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Unit 7 > Physio - Howell - Intestinal Transport I: Fluid and Electrolytes - 2/18 > Flashcards

Physio - Howell - Intestinal Transport I: Fluid and Electrolytes - 2/18 Flashcards

1
Q

How is the duodenum demarcated from the jejunum?

A

Ligament of Treitz

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2
Q

T/F: The jejunum has 3x more SA than the ileum, consistent with greater absorption.

A

True

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3
Q

What is the function of Paneth cells?

A

Paneth cells produce antimicrobial agents.

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4
Q

Where are the macroscopic folds of Kerckring found (to increase SA)?

A

Small intestine

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5
Q

Where are macroscopic semilunar folds found (to increase SA)

A

Large intestine

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6
Q

How much of the absorptive area of the intestine can be removed without compromising function?

A

About 1/2

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7
Q

What is tropical sprue?

A

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

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8
Q

How are goblet cells stimulated to secrete their protective mucous?

A

PS fibers –> ACh –> goblet cells

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9
Q

The villi are primarily made up of:

A

Columnar epithelium layer, enterocytes (absorptive cells)

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10
Q

What is the role of the undifferentiated cells of the crypt?

A

Undifferentiated cells of the crypt secrete NaCl from the blood into the lumen (water flows by osmosis). They change their function as they travel up the crypt toward the villus and take on absorptive functions, absorbing NaCl or NaHCO3.

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11
Q

Why do radiation victims experience intestinal bleeding, diarrhea, and slow death from dehydration and malabsorption?

A

Because of high turnover of cells in intestinal mucosa, they are very sensitive to radiation damage.

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12
Q

What is the shunt pathway in the intestinal epithelium?

A

Materials can traverse the tight junction and extracellular space.

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13
Q

Give 3 examples of ectoenzymes.

A

Enterokinase
Peptidase
Disaccharidase
All found at the brush border to help complete digestion

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14
Q

Where are tight junctions leakiest?

A

Loosest in jejunum (fast uptake of water), becoming progressively tighter toward the colon

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15
Q

Where is the most fluid absorbed after a meal?

A

Jejunum

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16
Q

T/F: Removal of the jejunum is fatal due to malabsorptive effects.

A

False. The ileum can take over the function of the jejunum.

17
Q

What part of the ileum should never be removed, if possible, and why?

A

The distal ileum should never be removed if possible because it is the sole site of B12 absorption AND bile salt absorption.

B12 is absorbed in a complex with intrinsic factor (secreted by parietal cells)

18
Q

What metals are most dramatically absorbed in the duodenum?

A

Ca, Fe

19
Q

By what two methods does Na+ enter the jejunal enterocyte? How does Na then leave the cell (basolateral side)

A
  1. Na/glucose or Na/aa cotransport
  2. Na/H antiport –> helps to keep lumen of intestine at normal pH

Na then leaves the cell via the Na/K pump.

20
Q

What is the process by which NaHCO3 is abrosbed by the jejunal absorptive cell?

A
  1. Na absorbed from lumen, leaves basolaterally via Na/K pump
  2. H secreted to lumen
  3. H combines with HCO3
  4. H2CO3 –> H2O and CO2
  5. CO2 diffuses into cell
  6. CO2 + OH in cell –> HCO3
  7. HCO3 leaves basolaterally
21
Q

T/F: ACh stimulates cAMP, which inhibits NaCl absorption by the ileum.

A

True. This is what gets overstimulated in the case of cholera or E. Coli infection.

22
Q

How is NaCl absorbed in the ileal absorptive cell?

A
  1. Na enters cell via Na/H antiporter
  2. Cl enters cell via Cl/HCO3 exchanger
  3. Cl passes down BL membrane via electrochemical gradient to blood
  4. Na leaves in the usual way, Na/K pump
  5. HCO3 combines with H in lumen
  6. H2CO3 –> H2O and CO2
23
Q

What is a vipoma, and what are the effects in the intestine?

