GI system lesson 5
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what are the salivary glands in the oral region?
- 1. parotid gland
- 2. sublingual gland
- 3. submandibular gland
- 4. buccal gland
What are the types of saliva, and what type do the salivary glands secrete?
- 1. mucous secretion (thick)
- 2. serous secretion (watery)
- parotid gland- serous
- submandibular- serous
- buccal and sublingual- mucous
what do mucous secretions contain?
mucin = major protein of saliva mix with water to form mucous
highly viscous, lubricates food, responsible for holding bolus together
*What is saliva composed of?
variable based on gland secreting and stimulus that cuases its secretion. 97%-99.5% water, pH from 6 - 7 (little acidic), kallikrein (causes vasodilation of BVs of salivary glands --> > activation of glands). blood group substances
*What is the importance of salivary amylase?
- 1. splits starch molecules into smaller units
- 2. optimal pH 6.9
- 3. range 4 to 11 (pH)
- 4. begins digestion of carbs
- 5. continues in stomach until acids inactivate
What are the functions of saliva?
- 1. lubrication (food easier to swallow)
- 2. Digestion- salivary amylase and lipase
- 3. bolus formation
- 4. dissolves food so we can taste (spices)
- 5. aids in speech
- 6. bacteriostatic- food not steral (can't grow further (stop growth)
- 7. bactericital = kills
*What controls salivary secretions?
- 1. neural control
- 2. salivary nuclei in pons-medulla receive input from mouth and pharynx
- 3. ANS carries input to salivary glands
What are factors that enhance secretion?
1. sight, thought, odor, presences of food, and chewing (all neural components)
What are factors that inhibit secretion?
stress, dehydration, fear, anxiety
*What are the 3 cell types of gastric secretions, what do they secrete, and where are they located?
- 1. Parietal cells; HCl and IF (intrinsic factor); in fundus of stomach
- 2. Chief cells; pepsinogen (precurser to pepsin); body of stomach
- 3. G-cells; gastrin (goes back to pareital cells through + feedback and cause increase in secretion of HCl; pyloric region of stomach
*Describe characteristics of mucus
- 1. secreted by mucous cells which coats epithelial cells
- 2. viscous and alkaline as buffer mechanism
- 3. protects from acidic chyme and enzyme pepsin
- 4. irritation of stomach mucosa causes greater mucus
*Describe intrinsic factor
- 1. secreted by parietal cells
- 2. Binds with itamin B12 and helps it to be absorbed b/c B12 needs a co-factor for digestion/absorption
- 1. secreted by pareital cells
- 2. kills bacteria
- 3. stops carbs digesting by inacivating salivary amylase
- 4. Denatures porteins (breaks bonds)
- 5. helps convert pepsinogen to pepsin (only in acid pH)
- 1. secreted by cheif cells
- 2. packaged in zymogen granules (precurser to proteins) released by exocytosis.
- 3. pepsin catalyzes breaking of covalent bonds in proteins
- 1. secreted by G-cells
- 2. stimulates HCl secretion from pareital cells (acts via + feedback)
*Explain HCL production
- 1. CO2 and Cl- diffuse from the blood into the stomach cell
- 2. CO2 combines with H2O to form H2CO3
- 3. H2CO3 dissociates into HCO3- and H+
- 4. H+ combines with Cl- in duct of gastric gland to form HCl-
- 5. an ATP pump is necessary to pump the HCl- into the duct
***Explain how gastric secretion is regulated
- 1. neural and hormonal mechanisms regulate the release of gastric fuice
- 2. Occurs in 3 phases: Cephalic (reflex) phase- prior to food entry, Gastric phase- once food enters the stomach, and Intestinal phase- as partially digested food enters the duodenum (- feedback mech)
- 3. the 1st 2 phases are + feedback mech
*Explain the cephalic phase of gastric secretion regulation
- 1. taste, smell, tactile sensations of food in mouth, or thoughts of food stimulate medulla
- 2. Parasymp APs are carried by vagus n. to stomach
- 3. Stimulate postgang. neurons in enteric plexus of stomach- stimulate secretion by pareital and chief cells (HCl and pepsin) and stimulate the secretion of hormone gastrin
- 4. Gastrin is carried through the circulation back to stomach where it stimulates further section of HCl and pepsin (+ feedback)
*Explain the gastric phase (phase 2) of gastric secretion regulation
- 1. distention of stomach activates a parasymp. reflex. APs are carried by vagus n. to medulla
- 2. Medulla stimulates further secretions of stomach
- 3. Distention also stimulates local reflexes that amplify stomach secretion (+ feedback mech)
Explain the intestinal phase (phase 3) of the gastric secretion regulation
1. chyme in duodenum with a pH less than 2 or containing lipids inhibis gastric secretions by 3 mechs: sensory input to medulla from duodenum inhibits the motor input from medulla to stomach and stops secretion of pepsin and HCl. Local reflexes inhibit gastric secretion. Secretin, gastric inhibitory polypeptide, and cholecystokinin produced by duodenum inhibit gastric secretions in stomach (- feedback)
*Explain gastric emptying
1. pyloric region contracts to propel food into duodenum: rate of emptying is fastest if stomach contents are isotonic. if hyper- or hypotonic, emptying is slower. Fats inhibit emptying by releasing CCK. H+ in duodenum inhibits emptying via direct neural reflexes. H+ receptors in duodenum --> info to gastric SMCs
- 1. not active enzyme
- 2. chief cells (zymogenic)
- 3. precursor to pepsin = active enzyme
- 4. acidic environment causes conversion
- 1. works best in acid environ.
- 2. digest proteins by breaking peptide bonds involving: trytophan, phenylalanine, and tyrosine
- 3. produces smaller peptide chains
*What secretions are found in the SI?
- 1. mucus (protective coating)
- 2. intestinal juice
- 3. pancreatic juice
- 4. bile
Where are the sites of secretion?
- 1. goblet cells (produce mucus)
- 2. Duodenal cells (produce duodenal secretions
- 3. Intestinal glands (produce intestinal secretions)
*What are factors that stimulate secretion?
- 1. tactile stimulation of mucosa (chyme)
- 2. Irritation of mucosa (spices- secrete more mucosa for protection)
- 3. Vagal stimulation
- 4. Secretin and other intestinal hormones
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