Biology: All About The Skin

Topic: THE SKIN

Contents:

The Skin

Care of the Skin

Functions of The Skin

Common Skin Diseases

A. THE SKIN

The skin is one of the hard working organs in the body. The skin is the outer covering of the body. In humans, it is the largest organ and sense organ.  Skin is a thin layer of tissue forming the natural outer covering of the body of a person or an animal. It is the largest organ of the body. The skin protects us from microbes and the elements helps regulate body temperature, and permits the sensations of touch, heat, and cold. The skin’s color is created by special cells called melanocytes, which produce the pigment melanin. Melanocytes are located in the epidermis. The skin is made up of two main layers namely:

1. The Dermis: This is the inner layer also known as the “true skin”. It is directly under the outer layer. Inside the true skin, you will find other structures like the oil gland (sebaceous gland), sweat gland, sweat duct, fat deposit e.t.c
2. The Epidermis: This is the outer layer. It has no blood vessels or nerves. It is covered with hair and tiny holes called “seat pores”

Structure of the Skin

The mammalian skin consists of two main layers: the epidermis, and the dermis.

Epidermis: is the outermost layer of the skin. It provides a waterproof barrier and creates our skin tone. The epidermis consists of three layers:

• The innermost Malpighian layer
• The middle Granular layer, and
• The outermost (surface) Cornified layer.

1. Malpighian layer: Also known as germinative layer. It consists of actively dividing cuboidal cells. They contain melanin, a pigment that gives the skin its colour and absorbs ultra violet radiation. The cells of this layer get their nutrients and supply of oxygen by diffusion from the blood of the capillaries found in the dermis.
2. Granular Layer: This consists of living cells produced by the malpighian (germinative) layer beneath. These cells are continuously converted to cornified cells. Keratin is deposited inside them, and they lose their nuclei and become flattened in shape.
3. Cornified Layer: This consists of scale-like dead cells impregnated with keratin. The keratin makes this layer tough, flexible and waterproof. They are constantly wearing away and are replaced from the granular layer beneath.

Dermis: This is beneath the epidermis. It is a layer of connective tissue containing blood capillaries, hair follicles, sweat glands, sebaceous gland, sensory nerve ending and fat cells.

1. Blood capillaries: This supplies food and oxygen to the dermal and epidermal cells and remove wastes. The capillary loops close to the body surface help to regulate the body temperature.
2. Hair Follicles: This is a deep pit formed by the in-folding of the Malpighian layer. Each hair is a cylinder composed of dead cells; grow as new cells at the ‘root’. A hair erector muscle is attached to each follicle. Its contraction pulls the hair to a more upright position, i.e. it makes the hair ‘stand up’.
3. Sebaceous gland: Secretes sebum which repels water (waterproof) and also prevents microbes from multiplying.
4. Sweat gland: Absorbs fluid from the surrounding tissues and capillaries. This fluid is then passed out as sweat through the sweat duct. Sweat is 99% water, 0.3% salt, and minute amounts of urea and lactic acid.
5. Sensory nerve ending: The skin is also a sense organ. Various nerve endings, capable of responding to touch, heat, cold and pressure.
6. Subcutaneous fat: It is found beneath the dermis. It acts as a food reserve and an insulating layer, to prevent heat loss. 

FUNCTIONS OF THE SKIN

1. It keeps the body warm in cold weather
2. It helps the body to get rid of waste products through sweating
3. It protects the body against dehydration, invading microbes, mechanical damage and damage due to ultra violet rays and poisonous chemicals.
4. It contains receptors sensitive to heat, cold, touch and pressure.
5. It plays a major role in temperature control (vasodilation and vasoconstriction).
6. It has a minor role as an excretory organ. Urea and lactic acid are lost.
7. The skin produces vitamin D in the fatty cells by using infra-red rays of the sun
8. It helps to keep the body temperature normal by producing sweat during hot weather
9. It protects the body from bacterial infections (germs) poor weather and injury
10. When the sun shines on the skin, vitamin D is produced by the skin
11. Sensation: contains a variety of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury.
12. Heat regulation: the skin contains a blood supply far greater than its requirements which allows precise control of energy loss by radiation, convection and conduction. Dilated blood vessels increase perfusion and heatloss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat.
13. Control of evaporation: The skin provides a relatively dry and semi-impermeable barrier to fluid loss. Loss of this function contributes to the massive fluid loss in burns.
14. Storage and synthesis: Acts as a storage center for lipids and water, as well as a means of synthesis of vitamin D.
15. Excretion: Sweat contains urea, however its concentration is 1/130th that of urine, hence excretion by sweating is at most a secondary function to temperature regulation.
16. Water resistance: The skin acts as a water resistant barrier so essential nutrients aren’t washed out of the body.

