salivary & gastric secretions Flashcards
what are exocrine glands?
glads with a duct
what are endocrine glands?
glands without a duct
give some examples of exocrine glands
- salivary glands
- gastric glands
give some examples of endocrine glands
enteroendocrine cells in stomach and small intestine
what is the role of salivary secretions?
- lubrications
- protection (oral hygiene)
- imitate chemical digestion
what are the 3 main salivary glands?
- parotid
- submandibular
- sublingual
where are the salivary glands dispersed?
- mucosa of mouth and tongue
- labial, buccal, palatal, lingual
what are the key features of parotid glands?
- serous
- watery secretions containing salivary amylase for starch digestion
what are the key features of submandibular glands?
mixed serous and mucus
what are the key features of sublingual glands?
mucus: thicker mucus dominant secretions for lubrications
what are the unique properties of acinar structure of salivary glands?
- large volume of saliva produced compared to gland
- low osmolarity
- high potassium concentrations
what are the 2 stages of hypotonic saliva formation?
1) acinar cells secrete isotonic saliva similar to blood plasma in electrolyte composition
2) ductal cells secrete HCO3- and K+ ions with reabsorption of NaCl and limited movement of water by osmosis. This produces HCO3- and K+ rich hypotonic saliva
how does the composition of saliva change with low rate of secretion?
maximum reabsorption of electrolytes produces hypotonic saliva
how does the composition of saliva change with the high rate of secretion?
reduced reabsorption of electrolytes produce alkaline, HCO3- rich saliva with increased osmolarity closer to that of primary isotonic saliva
how does the parasympathetic ANS regulation dominate the salivary & gastric secretions?
- sight, thought, smell, taste, tactile stimuli, nausea
- signal superior and inferior salivary nuclei in the medulla
- via cranial nerve VII (facial nerve) for the sublingual and submandibular gland
- cranial nerve IX (glossopharyngeal nerve) for the parotid gland
- increase salivary secretion, vasodilation, myoepithetlail cell contraction
- inhibitors: fatigue, sleep, fear, dehydration
how does the sympathetic system stimuli neural system?
- overall slight increase in secretion
- produces mucin and enzyme rich saliva
- activity is via superior cervical ganglion
- initial vasoconstriction
- later vasodilation
what is Sjogren’s syndrome?
- salivary gland dysfunciton
- an autoimmune disease that destroys the exocrine glands
- commonly affects tear and salivary production
- dry eyes and dry mouth, known as sick symptoms
what is Xerostomia?
- salivary gland dysfunction
- dry mouth
- patients lack inadequate saliva
- dental caries and halitosis common due to bacterial overgrowth
- difficulty speaking or swallowing solid food due to inadequate lubrication
what are the 2 types of gastric glands?
- body & fundus
- antrum
what are the key features of body & fundus gastric glands?
- 80%
- gastric/oxyntic glands
- exocrine secretion of HCl, pepsinogen, intrinsic factor and mucus
- paracrine ECL cell secretion of histamine, paracrine D cell secretion of somatostatin
what are the key features of antrum gastric glands?
- 20%
- pyloric glands
- mucus and endocrine hormone gastrin
- paracrine/endocrine somatostatin
how is HCl secreted by parietal cells?
- parietal cells have an intracellular branched canalicular structure and are packet with tubulovesicles in resting state
- these contain enzymes carbonic anhydrase and H+/K+-ATPase for acid secretion
- on stimulation of acid production tubulovesicles fuse with the canalicular membrane to form microvilli
- HCl is formed at these microvilli and secreted
how does HCl secretion occur?
- H+/K+-ATPase proton pump drives active secretion of H+
- carbonic anhydrase (CA) catalysed formation of HCO3- producing H+ ions
- HCO3- exchanged for Cl-
- Cl- diffuses into lumen
what activates gastric acid secretion?
- ACh: acetylcholine release from vagus
- gastrin: from G cells
- histamine: from ECL cells
what inhibits gastric acid secretion?
- somatostatin: from D cells which inhibits adenylate cyclase (AC)
- mucosal prostaglandin antagonists for H receptor
what are the pharmacological inhibitors of gastric acid?
- omeprazole: proton pump inhibitor inactivates H+/K+-ATPase
- cimetidine: H2 receptor antagonist inhibits stimuli for acid secretion
- atropine: inhibits muscarinic receptors and vagal stimulation of acid secretion
what are the 3 phases of gastric secretion?
- cephalic
- gastric
- intestinal
what happens in the cephalic phase of gastric secretion?
vagus stimulated parietal, chief cell production of gastric juice and hormone gastrin secretion
what happens in the gastric phase of gastric secretion?
stimulate parietal, chief mucus secretion, antral G cells
what happens in the intestinal phase of gastric secretion?
- excitatory: chyme with pH>3, peptides stimulate gastric secretions via vagus and gastrin
- inhibitory: chyme with pH<2, distention, protein breakdown produces hypo/hyper-osmotic products, inhibit gastric secretions via cholecystokinin, secretion, gastric inhibitory polypeptide
why is the gastric mucosa not damaged?
- surface mucous glands secrete viscous mucus layer of mucopolysaccharides/proteins
- mucus viscosity generates mucosal barrier: mucin has basic side chains. HCO3- secreted from surface epithelial cells. Both neutralise H+ ions
- tight junctions stop acid damaging underlying tissue
- net result: unstirred layer is around pH7, pepsinogen not activated, prevents enzymatic and chemical damage
what are the key features of gastritis?
- dysfunction & inflammation of gastric mucosa
- most commonly caused by an infection by the bacterial Helicobacter pylori
- gram negative bacteria produce urease which forms ammonia from urea, ammonia neutralises bacterial acid and is toxic to mucosal barrier
- also caused by smoking, alcohol, non-steroidal anti-inflammatory drugs, chronic stress
- following acute damage, rapid regeneration is via a process caused restitution: rapid division of stem cells located in neck of gastric glands
what is autoimmune atrophic gastritis?
- an antibody mediated destruction of gastric parietal cells, which causes hypochlorydria and a deficiency of intrinsic factor If
- the loss of If results in vitamin B12 Mal-absorption and pernicious anaemia
