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Physiology > Intestine I U6L04 > Flashcards

Intestine I U6L04 Flashcards

1
Q

how long is the duodenum?

A

first 11 inches

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2
Q

what seperates the duodenum from the jejunum?

A

ligament of Treitz.

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3
Q

The jejunum is ____ feet long, and is defined as the proximal 2/5 of the small intestine.

A

8

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4
Q

The ileum is ___ feet long, and is defined as the distal 3/5 of the small intestine

A

12

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5
Q

surface area of jejnum compared to ileium?

A

jejunum has 3x more surface area than the ileum

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6
Q

greater absoprtion occurs in the jejunum or ileum?>

A

jejjunum

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7
Q

how is increased surface area achieved in the GI system?

A

successive folding of the surface

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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.

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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

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10
Q

average length of the small intestine is

A

21 FEET

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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

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12
Q

total absorptive surface area of the small intestine is 700 square memters or x ___ in size

A

x 1000

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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

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14
Q

celiac disease is associated with a ____ in absorptive surface area

A

celiac disease is associated with a decrease in absorptive surface area

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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

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16
Q

Sprue is a type of malabsorption syndrome caused by sensitivity to___

A

gluten

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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

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18
Q

what is Tropical sprue?

A

infectious disease associated with diarrhea, malapsprtion, and nutritional deficiencies

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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

  1. then migrate toward the tip, where they are extruded 3-8 days later.
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20
Q

how long are the cells of the intestinal mucosa replaced?

A

every week

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21
Q

goblet cells secrete protective mucous when stimulated by

A

acetylcholine

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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

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23
Q

what reduce the rate of cell renewal in the intestinal epithelium? (3)

A

radiation, malnutrition, or sprue.

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24
Q

The villi are comprised of absorptive cells called ____,

these are columnar epithelial cells in a single layer.

A

enterocytes

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25
Q

___ secretes the mucuous the lubricates the small intestine during peristalsis

A

goblet cells

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26
Q

what is common about goblet cells and enterocytes?

A

they have a common stem cell in the base of the crypts

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27
Q

The undifferentiated cells of the crypt secrete what? What does this cause

A

secretes NaCl from the blood into the lumen, and water follows osmotically

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28
Q

when do crypt cells stop secreting NaCL? what do they do after

A

stop secreting when they migrate upwards

get an absorptive function, absorbing with NaHCO3 or NaCl

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29
Q

radiation victims can experience what GI sx?

A

intestinal bleeding

diarrhea

slow death from malapsroption and dehydration

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30
Q

why are cells of the intestinal mucosa particularly vulnerable to radiation damage?

A

there is a high turnover of these cells

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31
Q

Intestinal absorptive cell. Transfer of materials occurs via two parallel pathways:

A
  1. transcelular pathway
  2. paracellular pathway
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32
Q

transcellular pathway

A

across the brush border, then through the cytoplasm, and finally across the basolateral membrane;

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33
Q

the shunt pathway (also called the paracellular pathway)?

A

viz. through the tight junction and the extracellular space.

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34
Q

tight junctions have high permeability for what?

low permeability for what?

A

high affinity – H20 and cations (like Na and K)

low permeability – anions

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35
Q

what is the major mamebrane for absorption of nutrients?

A

the brush border

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36
Q

The ___ membrane contains ectoenzymes

A

apical (brush border)

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37
Q

what are ectoenzymes?

A

ectoenzymes (enterokinase, disaccharidases, and peptidases) complete the digestive process.

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38
Q

what does the basement membrane (lamina propria) contain?

A

capillaries and lacteals

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39
Q

how is the tight junction in a intestinal cell?

A

wraps around the cell like a collar

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40
Q

from leaky to most tight…

ilium? colon? jejunum?

A

jejenum (most leaky) –> ileum –> colon (most tight)

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41
Q

When you drink a glass of water, the liquid is rapidly absorbed in the ___ by osmosis.

A

jejunum

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42
Q

difference between dietrary intake and feacal otuflow equals

A

loss through kidney, lungs, sweat

this maitnains body fluid in a steady state

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43
Q

9.5L of fluid enters the body each day and must be ___

A

absorbed to prevent diarrhea and dehydration

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44
Q

___ absorption is responsible for more than half of the total fluid absorbed.

A

jejunal

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45
Q

what takes over it function if the jejunum is removed surgically?

A

ilum

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46
Q

Water and most nutrient substances are absorbed from the

A

duodenum and upper jejunum, being completely absorbed by the end of the jejunum.