TYPES OF SKIN

It very important to know our skin type. This helps us to know how to care for them properly. Below are types of skin

1. Normal skin: It is soft, clear, smooth and without spots or blemish.
2. Oily skin: This is greasy and occur when the oil glands produce too much oil.
3. Dry skin: This kind of skin is usually thin, sensitive and have wrinkles easily especially around the mouth and eyes. This can result from poor feeding, ill health, dry weather and lack of care.
4. Combination (oily and dry skins): Has some part of the skin oily i.e. the nose and forehead. While other parts are dry i.e. cheeks

B. CARE OF THE SKIN

 It is necessary to keep the skin clean by having regular bath. In order to care for the skin, it is important to:

1. Wash your whole body daily more than once during hot, dry and dusty season
2. Have a shower after serious exercise or games to avoid body odor
3. Keep your towel, under wears and other clothes clean
4. Use good toilet soap and sponge
5. Take abundant fresh air
6. Do not use bleaching cream
7. Eat balanced diet that is rich in milk, proteins, fruits, cold-liver oil, vegetable e.t.c

RESULTS OF NEGLIGENCE OF THE SKIN

If the skin is left to remain dirty, the following will result:

1. Air will not pass into the body through the skin
2. The sweat pores will be blocked
3. Bad odour and different kinds of skin problems will occur e.g. pimples, irritation e.t.c

C. COMMON SKIN DISEASES

Below are some common skin diseases which might result to the skin problems due to lack of are:

1. Ringworm
2. Pimples
3. Scabies
4. Eczema
5. Chicken pox or Measles
6. Diaper Rash
7. Heat Rash
8. Boil

SKIN INJURIES

1. Bruises: These result when the body is given a blow with sufficient force. There is bleeding under the skin without breaking it. Swelling and discoloration of the injured area occur

Treatment: Place a clean piece of cloth or handkerchief soaked in very cold water, over the bruised area.

2. Stings: They are bites from insect such as wasp, bee and scorpion. The sting may some times remain in the skin and should be removed.
3. Cuts: These occur whenever the skin is opened, torn or punctured by a sharp object like knives, broken bottles and glasses, scissors or any rough edge.

Treatment: Wash with anti septic solution i.e. clean water into which some drops of antiseptic e.g. addition of dettol

4. Burns and Scalds: these are skin injuries caused by heat. Burns are caused by dry heat or boiling liquids on the skin

Treatment: (i) Cover the burnt or scalded area immediately with cold water (ii) cover the area with Vaseline petroleum jelly and place a layer of gauge over it

Control of Body Temperature

Under normal conditions, the heat the body gain is balanced by the heat it loses. The balance, however, can be upset by hot weather, vigorous exercise, high fever or exposure to solar radiation. The balance is restored by the actions of the hypothalamus and the skin.

•   A rise in body temperature stimulates the following processes to get rid of excess body heat:

1. Vasodilation: The arteriole in the skin (swell) increases the flow of blood through the skin. This leads to increased loss of heat through the dermis by convection and radiation.
2. Sweating: The sweat glands become active and produce large amounts of sweat that flow out onto the surface of the skin. As this sweat evaporates, heat from the body is used up, thus cooling the body.

•   A fall in body temperature stimulates the following processes to produce and conserve heat:

1. Vasoconstriction: The arterioles are narrowed, thereby reducing the flow of blood to the skin and so minimizing heat loss.
2. Sweating: The sweat glands become inactive and produce very little sweat that flows out to the skin surface, thereby conserving body heat.

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