Integumentary System Overview

Integumentary System Overview

• The integumentary system is a body system that encompasses skin and its appendages.
• It has key roles in protection, temperature regulation, and sensation.

What is Essential, Important, or Complementary?

• The presenter uses traffic lights to differentiate the significance of material:
  • Green (essential): Crucial information.
  • Yellow (important): Helpful, but not as crucial.
  • Red (complementary): Supplementary, but not essential, and shouldn't be seen as useless.
• Slides containing links between concepts are not marked with a symbol.
• This is meant to guide students in assessing slide importance to follow session flow.

Today's Topics

• Defining the structure and function of skin.
• Exploring various skin cell types.
• Identifying skin layers.
• Understanding the basement membrane and dermis.
• Interpreting the hair cycle.
• Investigating the appendages of the integumentary system (e.g., nerve cells, nails, sweat glands).

Components of the Integumentary System

• Skin and its appendages
• Hair
• Nails
• Sensory receptors
• Sweat, wax, and oil glands
• Mammary glands
• Teeth

Pathology of the Skin

• Solar (actinic) keratosis (a precancerous skin condition) is covered.
• Various skin melanomas are mentioned.

Structure of the Skin

• Acid mantle: Substances like amino acids, lactic acid, and fatty acids create an acidic layer important for protection.
• Friction ridges: Criss-crossing ridges and valleys on the epidermis and dermis.
• Epidermis: The outermost layer of skin, crucial for protection.
• Basement membrane zone: Connects the epidermis to the underlying dermis.
• Dermis: The second layer of skin; houses sweat glands, hair follicles, muscles, sensory neurons, and blood vessels.
• Subcutaneous tissue: Fatty tissue, the lowest layer of the skin.

Cell Types in Skin

• Epidermis is composed of three main cell types:
  • Keratinocytes (skin cells)
  • Melanocytes (pigment-producing cells)
  • Langerhans cells (immune cells)
  • Merkel cell (neuroendocrine cells)

Cell Types - Keratinocytes

• Make up 95% of the skin surface
• Are continually renewed every 15-30 days.
• Differentiate as they move upwards.
• Produce keratin, a tough and water-resistant protein.
• Keratinization: The process of replacing cell contents with keratin.

Cell Types - Melanocytes

• Develop from neural crest cells.
• Migrate to various areas of skin, etc.
• Produce melanin, vital for skin and hair color protection against UV radiation.
• Melanin is packaged into melanosomes and transferred to keratinocytes.
• Melanocyte stem cells reside in hair follicle bulges.

Cell Types - Langerhans Cells

• First line of immunological defense in skin.
• Specific dendritic cells.
• About 5% of epidermal cells.
• Characterized by cytoplasmic Birbeck granules.
• Migrate to lymph nodes.
• Responsible for allergen recognition; present antigens to lymphocytes.

Epidermal Layers

• Stratum corneum: Horny layer, outermost layer.
• Stratum lucidum: (Not always visible), clear layer.
• Stratum granulosum: Granular cell layer, with cells losing nuclei.
• Stratum spinosum: Prickle cell layer; cells communicate with desmosomes.
• Stratum basale: Basal cell layer; responsible for continuous cell production.

Stratum Basale

• Located adjacent to dermis.
• Mostly contains dividing and non-dividing keratinocytes.
• Melanocytes (pigment-producing cells) are found here.
• Merkel cells (neuroendocrine cells): Present in very small numbers in sensitive areas.

Stratum Spinosum

• 5-12 layers of polygonal keratinocytes; become flatter toward the surface.
• Cells communicate with each other via desmosomes.
• Langerhans cells are found here.

Stratum Granulosum (+Lucidum)

• 3–5 layers of flattened cells.
• Filled with irregular dark keratohyaline granules.
• Filled with cells losing nuclei.
• Stratum lucidum: A thin, clear layer consisting primarily of eleidin.

Stratum Corneum

• Outermost layer; flattened, dead cells (corneocytes).
• No nuclei or organelles remain; the cells are filled with keratin.
• 10 to 30 layers thick in most parts of skin; thicker in palms and soles.
• Lipids surround the corneocytes.

Basement Membrane (Basal Lamina)

• Thin, dense sheet of matrix to anchor skin cells to underlying connective tissue.
• Made of laminin and type IV collagen.
• Consists of distinct layers: lamina lucida, lamina densa, and lamina reticularis.

Dermis

• Fibrous connective tissue
• Houses mast cells, vascular smooth muscle cells, and fibroblasts.
• Epidermis and dermis communicate via cytokines and chemotactic factors.
• Contains sweat glands, hair follicles, muscles, sensory neurons, and blood vessels.

Layers of the Dermis

• Papillary layer: Composed of loose connective tissue, containing many blood capillaries and touch receptors.
• Reticular layer: Composed of interlacing collagen and elastin fibers, providing strength and elasticity to the skin.

Nerve Tissue within the Dermis

• Numerous nerve fibers (both motor and sensory).
• Locations of touch receptors: Pacinian corpuscle (heavy pressure), Merkel's disc (light touch), Meissner's corpuscle (light touch), and Ruffini's corpuscle (touch and heat)

Hair

• Found on all skin surfaces.
• Develops from groups of epidermal cells forming a hair follicle.
• Vellus hair (soft, short, and pale) and terminal hair (hard, long, dark).
• Extends into the dermis and sometimes into the subcutaneous layer.

Hair Growth Cycle

• Anagen: Active growth phase of the hair.
• Catagen: Regression phase of the hair follicle.
• Telogen: Resting phase of the hair follicle.

Sweat Glands

• Eccrine glands: Most numerous, respond to elevated temperature. Produce watery perspiration.
• Apocrine glands: Respond to emotional stress and sexual stimulation; concentrated in axillae.

Learning Outcomes

• Students are expected to recognize the structure, function, and histology of the skin and its accessory organs.