B5-096 GI Physiology III Flashcards
(94 cards)
1
Q
what phase of digestion has a large secretion of insulin?
A
cephalic phase
2
Q
where are carbohydrates and lipids absorbed?
A
duodenum > jejunum > ileum
3
Q
where is iron absorbed?
A
duodenum
4
Q
where is folate absorbed?
A
duodenum
5
Q
where is calcium absorbed?
A
primarily duodenum but jejunum and ileum as well
6
Q
where are bile acids absorbed?
A
iluem > jejunum, colon > duodenum
7
Q
where is cobalamin absorbed?
A
ileum
8
Q
breaks down carbohydrates at the a 1-4 linkages
A
a-amylase
9
Q
can a-amlyase split a1-6 linkages?
A
no
10
Q
continued breakdown of carbohydrates after a-amylase is carried out by enzymes at the
A
brush border
11
Q
coupled transporter that brings Na+ and glucose into cell
A
SGLT-1
12
Q
mediates facilitated diffusion of fructose into cell
A
GLUT5
13
Q
mediates monosaccharide efflux into interstial space
A
GLUT2
14
Q
lactase splits […]
both monomers are transported via […]
A
lactose
SGLT-1
15
Q
- two enzymes
- sucrase moiety splits sucrose/maltose
- isolmaltase activity splits a-limit dextrins/maltose
A
sucrase-isomaltase
16
Q
removes glucose monomers for transport
A
glucoamylase
17
Q
what do brush border peptidases do?
A
progressively hydrolyze oligopeptides to amino acids
18
Q
H/oligopeptide cotransporter
A
PepT1
there is also a Na/AA cotransporter
19
Q
the enterocyte can directly absorbs some oligopeptides through […]
these are then disgested to amino acids by […] within the cytoplasm
transporter/ enzyme
A
PEPT1
peptidases
there is also a Na/AA cotransporter
20
Q
enterocytes take up 90% of protein resulting in […]
A
complete lysosomal degradation
21
Q
M cells take up 10% of protein but half […]
A
emerges from the membrane intact
22
Q
package proteins and present them to APCs in interstitium
A
M cells
23
Q
endopeptidases
3
A
- trypsin
- chymotrypsin
- elastase
24
Q
exopeptidases
2
A
carboxypeptidases A and B
25
result in oligopeptides (2-6 AA)
| endo or exopeptidases
endopeptidases
26
result in single amino acids
| endo or exo peptidases
exopeptidase
27
produce peptide with C terminal basic AA
trypsin
28
produce peptide with C terminal neutral AA
| 2
chymotrypsin
elastase
29
what is the advantage of oligopeptide absorption?
| think about PepT1
PepT1 moves several AA per turnover = faster absorption
30
act within the AA chain
| endo or exo peptidases
endopeptidase
31
act on either end of the AA chain
| endo or exopeptidases
exopeptidases
32
hydrolyze TAGs at surface
| TAGs from core replace them, causing droplet to shrink
pancreatic lipase
33
describe the breakdown of emulsion droplets to mixed micelles
1. emulsion droplet: pancreatic lipase breaks down TAGs to shrink core
1. multilamellar liquid-crystalline: bile salts cause small pieces to bud off into multilamellar vesicle
1. unilamellar vesicle- formed by addition of more bile salts to multilamellar vesicle
1. mixed micelle: even more bile salts
34
how to lipids enter enterocytes?
| 3 ways
mixed micelle crossed into acidic microenviornment to release lipids:
* non ionic diffusion
* incorporation into enterocyte membrane
* carrier-mediated transport
35
why do the lipids release when the mixed micelle crosses into the acidic microenvironment?
protanation of FFA is favored in the acidic environment
36
FAT/CD36 does what?
