Gi Physiology - Digestion And Absorption

Front 1

Cellular pathway

Back 1

Absorption through intestinal epithelial cells (across apical and basolateral surfaces).

Front 2

Paracellular pathway

Back 2

Absorption between intestinal epithelial cells; must cross tight junctions between cells.

Front 3

Salivary amylase

Back 3

Breaks down starch into glucose. Minor role as it is quickly inactivated in low pH of stomach.

Front 4

Pancreatic amylase

Back 4

Functions in the small intestine to convert starch to disaccharides.

Front 5

Brush border disaccharidases

Back 5

Converts disaccharides to monosaccharides.

Front 6

SGLT1 and GLUTs

Back 6

Na-glucose transporter

Front 7

Pepsin

Back 7

Must be activated by low pH.
Works in the stomach to convert proteins to amino acids and peptides.
Not essential!

Front 8

Trypsinogen and trypsin

Back 8

Trypsinogen is cleaved by enterokinase to form active trypsin.

Front 9

Pancreatic proteases

Back 9

Function in the small intestine
Converts proteins to oligopeptides, short peptides, and amino acids.
Exopeptidases-remove amino acids from the C-termini of proteins.
Endopeptidases-cleave peptide bonds within proteins.

Front 10

Brush border peptidases

Back 10

Expressed on intestinal cell surfaces of the microvilli.
Convert oligopeptides to amino acids, dipeptides, and tripeptides.

Front 11

Cytosolic peptidases

Back 11

Expressed within intestinal epithelial cells.
Convert dipeptides and tripeptides to amino acids.

Front 12

Enterokinase

Back 12

Brush border enzyme that cleaves small amount of trypsinogen to form active trypsin; essential to occur in small intestine so pancreas isn’t autodigested.

Front 13

Lingual and gastric lipases

Back 13

Account for about 10% of lipid digestion.
Convert triglycerides to monoglyceride and fatty acids.

Front 14

Pancreatic lipase

Back 14

Secreted in active form
Works in the small intestine
Converts triglycerides to monoglycerides and fatty acids.

Front 15

Colipase

Back 15

Secreted by pancreas
Works in the small intestine to displace bile salts.
Increases access of pancreatic lipase to triglycerides.

Front 16

Cholesterol ester hydrolase

Back 16

Secreted in active form
Works in the small intestine
Convert cholesterol esters to cholesterol and fatty acids.

Front 17

Phopholipase A2

Back 17

Secreted in active form
Works in the small intestine to convert phospholipids to lysolecithin and fatty acids.

Front 18

What features contribute to the large, absorptive surface area of the small intestinal mucosa?

Back 18

From biggest to smallest:
- Folds of Kerckring
- Villi
- Microvilli
Increase surface area by 600 fold.

Front 19

How do intestinal features change from the duodenum to the ileum?

Back 19

They diminish as you move distally along the intestine. They are more prominent in the duodenum and less prominent in ileum.

Front 20

What are the ingested forms of carbohydrates?

Back 20

Starch
Disaccharides
Monosaccharides

Front 21

What are the digestive enzymes for carbohydrates?

Back 21

Salivary amylase
Pancreatic amylase
Disaccharidases

Front 22

What are the absorbable forms of carbohydrates?

Back 22

Fructose
Glucose
Galactose

Front 23

Where does the digestion and absorption of carbohydrates, protein and lipids take place?

Back 23

Small intestine

Front 24

What are the ingested forms of proteins?

Back 24

Proteins
Amino acids

Front 25

What are the digestive enzymes for proteins?

Back 25

Pepsin
Pancreatic proteases
Brush border peptidases
Cytosolic peptidases

Front 26

What are the absorbable forms of proteins?

Back 26

Amino acids
Dipeptides
Tripeptides

Front 27

What are the ingested forms of lipids?

Back 27

Triglycerides (fats and oils)
Cholesterol
Phospholipids

Front 28

What are the digestive enzymes for lipids?

Back 28

Lingual lipase
Gastric lipase
Pancreatic lipase
Colipase
Cholesterol ester hydrolase
Phospholipase A2

Front 29

What are the absorbable forms of lipids?

Back 29

Monoglycerides
Free fatty acids
Free cholesterol
Lysolecithin (packaged into mycelles)

Front 30

For carbohydrates and proteins, what type of transport is respectively needed for apical and basolateral transport of absorbable forms?

Back 30

Apical transport - co-transport with Na
- carbs via SGLT1
- proteins via H+

Basolateral transport - facilitated diffusion
- carbs via GLUT

Front 31

List the steps for lipid absorption in the correct order.

Back 31

1. Formation of micelles
2. Micelles contact brush border of intestinal cells
3. Re-esterification w/free fatty acids in cytosol
4. Packaged with apoproteins to form chylomicrons
5. Leave through basolateral membrane and picked up by lymphatic capillaries

Involves simple diffusion

Front 32

List the absorptive mechanism for fat-soluble vitamins.

Back 32

Vitamins A, D, E, K
- incorporated into micelles and chylomicrons, follow along with lipid absorption

Front 33

List the absorptive mechanism for water-soluble vitamins.

Back 33

B vitamains (except B12), Vit C, folic acid, biotin, etc.
- Utilize mostly Na+ co-transport

Front 34

Where is B12 absorbed?

Back 34

Ileum

Front 35

Micelles

Back 35

Products of lipid digestion composed primarily of bile salts.

Front 36

Chylomicrons and apoproteins

Back 36

Re-esterified lipids are packaged with apoproteins to form chylomicrons.
Apoproteins are necessary for chylomicron formation.

Front 37

Intrinsic factor

Back 37

Essential for B12 absorption in the ileum.

Front 38

Calbindin

Back 38

Synthesis is increased by Vitamin D.
Sponges up and binds to absorbed calcium.

Front 39

Apoferritin and transferrin

Back 39

Apoferritin binds free iron in cytosol and transports across basolateral membrane into blood.

Once in the blood, iron can bind to transferrin and be transported to storage sites in liver and ultimately to bone marrow for hemoglobin synthesis.