Guyton Phys 65: Digestion And Absorption In The Gi Tract

Front 1

Most carbohydrates of the diet are…

Back 1

large polysaccrides or disaccharides

Front 2

Process of separating poly/disaccharides

Back 2

hydrolysis

Front 3

Most fats in diet are…

Back 3

triglyccerides

Front 4

What are triglycerides composed of

Back 4

glycerol plus fatty acids

Front 5

3 major sources of carbohydrates

Back 5

sucrose, lactose, starches (others: amylose, glycogen, alcohol, lactic acid, pyruvic acid, pectins, dextrins, carbohydrate derivatives in measts)

Front 6

What enzymes does saliva contain

Back 6

ptyalin (alpha-amalase secreted by parotid glands);

Front 7

No more than what percent of food is hydrolyzed in the mouth

Back 7

5%

Front 8

How long can food continue digesting in stomach before mixing with gastric secretions

Back 8

1 hour

Front 9

What pH does salivary amalase become inactive

Back 9

4

Front 10

how much starch is hydrolyzed before mixing with gastric secretions

Back 10

as much as 30-40%

Front 11

How long does it take for starches to be completely hydrolyze once entering duodenum

Back 11

15-30 minutes (pancreatic amalase is several times more powerful)

Front 12

What enzymes do the enterocytes lining villi of small intestine contain?

Back 12

lactase, sucrase, maltase, and alpha-dextrinase

Front 13

What makes up lactose

Back 13

glucose and galactose

Front 14

what makes up sucrose

Back 14

fructose and glucose

Front 15

How are monosaccrides absorbed

Back 15

fdirectly into portal blood

Front 16

monosaccride breakdown percents once digested

Back 16

glucose 80%, galactose and fructose each around 10%

Front 17

What secrets HCl

Back 17

parietal (oxyntic) cells (pH of 0.8 when first secreted, then 2-3 when mixed in stomach)

Front 18

Major constituent of intercellular CT of meat

Back 18

collagen; broken down by pepsin (must be broken down before other proteins an penetrate meat)

Front 19

Where does most digestion occur

Back 19

upper small intestine in duodenum and jejunum

Front 20

pancreatic enzymes that act on chyme entering duodenum

Back 20

trypsin, chymotrypsin, carboxypeptidase, proelastase

Front 21

what does carboxypeptidase do

Back 21

cleaves individual aas from carboxyl ends of polypeptides

Front 22

What do trypsin and chymotrypsin do

Back 22

split protein molecules into small polypeptides

Front 23

Most proteins get digested down to…

Back 23

dipeptides and tripeptides

Front 24

where are peptidases located

Back 24

brush border microvilli membranes

Front 25

Two types of peptidase enzymes that are especially important

Back 25

1) aminopolypeptidase 2) several dipeptidases (split remaining polypepetides into di and tri pieces)

Front 26

Where are di and tripeptides transported

Back 26

through microvillar membrane into interior of enterocyte

Front 27

Where are most peptides split into individual aas

Back 27

in cystol; they pass into blood once formed

Front 28

Fat digestion in stomach

Back 28

small amount by lingual lipase (from saliva); less than 10% fat digestion

Front 29

Where does emulsification begin

Back 29

in stomach with agitation to mix food/fat with products of digestion

Front 30

Most emulsification occurs where

Back 30

in duodenum with bile (bile salts plus lecithin)

Front 31

What is the purpose of bile

Back 31

emusification; reduces interfacial tension of fat and makes it soluble

Front 32

average diameter of fat after emulsification

Back 32

~1 um; 1000-fold increase in SA

Front 33

Most important enzymes for digesting triglycerides

Back 33

pancreatic lipase (enough released to digest everything it can reach in 1 minute); enterocytes also have lipase, not usually needed

Front 34

What transports fatty acids to prevent reversal of digestion

Back 34

bile salts (remove monoglycerides and free fatty acids)

Front 35

Bile salt micelle specs

Back 35

3-6 um with 20-40 molecules; ferries

Front 36

Cholesterol esters

Back 36

combination of cholesterol and one fatty acid molecule; most common dietary cholesterol

Front 37

quantity of fluid absorbed by intestines each day

Back 37

1.5 L from ingested fluid and 7 L of GI secretions

Front 38

How much fluid is absorbed in small intestines

Back 38

all but 1.5 L

Front 39

What substances can be absorbed through the stomach

Back 39

high lipid-soluble substances like alcohol and aspirin in small quantities

Front 40

folds that increase the suface area in small intestine

Back 40

valvulae conniventes; increase SA 3 fold

Front 41

where are the folds most developed

Back 41

duodenum and jejunum; protrude as much as 8 mm into lumen

Front 42

How far do villi project from suface of mucosa

Back 42

~1 mm; increase SA 10 fold

Front 43

how much do microvilli increase SA

Back 43

at least 20 fold

Front 44

Organization of villus

Back 44

1) vascular system to absorb 2) central lacteal

Front 45

daily absorption from small intestine

Back 45

several hundred grams carbs, 100+ grams fat, 50-100 grams aas, 50-100 grams ions, 7-8 L water

