Transport of substances from the blood into the hepatocyte occurs through the sinusoidal membrane. The following statement(s) is/are true concerning this plasma membrane.
- The high lipid content of this phospholipid bilayer allows lipid-soluble molecules to enter the cell by simple diffusion
- Carrier proteins within the phospholipid bilayer bind to a solute in blood and by conformational change allow it to be transported into the cell
- Large glycoprotein molecules of the sinusoidal membrane known as receptors always transport the binding ligand into the cell
- The transmission of a signal to the interior of the cell by receptor-ligand binding which generates intracellular second messengers is known as signal transduction
Medicine
a.The high lipid content of this phospholipid bilayer allows lipid-soluble molecules to enter the cell by simple diffusion
b.Carrier proteins within the phospholipid bilayer bind to a solute in blood and by conformational change allow it to be transported into the cell
d.The transmission of a signal to the interior of the cell by receptor-ligand binding which generates intracellular second messengers is known as signal transduction
The hepatocyte plasma membrane consists of a phospholipid bilayer in which hydrophobic fatty acid tails are oriented to the interior membrane and hydrophilic phospholipid head groups are oriented to the exterior (sinusoidal or cytoplasmic) membrane. Within this phospholipid bilayer are proteins which serve either structural functions or metabolic functions. The hepatocyte sinusoidal plasma membrane is heavily studded with microvilli to increase the absorptive area in contact with sinusoidal blood. The cell membrane, by virtue of its high lipid content, allows lipidsoluble molecules to enter the cell by simple diffusion. Polar molecules must enter cells via membrane transport proteins. Channel proteins allow molecules to diffuse simply into cells without binding, whereas carrier proteins first bind the solute and, by conformational change, allow it to be transported into the cell. The glucose carrier in hepatocytes is an example of carrier-facilitated diffusion. The sinusoidal membrane is studded with receptors, which are large glycoprotein molecules that span the plasma membrane lipid bilayer. A ligand-binding site of this receptor molecule projects into the space of Disse. When appropriate ligand-receptor binding occurs, the entire ligand may be internalized for intracellular degradation or biliary transport, or the ligand may transmit a signal to the interior of the hepatocyte by a number of intracellular second messenger systems, a process known as signal transduction. Such second messengers include cAMP, inositol triphosphate, and diacylglycerol. Each of these structurally simple chemicals can amplify cell membrane events and bring about major changes in cellular physiology.
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