Digestion and Absorption in the GI Tract

Question 1

What do digestive juices do?

Answer 1

Breakdown of ingested food (digestion) and intake of the nutrients (absorption)

Question 2

Very little absorption occurs here

Answer 2

Stomach

Question 3

What are the folds of the intestinal mucosa called? And how much do they increase the surface area?

Answer 3

Valvulae Conniventes; 3-fold increase in absorptive mucosal surface area

Question 4

What is found inside the villi of the intestines? How much does villi increase the absorptive surface?

Answer 4

Lymph and blood vessels; 10-fold

Question 5

Where is the brush border found and what does it contain?

Answer 5

Each intestinal epithelial cell on each individual villus is covered with a Brush Border, which is characterized by as many as 1000 microvilli.
1 micrometer in length protruding into the lumen

Question 6

Absorption into the lymphatic system through the villi occurs through what structure

Answer 6

Central Lacteal

Question 7

Three major sources of dietary carbohydrates

Answer 7

Sucrose- A disaccharide known as table sugar

Lactose- A disaccharide found in dairy products

Starches- Large polysaccharides present in almost all non-animal foods (potatoes, corn, grains, etc.)

Question 8

Saliva contains an enzyme called _____ for digesting carbohydrates. What does this enzyme initiate?

Answer 8

Ptyalin (an amylase); initiate breakdown of starches

Question 9

What causes the activation of Salivary Amylase?

Answer 9

Low pH in the stomach

Question 10

20-40% of the starches will have been hydrolyzed to form _____, before what process can happen

Answer 10

Disaccharide Maltose; Salivary Amylase creation

Question 11

Carbs are very quickly digested in the duodenum by what enzyme

Answer 11

Pancreatic Amylase

Question 12

The Enterocytes that make up the Brush Border contain these four enzymes that split disaccharides further into monosaccharides.

Answer 12

Maltase, Alpha-Dextrinase, Lactase, and Sucrase

Question 13

Carbs must reach this state before intestinal absorption can occur

Answer 13

monosaccharide (almost all glucose)

Question 14

Which form of transport moves glucose into the intestinal cells to be absorbed? what molecule is involved?

Answer 14

Secondary active transport; Sodium moves with glucose into the cell

Question 15

Which mode of transport moves glucose from the basal surface of the epithelial cells into capillary blood flow?

Answer 15

Facilitated diffusion

Question 16

Digestion of proteins starts here, and uses what enzymes?

Answer 16

Stomach; hydrochloric acid and pepsin
The acid helps to denature and unfold protein structures.
Pepsin hydrolyzes large protein structures, such as collagen, into small peptones and polypeptides.

Question 17

What are Trypsin, chymotrypsin, and carboxypolypeptidase and what do they do?

Answer 17

Proteolytic pancreatic enzymes; breakdown proteins into small dipeptides or tripeptides or single amino acids.

Question 18

What controls the last stage of protein digestion?

Answer 18

Membrane protein peptidases within the microvilli of the enterocytes
These split the remaining polypeptides into smaller amino acid pieces (1, 2, or 3 AAs), which are easily transported into the cell.

Question 19

Transport utilized for Protein absorption

Answer 19

The majority of the digested proteins are brought into the cell using the secondary active cotransport using Sodium ions or Hydrogen ions as a co-transporter.

Question 20

Through _______ amino acids are absorbed into the vascular circulation for use by the body

Answer 20

Sodium-Amino Acid Transporter

Question 21

Dietary fats contain _______ the number of calories that we obtain from carbohydrates and proteins

Answer 21

Twice

Question 22

Digestion of fats primarily occurs here

Answer 22

duodenum and jejunum

Question 23

Fats become emulsified by what primarily?

Answer 23

Bile acids

Question 24

What does pancreatic lipase do to fat?

Answer 24

Pancreatic Lipase is an aggressive digestive enzyme that attacks the emulsified fat, hydrolyzing these fatty lipids into free fatty acids, monoglycerides, and cholesterol.

Question 25

Fat hydrolysis is highly reversible, so bile acids are available to quickly surround the digested fat, creating _____

Answer 25

Micelles

Question 26

Micelles act as a good transport medium for ____

Answer 26

cholesterol, glycerides, and fatty acids

Question 27

Where are triglycerides formed and how?

Answer 27

In the intestinal epithelial cells, fatty acids link with glycerol to form triglycerides

Question 28

What structure in the cell forms chylomicrons?

Answer 28

Within the Golgi, globules of triglycerides and cholesterol are coated with proteins to form Chylomicrons (transport lipoprotein).

Question 29

The intestines must absorb roughly _____ grams of sodium each day to prevent a net loss

Answer 29

25-35 grams

Question 30

Large amounts of sodium can be lost with _____

Answer 30

Diarrhea

Question 31

How is water absorbed from the intestines?

Answer 31

Diffusion, following the laws of Osmosis

Question 32

Where does osmotic leakage occur?

Answer 32

Through the paracellular tight junctions, as well as through the cell itself (transcellular).

Question 33

What are Bicarb-Chloride exchangers and where are they found?

Answer 33

Bicarb-Chloride exchangers in the epithelium result in fecal excretion of Bicarbonate, which is needed to neutralize the acidic end products of bacterial action in the colon.

Question 34

Where does the brown color of feces come from? The odor?

Answer 34

Color: Derivatives of Bilirubin being excreted
Odor: Bacterial action (gas production)

Question 35

Water absorption maxes out at _____ daily

Answer 35

5-8 liters daily

Question 36

An infection like cholera can cause what with water secretion?

Answer 36

The crypts may secrete 10+ liters per day! Major dehydration possible

Question 37

Epidemiology of Celiac Disease

Answer 37

Most prevalent in Western Europe and the United States.
Bimodal distribution of age at diagnosis:
8-12 months of age
20-40 years of age
Symptoms may become apparent in young infants when they start eating gluten foods.
Symptoms may persist throughout childhood if untreated and then usually diminish in adolescence.
Symptoms then often reappear between 20-40 years of age.

Question 38

What is Celiac Disease?

Answer 38

Also known as Gluten-Sensitive Enteropathy or Celiac Sprue, this is a chronic digestive disorder characterized by the inability to tolerate Gliadin, an alcohol soluble fraction of gluten.

Question 39

How is Celiac Disease diagnosed? How is it managed?

Answer 39

Lab studies are the best initial test:
Anti-Tissue Transglutaminase (tTG IgA)
Most common and best predictive value of serology tests
Upper Endoscopy with at least 6 duodenal biopsies is confirmatory.
Management: completely gluten free diet (It takes generally 4-8 weeks of a Gluten-Free diet for patients to notice a difference in their symptoms)

Question 40

What is Gliadin and what is it’s role in celiac disease?

Answer 40

Gliadin - an alcohol soluble fraction of gluten.
Gliadin-tTG complex is inappropriately presented to helper T cells, which mediates an inflammatory response and antibodies against Gliadin-tTG.
The inflammatory cytokines released into the intestinal epithelium, as well as the presence of antibodies against Gliadin-tTG, triggers epithelial invasion by Lymphocytes, resulting in destruction of the absorptive surface of the intestine.