Intestine I U6L04 Flashcards
(126 cards)
1
Q
how long is the duodenum?
A
first 11 inches
2
Q
what seperates the duodenum from the jejunum?
A
ligament of Treitz.
3
Q
The jejunum is ____ feet long, and is defined as the proximal 2/5 of the small intestine.
A
8
4
Q
The ileum is ___ feet long, and is defined as the distal 3/5 of the small intestine
A
12
5
Q
surface area of jejnum compared to ileium?
A
jejunum has 3x more surface area than the ileum
6
Q
greater absoprtion occurs in the jejunum or ileum?>
A
jejjunum
7
Q
how is increased surface area achieved in the GI system?
A
successive folding of the surface
8
Q
The surface area of the small intestine is amplified at three levels:
A
(1) macroscopic folds of Kerckring
(2) microscopic villi and crypts of Lieberkuhn
(3) submicroscopic microvilli.
9
Q
The surface area of the large intestine is amplified at three levels:
A
(1) macroscopic semilunar folds
(2) crypts (but not villi)
(3) microvilli
10
Q
average length of the small intestine is
A
21 FEET
11
Q
average increase due to mucusal folds?
average increase due to villi?
average increase due to microvilli?
A
mucosal folds – x 5
villi – x 10
microvilli – x 120
12
Q
total absorptive surface area of the small intestine is 700 square memters or x ___ in size
A
x 1000
13
Q
about ___ of the absorptive surface area is required for absorption.
what is the clinical implication for this?
A
half the absorptive surface area
half of the absorptive surface area can be surgically removed without compromising absorptive function
14
Q
celiac disease is associated with a ____ in absorptive surface area
A
celiac disease is associated with a decrease in absorptive surface area
15
Q
celiac disease is associated with a decrease in absorptive surface area due to a reduction in the
A
number and size of microvilli
16
Q
Sprue is a type of malabsorption syndrome caused by sensitivity to___
A
gluten
17
Q
Effect of gluten on small intestine? (2)
A
Gluten in bread by some means destroys absorptive cells and decreases the number of villi
18
Q
what is Tropical sprue?
A
infectious disease associated with diarrhea, malapsprtion, and nutritional deficiencies
19
Q
where are cells generated in the small intestine? where do they go?
A
. 1. Cells are constantly being generated at the base of the villi
- then migrate toward the tip, where they are extruded 3-8 days later.
20
Q
how long are the cells of the intestinal mucosa replaced?
A
every week
21
Q
goblet cells secrete protective mucous when stimulated by
A
acetylcholine
22
Q
what happens to old extruded cells of the intestinal epithelium
A
extruded cells are digested in the gut, and their useful contents are recycled
23
Q
what reduce the rate of cell renewal in the intestinal epithelium? (3)
A
radiation, malnutrition, or sprue.
24
Q
The villi are comprised of absorptive cells called ____,
these are columnar epithelial cells in a single layer.
A
enterocytes
25
\_\_\_ secretes the mucuous the lubricates the small intestine during peristalsis
goblet cells
26
what is common about goblet cells and enterocytes?
they have a common stem cell in the base of the crypts
27
The undifferentiated cells of the crypt secrete what? What does this cause
secretes NaCl from the blood into the lumen, and water follows osmotically
28
when do crypt cells stop secreting NaCL? what do they do after
stop secreting when they migrate upwards
get an absorptive function, absorbing with NaHCO3 or NaCl
29
radiation victims can experience what GI sx?
intestinal bleeding
diarrhea
slow death from malapsroption and dehydration
30
why are cells of the intestinal mucosa particularly vulnerable to radiation damage?
there is a high turnover of these cells
31
Intestinal absorptive cell. Transfer of materials occurs via two parallel pathways:
1. transcelular pathway
2. paracellular pathway
32
transcellular pathway
across the **brush border**, then through the cytoplasm, and finally across the **basolateral membrane**;
33
the shunt pathway (also called the paracellular pathway)?
viz. through the tight junction and the extracellular space.
34
tight junctions have high permeability for what?
low permeability for what?
high affinity -- H20 and cations (like Na and K)
low permeability -- anions
35
what is the major mamebrane for absorption of nutrients?
the brush border
36
The ___ membrane contains ectoenzymes
apical (brush border)
37
what are ectoenzymes?
ectoenzymes (enterokinase, disaccharidases, and peptidases) complete the digestive process.
