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FHB Block 3 > Digestion and Absorption > Flashcards

Digestion and Absorption Flashcards

1
Q

What form of carbohydrates can be absorbed through the intestinal epithelial cells?

A

Monosaccharides- thus all carbohydrates must be digested to monosaccharides in order to be absorbed by the intestine

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2
Q

Differentiate amylose from amylopectin

A

Amylose- straight chain polymers of glucose

Amylopectin- branched-chain polymers of glucose

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3
Q

What are the three disaccharides in food?

A

Trehalose, sucrose and lactose

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4
Q

What is the composition of trehalose?

A

two monomers of glucose

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5
Q

What is the composition of sucrose?

A

glucose and fructose

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6
Q

What is the composition of lactose?

A

Glucose and galactose

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7
Q

Why can cellulose not be absorbed?

A

Cellulose has 1,4 beta linkages, and we only have alpha amylose to break down carbohydrates, which breaks down alpha 1-4 linkages

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8
Q

The majority of carbohydrate digestion occurs where/by what enzyme?

A

Small intestine by pancreatic alpha amylase

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9
Q

What is the digestion product of pancreatic amylase?

A

Dextrins, maltose and maltotriose –> all di/tri or oligosacchardies

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10
Q

What enzyme is responsible for completing the digestion of disaccharides?

A

brush border enzymes –> alpha dextrinase, maltase and sucrase

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11
Q

Differentiate the digestion of three disaccharides in food vs. starch

A

Starches require amylase, the three disaccharides (trehalose, lactose and sucrose) do not.

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12
Q

How are glucose and galactose absorbed across the apical membrane of the small intestine?

A

SGLT1: sodium glucose transporter 1 transports glucose and galactose against their concentration gradients by coupling their transport to sodium

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13
Q

How are glucose and galactose extruded across the basolateral membrane into the blood?

A

Facilitated diffusion- GLUT2 transporter

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14
Q

How is fructose absorbed?

A

Fructose is absorbed via facilitated diffusion across both the apical and basolateral membrane

GLUT5 (apical)
GLUT2 (basolateral)

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15
Q

What causes lactose intolerance?

A

Lack or deficiency of lactase - the brush border enzyme responsible for digesting lactose into glucose and galactose

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16
Q

Is lactose intolerance normal?

A

Yes- this is the normal developmental decline in the expression of lactase by enterocytes

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17
Q

Where does protein digestion start?

A

Stomach- by pepsin

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18
Q

What are the two main classes of peptidases in the small intestine?

A

Endopeptidases and exopeptidases

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19
Q

Where is pepsinogen released from?

A

Chief cells- in response to a meal

20
Q

How is pepsinogen converted to pepsin?

A

Low pH

21
Q

How is pepsin inactivated?

A

Pepsin is inactivated by pancreatic HCO3- in the duodenum

22
Q

Is pepsin a necessary enzyme?

A

No- people with their stomach removed still have normal protein digestion

23
Q

What digests protein in the small intestine?

A

Combo of pancreatic enzymes and brush border proteases

24
Q

What form of protein is absorbable?

A

amino acids, di- and tri-peptides are absorbable

25
Q

How are amino acids/ di/tri peptides absorbed?

A

Mostly symporters with Na

26
Q

What else can peptide transporters take up?

A

Some drugs

27
Q

How to amino acids exit the cell and enter the blood stream?

A

facilitated diffusion

28
Q

What is the major lipid in the diet?

A

Triglycerides

29
Q

Why are lipids a challenge to digest?

A

They are water insoluble and float on the surface of the gastric contents

30
Q

What is the major contribution of the stomach to lipid digestion?

A

slow emptying of chyme into the small intestine- allows for adequate time for pancreatic enzyme action

CCK reduces gastric emptying

31
Q

What is the role of pancreatic lipase?

A

Hydrolyze triglycerides to monoglycerides and fatty acids

32
Q

What is the role of phospholipase A2?

A

Hydrolyze phospholipids such as those present in cell membranes to lysolecithin and fatty acids

33
Q

What is the role of cholesterol ester hydrolase

A

Hydrolyzes cholesterol ester to free cholesterol and fatty acids

34
Q

Is glycerol water soluble?

A

Yes

35
Q

Briefly describe how lipids are absorbed into the bloodstream from the lumen of the intestine.

A

Lipids are surrounded by bile salts that form a micelle around them, which then diffuse to the membrane of the brush border epithelium.

Lipids are then released from the micelle and and diffuse into the cell (down their concentration gradient).

Once in the cell, they are modified and packaged into chylomicrons, which leave the cell via exocytosis, are taken up into the lymphatics, and return to circulation via the thoracic duct.

36
Q

Where is bile primarily reabsorbed?

A

In the ileum

37
Q

What proteins are responsible for repackaging the lipids in a cell into chylomicrons?

A

Apoproteins

38
Q

Where is the majority of water absorbed?

A

Small intestine

39
Q

Compare the tight junctions of the colon vs. small intestine.

A

Small intestine: leaky- permits paracellular transport

Colon: tight- no paracellular transport (even water)

40
Q

What is the net absorption of salt in the ileum and jejunum?

A

Ileum: NaCl
Jejunum: NaHCO3-

41
Q

How are crypts different in function than the majority of cells lining the small intestine?

A

epithelial cells of the intestinal crypt SECRETE fluid and electrolytes

42
Q

Describe how Cl- channels in the apical membrane of the intestinal epithelial cells are normally regulated vs. in cholera.

A

Normal: hormones and neurotransmitters such as ACh and VIP bind to the basolateral receptors and activate adenylyl cyclase which increases cAMP production. cAMP opens the Cl- channels and causes Cl- secretion.

Cholera activates the Cl- channels via a different receptors and overwhelms the absorptive capacity of the villus cells causing life-threatening diarrhea.

43
Q

What cofactor is required for the absorption of calcium?

A

The active form of vitamin D: 1,25-dihydroxycholecalciferol

44
Q

WHat protein binds Ca2+ in the cell and allows it to be pumped across the basolateral membrane?

A

Calbindin D-28K

45
Q

What cofactor is required for the absorption of vitamin B12?

A

Intrinsic Factor

46
Q

What cells secrete intrinsic factor?

A

parietal cells

FHB Block 3 (26 decks)

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