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56 Cards in this Set
- Front
- Back
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what body fluid is saliva derived from
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plasma
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what glands produce saliva?
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3 paired, branched glands:
parotid submandibular sullingual unpaired, simple glands eg buccal |
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which glands are responsible for producing how much saliva?
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mostly from submadibular, then from parotid, least is form sublingual and simple glands
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which glands are mucous, mixed or serous?
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parotid: serous
submandibular: mostly serous sublingual: mostly mucous simple: mucous |
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which cells produce the pimary secretion?
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the acinar cells
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what is the primary secretion?
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produced by acinar cells
isotonic to plasma |
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what happens in the duct of the salivary gland?
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striated cells absorb Na, Cl and secrete HCO3- and K+
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how is electroneutrality maintained?
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secrete / absorb same amount of -ve/+ve ion
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what happens to water in the primary secretion
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duct cells impermeable to water so is not absorbed
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what happens to the concentration of the secretion as it passes thorugh the duct
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becomes more dilute - hypotonic to plasma
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is reabsorbtion of Na Cl in the duct active or passive
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active
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how does the composition of saliva vary with flow rate? explain in terms of each of 4 ions, and explain why
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Na, Cl increases, as there is less time for reabsorption
K decreases, as there is less time for secretion HCO3 increases as it is under neuronal control |
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in general, does the saliva get more or less like plasma if there is a faster secretion rate?
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more like plasma - except for bicarbonate levels which increase, away from plasma levels
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apart from electrolytes what does saliva contain
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mucous
proteins eg IgA enzymes eg lysozyme, amylase |
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what are the 6 functions of saliva
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dental hygein- bicarbonate neutralises acidity in food, prevents cavities
moisture aids speech protective function: contains IgA and lysozymes digstive function: amylase aids carbohydrate digestion mucous: aids swallowing taste: acts as a solvent to stimulate tatse |
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what two reflexes control salivation
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conditioned reflex
simple reflex |
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explain the conditioned reflex and how it controls salivation
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inputs into the cerebral cortex are then relayed to the salivary centre in the medulla
output from the medulla is relayed by autonomic nerves to the salivary glands which then adapt salivary secretion |
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explain the simple reflex and how it controls salivation
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input from taste, smell, chewing effects pressure receptors and chemoreceptors in the mouth
this is relayed to the salivary centre in the medulla ouput from here is relayed by autonomic nerves to salivary glands salivary glands adapt the saliva |
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what volume / type of saliva is produced from parasympathetic innervation
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large volume, serous, rich in enzymes
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what voluem / type of saliva is produced from sympathetic innervation
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small, mucousy and thick
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descrive the sequence events after parasympathetic innervation of salivary glands occurs
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substrate is converted to bradykinin, a process which is undertaken by kallikrein in the salivary gland.
bradykinin has 2 effects, increased capillary permeability, and arteriole vasodilation parasympathetic stimulation also causes increased secretion from the gland |
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what two ways are involved in increasing blood supply to salivary glands
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1) conversion of substrate to bradykinin, bradykinin causes vasodilation and increased capillary permeability
2) neural influences cause vasodilation of arterioles |
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what are the two phases of swallowing
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oropharyngeal
oesophageal |
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describe 2 things which must happen in the oropharyngeal phase
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nasal cavity closed off by soft palate and uvula
trachea closed off by glottis |
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what are the 4 functions of the stomach
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churning of food to produce chyme
acidity to kill bacteria initation of protein digestoin storage of food |
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what prevents an increase in intergastric pressure when food arrives in the stomach
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1) wall of stomach distends
2) a reflex prevents increase in tone of the stomach wall |
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what pumps are in the parietal cell of the stomach? (draw a parietal cell)
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HCO3-/Cl pump
H+/K+ antiporter K+/Cl- symporter |
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how does the parietal cells generate new H+
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forms H2CO3 from water and Carbon dioxide in plasma
H+ secreted via H/K antiporter |
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how does the parietal cell get Cl-
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secretes HCO3- to the plasma in exchange for Cl-
Cl- secreted into lumen with K+ by Cl/K+ symporter |
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what enzyme does the parietal cell have?
