GI-saliva Flashcards
what are the 4 functions of saliva?
1-tooth maintenance
2-lubrication
3-antibacterial/ antibacterial-IgA
4-digestive (amylase)
at what pH must the saliva be kept close to?
pH 7
what happens to the pH of saliva after a meal?
pH decreases as plaque bacteria makes acid
at what pH do teeth demineralise?
pH 5.5
how many pairs salivary glands do we have?
3
name the salivary glands
- submandibular
- sublingual
- parotid
which salivary glands are innervated by the facial nerve (CN VII)?
- submandibular
- sublingual
which nerve innervates the parotid gland?
glossopharyngeal nerve (CN IX)
what does the parotid gland secrete?
serous saliva
what does the sublingual gland secrete?
mucous saliva
what does the submandibular gland secrete?
-serous/ mucous
or
-mixed saliva
name some stimulants for saliva secretion
- mastication
- taste
- smell
- anticipation
what inhibits saliva secretion?
- fear
- vomiting
what are the constituents of saliva?
Glycoproteins - layers slide over each other; difficult to pull apart
what do all salivary glands secrete?
both protein and fluid
what are the 2 cell types of salivary glands?
- Myoepithelial cells contract to increase speed of release
- Acinar cells can either be serous or mucous, but these produce saliva
what is the stimulus secretion coupling process?
process whereby both protein and fluid are secreted simultaneously as to prevent protein from blocking the apical side of the acinar cells
describe the process of protein secretion in saliva?
1-The sympathetic NS stimulates release of noradrenaline
2-Noradrenaline binds to a beta-adrenergic receptor on the acinar cell which is coupled to a G protein (GS TYPE)
3-G protein subunit activates adenylate cyclase
4-Adenylate cyclase causes cAMP production
5-cAMP stimulates transcription of proteins, formation of secretory vesicles and exocytosis
describe how acinar cells secrete IgA
1-IgA binds to a polymeric immunoglobulin receptor (PIgR) **on the basolateral membrane of acinar cell
2-endocytosis of receptor with the protein
3-The IgA and its receptor are transported to the apical membrane where the IgA is released into the gland
describe how fluid secretion occurs in saliva
1-The parasympathetic NS stimulates release of acetylcholine
2-Acetylcholine binds to a M3 muscarinic receptor bound to a G protein (GQ TYPE) which initiates activation of phospholipase C
3-Phospholipase C causes production of IP3 which binds to IP3 receptors (on ER) and so stimulates release of Ca 2+ on ER
4-Ca 2+ activates K + channels on the basolateral membrane to open and Cl - channels on the apical (more -ve side) membrane to open causing a charge gradient
5-This causes Na + to move across the paracellular junction (permeable to Na+) causing an osmotic gradient moving water into the salivary gland
name the layers of the GI tract (from deep to superficial)
- mucosa (epithelium/ lamina propria/ muscularis mucosae)
- submucosa (contains submucosal plexus)
- muscularis (circular muscle/ myenteric plexus/ longitudinal muscle)
- serosa (areolar connective tissue/ visceral peritoneum)
which 2 types of epithelial are in the mucosa layer of the GI tract?
- simple columnar
- non-keratinised squamous
what is food in the gut detected by in the enteric NS?
-chemoreceptors (detect chemicals in food) -baroreceptors (detect distention of the gut from the bolus)
what does food in the gut trigger in the enteric NS?
- sensory (afferent) neurons (Vagal / CN X Nerves)
- relay information to the Central Nervous System (CNS) and to the Enteric Nervous System (ENS)
which 2 plexuses is the ENS made up of?
- Myenteric Plexus (Auerbach)
- The Submucosal Plexus (Meissner)
where is the myenteric plexus located in the gut wall?
Located in between the circular and longitudinal muscles.
where is the submucosal plexus located?
Located in the submucosa of the GI wall
what is the role of the myenteric plexus?
Cause contractions of the muscle wall, to help push the bolus along
what is the role of the submucosal plexus?
controls secretion and absorption within the gut.
what connects the 2 ENS plexuses and why?
Inter-neurons connect the 2 ENS plexuses. This way, they can coordinate their actions together
what is the rate of action of the ENS modulated by?
the CNS
how does the CNS regulate the ENS?
- by sending impulses from the brain, down to the gut (efferent neurons)
- Increasing Action ->Parasympathetic NS increases gastric motility + secretion (‘rest and digest’)
-Decreasing Action->
Sympathetic NS decreases gastric motility (‘fight or flight’)
what happens in the propulsive/ contracting segment of the GI tract?
- circular muscle contracts
- longitudinal muscle relaxes
- neurons release noradrenaline
what happens in the receptive/ relaxing segment of the GI tract?
