*Blood flow is regulated in all three types of blood vessels through constriction and dilation.
*Contraction of blood vessels slows blood flow, while relaxation of blood vessels, or dilation, allows free flow of blood.
*Muscle fibers control the constriction and dilation of vessels. In the capillaries, rings of muscle called capillary sphincters control blood flow.
*The directional flow of blood in the veins is controlled with valves , which prevent backward blood flow when closed, and allow blood to flow only toward the heart when open.
Vasoconstriction and vasodilatation allow blood vessels (arteries and veins) to control blood flow and thus control the blood pressure. This is possible because of the smooth muscle cells that surround the vessels. The contraction and dilatation of those muscles is controlled by chemical signals (e.g. norepinephrine constricts the vessels, while NO dilates them).
Through electrical impulses
In photosynthesis, the movement of protons from the stroma to the thylakoid lumen is proton gradient and is coupled to<u> transfer of </u><u>protons</u>.
Protons are transported across the thylakoid membrane and into the lumen through the electron transport chain (the space inside the thylakoid disk). Protons are simultaneously removed from the stroma by reduction of NADPH and added to the lumen via water splitting (the space outside the thylakoids). Protons are pumped from the stroma to the thylakoid lumen as a result of the electron passing through the first link in the electron transport chain. A fourth protein complex in the thylakoid membrane, ATP synthase, then uses the energy stored in this proton gradient to produce ATP. This protein complex, like the mitochondrial enzyme, links proton flow back across the membrane to the creation of ATP.
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