Overview
This lecture covers the structure, functions, and layers of the skin, highlighting its role as the main organ of the integumentary system.
Introduction to the Skin and Integumentary System
- Skin is the largest organ, protecting against infection, temperature, fluid loss, and synthesizes vitamin D.
- The integumentary system includes skin, hair, nails, sweat, and oil glands.
- Skin communicates health and emotions through changes like blushing, flushing, and sweating.
Functions and Properties of Skin
- Skin senses the external environment through nerve endings.
- Sweat glands and blood vessels regulate body temperature.
- Skin serves as a first-line defense against pathogens.
Structure and Layers of the Skin
- Skin has three layers: epidermis (outer), dermis (middle), and hypodermis/subcutis (inner).
- The epidermis is made of stratified squamous epithelial tissue and is visible.
- The dermis is responsible for most skin functions, including sensation, blood flow, sweating.
- The hypodermis consists mainly of adipose (fat) tissue for insulation and shock absorption.
Cells of the Epidermis
- Keratinocytes produce keratin, providing toughness and waterproofing.
- Melanocytes produce melanin, dictating skin color by extension size, not quantity.
- Langerhans (dendritic) cells are immune cells that defend against invaders.
- Merkel cells act as touch receptors at the epidermis-dermis boundary.
Epidermal Layers and Regeneration
- Thick skin (palms, soles) has five epidermal layers; thin skin has four.
- Layers from outer to inner: stratum corneum, stratum lucidum (only in thick skin), stratum granulosum, stratum spinosum, stratum basale.
- Cells regenerate from the stratum basale upward, moving outward and dying as they lose nutrient access.
Dermis and Subcutaneous Layer Details
- Dermis contains collagen, elastin, capillaries, nerve fibers, hair follicles, oil and sweat glands.
- The papillary layer contains dermal papillae, forming fingerprints in thick skin.
- The reticular layer provides strength and flexibility.
- The hypodermis anchors skin, providing insulation, energy storage, and shock absorption.
Skin Health and Damage
- Sunburn can damage the epidermis, depress immune function, and increase cancer risk by DNA alteration.
- Cuts or tattoos reaching the dermis cause pain and bleeding; tattoos are permanent because they reach this layer.
Key Terms & Definitions
- Epidermis — Outer layer of skin made of epithelial tissue.
- Dermis — Middle layer with connective tissue, blood vessels, nerves.
- Hypodermis/Subcutis — Fatty bottom layer providing insulation and energy storage.
- Keratinocyte — Cell producing keratin for strength and waterproofing.
- Melanocyte — Pigment-producing cell determining skin color.
- Langerhans Cell — Immune cell of the skin.
- Merkel Cell — Sensory touch receptor cell.
- Stratum Corneum/Lucidum/Granulosum/Spinosum/Basale — Layers of the epidermis, each with specific functions.
Action Items / Next Steps
- Review skin structure diagrams and memorize the order and function of epidermal layers.
- Read up on the effects of sunlight on skin and the importance of sunscreen.
- Next lecture: effects of lotion, deodorants, and hair care products on the integumentary system.