M10.04.01 Anatomy and Physiology of the Skin

The skin is the body’s largest organ, serving as a vital barrier and interface between the external environment and the internal body systems. Understanding the anatomy and physiology of the skin is crucial for identifying and managing dermatological conditions.

Anatomy of the Skin

1. Layers of the Skin

• Epidermis
  • Outermost layer
  • Contains keratinocytes, melanocytes, Langerhans cells, and Merkel cells
• Dermis
  • Middle layer
  • Comprised of collagen and elastin fibers
  • Contains blood vessels, nerves, hair follicles, and sweat glands
• Hypodermis (Subcutaneous Tissue)
  • Deepest layer
  • Composed of adipose tissue and connective tissue

2. Epidermal Layers

• Stratum Corneum
  • The outermost layer of dead keratinized cells
• Stratum Lucidum
  • Present only in thick skin (palms, soles)
• Stratum Granulosum
  • Layer with granular cells
• Stratum Spinosum
  • Spiny appearance due to desmosomes
• Stratum Basale
  • The deepest layer, the site of cell division

3. Dermal Components

• Papillary Dermis
  • Upper layer with loose connective tissue and capillaries
• Reticular Dermis
  • Lower layer with dense connective tissue, larger blood vessels

4. Skin Appendages

• Hair Follicles
  • Hair growth and sebaceous glands
• Sweat Glands
  • Eccrine and apocrine glands
• Sebaceous Glands
  • Secrete sebum for lubrication

5. Vascular and Nerve Supply

• Extensive network of blood vessels and nerves
• Functions in thermoregulation and sensory perception

Table 1: Layers and Functions of the Skin

Physiology of the Skin

1. Barrier Function

• Protects against mechanical injury, pathogens, and chemicals
• Prevents water loss

2. Thermoregulation

• Regulates body temperature via sweat production and blood vessel dilation/constriction

3. Sensory Perception

• Contains receptors for touch, pain, temperature

4. Immune Function

• Langerhans cells play a role in the immune response

5. Metabolic Functions

• Synthesis of Vitamin D

Key Points to Remember

• The skin consists of three primary layers: epidermis, dermis, and hypodermis.
• Each layer has distinct cells and functions, contributing to the skin’s protective, regulatory, and sensory roles.
• Skin appendages such as hair follicles, sweat glands, and sebaceous glands play critical roles in thermoregulation and protection.
• The skin’s extensive vascular and nerve networks are essential for its multiple functions.

Related Abnormal Conditions

1. Psoriasis
   • Chronic autoimmune condition causing rapid skin cell turnover
2. Eczema (Atopic Dermatitis)
   • Inflammatory condition with itchy, red, and dry skin
3. Acne Vulgaris
   • Blockage and inflammation of hair follicles and sebaceous glands
4. Melanoma
   • Malignant tumor of melanocytes
5. Basal Cell Carcinoma
   • Most common type of skin cancer, arising from basal cells
6. Squamous Cell Carcinoma
   • Cancer arising from squamous cells of the epidermis

Bibliography

1. Bolognia, J. L., Schaffer, J. V., & Cerroni, L. (2018). Dermatology. Elsevier.
2. James, W. D., Berger, T. G., & Elston, D. M. (2016). Andrews’ Diseases of the Skin: Clinical Dermatology. Elsevier.
3. Goldsmith, L. A., Katz, S. I., Gilchrest, B. A., Paller, A. S., Leffell, D. J., & Wolff, K. (2012). Fitzpatrick’s Dermatology in General Medicine. McGraw-Hill Education.