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unit 6: physiology > intestinal transport (4) > Flashcards

intestinal transport (4) Flashcards

1
Q

what is the longest part of the small intestine?

A

the ileum (12 feet)

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2
Q

how many feet is the small intestine?

A

21 ft

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3
Q

what part of the SI is the smallest?

A

the duodenum- 1 foot

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4
Q

compare the surface area of the jejunum to the ileum

A

the jejunum has 3x more SA then ileum

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5
Q

how is SA increased in the GI tract

A

achieved by successive foldings of the surface

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6
Q

what are the 3 levels of amplification in the SA of the small intestine?

A
  1. the macroscopif fods of kerckring
  2. microscopic villi and crypts of lieberkuhn
  3. submicroscopic microvilli
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7
Q

what are the 3 levels of amplification in the SA of the colon?

A
  1. macroscopic semilunar folds
  2. crypts (but not villi)
  3. microvilli
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8
Q

in the SI, how much does the SA increase due to the mucosal folds?

A

5x

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9
Q

in the SI, how much does the SA increase due to the villi?

A

10x

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10
Q

in the SI, how much does the SA increase due to the microvilli?

A

20x

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11
Q

what is the total absorptive surface area of the SI?

A

700 sq meters (1000x than if it didn’t have any of the increases in SA due to its foldings etc)

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12
Q

whats another name for celiac disease?

A

non-tropical sprue or sprue

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13
Q

what does gluten do to ppl with celiacs?

A

destroys the absorptive cells and decreases the number of functional villi

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14
Q

what is tropical sprue?

A

an infectious disease present in certain areas of tropical countries associated with diarrhea, malabsorption and nutritional deficiencies

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15
Q

describe celiac disease

A

decrease in absorptive SA primarily due to reduction in the number & size of microvilli due to gluten consumption. the unabsorbed food leads to diarrhea, malnutrition and dehydration

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16
Q

after how many days are the cells of the villi extruded?

A

3-8 days after they reach the villi tip

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17
Q

about how much weight of cells are shed from the villi each day?

A

250 grams

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18
Q

how many days does it take for a given cell to mature and reach the tip of the villus from the crypt?

A

5 days

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19
Q

how often are all the cells of teh intestinal mucosa replaced?

A

after 1 wk- every week you get a new intestinal epithelium

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20
Q

what types of things could affect the rate of villi cell renewal?

A

the rate is reduced as a result of radiation, malnutrition or sprue

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21
Q

what triggers goblet cells to secrete mucous?

A

in response to acetylcholine released from parasymp cholinergic nerve fibers

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22
Q

what do undifferentiated cells of the crypt secrete?

A

NaCl from the blood into the lumen

you should know this from MCP!

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23
Q

once the crypt cells migrate up the villus and take on an absorptive function, what do they absorb?

A

NaHCO3 or NaCl

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24
Q

what type of symptoms can be seen in victims of radiation poisoning?

A

intestinal bleeding
diarrhea
slow death from malabsorption & dehydration

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25
Q

what are teh two parallel pathways in which intestinal absorptive cells transfer materials?

A
  1. transcellular pathway

2. shunt pathway (aka paracellular pathway)

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26
Q

describe the path of the transcelluar pathway

A

from the lumen, across the brush border, then through the cytoplasm and then across the basolateral membrane

27
Q

describe the pathway of the shunt pathway

A

through the tight junction and through the extracellular space

28
Q

what is contained within the basement membrane (lamina propria) contain?

A

capillaries and lacteals

29
Q

describe the permeability of the tight junctions

A

quite permeable to H2O and cations (Na & K) but have low permeability to anions
tight junctions are a low resistance (high conductance) pathway

30
Q

where is most of the total fluid in the body absorbed?

A

in the jejunum (it does more than half)

31
Q

about how much fluid does colonic absorption account for?

A

about 5 L/day

32
Q

where are most nutrients absobed?

A

in the duodenum and the upper jejunum

33
Q

what are the two exceptions that don’t get absorbed in the duodenum/upper jejunum? where are they absorbed?

A

B 12 and ionized bile salts get absorbed in the distal ileum

34
Q

what disorder is caused by a B12 deficiency?

