intestinal transport (4)

Question 1

what is the longest part of the small intestine?

Answer 1

the ileum (12 feet)

Question 2

how many feet is the small intestine?

Answer 2

21 ft

Question 3

what part of the SI is the smallest?

Answer 3

the duodenum- 1 foot

Question 4

compare the surface area of the jejunum to the ileum

Answer 4

the jejunum has 3x more SA then ileum

Question 5

how is SA increased in the GI tract

Answer 5

achieved by successive foldings of the surface

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

5x

Question 9

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

Answer 9

10x

Question 10

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

Answer 10

20x

Question 11

what is the total absorptive surface area of the SI?

Answer 11

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

Question 12

whats another name for celiac disease?

Answer 12

non-tropical sprue or sprue

Question 13

what does gluten do to ppl with celiacs?

Answer 13

destroys the absorptive cells and decreases the number of functional villi

Question 14

what is tropical sprue?

Answer 14

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

Question 15

describe celiac disease

Answer 15

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

Question 16

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

Answer 16

3-8 days after they reach the villi tip

Question 17

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

Answer 17

250 grams

Question 18

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

Answer 18

5 days

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

what triggers goblet cells to secrete mucous?

Answer 21

in response to acetylcholine released from parasymp cholinergic nerve fibers

Question 22

what do undifferentiated cells of the crypt secrete?

Answer 22

NaCl from the blood into the lumen

you should know this from MCP!

Question 23

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

Answer 23

NaHCO3 or NaCl

Question 24

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

Answer 24

intestinal bleeding
diarrhea
slow death from malabsorption & dehydration

Question 25

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

Answer 25

1. transcellular pathway | 2. shunt pathway (aka paracellular pathway)

Question 26

describe the path of the transcelluar pathway

Answer 26

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

Question 27

describe the pathway of the shunt pathway

Answer 27

through the tight junction and through the extracellular space

Question 28

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

Answer 28

capillaries and lacteals

Question 29

describe the permeability of the tight junctions

Answer 29

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

Question 30

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

Answer 30

in the jejunum (it does more than half)

Question 31

about how much fluid does colonic absorption account for?

Answer 31

about 5 L/day

Question 32

where are most nutrients absobed?

Answer 32

in the duodenum and the upper jejunum

Question 33

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

Answer 33

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

Question 34

what disorder is caused by a B12 deficiency?

Answer 34

pernicious anemia- type of macrolytic anemia

Question 35

what does the jejunal enterocyte absorb?

Answer 35

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

Question 36

what organ secretes NaHCO3? what is its function?

Answer 36

the pancreas | serves to neutralize acid from the stomach

Question 37

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

Answer 37

1. by Na/glucose and by Na/amino acid cotransport | 2. by Na/H antiport

Question 38

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

Answer 38

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

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

in the jejunum and less so in the ileum

Question 42

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

Answer 42

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

Question 43

what is the effect of cAMP on NaCl?

Answer 43

it inhibits NaCl absorption in the ileum

Question 44

what is the result of vipoma tumors on NaCl absorption?

Answer 44

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

Question 45

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

Answer 45

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

Question 46

what type of cells sercrete NaCl into the lumen?

Answer 46

crypt cells/immature enterocytes

Question 47

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

Answer 47

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

Question 48

what is the effect of cAMP on the CFTR channel

Answer 48

it increases its conductance

Question 49

list the endogenous secretory stimuli (8)

Answer 49

``` ACh histamine CCK secretin gastrin GIP motilin VIP ```

Question 50

list the exogenous secretory stimuli (5)

Answer 50

``` vibrio cholerae e coli salmonella bile salts & fatty acids laxatives ```

Question 51

list the endogenous absorptive stimuli (5)

Answer 51

``` epi/norepi dopamine ENKs somatostatin mineralocorticoids ```

Question 52

list the exogenous absorptive stimuli (1)

Answer 52

nutrients (glucose, AA, peptides)

Question 53

how many mgs of Fe++ are needed daily?

Answer 53

1 mg

Question 54

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

Answer 54

if the body Fe++ is low

Question 55

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

Answer 55

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

Question 56

what are the two pathways by which iron is absorbed?

Answer 56

1. heme iron- more efficient | 2. nonheme iron

Question 57

what form does plasma transferrin carry?

Answer 57

Fe+++

Question 58

how is non heme Fe++ absorbed?

Answer 58

via cotransport with a proton

Question 59

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

Answer 59

ascorbic and citric acids

Question 60

what is calbindin?

Answer 60

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

Question 61

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

Answer 61

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

Question 62

what is the effect of sunlight on the skin?

Answer 62

7 dehydrocholesterol in the skin forms Vit D3 (cholecalciferol)

Question 63

what happens to vit D3 in the liver?

Answer 63

it is hydroxylated to 25(OH)D3

Question 64

what reaction does PTH sitmulate?

Answer 64

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