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U6 Physiology > Intestine 1 - RM > Flashcards

Intestine 1 - RM Flashcards

1
Q

How is the jejunum demarcated from the duodenum?

A

ligament of treitz

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2
Q

What increases the surface area for absorption in the small intestine?

A

mucosal folds of kerking (7.5x in jejunum, 2.4x in ileum), villi (10x), microvilli (20x)

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3
Q

The jejunum has ___x as much surface area as the ileum. Why does this make sense?

A

3x as much, jejunum has greater absorption

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4
Q

How is the colon’s surface amplified?

A

macroscopic semilunar folds, crypts, microvilli

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5
Q

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

A

half of it

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6
Q

What is Celiac disease?

A

malabsorptive syndrome due to gluten intolerance
gluten destroys absorptive cells and decreases the number of functional villi so food that is digested can’t be absorbed
-get diarrhea, malnutrition and dehydration

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7
Q

What is sprue?

A

malabsorption syndrome typically found in tropical areas

-associated with decrease in absorptive SA due primarily to reduction in size and number of microvilli

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8
Q

What are villi composed of a layer of?

A

absorptive enterocytes

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9
Q

What is the function of crypt cells?

A

generate new undifferentiated cells that migrate to tip of villi and secrete NaCl into lumen (with water following)

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10
Q

What reduces rate of cell renewal of crypt cells?

A

radiation, malnutrition, sprue

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11
Q

What is the function of goblet cells?

A

secrete mucus in response to Ach from vagus to form protective barrier and lubricate tissue for peristalsis

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12
Q

What is radiation sickness?

A

because of high turnover of intestinal mucosa, it is highly sensitive to radiation damage
-get intestinal bleeding, osmotic diarrhea cause you can’t absorb things, malabsorption, and dehydration

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13
Q

What are the two pathways of transport for absorption by enterocytes?

A

transcellular- across brush border, through cytoplasm, across basolateral membrane
paracellular- via tight junctions permeable to cations

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14
Q

How does the tightness of tight junctions vary along the length of the intestine?

A

more leaky/permeable at beginning in jejunum and gets less permeable as you proceed towards the colon

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15
Q

How much fluid must be absorbed in a day to prevent dehydration or diarrhea?

A

9.5 L (equal to input)

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16
Q

Where are most of the nutrients and water absorbed in the intestines?

A

jejunum

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17
Q

What is absorbed in the ileum?

A

vitamin B12 bound to intrinsic factor

ionized bile salts

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18
Q

If jejunum is removed, can the ileum adapt to take over its function and absorb all the nutrients? Can the jejunum take over for the ileum if the ileum is removed?

A

yes for ileum adapting

no for jejunum adapting-> can’t absorb bile salts or vit. B12

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19
Q

What is R protein?

A

binds vitamin B12 to protect it until it can complex with intrinsic factor and be absorbed

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20
Q

What do jejunal absorptive cells absorb? How?

A

Na and HCO3-, glucose, and amino acids
Na enters via Na/glucose cotransporter, Na/amino acid cotransporter, Na/H antiporter
HCO3- transfers as CO2 diffusion (converted to bicarb in cell)

21
Q

What is the primary mechanism of postmeal Na absorption?

A

nutrient coupled Na absorption–Na/glucose cotransport, Na/amino acid cotransport

22
Q

What is Na/H exchange caused by?

A

extrude H+ to keep cell from acidifying while it exports Na

23
Q

What is Na/H and Cl/HCO3 exchange coupled to?

A

changes in intracellular pH resulting in electroneutral NaCl absorption

24
Q

What inhibits NaCl absorption in ileum?

A

cAMP, stimulated by Ach

25
Q

What is VIP? When is its contribution significant?

A
  • neurotransmitter that increases pancreatic secretions
  • in vipomas (VIP secreting tumor), increases VIP, greatly decreased NaCl absorption, increased osmolarity in lumen and osmotic diarrhea
26
Q

What can stimulate production of cAMP?

A

ecoli, vibrio cholera, Ach

27
Q

How is NaCl secreted by crypt cells?

A

CFTR-apical membrane Cl channel to let Cl go to lumen
Na/K/2Cl cotransporter- basolateral membrane moves them into lumen of cell
Na moves through paracellular transport

28
Q

How does increased cAMP affect crypt cell?

A
  • increases conductance of CFTR to Cl

- Cl is driven out of cell by negative internal electrical potential

29
Q

How does cholera cause diarrhea?

A

increases cAMP, inhibits absorption of NaCl in ileum, increases NaCl secretion of crypt cells, water follows the increased NaCl secretion to give osmotic diarrhea

30
Q

How do secretory stimuli and absorptive stimuli interact?

A
  • substances that promote secretion tend to inhibit absorption
  • substances that promote absorption tend to inhibit secretion
31
Q

What are endogenous secretory stimuli (8)?

A

Ach, histamine, CCK, secretin, gastrin, GIP, motilin, VIP

32
Q

What are exogenous secretory stimuli (6)?

A

vibrio cholera, ecoli, salmonella, enterotoxins, bile salts and fatty acids, laxatives

33
Q

What are endogenous absorptive stimuli?

A

E, NE, dopamine, enkephalins, somatostatin, mineralocorticoids

34
Q

What are exogenous absorptive stimuli?

A

nutrients (glucose, amino acids, peptides)

35
Q

What form of iron is absorbed?

A

Fe2+ (not Fe3+)

36
Q

How can you absorb ingested Fe3+? What agents help?

A

reducing agents in GI convert it to Fe2+ to absorb

-ascorbate and citrate

37
Q

What is transferrin?

A

iron binding protein that is how it travels in blood

38
Q

If body Fe2+ is low, what happens? If too high?

A
  • too low–number of brush border transporters increases

- too high–number of brush border transporters decrease and amount of ferritin increases

39
Q

What are the two sources of iron absorption?

A

heme iron–freed in the cell by heme oxygenase and binds to intracellular mobilferrin
nonheme iron–Fe2+ forms insoluble complexes with food that is released by gastric acid

40
Q

What can insufficient gastric acid cause?

A

iron deficient anemia

41
Q

What transports Fe2+ across the apical membrane? What is it driven by?

A

DMT1, driven by H+ gradient

42
Q

What binds cytoplasmic Fe2+?

A

mobilferrin

43
Q

How does Fe2+ exit via the basolateral membrane?

A

IREG1

44
Q

How many Fe3+ bind per transferrin in plasma?

A

2

45
Q

What is Ca-ATPase activated by?

A

calmodulin

46
Q

What does 1,25-diOHD3 stimulate synthesis of? What does this protein do?

A

calbindin- it is a Ca-binding protein that is membrane carrier for Ca2+ across brush border

47
Q

Where is the only place there is active transcellular Ca2+ transport? What is it stimulated by?

A

duodenum, stimulated by vitamin D

48
Q

Is absorption of calcium in jejunal absorptive cells down or against the gradient?

A

against the gradient

U6 Physiology (13 decks)

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