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47
Q

what are two examples of substances not absorbed completely absorbed by the end of the jejunum.

A

vitamin b12 and ionized bile salts

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48
Q

what does vitamin b12 require to be absorbed?

A

combined with intrinsic factor

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49
Q

ionized bile salts undergo

A

enterohpetic circulation

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50
Q

where are ionized bile salts and vitamin b12 absorbd

A

in the distal ileum

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51
Q

how does the ileium take up ionized bile salts?

A

sodium dependent cotransport.

52
Q

implications of removing the distal ileum?

A

other parts of the gastrointestinal tract cannot adapt to absorb ionized bile salts and Vitamin B12

53
Q

Vitamin B12 deficiency causes pernicious anemia which is a type of anemia that is characterized by

A

unsuually large rbc

54
Q

what is intrinsic factor secreted by

A

parietal cells

55
Q

what does the jejunal enterocyte absorb?

A

Na+ and HCO3-, along with glucose and amino acids.

56
Q

The jejunal absorptive cell shown above avidly absorbs ___ to maintain fluid balance and thereby prevents diarrhea

A

NaHCO3

57
Q

Na+ enters the jejunal enterocyte across the apical membrane by two mechanisms:

A

(1) by Na+/glucose and by Na+/amino acid cotransport,
(2) by Na+/H+ antiport,

58
Q

____ is a an important mechanism for

absorption of Na+, glucose and amino acids in the jejunum

A

Na+/glucose and by Na+/amino acid cotransport

59
Q

Na+/H+ antiport, a mechanism that serves to keep the internal pH of the
enterocyte near ___

A

neutral

60
Q

Na entry into the jejunal absorptive cell is balanced by

A

active efflux of Na+ across the basolateral membrane mediated by the Na+/K+ pump

61
Q

The membrane potential is +5 mV at rest on the serosal side and rises to about ___ mV during absorption

A

+15

62
Q

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

A

Na+/K+ pump.

63
Q

Nutrient-coupled Na+ absorption occurs in the villous cells of the___ and ___

A

jejunum and ileum

64
Q

Na+ absorptive flux through nurtuent coupled Na tranports occurs more in jejnum or ileum>

A

jejunum

65
Q

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

A

high pH

occurs mostly in duodenum and jejnum

66
Q

Na-H and Cl-HCO3 exchange is coupled by a change in intracellular pH that results in electroneutral ___ absorption

A

NaCl

67
Q

what is the primary mechanism for interdigestive Na+ absorption?

A

Na-H and Cl-HCO3 exchange is coupled by a change in intracellular pH

68
Q

In electrogenic Na+ absorption, the apical step of Na+ movement occurs through the

A

epithelial na channel carbonic anhydrase

69
Q

electrogenic an absoprion occurs msotly in the

A

distal colon

70
Q

A lot of Na+ and Cl- is secreted by the liver and the pancreas, and is then reabsorbed by the ___ absorptive cell

A

ileal

71
Q

how do Na and Cl enter the ileal absorptive cell?

A

Na+/H+ antiport in parallel with Cl-/HCO3- exchange.

72
Q

transport of Cl in the ileum?

A

A Cl- channel in the basolateral membrane allows Cl- to pass down its electrical gradient into the serosal fluid and into the blood.

73
Q

___ inhibits NaCl absorption by the ileum.

A

Cyclic AMP

74
Q

how does acetylcholine decrease NaCL absorption

A

ACh stimulates cAMP production, thereby decreasing NaCl absorption

75
Q

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

A

VIP

76
Q

how does VIP from a VIPOMA TUMOR cause diarrhea?

A

decreased NaCL absorption –> increased osmolarity –> osomatic diarrhea

77
Q

how do ecoli and briocholera cause diarrhea?

A

increase CAMP –> decreased NACL absorption –> increase osmolaterity –> diarrhea

78
Q

where are crypt cells located?

A

jejunum, ileum, and colon

79
Q

Na+, K+, and Cl- enter the crypt cell via a____ cotransporter in the basolateral membrane. T

A

Na+/K+/2Cl-

80
Q

where is the Na+/K+/2Cl- cotrnaporter found? where is it lost?

A

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
Q

Na+/K+/2Cl- cotranspoirter is sensitive to (3)

A

furosemide, bumetanide, and other loop diuretics

82
Q

what can enter crypt cell by electrodiffusion (going down electrical gradient?)

A

K

Na can leave

83
Q

In the crypt cell, increased cAMP increases the conductance of the

A

CFTR channel to Cl-.

