GI tract physiology Flashcards
what are the three phases of deglutition
oral phase
pharyngeal phase
oesophageal phase
what are the anterior boundaries of the mouth
the lip and vestibule
what is the posterior boundary of the m outh
the palatoglossal arch - the pillars of the mouth
which muscles depress the mandible to open the mouth for eating
- lateral pterygoid
- diagastric interior belly of the hyoid
- mylohyoid muscle
- geniohyoid
what innervates the muscles responsible for depressing the mandible
the mandibular division of the trigeminal nerve
geniohyoid is innervated by C1 of the cervical plexus
describe depression of the mandible
- 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
what are the muscles that elevate the mandible
masseter
temporalis
medial pterygoid
what innervates the elevator muscles
the mandibular division of the trigeminal nerve
which two mechanisms combine to break food into smaller pieces
combination of the muscles of mastication and teeth
what activates the inhibition of the trigemical nerve to drop the mandible into resting position
pressure receptors in the oral mucosa and gingiva
what are the extrinsic salivary glands
major
what proportion of all saliva in the mouth is secreted by the major glands
90%
what is the bolus
compact mass of food post chew
why is it important that food is converted to bolus before swallowing
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
describe what happens to the tongue during swallowing
takes on a special shape via its intrinsic muscles to allow the bolus to move down toward the pharynx
describe how the tongue changes shape
intrinsic muscles form a central trough on the back
extrinsic muscles elevate the tongue so the tip of the tongue touches the palata
what are the extrinsic muscles of the tongue
styloglossus
genioglossus
what are the intrinsic muscles of the tongue
superior longitudinal
inferior longitudinal
vertical
transverse muscles of the tongue
what can the mylohyoid muscle do to the tongue
elevate it during swallowing
what are the pillars of the mouth
palatoglossal arch
palatopharyngeal arch
palatoglossal is more anterior
what happens when the bolus touches the pharynx
stimulatio of afferent glossopharyngeal nerve fibres which stimulates action potentials down its axons to the CNS to activate the vagus nerve
what does activation of the vagus nerve during swallowing lead to
- 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.
which mechanisms happen to close the larynx during swallowing
lateral crico arytenoids and oblique arytenoid muscles move the vocal cords together.
bolus touches the epiglottis and moves it down, closing off the trachea
what function do the palatoglossal and palatopharyngeal muscles carry out for swallowing
they contract and pull together to push the bolus out, so only the smallest bolus can go into the pharynx
what are the longitudinal muscles of the pharynx
- stylopharyngeus
- salpingopharyngeus
- palatopharyngeus
function of the longitudinal muscles of the pharynx
pull the pharynx and larynx up
what attaches the larynx to the trachea
the cricoid cartilage
what innervates the stylopharyngeus
glossopharyngeal
what is the only motor component of the glossopharyngeal
the stylopharyngeus
what innervates the salpingopharyngeus and palatopharyngeus
vagus nerve
what are the muscles of the inner circular layer of the pharynx
the pharyngeal constrictors
what is pharyngeal peristalsis
alternating wave of contraction and relaxation to push the bolus down
what happens to the larynx during pharyngeal peristalsis
the suprahyoid muscles contract and pull upward, which makes the larynx move anteriorly
what are the suprahyoid muscles
stylohyoid
geniohyoid
mylohyoid
digastric
what is the muscle of the upper oesophageal sphincter
the cricopharyngeus
what innervates the cricopharyngeus
vagus nerve
what innervates the muscles of the oesophagus
the vagus nerve
what happens if food gets stuck in the oesophagus
the oesophageal walls stretch
stretch receptors will stimulate longitudinal muscle and inhibit the circular to ensure the bolus moves down.