- circular muscle relaxes
- longitudinal muscle contracts
- neurons release ACh and NO
what is the function of rugae in the mucosa layer of the stomach?
-increase SA
what are the major cell types in the fundus of the stomach?
mucous/ epithelial cells
what is secreted by the cells of the stomach fundus?
- mucous, HCO3-
- gastric lipase
what is the function of gastric lipase?
-lipid digestion
what are the functions of mucous and HCO3- secretions?
- provides lubrication
- higher pH microenvrionment next to gastric epithelial lining-protective mechanism against harsh contents of stomach
what are the 4 major cell types of the corpus of the stomach?
- mucous/ epithelial
- chief
- parietal
- enterochromaffin-like (ECL)
what do chief cells secrete?
pepsingoen
what is the role of of pepsingoen?
a pro-peptide which is then activated by stomach acid into the active enzyme pepsin-protein digestion
what do parietal cells secrete?
- HCl- breaks down food/ kills bacteria/ converts pepsinogen to pepsin
- intrinsic factor-transportation and absorption of B12 to the terminal ileum (vitamin B12 needed for erythropoiesis)
what do ECL cells secrete?
histamine
what is the role of histamine in the GI tract?
stimulates parietal cells to release HCl
what are the 4 major cell types of the antrum of the stomach?
- mucous/ epithelial cells
- chief cells
- G-cells
- D-cells
what do G-cells secrete?
gastrin
What are the roles of gastrin?
- increases gastric motility
- increases secretion
- increases secretion of HCl directly by stimulating parietal cells, and indirectly by stimulating ECLs
what do D-cells secrete?
somatostatin
what is the role of somatostatin on the GI tract?
acts locally to decrease gastric secretions, gastric motility and gastric hormones such as gastrin
what are the 3 methods of stimulation?
1-CN X vagus nerve releases acetylcholine-binds M3 receptors
(also encourages the release of histamine and gastrin)
2-ECL cells histamine-binds to H2 receptors
3-G-cells release gastrin-CCK2 receptors
(also encourages the release of histamines)
how is HCl inhibition?
D-cells release somatostatin (binds to SST2 receptors)
-somatostatin also inhibits histamine and gastrin
how is HCl released?
1-The reaction [CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-] is carried out by carbonic anhydrase.
a-HCO3- 🡪 transported out of the basolateral membrane of the cell***, into the blood, whilst Cl- is brought in (HCO3 -/Cl- antiporters)
b-H+ 🡪 transported out of the apical membrane of the cell, into the lumen, whilst K+ is brought in (H+/K+ ATPases)
3-Cl- (and K+) are transported out of the apical membrane, into the lumen
4-H+ and Cl- join inside the stomach to form HCl (i.e. HCl is not formed inside parietal cells). (Stomach pH 1.5-2.5)
what are the 3 phases of gastric secretion?
1-cephalic
2-gastric
3-intestinal
describe the cephalic phase
Upon smelling/seeing/anticipating food, a large amount gastric acid (HCl + enzymes) will be released for a short amount of time
describe the gastric phase
- 2 stimuli result in a large amount of gastric acid being released over a long period time
- Stomach receives bolus and distends (detected by afferent vagal fibres). This results in a decrease in gastric tone and receptive relaxation to help accommodate the food (carried out by efferent vagal fibres) (vago-vagal reflex)
- Stomach detects peptides and amino acids by chemoreceptors – peptides are buffers and they make the stomach more alkaline. The stomach releases more acid to compensate.
describe the intestinal phase
Duodenal cells can also detect stretch and the acidity of chyme – G-Cells in the duodenum can release gastrin which travels via the blood to the stomach to act on parietal cells
The myenteric (Auerbach’s) Plexus of the ENS is located in between which 2 layers of GI tract wall? A-Mucosa + Submucosa B-Submucosa + Muscularis Mucosae C-Submucosa + Circular Muscle D-Circular Muscle + Longitudinal Muscle E-Longitudinal Muscle + Serosa
D
The following will result in increased gastric secretion
A-Increased circulating secretin
B-Inhibitory vagal efferents
C-Acid in the stomach lumen
D-Pepsins and amino acids in the stomach lumen
E-Increased circulating somatostatin
D
Which of the following neurotransmitters is responsible for the relaxation of the gut lumen distal to the bolus during peristalsis? A-Nitric Oxide B-Prostaglandin C-Arachidonic Acid D-Noradrenaline E-Somatostatin
A
Which cranial nerve senses distension in the gut lumen via baroreceptors, and sends signals to the CNS via afferent nerve fibres? A-Trigeminal B-Facial Nerve C-Glossopharyngeal D-Vagus E-Hypoglossal
D
