So thinks Eddy M. del Rio, MD., on the baroreceptor system, writing at at Reasons to Believe:
If you’ve ever picked up a water balloon by the knotted end, then you know that all the water just flops to the bottom. Humans are like water balloons. When we stand up, the arterial blood heading to the brain has to move uphill against gravity, and so suffers impedance. Simultaneously, the venous blood in the lower extremities trying to return to the heart is also impeded, causing a decreased supply of blood to the heart and, consequently, a decreased cardiac output. Together, these two phenomena may cause a decrease in blood supply to the brain, making an individual feel light-headed and weak (pre-syncope) or susceptible to losing consciousness (syncope). Obviously, the average healthy person rarely faints upon standing up. Why is that? Because we have a g-suit system built into our bodies!
Like the accelerometer in the aircraft that detects changing g-forces, humans have baroreceptors in the sinuses of the carotid arteries that detect changes in blood (hydraulic) pressure. If these receptors detect a sudden drop in pressure, they emit a signal to the brainstem via the glossopharengeal nerve. After several connections and pathways, some excitatory and some inhibitory, activity of the sympathetic branch of the autonomic nervous system increases and constricts the arteries (vasoconstriction) in the bilateral lower extremities.More.
Readers? Of course, it could have been natural selection acting on random mutation (Darwinism) over how many years, until the system randomly assembled itself, right?
Follow UD News at Twitter!