Digestion and Absorption Flashcards
2 major sites of digestion:
duodenum
upper jejunum
3 diasaccharides are:
lactose (G-Ga)
sucrose (G-F)
maltose (G-G)
3 monosaccharides:
glucose
fructose
galactose
a-amylase hydrolyses what?
1:4a linkages between glucose molecules
what happens to a-amylase at low pH?
inactivated
what happens to a-amylase in duodenum?
re-activated after neutral pH is achieved
is a-amylase active in small bowel?
not really
CCK from starches?
not so much.
more so from proteins and fat
pancreatic a-amylase secreted due to?
CCK
pancreatic and salivary a-amylase are ineffective at what?
breaking 1:6a linkages
where are 1:6a linkages broken down?
at the brush borders of mucosal enterocytes
3 enzymes that break 1:6a linkages at brush border?
isomaltase
sucrase
maltase
Maltase and sucrase and made as a single large glycoprotein in the brush border membrane, how do you activate it?
pancreatic proteases
where on the villi and the GI are glucose and fructose absorbed?
tips of villi
duodenum/jejunum epithelium
glucose absorption depends on what electrolyte?
Na+
2 ways to enhance glucose transport:
high salt intake
enhance sweet taste receptor
sodium and glucose and transported together through:
SGLT1
sodium-dependent glucose transporter
what does GLUT5 transport? how?
fructose via facilitated diffusion into CELL
what does GLUT2 do?
fructose transporter into interstitium
where does proteins start to get digested? by what?
stomach with pepsin
pepsinogen activated by?
gastric acid
where is pepsinogen I secreted? vs. pepsinogen II
pepsinogen I: acid secreting regions
pepsinogen II: pylorus
pepsin hydrolyses which bonds?
between phenyalanine and tyrosine and the 2nd amino acid
how is pepsin inactivated?
neutral pH
pepsin is important in breaking down this cellular structure:
cell-cell adhesions
CCK triggers release of what?
pancreatic proteases in proenzyme form
How is pancreatic juice first activated?
via enterokinase
enterokinase does what?
activates proenzymes to active form: eg. trysinogen>trypsin
What does trypsin, elastase, chymotrypsin digest? products?
they are endopeptidases
interior bonds of proteins
make short polypeptides
what digests the short polypeptides after the endopeptidases?
pancreatic carboxypeptidases
at the brush border there are a mix of 4 peptidases, they are:
- aminopeptidases
- dipeptidases
- carboxypeptidases
- endopeptidases
can only free amino acids be transported into enterocytes?
nope, di- tri- can be transported and broken by enterocyte small peptidases
one universal amino acid transporter?
nope, at least 7 that we know of
what do you need to co-transport for Amino acids into enterocytes
Na+
Cl-
what happens to AAs and sugars once in the cells?
into interstitium>circulation>portal vein>liver
where does fat digestion start? with what? is it effective?
mouth
lingual lipase
just for taste
gastric lipase big role in digestion? what’s it for?
not really
probably triggers CCK from duodenum
how is lipase activated? where?
duodenum via colipase
how is colipase activated?
via trypsin via CCK
how is cholesterol esterase activated?
by bile
what does emulsify mean?
make into very small droplets (micelles) for better mixing
just add bile and lecithin to your chyme and you’re good right?
need VIGOROUS MIXING!
fats absorbed where on villi? how?
tips of villi
micelles allow the lipids to dissolve through membrane
what happens to fat after it enters the cell?
reformed into triglycerides in smooth ER
how are triglycerides packaged in enterocytes?
coated with apo-lipoproteins and form chylomicrons
how are chylomicrons transported?
lymphatics
do all fats go into lymphatics?
shorter 10-12 carbon fatty acids diffuse to venules directly
how are short chain fatty acids made in the proximal colon? how?
fermentation of fibre by our microbiota
where are the short chain fatty acids made in the proximal colon absorbed?
distal small bowel
proximal part of colon
