You couldnt survive without your skin. It has many important functions. The main function of the skin is controlling what enters and leaves the body. It prevents the loss of too much water from the body. It also prevents bacteria and other microorganisms from entering the body. The skin helps maintain a constant body temperature. It keeps the body cool in two ways. Sweat from sweat glands in the skin evaporates to cool the body. Blood vessels in the skin dilate, or widen. This action increases blood flow to the body surface. This allows more heat to reach the surface. The heat is then able to radiate off the body. The opposite happens to retain body heat. Blood vessels in the skin constrict, or narrow. This decreases blood flow to the body surface. This reduces the amount of heat that reaches the surface. When this happens, less heat can be lost to the air.

What increases blood flow to the body's surface?

You might want to know how cold it is. You may need to know how fast the wind is blowing. Maybe it rained last night? Do you know how much? Does it feel humid to you? You have heard all these questions before. To answer these questions, we need data. That data comes from special tools. These tools collect data about the weather. You can see some of the common tools listed below: A thermometer measures temperature. An anemometer measures wind speed. A rain gauge measures the amount of rain. A hygrometer measures humidity. A wind vane shows wind direction. A snow gauge measures the amount of snow.

What data are collected by special tools?

The dermis is the inner layer of skin. The dermis has blood vessels and nerve endings. The nerve endings explain why your skin is sensitive. You can sense pain, pressure, and temperature. You cut your finger and it starts to bleed. What has happened? If your skin bleeds, it means you have cut the dermis layer and damaged blood vessels. The cut really hurts. It hurts because of the nerve endings in this skin layer. The dermis also contains hair follicles and two types of glands. Hair follicles are structures where hairs originate. Each hair grows out of a follicle. Hair passes up through the epidermis. It then extends above the skin surface. Oil glands produce an oily substance. The oil is secreted into hair follicles.
What is the composition of the skin?