Unit 2.13 – Appendages of the Skin Copy


Hairs are dead structures that are made of a hardened protein called keratin and grow out from follicles. Most of the body is covered with hairs, with the exception of the palms of the hands and the soles of the feet. They help to keep the body warm and are also a form of protection. The eyelashes prevent substances from entering the eyes, and the hairs that line the nose and ears help to trap dust and bacteria.

The hair is made up of three layers:

Cuticle – which is the outer part of the hair and consists of a single layer of scale like cells. These cells overlap rather like tiles on a roof. No pigment is contained within this layer.

Cortex – lies inside the cuticle and forms the bulk of the hair. It contains melanin, which determines the color of the hair. The cortex helps to give strength to the hair.

Medulla – is the inner part of the hair and is not always present. Air sacs in the medulla determine the colour tone and sheen of the hair because of the reflection on light.

Hair follicles – is an indentation of the epidermis with the walls of the follicle being formed from a continuation of the cellular layer of the skin’s surface. They are in the form of deep pits that extend into the dermis.

Arrector pili muscle – are small muscles attached to the hair follicles. When we are cold or frightened the contraction of these muscles cause the hairs to stand on end. This results in the appearance of goosebumps. Air is trapped between the skin and hair and is warmed by body heat.

Sweat glands – sweat consists of 99.4 percent water, 0.4 percent toxins and 0.2 percent salts. There are two types of sweat glands in the body: Eccrine glands – which excrete sweat and are found all over the body. The sweat duct opens directly on to the surface of the skin through an opening called a pore. Sweat is a mixture of water, salt and toxins. Black skins contain larger and more numerous sweat glands than white skins. Apocrine glands – these are found in the armpits, around the nipples and in the groin area. They secrete a milky substance. These glands are larger than eccrine glands are attached to the hair follicle; they are controlled by hormones and become active at puberty. Body odor is caused by the breaking down of the apocrine sweat by bacteria. Substances called pheromones are present in this milky substance, the smell is thought to play a part in sexual attraction between individuals and the recognition of mothers by their babies.