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Revision > GI tract physiology > Flashcards

GI tract physiology Flashcards

1
Q

what are the three phases of deglutition

A

oral phase
pharyngeal phase
oesophageal phase

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2
Q

what are the anterior boundaries of the mouth

A

the lip and vestibule

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3
Q

what is the posterior boundary of the m outh

A

the palatoglossal arch - the pillars of the mouth

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4
Q

which muscles depress the mandible to open the mouth for eating

A
  • lateral pterygoid
  • diagastric interior belly of the hyoid
  • mylohyoid muscle
  • geniohyoid
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5
Q

what innervates the muscles responsible for depressing the mandible

A

the mandibular division of the trigeminal nerve
geniohyoid is innervated by C1 of the cervical plexus

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6
Q

describe depression of the mandible

A
  • muscles contract to depress the mandible
  • stretches the elavators and activates muscle spindles, which respond and activate the afferent fibres of the trigeminal nerve to elevate the mandible to close the mouth for chewing
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7
Q

what are the muscles that elevate the mandible

A

masseter
temporalis
medial pterygoid

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8
Q

what innervates the elevator muscles

A

the mandibular division of the trigeminal nerve

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9
Q

which two mechanisms combine to break food into smaller pieces

A

combination of the muscles of mastication and teeth

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10
Q

what activates the inhibition of the trigemical nerve to drop the mandible into resting position

A

pressure receptors in the oral mucosa and gingiva

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11
Q

what are the extrinsic salivary glands

A

major

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12
Q

what proportion of all saliva in the mouth is secreted by the major glands

A

90%

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13
Q

what is the bolus

A

compact mass of food post chew

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14
Q

why is it important that food is converted to bolus before swallowing

A

because the mastication and salivary mechanisms that produce bolus increase its surface area for chemical digestion by salivary amylase and lingual lipase, and decrease the possibility of abrasion on the gastrointestinal lining

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15
Q

describe what happens to the tongue during swallowing

A

takes on a special shape via its intrinsic muscles to allow the bolus to move down toward the pharynx

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16
Q

describe how the tongue changes shape

A

intrinsic muscles form a central trough on the back
extrinsic muscles elevate the tongue so the tip of the tongue touches the palata

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17
Q

what are the extrinsic muscles of the tongue

A

styloglossus
genioglossus

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18
Q

what are the intrinsic muscles of the tongue

A

superior longitudinal
inferior longitudinal
vertical
transverse muscles of the tongue

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19
Q

what can the mylohyoid muscle do to the tongue

A

elevate it during swallowing

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20
Q

what are the pillars of the mouth

A

palatoglossal arch
palatopharyngeal arch
palatoglossal is more anterior

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21
Q

what happens when the bolus touches the pharynx

A

stimulatio of afferent glossopharyngeal nerve fibres which stimulates action potentials down its axons to the CNS to activate the vagus nerve

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22
Q

what does activation of the vagus nerve during swallowing lead to

A
  • activation of the uvula to block the nasopharynx
  • levator velipalatonei muscle pulls on the soft palate to increase the distance between the bolus and the soft palate
  • trigeminal nerve has fibres to innervate the tensor velipalatonei, which tenses the soft palate to accentuate the action of the levator veli palatini to elevate the palate even more.
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23
Q

which mechanisms happen to close the larynx during swallowing

A

lateral crico arytenoids and oblique arytenoid muscles move the vocal cords together.
bolus touches the epiglottis and moves it down, closing off the trachea

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24
Q

what function do the palatoglossal and palatopharyngeal muscles carry out for swallowing

A

they contract and pull together to push the bolus out, so only the smallest bolus can go into the pharynx

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25
Q

what are the longitudinal muscles of the pharynx

A
  • stylopharyngeus
  • salpingopharyngeus
  • palatopharyngeus
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26
Q

function of the longitudinal muscles of the pharynx

A

pull the pharynx and larynx up

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27
Q

what attaches the larynx to the trachea

A

the cricoid cartilage

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28
Q

what innervates the stylopharyngeus

A

glossopharyngeal

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29
Q

what is the only motor component of the glossopharyngeal

A

the stylopharyngeus

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30
Q

what innervates the salpingopharyngeus and palatopharyngeus

A

vagus nerve

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31
Q

what are the muscles of the inner circular layer of the pharynx

A

the pharyngeal constrictors

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32
Q

what is pharyngeal peristalsis

A

alternating wave of contraction and relaxation to push the bolus down

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33
Q

what happens to the larynx during pharyngeal peristalsis

A

the suprahyoid muscles contract and pull upward, which makes the larynx move anteriorly

