GIT physiology 1 Flashcards
What are the receptor classes within the GIT and what do they detect
Chemorecetors: Detect changes in the content of the GIT, the nutriance (fats, proteins, carbs) and pH
Mechanoreceptors: Detect changes in stretch caused by the movement of food/chyme throughout the GIT
Osmoreceptors: Detect changes in the luminal osmolarity (ion concs)
What are the three types of control which are present to adapt the response of the GIT
Nervous control - Fast reponses, 2 branches
Enteric nervous system: Self contained nervous system which functions seperate to the CNS
- Myenteric plexus = effect muscular contractions
- submucosal plexus = effects secretions
CNS: modulates the ENS with the rest of the body/ environment
- parasympathetic = rest + digest, promotes ENS activity
- sypathetic = fight + flight, inhibits ENS activity
Hormonal control: Slow, long lasting effects to many areas of the GIT
- released by enteroendocrine cells - detect changes and release hormones
- important sections: gastrin, secretin, CCK, GIP
What is the short reflex pathway
Function: retrun the GIT to its resting state
Stimulation: change in the luminal content
Detected: receptors send information to ENS (also CNS for long pathway)
Effect: ENS promotes smooth muscle and secretion activity in the body
What is the long reflex pathway
Functions: intergrate the GIT with external input + return GIT to its resting state
Stimulation: change to the luminal content or external stimulus
effect: CNS triggers the PS or sympathetic nervous system to effect the GIT
What are the definitions of:
mechanical vs chemical digestion
Tonic vs phasic contrations
Mechanical digestion: physcially breaking appart the food into smaller peices -> ends as chyme- occurs mouth + stomach
Chemical diestion: Enzyme and pH digestion to break macromolecules into smaller monomers which can be absorped
Tonic contractions - long sustained contractions (min-hours)
Phasic contractions - short waves of contractions (seconds)
- controled by pace maker cells in smooth muscle
- frequence dependant on locations and doesnt change
- strength effected by the ENS
number of contractions per minute of the GIT:
Stomach = 3 , duodenum = 12, ileum = 9 contractions
What are the motility patturns within the fed state
Chewing - mechanical digestion
peristalsis - wave movement = push chyme along GIT
relaxation - causing increase in volume without pressure change
contraction/relaxation of sphincters - control the movment between sections of the GIT + prevent backflow
Segmentation - mix the luminal content, chyme + enzymes/chemcials
What are the motility patturns of the fasting state
Migrating motor complex:
Functions -> remove undigested material, remove excess secretions, promote epithelium turn over
Locations - Stomach + small intestine
Timing: starts 4h after eating, cycle repeates every 1.5-2h until eaten
- 45- 60min of low activity
- 30min intermitant uncoordinated activity
- 5-15min peristaltic contractions
What are the motility patteruns found in the mouth
Chewing - mastication = volentary chewing of food, mechncial digestion mixes with saliva
- salive for protection, lubrication and taste
What are the motility patteruns found in the esophagus
Relaxation of sphincters - ENables food to enter and exit the esophagus
peristalsis - wave of contraction to push bolus towards stomach
volentary initation -> moves to reflex
Protecting regions - uvula + softpalete = protect nasopharynx, epiglottis = protect tracta + larynx
What are the motility patteruns found in the stomach
Peristalisis - 3x/min, gentil first 60min, strong 60-300min
Relaxation - body + fundus - increase space
- receptive relaxation, when moving down esophagus
- accomidative relaxation, when food in the stomach
Pyloric sphincter - control of gastric empying, ensure sufficnet digestion
- closed in gental contractions, partally open in strong contraction
- Regulation from stomach + duodenum, ensures emptying matches bile, bicarb + enzyme production
- Retropulsion: combination of sphincter + peristalis, occurs in body and atrum, grinds food into sphincter to mechanically digest food
What are the motility patteruns found in the small intestine
Segmentation - mix the luminal content, increase exposure to the absorpitive surfaces, predominent patturn
Peristalsis -
What are the motility patteruns found in the Large intestine
Segmentation – absorption of Na+ and H2O
Relaxation – increase volume -> storage feces
Peristalsis – 1-2x a day to promote defecation
How is the digestive rate effected by meal size
Larger meal, faster rate of digestion
What is the function of the duodenum in regulating the motility patteruns of the GIT
Detects the properties of the chyme entering the duodenum, regulate to ensure that the acessory stuctures can maintain production
Chemo and osmo receptors - detect changes and trigger the short and long reflex pathways
- PS decreased, sympathetic increase
enteroendocytes - release CCK and secretin
- decrease peristaltic contraction strength
- slow gastric emptying
