Digestion and Absorption in the GI Tract

Question 1

What causes lactose intolerance?

Answer 1

when the brush border lactase enzyme activity is deficient or absent, which results in undigested and unabsorbed lactose

Question 2

what happens when lactose is unabsorbed?

Answer 2

it is converted to SCFAs and hydrogen gas in the SI; it remains in the lumen

Question 3

how do you get osmotic diarrhea with lactose intolerance?

Answer 3

the lactose remains in the lumen and holds H20 in the lumen as well and that is what causes the osmotic diarrhea

Question 4

what does the lactose ferments into?

Answer 4

methane and H+ gas

Question 5

what breaks down starches in the mouth?

Answer 5

salivary amylase

Question 6

what is starch broken down into?

Answer 6

maltose and then the maltose is broken into glucose

Question 7

where does most of the starch breakdown occur?

Answer 7

in the small intestine

Question 8

what breaks down the starch in the small intestine?

Answer 8

pancreatic amylase

Question 9

the lumen surface of the small intestine is arranged in longitudinal folds known as what?

Answer 9

folds of Kerckring

Question 10

where are villi longest?

Answer 10

in the duodenum

Question 11

what is lactose normally broken down into?

Answer 11

glucose and galactose

Question 12

how does glucose and galactose get into the epithelial cell of the SI duodenum from the lumen?

Answer 12

through the SGLT1 co-transporter- secondary active transporter

Question 13

how does fructose get into the epithelial cells of the SI duodenum?

Answer 13

through the GLUT5 transporter- facilitated diffusion

Question 14

how does glucose, galactose, and fructose get into the blood?

Answer 14

GLUT2 transporter (facilitated transport)

Question 15

what could be used to reduce glucose absorption into the epithelial cell?

Answer 15

sotagliflozin

Question 16

how can you test for a carbohydrate assimilation disorder (global)?

Answer 16

you can administer D-xylose- it should be in the urine; if you have an absorption issue and you aren’t absorbing the sugars, the d-xylose will not be absorbed- it will go through the SI and end up in the feces

Question 17

how can you test for a specific sugar enzyme deficiency?

Answer 17

you can use a hydrogen breath test

Question 18

what are the five protein assimilation disorders we discussed?

Answer 18

chronic pancreatitis, congenital trypsin absence, cystinuria, hartnup disease, and cystic fibrosis

Question 19

what does chronic pancreatitis lead to?

Answer 19

deficiency of pancreatic enzymes (lack of proteases e.g. trypsinogen)

Question 20

what does congenital trypsin absence lead to?

Answer 20

the absence of all pancreatic enzymes

Question 21

why does congenital trypsin absence lead to the absence of all pancreatic enzymes?

Answer 21

pancreatic enzymes are secreted as zymogens and activated by either enterokinase (aka TRYPSINOGEN) or trypsin itself

Question 22

what is defected in cystinuria?

Answer 22

SLC3A1 or SLC7A9

Question 23

what is a sign of cystinuria?

Answer 23

AA secreted into the feces or urine

Question 24

what are three important symptoms of hartnup disease?

Answer 24

3 Ds: diarrhea, dermatitis, and dementia

Question 25

what results will you see with Hartnup's disease?

Answer 25

they will have urinary excretion of tryptophan

Question 26

what are some CFTR mutations associated with?

Answer 26

loss of HCO3- secretion; therefore they can't move enzymes from the ducts, acute or chronic pancreatitis

Question 27

what are the brush border enzymes that break down proteins?

Answer 27

aminopolypeptidase and dipeptidases

Question 28

how are amino acids transported into the epithelial cell of the small intestine from the lumen?

Answer 28

Na+-AA cotransporter

Question 29

how are dipeptides and tripeptides transported into the epithelial cell of the small intestine from the lumen?

Answer 29

H+ dependent cotransporter

Question 30

once inside the epithelial cell of the small intestine, what happens to most of the di-/tri- peptides?

Answer 30

they are hydrolyzed to amino acids by peptidase

Question 31

how do the amino acids get out of the epithelial cell of the small intestine into the blood?

