Intestine 1 - RM Flashcards by Ryan Schiedo

How is the jejunum demarcated from the duodenum?

ligament of treitz

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

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

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

3x as much, jejunum has greater absorption

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How is the colon’s surface amplified?

macroscopic semilunar folds, crypts, microvilli

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

half of it

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What is Celiac disease?

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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What is sprue?

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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What are villi composed of a layer of?

absorptive enterocytes

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What is the function of crypt cells?

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

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What reduces rate of cell renewal of crypt cells?

radiation, malnutrition, sprue

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What is the function of goblet cells?

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

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What is radiation sickness?

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

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

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

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

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

9.5 L (equal to input)

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

jejunum

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What is absorbed in the ileum?

vitamin B12 bound to intrinsic factor

ionized bile salts

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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?

yes for ileum adapting

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

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What is R protein?

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

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What do jejunal absorptive cells absorb? How?

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)

What is the primary mechanism of postmeal Na absorption?

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

What is Na/H exchange caused by?

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

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

changes in intracellular pH resulting in electroneutral NaCl absorption

What inhibits NaCl absorption in ileum?

cAMP, stimulated by Ach

What is VIP? When is its contribution significant?

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

What can stimulate production of cAMP?

ecoli, vibrio cholera, Ach

How is NaCl secreted by crypt cells?

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

How does increased cAMP affect crypt cell?

- increases conductance of CFTR to Cl | - Cl is driven out of cell by negative internal electrical potential

How does cholera cause diarrhea?

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

How do secretory stimuli and absorptive stimuli interact?

- substances that promote secretion tend to inhibit absorption - substances that promote absorption tend to inhibit secretion

What are endogenous secretory stimuli (8)?

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

What are exogenous secretory stimuli (6)?

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

What are endogenous absorptive stimuli?

E, NE, dopamine, enkephalins, somatostatin, mineralocorticoids

What are exogenous absorptive stimuli?

nutrients (glucose, amino acids, peptides)

What form of iron is absorbed?

Fe2+ (not Fe3+)

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

reducing agents in GI convert it to Fe2+ to absorb | -ascorbate and citrate

What is transferrin?

iron binding protein that is how it travels in blood

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

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

What are the two sources of iron absorption?

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

What can insufficient gastric acid cause?

iron deficient anemia

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

DMT1, driven by H+ gradient

What binds cytoplasmic Fe2+?

mobilferrin

How does Fe2+ exit via the basolateral membrane?

IREG1

How many Fe3+ bind per transferrin in plasma?

What is Ca-ATPase activated by?

calmodulin

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

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

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

duodenum, stimulated by vitamin D

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

against the gradient