A

A vipoma is a VIP-secreting tumor. The amount of VIP is greatly increased, stimulating cAMP, which inhibits NaCl absorption, leading to an osmotic shift, causing diarrhea.

24
Q

What is the role of the apical CFTR channel?

A

To permit movement of Cl from the crypt cell to the lumen

Note that increased cAMP increases the behavior of this channel in jejunal crypt cells.

The CFTR channel is deficient in patients with cholera, thus it is expected that cholera would be ineffectual in CF patients.

25
Q

How do Na, K and Cl get into crypt cells on the BL membrane?

A

1 Na/1 K/2 Cl channel

26
Q

Why is oral rehydration therapy with saline and glucose better than plain water in treating cholera?

A

Intestinal Na/glucose cotransporter helps to absorb Na, decreasing diarrhea and dehydration.

27
Q

T/F: Substances that promote secretion tend to inhibit absorption and vice versa.

A

True

28
Q

Name 5 endogenous intestinal secretory stimuli.

A 
ACh
Histamine
CCK
Secretin
Gastrin
GIP
VIP
Motilin
29
Q

Name 5 exogenous intestinal secretory stimuli.

A 
E. Coli
Vibrio cholera
Salmonella
Bile salts and fatty acids
Laxatives
30
Q

What do these substances have in common?
Epi, Norepi and other alpha-adrenergic agonists
Dopamine
Enkephalins ie morphine
Somatostatin
Mineralcorticoids ie aldosterone (in the colon)

A

They are all endogenous promoters of absorption

31
Q

Congenital hemochromatosis involves:

A

too much iron absorption

32
Q

T/F: If body Fe is low, brush border transporters increase. If body Fe is high, the brush border transporters decrease AND ferritin increases.

A

True

33
Q

Iron absorption occurs by 2 pathways: heme iron and non-heme iron. Explain the absorption of iron in either case.

A
  1. DcytB reduces Fe3+ to Fe2+ for absorption (body cannot take up Fe3+)
  2. Fe2+ and H+ enter duodenal cell via DCT1 (aka DMTI) cotransporter
  3. Fe combines with mobilferrin
  4. Mobilferrin-Fe leaves cell on BL side via IREG1
  5. Fe gets oxidized to Fe3 again
  6. Fe3 binds to transferrin
    OR
  7. Heme enters cell
  8. Heme oxygenase releases Fe3+
  9. Fe3+ reduced to Fe2+
  10. See above step 4.
34
Q

What vitamin can aid in iron absorption?

A

Vitamin C, bc it reduced Fe3+ to Fe2+

For the same reason, patients with low gastric acid absorb less iron and can become anemic.

35
Q

What is the major dietary source of iron?

A

Red meat (bc it contains a lot of heme)

36
Q

The small intestine absorbs Ca by two mechanisms. The passive, paracellular absorption (through tight junctions) of Ca occurs throughout the small intestine and is not under vitamin D control. The second mechanism, the active transcellular absorption of Ca, occurs only in the duodenum. Explain this active process.

A
  1. Ca enters duodenal enterocyte
  2. Ca binds to calbindin, and is taken up by organelles as needed
  3. Ca leaves on BL side via Ca/Na exchanger, with a net effect of Ca absorption.
    Vitamin D stimulates these actions by stimulating the synthesis of proteins involved in Ca uptake.
37
Q

What factors influence Ca absorption?

A
  1. Increased fatty acids due to formation of soap
  2. Oxalate reduces bioavailability of Ca (leafy greens)
  3. Bile salts form complexes with Ca which facilitate absorption
38
Q

Where does Vitamin D become active?

A

In the kidney, after a second hydroxylation (stimulated by PTH)

First hydroxylation occurs in the liver.

39
Q

Fill in “increase” or “decrease”
Increase in Ca in plasma –> __1__ PTH secretion –> __2__ formation of 1,25-OH2-VitD3 –> __3__ synthesis of calbinding –> __4__ Ca absorption

A

All decrease

Unit 7 (28 decks)

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