SS2 Biology Lesson Note on The Skin

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THE SKIN

The skin is the outer covering of the body. It covers the entire body surface and it is thickly covered with hair in most mammals but in man, it is sparsely covered except the head where the hair is thick and long

Structure of the skin

The skin is made up of two main layers:

1. The external epidermis
2. The dermis

 

1. THE EPIDERMIS

The epidermis is made up of three layers, namely

• • The cornified layer
  • The granular layer and
  • The malpighian layer

1. The Cornified layer is the outermost layer of the skin. It is composed of dead cells. It is scaly and the dead constantly peel off it. The dead cells are impregnated with keratin, a fibrous protein. The cornified layer is well developed and very thick in the sole of the feet and palms of the hands. As the cells of the cornified layer are sloughed, they are constantly replaced by new cells from the granular layer
2. The Granular layer is the middle layer of the epidermis containing living cells rich in keratin. The cells are constantly pushed up and flattened out to replace the cells of the cornified layer as dead cells.
3. The Malpighian layer is made up of cells that are actively dividing. They are unboidal cells that are constantly being pushed up to replace cells in the granular layer. They are rich in melanin (the pigment which impact colour to the skin). The layer has many folding into the dermal layer where sebaceous glands and hair follicles are located. Because they are also actively growing, they are well supplied with nutrient and oxygen by the capillaries in the dermal layer.

Skin Cancer

The dark patch on this person’s lower leg is a dangerous form of skin cancer known as malignant melanoma. Overexposure to ultraviolet radiation in sunlight is the cause of most skin cancers.

2. THE DERMIS

The dermis is thicker than the epidermis. It is made up of connective tissues. Most of the special structures of the skin including blood capillaries, hair follicles, sweat gland sensory nerve ending, sebaceous glands and fat cells are located here.

Blood capillaries supply the dermis and lower epidermis with nutrient and oxygen. They also remove wastes. They form a network around the root of the hair follicles and sweat glands.

Hair follicles contained the hairs of the skin. The hair follicle is an invargination into the dermal layer which is the lining with malpighian layer. The hair is a shaff made up of keratin with a bulbous base which is richly supplied with blood capillaries and nerve endings. The nerve endings are what makes the hair very sensitive to touch. Also attached to the base of the hair is the erector muscle.

The rector muscle contracts when the weather is clod causing the hair to become erect. This also happens when the animal is in fear. This is what gives rise to the so called goose pimples.

Sebaceous gland is a bulbous gland lined with malpighian cell layer on the side of the hair follicle. It secretes oil called sebum which helps to keep the hair and epidermal layer oily and water proof. It also wards off micro-organisms.

Sweat gland is a coiled tube embedded in the dermis that leads to an opening on the skin surface called sweat pore via the sweat duct. The capillaries associated with sweat gland release water and mineral salts; the mineral salts and water form what is called sweat which moves to the skin surface as droplets of water. This has both excretory and regulatory functions.

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