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Medicine yr1 > GI-saliva > Flashcards

GI-saliva Flashcards

1
Q

what are the 4 functions of saliva?

A

1-tooth maintenance
2-lubrication
3-antibacterial/ antibacterial-IgA
4-digestive (amylase)

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2
Q

at what pH must the saliva be kept close to?

A

pH 7

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3
Q

what happens to the pH of saliva after a meal?

A

pH decreases as plaque bacteria makes acid

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4
Q

at what pH do teeth demineralise?

A

pH 5.5

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5
Q

how many pairs salivary glands do we have?

A

3

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6
Q

name the salivary glands

A
  • submandibular
  • sublingual
  • parotid
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7
Q

which salivary glands are innervated by the facial nerve (CN VII)?

A
  • submandibular

- sublingual

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8
Q

which nerve innervates the parotid gland?

A

glossopharyngeal nerve (CN IX)

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9
Q

what does the parotid gland secrete?

A

serous saliva

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10
Q

what does the sublingual gland secrete?

A

mucous saliva

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11
Q

what does the submandibular gland secrete?

A

-serous/ mucous
or
-mixed saliva

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12
Q

name some stimulants for saliva secretion

A
  • mastication
  • taste
  • smell
  • anticipation
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13
Q

what inhibits saliva secretion?

A
  • fear

- vomiting

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14
Q

what are the constituents of saliva?

A

Glycoproteins - layers slide over each other; difficult to pull apart

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15
Q

what do all salivary glands secrete?

A

both protein and fluid

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16
Q

what are the 2 cell types of salivary glands?

A
  • Myoepithelial cells contract to increase speed of release

- Acinar cells can either be serous or mucous, but these produce saliva

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17
Q

what is the stimulus secretion coupling process?

A

process whereby both protein and fluid are secreted simultaneously as to prevent protein from blocking the apical side of the acinar cells

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18
Q

describe the process of protein secretion in saliva?

A

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

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19
Q

describe how acinar cells secrete IgA

A

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

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20
Q

describe how fluid secretion occurs in saliva

A

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

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21
Q

name the layers of the GI tract (from deep to superficial)

A
  • mucosa (epithelium/ lamina propria/ muscularis mucosae)
  • submucosa (contains submucosal plexus)
  • muscularis (circular muscle/ myenteric plexus/ longitudinal muscle)
  • serosa (areolar connective tissue/ visceral peritoneum)
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22
Q

which 2 types of epithelial are in the mucosa layer of the GI tract?

A
  • simple columnar

- non-keratinised squamous

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23
Q

what is food in the gut detected by in the enteric NS?

A

-chemoreceptors (detect chemicals in food) -baroreceptors (detect distention of the gut from the bolus)

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24
Q

what does food in the gut trigger in the enteric NS?

A
  • sensory (afferent) neurons (Vagal / CN X Nerves)

- relay information to the Central Nervous System (CNS) and to the Enteric Nervous System (ENS)

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25
Q

which 2 plexuses is the ENS made up of?

A
  • Myenteric Plexus (Auerbach)

- The Submucosal Plexus (Meissner)

26
Q

where is the myenteric plexus located in the gut wall?

A

Located in between the circular and longitudinal muscles.

27
Q

where is the submucosal plexus located?

A

Located in the submucosa of the GI wall

28
Q

what is the role of the myenteric plexus?

A

Cause contractions of the muscle wall, to help push the bolus along

29
Q

what is the role of the submucosal plexus?

A

controls secretion and absorption within the gut.

30
Q

what connects the 2 ENS plexuses and why?

A

Inter-neurons connect the 2 ENS plexuses. This way, they can coordinate their actions together

31
Q

what is the rate of action of the ENS modulated by?

A

the CNS

32
Q

how does the CNS regulate the ENS?

A
  • 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’)

33
Q

what happens in the propulsive/ contracting segment of the GI tract?

A
  • circular muscle contracts
  • longitudinal muscle relaxes
  • neurons release noradrenaline
34
Q

what happens in the receptive/ relaxing segment of the GI tract?

A
  • circular muscle relaxes
  • longitudinal muscle contracts
  • neurons release ACh and NO
35
Q

what is the function of rugae in the mucosa layer of the stomach?

A

-increase SA

36
Q

what are the major cell types in the fundus of the stomach?

A

mucous/ epithelial cells

37
Q

what is secreted by the cells of the stomach fundus?

A
  • mucous, HCO3-

- gastric lipase

38
Q

what is the function of gastric lipase?

A

-lipid digestion

39
Q

what are the functions of mucous and HCO3- secretions?

A
  • provides lubrication

- higher pH microenvrionment next to gastric epithelial lining-protective mechanism against harsh contents of stomach

40
Q

what are the 4 major cell types of the corpus of the stomach?

A
  • mucous/ epithelial
  • chief
  • parietal
  • enterochromaffin-like (ECL)
41
Q

what do chief cells secrete?

A

pepsingoen

42
Q

what is the role of of pepsingoen?

A

a pro-peptide which is then activated by stomach acid into the active enzyme pepsin-protein digestion

43
Q

what do parietal cells secrete?

A
  • 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)
44
Q

what do ECL cells secrete?

A

histamine

45
Q

what is the role of histamine in the GI tract?

A

stimulates parietal cells to release HCl

46
Q

what are the 4 major cell types of the antrum of the stomach?

A
  • mucous/ epithelial cells
  • chief cells
  • G-cells
  • D-cells
47
Q

what do G-cells secrete?

A

gastrin

48
Q

What are the roles of gastrin?

A
  • increases gastric motility
  • increases secretion
  • increases secretion of HCl directly by stimulating parietal cells, and indirectly by stimulating ECLs
49
Q

what do D-cells secrete?

A

somatostatin

50
Q

what is the role of somatostatin on the GI tract?

A

acts locally to decrease gastric secretions, gastric motility and gastric hormones such as gastrin

51
Q

what are the 3 methods of stimulation?

A

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)

52
Q

how is HCl inhibition?

A

D-cells release somatostatin (binds to SST2 receptors)

-somatostatin also inhibits histamine and gastrin

53
Q

how is HCl released?

A

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)

54
Q

what are the 3 phases of gastric secretion?

A

1-cephalic
2-gastric
3-intestinal

55
Q

describe the cephalic phase

A

Upon smelling/seeing/anticipating food, a large amount gastric acid (HCl + enzymes) will be released for a short amount of time

56
Q

describe the gastric phase

A
  • 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.
57
Q

describe the intestinal phase

A

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

58
Q 
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
A

D

59
Q

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

A

D

60
Q 
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

A

61
Q 
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
A

D

Medicine yr1 (55 decks)

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