Sharks have skin covered in millions of tiny teeth-like scales that point to the tail. If you rub along a shark towards the tail, it would feel smooth, but if you rub the other way, it would be rough. Sharks' teeth can be 20 times as big as human teeth and they can grow back if they are lost. Fins
Vertebrobasilar insufficiency is a condition characterized by poor blood flow to the posterior (back) portion of the brain, which is fed by two vertebral arteries that join to become the basilar artery. Blockage of these arteries occurs over time through a process called atherosclerosis, or the build-up of plaque.
Chronic venous insufficiency (CVI) results when the veins in the legs no longer pump blood back to the heart effectively. Normally, when the leg muscles contract, they squeeze the deep veins of the legs, aiding in circulation. Veins contain one-way valves that keep the blood from flowing in the opposite direction, toward the foot. These valves can wear out over time, leading to blood leaking backward and pooling in the veins of the leg.