Lecture 5: Salivary and Gastric Secretion Flashcards
what are the glands involved in salivary secretions
- parotid
- submandibular
- sublingual
what are the enzymes present in saliva
- alpha amylase
- lysozyme
- lingual lipase
- lactoferrin
- kallikrein
what does alpha amylase do
hydrolyses α-1,4 glycosidic bonds in starch to disaccharides and trisaccharides
what do lysozymes do
hydrolyse peptidoglycans in gram negative bacteria walls
what does lingual lipase do
- hydrolyse triglycerides to fatty acid and diglycerides
- optimal in low pH
what does lactoferrin do
chelates iron to prevent microbial multiplication
what does kallikrein do
converts plasma protein α-2-globulin to bradykinin
what are the constituents of saliva
- water
- electrolytes
- enzymes
- secretory IgA
- mucin
- organic urea and uric acid
what does the parasympathetic ANS signal to for saliva production
superior and inferior salivatory nuclei
which nerves carry parasympathetic impulses to salivary glands
- cranial nerve VII for sublingual and submandibular gland
- cranial nerve IX for parotid gland
what effect does parasympathetic stimulation have on salivary glands
- increase salivary secretion
- vasodilation
- myoepithelial cell contraction
what are inhibitors of the parasympathetic ANS for saliva secretion
- fatigue
- sleep
- fear
- dehydration
effect of sympathetic neural stimulation on salivary glands
- overall slight increase in secretion
- produces mucin and enzyme rich saliva
- initial vasoconstriction as noradrenaline released
- later vasodilation as bradykinin released
how is sympathetic activity of salivary glands regulated
via superior cervical ganglion
what happens in Sjogren’s syndrome
- autoimmune disease that destroys exocrine salivary glands
- commonly affects tear and saliva production
- dry eyes and dry mouth, known as sicca symptoms
what happens in xerostomia
- patients lack adequate saliva
- dental caries and halitosis common due to bacterial overgrowth
- difficulty speaking or swallowing solid food due to inadequate lubrication
what are the exocrine cells of the gastric glands and what do they secrete
- mucous neck cells: thin mucus
- parietal cells: HCl and intrinsic factor
- chief cells: pepsinogen, gastric lipase and rennin in neonates
what are the endocrine cells of the gastric glands and what do they secrete
- G cells: gastrin
- D cells: somatostatin
- ECL cells: histamine
what are the gastric glands in the body and fundus
gastric / oxyntic glands
what are the gastric glands in the antrum
pyloric glands
what is the purpose of mucus in gastric juice
protects surface epithelium from acid / pepsin
what is the purpose of pepsinogen in gastric juice
- is a proenzyme
- active form is pepsin
what is the purpose of rennin in gastric juice
- in neonates only
- coagulates milk through casein proteolysis
what is the purpose of gastric lipase in gastric juice
converts triglycerides to fatty acids and diglycerides
what is the purpose of HCl in gastric juices
- converts pepsinogen to pepsin
- denatures proteins
- kills microorganisms
what is the purpose of intrinsic factor
- vitamin B12 absorption in the ileum
- erythropoeisis in bone marrow
- deficiency can cause pernicious anaemia
what are the components of gastric juice and what are they secreted by
- water and electrolytes
- mucus by mucus neck cells
- pepsinogen pro enzyme, rennin in neonates and gastric lipase by chief cells
- HCl and intrinsic factor by parietal cells
what stimulates gastric acid secretion
- acetylcholine release from vagus nerves
- gastrin from G cells
- histamine from ECL cells
which hormones inhibit gastric acid secretion
- somatostatin from D cells
- mucosal prostaglandin
which drugs inhibit gastric acid secretion
- omeprazole: proton pump inhbitor
- cimetidine: H2 receptor antagonist
- atropine: muscarinic receptor inhibitor and inhibits vagal stimulation of acid secretion
what promotes gastrin secretion
- vagus nerve
- distension
- peptides
what effects does gastrin have
- promotes parietal cell secretion of pepsinogen
- chief cell secretion of pepsinogen
- lower oesophageal sphincter contraction
- increased motility of stomach
- relaxation of pyloric sphincter
what happens in gastritis and what are its causes
- inflammation of the gastric mucosa
- most commonly caused by Helicobacter pylori bacteria
- gram negative bacteria produce urease. forms ammonia which neutralises bactericidal acid and is toxic to mucosal barrier
- also caused by smoking, alcohol, NSAIDs and chronic stress
what happens in autoimmune atrophic gastritis
- antibody mediated destruction of gastric parietal cells
- causes hypochlorhydria
- and intrinsic factor insufficiency
- loss if IF results in vitamin B12 malabsorption and pernicious anaemia