Answer 31

via facilitated diffusion (separate for each amino acid)

Question 32

what does celiac sprue/ disease lead to?

Answer 32

the destruction of small intestine villi (atrophy) and hyperplasia of the intestinal crypts

Question 33

what are the common malabsorption deficiencies associated with celiac's?

Answer 33

folate, iron, calcium, and vitamins A B12 and D

Question 34

what is tropical sprue and what is it caused by?

Answer 34

it is a loss or decreased number of intestinal epithelial cells; intestinal infection

Question 35

what are the nutritional deficiencies associated with tropical sprue?

Answer 35

folate and vitamin B12

Question 36

what is the major symptom of tropical sprue?

Answer 36

diarrhea

Question 37

how do you treat tropical sprue?

Answer 37

tetracycline and folate for 6 months

Question 38

what is the digestion of lipids complicated by?

Answer 38

their insolubility

Question 39

what is the effect of CCK on the stomach?

Answer 39

it inhibits gastric emptying

Question 40

where does most of the digestion of lipids occur?

Answer 40

in the small intestine

Question 41

what is pancreatic lipase inactivated by?

Answer 41

by bile salts

Question 42

what is needed to reactivate the pancreatic lipase?

Answer 42

colipase (which is activated by trypsin)

Question 43

once the fatty acids are are emulsified by the micelle, how do they get into the epithelial cell of the small intestine from the apical membrane?

Answer 43

there is diffusion of the micellar content across the apical membrane

Question 44

what happens to the products of lipid digestion once inside the intestinal epithelial cells?

Answer 44

they are reesterified

Question 45

Inside the epithelial cells of the small intestine, what are the reesterified lipids packaged with and what do these form?

Answer 45

they are packaged with apoproteins and form chylomicrons

Question 46

failure to synthesize Apo B leads to what?

Answer 46

abetalipoproteinemia, aka no lipid absorption

Question 47

what happens to the chylomicrons?

Answer 47

they are exocytosed into the lymphatics

Question 48

problems anywhere along the path of lipid digestion/absorption leads to what?

Answer 48

steatorrhea

Question 49

What could lead to problems with lipid digestion/absorption? associated with pancreatic enzyme secretion

Answer 49

pancreatitis, pancreatic insufficiency, or zollinger-ellison syndrome (improper acidity in the duodenum contents)

Question 50

what are two main causes of SIBO?

Answer 50

too little gastric secretion and small intestine dysmotility

Question 51

what effect does SIBO have on bile salts?

Answer 51

they deconjugate them, so they will not be able to emulsify lipids/micelle formation, leads to lipid digestion/absorption issues

Question 52

how can you diagnose SIBO?

Answer 52

use a breath test and test for methane and hydrogen

Question 53

what are the water-soluble vitamins?

Answer 53

b vitamins and vitamin C

Question 54

when does intrinsic factor bind to the vitamin b12?

Answer 54

not until the small intestine (ileum)

Question 55

what are the symptoms of a vitamin B12 deficiency?

Answer 55

pernicious anemia, weakness, and nerve conductance issues

Question 56

what is the common cause of pernicious anemia?

Answer 56

atrophic gastritis

Question 57

what does vitamin d deficiency result in?

Answer 57

inadequate calcium absorption

Question 58

how does Fe2+ get out of the enterocyte/ where is the regulation at?

Answer 58

through ferroportin

Question 59

what is the absorption like in the jejunum?

Answer 59

lots of sodium is absorbed

Question 60

what is the absorption like in the ileum?

Answer 60

sodium is absorbed and HCO3- is secreted

Question 61

what is the absorption/secretion like in the colon?

Answer 61

Na absorption and K secretion

Question 62

what is the effect of cholera?

Answer 62

it increases cAMP, which results in increased Cl- secretion

Question 63

in cholera, what does the resulting Cl- secretion accompanied by?

Answer 63

secretion of Na+ and H20

Question 64

what does cholera lead to?

Answer 64

massive secretory diarrhea--> look for chloride