38
what does the basement membrane (lamina propria) contain?
capillaries and lacteals
39
how is the tight junction in a intestinal cell?
wraps around the cell like a collar
40
from leaky to most tight...
ilium? colon? jejunum?
jejenum (most leaky) --\> ileum --\> colon (most tight)
41
When you drink a glass of water, the liquid is rapidly absorbed in the ___ by osmosis.
jejunum
42
difference between dietrary intake and feacal otuflow equals
loss through kidney, lungs, sweat
this maitnains body fluid in a steady state
43
9.5L of fluid enters the body each day and must be \_\_\_
absorbed to prevent diarrhea and dehydration
44
\_\_\_ absorption is responsible for more than half of the total fluid absorbed.
jejunal
45
what takes over it function if the jejunum is removed surgically?
ilum
46
Water and most nutrient substances are absorbed from the
duodenum and upper jejunum, being completely absorbed by the end of the jejunum.
47
what are two examples of substances not absorbed completely absorbed by the end of the jejunum.
vitamin b12 and ionized bile salts
48
what does vitamin b12 require to be absorbed?
combined with intrinsic factor
49
ionized bile salts undergo
enterohpetic circulation
50
where are ionized bile salts and vitamin b12 absorbd
in the distal ileum
51
how does the ileium take up ionized bile salts?
sodium dependent cotransport.
52
implications of removing the distal ileum?
other parts of the gastrointestinal tract cannot adapt to absorb ionized bile salts and Vitamin B12
53
Vitamin B12 deficiency causes pernicious anemia which is a type of anemia that is characterized by
unsuually large rbc
54
what is intrinsic factor secreted by
parietal cells
55
what does the jejunal enterocyte absorb?
Na+ and HCO3-, along with glucose and amino acids.
56
The jejunal absorptive cell shown above avidly absorbs ___ to maintain fluid balance and thereby prevents diarrhea
NaHCO3
57
Na+ enters the jejunal enterocyte across the apical membrane by two mechanisms:
(1) by Na+/glucose and by Na+/amino acid cotransport,
(2) by Na+/H+ antiport,
58
\_\_\_\_ is a an important mechanism for
## Footnote
absorption of Na+, glucose and amino acids in the jejunum
Na+/glucose and by Na+/amino acid cotransport
59
Na+/H+ antiport, a mechanism that serves to keep the internal pH of the
enterocyte near \_\_\_
neutral
60
Na entry into the jejunal absorptive cell is balanced by
active efflux of Na+ across the basolateral membrane mediated by the Na+/K+ pump
61
The membrane potential is +5 mV at rest on the serosal side and rises to about ___ mV during absorption
+15
62
The membrane potential is +5 mV at rest on the serosal side and rises to about +15 mV during absorption after a meal due to the electrogenicity of the
Na+/K+ pump.
63
**Nutrient-coupled Na+ absorption** occurs in the villous cells of the\_\_\_ and \_\_\_
jejunum and ileum
64
Na+ absorptive flux through nurtuent coupled Na tranports occurs more in jejnum or ileum\>
jejunum
65
Electroneutral Na-H exchange at the apical membrane, in the absence of Cl-HCO3 exchange, is stimulated by the high ____ of the -rich luminal contents
high pH
occurs mostly in duodenum and jejnum
66
Na-H and Cl-HCO3 exchange is coupled by a change in intracellular pH that results in electroneutral ___ absorption
NaCl
67
what is the primary mechanism for interdigestive Na+ absorption?
Na-H and Cl-HCO3 exchange is coupled by a change in intracellular pH
68
In electrogenic Na+ absorption, the apical step of Na+ movement occurs through the
epithelial na channel carbonic anhydrase
69
electrogenic an absoprion occurs msotly in the
distal colon
70
A lot of Na+ and Cl- is secreted by the liver and the pancreas, and is then reabsorbed by the ___ absorptive cell
ileal
71
how do Na and Cl enter the ileal absorptive cell?
Na+/H+ antiport in parallel with Cl-/HCO3- exchange.
72
transport of Cl in the ileum?
A Cl- channel in the basolateral membrane allows Cl- to pass down its electrical gradient into the serosal fluid and into the blood.
73
\_\_\_ inhibits NaCl absorption by the ileum.
Cyclic AMP
74
how does acetylcholine decrease NaCL absorption
ACh stimulates cAMP production, thereby decreasing NaCl absorption
75
is normally of minor importance in stimulating cAMP production in the ileum, but in vipoma tumors, the amount of it is increased ----\> decreased NaCl absorption
VIP
76
how does VIP from a VIPOMA TUMOR cause diarrhea?
decreased NaCL absorption --\> increased osmolarity --\> osomatic diarrhea
77
how do ecoli and briocholera cause diarrhea?
increase CAMP --\> decreased NACL absorption --\> increase osmolaterity --\> diarrhea
78
where are crypt cells located?
jejunum, ileum, and colon
79
Na+, K+, and Cl- enter the crypt cell via a\_\_\_\_ cotransporter in the basolateral membrane. T
Na+/K+/2Cl-
80
where is the Na+/K+/2Cl- cotrnaporter found? where is it lost?
also in the thick ascending limb of the Loop of Henley in the kidney
it is lost during maturation of crypt cells into absorptive cells
81
Na+/K+/2Cl- cotranspoirter is sensitive to (3)
furosemide, bumetanide, and other loop diuretics
82
what can enter crypt cell by electrodiffusion (going down electrical gradient?)
