Structure of the Skin

The skin is the largest organ of the human body and serves multiple vital functions. It consists of three primary layers:

1. Epidermis (Outer Layer)

• Structure: The epidermis is composed mainly of keratinocytes, which are produced in the basal layer and move upwards, becoming more keratinised until they form the stratum corneum (outermost layer).
• Key Features:
  • Stratum corneum: Made of dead cells rich in keratin; acts as a barrier.
  • Melanocytes: Found in the basal layer, produce melanin, which protects against UV radiation.
  • Langerhans cells: A type of immune cell that helps fight off infections.
  • No blood vessels: Nutrients are supplied from the underlying dermis.

2. Dermis (Middle Layer)

• Structure: This layer consists of collagen and elastin fibres that provide strength and elasticity.
• Key Features:
  • Blood vessels: Supply nutrients and help regulate temperature.
  • Nerve endings: Detect sensations such as pain, pressure, and temperature.
  • Sweat glands: Help in thermoregulation.
  • Sebaceous (oil) glands: Produce sebum, a natural moisturiser.
  • Hair follicles: Produce hair, which helps regulate temperature and provides sensory input.

3. Hypodermis (Subcutaneous Layer)

• Structure: Made of fat cells (adipose tissue) and connective tissues.
• Key Features:
  • Insulation: Helps regulate body temperature by storing fat.
  • Cushioning: Protects underlying muscles and bones.
  • Blood vessels and lymphatic vessels: Transport nutrients and remove waste.

Functions of the Skin

The skin has five major functions:

1. Protection

• Acts as a physical barrier against pathogens, chemicals, and UV radiation.
• Prevents dehydration by reducing water loss.
• Protects internal organs from injury.

2. Thermoregulation

• Sweating: Evaporation of sweat helps cool the body.
• Vasodilation/Vasoconstriction: Blood vessels expand (release heat) or contract (retain heat).
• Fat insulation: The hypodermis helps maintain body temperature.

3. Sensation

• Specialised nerve endings detect:
  • Temperature (hot/cold)
  • Pain
  • Pressure and vibration
  • Fine touch

4. Immune Defence

• Langerhans cells in the epidermis detect foreign substances and activate the immune response.
• The acidic pH of the skin helps prevent bacterial growth.

5. Excretion & Vitamin D Production

• Excretes waste (salts, urea) through sweat.
• Synthesises Vitamin D when exposed to sunlight, which is essential for calcium absorption.

Skin Appendages

The skin contains specialised structures known as appendages, which include:

1. Hair

• Grows from hair follicles in the dermis.
• Provides protection (e.g., eyelashes prevent debris from entering the eyes).
• Assists in temperature regulation (e.g., goosebumps trap heat).

2. Nails

• Composed of keratin, the same protein found in hair.
• Function: Protects fingertips and enhances fine motor control.

3. Glands

• Sweat Glands:
  • Eccrine glands: Found all over the body; help cool the body via sweat.
  • Apocrine glands: Found in armpits/groin; produce thicker sweat (bacteria break it down, causing body odour).
• Sebaceous Glands:
  • Secrete sebum (oil) to moisturise and protect skin.
• Ceruminous Glands:
  • Located in the ear, produce earwax (cerumen).
• Mammary Glands:
  • Specialised sweat glands that produce milk for infants.

Concise Summary for Quick Revision

References

1. Cleveland Clinic. (n.d.). Skin: Structure, Function, and Common Conditions. Retrieved from https://my.clevelandclinic.org/health/body/10978-skin

2. Lumen Learning. (n.d.). Layers of the Skin. Retrieved from https://courses.lumenlearning.com/suny-ap1/chapter/layers-of-the-skin/

3. Cleveland Clinic. (n.d.). Integumentary System: Function and Components. Retrieved from https://my.clevelandclinic.org/health/body/22827-integumentary-system

4. MSD Manual. (n.d.). Structure and Function of the Skin. Retrieved from https://www.msdmanuals.com/home/skin-disorders/biology-of-the-skin/structure-and-function-of-the-skin

5. Kenhub. (n.d.). Histology of the Skin and Appendages. Retrieved from https://www.kenhub.com/en/library/anatomy/histology-of-the-skin-appendages