84
Q

inc camp –> ionc conductance of CFTR channel –> CL is the

A

driven out by negative electro gradient

85
Q

ACh increases intracellular Ca via ___

A

ITP

86
Q

ACh increases intracellular Ca via ITP, causing increased ___ and then ___

A

conductance to K+ —> increase driving Cl out of the cell

87
Q

effects of vibriocholea on the ileum and the jejunum

A

ileum: inhbiits NaCL absorption
jejunum: increases secretion of NaCL by crypt cells

88
Q

Cholera toxin activates ___ –> increasing CAMP

A

adenylyl cyclase

89
Q

oral rehdyrationt herapy for cholera includes?

A

miuxture of saline and glucose

90
Q

Substances that promote secretion tend to inhibit ___

A

absorption

91
Q

exogenous secretory stimuli

A
92
Q

exogenous substances that stimulate absorption

A

nutrients (glucose, amino acids, peptides)

93
Q

endogenous sunstances that increase absorption

A
  1. a-adrenergic agonists
  2. dopamine
  3. enkepahlins (endogenous opoids)
  4. soamtostatin
  5. mineralcorticoids (adolesterone)
94
Q

When body stores of Fe are low, the number of ___ increases

A

brush border transporters

95
Q

increase in thenumber of brush border transporters increases

A

absorption of iron

96
Q

Fe+++ cannot be

A

absorbed

97
Q

only __ percent of ingested iron is absorbed

A

5 percent

98
Q

most ferrtin bound fe is lost when cell exfoliates, a small amount is needed is released to

A

transferrin and absorbed

99
Q

Most of the ingested Fe is in the __ form

A

Fe+++

100
Q

Fe++ may be transported across the basolateral membrane or be stored in the ___ as ferritin.

A

absorptive enterocyte

101
Q

Fe++ is only absorbed when?

A

as needed (like with menstration)

102
Q

The most efficient pathway is iron absorbed as __

A

heme

103
Q

The most efficient pathway is iron absorbed as heme.

This iron is then freed within the cell by___ and bound to intracellular mobilferrin.

A

heme oxygenase

104
Q

Fe++ forms insoluble complexes with food, but is more soluble at __ pH.

A

acid

105
Q

Fe++ is thus released from food by

A

gastric acid. since fe++ is more easily absorbedat acidic ph

106
Q

Fe++ spontaneously oxidizes to Fe+++, but___ and ___in the stomach help reduce Fe+++ to Fe++.

A

ascorbate and citrate

107
Q

Transferrins are iron-binding proteins with a stoichiometry of__ Fe+++/TF

A

2

108
Q

The absorption of nonheme iron occurs almost exclusively as ___

A

Fe2+

109
Q

nonheme iron absorption occurs almost exclusively as Fe2+, which crosses the duodenal apical membrane through DMT1, driven by a___ gradient

A

H+

this graident is maintained by the Na-H exchange

110
Q

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.

A

mobilferrin

111
Q

nonheme Fe is absorbed via

A

contransport with a protn

112
Q

Fe forms ___ complexes with food

A

insolubable

113
Q

The overall transport of calcium in the jejunum is ___ its electrochemical gradient.

A

against

114
Q

The passive, paracellular absorption of Ca2+ occurs throughout the ____

A

small intestine

115
Q

The passive, paracellular absorption of Ca2+ is ___ the control of vitamin d

A

not under

116
Q

the active, transcellular absorption of Ca2+-occurs only in the____

A

duodenum

117
Q

calbindin is the membrane carrier for Ca across the

A

brush border membrane

118
Q

what buffers itnracellular Ca in the duodenum?

A

intracellualr calbinden

mitocondrial stores

119
Q

7-dehydrocholesterol in the skin forms

A

Vitamin D3

120
Q

In the ____ Vitamin D3 is hydroxylated to 25(OH)D3

A

liver

121
Q

25(OH)D3 is hydroxylated in the ___ to form the active form 1,25-Dihydroxycholecalciferol

A

kidney

122
Q

parathyroid ghormone stimulates

A

25(OH)D3 —> 1,25-Dihydroxycholecalciferol

123
Q

increase in calcium ___ parathyroid homrone

A

decreases

124
Q

increase ca plasma leads to a ___ in ca absorption

A

decrease

125
Q

increas ein plasma ca leads to a decrease in

A

dec parathryoid hormone

dec formation of active vitamin D2

dec in sthesis of calcium binding proteins

126
Q
A

Physiology (5 decks)

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