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34
Q

what are the suprahyoid muscles

A

stylohyoid
geniohyoid
mylohyoid
digastric

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35
Q

what is the muscle of the upper oesophageal sphincter

A

the cricopharyngeus

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36
Q

what innervates the cricopharyngeus

A

vagus nerve

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37
Q

what innervates the muscles of the oesophagus

A

the vagus nerve

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38
Q

what happens if food gets stuck in the oesophagus

A

the oesophageal walls stretch
stretch receptors will stimulate longitudinal muscle and inhibit the circular to ensure the bolus moves down.

39
Q

what is a secondary peristalsis

A

local reflex to ensure the bolus makes it to the stomach if it gets stuck

40
Q

what are the phases of gastric secretion

A

cephalic
gastric
intestinal

41
Q

how much gastric juice is secreted in the cephalic phase

A

one third

42
Q

how much gastric juice is secreted in the gastric phase

A

two thirds

43
Q

what is involved in cephalic secretion

A

sight of food
thought of food
smell of food

44
Q

when gastric juice secretion start

A

before food has even entered the stomach

45
Q

how does cephalic stimulus lead to gastric secretion

A
  • cerebral cortex is stimulated
  • information sent to hypothalamus
  • hypothalamus sends to descending axons to a nucleus in the medulla called the dorsal nucleus of vagus
  • vagus nerve comes out of the medulla through the jugular foramen to the stomach
46
Q

which part of the stomach has a sphincter

A

pylorus

47
Q

what protects us from ulcer generation if the stomach is so acidic

A

mucous membrane

48
Q

which innervation is vital for gastric juice production

A

parasympathetic

49
Q

what is the stimuli for gastric secretion

A

distension

50
Q

where are the stretch receptors in the stomach

A

around the stomach in the submucosa and in the muscularis externa.

51
Q

what is the course of events once the stomach has detected stretch

A
  • receptors stimulate the vagus nerve to stimulate chief and parietal cell secretion
  • submucosal plexus stimulates the gastric cells
52
Q

which cells are found in the antrum of the stomach

A

enteroendocrine g cells and d cells

53
Q

what do g cells of the stomach do

A

respond to partially digested proteins and are stimulated by them to produce gastrin.

54
Q

what is gastrin

A

a hormone that travels through the blood to the parietal cells and chief cells

55
Q

describe the effect of gastrin on parietal cells

A

and bind to CCK type 2 receptors to activate an intracellular signalling mechanism to increase calcium levels and activate a special pump on the parietal cells to push hydrogen into the stomach lumen.

56
Q

describe the effect of gastrin on chief cells

A

binds to CCK type 1 receptors which stimulate an increase in calcium levels to stimulate the vesicle to fuse with the cell membrane and make exoctyosis pocket to allow pepsinogen molecules to enter the lumen of the stomach.
pepsinogen is converted to pepsin

57
Q

what must the pH be to convert pepsinogen to pepsin

A

1.5-3.5

58
Q

what is the primary inhibitor of gastric secretion

A

the sympathetic nervous system

59
Q

how do parietal cells make hydrochloric acid

A
  • these cells undergo aerobic respiration and release carbon dioxide. the carbon dioxide combines with water to give protons and bicarbonate.
  • bicarbonate goes into the blood and makes blood leaving the stomach more alkaline, activating chloride channels and releasing chlorine which combines with the protons to make HCl
60
Q

what are the d cells of the stomach

A

found in the antrum, function to secrete somatostatin to inhibit g cells and decrease gastrin production

61
Q

what inhibits antral d cells from releasing somatostatin

A

acetylcholine

62
Q

what can inhibit parietal cells

A

somatostatin

63
Q

what can stimulate parietal cells

A

gastrin
acetylycholine
histamines

64
Q

what can increase the release of pepsinogen

A
  • histamines
  • acetylcholine
  • secretin
65
Q

where in the stomach are the parietal and chief cells

A

the corpus (body)

