Appendages of the skin
- Hair – 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 ands 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 consist 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 colour 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 skins 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 goose bumps. Air is trapped between the skin and hair and is warmed by body heat.
- Sweat Glands – Sweat consists of 99.4 per cent water, 0.4 per cent toxins and 0.2 per cent salts. There are two type 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 that 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 odour 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.
- Sebaceous glands – are small, sac-like structures which produce a substance called Sebum. These glands are found all over the body except for the soles of the feet and the palms or hand. They are more numerous on the scalp and areas of the face, such as the nose, forehead and chin. The glands are attached to the upper part of the follicle and its duct enters directly into the hair follicle. Hormones Control the activity of these glands and as we get older the secretion of sebum decreases, causing the skin to become drier.
- Sebum – is a fatty substance and is the skin’s natural moisturiser. It keeps the skin supple and helps to waterproof it. Men generally secrete more sebum than women. Sebum and sweat mix together on the skin to form an acid mantle. The acid mantle maintains the pH (acid/alkaline level) of the skin.
- Blood and capillary network – blood is supplied to the skin by small blood vessels known as blood capillaries, these enter the lower regions of the dermis and rise to supply the pilo-sebaceous follicles and the sub-epidermal network which also supplies the epidermis. The blood flow within the skin operates as an aid to vital respiration. Capillaries also help with the heat regulation by dilating (widening) and constricting (narrowing) to prevent body heat losses.
- Sensory Nerves – the skin contains sensory nerve endings that detect changes in the environment and send messages to the brain. These nerves respond to touch, pressure, pain, cold and heat and allow us to recognise objects from their feel and shape.
- Motor Nerves – the skin contains motor nerve endings that convey impulses from the brain, though the spinal cord to the muscles, glands and smooth muscular tissue.
- Fibres – nerves are cordlike structures carrying impulses from the periphery, muscles and joints to the brain and spinal cord. Messages pass along the nerve fibres as electrical impulses via a network of interlocking fibres surrounding the upper part of the follicle forming a collar. Fibres extend to the sebaceous glands, epidermis, erector pili and sweat glands.