Скачать или смотреть Skin diseases | Lec 1

this comprehensive lecture, we provide a detailed introduction to skin diseases, starting from the basic structure of the skin and moving step-by-step into the classification of primary and secondary skin lesions.

🔬 Structure of the Skin

The skin is the largest organ of the human body and plays a vital protective and immunological role. It consists of three main layers:

1️⃣ Epidermis
2️⃣ Dermis
3️⃣ Subcutis

The epidermis is composed mainly of:

Keratinocytes (90–95%) responsible for keratin production

Melanocytes (1–5%), pigment-producing cells located in the basal layer

Langerhans cells (3–8%), which function as antigen-presenting immune cells


The epidermis itself is divided into four layers:

Stratum basale

Stratum spinosum

Stratum granulosum

Stratum corneum


The dermis contains collagen, elastin, fibroblasts, blood vessels, lymphatics, and nerve endings, providing structural support and sensation.

We also discuss epidermal appendages, including hair, nails, sebaceous glands, and sweat glands (eccrine and apocrine).

☀️ Functions of the Skin

Acts as a protective barrier

Prevents infection

Protects against UV radiation and mechanical injury

Thermoregulation

Sensory function

Immunological role

Vitamin D synthesis



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🩺 Basic Skin Lesions

Understanding skin lesions is essential for diagnosis in dermatology.

A) Primary Lesions

These are the original manifestations of skin diseases:

Macule: Flat discoloration less than 1 cm

Patch: Macule larger than 1 cm

Papule: Small solid elevation less than 0.5 cm

Plaque: Elevated lesion more than 1 cm

Nodule: Larger, deeper dome-shaped lesion

Vesicle: Small fluid-filled blister less than 0.5 cm

Bulla: Fluid-filled lesion larger than 0.5 cm

Pustule: Contains purulent material

Comedo: Keratin plug in pilosebaceous unit (characteristic of Acne vulgaris)

Burrow: Epidermal tunnel characteristic of Scabies

Wheal: Transient edematous lesion caused by dermal edema



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B) Secondary Lesions

These develop due to evolution, trauma, infection, or healing of primary lesions:

Scale: Desquamated keratinocytes (seen in Psoriasis and desquamation in Scarlet fever)

Crust: Dried serum and exudate

Fissure: Linear crack extending to dermis

Erosion: Loss of epidermis (heals without scarring)

Ulcer: Loss of epidermis and dermis (heals with scarring)

Lichenification: Thickened skin due to chronic rubbing or scratching



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🧪 Important Pathological Terms

Hyperkeratosis: Increased thickness of the stratum corneum

Hypergranulosis: Increased thickness of the granular layer

Acanthosis: Increased thickness of the epidermis



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🎓 This lecture is ideal for:

Medical students

Nursing students

Physical therapy students

Dermatology beginners


By the end of this video, you will clearly understand how to identify and differentiate various skin lesions clinically — an essential skill for dermatological diagnosis.

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