A

pernicious anemia- type of macrolytic anemia

35
Q

what does the jejunal enterocyte absorb?

A

Na+ and HCO3- as well as glucose and amino acids

36
Q

what organ secretes NaHCO3? what is its function?

A

the pancreas

serves to neutralize acid from the stomach

37
Q

what are the two mechanisms by which Na+ enters the jejunal enteroctye across teh apical membrane?

A
  1. by Na/glucose and by Na/amino acid cotransport

2. by Na/H antiport

38
Q

what is the importance of the Na+/H+ antiport?

A

it serves to keep the internal pH of the enterocyte near neutral away from electrochemical equilibrium

39
Q

how is Na+ entry into the jejunal absorptive cell balanced?

A

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

40
Q

describe the membrane potential of the serosal side of the jejunal absorptive cell

A

it is +5mV at rest and rises to +15 mV during absorption after a meal due to the electrogenicity of the Na+/K+ pump

41
Q

where does the majority of Na+ absorption through the Na/glucose and Na/amino acid cotransport pathway take place?

A

in the jejunum and less so in the ileum

42
Q

how does Na+ and Cl- enter the ileal absorptive cell?

A

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

43
Q

what is the effect of cAMP on NaCl?

A

it inhibits NaCl absorption in the ileum

44
Q

what is the result of vipoma tumors on NaCl absorption?

A

these tumors cause excessive VIP secretion, which results in greatly decrease NaCl absorption which leads to increased osmolarity in the lumen and osmotic diarrhea

45
Q

what are the effects of E. coli and vibriocholera toxins?

A

they stimulate cAMP production–> which leads to increased secretion of NaCl (and also KCl) causing diarrhea which is massive (a boat load)

46
Q

what type of cells sercrete NaCl into the lumen?

A

crypt cells/immature enterocytes

47
Q

how does Na+, K+ and Cl- enter the crypt cell?

A

via a Na/K/2Cl cotransporter in the basolateral membrane

48
Q

what is the effect of cAMP on the CFTR channel

A

it increases its conductance

49
Q

list the endogenous secretory stimuli (8)

A 
ACh
histamine
CCK
secretin
gastrin
GIP
motilin
VIP
50
Q

list the exogenous secretory stimuli (5)

A 
vibrio cholerae
e coli
salmonella
bile salts & fatty acids
laxatives
51
Q

list the endogenous absorptive stimuli (5)

A 
epi/norepi
dopamine
ENKs
somatostatin
mineralocorticoids
52
Q

list the exogenous absorptive stimuli (1)

A

nutrients (glucose, AA, peptides)

53
Q

how many mgs of Fe++ are needed daily?

A

1 mg

54
Q

when will the number of brush border trasporters for iron increase?

A

if the body Fe++ is low

55
Q

what will occur if the body’s Fe++ is high?

A

the number of brush border transporteres decreases but ferritin amount stays the same

56
Q

what are the two pathways by which iron is absorbed?

A
  1. heme iron- more efficient

2. nonheme iron

57
Q

what form does plasma transferrin carry?

A

Fe+++

58
Q

how is non heme Fe++ absorbed?

A

via cotransport with a proton

59
Q

what in the stomach can reduce Fe+++ to Fe++?

A

ascorbic and citric acids

60
Q

what is calbindin?

A

a calcium binding protein which is supposedly the membrane carrier for Ca++ across the brush border membrane
soluble intracellular calbinden binds & buffers Ca++ within the cell

61
Q

what are the two mechanisms by which the SI absorbs calcium?

A
  1. the passive paracellular absorption of Ca - this pathway is NOT under vit D control
  2. the active thranscellular absorption of Ca only through duodenum
62
Q

what is the effect of sunlight on the skin?

A

7 dehydrocholesterol in the skin forms Vit D3 (cholecalciferol)

63
Q

what happens to vit D3 in the liver?

A

it is hydroxylated to 25(OH)D3

64
Q

what reaction does PTH sitmulate?

A

hydroxylation of vit D3 to 25(OH)D3 in the kidney

unit 6: physiology (13 decks)

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