Salivary and gastric secretions Flashcards
Lubrication
Moisten mouth to aid swallowing
Facilitate movement
Help dissolve chemicals
Saliva functions
Lubrication
Protection (lactoferrin)
Digestion (alpha amylase and lingual lipase)
Sjögren’s syndrome
Autoimmune
Destroys exocrine glands (tear and saliva)
Xerostomia
Dry mouth
Types of secretion
Serous
Mucous
Serous secretion
the main type of protein secreted is ptyalin (hydrolizes starch)
Mucous secretion
main protein is mucin, acting as lubricant
Major salivary glands
The submandibular glands secrete approximately 70% of saliva (mixed).
The parotid glands secrete 25% (serous).
The sublingual glands secrete 5% (mucus
Salivary gland contain
blind-ended acini connecting with ducts draining into major ducts
Functional unit of salivary gland
Acinar cells - secrete primary saliva into duct system
Isotonic solution - duct reabsorb NaCl
Acinar cells
Cl- via uptake by basolateral NaK2Cl con transporter and release through apical chloride channel
Process sustained by NaK ATPase
Na+ enters paracellularly though leaky tight junctions
Ductal cells
Remove Na+ from saliva via apical sodium channel and basolateral NaK ATPase
Cl- removal via different chloride channel in apical and basolateral membrane
Secrete bicarbonate and potassium (unidentified apical bicarbonate chloride and potassium proton exchanger)
Saliva always hypotonic
low rate of secretion – maximum reabsorption of electrolytes
high rate – less time to reabsorb so higher osmolality
Central control of salivary secretions
Efferent nerves reach the salivary glands via the glossopharyngeal and facial nerves. Acinar secretion is stimulated by the release of acetylcholine, which acts via the muscarinic receptors.
Parasympathetic stimulation
Promote watery secretion myoepithelial cells surrounding acini and ducts contract and eject preformed saliva
Sympathetic stimulation
does increase output of amylase but …
- blood flow reduced (vasoconstriction) and fall in rate of secretion e.g. in dry mouth associated with fear
Only hormonal effect
Aldosterone secretion
increases ductal Na+ absorption and K+ secretion.
Composition of gastric juice
pH 1-3 pepsinogen
Pepsin: Endopeptidases
Mucus bicarbonate barrier
Intrinsic factor - glycoprotein binds vit B12
Stomach has 2 major regions
an exocrine or glandular portion that consists of the fundus and body or acid-secreting area
an endocrine or hormone secreting area portion that is located in the antrum or gastrin-secreting area
Endocrine - D cells
Very few parietal cells
secrete somatostatin- regulator of gastrin release and gastric acid secretion
Exocrine region
acid secreting, IF
Histamine cells
Protection against self digestion
Lumen
Mucous viscosity
Mucin has basic side chains.
HCO3- secreted from surface epithelial cells.
Both neutralise H+ ions
Gastritis
infection by the bacteria Helicobacter pylori
Alcohol, smoking and NSAIDs
Rapid regeneration = restitution
