Saliva and gastric secretions Flashcards
What are the functions of saliva ?
- digestion
- protection
- lubrication
- antibacterial roles
- blood clotting
- calcification of teeth
Describe how saliva carries out digestion
- amylase cleaves the 1,4-glycosidic bonds
- lingual lipase hydrolyses lipids
Describe how saliva carries out protection
- it prevents drying of the oral cavity (drying causes weakening of the oral tissue)
Describe how saliva carries out lubrication
- its involved in the swallowing of bolus
Describe how saliva has antibacterial roles
- lactoferrin chelates iron as a lot of bacteria require iron to survive
- lysozymes are involved in the degradation of bacterial cell walls
- it contains immunoglobulins
Describe how saliva carries out blood clotting
- prevents gum disease
- promotes wound healing
Describe how saliva calcifies the teeth
- acids from food decalcify the teeth and so calcium phosphates and phosphoproteins buffer these acids
What are the major salivary glands ?
- parotid glands
- submaxillary glands
- sublingual glands
Describe the secretion of the parotid gland
- secretes 25% of saliva
- serous and watery secretion
Describe the secretion of the submaxillary gland
- secretes 70% of saliva
- serous and mucous secretion
Describe the secretion of the sublingual gland
- predominantly mucous secretion
Give some examples of conditions associated with producing less saliva
- xerostomia
- Sjogren’s syndrome
- hyperaldosteronism
Describe xerostomia
- significant reduction or absence of saliva
- leads to a decrease in chewing, swallowing and digesting
- caused by some medications, congenital diseases and cranial nerve damage
Describe Sjogren’s syndrome
- autoimmune inflammatory disease
- blocked ducts causes atrophy of glands
Describe hyperaldosteronism
- can be primary or secondary
- increase in aldosterone secretion
- causes include hypertension and hypokalaemia
What is hypokalaemia ?
- low potassium in the blood
- impacts the sodium content of the saliva
What are the 2 types of saliva secretion ?
- basal secretion : happening continuously
- stimulated secretion : increase in secretion upon stimulation of the salivary glands
What is the rate of saliva secretion ?
0.5 - 7 ml/min
How is saliva secreted ?
- regulation of salivary secretion is controlled by the autonomic nervous system
- sensory receptors relay information to salivatory nuclei in the medulla
What is the effect of parasympathetic stimulation on the secretion of saliva ?
- promotes watery saliva
- rich in amylase and mucins
What is the effect of sympathetic stimulation on the secretion of saliva ?
- has a variable effect
- can increase or inhibit secretion of saliva
Describe the formation of saliva
1) parasympathetic stimulation will bring in chloride ions into the acinar cells through a cotransporter protein
2) sodium ions and potassium ions will also move into the cells via the cotransporter
3) chloride ions are pumped out of the cell into the acinus region and this makes the acinus region have a slightly negative potential
4) this negative potential drives the movement of water and sodium ions into the acinus region through paracellular channels
5) sodium ions are pumped out of the acinar cells in exchange for potassium ions so sodium ions can move paracellularly
6) potassium ions are pumped out of the acinar cells so they can come in with chloride ions or in exchange for sodium ions
What is meant by paracellular movement ?
movement between cells
Describe the how saliva is modified
- the ducts are relatively impermeable to water and this allows saliva to change from isotonic to hypotonic
- the removal of chloride ions and sodium ions will change the saliva from isotonic to hypotonic
How does the flow rate of saliva from the acinus region to the duct affect affect the modification of saliva ?
- a fast flow rate will mean there is less time for the removal of sodium and chloride ions and so the saliva at the duct will be more isotonic and less modification has occurred
- a slow flow rate will mean more modification can be done
What are the receptors found on the basolateral membrane of the acinar cells ?
- muscarinic cholinergic receptors : bind acetylcholine
- α adrenergic receptors : bind noradrenaline
- substance P receptors : bind substance P
What is the effect of the receptors on the acinar cells ?
- receptors result in an influx of calcium ions into the acinar cells
- this will increase the the internal calcium ion concentration
- this results in exocytosis of amylase into the saliva
Describe the ion composition of isotonic saliva
- very similar composition to plasma in terms of sodium ion and chloride ion concentration
Describe the ion composition of hypotonic saliva
- low concentration of sodium ions and chloride ions
What are the different regions of the stomach ?
- Cardia region
- Fundus
- Body or Corpus
- Antrum
- Pylorus
What is the function of the pylorus ?
regulates the food exiting the stomach and entering the small intestine
Describe the structure of the antrum
it is more muscular than any other region - has a much thicker smooth muscle
What are the different gastric glands ?
- cardiac glands
- oxyntic glands
- pyloric glands
Describe the structure and function of the rugae
- folds
- allow the stomach to take in food contents without increasing the pressure
What do the cardiac glands secrete ?
- mucus : eases friction
What do the oxyntic glands secrete ?
- mucus : lines the stomach cells to protect the stomach from chyme
- HCl
- pepsinogen : pepsin precursor
- intrinsic factor : important in the absorption of vitamin B12
What do the pyloric glands secrete ?
- pepsinogen
What are the different cells found in the gastric glands ?
- mucous neck cells
- parietal cells
- chief cells
- enteroendocrine cells or G cells
- enterochromaffin cells or mast cells or H cells
What is the function of the mucus neck cells ?
they empty mucus into the stomach lumen
What is the function of the parietal cells ?
secrete HCl when needed and intrinsic factor
What is the function of the chief cells ?
- secrete pepsinogen
- make up 25% of all gastric cells
What is the function of the G cells ?
they produce gastrin
What is the function of the H cells ?
produce histamine
Describe the structure of parietal cells in the resting state
- acid secretion is low
- tubulovesicles are present in the cell and they contain H+ pumps
- tubulovesicles are relatively impermeable to potassium ions which prevents the H+ pump from being activated
Describe the structure of parietal cells in the active state
- tubulovesicles fuse with canaliculus which increases the surface area
- H+ pumps and chloride ions and potassium ions are inserted into the canalicular membrane
- this increases acid secretion
Why do parietal cells have lots of mitochondria ?
Secreting HCl requires lots of energy
