By exploring skin, we will learn about cell division and how cells regulate the process. We will also explore different modes of inheritance. Skin also helps us regulate body temperature, conserve water, and keep germs out. Finally, we will look at the development of antibiotic resistance in germs that live on the skin.

2a. Why do we have skin?

Our skin is more than just a covering for the body, it is the boundary between our “insides” and the outside world. And it is complex. Packed into a thin layer of skin are hundreds of miles of blood vessels and nerves.

Why this is important…Picture your arm or leg without any skin. That is probably a gross idea, but it points out how exposed we would feel without skin. Our skin is our protective layer and so much more.

Foundations

The skin is part of the integumentary system, along with our hair and nails.

Man's face with cut over eye and sweaty hair. Woman's fee with sandals and painted toenails.

FIGURE 2-1. Integumentary system. This system is made up of skin, hair and nails. ("Cut from headbutt inLethwei " by Lethweimaster is licensed under CC BY-SA 4.0 "Didi wearing simple wedge heel thong sandals" by Vicky Lawrenson is licensed under CC BY-SA 3.0)

Key terms

Microorganism – living being that is too small to be seen without magnification; refers to bacteria, virus, algae, fungi and others (“germ” usually refers to harmful microorganisms)

Details

There is a lot of complexity packed into in this 2-millimeter-thick organ which performs many tasks:

Helps us cool down by radiating heat and sweating
Fat layer under the skin insulates us and stores energy
Protects from injury and germs
Senses information about the world, such as temperature, touch, and pressure
Keeps the moisture in our bodies from escaping

Skin is made up of three main layers, each with its own function (Figure 2-2). The structure of each layer reflects the jobs that it does. You will see this theme a lot – form reflects function.

Outer layer (epidermis) – layers of cells filled with a tough protein (keratin). It forms a flexible shield around the body.
Middle layer (dermis) – complex layer with many small organs embedded in a matrix of protein fibers. The protein fibers make skin tough. Each organ – blood vessels, sweat glands, oil glands, nerves – has its own job.
Inner layer (hypodermis) – fat layer that provides a layer of cushion, insulation and energy storage.

Cross section of skin with three layers labeled.

FIGURE 2-2. Layers of skin. Three major layers are shown as well as major structures embedded in each such as sweat glands, nerves and blood vessels. ("Integumentary system" by Scientific Animations is licensed under CC BY-SA 4.0)

The outer layer of skin is replaced monthly. Most of the outer layer of skin, along with the hair and nails, are all dead. They are too far away from the nourishing blood vessels to remain alive. They function as a non-living shield around your body. Since skin, hair and nails are all rich in protein (mostly keratin) this provides a tough shield, but it also takes a lot of raw materials to produce. The process of making new skin will be our focus in the next section.

Learning objectives

Identify the major organs of the integumentary system
Describe the major functions of skin