T1 L5 salivary and gastric secretions Flashcards
(32 cards)
what is the function of salivary and gastric secretions
Lubricate, protect and aid digestion
how are salivary and gastric secretions secreted
Exocrine glands (with duct) eg salivary and gastric glands Endocrine glands eg enteroendocrine cells in stomach and small intestine
what is the role of salivary secretions
lubrication, protection (oral hygiene), initiate chemical digestion
how are salivary secretions secreted
Major salivary glands – parotid, submandibular, sublingual
Dispersed salivary glands – mucosa of mouth and tongue (eg labial, buccal palatal, lingual)
what are the major salivary glands
Parotid gland – serous, watery secretions containing salivary amylase for starch digestion
Submandibular gland – mixed serous and mucus
Sublingual gland – mucus (thicker mucus dominant secretions for lubrication)
what is the composition of saliva
water (99.5%)
Electrolytes (K+, HCO3-, Na+, Cl-, (PO4)3-)
Enzymes (a-amylase, lysozyme, lingual lipase, lactoferrin, kallikrein)
Secretory IgA
Mucin
Organic urea and uric acid
what is the role of water in saliva
solvent dissolves food components to aid taste, swallowing, initiating digestion, oral hygiene
what is the role of electrolytes in saliva
buffer for acidic food contents
what is the role of enzymes in saliva
amylase - breakdown starch
lysozyme - hydrolyse peptidoglycans
lingual lipase - TG to FA and diglycerides
what is the role of secretory IgA in saliva
prevent microbial attachment to epithelium
what is the role of mucin in saliva
lubrication
what is the role of organics urea and uric acid in saliva
waste product removal for excretion
what is the acing structure of salivary glands
Acinar – secrete primary saliva into duct lumen
Myoepithelial cells – surround acinar, contractile, drive secretions along duct
Ductal cells – modify saliva
Unique properties – large volume of saliva produced compared to mass of gland, low osmolarity, high K+ concentration
Two stage formation of hypotonic saliva
Stage 1 – acinar cells secrete isotonic saliva similar to blood plasma in electrolyte composition
Stage 2 – ductal cells secrete HCO3- and K+ ions with reabsorption of NaCl and limited movement of water by osmosis
Produces HCO3- and K+ rich hypotonic saliva
how does the composition of saliva changes with flow rate
Electrolyte composition – Na+ and Cl- plasma
Low rate of secretion – maximum reabsorption of electrolytes produces hypotonic saliva (low concentration of osmotically active electrolytes)
High rate – reduced reabsorption of electrolytes produces alkaline, HCO3- rich saliva with increased osmolarity closer to that of primary isotonic saliva
how are secretions controlled parasympathetically
dominant
Sight, thought, smell, taste (esp sour acidic taste), tactile stimuli and nausea
Signal superior and inferior salivatory 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
Increases salivary secretion, vasodilation, myoepithelial cell contraction
Inhibitor – fatigue, sleep, fear, dehydration
Sympathetic neural stimulation of secretions
Overall slight increase in secretion
Produces a mucin and enzyme rich saliva
Activity is via superior cervical ganglion
Initial vasoconstriction (NT NA stimulates B adrenergic receptors)
Later vasodilation (salivary enzyme kallikrein on blood plasma protein alpha 2 globulin to form vasodilator bradykinin)
Salivary gland dysfunction
Sjoren’s syndrome – an AI disease that destroys exocrine glands, commonly affects tear and saliva production, dry eyes and mouth (sicca symptoms)
Xerostomia (dry mouth) – lack adequate saliva, dental caries and halitosis common due to bacterial overgrowth, difficulty speaking or swallowing solid food due to inadequate lubrication
Gastric secretions - where do they come from
Gastric pits in mucosa branch into gastric glands
Exocrine gland cells (secrete gastric juice)
Mucous neck cells- thin mucus
Parietal cells- HCl and intrinsic factor
Chief cells- pepsinogen (also renin in neonates), gastric lipase
Endocine cells
G cells – hormone gastrin (antrum)
D cells – hormone somatostatin
Enterochromaffin-like (ECL) cells secrete histamine
Two major types of gastric glands
Body and fundus (80%)
Gastric/oxyntic glands – exocrine secretion of of HCL, pepsinogen, intrinsic factor and mucus, paracrine ECL secretion of histamine, paracrine D cell secretion of somatostatin
Antrum (20%)
Pyloric glands – mucus and endocrine hormone gastrin, paracrine/endocrine somatostatin
what makes up gastric juice
water, electrolytes, mucus, pepsinogen pro-enzyme, renin in neonates, gastric lipase, HCL, IF
what allows parietal cells to secrete
Parietal cells have an intracellular branched canalicular structure and are packed with tubulovesicles in resting state
Contain enzymes carbonic anhydrase and H+/K+-ATPase for acid secretion
Stimulation of acid production tubulovesicles fuse with the canalicular membrane to form microvilli
How does HCl secretion occur
H+/K+-ATPase proton pump drives active secretion of H+ Carbonic anhydrase (CA) catalyses formation of HCO3-, producing H+ ions HCO3- exchanged for Cl- (alkaline tide- gastric venous blood becomes alkaline postprandially) Cl- diffuses into lumen
