Lecture 41 11/27/23

Question 1

What is digestion?

Answer 1

breaking down complex nutrients to simple molecules

Question 2

What is absorption?

Answer 2

transporting simple molecules across intestinal epithelium

Question 3

Which three features increase intestinal surface area?

Answer 3

-plicae circulares
-villi
-brush border

Question 4

What are the characteristics of enterocytes?

Answer 4

-epithelial cells covering villi and crypts
-apical membrane faces intestinal lumen and contains microvilli
-basolateral membrane allows nutrients to exit into the bloodstream

Question 5

What are the characteristics of enterocyte tight junctions?

Answer 5

-connect the apical half of enterocytes
-allow passage of water and electrolytes

Question 6

Which substances are found at the small intestinal surface/diffusion layer?

Answer 6

-mucus
-glycocalyx
-unstirred water layer

Question 7

What are the functions of physical breakdown of food?

Answer 7

-allows food to flow through intestinal space
-enlarges surface area for chemical digestion

Question 8

What is hydrolysis?

Answer 8

splitting of chemical bond through insertion of water

Question 9

What are the characteristics of the luminal phase of digestion?

Answer 9

-occurs first
-enzymes originate from major GI glands
-mix with ingesta in gut lumen
-incomplete hydrolysis

Question 10

What are the characteristics of the membranous phase of digestion?

Answer 10

-occurs second
-enzymes bound to epithelial surface
-complete hydrolysis

Question 11

How do simple and complex carbohydrates differ?

Answer 11

-simple carbs have one molecular unit
-complex carbs have 2+ molecular units

Question 12

What is a starch?

Answer 12

-polymeric carbohydrate
-large number of glucose units
-alpha [1,4] glycosidic bonds

Question 13

What is a fiber?

Answer 13

-non-starch polysaccharide
-beta [1,4] glycosidic bonds
-undigestible by mammals

Question 14

Which enzyme mediates luminal starch digestion?

Answer 14

alpha-amylase from the pancreas/salivary glands

Question 15

Which type of breakdown happens in the luminal phase?

Answer 15

breakdown of starch by amylase

Question 16

Which type of breakdown happens in the membranous phase?

Answer 16

breakdown of sugars into glucose by specific enzymes (ex. maltose broken down by maltase)

Question 17

Which nutrient is provided by proteins?

Answer 17

amino acids

Question 18

What are the characteristics of luminal protein digestion?

Answer 18

-HCl begins the process
-requires a large number of different enzyme types due to the different AA combinations

Question 19

What are the characteristics of dietary fats?

Answer 19

-triglycerides are the most abundant type
-most digestion occurs in small intestine

Question 20

What are the four phases of lipid assimilation?

Answer 20

-emulsification
-hydrolysis
-micelle formation
-absorption

Question 21

What is emulsification?

Answer 21

physical breakdown of fat globules into a smaller size to promote contact with digestive enzymes

Question 22

How is emulsification done in the stomach?

Answer 22

grinding and mixing

Question 23

How is emulsification done in the intestines?

Answer 23

bile salts and phospholipids

Question 24

How do bile salts and phospholipids emulsify fats?

Answer 24

-fat soluble ends break down the fat globule surface
-hydrophilic ends stick out and make the globules more water soluble/easier to break apart

Question 25

Which enzyme is used to emulsify triglycerides?

Answer 25

pancreatic lipase

Question 26

What does pancreatic lipase emulsify triglycerides into?

Answer 26

2-MAG and FFAs

Question 27

What is the role of cholesterol esterase?

Answer 27

cholesterol digestion

Question 28

What is the role of phospholipase A2?

Answer 28

phospholipid digestion

Question 29

What are the characteristics of triglyceride breakdown?

Answer 29

co-lipase makes a path for lipase to penetrate bile-coated triglycerides
-lipase hydrolyzes the triglycerides into FFAs and 2-MAG

Question 30

What is a micelle?

Answer 30

globular structure with polar head groups on the outside and hydrophobic fatty acyl chains on the inside

Question 31

How are micelles formed?

Answer 31

bile salts bind with hydrolyzed lipid products to form micelles

Question 32

What happens to dietary fat in the stomach?

Answer 32

warming and mixing to form liquid fat globules

Question 33

What happens to dietary fat in the duodenum?

Answer 33

exposure to bile leads to production of emulsified fat droplets

Question 34

What happens to dietary fat in the jejunum?

Answer 34

-lipase, co-lipase, and bile components lead to micelle formation
-diffusion of micelles through unstirred water layer allows direct transport of micelle components (except bile acids) into enterocytes

Question 35

What happens to dietary fat in the ileum?

Answer 35

bile acid absorption occurs through sodium co-transport

Question 36

What is the main function of micelle formation?

Answer 36

to allow small lipids to cross the unstirred water layer

Question 37

What are the characteristics of bile acid absorption?

Answer 37

-occurs in ileum
-co-transport with sodium
-portal circulation to the liver allows for recycling

Question 38

What are the characteristics of chylomicron formation?

Answer 38

-occurs within enterocyte
-micelle lipids go to ER and are reformed into triglycerides and phospholipids
-packaged with cholesterol and other proteins to form chylomicrons

Question 39

Where are chylomicrons absorbed?

Answer 39

into lymphatic circulation