Monday, November 18

Skin anatomy - Skin physiology

› Skin anatomy and physiology
The study of anatomy and physiology of skin is very essential for its healthy upkeep. Knowledge of the skin physiology helps us in understanding its complex functional mechanisms.
Skin anatomy and its histology gives insights into its basic structure and structural components.

Understanding biological processes of keratinocyte cell formation, growth, differentiation, migration and death is necessary for proper skin care. These studies also help in evolving methods to protect the skin and the inner organs from pathogens, toxic agents, oxidants, dehydrating circumstances, chemicals, environment, ultraviolet radiation and physical stress.

Study of skin structure

The human skin is composed of two layers, epidermis and dermis, which are unique in structure and function. The study of skin structure is important for clinical and cosmetic research. The study of the skin anatomy gives us insights into the complex mechanisms involved in its functional physiology.

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Human complexion colors

Human complexion color is brought about by the concentration of melanin deposits and their various types. The deposition of pigments is mostly determined by four to six genes. These genes have several alleles, creating the possibility of several combinations, produce a great variety in the skin tone.

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Physiology

The skin is the largest organ of the human body. It has a highly dynamic interface and covers and protects the internal organs by multiple mechanisms. Functioning as a physical barrier, it protects the body from the environmental elements and harmful microbes. Its functions include temperature regulation, sensory transduction and tactile discrimination.

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Hydration and desquamation

Hydration and desquamation are necessary processes by which the skin is kept healthy, soft, smooth and supple. Any impediment to continuous hydration of the stratum corneum and continuous desquamation of dead cells will lead to many dermatological conditions like dry, thickened and scaly epidermis and dermatitis.

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Histology and anatomy

Histology of skin deals with the microscopic study of the anatomy of its layers and cells. Skin consists of squamous keratinized outer layer called epidermis and fibrous and elastic inner connective tissue called dermis. The epidermis consists of five sublayers and dermis consists of two sublayers.

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Epidermis

The epidermis is the outermost protective layer of the integumentary system. Epidermis has no blood vessels and is nourished by the diffusion of nutrients from the dermis. The anatomy of epidermis shows that keratinocytes form 90% of the cells. Melanocytes, melanosomes, melanin pigments, Langerhans cells and Merkel cells are also present in epidermis.

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Five layers of epidermis

The epidermis is composed of five well defined sublayers. The outermost sublayer of the skin is stratum corneum. The sublayers in their descending order are stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum and stratum germinativum (stratum basale). Keratinocytes present in stratum basale undergo continuous mitotic cell division.

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Epidermal keratinocyte cells

The cells constituting epidermis are mostly keratinocytes (95% of the cells). Keratinocytes function as stem cells (transit amplifying (TA) cells) and undergo continuous mitosis in stratum basale. These cells move upwards and differentiate into various layers and finally get sloughed off as dead skin.

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Stratum corneum functions

Stratum corneum is the outermost layer of the epidermis. Being formed of functions as a barrier by the death of keratinocyte cells, stratum corneum functions as barrier to environment. It is multilayered and is composed of 15-20 layers flattened corneocytes. These corneocytes embedded within the multiple lamellar sheets of lipid matrix and are dead and anucleate.

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Stratum lucidum functions

Stratum lucidum is a well defined epidermal layer found under the corneum in regions of thicker skin like the palms and soles. This transparent or translucent layer is composed of three to five tiers of dead flattened keratinocytes without distinct boundaries. They contain a clear intracellular protein called eleidin.

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Stratum granulosum functions

Stratum granulosum is also known as granular layer due to visible granules present in its structure. It is found under the lucidum layer in the palms and soles and under corneum in the other areas of the skin. The keratinocytes present in stratum granulosum are the last layer of living cells which are in the process of losing their nuclei and dying.

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Stratum spinosum functions

Stratum spinosum also known as prickle cell layer is the fourth tier from the exterior and is situated between stratum granulosum and germinativum (basale). Stratum spinosum is 5-10 keratinocyte cells in thickness. They are modified basal keratinocytes having large nuclei with very prominent nucleoli.

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Stratum basale

Stratum basale (stratum germinativum) is the basal layer of epidermis. It contains one row of constantly dividing columnar or cubical undifferentiated keratinocytes with melanocytes and Langerhans or immune cells dispersed in between. The basement membrane separates the stratum basale from the inner dermis layer.

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Dermis layers

Dermis layer is present below the epidermis layer of the skin. Dermis is composed of outer papillary layer and lower reticular layer. Dermis contains a gelatinous matrix of elastic fibers, reticular fibers, glycosaminoglycans and collagen. Adipocytes (fat cells), fibroblasts (fiber forming cells), leukocytes and nerve cells are present in the matrix.

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Papillary layer of dermis

The papillary layer of dermis lies above the reticular layer. Papillary layer has finger-like (nipple-like) projections, which extending into the epidermis. These projections increase the contact surface and strengthens the bond between the skin layers. Papillary layer contains areolar tissue (loose connective tissue).

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Reticular layer of dermis

The reticular layer of dermis is present below the papillary layer. It is the deepest part of the skin lying above the hypodermis. The reticular layer is thicker than the papillary layer and ranges from 1-3 mm in thickness. Dense irregular connective tissue and adipose tissue are the major constituents of the reticular layer.

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Hypodermis layer

Hypodermis is the subcutaneous tissue forming the lowermost layer of our integumentary system. Though hypodermis is not considered as part of the skin, it is very essential for anchoring the skin to the body. Blood vessels and lymphatic vessels traverse hypodermis. Fibroblasts, fat cells (adipocytes) and leukocytes are present in hypodermis.

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Know your skin

Skin is a dynamic organ in a state of constant change. It is the largest organ in human body. In an average adult, its surface area including hair, nails and glands, may measures about 1.5-2 square meters (about 17-22 square feet) and weigh about 3.5 kilograms (about 8 pounds). It is a very complex structure made up of millions of different types of cells carrying out many varied functions.

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Nourishing skin

For a lasting smooth clear complexion and a healthy glow of your face incorporate different fruits and vegetables into your diet on a daily basis. The Center for Nutrition Policy and Promotion recommends including half of our food plate with fruits and vegetables to get nutrients vital for the healthy maintenance of our body.

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Current topic: Anatomy and physiology of skin.

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