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Kaplan: GI system > GI hepatic excretion; digestion and absorption > Flashcards

GI hepatic excretion; digestion and absorption Flashcards

1
Q

What physiologic roles does hepatic excretion play in GI tract?

A
  • excretion of bilirubin, cholesterol, drugs and toxins
  • promotion of intestinal lipid absorption
  • delivery of IgA to small intestine
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2
Q

What are the components of bile?

A

bile salts; phospholipids; cholesterol; bilirubin; water; electrolytes

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3
Q

Where is bile produced and stored?

A

produced in hepatocytes;
drains into hepatic ducts
=> stored in gallbladder

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4
Q

What are the primary and secondary bile acids made from?

A

primary=> cholesterol

secondary=> products of bacterial metabolism of primary bile acids in gut

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5
Q

What must ALL bile acids have happen before being secreted into bile?

A

conjugated w/ glycine or taurine to form their bile salt

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6
Q

What are micelles?

A

water soluble spheres w/ lipid soluble interior that form from bile salts above a *critical micellar concentration

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7
Q

Why are micelles important?

A

vital in digestion, transport and absorption of lipid soluble substances from duodenum to distal ileum => allows for bile salts to be reabsorbed
=> enterohepatic recirculation

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8
Q

What is enterohepatic recirculation?

A

bile salts active reabsorbed and recycled via micelles at distal ileum

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9
Q

What can cause malabsorption, gallstones and *steatorrhea?

A

lack of reabsorbing mechanisms or distal ileal disease can lead to deficiency of bile salts

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10
Q

What is the primary role for gallbladder?

A

concentrates and stores bile for release during meals

=> concentrates bile by water and electrolyte absorption

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11
Q

During interdigestive period, how does gallbladder remain filled?

A

sphincter of Oddi is closed and gallbladder is relaxed

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12
Q

When will the gallbladder release bile?

A

small peptides & FA in duodenum cause CCK secretion
=> gallbladder contraction and relaxation of sphincter of Oddi
=> ACh helps in process

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13
Q

What is involved in hepatic excretion and a product of heme metabolism?

A

bilirubin

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14
Q

when is bilirubin taken up and how?

A

prior to bile secretion=> taken up by hepatocytes and *conjugated w/ glucuronic acid

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15
Q

What happens to bilirubin in large intestine?

A

deconjugated and metabolized by bacteria to form urobilinogens

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16
Q

What gives feces its brown color?

A

stercobilins

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17
Q

What is a result of elevated bilirubin?

A

jaundice

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18
Q

What role does secretin play in regulation of bile secretion?

A

stimulates secretion of bile w/ high HCO3 content from biliary ductules => does NOT alter bile salt output

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19
Q

What is the main regulator of bile acid secretion?

A

secretion of bile salts by hepatocytes is directly proportional to hepatic portal vein concentration of bile salts

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20
Q

What is digested and absorbed in small intestine?

A

carbs, proteins, lipids

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21
Q

What aids the small intestine to absorb nutrients?

A

brush border of small intestine increases surface area

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22
Q

Regarding carbohydrate digestion, how are they absorbed?

A

converted to monosaccharides to be absorbed

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23
Q

Where does carb digestion start? How does it work?

A

mouth has salivary amylase => hydrolyzes 10-20% of ingested starch

=> hydrolyzes only a(1:4)-glycosidic linkages to maltose, maltotriose and a-limit dextrins

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24
Q

Where is pancreatic amylase found in high [ ]? what is its function?

A

duodenal lumen

=>rapidly hydrolyzes starch to oligosaccharides, maltose, maltotriose, a-limit dextrins

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25
Q

what are found in high concentrations in brush border of mid-jejunum and proximal ileum?

A

maltase; a-dextrinase; lactase; sucrase; isomaltase

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26
Q

action of alpha-dextrinase

A

cleaves terminal a-1,4 bonds => produces free glucose

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27
Q

action of lactase

A

converts lactose to glucose and galactose

28
Q

action of sucrase

A

converts sucrose to glucose and fructose

29
Q

action of maltase

A

converts maltose and maltotriose to 2 and 3 glucose units

30
Q

What are the monosaccharide end products? where are they absorbed?

A

glucose, galactose, fructose

=> absorbed from small intestine; jejunum primarily

31
Q

What does a lactase deficiency cause? consequence

A

inability to digest lactose into glucose and galactose

=> increase osmotic load => osmotic diarrhea; flatulence

32
Q

How are glucose and galactose absorbed at luminal membrane?

A

compete for transport across brush border by Na+ dependent coporter (SGLT-1)
=>Na+ then pumped out by Na-K ATPase
=>sugars move against concentration gradient into enterocyte

33
Q

how is fructose absorbed at luminal membrane?