66
Q

why do hydrochloric acid and pepsin not digest the stomach if it is so corrosive

A

the protective factor is the presence of mucous cells
- foveolar cells
- mucous neck cells
- secrete molecules to form a mucosal barrier

67
Q

describe what is found in the mucosal barrier lining the stomach

A
  • 95% water
  • electrolytes like sodium and potassium
  • phospholipids
  • mucins
  • bicarbonate
68
Q

how much gastric juice is produced from the intestinal phase

A

very little

69
Q

what is the difference between antral g cells and intestinal g cells

A
  • antral is G17
  • intestinal is G34
    they differ in amino acid composition but they exert the same function
70
Q

where does stomach contraction begin

A

the cardia

71
Q

where in the stomach is the peristaltic wave the strongest

A

the pylorus

72
Q

describe pyloric contraction

A
  • 27ml pushed back into the stomach (retropulsion)
  • 3ml into chyme
73
Q

what are peptones

A

partially digested proteins

74
Q

what do peptones do in the intestines

A

stimulate duodenal g cells to secrete intestinal gastrin

75
Q

what does intestinal gastrin do

A

travel through the blood like a hormone to get to the corpus parietal cells to secrete intrinsic factor to absorb vitamin B12
- gastrin has receptors on chief cells which is stimulated by partially digested proteins to produce more pepsinogen.

76
Q

what is secretin

A

secreted by s cells of the duodenal mucosa in resopnse to increased concentration of protons and fat in the chyme

77
Q

what does secretin do

A
  • travels to antral g cells to reduce gastrin secretion
  • travel to the liver to stimulate hepatocytes to convert any cholesterol into bile
  • act on ductal epithelial cells to stimulate bicarbonate production
  • stimulate chief cells to make pepsinogen
78
Q

describe the bile pathway

A
  • produced in the liver by hepatocytes
  • travel through bile canaliculi to common hepatic duct
  • drains to form common bile duct
  • this fuses with the main pancreatic duct to form the hepatopancreatic ampula
79
Q

what does bile do

A

emulsify fatty acids

80
Q

what muscle wraps around the hepatopancreatic ampula

A

the sphincter of oddi

81
Q

which cells release CCK

A

enteroendocrine I cells

82
Q

what does CCK do

A

travel to parietal cells to inhibit proton pumps
accentuates the action of secretin to stimulate bile synthesis

83
Q

how does the gall bladder concentrate the bile

A

by removing water and electrolytes to ensure it is mostly just bile salts, bilirubin, and phospholipids

84
Q

what makes the sphincter of oddi relax to allow bile and bicarbonate to flow into the duodenal mucosa

A

binding of CCK

85
Q

what are some digestive enzymes found in the pancreas acini

A
  • trypsin
  • amylase
  • lipase
  • nucleases
86
Q

what can stimulate I cells to produce CCK

A

fatty chyme
peptones
oligosaccharide

87
Q

what does CCK do in the pancreas

A

bind to acinar cells to stimulate release of digestive enzymes

88
Q

what happens if there is a lot of chyme in the intestines

A

endocrine cells in the duodenum release peptide YY and neurotensin to inhibit parietal cells to ensure less hydrochloric acid is being produced, which means less acidic chyme is being released.

89
Q

what releases gastric inhibitory peptide

A

enteroendocrine K cells

90
Q

what does gastric inhibitory peptide do

A

act on the islets of langerhans beta cells to stimulate insulin release.

91
Q

what happens if chyme is really acidic

A

chemoreceptors detect it and inhibit the vagus nerve so there is less HCl produced.
sympathetic fibres stimulate the pyloric sphincter using alpha one adrenergic receptors to squeeze and prevent release of chyme into the duodenum

92
Q

describe the two main layers of the mucosal barrier that protects the entire stomach

A

mucous gel layer on the top
bicarbonate below
protons and pepsin struggle to penetrate the gel layer and when they do they are inactivated by the bicarbonate.

93
Q

what is the epithelial lining of the intestine

A

simple columnar

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