what is a secondary peristalsis
local reflex to ensure the bolus makes it to the stomach if it gets stuck
what are the phases of gastric secretion
cephalic
gastric
intestinal
how much gastric juice is secreted in the cephalic phase
one third
how much gastric juice is secreted in the gastric phase
two thirds
what is involved in cephalic secretion
sight of food
thought of food
smell of food
when gastric juice secretion start
before food has even entered the stomach
how does cephalic stimulus lead to gastric secretion
- 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
which part of the stomach has a sphincter
pylorus
what protects us from ulcer generation if the stomach is so acidic
mucous membrane
which innervation is vital for gastric juice production
parasympathetic
what is the stimuli for gastric secretion
distension
where are the stretch receptors in the stomach
around the stomach in the submucosa and in the muscularis externa.
what is the course of events once the stomach has detected stretch
- receptors stimulate the vagus nerve to stimulate chief and parietal cell secretion
- submucosal plexus stimulates the gastric cells
which cells are found in the antrum of the stomach
enteroendocrine g cells and d cells
what do g cells of the stomach do
respond to partially digested proteins and are stimulated by them to produce gastrin.
what is gastrin
a hormone that travels through the blood to the parietal cells and chief cells
describe the effect of gastrin on parietal cells
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.
describe the effect of gastrin on chief cells
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
what must the pH be to convert pepsinogen to pepsin
1.5-3.5
what is the primary inhibitor of gastric secretion
the sympathetic nervous system
how do parietal cells make hydrochloric acid
- 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
what are the d cells of the stomach
found in the antrum, function to secrete somatostatin to inhibit g cells and decrease gastrin production
what inhibits antral d cells from releasing somatostatin
acetylcholine
what can inhibit parietal cells
somatostatin
what can stimulate parietal cells
gastrin
acetylycholine
histamines
what can increase the release of pepsinogen
- histamines
- acetylcholine
- secretin
where in the stomach are the parietal and chief cells
the corpus (body)
why do hydrochloric acid and pepsin not digest the stomach if it is so corrosive
the protective factor is the presence of mucous cells
- foveolar cells
- mucous neck cells
- secrete molecules to form a mucosal barrier
describe what is found in the mucosal barrier lining the stomach
- 95% water
- electrolytes like sodium and potassium
- phospholipids
- mucins
- bicarbonate
how much gastric juice is produced from the intestinal phase
very little
what is the difference between antral g cells and intestinal g cells
- antral is G17
- intestinal is G34
they differ in amino acid composition but they exert the same function
where does stomach contraction begin
the cardia
where in the stomach is the peristaltic wave the strongest
the pylorus
describe pyloric contraction
- 27ml pushed back into the stomach (retropulsion)
- 3ml into chyme
what are peptones
partially digested proteins
what do peptones do in the intestines
stimulate duodenal g cells to secrete intestinal gastrin
what does intestinal gastrin do
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.
what is secretin
secreted by s cells of the duodenal mucosa in resopnse to increased concentration of protons and fat in the chyme
what does secretin do
- 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
describe the bile pathway
- 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
what does bile do
emulsify fatty acids
what muscle wraps around the hepatopancreatic ampula
the sphincter of oddi
which cells release CCK
enteroendocrine I cells
what does CCK do
travel to parietal cells to inhibit proton pumps
accentuates the action of secretin to stimulate bile synthesis
how does the gall bladder concentrate the bile
by removing water and electrolytes to ensure it is mostly just bile salts, bilirubin, and phospholipids
what makes the sphincter of oddi relax to allow bile and bicarbonate to flow into the duodenal mucosa
binding of CCK
what are some digestive enzymes found in the pancreas acini
- trypsin
- amylase
- lipase
- nucleases
what can stimulate I cells to produce CCK
fatty chyme
peptones
oligosaccharide
what does CCK do in the pancreas
bind to acinar cells to stimulate release of digestive enzymes
what happens if there is a lot of chyme in the intestines
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.
what releases gastric inhibitory peptide
enteroendocrine K cells
what does gastric inhibitory peptide do
act on the islets of langerhans beta cells to stimulate insulin release.
what happens if chyme is really acidic
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
describe the two main layers of the mucosal barrier that protects the entire stomach
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.
what is the epithelial lining of the intestine
simple columnar
