Layers of the Skin Overview

Layers of the Skin

• The skin is composed of three main layers: epidermis, dermis, and hypodermis (subcutaneous tissue).
• The epidermis is the outermost layer, acting as a waterproof barrier and protecting the body from pathogens and UV radiation.
• The dermis lies beneath the epidermis, containing connective tissue, blood vessels, nerves, hair follicles, and sweat glands. It supports the epidermis and provides structure.
• The hypodermis, or subcutaneous tissue, is the innermost layer. Primarily composed of fat, it acts as insulation and cushions the body.

Epidermis

• The epidermis is further divided into several layers, arranged from top to bottom.
• The stratum corneum is the outermost layer, consisting of dead, flattened keratinocytes. These cells are constantly shed and replaced.
• The stratum lucidum (in thick skin only) is a thin, clear layer above the stratum granulosum.
• The stratum granulosum is where cells begin to die and keratinize.
• The stratum spinosum is where keratinocytes take on a spiny appearance as they mature.
• The stratum basale is the deepest layer. This is where new skin cells are produced from stem cells and migrate upwards to replace outer layers. Melanocytes (pigment-producing cells) reside here, and they determine skin tone.
• Keratinocytes are the primary cell type in the epidermis, producing keratin, a tough protein that provides protection.
• Melanocytes produce melanin, a pigment that protects against UV radiation.

Dermis

• The dermis is composed of connective tissue, primarily collagen and elastin fibers.
• Collagen provides strength and structure, while elastin allows the skin to stretch and recoil.
• Blood vessels in the dermis deliver nutrients and oxygen to the skin cells and regulate skin temperature.
• Sensory receptors in the dermis detect touch, temperature, and pain.
• Hair follicles originate in the dermis, with associated sebaceous glands that produce sebum, an oily substance that moisturizes the hair and skin.
• Sweat glands are also embedded in the dermis, releasing sweat to regulate body temperature.

Hypodermis (Subcutaneous Tissue)

• The hypodermis is primarily composed of adipose tissue (fat).
• This layer acts as insulation, helping to regulate body temperature.
• It also provides cushioning and protection to underlying structures.
• Blood vessels in the hypodermis are important for supplying nutrients and oxygen to the deeper tissues.

Function of the Skin

• Protection: The skin shields the body from pathogens, UV radiation, and mechanical damage.
• Sensation: Sensory receptors in the skin detect touch, temperature, pain, pressure, and vibration. The information is transmitted to the nervous system.
• Thermoregulation: Sweat glands and blood vessels in the skin help to regulate body temperature by sweating or altering blood flow.
• Excretion: The skin excretes waste products through perspiration, which contains small amounts of salts, urea, and other metabolic byproducts.
• Vitamin D synthesis: Exposure to sunlight stimulates the production of Vitamin D in the skin, crucial for calcium absorption.
• Absorption: Certain substances, like certain medications and creams, can be absorbed through the skin, varying by skin type.
• Immunity: The skin contains cells of the immune system that protect against pathogens.
• Blood reservoir: Skin blood vessels have a role in regulating blood flow and blood volume.
• Displaying emotions: Facial expression is dependent on muscular action within the skin.