Physiology Flashcards
components of alimentary canal
mouth/oropharynx oesophagus stomach small intestine large intestine rectum and anus
4 functions of alimentary canal
motility
secretion
digestion
absorption
describe lumen during circular muscle contraction
narrowed lumen and longer
describe lumen during longitudinal muscle contraction
shorter, fatter intestine
how is a synchronous wave of contraction achieved in the smooth muscle of the GI tract
gap junctions between cells
how is GI smooth muscle contraction driven
pacemaker cells
what do interstitial cells of cajal do?
drive slow waves coupled to smooth muscle to control rate of contraction
when does intestinal muscle contraction occur
when slow waves exceed threshold to contract
what increases force of contraction in intestinal muscle
number of APs discharged
true/false - frequency of slow waves vary along GI tract
true
where do parasympathetic nerves for the GI tract originate from
vagus nerve sacral outflow (S2-S4)
true/false - preganglionic parasympathetic fibres of the GI tract synapse with gaglia and connect to postganglionic neurons of parasympathetic system
false - synapses with ganglia then connects to postganglionic neurons of ENS
true/false - preganglionic neurons of the sympathetic system synapse at the sympathetic chain
false - they synapse at prevertebral ganglia
inflences of parasympathetic nervous system
increased gastric, pancreatic and small intestine secretion
increased blood flow and smooth muscle contraction
relaxation of sphincters
influences of sympathetic nervous system
increased sphincter tone
decreased motility, secretion and blood flow
true/false - ANS/hormones can modulate myenteric and submucosal plexus
true
what is peristalsis
wave of relaxation followed by contraction in aboral direction
in peristalsis, what happens behind the bolus
NO/VIP cause longitudinal muscle to relax
ACh causes circular muscle to contract to push bolus
in peristalsis, what happens in front of the bolus
longitudinal muscle contracts due to ACh
circular muscle relaxes due to VIP/NO
what is colonic mass movement
sweeping contraction that forces faeces into rectum
function of upper oesophageal sphincter
relaxes to allow swallowing and closes in inspiration
skeletal muscle
function of lower oesophageal sphincter
relaxes to allow food entry to stomach
prevents acid reflex into oesophagus
function of pyloric sphincter
regulates gastric emptying and prevents duodenal gastric reflux
function of ileocaecal valve
controls flow from ileum to caecum
ileal distention opens it and proximal colon distention closes it
internal and external anal sphincters
defaecation reflex
skeletal muscle - voluntary control
function of orad stomach
accomodate food in feeding
digestion by amylase
what effect does vagal tone have on the orad stomach
relaxation to allow for storage of ingested food
tonic contraction to propel food into caudad stomach
what is the orad stomach made up of
fundus and proximal body
what is the caudal stomach made up of
distal body and antrum
function of caudad stomach
digestion by pepsin and HCl, intrinsic factor and gastrograffin
phasic peristaltic contractions to allow chyme into duodenum
what is retropulsion
rebound of chyme back into caudad stomach due to faster contraction than chyme movement - churns chyme
gastric factors controlling stomach emptying
stretch of smooth muscle intrinsic nerve plexus stimulation increased vagal activity increased gastrin thicker chyme
duodenal factors controlling stomach emptying
enterogastric reflex - decrease in antral activity due to decrease in ANS and intrinsic nerve plexus
release of enterogastrones from duodenum to inhibit contraction
stimuli for slower secretion of chyme into stomach
high fat
high acid concentration
hypertonicity - carbohydrates and protein
duodenal distention
what is the oxyntic gland area
fundus and body
what is the pyloric gland area
antrum
secreting cells and their secretions in the pyloric gland
G cells - gastrin
D cells - somatostatin
Mucus secretion
secreting cells and their secretions in the oxyntic gland
enterochromaffin - histamine
parietal cells - HCl, intrinsic factor, gastroferrin
Chief cells - pepsinogen
Mucus secretion
Function gastrin
stimulates gastric secretion and acid production
growth of gastric mucosa
G cells
function somatostatin
reduces astric secretion and acid production
function HCl
denatures proteins, kills microorganisms, pepsinogen to pepsin
function intrinsic factor
binds to vitamin B12 to facilitate absorption, sometimes iron
function gastroferrin
binds to iron to facilitate absorption
function pepsinogen
inactive precursor of pepsin, once activated it can further activate pepsin
function histamine
stimulates HCl secretion
describe HCl secretion by parietal cells
CO2 and H2O combine by carbonic anhydrase to form carbonic acid. dissociates to H, pumped into canaliculus by proton pump. bicarbonate removed by antiport with chloride, which leaves cell by CFTR at canaliculus
true/false - acid secretion is a passive process
false - it is active
name 3 secretagogues
ACh
Gastrin
Histamine
where does the proton pump translocate from on stimulation by secretagogues
cytoplasmic tubulovesicles
what is the cephalic phase of acid secretion and what drives it
anticipatory signal telling stomach to secrete acid
driven by vagus nerve
Vagus nerve stimulates enteric nervous system to release ACh in the cephalic and gastric phase. what does it do?
