Dermatology Quiz: Skin Structure and Function

Lecture 1: Basic Anatomy and Physiology of The Skin

• Dermatology is the branch of medicine dealing with the skin and related diseases.
• The skin is the largest organ of the body, making up about 15% of the adult body weight (approximately 4 kg).
• It performs vital functions, including protection against physical, chemical, and biological agents.
• It also prevents excess water loss and regulates body temperature.

Skin Layers

• The skin has three layers: epidermis, dermis, and hypodermis.

Epidermis Layers

• Stratum basale (stratum germinativum): The deepest layer, composed of a single layer of columnar, mitotically active cells that produce keratinocytes. It also contains melanocytes.
• Stratum spinosum (prickle cell layer): Composed of 8-10 layers of cells with cytoplasmic processes (spines) connected by desmosomes. Contains Langerhans cells.
• Stratum granulosum: Contains 3-5 cell layers of diamond-shaped cells with keratohyalin and lamellar granules. Keratohyalin facilitates keratin aggregation; lamellar granules secrete glycolipids maintaining cellular cohesion.
• Stratum lucidum: A thin, clear layer present in thick skin (e.g., palms, soles). Consists of eleidin, a transformation product of keratohyalin.
• Stratum corneum: The outermost layer comprised of 20-30 layers of dead, keratinized cells (anucleate squamous cells) that form horny scales. They release defensins for immune defense.

Epidermal Cells

• Keratinocytes: The predominant cells (90%) originating from the basal layer. These cells produce keratin and lipids for the epidermal water barrier and contribute to calcium regulation by enabling UVB light absorption.
• Melanocytes: Dendritic pigment-synthesizing cells primarily in the basal layer responsible for melanin production and transfer to keratinocytes. Melanin is produced within melanosomes (membrane-bound organelles).
• Langerhans cells: Dendritic cells acting as the skin's first-line immune defenders. They contain Birbeck granules and tennis racket-shaped cytoplasmic organelles, expressing MHC I and MHC II molecules, taking up antigens, and transporting them to lymph nodes.
• Merkel cells: Oval-shaped modified epidermal cells in the stratum basale, serving as mechanoreceptors for light touch, found in the palms, soles, and oral/genital mucosa, especially in fingertips.

Dermo-Epidermal Junction

• The interface between epidermis and dermis is a porous basement membrane that allows cell and fluid exchange, holding the layers together.
• Basal keratinocytes are crucial components.
• The junction comprises the basal cell plasma membrane with hemidesmosomes, lamina lucida, lamina densa, and lamina fibroreticularis.
• Functions include epidermal-dermal adherence, mechanical support for the epidermis, and a barrier against large molecule exchange.

Dermis

• The dermis consists of two connective tissue layers: papillary (thinner) and reticular (thicker).
• The papillary layer contacts the epidermis, composed of loose connective tissue.
• The reticular layer has dense connective tissue with collagen fiber bundles, housing sweat glands, hair follicles, muscles, sensory neurons, and blood vessels.
• Cell types include fibroblasts, macrophages, mast cells, and white blood cells.

Hypodermis

• Also known as the subcutaneous fascia, this is the deepest layer beneath the dermis.
• It contains adipose lobules, sensory neurons, blood vessels, and sparse skin appendages (e.g., hair follicles).

History taking

• Attitude: Greet patient, introduce yourself, ask for permission.
• Personal Data: Name, age, sex, occupation, residence, marital status, and origin.
• Complaint: Symptoms (use patient's words), name of lesion, site of lesion, duration, and example: itchy pimples and bumps on both legs for one month.
• History of Present Illness (HPI): Fitzpatrick seven questions: onset (sudden or gradual), location of first appearance, symptom analysis, disease evolution, single lesion evolution, aggravating/relieving factors, and current medications.
• Systemic Review, Past History, Family History, Drugs History, and Social History

Dermatological Examination

• Skin Lesions:
  • Primary skin lesions: Macules (circumscribed discoloration < 5mm), Patch (circumscribed discoloration > 5mm), Papules (<5mm solid elevation), Plaque (solid elevation >1cm), Vesicle/Bulla (< or > 5mm fluid-filled), Nodule (>5mm solid elevation), Wheal (transient edematous), and Pustule (pus-filled).
  • Secondary skin lesions: Scar, Atrophy, Erosion, Ulcer, Crust, Scale, Fissure, Lichenification, and Excoriation.
  • Special skin lesions (e.g., Comedone, Burrow, Dandruff, Ecchymosis, Petechiae, Purpura, Telangiectasia).
• Examination of the Lesions: Includes location, color, shape, surface, size, margin, and distribution (e.g., linear, annular, dermatomal).
• Examination of Special Sites: Examines scalp, palms, soles, mucous membranes (eyes, nose, genitalia).
• Eliciting Disease-Related Signs: Observe for any additional signs related to the condition being investigated.