Integumentary System

OT Dude Academy’s Free NBCOT® Exam Prep Course Medical Terminology, Anatomy, and Physiology Integumentary System

Source 1  licensed under Creative Commons Attribution 4.0 International License.

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1 Background
2 Accessory Structures
2.1 Hair
2.2 Nails
2.3 Sweat Glands
2.4 Sebaceous Glands

Background

  • Made of the skin and its accessory structures.
  • Provides the body with overall protection, e.g., infection.
  • Skin is made of multiple layers of cells and tissues, held by connective tissue.
  • Deeper layers of skin are vascularized.
  • Contains sensory, autonomic, and sympathetic nerve fibers for communication with the brain.
  • Layers are composed of: epidermis, dermis, and hypodermis (deepest).
  • Epidermis – composed of keratinized, stratified squamous epithelium; avascular.
    • Thin skin – 4 layers of cells: stratum basale, stratum spinosum, stratum granulosum, and stratum corneum (deep to superficial). Most skin is classified as thin skin.
    • Thick skin – found on the palms of the hands and soles of the feet. Contains a fifth layer called the stratum lucidum, located between the stratum corneum and the stratum granulosum.
  • Dermis – contains blood and lymph vessels, nerves, and other structures, e.g., hair follicles and sweat glands. Made of two layers of connective tissue (papillary and reticular) that compose an interconnected mesh of elastin and collagenous fibers, which are produced by fibroblasts.
  • Papillary Layer – made of loose, areolar connective tissue. This superficial layer of the dermis projects into the stratum basale of the epidermis to form finger-like dermal papillae. Contains fibroblasts, adipocytes, small blood vessels, phagocytes, lymphatic capillaries, nerve fibers, and Meissner corpuscles.
  • Reticular Layer – underlies the papillary layer. The thicker layer is composed of dense, irregular connective tissue. Vascularized with a rich sympathetic nerve supply. Elastin fibers provide some elasticity to the skin and enable movement. Collagen fibers provide structure and tensile strength, with strands of collagen extending into both the papillary layer and the hypodermis. Keeps skin hydrated.
  • Hypodermis – connects the skin to the underlying fascia of bones and muscles. Not strictly part of the skin. Between the hypodermis and dermis. Consists of vascularized, loose, areolar connective, and adipose tissue (fat storage and insulation)
  • Function of the integumentary system: protection from invasion by foreign organisms, chemicals, and environmental factors; preventing dehydration; acts as a sensory organ; modulates body temperature and electrolyte balance; synthesizes vitamin D. Plays a role in the storage of fats, forming a cushion over underlying structures, and providing insulation from cold temperatures.

Accessory Structures

Hair

Hair serves a variety of functions, including protection, sensory input, thermoregulation, and communication. For example:

  • Hair on the head protects the skull from the sun.
  • Hair in the nose and ears, and around the eyes (eyelashes) defends the body by trapping and excluding dust particles that may contain allergens and microbes.
  • Hair of the eyebrows prevents sweat and other particles from dripping into and bothering the eyes.
  • Hair also has a sensory function due to sensory innervation by a hair root plexus surrounding the base of each hair follicle. Hair is extremely sensitive to air movement or other disturbances in the environment, much more so than the skin surface. This feature is also useful for the detection of the presence of insects or other potentially damaging substances on the skin surface.

Each hair root is connected to a smooth muscle called the arrector pili that contracts in response to nerve signals from the sympathetic nervous system, making the external hair shaft “stand up.” The primary purpose for this is to trap a layer of air to add insulation. This is visible in humans as goosebumps and even more obvious in animals, such as when a frightened cat raises its fur. Of course, this is much more obvious in organisms with a heavier coat than most humans, such as dogs and cats.

Nails

The nail bed is a specialized structure of the epidermis that is found at the tips of our fingers and toes. The nail body is formed on the nail bed and protects the tips of our fingers and toes as they are the farthest extremities and the parts of the body that experience the maximum mechanical stress. The nail body forms a back-support for picking up small objects with the fingers. The nail body is composed of densely packed dead keratinocytes.

The nail bed is rich in blood vessels, making it appear pink, except at the base, where a thick layer of epithelium over the nail matrix forms a crescent-shaped region called the lunula (the “little moon”). The area beneath the free edge of the nail, furthest from the cuticle, is called the hyponychium. It consists of a thickened layer of stratum corneum.

Sweat Glands

When the body becomes warm, sudoriferous glands produce sweat to cool the body.

Sebaceous Glands

A type of oil gland that is found all over the body and helps to lubricate and waterproof the skin and hair. Most sebaceous glands are associated with hair follicles. They generate and excrete sebum, a mixture of lipids, onto the skin surface, thereby naturally lubricating the dry and dead layer of keratinized cells of the stratum corneum, keeping it pliable. The fatty acids of sebum also have antibacterial properties and prevent water loss from the skin in low-humidity environments.

  1. Betts, J.G., Young, K.A., Wise, J.A., Johson, E., Poe, B., Kruse, D. H., Korol, O., Johnson, J.E., Womble, M. & DeSaix, P. (2013). Anatomy and Physiology. OpenStax. http://cnx.org/content/col11496/latest/[↩]
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