Anatomy of skin: Layers, Accessory Structures, Sensory Receptors, Specialized Cells & Functions

• The skin is the largest organ of the human body and serves numerous essential functions, including protection, sensation, regulation of temperature, and vitamin D synthesis.

Flowchart of anatomy of skin

Here's a brief overview of the anatomy of the skin:

Layers of the Skin:

i. Epidermis:

• The outermost layer, primarily responsible for protection. It is further subdivided into several layers:

  1. Stratum corneum: The outermost layer, made of dead, flat skin cells that shed approximately every 2 weeks.

  2. Stratum lucidum: Thin layer present only in the palms of the hands and soles of the feet.

  3. Stratum granulosum: Cells here produce keratin, which provides strength to the skin.

  4. Stratum spinosum: Contains immune cells that help fight off infections.

  5. Stratum basale: The innermost layer, where new skin cells are formed. It also contains melanocytes that produce melanin, the pigment responsible for skin color.

ii. Dermis:

• Located beneath the epidermis, it is responsible for the skin's structural integrity and contains:

  1. Collagen and elastin fibers: Providing strength and elasticity.

  2. Blood vessels: To nourish the skin and regulate temperature.

  3. Nerve endings: Allowing for sensation, such as touch and pain.

  4. Sweat glands: Producing sweat, which helps regulate temperature.

  5. Sebaceous (oil) glands: Producing sebum that moisturizes the skin and hair.

  6. Hair follicles: The root structures from which hairs grow.

  7. Lymph vessels: Part of the body's immune system, they help clear away waste and pathogens.

iii. Hypodermis (Subcutaneous layer):

• This is not technically part of the skin but lies beneath the dermis. It contains:

  1. Fat cells (adipose tissue): Providing insulation and cushioning.

  2. Blood vessels: Larger vessels than those in the dermis.

  3. Connective tissue: Holding everything together.

Accessory Structures:

1. Hair: Provides protection, sensory input, and thermoregulation. Each hair grows from a hair follicle located in the dermis.

2. Nails: Protect the tips of the fingers and toes and help in fine manipulation tasks. They are made of keratin.

3. Sweat Glands: Two types, eccrine (for cooling) and apocrine (found in areas like armpits, produce a thicker sweat).

4. Sebaceous Glands: Produce sebum, an oily secretion that moisturizes the skin and hair.

Sensory Receptors:

• The skin contains various receptors that detect temperature, pressure, touch, and pain.

Specialized Cells and Structures:

• Keratinocytes: The most common cell type in the epidermis, producing keratin, a protein that gives skin its strength.

• Melanocytes: Produce melanin, which protects against UV radiation.

• Merkel Cells: Function in light touch sensation.

• Mast Cells: Involved in inflammatory responses.

• Lymphatic Vessels: Present in the dermis, they help in immune responses.
  

Functions of the Skin:

1. Protection: Against mechanical impact, pathogens, and UV radiation.

2. Sensation: Nerve endings detect temperature, touch, vibration, and pain.

3. Thermoregulation: Through sweat production and blood vessel dilation/constriction.

4. Metabolic Functions: Like Vitamin D synthesis.

5. Immune Defense: Langerhans cells and other immune cells in the skin detect and fight pathogens.

The complexity of the skin's anatomy underlies its multifaceted role in protection, sensation, and regulation. Each layer and structure has specific functions that contribute to the overall health and well-being of the body.