretion from pancreatic acinar cells.
- CCK (from duodenal I-cells)
2. ACh
How do cystic fibrosis patients get pancreatitis?
Lack of CFTR channel prevents water from entering the lumen of the pancreatic ducts. The zymogens cannot flow into the duodenum and remain in the pancreas where they are activated.
Name the 2 major stimulators of bicarb and potassium secretion from pancreatic ductal cells.
- Secretin (from S-cells, stimulated by acid, fats, proteins)
- VIP
What is the regulator of bile production in the liver?
The amount of bile that is recycled in the enterohepatic circulation.
Regulator that relaxes the sphincter of oddi and contracts gallbladder smooth muscle.
CCK
Regulator that increases liver ductal secretion of bicarb to increase flow of bile salts into the biliary system.
Secretin
How does bile enter the portal circulation from the ileum?
Thru a Na+/bile symporter
Name 4 causes of gallstones.
- Gallbladder concentrates bile to 5x that of circulation. stones can be caused by reabsorbing too much water
- Reabsorbing too much bile salts
- Too much cholesterol
- Inflamed epithelium
What neutralizes acid in the early duodenum?
Brunner’s glands which secrete mucous.
Bicarb from the pancreas and duodenal mucosa
Name the 2 major stimulators of bicarb and potassium secretion from intestinal ductal cells.
- Secretin
- VIP
(same as pancreatic ductal cells)
Main secretion in the colon.
Potassium. Chronic diarrhea leads to hypokalemia
