Physio: Gi - Carb Digestion And Absorption

Front 1

Describe the roles of mastication and salivary amylase in the oral cavity during carb digestion in monogastrics.

Back 1

Mastication: decreases particle size and increases area for enzyme digestion.

Salivary amylase converts starch (~5%) to maltose and smaller oligosaccharides (pigs, dogs?).

Front 2

Describe the role of salivary amylase in the corpus and fundus during carb digestion in monogastrics.

Back 2

Converts starch (~30%) to maltose and smaller oligosaccharides - imp in pigs. Rapidly inactivated by low pH.

Front 3

Describe the role of pancreatic amylase in the intestine during carb digestion in monogastrics.

Back 3

Converts remaining starch and polysaccharides to monosaccharides.

Front 4

What occurs during the luminal phase of intestinal digestion in monos and ruminants?

Back 4

Enzymes active in gut lumen.

Digestive enzymes from salivary, gastric, pancreatic glands work to break down large polymers (starch, protein).

Front 5

What occurs during the membranous phase of intestinal digestion in monos and ruminants?

Back 5

Enzymes active at surface of gut.

Digestive enzymes, synthesized in enterocytes and attached to apical memb, work to break down small polymers (polysaccharides, peptides).

Result: monomers suitable for absorption.

Front 6

In monos and ruminants, list the following for SGLT1:

-major location

-functions

Back 6

Kidney, intestine

Glucose reabsorption in intestine and kidney

Front 7

In monos and ruminants, list the following for SGLT2:

-major location

-functions

Back 7

kidney

low affinity - high selectivity for glucose

Front 8

In monos and ruminants, list the following for SGLT3:

-major location

-functions

Back 8

SI, skeletal muscle

glucose-activated Na+ channel

Front 9

In monos and ruminants, list the following for GLUT1:

-maj location

-function

Back 9

Ubiquitous: RBC, brain, eye, mammary gland

Basal glucose uptake; transport across blood-tissue barrier

Front 10

In monos and ruminants, list the following for GLUT2:

-maj location

-function

Back 10

Liver, kidney, pancreas, SI

High capacity low-affinity transport

Front 11

True or false?

GLUT1 is tightly regulated.

Back 11

False

Front 12

In monos and ruminants, list the following for GLUT3:

-maj location

-function

Back 12

Brain, nerve cells

Neuronal transport

Front 13

In monos and ruminants, list the following for GLUT4:

-maj location

-function

Back 13

muscle, fat, heart

Insulin-regulated transport in muscle and fat.

Front 14

What makes GLUT4 unique among the facilitative glucose transporters?

Back 14

Requires insulin

Not found in GIT

Front 15

In monos and ruminants, list the following for GLUT5:

-maj location

-func

Back 15

Intestine, kidney, testis

Fructose transport

Front 16

In monos and ruminants, list the following for GLUT7:

-maj location

-func

Back 16

SI, colon, testis

Fructose transport

Front 17

In monos and ruminants, list the following for GLUT8:

-maj location

-func

Back 17

Testis, blastocyst, brain, muscle, fat

Fuel for mature sperm; insulin-responsive transport in blastocyst

Front 18

In monos and ruminants, list the following for GLUT11:

-maj location

-func

Back 18

Heart and muscle

Muscle-specific; fructose transporter

Front 19

What is the first step of intestinal sugar absorption in monos and ruminants?

Back 19

AKA solvent drag

Occurs at high luminal glucose concs (<25mM)

Front 20

Describe the facilitative transport aspect of active transport during intestinal sugar absorption in monos and ruminants.

Back 20

GLUT1-12

Fructose transport (GLUT5): insignificant in ruminants

GLUT1: ubiquitous, basal

GLUT4: insulin sensitive, fat and muscle

Front 21

Describe the sodium dependent glucose transport (SGLT1-3) aspect of active transport during intestinal sugar absorption in monos and ruminants.

Back 21

High affinity (Km>100uM), low capacity (50-200 cycles/sec.

Distributed throughout GIT (greatest activity in jejunum)

Transports 1 glucose + 2 water molecules for 2Na+

Rapidly inducible by glucose (eg high grain diets)

Front 22

How do spp differ in regards to expression of SGLT1 and disaccharidases (sucrase, maltase, lactase), and capacity to digest and absorb?

Back 22

Dogs > cats (cats aren't very good at digesting carbs)

Front 23

In ruminants, where is carb digestion the most efficient?

Back 23

SI (90%)

LI (80%)

rumen (60% - efficiency lower in rumen bc of fermentation)

Front 24

What are the 5 requirements for fermentation?

Back 24

1. Substrate

2. Microbes

3. Mixing and propulsion

4. Fermentation end prods

5. Stable intraruminal conditions

Front 25

What are 4 conditions that make the rumen stable?

Back 25

1. optimum T: 37 degrees C

2. osmolality: 300 mOsm (slightly hypotonic compared to blood)

3. pH ~6.4

4. anaerobic: most microbes (protozoa) are strictly anaerobic; neg REDOX potential (-250 to -450 mV)

Front 26

What is the function of protozoan rumen microbes?

