Intro to digestion and absorption

Question 1

Digestion

Answer 1

The breakdown of larger molecules to simpler, smaller chemical compounds that can be absorbed

Question 2

Digestion is complete when…

Answer 2

molecules are small enough to be absorbed

Question 3

3 main types of digestion

Answer 3

1. physical/mechanical digestion
2. chemical digestion
3. enzymatic digestion - primary importance

Question 4

4 ways in which physical digestion occurs

Answer 4

1. chewing (mastication)
2. grinding in the GI tract (gizzard, birds only)
3. omasum - ruminant only
4. digestive turbulence (stomach rumbles)

Question 5

Chemical digestion (2)

Answer 5

1. HCl - produced in the stomach, digest protein
2. bile acids - produced by the liver, and function in lipid digestion and absorption

Question 6

Enzymatic digestion

Answer 6

• proteins make up the enzymes
• enzymes have specific substrates
• work within a narrow set of conditions (pH)
• require cofactors
• function via hydrolysis

Question 7

Absorption

Answer 7

a set of processes that result in the passage of small molecules from the lumen (interior) of the gut through cells of the GI tract to the bloodstream

Question 8

The best way to make absorption more efficient is….

Answer 8

to increase surface area via intestinal modification (villi and microvilli)

Question 9

microvilli are also called…

Answer 9

the brush border of the intestine

Question 10

Types of absorption (5)

Answer 10

1. passive diffusion
2. active transport
3. secondary active transport
4. facilitated diffusion
5. phagocytosis

Question 11

Passive diffusion

Answer 11

substances move down concentration gradient (from high -> low concentration)
does NOT require energy

Question 12

Active transport

Answer 12

absorption from the lumen to an intestinal cell AGAINST the concentration gradient (from low concentration -> high concentration)
requires a carrier protein and energy (ATP)

Question 13

Secondary active transport

Answer 13

requires a transport protein
indirectly requires energy - Na/K pump creates the gradient of sodium and potassium
moving one substance (usually sodium) down the concentration gradient in exchange for moving another molecule against the concentration gradient (like glucose)

Question 14

facilitated diffusion

Answer 14

requires a carrier protein, but not energy
molecules move down concentration gradient (high->low concentration)

occurs when molecules are too large/polar/etc to diffuse through the membrane by itself

Question 15

phagocytosis

Answer 15

occurs when a part of a villi cell breaks off and engulfs a nutrient
does not require digestion
occurs soon after birth as the infant absorbs antibodies from colostrum - MOST COMMON
phagocytosis stops a few days after birth

Question 16

Nutrient metabolism/metabolic pathways are basically the same across species but….

Answer 16

nutritional requirements, diet type, and digestion varies

this is because digestive tract morphology determines what an animal can consume