High upstream blood pressure (BP) not only causes the forward movement of blood (flow arrow) but also presses outward on the vessel walls. This force is called hydrostatic pressure (HP) (HP block arrow). The great arteries are elastic and stretch (dashed outline of vessel) under this high blood pressure. However, they then recoil (RC block arrow) and prevent pressure from dropping too much.
Blood pressure drops as it flows through vessels. The drop is due to the work done in stretching the vessels and frictional drag on the vessel walls (not shown here). The drop in pressure is important because blood moves (i.e., flows) along a pressure gradient, that is, from high pressure to lower pressure. The gradient is represented by the difference in the size of the BP acronyms at the two ends of the flow arrow.
With the decrease in pressure due to the forward flow of blood, the previously stretched elastic walls of these vessels recoil (RC block arrow). This returns the vessel to its original diameter (solid vessel outline). This recoil helps counteract the drop in blood pressure and acts as a 'squeeze' to assist continued blood flow (block flow arrow entering next vessel).
A carotid sinus (CS) is located in the walls of the carotid arteries. It contains stimulatory neurons (solid line) that increase their signals to the brain as blood pressure increases. The relationship between carotid blood pressure (BP) and activation of the carotid sinus (CS) is direct (solid line).
Last updated: 7/15/2005