K
Na can leave
83
In the crypt cell, increased cAMP increases the conductance of the
CFTR channel to Cl-.
84
inc camp --\> ionc conductance of CFTR channel --\> CL is the
driven out by negative electro gradient
85
ACh increases intracellular Ca via \_\_\_
ITP
86
ACh increases intracellular Ca via ITP, causing increased ___ and then \_\_\_
conductance to K+ ---\> increase driving Cl out of the cell
87
effects of vibriocholea on the ileum and the jejunum
ileum: inhbiits NaCL absorption
jejunum: increases secretion of NaCL by crypt cells
88
Cholera toxin activates ___ --\> increasing CAMP
adenylyl cyclase
89
oral rehdyrationt herapy for cholera includes?
miuxture of saline and glucose
90
Substances that promote secretion tend to inhibit \_\_\_
absorption
91
exogenous secretory stimuli
92
exogenous substances that stimulate absorption
nutrients (glucose, amino acids, peptides)
93
endogenous sunstances that increase absorption
1. a-adrenergic agonists
2. dopamine
3. enkepahlins (endogenous opoids)
4. soamtostatin
5. mineralcorticoids (adolesterone)
94
When body stores of Fe are low, the number of ___ increases
brush border transporters
95
increase in thenumber of brush border transporters increases
absorption of iron
96
Fe+++ cannot be
absorbed
97
only __ percent of ingested iron is absorbed
5 percent
98
most ferrtin bound fe is lost when cell exfoliates, a small amount is needed is released to
transferrin and absorbed
99
Most of the ingested Fe is in the __ form
Fe+++
100
Fe++ may be transported across the basolateral membrane or be stored in the ___ as ferritin.
absorptive enterocyte
101
Fe++ is only absorbed when?
as needed (like with menstration)
102
The most efficient pathway is iron absorbed as \_\_
heme
103
The most efficient pathway is iron absorbed as heme.
This iron is then freed within the cell by\_\_\_ and bound to intracellular mobilferrin.
heme oxygenase
104
Fe++ forms insoluble complexes with food, but is more soluble at __ pH.
acid
105
Fe++ is thus released from food by
gastric acid. since fe++ is more easily absorbedat acidic ph
106
Fe++ spontaneously oxidizes to Fe+++, but\_\_\_ and \_\_\_in the stomach help reduce Fe+++ to Fe++.
ascorbate and citrate
107
Transferrins are iron-binding proteins with a stoichiometry of\_\_ Fe+++/TF
2
108
The absorption of nonheme iron occurs almost exclusively as \_\_\_
Fe2+
109
nonheme iron absorption occurs almost exclusively as Fe2+, which crosses the duodenal apical membrane through DMT1, driven by a\_\_\_ gradient
H+
this graident is maintained by the Na-H exchange
110
Inside the cell, heme oxygenase releases Fe3+, which is then reduced to Fe2+.
Cytoplasmic Fe2+ then binds to ___ for transit across the cell to the basolateral membrane.
mobilferrin
111
nonheme Fe is absorbed via
contransport with a protn
112
Fe forms ___ complexes with food
insolubable
113
The overall transport of calcium in the jejunum is ___ its electrochemical gradient.
against
114
The passive, paracellular absorption of Ca2+ occurs throughout the \_\_\_\_
small intestine
115
The passive, paracellular absorption of Ca2+ is ___ the control of vitamin d
not under
116
the active, transcellular absorption of Ca2+-occurs only in the\_\_\_\_
duodenum
117
calbindin is the membrane carrier for Ca across the
brush border membrane
118
what buffers itnracellular Ca in the duodenum?
intracellualr calbinden
mitocondrial stores
119
7-dehydrocholesterol in the skin forms
Vitamin D3
120
In the ____ Vitamin D3 is hydroxylated to 25(OH)D3
liver
121
25(OH)D3 is hydroxylated in the ___ to form the active form 1,25-Dihydroxycholecalciferol
kidney
122
parathyroid ghormone stimulates
25(OH)D3 ---\> 1,25-Dihydroxycholecalciferol
123
increase in calcium ___ parathyroid homrone
decreases
124
increase ca plasma leads to a ___ in ca absorption
decrease
125
increas ein plasma ca leads to a decrease in
dec parathryoid hormone
dec formation of active vitamin D2
dec in sthesis of calcium binding proteins
126
