Structure and Function of the Skin: Anatomy & Physiology Study Notes

Structure and Function of the Skin

Overview of Skin Anatomy

The skin is the largest organ of the human body, serving as a protective barrier and playing a vital role in sensation, thermoregulation, and excretion. It is composed of multiple layers and specialized structures, each with distinct functions.

• Epidermis: The outermost layer, providing a waterproof barrier and creating our skin tone.

• Dermis: Beneath the epidermis, containing tough connective tissue, hair follicles, and sweat glands.

• Hypodermis (Subcutaneous layer): Made of fat and connective tissue, providing insulation and cushioning.

Main Structures of the Skin

• Hair Shaft: The visible part of the hair above the skin surface.

• Hair Follicle: The structure in the dermis from which the hair grows.

• Hair Root: The part of the hair located below the surface of the skin.

• Arrector Pili Muscle: Small muscle attached to hair follicles; contraction causes 'goosebumps.'

• Sweat Pore: Opening on the skin surface for sweat excretion.

• Sebaceous Gland: Secretes sebum (oil) into the hair follicle to lubricate the skin and hair.

• Eccrine Sweat Gland: Produces sweat for thermoregulation, found throughout the body.

• Apocrine Gland: Found in axillary and pubic areas, secretes a thicker fluid into hair follicles.

• Lamellar (Pacinian) Corpuscles: Sensory receptors for deep pressure and vibration.

• Meissner's Corpuscles: Sensory receptors for light touch.

• Merkel's Disks: Sensory receptors for steady pressure and texture.

• Ruffini Corpuscles: Sensory receptors for continuous pressure and skin stretch.

• Papillary Dermis: Upper layer of the dermis, contains capillaries and sensory neurons.

• Basal Stratum Granulosum: Layer of the epidermis involved in keratinization.

Skin Layers and Their Functions

Layers of the Epidermis

The epidermis consists of several distinct layers, each with specialized cells and functions. From superficial to deep:

1. Stratum Corneum: Outermost layer; consists of dead, flattened keratinocytes. Provides a tough, protective barrier against environmental damage and water loss. Thicker on palms and soles.

2. Stratum Lucidum: Thin, clear layer found only in thick skin (palms, soles). Adds extra protection.

3. Stratum Granulosum: Thin layer of keratinized cells. Helps regulate skin temperature and prevents water loss.

4. Stratum Spinosum: Contains keratinocytes that produce and secrete keratin, making skin strong and flexible.

5. Stratum Basale (Stratum Germinativum): Deepest layer; responsible for continuous cell division and regeneration. Contains keratinocytes, melanocytes (produce pigment), and Merkel cells (sensory function).

Functions of the Skin

• Protection: Acts as a barrier against pathogens, chemicals, and physical injuries.

• Sensation: Contains nerve endings for touch, pain, temperature, and pressure.

• Thermoregulation: Regulates body temperature through sweat production and blood flow.

• Excretion: Removes waste products via sweat.

• Vitamin D Synthesis: Initiates production of vitamin D when exposed to UV light.

Sensory Receptors and Glands of the Skin

Sensory Nerve Endings

The skin contains various specialized nerve endings that detect different types of stimuli.

Nerve Ending	Location	Function
Open-ended nerves	Throughout the body, in skin, connective tissue, and joints	Transmit sensations for pain, temperature, and touch
Pacinian (Lamellar) Corpuscles	Palms, soles of feet, fingertips	Detect deep pressure and vibration
Ruffini Corpuscles	Deep in the dermis, may extend into hypodermis	Detect continuous pressure and changes in joint angles

Glands of the Skin

Several types of glands are present in the skin, each with specific secretions and functions.

Gland	Location	Function
Eccrine	Palms and soles	Secretes salt water/sweat for thermoregulation
Sebaceous	Hair follicle	Secretes sebum (oil) to lubricate skin and hair
Apocrine	Axillary/public area	Secretes lipoproteins (transports lipids)

Skin Cancer Types

Skin cancer is classified based on the type of cell from which it originates. The three main types, listed from most to least dangerous, are:

1. Melanoma: Originates from melanocytes. Appears as a mole with an irregular shape, uneven color (brown, black, red, tan, white, or blue), and blurry borders. Typically larger than 6 mm. Most dangerous due to high risk of metastasis.

2. Squamous Cell Carcinoma: Originates from squamous cells. Appears as a firm bump or nodule with a rough, scaly texture. Can be red and discolored, may crust or bleed. Less dangerous than melanoma but can spread if untreated.

3. Basal Cell Carcinoma: Originates from basal cells. Appears as a small bump, color ranges from pink to pearly or brown. Common on sun-exposed areas (face, neck, ears). Texture can be smooth, waxy, or slightly scaly. Least dangerous, rarely metastasizes.

Summary Table: Epidermal Layers and Functions

Layer	Location	Function
Stratum Corneum	Outermost	Protection, reduces friction, prevents water loss
Stratum Lucidum	Thick skin only (palms, soles)	Extra protection
Stratum Granulosum	Middle layer	Keratinization, prevents water loss
Stratum Spinosum	Above basal layer	Strength, flexibility, keratin production
Stratum Basale	Deepest layer	Cell division, regeneration, pigment production

Key Terms

• Keratinocyte: Main cell type in the epidermis, produces keratin.

• Melanocyte: Produces melanin, the pigment responsible for skin color.

• Merkel Cell: Sensory cell involved in touch sensation.

• Sebum: Oily substance secreted by sebaceous glands.

• Lipoprotein: Molecule that transports lipids in the body.

Additional info: The notes above include expanded academic context and definitions to ensure completeness and clarity for exam preparation.