Gastrointestinal Secretions
- Water, mucous, K+ secreted everywhere
- Duct cells in stomach, goblet cells in intestine secrete mucous
- Saliva contains HCO3- and amylase
- Gastric - HCl, pepsinogen, gastric lipase, intrinsic factor, water, mucous
- Pancreatic - HCO3-, water, amylase, lipase, proteases, nucleases -
and inactive Zymogens (must be converted into active form)
- 7 L of fluid a day is secreted by GI tract, either through Duct delivery systems
or through Direct secretion in the lumen of the alimentary canal (full GI traxt)
- Ducts include: salivary ducts, pancreatic ducts, biliary ducts
- GI input = GI output
- Brunner's gland in duodenum secretes with high basicity due to
large concentration of bicarbonate (pH = 8-9)
- Saliva is an exocrine secretion - 1.5 L of secretion a day
- PSNS controls salivary secretion
- Basic secretory unit of saliva is acinar cells - always hypotonic to plasma
- Major glands - parotid (serous), submandibular (serous and mucus), sublingual (mucus)
- Sensory reflexes, pressure, nausea stimulate secretion
- Fatigue, fear, sleep, depression inhibit secretions
- Saliva is composed of 99.5% water, along with
- electrolytes (bicarbonate, sodium, potassium, chloride)
- mucins
- WBCs
- IgA, lysozyme (Paneth cells), lactoferrin, lactoperoxidase
- Amylase (hydrolysis of starch), lipase (hydrolysis of fats),
kallikrein (serine protease)
- Minor salivary glands secrete mainly mucous
- Problems with dentures mainly involve minor salivary glands
- Parotid is 30% of total output and has most of the enzymes and IgA,
submandibular is 60% of output
- Saliva lubricates, digests, transports, and defends
- Saliva facilitates taste and neutralizes gastric acid
- Secretion is mainly dependent on calcium ion signaling
- Duct cells absorb NaCl, potassium and HCO3- are secreted
- Gastric secretions
- HCl
- Intrinsic factor - binds B12
- Pepsinogen
- Mucous
- During meals, more H+ secretion, during rest, more NaCl
- Gastric juice can kill bacteria and parasites
- Parietal cells (oxynytic cells) -
release HCl, intrinsic factor to active pepsin and kill bacteria
- Mucuous cells (duct cells) release mucuous and bicarbonate
- Enterochromaffin cells release histamine to stimulate gastric acid secretion (parietal cells)
- Chief (peptic) cells release pepsin and gastric lipase
- D cells release somatostatin to inhibit gastric acid secretion
- G cells release gastrin to stimulate gastric acid secretion
- Acetylcholine, gastrin, histamine stimulate parietal cells
- In Zollinger-Ellison syndrome (gastrinoma), gastric acid output is greatly increased
- Mucuous and bicarbonate protect the surface of the stomach from autodigestion