Lectures 5-7: Small Intestine Flashcards Preview

Gastrointestinal and Liver > Lectures 5-7: Small Intestine > Flashcards

Flashcards in Lectures 5-7: Small Intestine Deck (91):
1

Where are new cells born in the small intestine? What is there pathway?

Born near crypt, differentiate and mature as they migrate up the villus

2

How much fluid is presented to the SI? How much is drank? How much of this gets to the colon? How much excreted fecally?

8000 mL, 2000 mL, 1500 mL, 150 mL

3

Max abs capacity of SI and colon

12 L, 5 L

4

What solute drives absorption through the mucosa?

Na+

5

What are the sodium channels in the intestine? (4, 1 basolateral)

1. Apical Na+ channel; 2. Basolateral Na-K ATPase (balances Na+ in); 3. Solute-coupled Na+ transport; 4. Na/H exchanger (w/ HCO3/Cl exchanger as well)

6

What does aldosterone do?

Increases function of apical Na+ channel

7

What is the mechanism of oral rehydration therapy?

Requires glucose and Na+ to bring water into cell via solute-coupled Na+ transport, meaning that Na+ can be absorbed in the lumen (hence, ORAL rehydration)

8

Describe the Na/H Exchanger (what in, what out)

Na+ AND Cl- in, H+ AND HCO3- out

9

What enhances sodium absorption?

Mineralcorticoids (aldosterone), glucocorticoids, somatostatin, adrenergic agonists (epinephrine)

10

What slows the intestinal transit? How does this affect Na+ absorption?

Opiates and somatostatin; increases sodium absorption

11

What is the key ion that drives secretion?

Cl-

12

How does Cl- get into the body?

Via the Na/H exchanger

13

How does Cl- enter the cell to drive secretion? How is it secreted?

Basolaterally (Na/K/2Cl transporter); apically (Cl channel = CFTR)

14

Cl- secretion becomes increased by any factor that activates what?

cAMP, cGMP, intracellular calcium

15

What four hormones/NTs increase cAMP leading to diarrhea?

VIP, secretin, PGE1, bradykinin

16

What three hormones/NTs increase calcium leading to diarrhea?

ACh, 5-HT, histamine

17

What four bacteria increase cAMP leading to diarrhea?

V. cholera, E. coli (heat labile), campylobacter, salmoneella

18

What two bacteria increase cGMP leading to diarrhea?

Yersinia enterocolitica, E. coli (heat stable)

19

What are some laxatives that act on the cAMP/calcium pathways?

Bile acids, long chain fatty acids, castor oil, senokot

20

What factors increase colonic transport?

Cholinergics, anxiety, feeding, laxatives/hormones, distention

21

What factors slow colonic transit?

Anti-cholinergics, depression, colonic wall inflammation, opiates, electrolyte disturbances

22

Which will cause more water in the stool: small intestinal or colonic dysfunction?

Small intestinal (does the majority of the water absorption, about 7 L)

23

Sx of small bowel/colonic diarrhea

Large amount of stool, moderate increase in number, minimal urgency, no tenesmus, little mucus

24

Sx of recto-sigmoid diarrhea

Small amount of stool, frequency, urgency, tenesmus, mucus, blood

25

Bile acid-induced diarrhea results from _______ dysfunction. Why?

Ileal; ileum is the ONLY site of active bile acid absorption

26

Mechanisms of osmotic diarrhea. What is intact?

Nonabsorbable solute in bowel lumen --> water enters lumen --> solute/water load exceeds colonic absorptive capacity; mucosal transport processes intact

27

What are some examples of osmols that will not be absorbed and will increase secretion?

Carbohydrates: lactose (if lactase deficiency), sorbital; Minerals: Na Sulfate lavage, Mg Citrate

28

Osmotic diarrhea: what is depleted? What is not depleted?

Water (NOT Na+ depletion) = not life threatening

29

Osmotic diarrhea: stool volume __________ with fasting

Decreases

30

Osmotic diarrhea: what can you detect in fecal fluid (osmolality and pH)

Osmotic gap = unmeasured osmolality due to nonabsorbed solute; acidic stool pH due to bacterial fermentation of solute

31

Mechanism of secretory diarrhea. What is intact?

Stimulation of normal secretory processes; absorptive processes intact but overwhelmed

32

What 2nd transporters cause secretory diarrhea?

cAMP, cGMP, Ca2+

33

What is the mechanism of cholera toxin?

Increases intracellular cAMP via AC, driving Cl- out of cell and decreasing Cl- reabsorption (via Na/H transporter), keeping water out of the cell. NOTE the Na/Glucose transporter is spared, hence oral rehydration

34

Secretory diarrhea: what is depleted?

Salt and water (life-threatening)

35

Secretory diarrhea: stool volume while fasting

Persists despite fasting

36

Secretory diarrhea: osmotic gap? pH?

NOPE: all osmolality accounted for by electrolytes; neutral pH

37

Describe two types of motility diarrhea

Hypermotility: insufficient contact time for absorption (laxatives, anxiety); Hypomotility: altered peristalsis --> stasis (water can flow aound stool and cause both diarrhea and constipation)

38

What is preferentially absorbed in the duodenum?

Iron and other minerals

39

What is preferentially absorbed in the ileum?

Cobalamin and bile acids

40

Secretin

Released by duodenum in response to low pH, increase pancreatic bicarbonate secretion

41

CCK (cholecystokinin)

Released by duodenum in response to FAs and AAs, causes gallbladder emptying (bile acids) and increases pancreatic enzyme secretion

42

Starch digestion

Amylase (saliva, pancreas) --> maltose, maltase (BBM) --> glucose

43

Sucrose digestion

Sucrase-isomaltase (BBM) --> glucose, fructose

44

Lactose digestion

Lactase (BBM) --> glucose, galactose

45

How are monosaccharides absorbed?

