SR

Skin Accessory Structures

Skin Accessory Structures

Skin accessory structures are specialized organs that originate from the epidermis but extend into the dermis. They include hair, glands, and nails, each with distinct functions crucial for protection, sensation, and regulation.

Hair

Hair is a filamentous epidermal outgrowth that provides protection, sensory input, and thermoregulation. It consists of several components:

  • Hair Shaft: The portion of the hair that extends beyond the skin surface. It is composed of dead, keratinized cells.
  • Hair Root: The portion of the hair embedded within the skin, extending into the dermis or hypodermis.
  • Hair Follicle: A sac-like invagination of the epidermis that surrounds the hair root, responsible for hair growth.
  • Arrector Pili Muscle: A small, smooth muscle attached to the hair follicle. When it contracts, it pulls the hair upright, causing "goosebumps" (piloerection), often in response to cold or fright. This action also helps trap a layer of air for insulation.
  • Hair Bulb: The base of the hair follicle, which is a bulb-shaped structure containing the dermal papilla (supplying nutrients) and the hair matrix (where new hair cells are produced).

Glands

The skin contains various exocrine glands that secrete substances with different functions.

Sebaceous Glands

  • Description: These glands are typically associated with hair follicles, though some are found on hairless skin areas like the lips and genitalia.
  • Product: They produce sebum, an oily, waxy substance.
  • Function: Sebum lubricates the hair and skin, prevents water loss from the skin, and has antibacterial properties.

Sweat Glands (Sudoriferous Glands)

Sweat glands are responsible for producing sweat, primarily for thermoregulation.

  • Eccrine Glands:
    • Abundance: These are the most abundant type of sweat gland, found across most of the body's surface, particularly concentrated on the palms, soles, and forehead.
    • Product: Produce a watery secretion containing water, salts, urea, and other waste products.
    • Function: Their primary role is in thermoregulation through evaporative cooling.
  • Apocrine Glands:
    • Location: Primarily found in the axillary (armpit), anogenital, and areolar regions.
    • Product: Their secretion is thicker and contains lipids and proteins, in addition to the components of eccrine sweat. This secretion is initially odorless but can be broken down by bacteria on the skin, causing body odor.
    • Function: They become active at puberty and are associated with emotional sweating and contain pheromones, playing a minor role in signaling.

Ceruminous Glands

  • Location: Modified apocrine glands found only in the external ear canal.
  • Product: They produce cerumen, commonly known as earwax, a sticky, yellowish substance.
  • Function: Cerumen protects the ear canal by trapping foreign particles (dust, insects), preventing them from reaching the eardrum, and providing lubrication and antimicrobial properties.

Nails

Nails are hard plates of keratinized epidermal cells that provide protection to the tips of the fingers and toes and aid in grasping and manipulating small objects.

  • Nail Body (Nail Plate): The visible, flattened portion of the nail that we typically refer to as the fingernail or toenail.
  • Nail Root: The portion of the nail embedded within the skin at the base of the nail, where nail growth originates from the nail matrix.
  • Lunula: The crescent-shaped, whitish area at the base of the nail body. It represents the visible part of the nail matrix, where the cells are still nucleated and not fully keratinized.
  • Cuticle (Eponychium): A fold of skin that protects the nail matrix and the area where the nail emerges from the skin, sealing the space between the nail and the epidermis.