Třídenní dieta bypass 6.0
When intestinal lining cells absorb phytosterols, in place of cholesterol, they usually excrete the phytosterol molecules back into the GI tract, an important protective mechanism.In vertebrates the hepatic cells typically produce greater amounts than other cells.It is also important to recognize, however, that the concentrations measured in the blood plasma of samples vary with the measurement methods utilized.The structure of the tetracyclic ring of cholesterol contributes to the decreased fluidity of the cell membrane as the molecule is in a trans conformation making all but the side chain of cholesterol rigid and planar.a lipid molecule and is biosynthesized by all animal cells because it is an essential structural component of all animal (not plant or bacterial) cell membranes that is required to maintain both membrane structural integrity and fluidity.Through the interaction with the phospholipid fatty-acid chains, cholesterol increases membrane packing, which reduces membrane fluidity.Traditional, simpler, cheaper methods do not reflect (a) in which lipoproteins the various fat molecules are being transported or (b) which cells are ingesting, burning or exporting the fats molecules being measured as totals from samples of blood plasma. The liver excretes it in a non-esterified form (via bile) into the digestive tract.Within the cell membrane, cholesterol also functions in intracellular transport, cell signaling and nerve conduction.Cholesterol enables animal cells to dispense with a cell wall to protect membrane integrity and cell viability, thus allowing them to change shape and move about (unlike bacteria and plant cells which are restricted by their cell walls).
Typical daily cholesterol dietary intake for a man in the United States is 307 mg (above the upper limit recommended by the Dietary Guidelines Advisory Committee.Cholesterol is the principal sterol synthesized by all animals.The hydroxy group on cholesterol interacts with the polar head groups of the membrane phospholipids and sphingolipids, while the bulky steroid and the hydrocarbon chain are embedded in the membrane, alongside the nonpolar fatty-acid chain of the other lipids.It is absent among prokaryotes (bacteria and archaea), although there are some exceptions such as Mycoplasma, which require cholesterol for growth.Typically, about 50% of the excreted cholesterol is reabsorbed by the small bowel back into the bloodstream. Plants manufacture phytosterols (substances chemically similar to cholesterol produced within plants), which can compete with cholesterol for reabsorption in the intestinal tract, thus potentially reducing cholesterol reabsorption.