Largest Organ In Human Body

Introduction

The skin is the body’s outermost layer which functions to protect the body from all sorts of things, including infections, temperature changes, physical, chemical and mechanical stresses, etc. Being the largest organ of the body, the skin of an average adult human spans about 1.5-2.5 metres and is quite thick as well. A square inch of skin contains thousands of nerves, hundreds of sweat glands, and several blood vessels. This makes the skin a highly sensitive and protective organ.

Structure of Skin (skin cells and layers)

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The skin is a complex organ built on three layers, namely, epidermis, dermis and hypodermis. All of these layers perform different functions, owing to their different anatomies.

The Epidermis

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The epidermis comprises the following layers −

• Stratum basale − It is also known as the stratum germinativum or the basal layer, it is a single layer of cells and the deepest layer of the epidermis, built with cuboidal epithelial cells.

• This layer attaches the skin to the basement membrane. This layer contains the keratinocytes, melanocytes and tactile cells (aka Merkel cells).

• The cells of the basal layer epidermis divide continuously to form new cells. These cells later move to the upper layers and replace the shed skin.

• Stratum spinosum − It is also known as the “spiny layer” this layer lies above the basal layer and is about 8-10 cells thick.

• It comprises squamous cells.

• It is constituted by the keratinocytes, Langerhans’ cells, dendritic cells, and Merkel cells.

• Stratum granulosum − It contains mature keratinocytes and keratohyalin granules that are involved in the keratinization of the skin. This layer, which is 3-5 cells thick, also contains lamellar granules that produce glycolipids, which help to glue the cells together.

• Stratum lucidum − It is presentonly in areas of thick skin, this layer is about 3 cells thick, and consists of eleidin.

• Stratum corneum − The uppermost and the thickest layer (about 30 cells thick) of the epidermis, it is a dead tissue layer, made up of corneocytes. The cells are anucleate squamous epithelial cells

The Dermis

• The dermis follows the epidermal layer’s basement membrane and is built on two layers, namely, the top papillary and the lower reticular layer.

• It is the thickest layer of the skin (about 4mm thick).

• The papillary layer is a loose connective tissue layer that consists of thin collagen fibres and an extensive vascular system.

• The reticular layer also contains collagen, albeit thicker fibres than the papillary layer. It also harbours sweat and oil glands, hair follicles, etc.

• It comprises sweat glands, sebaceous glands, muscle cells, blood vessels, hair follicles, and nerve cells.

The Hypodermis

• Also known as the subcutis or subcutaneous fascia, which is the innermost layer of the skin.

• Majorly comprises the collagen, elastin and fat cells, along with hair follicles, blood vessels, and nerve cells.

• Helps attach the skin to bones and muscles.

Functions

The skin performs various important functions, considering its location and structure.

• Perhaps the most important function of the skin is its role as a barrier - it protects the internal structures of the body from microbial infections, chemical or mechanical hazards and physical trauma such as exposure to UV light.

• The skin is a sensory organ that enables us to touch and feel things. Thermoreceptors, mechanoreceptors, and nociceptors are present within the dermis and impart the skin its sensory capabilities.

• The skin helps prevent loss of moisture and stores fat that serves as an energy store.

• The skin is involved in the regulation of temperature and maintenance of homeostasis.

• The skin also protects from microbial infection, owing to the Langerhans’ cells and hence performs the immunological function.

• The dermis produces sebum which helps prevent water loss. It also supplies nutrient-enriched blood to the skin cells.

• The keratinocytes are actively involved in the synthesis of vitamin D.

Disorders of the Skin

• Acne &mins; It is a common condition that affects adolescents and adults around the world, acne results from bacterial infection of the sebaceous glands of the skin.

• Eczema − It also known as atopic dermatitis, eczema is an inflammation of the skin, characterised by itchiness, rashes and swelling of the skin. Often the skin appears rough and cracked.

• Rosacea − It is a condition that results from the flushing of the blood vessels in the skin. This may sometimes be accompanied by burning sensations and pimples on the face. Rosacea may affect the eyes as well, in a condition known as ocular rosacea.

• Psoriasis − It is a fairly common condition, psoriasis is characterised by inflammation of the skin and itchy, scaly patches on the skin. It is a chronic disease, which can affect any part of the skin and the nails.

• Melanoma − It is the cancer of the melanocytes of the skin. It is the most fatal type of skin cancer. Melanoma can sometimes occur in the internal organs and the eye as well. The main cause of melanoma is believed to be exposure to UV radiation.

• Vitiligo − A condition in which the skin loses its pigmentation, resulting in discoloured blotches on the skin surface. Vitiligo affects other parts of the body too, such as hair and the mouth. Contrary to popular misconception, vitiligo is not contagious.

Conclusion

The skin is the largest organ of the body, weighing about 3 kg and spanning a length of about 2.5 meters. The skin is built of three layers- the outermost epidermis, followed by the dermis, and lastly the hypodermis. The skin contains important cells that impart its functional capabilities. These include the keratinocytes, melanocytes, Merkel cells, nerve cells, the fat cells. This organ performs several important functions, including providing sensation, protecting against infections and physical and mechanical stresses, preventing loss of moisture, and storing fat as an energy reserve. The skin is subjected to several kinds of disorders, some of which may be non-fatal like acne and vitiligo to fatal diseases such as melanoma.

FAQs

Q1. What are the different degrees of skin burns?

Ans. Skin burns are classified into three degrees. First-degree burns are limited to the epidermis; the second-degree burns extend to the dermis. And third-degree burns are the most serious, completely burning the epidermis and the dermis, and destroying the nerve cells in the dermis.

Q2. How often is the skin shed in humans?

Ans. Humans are known to shed as much as 0.03-0.09 grams of skin per hour, amounting to about 200 million-500 million cells per hour.

Q3. Why do fingertips have ridges?

Ans. The ridges found on fingertips are due to the papillary layer, which extends finger-like projections into the epidermal layer.

Q4. What are corneocytes?

Ans. Corneocytes are permanently differentiated, dead keratinocytes that lack nuclei and other cytoplasmic organelles.

Q5. What are the two kinds of sweat glands present in the skin?

Ans. Apocrine glands and eccrine glands are the two kinds of sweat glands found in the skin. Apocrine glands occur in the skin of the armpits and pubic areas, while eccrine glands are the normal sweat glands that occur across the body.