Did you know that blood vessels come fully equipped with the ability to help regulate blood pressure? This is possible because of smooth muscle cells that wrap around blood vessels (see image above). Because they wrap around the inner layers of the blood vessel, when these cells contract, the lumen od the blood vessel becomes narrow and increases blood pressure. When they relax, the blood vessels widen thereby lowering blood pressure. It is important that this system functions properly because failure can lead to uncontrolled high (or low) blood pressure and can damage blood vessels.
There are many known factors that can control whether the smooth muscle cells contract or relax, such as chemicals released from the inner lining of the blood vessel, hormones, as well as drugs. What is less known is how these smooth muscle cells can detect and respond to mechanical changes themselves (ex: stretching of the blood vessel). For example, if the pressure inside of a blood vessel increases, the smooth muscles cells will respond by constricting. Dr. Heather Drummond recently published an article in Physiology exploring the possible mechanisms that enable smooth muscle cells to detect changes. Studies of nematodes suggest that special sodium channels in the cell membrane of the smooth muscle cells are most likely responsible for sensing when the cell stretches. Activation of these channels pulls sodium into the cell, which then activates other channels like transient receptor potential (Trp) channels that pull in more sodium and calcium inside the cell resulting in contraction. It is suspected that a similar mechanism may also exist in mammals.
HA Drummond. What evolutionary evidence implies about the identity of the mechanoelectrical couplers in vascular smooth muscle cells. Physiology. 36(5): 292-306, 2021. https://doi.org/10.1152/physiol.00008.2021