All major dietary carbohydrates contain glucose, either as their only
building block, as in starch and glycogen, or together with another
monosaccharide, as in sucrose and lactose. In the lumen of the
duodenum and small intestine the oligo- and polysaccharides are broken
down to monosaccharides by the pancreatic and intestinal glycosidases.
Glucose is then transported across the apical membrane of the
enterocytes by SLC5A1 and later across their basal membrane by SLC2A2
(ref). Some of glucose goes directly to fuel brain cells and
erythrocytes, while the rest makes its way to the liver and muscles,
where it is stored as glycogen, and to fat cells, where it is stored
as fat. Glycogen is the body's auxiliary energy source, tapped and
converted back into glucose when there is need for energy
http://en.wikipedia.org/wiki/Glucose
Fatty acids are usually ingested as triglycerides, which cannot be
absorbed by the intestine. They are broken down into free fatty acids
and monoglycerides by lipases with the help of bile salts. Most are
absorbed as free fatty acids and 2-monoglycerides, but a small
fraction is absorbed as free glycerol and as diglycerides. Once across
the intestinal barrier, they are reformed into triglycerides and
packaged into chylomicrons or liposomes, which are released in the
lymph system and then into the blood. Eventually, they bind to the
membranes of adipose cells or muscle, where they are either stored or
oxidized for energy. The liver also acts as a major organ for fatty
acid treatment, processing liposomes into the various lipoprotein
forms, namely VLDL, LDL, IDL or HDL.
Triglycerides undergo lipolysis (hydrolysis by lipases) and are broken
down into glycerol and fatty acids. Once released into the blood, the
free fatty acids bind to serum albumin for transport to tissues that
require energy. The glycerol backbone is absorbed by the liver and
eventually converted into glyceraldehyde 3-phosphate (G3P), which is
an intermediate in both glycolysis and gluconeogenesis
http://en.wikipedia.org/wiki/Fatty_acid_oxidation |
