Understanding the Skin and its Functions

• The skin is the body's first defense line, protecting against physical damage, chemicals, and extreme temperatures.
• It regulates body temperature, facilitates sensation, helps detoxify the body through sweat, and aids in vitamin D synthesis for calcium absorption.

Protective Barrier

• The skin prevents microorganisms and chemicals from entering the body, maintaining internal homeostasis and preventing infections.

Thermoregulation

• It controls heat loss and conserves body fluids to maintain optimal body temperature, essential for metabolic processes.

Sensory Function

• Specialized receptors detect changes in temperature, touch, pressure, and pain and send signals to the brain for appropriate responses.

Limited Waste Removal

• The skin excretes salts, urea, and water through sweat, aiding in the body's detoxification.

Vitamin Synthesis (Vitamin D)

• The skin produces vitamin D when exposed to sunlight which is crucial for calcium absorption and bone health.
• Ultraviolet (UV) light activates a precursor molecule in the skin, initiating vitamin D production.

Epidermis

• The epidermis is the outermost layer that serves as a protective barrier with varying thickness based on the body area
• Palms and soles have a thicker layer, other areas are thinner.

Dermis

• The dermis is located beneath the epidermis and composed of connective tissue
• It contains blood vessels, hair follicles, sweat glands, and sensory receptors.
• It supports the epidermis and aids in thermoregulation due to blood flow.

Subcutaneous Layer (Hypodermis)

• This layer consists of loose connective tissue and fat cells.
• It serves as an insulating layer, protecting against extreme temperatures and forming a cushioning system for underlying organs.

Stratum Corneum

• The outermost epidermal layer is made of dead, flattened cells filled with keratin.
• It protects against water loss and prevents pathogen entry.

Stratum Lucidum

• Found only in thick skin (palms and soles), it consists of flattened, dead cells, providing additional protection for high-friction areas.

Stratum Granulosum

• Cells undergo keratinization, flattening and filling with keratin in this layer
• Lamellar granules release lipids to form a moisture barrier, reducing water loss.

Stratum Spinosum

• This layer contains cells producing keratin.
• Desmosomes provide structural integrity and resistance to mechanical stress.

Stratum Basale

• The deepest epidermal layer contains stem cells that divide and produce new cells, replacing those shed from the surface.
• Melanocytes in this layer produce melanin, giving skin its color.

Keratin Structure

• Keratin is a fibrous protein in skin, hair, and nails, providing strength and flexibility.
• The structure consists of alpha-helices that coil together with hydrophobic amino acids making it insoluble in water.

Hair Follicle

• The hair follicle is an epidermal in-growth into the dermis, made of specialized keratinocytes, responsible for hair production.
• It connects to the dermal papilla, which supplies nutrients to the growing hair.

Hair Shaft

• The hair shaft consists of the medulla (innermost), cortex (hard keratin), and cuticle (outermost).
• The cuticle is made of keratinocytes in a tile-like pattern to protect inner layers.

Hair Growth Cycle

• Hair growth occurs in three phases: anagen, catagen, and telogen.
• Anagen Phase: Active growth, cells divide rapidly, pushing upward.
• Catagen Phase: Transition, growth slows, hair bulb regresses.
• Telogen Phase: Resting, follicle inactive, shedding occurs; follicle re-enters anagen for new growth.

Hemoglobin

• Found in red blood cells, contributes to the skin's pinkish hue.
• Low oxygen levels (hypoxia) can cause cyanosis, a bluish appearance.

Carotene

• A yellow-orange pigment from foods like carrots.
• Excess consumption can cause a yellowish tint by depositing in the skin.

Melanin

• Produced by melanocytes, it is responsible for skin color and UV radiation protection.
• The amount and type determine skin color (light to dark brown), based on genetic factors.