Actively transported into cell --> portal vein

46

What happens to unabsorbed CHO?

Converted to short chain fatty acids in colon

47

Stomach's role in protein digestion

HCl denatures, pepsin hydrolyzes into polypeptides

48

Duodenum and pancreas role in protein digestion

Pancreas releases pro-proteases, enterokinase in duodenal BBM activates trypsin which then activates other pro-enzymes

49

Small intestine's role in protein digestion

BBM oligopeptidases hydrolyze oligopeptides into smaller peptides

50

How are AAs and oligopeptides absorbed?

They are transported into the cell --> portal vein

51

Stomach's role in lipid digestion

Churns fat (mostly TGs) into unstable emulsion

52

Duodenum and small intestine's role in lipid digestion

Emulsion stabilized by phospholipids (diet) and bile salts (liver), dietary fat --> CCK --> lipase (pancrease) and bile salts, micelles form

53

What does lipase do?

Lipase + co-lipase break down TGs into MGs and FFAs

54

Describe a micelle

MGs and FFAs inside with bile salts outside

55

How are MGs and FFAs absorbed?

Micelles bring them to the BBM and then they are released and passively diffuse into cell, then they are resynthesized into chylomicrons and VLDL, exported into lymphatics (lacteal)

56

What is different about medium chain TGs?

Bypass lymphatics and are absorbed into portal vein

57

What are the four stages of chylomicron formation?

Esterification, surface stabilization, addition of lipoprotein, and secretion via intracellular spaces into lacteals

58

How is B12 absorbed?

Ingested in food --> binds to R factor in saliva --> intrinsic factor (IF) made by parietal cells --> pancreatic proteases breaks up B12*R --> B12 binds with IF --> absorbed in ileum

59

What could go wrong with B12 levels?

Not enough B12 in diet, no IF (autoimmune gastritis), no R factor (salivary glands), no proteases (pancreatic insufficiency), no absorption (ileal disease), and bacterial overgrowth

60

Malabsorbed: protein

Edema

61

Malabsorbed: fats

Weight loss and steatorrhea

62

Malabsorbed: carbs

Diarrhea, bloat, gas

63

Malabsorbed: vit A

Hyperkeratosis, night blindness

64

Malabsorbed: vit D, Ca2+

Tetany, osteomalacia

65

Malabsorbed: vitamin E

Neuropathy (pins and needles); deficiency = hemolytic anemia, acanthocytosis, weakness, posterior column/spinocerebellar tract demyelination

66

Malabsorbed: vit K

Bruising (made by intestinal bacteria)

67

Malabsorbed: vit B12

Megaloblastic anemia, glossitis, cheilosis, neuropathy

68

Malabsorbed: folate

Megaloblastic anemia, glossitis

69

Malabsorbed: iron

Microcytic anemia, dyspnea, fatigue, glossitis

70

Lactase deficiency can be what two types?

Primary (genetic) and secondary (loss of enterocytes due to infection, resection, radiation)

71

How much pancreas must be lost before you have pancreatic exocrine insufficiency?

90-95%

72

What can cause pancreatic exocrine insufficiency?

CF, chronic pancreatitis, pancreatic resection

73

How do you treat pancreatic exocrine insufficiency?

Oral pancreatic enzyme replacement (enteric coated)

74

How does bile salt deficiency cause maldigestion?

Low bile salt pool = maldigestion of fat/fat-soluble vitamins

75

What can cause bile salt deficiency?

Severe cholestasis, distal ileal resection or disease (Crohn's), bacterial overgrowth

76

How do you treat bile salt deficiency?

Treat underlying condition and give medium chain triglycerides

77

What prevents bacterial overgrowth?

Gastric acids, small bowel motility, ileocecal valve, secreted immunoglobulins

78

What conditions are associated with the development of bacterial overgrowth? (2 classes)

Motility disorders (stasis) and anatomic disorders (fistula, diverticulitis, blind loop)

79

Consequences of bacterial overgrowth

Deconjugate the bile salts --> fat malabsorption and B12/iron deficiency due to bacterial consumption

80

How can bacterial overgrowth be dx?

Breath tests

81

How can bacterial overgrowth be treated?

Correct underlying problem and give antibiotics

82

What two broad categories of disease cause malabsorption?

Loss of absorptive surface and impaired mucosal/lymphatic transport

83

Three examples of loss of absorptive surface

Short bowel syndrome, celiac sprue, tropical sprue

84

Three examples of impaired mucosal/lymphatic transport

Abetalipoproteinemia, Whiple's disease, intestinal lymphangiectasia

85

How could one get short bowel syndrome?

Caused by resection or bypass

86

Celiac disease is an inappropriate response to...where does it favor in the bowel?

Gliadin (in gluten); proximal > distal

87

What is tropical sprue? Tx?

Infection seen after Central America, Caribbean, SE Asia that is histologically similar to celiac sprue but is PANenteric (not just duodenum); tx = antibiotics

88

What is abetalipoproteinemia? Tx?

AR disease in which epithelial cells CANNOT assemble chylomicros, so lipids accumulate in cells, causes fat malabsorption; tx = fat restriction and MCT oil

89

What des the D-Xylose test test? Describe.

Tests functioning of SI absorption; under normal conditions, 25% of ingested amount of D-Xylose should be in urine, if less, than not enough absorbed

90

There is fat malabsorption. D-Xylose normal =

Pancreatic disease

91

There is fat malabsorption. D-Xylose abnormal =

Small bowel disease