A

GLUT-5 transporter

34
Q

How is glucose, galactose and fructose absorbed at basolateral membrane?

A

transported across basolateral membrane via GLUT-2 transporter

35
Q

How are lipids digested in the stomach?

A
  • pulverized (decrease size, increase surface area);

* CCK slows gastric emptying to allow enough time for digestion and absorption in small intestine

36
Q

how are lipids digested in small intestine?

A

bile acid micelles emulsify fat;

pancreatic lipases digest fat

37
Q

What do pancreatic enzymes do to fat in the small intestine?

A

fats hydrolyzed to FFA, monoacylglycerols (cholesterol, fat soluble vitamins A,D,E,K) that collect in micelles

38
Q

What is the role of micelles in lipid absorption?

A

carry products of fat digestion in aqueous fluid of gut lumen to brush border => diffuse into enterocyte

39
Q

Role of enterocytes in lipid absorption?

A

*re-esterify FA to form TAG, phospholipids and cholesteryl esters => incorporated into apo-proteins and chylomicrons

40
Q

role of chylomicrons in lipid absorption?

A

*released by exocytosis into intercellular spaces => enter lacteals of lymph system
=> enter venous circulation via thoracic duct

41
Q

What are the outcomes of glycerol from lipid absorption?

A

end up in portal blood to be

1) oxidized for energy
2) stored as glycogen

42
Q

What does not require micelle formation for absorption? Why?

A

TAGs w/ medium and short chain FA => hydrolyzed quickly

  • undergo little re-esterification
  • absorbed directly into portal venous system
43
Q

What causes abetalipoproteinemia?

A

deficiency of apoprotein B causing an inability to transport chylomicrons out of intestinal cells

44
Q

Where and how does protein digestion begin?

A

pepsin in the stomach

=>functions best at pH 2; irreversibly deactivated at pH 5
=> deactivated in duodenum

45
Q

is pepsin essential for protein digestion?

A

no => it is not an essential enzyme

46
Q

How are proteins digested in the small intestine? are the associated enzymes required?

A

pancreatic proteases activated by brush border peptidases

yes=> essential enzymes => trypsin, chymotrypsin, elastase, carboxypeptidases A and B

47
Q

How are amino acids from protein digestion absorbed at the luminal membrane

A

*Na+ dependent AA cotransport

48
Q

how are dipeptides and tripeptides absorbed at luminal membrane?

A

*H+ dependent cotransport mechanism

49
Q

How are dipepetides and tripeptides absorbed at basal membrane?

A

hydrolyzed to AA intracellularly

50
Q

how are AA transported through basal membrane?

A

to the blood by facilitated diffusion

51
Q

What is Hartnup disease?

A

disorder that neutral AA cannot be absorbed

52
Q

Where does water and electrolyte absorption take place?

A

primarily in small intestine

53
Q

How and where is Na absorbed?

A
  • proximal intestine=> Na/H; Na/glucose; Na/aa; Na/Cl cotransports and passive diffusion
  • colon=> aldosterone stimulates passive diffusion
54
Q

How and where is Cl absorbed?

A

proximal intestine and colon via

=> Na/Cl cotransport; Cl/HCO3 exchange; passive diffusion

55
Q

Where and how is K absorbed or secreted?

A

absorbed in small intestine=> passive diffusion

secretion in colon=> via aldosterone

56
Q

Where and how is Ca+ absorbed?

A

small intestine => vit D dependent carrier

57
Q

Where is H20 absorbed?

A

isoosmotic absorption in gallbladder and small intestine;

permeability is lower in colon

58
Q

Where and how is iron absorbed?

A

duodenum primarily=> absorbed as free Fe+2 or as heme iron

59
Q

Once absorbed, what happens to Fe2+?

A

bound to transferrin in blood

60
Q

What are the different types of vitamins that are absorbed?

A

fat soluble=> A,D,E,K
water soluble
Vitamin B12

61
Q

Where are fat soluble vitamins (ADEK) absorbed?

A

incorporated into micelles and absorbed

62
Q

How are water soluble vitamins absorbed?

A

via Na+ dependent co-transporters

63
Q

How is vitamin B12 absorbed?

A

occurs in ileum => transported and bound to intrinsic factor

64
Q

What occurs if there is a decrease in intrinsic factor?

A

this might occur due to a gastrectomy => PERNICIOUS ANEMIA

65
Q

Where and how does water and electrolyte secretion occur?

A

secretion in crypts => Cl- main ion secreted

occurs via cAMP regulated channels in luminal membrane

66
Q

If cholera toxin is present in the GI tract, what will result and why?

A

SECRETORY DIARRHEA => it stimulates adenylate cyclase => increase cAMP => open Cl channels => Na and H2O follow => secretory diarrhea

Kaplan: GI system (11 decks)

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