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SFIV Test 1 > Digestion and Absorption > Flashcards

Digestion and Absorption Flashcards

1
Q

What must happen prior to the absorption of carbohydrates?

A

The must be digested into monosaccharides before being absorbed

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2
Q

Describe the digestion of carbohydrates prior to absorption

A

Starches conveted to malt-ose -triose and dextrins via pancreatic/salivary amylases

Brush border membrane enzymes hydrolyze these oligosaccharides to glucose

Sucrose, lactose, and trehalose also cleaved by brush border enzymes

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3
Q

What monosaccarhides are absorbed by the intestine?

A

Glucose

Galactose

Fructose

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4
Q

How are glucose and galactose absorbed?

A

Common Na-dependent active transport system (SLGT-1)

Almost all glucose/galactose absorbed and subsequently transported to blood via facilitated diffusion

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5
Q

How is fructose absorbed?

A

Exclusively by facilitated diffusion

Cannot go against concentration gradient

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6
Q

What is lactose intolerance?

A

Deficiency in lactase, causing lactose to remain in GI tract as unabsorbed solute

Undigested lactose metabolized by colonic bacteria

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7
Q

What is sucrase-isomaltase deficiency?

A

Inherited disorder resulting in an inability to digest sucrose and isomaltose

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8
Q

What is glucose/galactose malabsorption?

A

Deficiency in SLGT-1

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9
Q

What are the two sources of protein in the GI tract?

A

Endogenous - secretory proteins and cells shed into GI tract lumen

Exogenous - dietary protein

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10
Q

What are endopeptidases, exopeptidases, and brush border peptidases

A

Endopeptidases - hydrolyze interior peptide bonds

Exopeptidases - hydrolyze one amino acid at a time from C terminus

BB Peptidases - cleave peptides produced by pancreatic proteases to oligopeptides and AAs

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11
Q

Describe the process of pancreatic enzyme secretion and protein digestion

A

Pancreatic enzymes secreted as inactive precursors

Trypsinogen –> trypsin via enterokinase

Trypsin catalyzes conversion of trypsinogen, Chymotrypsinogen, and proelastase

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12
Q

How are amino acids absorbed?

A

Na-dependent cotransport

Separate transporters for neutral, acidic, basic, and imino acids

Transported to blood via facilitated diffusion

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13
Q

How are di- and tri-peptides absorbed?

A

H-dependent cotransporter peptide transporter 1 (PEPT1)

Following a meal, most protein is absorbed in form of di- and tri-peptides

Absorbed peptides are hydrolyzed in the enterocyte to AA’s

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14
Q

What is cystinuria?

A

Affects uptake of basic amino acids

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15
Q

What is Hartnup disease?

A

Affects uptake of neurtral amino acids

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16
Q

What is familial iminoglycinuria?

A

Affects uptake of proline and hydroxyproline

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17
Q

How are lipids digested in the stomach?

A

Mixing in stomach breaks lipids into droplets to increase total surface area

gastric lipase hydrolyzes triglycerides to diglycerides and FFA’s

CCK slows gastric emptying to allow sufficient time for digestion and absorption in duodenum

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18
Q

What is the role of bile salts and lecithin in the small intestine?

A

Emulsify fats

Emulsification requires neutral or slightly alkaline environment

19
Q

What is the function of pancreatic lipase?

A

Cleaves fatty acids from 1 and 3 positions of triglycerides

20
Q

What is the function of cholesterol ester hydrolase?

A

Cleaves fatty acid from cholesterol esters

Produces free cholesterol and gatty acid

21
Q

What is the function of Phospholipase A2?

A

Releases fatty acids from 2 position of phospholipids

produces lysophospholipids and FFAs

22
Q

What is colipase?

A

Non-enzymatic protein secreted as inactive precursor by pancreas

Activated by trypsin

Prevents inhibition of pancreatic lipase by bile salts, which displace enzyme from surface of emulsion droplet

23
Q

How are lipids absorbed?

A

Micelles bring products of lipolysis through the unstirred water layer directly to the lumenal membrane

Lipid products diffuse directly into the enterocyte

24
Q

What is the monoglyceride acylation pathway?

A

Triglycerides synthesized from 2 monoglycerides and CoA-activated fatty acids

Long-chain reesterified in smooth ER

Medium chain enter bloodstream without resynthesis into triglyceride

25
Q

What is the phosphatidic acid pathway?

A

Formation of phospholipids from ingested fats

26
Q

How is cholesterol absorbed?

A

Absorbed in free form

Significant portion re-esterified with fatty acids in enterocyte

All transported in chylomicrons

27
Q

How are chylomicrons formed and transported?

A

Resynthesized triglycerides, cholesterol and phospholipids

Transported out via exocytosis and enter lymphatic lacteals

Reach bloodstream via thoracic duct

28
Q

What can cause lipid malabsorption?

A

Failure to digest fat - unsecreted or inactivated pancreatic enzymes

Absence of bile salts

Decrease number of absorbing cells

Failure to synthesize apoproteins

29
Q

What can cause the absence of bile salts?

A

Liver disease

Common bile duct obstruction

Bacterial overgrowth of small intestine (leads to deconjugation)

Increased duodenal acidity

30
Q

What is gluten enteropathy (celiac sprue)?

A

Allergic reaction to gluten in wheat products

Leads to loss of villi in small intestine

Also causes malabsorption of carbs and proteins

31
Q

What is abetalipoproteinemia?

A

Failure to synthesize ApoB

Results in lack of formation of chylomicrons

32
Q

How is heme iron absorbed?

A

Most easily absorbed form

Taken up by receptor-mediated endocytosis or transporter protein HCP1

Heme then broken down by oxygenase to release free iron

33
Q

How is free iron absorbed?

A

Gastric acid dissolves iron and permits it to form soluble complexes with ascorbic acid

This reduces it to ferrous iron, which is more easily absorbed

Ferrous iron transported across brush border by DMT1

Binds to apoferritin for storage

34
Q

What is the function of duodenal cytochrome b?

A

Dcytb reduces ferric to ferrous iron, allowing it to be absorbed

35
Q

What is ferroportin?

A

Protein that transports iron out of the enterocyte into plasma

36
Q

How is iron absorption regulated?

A

Hepcidin regulates entery of iron into plasma by binding to ferroportin

This leads to internalization and degradation of ferroportin

This blocks cellular iron export and reduces plasma iron

37
Q

What regulation occurs in low and high iron states?

A

Low iron - low hepcidin, causing increased iron absoprtion and elevated iron release from enterocytes

High iron - high hepcidin, decrease iron export from enterocytes, enterocytes containing iron lost to intestine

38
Q

What is hemochromatosis?

A

Chronic absorption of too much iron

Defect in HFE gene causes hepcidin levels to drop

Excess iron collects in liver, leading to cirrhosis and cancer

Can also lead to diabetes and coronary disease

39
Q

How does aging affect the mouth?

A

Lose taste buds, chewing weakens, may lose teeth

40
Q

How does aging affect the esophagus?

A

Swallowing becomes more difficult, LES function declines

41
Q

How does aging affect the stomach?

A

Lose parietal cells

Increase in ulcers because increased use of NSAIDs

42
Q

How does aging affect the small intestine?

A

Decrease in motility

Increase in malabsorption

43
Q

How does aging affect the colon?

A

Decrease in motility

Increase in polyps

SFIV Test 1 (16 decks)

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