The Skin
The skin is an organ because it consists of several kinds of tissues that are structurally arranged to function together.
The skin is the largest organ of the body, with a surface area of about 1.5 to2 m in adults.
Structure of the skin (skin layers)
There are two main layers :
1. Epidermis, and
2. Dermis.
Epidermis:
The epidermis is the outermost layer of the skin. It is composed of stratified keratinized squamous epithelium. It is devided in to five distinct layers:
1. The stratum corneum.
It is the outermost layer. It is composed of flat, thin, non-nucleated scale-like dead cells, in which the the cytoplasm has been replaced by keratin.
2. The stratum lucidum
It is a translucent, thin layer which evident in thick skin.
3. The stratum granulosum
It consists of 3 to 5 layer of flattended cells. The cytoplasm of these cells contain keratohyaline and lamellar granules.
4. The stratum spinosum
It is the thickest layer of the epidermis. It consists of several layer of large keratinocytes.
5. The stratum basale
It is the innermost layer. It consists of columnar or cuboidal cells. It produces new cells to replace the superficial keratinized cells that are continuously shed or worn
away.
Dermis :
The dermis has two layer:
1. Papillary layer
The thin superficial layer of loose areolar connective tissue in which the collagen and elastic fibres form aloosely woven mat.
2. Reticular layer
It is the thicker deeper layer of dermis. It consists of dense irregular connective
tissue.
Structures in the dermis:
1. blood vessels
2. lymph vessels
3. sensory (somatic) nerve endings
4. sweat glands and their ducts
5. hairs, arrector pill muscles and sebaceous glands.
Functions of the skin:
1. provides a cover for the underlying soft tissues
2. provides protection against injury, bacterial invasion, and desiccation
3. regulates body temperature
4. a very important sensory organ receiving continual sensations from the environment
5. excretes sweat from sweat glands.
6. can absorb ultraviolet radiation form the sun for vitamin D synthesis.
7. the pigment in the epidermis protects the tissues against harmful effects of light.
The skin is the largest organ of the body, with a surface area of about 1.5 to2 m in adults.
Structure of the skin (skin layers)
There are two main layers :
1. Epidermis, and
2. Dermis.
Epidermis:
The epidermis is the outermost layer of the skin. It is composed of stratified keratinized squamous epithelium. It is devided in to five distinct layers:
1. The stratum corneum.
It is the outermost layer. It is composed of flat, thin, non-nucleated scale-like dead cells, in which the the cytoplasm has been replaced by keratin.
2. The stratum lucidum
It is a translucent, thin layer which evident in thick skin.
3. The stratum granulosum
It consists of 3 to 5 layer of flattended cells. The cytoplasm of these cells contain keratohyaline and lamellar granules.
4. The stratum spinosum
It is the thickest layer of the epidermis. It consists of several layer of large keratinocytes.
5. The stratum basale
It is the innermost layer. It consists of columnar or cuboidal cells. It produces new cells to replace the superficial keratinized cells that are continuously shed or worn
away.
Dermis :
The dermis has two layer:
1. Papillary layer
The thin superficial layer of loose areolar connective tissue in which the collagen and elastic fibres form aloosely woven mat.
2. Reticular layer
It is the thicker deeper layer of dermis. It consists of dense irregular connective
tissue.
Structures in the dermis:
1. blood vessels
2. lymph vessels
3. sensory (somatic) nerve endings
4. sweat glands and their ducts
5. hairs, arrector pill muscles and sebaceous glands.
Functions of the skin:
1. provides a cover for the underlying soft tissues
2. provides protection against injury, bacterial invasion, and desiccation
3. regulates body temperature
4. a very important sensory organ receiving continual sensations from the environment
5. excretes sweat from sweat glands.
6. can absorb ultraviolet radiation form the sun for vitamin D synthesis.
7. the pigment in the epidermis protects the tissues against harmful effects of light.
