The circulatory system is 60,000 miles long. Each blood cell encircles the body up to 300,000 times in a period of 120 days. The lungs contain 300 billion capillaries. For every pound of fat, your body has to supply an extra 200 miles of blood capillaries. Nerve cells have long threadlike shapes which are capable of transmitting nerve impulses from one region of the body to the other.
Clear communication is important for health.
Epithelial cells line the inside of the mouth as a protection for the more delicate cells underneath. A cell consists of two major parts, one inside the other. Both are enveloped in a thin membrane. The cell membrane is a thin, flexible, living material, serving as a gateway, allowing certain chemicals to flow in and go out. How it is able to do this is not understood.