Back 26

Ingest and digest feed particles: produce VFA, CO2, NH3.

Front 27

What do protozoan rumen microbes store?

Back 27

Feed particles: CHO, fat, protein. Delay digestion.

Front 28

Where are protozoan rumen microbes stored?

Back 28

In both liquid and solid phases (ingest bacteria).

Front 29

Approximately how many protozoan rumen microbes are in the rumen? How big are they?

Back 29

~51% of microbial V

10^4-10^6/gram of rumen contents.

Front 30

How pH-sensitive are protozoan rumen microbes?

Back 30

Highly pH-sensitive. #s decrease when pH too high, eg on high-grain diets.

Front 31

What is the function of bacterial rumen microbes?

Back 31

Fermenting CHO, fat, protein to produce VGA, CO2, and NH3. (At least 28 diff spp.)

Front 32

What do bacterial rumen microbes store?

Back 32

Basically nothing.

Front 33

Where in the rumen do bacterial rumen microbes live?

Back 33

Free-living in rumen fluids; loosely/firmly attached to feed particles, protozoa and fungi; attached to rumen epithelium (fungi - mainly for fiber digestion).

Front 34

How many bacterial rumen microbes live in a rumen? How big are they?

Back 34

10^11-10^12 cells/gram of rumen contents. ~48% of microbial V.

Front 35

How pH-sensitive are bacterial rumen microbes?

Back 35

Some strains are pH-resistant.

Front 36

Where does stage I of VFA synthesis via rumen fermentation take place?

Front 37

What happens during stage I of VFA synthesis?

Front 38

Where does stage II of VFA synthesis occur?

Front 39

What happens during stage II of VFA synthesis?

Front 40

Where does stage III of VFA synthesis occur?

Front 41

What happens during stage III of VFA synthesis?

Front 42

Where does stage IV of VFA synthesis occur?

Front 43

What happens during stage IV of VFA synthesis?

Front 44

How does the amount of total VFA produced in the rumen change as the diet changes from forage-based to concentrate-based?

Front 45

How does the amount of propionic acid produced in the rumen change as the diet changes from forage-based to concentrate-based?

Front 46

How does the amount of acetic acid produced in the rumen change as the diet changes from forage-based to concentrate-based?

Front 47

How does the amount of butyric acid produced in the rumen change as the diet changes from forage-based to concentrate-based?

Front 48

How does rumen pH change as the diet changes from forage-based to concentrate-based?

Front 49

How does milk production and composition change as the diet changes from forage-based to concentrate-based?

Front 50

What is the first step of VFA absorption? Are VFAs entering or exiting the epithelial cell?

Back 50

Entering.

Undissociated short chain fatty acids (HSCFA) diffuse into the cell:

-mainly lipophilic acids (eg butyric); efficient absorption

-acids rapidly release their protons once inside the cell

Front 51

What is the second step of VFA absorption? Are VFAs entering or exiting the epithelial cell?

Back 51

Entering.

SCFA (acetic, propionic, and butyric acid) transporters:

-exchange of anions (SCFA-) w bicarb for apical uptake

-imp for acids w less lipophilicity (eg acetate)

mainly driven by bicarb imported from blood via Na/bicarb-cotransport. The apically-exported bicarb neutralizes one H+ in the rumen.

(Bicarb produced by carbonic anhydrase in ruminal epithelium.)

Front 52

What is the third step of VFA absorption? Are VFAs entering or exiting the epithelial cell?

Back 52

Entering.

Lactate anions can enter the cell in cotransport w their protons.

Front 53

What is the fourth step of VFA absorption? Are VFAs entering or exiting the epithelial cell?

Back 53

Exiting.

Diffusion of lipophilic and undissociated HSCFA.

Front 54

What is the fifth step of VFA absorption? Are VFAs entering or exiting the epithelial cell?

Back 54

Exiting.

Anion channel permeable to large anions (Cl-).

Front 55

What is the sixth step of VFA absorption? Are VFAs entering or exiting the epithelial cell?

Back 55

Exiting

SCFA-/bicarb exchange

Front 56

What is the seventh step of VFA absorption? Are VFAs entering or exiting the epithelial cell?

Back 56

Butyrate : metabolized extensively to ketone bodies (BHBA and acetoacetate)

Propionate: metabolized partly to lactate inside cells.

Prods expelled together w their protons acrss the basolateral memb via monocarbocylate transporter 1 (MCT1).

Front 57

What is the eighth step of VFA absorption? Are VFA entering or exiting the epithelial cell?

Back 57

H+ taken up w HSCFA or lactic acid can either be neutralized by bicarb from basolateral Na/bicarb-cotransport

OR

expelled by Na/H exchange across the apical or basolateral memb.

Na/K ATPase at basolateral memb provides E for all Na-driven transport.

Front 58

What is partially responsible for replenishing the bicarb and H+ pool inside the ruminal epithelial cell?

Back 58

The barbonic anhydrase rxn (from CO2).