carrier mediated transport of lipids into enterocytes
37
enterocytes can reform esters to make
apoliproteins and chylomicrons
38
describe the re-esterfication of lipids into chylomicrons and VLDLs
1. LCFA are coverted back to lipids in SER
2. fat droplets form in cisternae of SER
3. apoliproteins are synthesized in the RER and move to SER to associate with droplets (except Apoli A-1)
4. chylomicrons and VLDLs arrive at cis face of Golgi to be glycosylated
5. vesicles carrying VLDLs bud off trans-Golgi and move to membrane
6. vesicle fuse to membrane to be released
7. chylomicrons and VLDLs enter lymph
8. enter circulation
| Apoli A-1 associated with chylomicrons in Golgi
39
fatty acids most readily available to us after eating
short and medium chain
40
produce VLDLs and chylomicrons
enterocytes
41
after being synthesized in the RER, apoliprotein A moves to
Golgi to associate with chylomicrons
42
3 parts of folate
pteridine moiety (biologically active)
p-aminobenzoate
glutamate
| dietary folate just has more gluatmates
43
for folate breakdown, brush border peptidases remove
all but one glutamate
| **becomes PteGlu1**
44
brings PteGlu1 into enterocyte
| broken down folate
folate-OH exchanger
45
critical to serve as methyl donor for DNA synthesis or methionine synthesis
folate
| THF is methylated
46
describe the absorption of cobalamin
1. cobalamin bound to nutrients in food
2. gastric acid/pepsin release cobalamin from dietary protein
3. gastric glands secreted haptocorrin which binds to cobalamin
4. gastric parietal cells secrete intrinsic factor
5. pancreas secretes proteases and HCO3-
6. cobalamin is released after degradation of haptocorrin (duodenum)
7. IF-CBL complex forms
8. ileal enterocyte absorbs IF-CBL complex
47
[...] binds cobalamin in somach
haptocorrin
48
binds cobalamin in duodenum
intrinsic factor
49
the IF-CBL complex is absorbed in the
ileus
50
to efflux cobalamin out of enterocyte into interstitial space, it must bind to
trans-cobalamin II
51
describe active Ca++ absorption
1. Ca++ enters via channel
2. binds cytoplasmic calbindin or goes into intracellular organelles
3. effluxed into interstitial space via Na/Ca exhanger
52
where does active Ca++ uptake occur
duodenum
53
predominant paracellular absorption of Ca++ throughout small intestine
passive
54
active form of vitamin D drives the production of
calbindin
55
describe the absoprtion of non-heme iron
1. Dcytb reduces non-heme iron Fe3+ to Fe2+
2. DMT cotransports Fe2+ with H+
3. Fe2+ transfers to mobilferrin
4. Fe2+ leaves cell via ferroportin and hephaestin oxidizes it to Fe3+
5. iron binds to transferrin in plasma
56
heme iron absorbs at [..] the rate of nonheme iron
10x
57
why does hephaestin oxidize Fe2+ to Fe3+ ?
* keeps it in interstitial space
* allows to bind to transferrin
58
describe the absoprtion of heme iron in the duodenum
1. Heme Fe2+ enters cell (unknown mechanism)
2. Fe2+ transfers to mobilferrin
3. Fe2+ leaves cell via ferroportin and hephaestin oxidizes it to Fe3+
4. iron binds to transferrin in plasma
59
short chain and medium chain lipids directly enter
systemic circulation
60
which zone of the liver has highest oxygen tension?
zone 1
61
what zone of the liver do beta oxidation and gluconeogenesis occur in?
zone 1
| high oxygen demand, greatest area of oxygen
62
what zone of the liver do lipogenesis, ketogenesis, tryglyceride synthesis and glycolysis occur in?
zone 3
63
describe the synthesis of bile acid through CYP7A1
cholic acid -> deoxycolic acid -> glycine
64
cholic acid, deoxycholic acid, and glycine are products of which CYP route?
| bile acid synthesis
CYP7A1
65
describe bile synthesis through the CYP27A1 route
chenodeoxycholic acid -> lithocolic acid -> taurine
66
chenodeoxycholic acid, lithocolic acid, and taurine are products of which CYP route?
| bile acid synthesis
CYP27A1
67
* bile duct epithelial cells
* protect hepatocytes by transporting bile
cholangiocytes
68
what conjugates bile salts to bile acids?
bacteria
69
how much bile acids are reabsorbed?
90-95%
70
feedback to liver to prevent production of primary bile acids
| 2
FGF19
recycled bile acids
71
the production of amino acids produces [...] which has to be gotten rid of
ammonia
72
85% of the circulating [...] is taken up by the liver and processed to urea
ammonia
73
urea is excreted through to kidneys or [...] into the colon
recycled
74
deamination of hepatic amino acids results in
| 2
glutamate and keto acid
| amino group is transferred to alpha-ketoglutarate
75
the NH4+ that results from the regeneration of alpha-ketoglutarate is consumed in the
urea cycle
76
ApoB-48
chylomicrons
| exogenous lipids to liver
77
B100
VLDL
78
rate limiting step of cholesterol synthesis
HMG CoA reductase
79
why is cholesterol synthesis tightly regulated?
very energy expensive
80
only two ways to get rid of cholesterol
* secreted in bile acids
* secreted directly into bile duct -> feces
81
what can the liver do with cholesterol?
| 3
* excrete in bile
* excrete in feces
* package to VLDLs
82
moves peptides into intestinal epithelial cells together with a proton supplied by Na/K/H+ exchanger
PEPT1
83
receptors for B12 are in the [...]
terminal ileum
84
intrinsic factor is made by
parietal cells
85
moves vitamin B12 into blood
transcobalamin II
86
individuals who avoid meat/dairy intake have low levels of what vitamin?
B12
87
non-heme iron transporter
DMT1
88
functions to remove iron from heme
heme oxygenase
89
transports iron out of enterocyte
ferroportin
90
Roux-en-Y causes thaimine deficiency via
diversion of chyme from duodenum to jejunum
91
can cause thiamine deficiency
| 3
* Roux-en-Y
* excessive alcohol consumption
* excessive vomiting (especially in pregnancy)
92
cause a reduction in the sequential breakdown of emulsion droplets
bile acid sequestrants
93
increase bile acid synthesis in liver and do not decrease bile production
| drug class
bile acid sequestrants
94
a decrease in vitamin D results in a decrease of
calbindin