Describing a Skin Lesion (Inspection)

• Shape: Note any irregularities in the lesion.
• Size: Measure the lesion, especially if larger than 5 millimeters.
• Color: Can indicate diseases (e.g., red for inflammation, black for necrosis, yellow for infection).
• Appearance: Note whether it is flat, raised, or ulcerated.
• Distribution: Is it localized or spread? Does it follow a dermatome pattern?

Describing a Skin Lesion (Palpation)

• Consistency: Is the lesion soft, firm, or hard?
• Temperature: Warmer can indicate inflammation or infection.
• Tenderness: Indicates pain upon touch (often a clue for infection or inflammatory conditions).
• Mobility: Is the lesion fixed or movable? Fixed lesions may indicate malignancy.

Cyst

• A closed, fluid-filled sac that may be infected (forming an abscess).
• Typically smooth, well-circumscribed, and movable. Can be infectious or non-infectious.
• A sebaceous is a common type that forms from a blocked sebaceous gland.

Abscess

• A pocket of pus, often from bacterial infection.
• Typically painful, swollen, and warm to the touch.
• Unlike cysts, they are not lined by epithelium, and may require drainage for healing.

Ulcer

• A skin defect that extends into the dermis or deeper.
• Caused by physical damage, infection, or poor circulation (e.g., pressure ulcers).
• Venous often appear on the lower legs, especially around the ankles, associated with poor circulation.

Vascular Lesions

• Telangiectasias (Spider Veins): Small, dilated blood vessels appearing as red or purple lines, often seen in rosacea or liver disease.
• Hemangiomas: Benign growths of blood vessels presenting as red or purple masses. Strawberry hemangiomas are common in newborns and often resolve on their own.

Scale

• An accumulation of dead skin cells, usually from the stratum corneum.
• Occurs in conditions like psoriasis or eczema, feeling dry, waxy, or flaky.
• Often associated with chronic inflammatory skin conditions causing rapid skin cell turnover.

Atopic Dermatitis (Eczema)

• A chronic inflammatory condition commonly in children, causing red, itchy, and inflamed skin.
• Typically occurs due to a defect in the moisture barrier (low filaggrin levels) or dysfunctional tight junctions.
• Key Symptoms: Pruritus (itching), erythema (redness), and swelling.
• Common Areas: Flexor surfaces (elbows and knees), face, and scalp.

Psoriasis

• An autoimmune disorder characterized by epidermal hyperproliferation, leading to thick, scaly patches.
• The exact cause is unclear but is believed to be due to an immune-mediated process.
• Key Symptoms: Raised, scaly plaques that are often silver in color, commonly affecting the scalp, elbows, and knees.
• There is abnormal differentiation of epidermal keratinocytes, and cytokines drive inflammation.

Vitiligo

• A pigmentation disorder where the immune system attacks melanocytes, resulting in white patches of skin.
• Key Symptoms: Well-defined depigmented patches often appearing symmetrically, such as on the face, hands, and genitals.
• Though the exact cause is unclear, vitiligo is thought to involve autoimmune destruction of melanocytes.

Macule and Patch

• Macule: A flat, discolored spot less than 1 cm in size.
• Patch: Similar to a macule but larger than 1 cm.

Papule and Nodule

• Papule: A small, raised, solid lesion less than 1 cm in diameter (e.g., warts).
• Nodule: Similar to a papule but larger than 1 cm and may involve deeper tissues.

Vesicle and Bullae

• Vesicle: A small, fluid-filled blister less than 1 cm in diameter (e.g., chickenpox).
• Bullae: Larger blisters greater than 1 cm, often associated with burns or severe blistering disorders.

Pustule

• A small, pus-filled blister.
• Typically seen in conditions like acne, impetigo, or folliculitis.

Skin Examination

• Requires a thorough, methodical approach to detect abnormalities or conditions that indicate systemic disease or localized skin pathology.
• Descriptors such as size, shape, color, consistency, and distribution, along with palpation for temperature, tenderness, and texture, help in making an accurate diagnosis.
• Noting any chronic or recurring skin conditions and understanding the patient's history are important for a comprehensive assessment.