gastrointestinal system Flashcards
what does the apical membrane back onto?
the gastointestinal tract lumen
what does the basal membrane back onto?
the interstitial fluid
what are the two pathways to get fron the gastrointestinal lumen to the insterstitual fluid?
transcellular- across the cell membranes through the cytoplasm
paracellular- between the cells, across tight junctions between epithelial cells
secretion vs absorption
secretion (exocrine): movements of solutes and water from the body (blood) into the GIT lumen
absorption: movements of solutes and water from the GIT lumen into the body
endocrine secretions vs exocrine secretions
endocrine secretions move into the blood
exocrine secretions are produced by epithelia and move into the lumen.
what does the enteric system activate as a reponse in the GI system?
the submucosal plexus to regulate secretion
the myenteric plexus because it regulates motility =
what does activation of the parasympathetic system do to the GI system?
It increases overall activity through the ENS system, increased motility and secretion
what does the activation of the sympathetic nervous system do to the GI system?
it decreases activity through inhibition of the ENS system, less motility and secretion.
what cells in the GI system release hormones? What hormones are they?
The enteroendocrine cells, release gastrin, secretin CCK and GIP
what are phasic contractions and how regularly do they occur in the stomach, duodenum and the ileum?
waves of contraction and relaxation
stomach=3 per min
duodenum= 12 per min
ilium= 9 per min.
*number doesnt change, only strength of contraction does
where does relaxation occur and why is it important?
occurs in the fundus and the stomach body
important for storage and minimal change in pressure to prevent reflux
where does retropulsion occur and why is it important?
occuring in the pyloric atrium and pyloric sphincter, the peristaltic contractions grind food against the pyloric sphinter as a last part of mechanical digestion before entering the small intestine.
why is the pyloric sphincter important?
it allows for slow release gastric emptying of chyme into the duodenum so it can cope.
how does the duodenum know when chyme has arrived from the stomach?
chemoreceptors and enteroendocrine cells in the duodenum are able to detect fats, acids, or changes in osmoregularity which indicates what secretions it requires.
eg bile for fat or bicarb to neutralise acid.
what hormones do the enteroendocrine cells in the duodenum secrete and what function do they serve.
CCK and secretin, these decrease the force of peristalsis in the stomach which helps to slow gastric emptying so the small intestine and accessory organs can keep up with demand.
