INTERNAL MEDICINE - SKIN
Overview
● Largest single organ of the body
○ ~16% of body weight
○ Covers ~1.2–2.3 m²
Functions of the Skin
1. Protection
○ Against cold, heat, radiation
○ Shields from pressure, blows, abrasion
○ Barrier against chemical substances
○ Prevents invasion by microorganisms
2. Barrier Functions
○ Prevents heat and water loss
○ Minimizes absorption of harmful substances
○ Protects against allergens and pathogens
3. Physiologic Functions
○ Absorption: certain drugs or chemicals
○ Perspiration: fluid and electrolyte balance
○ Thermal regulation: via dermal vascular system
4. Sensory Functions
○ Sensory receptors for pressure, vibration, touch, pain, temperature
Layers of the Skin
1. Epidermis (outermost, avascular)
○ Thin, keratinized epithelium
○ Two main layers:
■ Stratum corneum (outer, dead keratinized cells)
■ Malpighian layer (inner cellular layer = stratum basale + stratum spinosum)
○ Turnover time: ~28 days
○ Stratum Basale
■ Contains progenitor cells (actively dividing)
■ DNA damage here may → skin cancer
○ Stratum Spinosum
■ Contains new skin cells, strengthens skin
○ Stratum Granulosum
■ Keratin granules present
○ Stratum Lucidum
■ Present only in thick skin (palms, soles)
○ Stratum Corneum
■ Flattened, anucleated corneocytes + lipids
■ Functions:
■ Barrier against pathogens and chemicals
■ Prevents transepidermal water loss
■ Defects → conditions like atopic dermatitis
, 2. Dermis
○ Dense connective tissue (collagen + elastin)
○ Contains: sebaceous glands, sweat glands, hair follicles, cutaneous nerve endings
○ Origin of appendages: nails, hair, glands
○ Damage to collagen/elastic fibers → wrinkles (aging)
○ Prevention: avoid excessive sun exposure
3. Subcutaneous Layer (Hypodermis)
○ Spongy connective tissue + adipocytes
○ Functions:
■ Protects blood vessels
■ Temperature regulation
■ Energy storage
■ Keeps skin smooth & youthful
○ Fat distribution differs by sex and body region
Skin Color
● Keratinocytes: main epidermal cells (~90%)
● Melanocytes: dendritic cells producing melanin; derived from neural crest
● Melanin Granules:
○ Protect DNA of keratinocytes from UV damage
○ Types:
■ Eumelanin – brown/black pigment
■ Pheomelanin – red/yellow pigment
● Responsible for skin, hair, and eye color
History Taking
A good dermatologic history is essential because skin lesions often look similar and can be influenced by
external/environmental factors.
Three main aspects to focus on:
1. Symptoms related to the lesion
○ Itching (pruritus)
○ Pain
○ Burning sensations
2. Chronology
○ When did the lesion first appear?
○ Has it changed (size, shape, color, number)?
○ Has it disappeared and recurred?
3. Conditions of exposure
○ Environmental triggers (sun, chemicals, allergens)
○ Injuries or trauma
○ Medications that may have induced or altered the disease
Original Lesion
Always describe the first observed lesion in detail:
● Exact site (location matters: face vs. flexural vs. sun-exposed)
● Duration (acute vs. chronic)
● Appearance (size, shape, color, borders, surface changes)
● Distribution (localized, generalized, symmetrical, asymmetrical)
Overview
● Largest single organ of the body
○ ~16% of body weight
○ Covers ~1.2–2.3 m²
Functions of the Skin
1. Protection
○ Against cold, heat, radiation
○ Shields from pressure, blows, abrasion
○ Barrier against chemical substances
○ Prevents invasion by microorganisms
2. Barrier Functions
○ Prevents heat and water loss
○ Minimizes absorption of harmful substances
○ Protects against allergens and pathogens
3. Physiologic Functions
○ Absorption: certain drugs or chemicals
○ Perspiration: fluid and electrolyte balance
○ Thermal regulation: via dermal vascular system
4. Sensory Functions
○ Sensory receptors for pressure, vibration, touch, pain, temperature
Layers of the Skin
1. Epidermis (outermost, avascular)
○ Thin, keratinized epithelium
○ Two main layers:
■ Stratum corneum (outer, dead keratinized cells)
■ Malpighian layer (inner cellular layer = stratum basale + stratum spinosum)
○ Turnover time: ~28 days
○ Stratum Basale
■ Contains progenitor cells (actively dividing)
■ DNA damage here may → skin cancer
○ Stratum Spinosum
■ Contains new skin cells, strengthens skin
○ Stratum Granulosum
■ Keratin granules present
○ Stratum Lucidum
■ Present only in thick skin (palms, soles)
○ Stratum Corneum
■ Flattened, anucleated corneocytes + lipids
■ Functions:
■ Barrier against pathogens and chemicals
■ Prevents transepidermal water loss
■ Defects → conditions like atopic dermatitis
, 2. Dermis
○ Dense connective tissue (collagen + elastin)
○ Contains: sebaceous glands, sweat glands, hair follicles, cutaneous nerve endings
○ Origin of appendages: nails, hair, glands
○ Damage to collagen/elastic fibers → wrinkles (aging)
○ Prevention: avoid excessive sun exposure
3. Subcutaneous Layer (Hypodermis)
○ Spongy connective tissue + adipocytes
○ Functions:
■ Protects blood vessels
■ Temperature regulation
■ Energy storage
■ Keeps skin smooth & youthful
○ Fat distribution differs by sex and body region
Skin Color
● Keratinocytes: main epidermal cells (~90%)
● Melanocytes: dendritic cells producing melanin; derived from neural crest
● Melanin Granules:
○ Protect DNA of keratinocytes from UV damage
○ Types:
■ Eumelanin – brown/black pigment
■ Pheomelanin – red/yellow pigment
● Responsible for skin, hair, and eye color
History Taking
A good dermatologic history is essential because skin lesions often look similar and can be influenced by
external/environmental factors.
Three main aspects to focus on:
1. Symptoms related to the lesion
○ Itching (pruritus)
○ Pain
○ Burning sensations
2. Chronology
○ When did the lesion first appear?
○ Has it changed (size, shape, color, number)?
○ Has it disappeared and recurred?
3. Conditions of exposure
○ Environmental triggers (sun, chemicals, allergens)
○ Injuries or trauma
○ Medications that may have induced or altered the disease
Original Lesion
Always describe the first observed lesion in detail:
● Exact site (location matters: face vs. flexural vs. sun-exposed)
● Duration (acute vs. chronic)
● Appearance (size, shape, color, borders, surface changes)
● Distribution (localized, generalized, symmetrical, asymmetrical)
