Intestinal Absorption Of Carbs And Proteins

Front 1

Dietary carbs

Back 1

complex; starch and fiber

sugars; mono and disacchs

Front 2

Starch digestion

Back 2

amylose = a1,4 linked linear chains

amylopectin = branched starch with alpha 1,4 and 1,6 linked branch pts.

salivary and pancreatic amylases are nearly identical but have different genes

amylose digestion yields disacch maltose and trisacch maltotriose

amylase cant do 1,6 bonds and is hindered at branch points of amylopectin

amylopectin digestions yields maltose, maltotriose, alpha limit dextrins and branch oligos

Front 3

Brush border membrane oligosacchases

Back 3

membrane hydrolysis of oligos is very rapid and not rate limiting

glucoamylase (maltase) removes single glucose from the non reducing end of the 1,4 alpha chain

sucrase-isomaltase is inactive until pancreatic proteases cleave it in the membrane leading to sucrase and isomaltase, sucrase hydrolyzes 1,4 linked oligos, isomaltase is the only enzyme that cleaves 1,6 alpha

Front 4

isomaltase

Back 4

1,6 alpha

Front 5

sucrase

Back 5

1,4 linked oligos

Front 6

maltasse

Back 6

reducing end of 1,4 chains

Front 7

amylase

Back 7

1,4 alpha chains not near branches

Front 8

Glucose carrier test

Back 8

transport against a conc. gradient, strucuturally specific for OH at 2 carbon, can be competitively inhibited by galactose, can be saturated, can be posioned, depends on metabolic energy, Na dependent, cells can concentrate glucose

Front 9

Glucose transporters SGLT1

Back 9

2 Na ions enter the enterocyte for each glucose molecule and is electrogenic

sodium increases the transporter affinity for glucose, generated by Na/K pump, high affinity low capacity glucose transporter

transports glucose galactose and other monos but NOT fructose

SGLT1 mutations cause severe watery diarrhea in newborns, use oral rehydration therapy

Front 10

Glut2 transporters

Back 10

basolateral membrane Na independet facilitative diffusion

transports glu glac fru

found at the brush border membrane, SLGT1 favors the rapid insertion into the brush border membrane via a signal transduction pathway involving protein kinase C beta 2

luminal glucose is high, Glut2 is recruited to the membrane

Front 11

Lactose

Back 11

lactase hydrolyzes lactose to glucose and galactose, rate limiting step in lactose absorption

second catalytic site hydrolyzes glycolipids

lactase declines post weaning, can have lactase persistance where protein and mRNA are rpresent in jejunal villus cells

lactase expressed at high level in neonate, congential lactate def is auto recessive cause by missense mutation or

Front 12

Lactose malabsorption

Back 12

not digested by the time it reaches the colon results in bacterial digestion causing the produciton of hydrogen, carbon dioxide and SCFAs

results in acid pH and diarrhea as well as H2 breath test

Front 13

Fructose transport

Back 13

can't transport against a concentration gradient, no structural specificity, no competitive inhibition, can be saturated, cant poisoned, doesnt depedn on metabolic energy cant concentrate fructose

Brush border membrane has GLUT5 and GLUT2 , GLUT 5 Na independent facilitated diffusion

Fructose not as well absorbed as glucose

basolateral membrane has Glut2

Front 14

Sucrose

Back 14

sucrase hydrolyzes sucrose to glucose and fructose

fructose absorption is more efficient when given as sucrose rather than an equivalent amount of monosaccharide

co-admin of glucose increase fructose absorption

glucose absroption via SGTL1 recruits GLUT2 to the brush border membrane increasing fructose absorption

Front 15

Dietary fiber

Back 15

cellulose, hemicellulose pectins

polysaccarides not digested by our enzymes

in the colon; induce osmotic water flow (less likely to be constipated) fermented by bacteria to organic anions and gas

produces SCFAs and leaves via the anus byproducts are gas

Front 16

Mechanism of SCFA absorption

Back 16

from bacteria; acetate propionate butyrate

utilizes a bicarb exchange generated by a Na/K pump

has nonionic diffusion which is the most significant pathway

SCFAs are a significant source of nutrition, butyrate is a major substrate for colonocytes and likely plays a role in inflammation

Front 17

Protein digestion and absorption

Back 17

pepsins hydrolyze a broad range of peptide bonds, participates in protein digestions and generates peptides that stimulate G cells and I cells

in neonates chymosin digests milke protein

two enzyme families Pep A and C, become inactivated immediately in the alkaline secertion of the duodenum

activated in acid, even with total gastectomy patients have normal protein digestion

Front 18

Pancreatic proteases

Back 18

secerted as proenzymes

activation is initiated by brush border membrane enzyme enteropeptidase that is stimulated by trypsinogen an dis released from the membrane by bile salts

enteropeptidases cleaves the hexapeptida from the N-terminus of trypsinogen to form trypsin which then goes ham

endopeptidaes and exopeptidases from 40% AAs and 60% oligopeptides

Front 19

Brush border membreane peptidases

Back 19

about 20 different peptidases

endopeptidases, aminopeptidases, carboxypeptidases and dipeptidases

in addition to protein digestion, brush border membraen peptidaes activate or catabolize peptide hormones

DPP Iv metabolizes incretin GLP1 and inhibitors are used in DM2 treatment

Front 20

Brush border AA transporters

Back 20

multiple systems with overlapping specificty

may require a salt, cofactor, be electrogenic or neutral

localized in the brush border membrane and may require partner proteins

transportes also transport orally administerd AA based drugs

more active in ileum

Front 21

BB membrane peptide transport

Back 21

more active in jejunem

lack of comp with AA transport

PEPT1 is major potentially sole peptide transporter, electrogenic H coupled transporter, transports myriad of di and tri peptides, water near the central binding region shields side chains

alsot transports beta lactam anti and ACE inhibitors

Front 22

PEPT1

Back 22

uses an Na/K pump that then creates an Na/H exchange at eh apical membrane with Na coming into the cell

peptide rides down with acid, peptide nutrition may be more benificial as opposed to AA in enteral

Na/H exchange used in

Front 23

Basolateral membrane transport

Back 23

intracellular peptidases

90% of protein absorbed as AAs

10% absorped as small peptides similar to PEPT1 probably driven by high intracellular peptide concentration no coupled to H