Lecture on Skin and the Integumentary System

Protection: Acts as a barrier against infection and injury.
Temperature Regulation: Through sweat glands and blood vessels.
Sensation: Nerve endings in dermis detect pressure, temperature, and pain.
Pigmentation: Melanocytes produce melanin, affecting skin color.

Introduction

Common associations with the term "organ" often exclude the skin.
Skin is the largest organ, critical for protection, temperature regulation, fluid balance, vitamin D synthesis, and sensory perception.
Skin can weigh 3-5 kilograms and cover about 2 square meters.
It's a waterproof, insulating, stretchy, self-repairing organ.

Layers of Skin: Skin has three layers: epidermis, dermis, and subcutis (hypodermis).
- Epidermis: Visible layer made of stratified squamous epithelial tissue.
  - Contains keratinocytes, melanocytes, Langerhans cells, and Merkel cells.
  - Divided into thinner and thicker skin (thicker on palms and soles).
  - 5 layers: Stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale.
- Dermis: Middle layer, contains nerves, blood vessels, and glands.
  - Two layers: papillary layer and reticular layer (thicker).
  - Functions in sensation, nutrient supply, and structural support.
- Subcutis (Hypodermis): Basal layer mainly composed of adipose tissue.
  - Provides insulation, energy storage, shock absorption, and anchors skin.

Tattoos must reach the dermis to be permanent.
Skin color is influenced by melanin, not the number of melanocytes but their activity.

Sun can damage epidermis, leading to issues like "leather face," immune suppression, and skin cancer.
Importance of sunscreen to protect against UV radiation.

Skin is a complex organ with multiple layers and functions crucial for maintaining overall health.
Next lesson will cover topics like lotion efficacy, deodorant function, and hair care.

This episode was produced by the Crash Course team, script by Kathleen Yale, and other contributors as mentioned.