Digestion and Absorption Flashcards by Jen Becker

Digestion of Carbohydrates

salivary and pancreatic amylase

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Amylase breaks down starches to

maltotriose, Dextrins, Maltose

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Glycosidases include

maltase, lactase, sucrase, isomaltase

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Glycosidases are located in

brush border

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Glycosidases break down saccharides to

glucose, galactose, and fructose

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Lactase

lactose –> glucose + galactose

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Sucrase

sucrose –> glucose + fructose

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GLUT-5

apical and basolateral membrane, transport of fructose

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SGLT-1

apical membrane, transports glucose and galactose, Na-dependent, Na/K ATPase for gradient

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GLUT-2

basolateral membrane, transports glucose and galactose

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Peptide digestion

pepsin, pancreatic proteolytic enzymes, aminopeptidase, cytoplasmic peptidase

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Pepsin

from chief cells activated by H (pH 1-2)

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Pancreatic proteolytic enzymes

oligopeptides to amino acids, activated by enterokinase and trypsin (pH 7)

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Brush border aminopeptidases

hydrolyze remaining oligopeptides, tri- and d-peptides to aa

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Cytoplasmic peptidases

within enterocytes, try- and di- peptides are broken into AA

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Pept-1

transports tri- and di-peptides across apical border with H+

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M-cell Pinocytosis

intact absorption of tri- and di-peptides (bacteria, antibodies)

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Triglyceride digestion

first broken down into 2-MG and FFA, 2-MG can form micelles

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Digestion of phospholipids

phospholipase A2 releases FFA and lysophospholipids and long-chain FFA which form micelles

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Cholesterol and long-chain FFA

form micelles

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Short-chain and medium-chain FFA

<12 C; do not form micelles

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Enzymatic cleavage of lipids must occur at

oil-water interface

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Emulsification

break down of large globules of fat, mastication, retropulsion, peristalsis

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Gastric Lipase

15% triglycerides to DAG and FFA

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Colipase

activated by CCK --> trypsin cleavage; binds lipase to the oil-water interface

Lipase

inhibited by bile acids, activated by colipase

Micelle incorporation

LCFFA, 2-MG, lysophospholipids, cholesterol

Will not incorporate into micelle

SCFFA or MCFFA, triglyceride, or bilirubin

Absorption of lipid products

micelle break down at apical surface, and contents diffuse

SCFFA and MCFFA transport

diffusion

Once in enterocyte,

DAG, 2-MG, LGFFA are converted back to TG and packaged in chylomicrons

Chylomicrons have a protein coat

apoprotein B

Cholesterols are esterified to

cholesterol esters

Fat-soluble vitamine ADEK

are incorporated into micelles

Vitamin B12 absorption

binds R protein of saliva in gastric lumen, in small intestine it binds intrinsic factor, in ileum intrinsic factor binds receptor and facilitates absorption of B12

TRPV5/6

Ca transport protein

within enterocytes calcium binds

calbindin Ca-BP

2 requirements to extrude Ca at basolateral membrane

Ca-ATPase and Na/Ca exchanger

Vitamin D effect on Ca absorption

increases number of apical Ca-channels, number of cytosolic Ca-BP, and activity of Ca-ATPase

PPI and Ca absorption

less solubilized Ca for absorption due to higher pH

Na Absorption transport mechanism

co-transport with glucose and galactose and exchange for H+

IN COLON Na absorption is influenced by aldosterone

synthesis and insertion of ENaC

Divalent metal transporter 1

Fe3+ to Fe2+ and enters enterocyte through DMT1

Heme oxygenase

release Fe from heme in enterocyte

Fe inside enterocyte is stored as

ferritin and exported via ferooportin-1

Once ferritin is being exported

hephestin converts Fe2+ to Fe3+ and Fe3+ binds apotransferrin

Small intestine digests and absorbs almost all carbs, fats, and proteins but

colonic bateria may digest it is they reach the colon

Carbohydrate + colonic bacteria

SCFFA (reabsorbed or excreted) and gas

Protein + colonic bacteria

ammonia and cadavarine

Triglycerides + colonic bacteria

NOT digested = steatorrhea

Bile Acids + colonic bacteria

Secondary bile acids (lipid-soluble) absorbed by simple diffusion

Osmotic gradient and water flux

high accumulation of nutrients and electrolytes produced an osmotic gradient

Hydrostatic pressure and water flux

presence of water in ECS or lumen

Absorption of water

water follows osmoles into ECS, increasing hydrostatic pressure in ECS, causing flow from ECS into capillaries

Passive water flux decreases as we move

distally

How to treat diarrhea and dehydration

H2O, glucose, and Na SLGT-1 transporter

Osmotic diarrhea - pancreatic insufficiency (bile obstruction, ZES, CF, pancreatitis)

maldigestion, oncotic forces pull water into lumen causing diarrhea

Reduced luminal bile acid concentrations

impaired micelle formation causing diarrhea (locked duct, ileal disease, ZES, bacteria overgrowth)

Lactose intolerance

lactose remains in lumen drawing in water

Mucosal Malabsorption

destruction of intestinal mucosa (celiacs or IBD) decreased nutrient absorption = osmotic diarrhea