Macronutrient Digestion and Absorption Review

metabolism

encompasses all chemical and physical changes in body tissues

catabolism

breakdown processes; breaks down large molecules into smaller ones, releasing energy

anabolism

synthesis processes; utilizes energy to convert small molecules into larger ones

ATP

produced by mitochondria fuels both anabolism and other cellular functions

macronutrients

proteins, fats, and carbohydrates that maintain the body’s structures and functioning; provide energy in form of calories

carbohydrates

provide fuel for body during exercise to preserve braking down proteins in muscles; provide energy for CNS; glycosylate proteins and lipids

complex carbohydrates

large polymers of simple sugars

simple sugar carbohydrates

disaccharides (sugars covalently linked) or monosaccharides (single sugars)

carbohydrates must be broken down into monsachharides

to be absorbed in small intestines

monomer

monosaccharides

glucose

monosaccharide; body’s preferred carb based energy source

fructose

needs to be converted into glucose by liver before it can be used

liver

only organ that can metabolize fructose in significant amounts

diet high in calories and fructose

liver gets overloaded and starts turning fructose into fat

dimers

disaccharides

maltose

formed from two alpha-glucose molecules

sucrose

formed from glucose and fructose

lactose

formed from glucose and galactose

disaccharides

maltose, sucrose, lactose

examples of polymers (polysaccharides)

starch (from plants), cellulose (plant polymer), and glycogen (found in animal muscles)

oral cavity

chewing in mouth mixes food w/ salivary gland secretions

salivary amylase

breaks down complex carbohydrates into disaccharides and trisaccharides

stomach

salivary amylase continues to digest carbohydrates until stomach pH drops below 4.5

arrival of chyme in duodenum

prompts secretion to release buffers

buffers

shift duodenal pH from acidic to alkaline, essential for intestinal enzyme function

CCK

triggers release of pancreatic buffers and enzymes, including pancreatic alpha amylase

GIP

stimulated by arrival of chyme in duodenum; stimulates insulin release

epithelial cells in jejunum

complete carbohydrate digestion

brush border’s plasma membrane

contains maltase, sucrase, and lactase

monosaccharides diffuse

through cytosol and reach interstitial fluid via facilitated diffusion across basolateral surfaces

hepatic portal vein

transports monosaccharides to the liver

indigestible carbohydrates

remain unaltered by intestines, arrive intact to colon; nutrient source for colonic bacteria

glucose is stored

in liver and in muscles as glycogen, as fat in adipocytes

glucose can be converted

to triglycerides in livers

early energy phase

glucose catabolism to generate ATP

second phase of energy needs

glycogen breakdown followed by glucose catabolism

third phase of energy needs

fatty acids are converted to Acytyl CoA and enter Krebs cycle to generate ATP

glucose can be used in building

glycoproteins, structural materials, or nucleic acids

glycerol

converted from glucose; essential for synthesizing triglycerides

when energy is needed

glucose is broken down into two pyruvate molecules via glycolysis

glycolysis

anaerobic process that results in net gain of 2 ATP for each glucose molecule

in the presence of oxygen, each pyruvate molecule

is converted into acetyl-CoA and transported into mitochrondria

processing of each pyruvate molecule by mitochondria

yields up to 32 ATP

for each molecule of pyruvate processed

3 oxygens are consumed

in the absence of oxygen, each pyruvate molecule

is converted to two ATP and lactic acid in the cytosol

lactic acid

leaves cell and sent to liver to be recycled into glucose via Cori cycle