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DrX Whiz Niraj
Structure & Function of Skin
Complete exam-oriented notes on the Integumentary System, Layers of Skin, Appendages, and clinical importance for B.Pharm students.
The Integumentary System consists of the skin, hair, nails, sweat glands, and sebaceous (oil) glands. The Skin (cutaneous membrane) is the largest organ of the human body in terms of surface area and weight. It covers an area of about 2 square meters and weighs around 4.5 to 5 kg (16% of total body weight).
The medical specialty that deals with the diagnosis and treatment of integumentary system disorders is called Dermatology.
Structurally, the skin consists of two main parts: the superficial, thinner Epidermis, and the deep, thicker Dermis. Below the dermis is the Hypodermis (Subcutaneous layer), which attaches the skin to underlying muscles and bones.
A. Epidermis
The outermost avascular layer. It is composed of keratinized stratified squamous epithelium. It contains 4 principal types of cells:
- Keratinocytes (90%): Produce keratin, a tough fibrous protein that protects the skin from heat and microbes.
- Melanocytes (8%): Produce the pigment melanin, which gives skin its color and absorbs damaging UV light.
- Langerhans Cells: Immune cells that participate in responses against invading microbes.
- Merkel Cells: Function in the sensation of touch.
B. Dermis
The deeper, much thicker vascular layer made of dense irregular connective tissue containing collagen and elastic fibers. It gives skin its tensile strength.
- Blood Vessels: Supply nutrients and regulate temperature.
- Nerve Endings: For pain, temperature, and touch sensing.
- Hair Follicles & Glands: Contains Sebaceous (oil) glands and Sudoriferous (sweat) glands.
Exam Trick: 5 Strata of Epidermis (Deep to Superficial)
Remember the mnemonic: "Come, Let's Get Sun Burned"
- C - Stratum Corneum (Topmost layer, 25-30 rows of dead flat cells)
- L - Stratum Lucidum (Clear layer, found ONLY in thick skin like palms/soles)
- G - Stratum Granulosum (Cells undergoing apoptosis/death)
- S - Stratum Spinosum (Provides strength and flexibility)
- B - Stratum Basale (Deepest layer, continuous cell division/mitosis)
Thermoregulation
Maintains normal body temperature through sweat production (cooling) and adjusting blood flow in the dermis (vasodilation for heat loss, vasoconstriction for heat conservation).
Protection
Keratin protects underlying tissues from microbes, abrasion, heat, and chemicals. Lipids retard water evaporation. Melanin protects against UV rays.
Cutaneous Sensations
Tactile sensations (touch, pressure, vibration) and thermal sensations (warmth, cold) are perceived by an extensive network of nerve endings in the skin.
Synthesis of Vitamin D
Activation of a precursor molecule in the skin by UV rays from the sun triggers the production of Vitamin D, which is essential for calcium absorption.
Clinical Correlation: Types of Burns
Burns are classified by the depth of tissue damage. This is a highly repeated exam question:
- First-degree burn: Involves only the epidermis (e.g., mild sunburn). Characterized by mild pain and redness. No blisters.
- Second-degree burn: Destroys the epidermis and part of the dermis. Characterized by redness, blister formation, edema, and severe pain.
- Third-degree burn (Full-thickness): Destroys the epidermis, dermis, and subcutaneous layer. Skin functions are lost. The region is actually numb because nerve endings are destroyed.