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carbonic anhydrase
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what is the pH at the gastric pits?
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around 1
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HCL has 3 functions, what are they?
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directly helps digestion by breaking down hydrogen bonds in connective tissue and muscle, giving access to these tissue for proteases
activates and provides optimal pH for pepsinogen kills bacteria |
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what is pepsinogen and how is it converted
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the inactive form of pepsin. converted by pepsin - pepsin is autocatalytic
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which nerve is extremely important in initiating the cephalic phase of gastric secretion?
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vagus nerve
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what are the 4 cells implicated in the control of gastric secretions and what do they all release
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parietal cell - HCL
enterochromaffin like cell - Histamine antral G cell - gastrin D cell - somatostatin |
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how does the vagus nerve control gastric secretion in the cephalic phase
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1)acts on parietal cell, Ach on M receptors causes release of HCl
2) acts on ELC, ach on M receptors cause histamine release, histamine traverses gap between cells, acts on H2 receptors on parietal cell, causes HCL release 3) acts on G cell, GRP acts on cell to cause gastrin release. gastrin goes to blood, acts on CCK receptors. in parietal cell increases HCL secretion, in ELC increases histamine secretion 4) inhibits D cell which usually produces somatostatin which inhibits G cell production of gastrin |
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what are the usual affects of somatostatin?
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inhibit G cell, prevent it form producing so much gastrin
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what receptors does gastrin work on?
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CCK receptors on parietal and ELC
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what receptors does histamine work on in the stomach?
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H2 receptors
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what neurotransmitter is important in control of antral G cells?
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GRP
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what do G cells secrete?
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gastrin
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where does gastrin go after secretion by antral G cell?
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blood, then affects both parietal and ELC
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what does parasympathetic innervation do to a D cell
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inhibits it
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what proportion of gastric secretion is accounted for by cephalic phase?
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30 - 60%
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describe control of gastric secretion in the gastric phase of the meal?
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1) local vagovagal reflexes due to mechanical stimulation of antrum
2)stimulation of G cells by peptide fragments to produce gastrin |
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what stimulates G cells in the gastric phase of the meal?
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peptide fragments
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is the CNS involved in the gastric phase of the meal?
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no
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describe the intestinal phase of gastric secretions
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circulation of amino acids may act on parietal cells
gastrin is produced in duodenal endocrine cells |
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what cells do circuatling amino acids stimulate in the intestinal phase of the meal?
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parietal cells
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what are the four ways of inhibiting gastric secretion?
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1) removal of peptide fragments removes stimulus for gastrin secretion
2) food moving out reduces the pH of the stomach. at pH of less than 1, gastrin release is inhibited, either directly or by stomatostatin release 3) distension of duodenum causes release of enterogastrones: inhibits gastrin release either directly or via somatostatin release 4) cephalic influences eg depression can reduce gastric secretions |
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what is entergastrone and what does it do?
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mixture of hormoens released from duodenum when it is distended, inhibits gastrin secretion either directly or via somatostatin
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what happens when pH falls below 2?
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gastrin release inhibited, either directly or via somatostatin release
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what happens to pH when food leaves stomach?
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it falls
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what are the four ways the stomach protects itself against Hcl and proteases
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1) negative feedback system i.e. if pH falls too low then gastrin release inhibited
2) mucous secretion 3) rapid turnover of cells 4) lumenal membrane impermeable to H+ absorption |
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how does mucous protect the stomach against acidity and proteases?
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bicarbonate ions in mucous neutralise acid and provide a barrier
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what is the effect of prostaglandin release in the stomach, and how?
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helps protect gastric mucosa
- encourages vasodilation and nutrient delivery to help turnover / repair of damaged mucosa - aid bicarbonate secretion |
