Flashcards in REVISION GUIDE GI: DIGESTION AND ABSORPTION Deck (91)
what is the primary site for digestion and absorption?
the small intesine
what are the 2 types of digestion?
what processes occur in absorption in the small intestine?
what are the adaptations of the epithelial lining of the small intestine?
has villi and microvilli - increase SA
has cell surface of enterocytes by membrane bound enzymes
what are the 3 ways that peptides modulate GI tract function?
what are the criteria for the endocrine modulation of GI tract function?
- physiological event (eg eating) must provide stimulus to one part of the GI tract that alters the activity of the others
- the effect must remain after the removal of nervous input
- the substance must be identified chemically
- actions may be antagonised/blocked
- synthesised endogenously
- released at a specific site in the blood stream in response to stimulus
how do paracrine modulate GI function?
activated by detection of nutrients
the mediator acts upon the immediate area around the cell
what is the neurocrine modulation of GI tract function?
sensory neuron activates an interneuron and activates a secretory motor neuron
this releases a neurotransmitter into the cleft activating adjacent cells
this can happen over a short or long distance
what is the result of negative feedback loop of stomach and duodenal digestion regulation?
acid activates D cells which release somatostatin - this acts to reduce the further release of acid
it inhibits G cells production of gastrin
it inhibits ECL cells release of histamine
it directly inhibits the release of acid from parietal cells
it stops chief cells production of pepsinogen
what is directly released as a result of duodenal digestion regulation?
nervous input from the brain
what is indirectly released as a result of duodenal digestion regulation?
distension of the gut
release of another hormone
what are the hormones that are involved in duodenal digestion regulation?
gastric inhibitory peptide
vasoactive intestinal peptide
what is the general effect of duodenal hormones?
they tend to inhibit stomach function
decreased stomach activity leads to increased duodenal absorption/ digestion
where is gastrin produced in the duodenum?
- secreted by G cells in duodenum in response to proteins
what is the effect of gastrin?
it promotes stomach motility
it stimulates production of gastric acid and enzymes
where is secretin produced in the duodenum?
released from duodenal S cells in response to high acid levels
it is released when chyme arrives in duodenum
what is the effect of secretin in the duodenum?
- increases secretion of bile from liver and gallbladder
- increases secretion of HCO3- and enzymes from pancreas
- increases pH of chyme and promotes digestion
- reduces gastric motility
-reduce gastric secretory rates
when is gastric inhibitory peptide secreted by the duodenum?
secreted when fats and carbohydrates enter the duodenum
what is the effect of gastric inhibitory peptide in the duodenum?
inhibits gastric activity
increases insulin activity
stimulates duodenal gland activity
stimulates lipid synthesis
increase glucose use by skeletal muscles
where is CCK produced?
released from I cells in duodenum, jejunum, less so from ileum
when is CCK secreted?
why chyme arrives in the duodenum
especially when high quantities of lipids and proteins
what are the pancreatic effects of CCK?
accelerates release of enzymes
increases HCO3- secretion
what are the liver and gallbladder effects of CCK?
sphincter of oddi relaxation
what is the effect of CCK on gastric activity?
it inhibits gastric activity and feeds to CNS to reduce sensation of hunger
what is the effect of vasoactive intestinal peptide?
stimulates the secretion of intestinal glands
dilates regional capillaries
inhibits acid production in stomach
dilation of capillaries allows more efficient absorption
how much protein does a healthy adult require per day?
40 - 50g
why are amino acids zwitterions?
they have both positive and negative groups on the same molecule
what is the pH of stomach acid?
HCl - pH 2
[H+] > 150mM
how much stomach acid is produced per day?
approx. 2 litres per day