pielea

Pielea is the largest organ of the integumentary system in humans and many other animals. It acts as a protective covering, interfaces with the environment, and performs essential physiological functions. In humans, the skin consists of three main layers: the epidermis, the dermis, and the hypodermis (subcutaneous tissue).

The epidermis is the outer layer that provides a waterproof barrier and is mostly made of keratinocytes, with pigment cells (melanocytes), immune cells (Langerhans cells), and tactile cells (Merkel cells). It comprises several sublayers, including the stratum basale, spinosum, granulosum, lucidum (present in thick skin), and corneum, with new cells formed in the basale and gradually moving outward.

The dermis lies beneath the epidermis and contains connective tissue rich in collagen and elastin, along with blood vessels, nerves, hair follicles, and glands. The deeper hypodermis consists largely of adipose tissue and connective tissue, helping insulate the body and anchor the skin.

Functions include acting as a barrier to pathogens and water loss, regulating temperature through sweat production and blood flow, providing sensory information via nerve endings, participating in immune defense, synthesizing vitamin D when exposed to sunlight, and contributing to wound healing through cellular and extracellular processes.

Skin characteristics vary by species and individual. In humans, melanin determines color; thickness varies by body site and can differ in thickness between regions of thick skin (palms, soles) and thin skin. Skin health depends on nutrition, hydration, sun exposure, and age.