Front 46

absorption capacity of small intestine per day

Back 46

serveral kg of carbs, 500 g fats, 500-700 g proteins, 20+ L water

Front 47

What can the large intestine absorb

Back 47

additional water, ions, very few nutrients

Front 48

How is water transported

Back 48

entirely through diffusion

Front 49

Sodium absorption/use in body

Back 49

20-30 g secreted into intestine, 5-8 g eaten; must absorb 25-30 g (1/7 of all body sodium)

Front 50

What percent of intestinal sodium passes into feces

Back 50

less than 0.5%; important in absorbing sugars and aas

Front 51

Na+ in intestinal epithelial cells

Back 51

1) transported actively into paracellular spaces 2)Cl- atoms follow Na+ 3) Na+ concentration in cells low (50mEq/L) 4)Na+ concentration in chyme ~142 mEq/L 5) Na+ follows gradient into cells

Front 52

How does aldosterone affect Na+

Back 52

within 1-3 hours of release, increases activation of enzyme and transport mechanisms for all aspects of Na+ absorption in intestinal epithelium

Front 53

Increased Na+ absorption causes…

Back 53

secondary increase in Cl- and water absorption (plus some other substances)

Front 54

Cl- ion absoprtion

Back 54

rapidly absorbed in upper small intestine; fixes the electronegativity in chyme/electropositivity in paracellular spaces created by Na+

Front 55

Bicarb absorption in small intestine

Back 55

1) when Na+ absorbed, moderate amount of H+ secreted into lumen 2) H+ combine with bicarb to form H2CO3 3) dissociated into water and CO2 4) water stays in chyme, CO2 absorbed directly into blood and expired in lungs

Front 56

Bicarb secretion in ileum and large intestine

Back 56

epithelial cells secrete bicarb in exchange for Cl-; neutralizes acid products formed by bacteria

Front 57

Flow of water in large intestines

Back 57

young/immature epithelial cells secrete NaCl into lumen which is reabsorbed by older/mature epithelial cells

Front 58

How does cholera and other diarrheal bacteria cause their effect

Back 58

stimulate fold secretion/young epithelial cells so greatly, old cells can not absorb quickly enough

Front 59

What specifically causes oversecretion with cholera

Back 59

formation of excess cyclic adenosine monophosphate, which opens large numbers of Cl- channels

Front 60

How are Calcium ions absorbed

Back 60

actively by duodenum; controlled by PTH and vit D

Front 61

Monovalent vs divalent ion absorption

Back 61

monovalent ions absorbed with ease in great quantities, divalent absorbed in small amounts

Front 62

Glucose absorption

Back 62

sodium co-transport mechanism (secondary active transport); facilitated diffusion into blood from epithelial cells

Front 63

Galactose absoption

Back 63

almost same as glucose (secondary active transport with Na+)

Front 64

Fructose absorption

Back 64

facilitated diffusion all the way through intestinal epithelium; transport rate 1/2 of glucose and galactose

Front 65

peptide/aa absorption

Back 65

most through Na+ co-transport; a few only use facilitated diffusion; at least 5 types of transport proteins for aa and peptides have been found

Front 66

lipid absorption

Back 66

transported by micelles and are immediately absorbed into epithelial cell membrane

Front 67

How much fat can be absorbed without/with bile micelles

Back 67

40-50 % versus 97%

Front 68

What happens to lipids once in epitheial cytoplasm

Back 68

taken up by smooth ER and used to make new triglycerides which are released as chylomicrons into lymph and go to thoracic duct

Front 69

Why so some lipids absorb directly into portal blood

Back 69

short and some medium chain fatty acids are water soluble and absorbed directly

Front 70

How much chyme enters colon each day

Back 70

1500 mL; most absorption in proximal 1/2 of colon

Front 71

tight jxns in large vs small intestine

Back 71

much tighter in large intestine; prevents back-diffusion of ions

Front 72

What causes osmotic gradient for water absorption in large intestine

Back 72

absorption od Na+ and Cl- ions

Front 73

max absorption of colon

Back 73

5-8 L of fluid and electrolytes/day

Front 74

Fxn of bacteria in colon

Back 74

1) digest some cellulose 2) vit K, vit B12, thiamine, riboflavin production 3) flatus (CO2, H2, and methane)

Front 75

composition of feces

Back 75

3/4 water 1/4 solid matter

Front 76

Solid matter composition of feces

Back 76

30% dead baccteria, 10-20% fat, 10-20 organic matter, 2-3% protein, 30% undigested roughage

Front 77

What causes brown color of feces

Back 77

stercobilin and urobilin (derivatives of bilirubin)