GI Secretions (L5+8) Flashcards
Which efferent nerves supply the salivary glands?
Glossopharyngeal
Facial
What is Sjogren’s Syndrome?
Autoimmune disease that destroys exocrine glands. It affects tear and saliva secretion, meaning the symptoms include dry eyes and a dry mouth (sicca symptoms)
What are the three salivary glands?
- Submandibular which secrete 70% of saliva (serous and mucous)
- Parotid which secrete 25% of saliva (serous)
- Sublingual which secrete 5% of saliva (mucous)
What are the three main functions of saliva?
- Protection
- Digestion
- Lubrication
What is the only hormone that can affect saliva secretion?
Aldosterone, which increases ductal Na+ reabsorption and K+ secretion.
What is gastric juice comprised of?
- Water and electrolytes
- HCl
- Pepsins
- Mucus (water + glycoprotein Mucin)
- Intrinsic Factor
What are pepsins?
Pepsins are endopeptidases with cleave peptide bonds (digest proteins).
They are first secreted as inactive pepsinogens but get activated into pepsin at a pH below 5.
What is the role of mucus in gastric juice?
To protect the surface epithelial cells from acid/pepsin erosion
What is the role of Endocrine cells (D-cells)?
To secrete somatostation, which regulates the release of gastrin and gastric acid secretion.
What is the role of Chief cells?
To secrete pepsinogen
What is gastritis?
This is the inflammation of the gastric mucosa. It is mainly caused by the bacteria Helicobacter pylori but can also be caused by smoking, alcohol and chronic stress.
What are Oxyntic/Parietal cells?
The cells in the stomach that secrete acid via H+/K+ ATPases on the tubulovesicular membrane.
Explain the activation of Oxyntic/Parietal cells.
Upon stimulation, the tubulovesicular membrane fuses into a canalicular membrane and H+/K+ ATPases, K+ channels and Cl- channels are inserted into the membrane.
Mechanism of Gastric acid secretion.
H+ and HCO3- are generated within the cell by carbonic anhydrase. .
H+ gets pumped across the luminal membrane by H+/K+ ATPase and Cl- leaves by diffusion.
Example of a proton pump inhibitor.
Omeprazole which inhibits H+/K+ ATPases on the luminal surface of parietal cells.
What are the three major stimulators of acid secretion?
- Gastrin
- Histamine
- Acetylcholine
What are the major inhibitors of acid secretion?
- Somatostatin
- Prostaglandins
Why is prostaglandins able to inhibit acid secretion?
Because it is an antagonist of histamine, meaning cAMP production is inhibited.
How do gastrin and ACh stimulate acid secretion?
By increasing intracellular Ca2+.
What is a crypt-villus unit?
The functional unit of the small intestine
What is the structure of a crypt-villus unit?
- The crypt is at the base and it contains rapidly dividing stem cells that force the migration of cells up the side of the villus. Crypt cells are the source of intestinal fluid secretion.
- The maturation zone is an intermediate zone where the cells are getting closer to the tip and are beginning to express enzymes and transport proteins for absorption.
- The villus tip is at the top and the cells are fully differentiated and absorb nutrients, electrolytes and fluids. After 3-4 days, the cells are removed as a defence mechanism to any possible insults.
What are Brunner glands?
Glands located in the duodenum which secrete an alkaline fluid which can act as an anti-acid, protected the epithelium from the acidic chyme from the stomach
Where in the small intestine does the majority of absorption take place?
Jejunum
What are Peyer’s patches?
Present in the ileum and develop immunity to antigens found
