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The parietal cell membrane is dynamic; the numbers of canaliculi rise and fall according to secretory need. This is accomplished by the fusion of canalicular precursors, or tubulovesicles, with the membrane to increase surface area, and the reciprocal endocytosis of the canaliculi (reforming the tubulovesicles) to decrease it. [2]
The gastric hydrogen potassium ATPase or H + /K + ATPase is the proton pump of the stomach.It exchanges potassium from the intestinal lumen with cytoplasmic hydronium [2] and is the enzyme primarily responsible for the acidification of the stomach contents and the activation of the digestive enzyme pepsin [3] (see gastric acid).
The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide. The gastric juice also contains digestive enzymes produced by other cells in the gastric glands – gastric chief cells. Gastric chief cells secrete an inactivated pepsinogen.
Thermodynamically the flow of substances from one compartment to another can occur in the direction of a concentration or electrochemical gradient or against it. If the exchange of substances occurs in the direction of the gradient, that is, in the direction of decreasing potential, there is no requirement for an input of energy from outside the system; if, however, the transport is against ...
In cell respiration, the proton pump uses energy to transport protons from the matrix of the mitochondrion to the inter-membrane space. [1] It is an active pump that generates a proton concentration gradient across the inner mitochondrial membrane, because there are more protons outside the matrix than inside.
One of these species is allowed to flow from high to low concentration, which yields the entropic energy to drive the transport of the other solute from a low concentration region to a high one. An example is the sodium-calcium exchanger or antiporter, which allows three sodium ions into the cell to transport one calcium out. [24]
Secondary active transport carriers use this H+ electrochemical gradient across the plasma membrane to co-transport solutes into the cell, therefore allowing nutrient uptake to occur. [13] Tip-growing systems. Pollen tubes and root hairs are examples of plant tip-growing systems, where a single cell expands in one direction only. The direction ...
A membrane transport protein is a membrane protein involved in the movement of ions, small molecules, and macromolecules, such as another protein, across a biological membrane. Transport proteins are integral transmembrane proteins ; that is they exist permanently within and span the membrane across which they transport substances.