Summary
Highlights
The stratum granulosum contains keratinocytes that flatten and develop granules before losing organelles. The stratum spinosum has many layers of keratinocytes and cells that consume worn-out cells or bacteria, appearing spiny under a microscope.
The integumentary system, primarily skin, is the largest organ and critical for homeostasis, maintaining body temperature, fluid balance, and acting as a physical barrier. It also produces Vitamin D and provides sensory functions.
The epidermis has several layers, starting with keratinocytes, cells that produce keratin, a protein making skin tough and water-resistant. A mnemonic, 'Can lemurs get some bamboo?', aids in remembering the epidermal layers from outer to inner.
The outermost layer is the stratum corneum, composed of dead, cornified cells that are continuously shed. The stratum lucidum, found only in thick skin like palms and soles, also consists of cornified cells with a transparent appearance.
The stratum basale is the deepest layer, containing basal cells that constantly divide to produce keratinocytes. It also includes melanocytes, which produce melanin for skin color and UV protection, and Merkel cells, involved in the sense of touch. Calluses form here due to frequent abrasion.
The dermis contains blood vessels, sweat glands, hair follicles, and nerves. Made of connective tissue, it features collagen for support and elastin for elasticity, produced by fibroblasts. Scars form when damage extends to the dermis, as collagen is not arranged in the original pattern, and can lead to keloids if collagen production is excessive.
The hypodermis, beneath the dermis, connects skin to bone and muscle, containing adipose tissue for insulation. Accessory structures include sweat glands for temperature regulation (with blood vessel dilation/constriction), sebaceous glands for oil production, hair (with follicles in the dermis), and nails (made of dead keratinocytes from the nail root).
Understanding the integumentary system is crucial for treating conditions like skin cancer (e.g., basal cell carcinoma from basal cells, melanoma from melanocytes, Merkel cell carcinoma from Merkel cells) and burns. Burns are categorized by depth (first to fourth degree), affecting different layers and compromising vital skin functions like fluid maintenance and infection protection, necessitating specialized medical care.