Integumentary System: Structure, Function, and Cellular Components

Integumentary System

Overview

The integumentary system is composed of the skin and its associated structures, serving as the body's primary barrier against the external environment. It plays crucial roles in protection, sensation, thermoregulation, and synthesis of vitamin D.

Key Definitions

• Apocrine gland: A type of sweat gland found mainly in the axillary and genital areas, responsible for scent-related secretions.

• Arrector pili muscle: Small muscles attached to hair follicles, causing hair to stand up (goosebumps) when contracted.

• Dermal papillae: Projections of the dermis into the epidermis, increasing surface area for exchange and forming fingerprints.

• Dermis: The thick layer of living tissue below the epidermis, containing blood vessels, nerves, and accessory organs.

• Eccrine gland: The most common type of sweat gland, involved in thermoregulation.

• Epidermis: The outermost layer of skin, composed of stratified squamous epithelium.

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

• Hair root: The part of the hair embedded in the follicle.

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

• Hypodermis: The subcutaneous layer beneath the dermis, mainly composed of adipose tissue.

• Keratination: The process by which keratinocytes produce keratin, leading to the formation of the tough, protective outer layer of the skin.

• Keratocyte: (Likely refers to keratinocyte) The predominant cell type in the epidermis, responsible for producing keratin.

• Lamelar (Pacinian) corpuscle: Sensory receptors in the skin that detect pressure and vibration.

• Melanocytes: Cells in the epidermis that produce melanin, the pigment responsible for skin color.

• Papillary layer (of the dermis): The upper layer of the dermis, containing thin collagen fibers and capillaries.

• Reticular layer (of the dermis): The deeper layer of the dermis, containing thicker collagen bundles and providing strength.

• Sebaceous (oil) gland: Glands that secrete sebum, an oily substance that lubricates skin and hair.

• Stratum basale: The deepest layer of the epidermis, where cell division occurs.

• Stratum spinosum: The layer above the stratum basale, providing strength and flexibility.

• Stratum granulosum: The layer where keratinocytes begin to die and keratinization intensifies.

• Stratum lucidum: A thin, clear layer found only in thick skin (palms, soles).

• Stratum corneum: The outermost layer of the epidermis, composed of dead, keratinized cells.

Structure of the Skin

Layers of the Epidermis

The epidermis consists of several distinct layers, each with specialized functions:

• Stratum basale: Single layer of stem cells; site of mitosis and melanocytes.

• Stratum spinosum: Several layers of keratinocytes; provides strength.

• Stratum granulosum: Cells accumulate keratin and begin to die.

• Stratum lucidum: Present only in thick skin; provides extra protection.

• Stratum corneum: Many layers of dead, flattened, keratinized cells; forms the protective barrier.

Layers of the Dermis

The dermis is divided into two main layers:

• Papillary layer: Thin, superficial layer with dermal papillae; contains capillaries and sensory receptors.

• Reticular layer: Thicker, deeper layer; contains dense irregular connective tissue, hair follicles, glands, and blood vessels.

Accessory Organs of the Skin

• Hair follicle, root, and shaft: Structures involved in hair growth and protection.

• Sebaceous (oil) glands: Secrete sebum to lubricate skin and hair.

• Eccrine sweat glands: Widely distributed; regulate body temperature.

• Apocrine sweat glands: Found in specific areas; involved in scent production.

• Lamelar/Pacinian corpuscles: Sensory receptors for pressure and vibration.

Microscopic Identification of Skin Structures

Key Structures to Identify

• Epidermal layers: Stratum basale, spinosum, granulosum, lucidum, corneum

• Dermal layers: Papillary and reticular layers

• Accessory organs: Hair follicle, hair root, hair shaft, sebaceous gland, sweat glands, lamellar corpuscle

Cells and Cell Types in Skin Layers

Major Cell Types

• Keratinocytes: Main cell type in the epidermis; produce keratin for protection.

• Melanocytes: Located in the stratum basale; produce melanin pigment.

• Langerhans cells: Immune cells in the epidermis; involved in defense.

• Merkel cells: Sensory cells in the epidermis; detect touch.

• Fibroblasts: Main cell type in the dermis; produce collagen and elastin.

Keratination and Melanocytes

Keratination Process

• Keratinocytes originate in the stratum basale and migrate upward.

• As they move, they produce keratin and eventually die, forming the stratum corneum.

• This process creates a tough, water-resistant barrier.

Role of Melanocytes

• Melanocytes produce melanin, which is transferred to keratinocytes.

• Melanin protects underlying tissues from UV radiation.

Functions of Skin Structures

Summary Table: Functions of Major Skin Structures

Structure	Function
Epidermis	Protection, barrier to pathogens, water loss prevention
Dermis	Support, elasticity, houses blood vessels and nerves
Hypodermis	Insulation, energy storage, shock absorption
Hair follicle	Hair growth, protection, sensation
Sebaceous gland	Secretes sebum for lubrication
Eccrine sweat gland	Thermoregulation via sweat production
Apocrine sweat gland	Scent production, emotional sweating
Lamellar/Pacinian corpuscle	Detects pressure and vibration
Melanocyte	Produces melanin for UV protection

Additional info:

• Keratinization is essential for forming the skin's protective barrier.

• Melanocytes are crucial for skin pigmentation and protection against UV damage.

• Accessory organs such as glands and hair follicles contribute to the skin's multiple functions, including thermoregulation and sensation.