parietal cells- increase secretion
D cells - reduce somatostatin
ECL - increase histamine
(GRP not ACh) G cells- increase gastrin
what is the gastric phase, and besides vagal innervation what else drives it
when food enters stomach
distention of stomach
amino acids on g cell to increase gastrin
high pH decreases somatostatin
what drives acid secretion in the intestinal phase
chyme enters duodenum to cause weak gastric secretion stimulation
what causes decreased acid secretion in cephalic phase
decreased vagal activity
what causes decreased acid secretion in gastric phase
decreased vagal activity
low pH - somatostatin from D cells
PGE - reduce histamine and gastrin mediated HCl
3 ways small intestine increases surface area and better absorption
circular folds of kerckring
villi
microvilli
what is segmentation and when does it occur
digestive state
vigorous alternating contraction and relaxation of segments of circular muscle
cause of segmentation and how to increase strength
interstitial pacemaker cells emitting slow waves, reach threshold upon distention
Parasympathetic innervation
what is the gastroileal reflex
segmentation in empty ileum due to gastrin from stomach
what is the migrating motor complex
strong peristaltic contraction that passes slowly across small intestine to clear debris, mucus and cells every 90-120 mins
___ and ___ induce the MMC and ___, ___ and ___ inhibit it
increase- motilin, macrolides
decrease - vagus, gastrin, CCK
location of secretin secretion and function
S cell duodenum
promotes secretion of bicarbonate from pancreas and gallbladder due to protons/fatty acid
location of CCK secretion and function
I cells duodenum
inhibits gastric emptying and pancreatic enzyme secretion, contraction of gallbladder and relaxation of sphincter oddi due to monoglycerides, fatty acid, amino acids
location of GIP secretion and function
K cell duodenum, jejunum
insulin release and impaired gastric emptying due to glucose, amino acids, fatty acids
location of GLP-1 secretion and function
L cell small intestine
insulin secretion
inhibits glucagon secretion
decrease gastric emptying and appetite
location of motilin secretion and function
M cells duodenum and jejunum
stimulates MMC on fasting
location of ghrelin secretion and function
Gr of gastric antrum, small intestine
stimulates appetite
innervation for succus entericus
distention gastrin CCK secretin parasympathetic activity
contents of succus entericus
mucus - goblet cell
aqueous salt - crypt lieberkuhn - secreted by chloride ion secretion into lumen by CFTR, drawing Na and H2O
2 endocrine pancreatic secretions
insulin
glucagon
describe how digestive enzymes converge in pancreatic duct
acinar cells secrete digestive enzymes that travel from acinus to duct and then converge
describe the formation of bicarbonate by pancreatic duct cells
Na/Cl transporter provides some bicarbonate
CO2 into cell with H20 and carbonic anhydrase produces carbonic acid
H dissociates and is pumped out by proton pump and Na/H transporter
bicarbonate secreted in bicarbonate/Cl exchanger with CFTR pumping chloride back out
what enzyme catalyses trypsinogen to trypsin
enterokinase
trypsin in active form activates what other proteases
chymotrypsin and carboxypeptidase A&B
what increases pancreatic secretion in cephalic phase
vagal stimulation
what increases pancreatic secretion in gastric phase
gastric distention leading to vagal stimulation
what increases pancreatic secretion in intestinal phase
acid in duodenum - increased secretin
fat and protein - increased CCK
what is luminal digestion
enzymes secreted into lumen
what is membrane digestion
enzymes present at brush border of epithelial cells
what is assimilation
the collective term for digestion and absorption
what linkage does amylose have
straight chain with alpha-1,4 linkage