GI Lecture 4 Flashcards
Secretion
The addition of fluids, enzymes, and mucus to the GI lumen.
Main cause of secretion
Presence of food, with the quantity corresponding to the amount of food for proper digestion. Type of enzyme also specific.
Daily secretory volume
6500, coming from the saliva (1000), gastric secretion (1500), pancreatic secretion (1000), bile (1000), small intestine secretion (1800), large intestinal secretion (200).
Secretion with lowest pH
Gastric secretion (1-3.5)
Secretion with highest pH
Pancreatic secretion (8-8.3)
Parotid glands
Serous, secrete saliva.
Submandibular and sublingual glands
Mixed mucous and serous, secrete saliva.
Smaller glands in oral cavity like buccal glands
Only mucus.
Structure of submandibular gland
- Acinar cells secrete salivary amylase
- mucus cells secrete mucins
- intercalated duct drains into salivary duct which consists of striated and excretory ducts
Primary secretion of saliva
The amylase containing primary secretion is nearly isotonic - levels of Na, K, Cl, and HCO3 are similar to plasma.
Secondary secretion of saliva
Hypotonic (reduced concentration)- ductal cells reabsorb Na and Cl ions from the saliva and secrete K and HCO3 into the saliva.
Explain how flow rate affects saliva composition
The faster the flow rate, the less time there is for ductal cells to act. Therefore, saliva is closer to isotonic during high rate of saliva flow.
What is the pH range of saliva
6-7
What are the functions of saliva
- Lubrication (by mucins)
- Protection
- Solubilization
- Oral hygiene
- Initiate carbohydrate digestion by alpha amylase (ptyalin) enzyme
- Initiate lipid digestion by lingual lipase enzyme
How is salivation controlled
Autonomic nervous system. Mainly parasympathetic, but sympathetic can slightly modify the content of saliva.
What are the two pathways of salivary secretion.
Salivatory nucleus of medulla sends parasympathetic signal to:
- Otic ganglion -> ACh NT -> Parotid gland -> increased salivary secretion via effects on acinar secretion and vasodilation.
- Submandibular ganglion -> ACh NT -> submandibular gland -> increased salivary secretion via effects on acinar secretion and vasodilation
What may stimulate the salivatory nucleus of the medulla?
Higher centres (smell, taste, etc)
Sleep, Fatigue, Fear
Pressure in mouth
Xerostomia
Dry mouth.
• Several different conditions can cause decreased saliva secretion. (E.g., Sjögren’s syndrome, side effect of many drugs, secondary to head and neck radiation).
• Decreased pH in the mouth leads to tooth decay and esophageal erosions.
• Difficulty swallowing
How much gastric secretion is produced a day? At what pH?
1.5-2L. ph 1-3.5.
Where do gastric secretions come from?
Surface epithelial cells, mucous neck cells, gastric glands. Largest volume from parietal cells.
What are the main electrolytes of gastric secretions
H, Na, K, Cl - mainly isotonic.
Mucus cells of gastric mucosa
Secrete mucus that coats and lubricates the gastric surface and protects the epithelium.
Parietal cells of stomach body
secrete HCl and intrinsic factor
Chief (peptic) cells of stomach body
Secrete pepsinogen (pepsin precursor)
G-cells of stomach antrum
Secrete gastrin hormone
Bariatric surgery effect on gastric secretion
Results in lowered gastric secretions after a meal.