GI digestion and absorption

Question 1

Enterocyte Surface Enzymes that Covert Small Polysaccharides to Sugar Monomers:

Isomaltase (alpha-dextrinase) – does what specifically?

Answer 1

converts alpha-limit dextrins to glucose

Question 2

Enterocyte Surface Enzymes that Covert Small Polysaccharides to Sugar Monomers: Maltase does what specifically?

Answer 2

converts maltose and maltotriose to glucose

Question 3

Enterocyte Surface Enzymes that Covert Small Polysaccharides to Sugar Monomers: Lactase – does what specifically?

Answer 3

converts lactose to glucose and galactose

Question 4

Enterocyte Surface Enzymes that Covert Small Polysaccharides to Sugar Monomers:Sucrase – does what specifically?

Answer 4

converts sucrose to glucose and fructose

Question 5

Enterocyte Surface Enzymes that Covert Small Polysaccharides to Sugar Monomers:
Trehalase – does what specifically?

Answer 5

converts trehalose to glucose

Question 6

_______ is the major enzyme in saliva and pancreatic secretions

Answer 6

Amylase

Question 7

________ is never the product of amylase digestion

Answer 7

free glucose

Question 8

amylases breaks down starches into _____

Answer 8

Maltose
Maltotriose
Alpha-limit dextrin

Question 9

what happens with lactose intolerance when you ingest lactose

Answer 9

Missing the brush border enzyme, lactase

Causes gas and diarrhea due to colonic bacterial digestion of lactose

Question 10

what is the SGLT1 transporter

Answer 10

Transports glucose & galactose across the apical membrane of the enterocyte,
Requires sodium as a co-transporter

Question 11

Fructose transport across the apical surface via ______ is sodium-independent

Answer 11

GLUT 5

Question 12

Glucose & galactose use the same transporter as fructose on the basolateral surface: __________

Answer 12

GLUT 2 – not Na+ dependent

Question 13

describe the 4 uptake pathways for protein

Answer 13

Sodium dependent co-transporters that utilize the N+/K+ ATPase gradient are the major route for the different classes of amino acids. Water follows.

Sodium independent transporters of amino acids

Specific carriers for small peptides (di- and tri-) linked to H+ uptake (co-transporter; example is PEP T1)

Pinocytosis of small peptides by enterocytes (infants)

Question 14

Name the Five major pancreatic proteases that are secreted in the small intestine as inactive precursors:

Answer 14

• Trypsinogen
• Chymotrypsinogen
• Pro-elastase
• Pro-carboxypeptldase A
• Pro-carboxypeptidase B

Question 15

________ are the most abundant fat in our diet

Answer 15

Triglycerides

Question 16

Triglycerides cannot be efficiently absorbed, and are enzymatically digested by pancreatic _____ into a 2-monoglyceride and two free fatty acids, all of which can be absorbed

Answer 16

lipase

Question 17

What does colipase do,

Answer 17

a protein that helps to anchor lipase to the surface of the droplets

Question 18

Inside the enterocytes, triglycerides are re-synthesized from monoglycerides and fatty acids. They are then packaged into lipoprotein particles called ________

Answer 18

chylomicrons

Question 19

In addition to containing triglycerides, chylomicrons contain ________

Answer 19

phospholipids,

cholesterol (also absorbed from micelles), apolipoproteins

Question 20

Inadequate triglyceride digestion results in ______

Answer 20

steatorrhea (excessive loss of fat in the stool)

Question 21

Fat soluble vitamins (A, E, D, K) are absorbed along the length of the small intestines and are carried in _____ and form _______ similar to dietary lipids.

Answer 21

micelles,

chylomicrons

Question 22

Water soluble vitamins either enter the enterocyte by ________(biotin, folic acid) or via specific transporters (e.g. _______)

Answer 22

simple diffusion,

Vit B12

Question 23

describe 3 Fat malabsorption digestive disorders

Answer 23

1) Liver disease with bile salt deficiency: patients with chronic liver disease cannot make micelles.
2) Pancreatic insufficiency: patients with chronic pancreatitis and cystic fibrosis lack enzymes to digest fat.
3) Weight loss medication: new anti-obesity drugs inhibit lipase activity resulting in fat malabsorption and so-called “anal leakage”.

Question 24

There is a net fluid _____ from cells in the intestinal crypts.

Answer 24

secretion

Question 25

there is a net fluid ______ from enterocytes on the villi.

Answer 25

absorption

Question 26

In the ileum, Most Cl- is absorbed by a transcellular pathway involving ______

Answer 26

Cl-/HCO3- exchange in the apical membrane, and facilitated diffusion across the basolateral membrane.

Question 27

In the duodenum and jejunum, the absorption of sugars and amino acids in co-transport with Na+ causes Cl- to follow for _____reasons, and H2O to follow for ______ reasons. Cl- and H2O move across the epithelium by ______ pathways.

Answer 27

electrical , osmotic paracellular

Question 28

the primary active transport process that drives all subsequent absorption processes is the ______

Answer 28

Na+/K+-ATPase

Question 29

Na is Absorbed all along the intestine, with most absorption in the _______ (60-80%).

Answer 29

jejunum

Question 30

Impaired absorption of B12 leads to a disease called

Answer 30

pernicious anemia

Question 31

give 3 examples of Osmotic diarrhea which is caused by impaired digestion or defects in absorption

Answer 31

- Lactase deficiency - Ileal resection – bile salts not absorbed - Celiac disease (Sprue) with gluten sensitivity (gliaden- induced destruction of villi)

Question 32

describe the pathophysiology of Secretory diarrhea

Answer 32

May be caused by Vibrio cholerae. Increases cAMP levels in cells and this in turn activates the CF chloride channel, (and thus water) on the luminal surface

Question 33

what are the 3 classes of diarrhea

Answer 33

motility disoreder osmotic diarrhea secretory diarrhea

Question 34

what does Oral rehydration therapy consist of

Answer 34

antibiotics plus KHCO3 to prevent hypokalemia and metabolic acidosis, glucose (or amino acids) with NaCl to facilitate the absorption of electrolytes and water