Integumentary System Overview

Integumentary System Overview

• The integumentary system is the body's covering, also known as the skin.
• It acts as the body's first line of defense against the environment.
• The system has three major components: cutaneous membrane, accessory structures, and superficial fascia.

Levels of Organization

• The organization of the human body includes different levels, from chemical to organismal.
• The integumentary system is located at the organ system level.
• It's composed of various organs, tissues, and cells.

Cutaneous Membrane

• The cutaneous membrane is the skin itself.
• The skin is composed of two layers, the epidermis and dermis.
• The epidermis is the outermost layer, and it is composed of keratinized stratified squamous epithelium.
• The dermis is the underlying layer composed of connective tissue.

Accessory Structures

• These structures are associated with the cutaneous membrane.
• Hairs, nails, sebaceous glands, and sweat glands are examples of accessory structures.
• These structures perform various functions such as protection, sensation, and thermoregulation.

Superficial Fascia (Subcutaneous Layer)

• The superficial fascia is also known as the subcutaneous layer or hypodermis.
• It separates the skin from deeper structures.
• It consists of both areolar and adipose tissue.

Epidermis

• The epidermis is the outermost layer of the skin.
• It contains 4-5 layers of cells called strata/strata.
• The primary cell type in the epidermis is a keratinocyte.
• Epidermal ridges are adjacent to dermal papillae. This increases surface area to enhance attachment to the underlying dermis.
• Layers of the epidermis include the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
• Stratum basale is connected to the basement membrane by hemidesmosomes.
• Keratinocytes divide in the stratum basale to replace more superficial keratinocytes.
• Melanocytes are also found in the stratum basale and produce melanin, determining skin tone.
• Stratum corneum is the outermost layer composed of dead, keratinized cells, providing a waterproof barrier.
• Stratum lucidum is only present in thick skin.

Dermis

• The dermis is below the epidermis.
• The dermis is composed of two layers: papillary layer and reticular layer.
• Papillary layer is superficial and consists of areolar connective tissue.
• Reticular layer is deep and consists of dense irregular connective tissue.

Hypodermis

• The hypodermis is also known as superficial fascia.
• It's located beneath the dermis.
• It consists of areolar and adipose tissue.
• It isolates the skin from deeper tissues and acts as an energy reserve.

Skin Color

• Skin color is determined by melanin, carotene, and blood.
• Melanin is produced by melanocytes in the stratum basale.
• Darker skin has a higher concentration of melanin.
• Carotene is an orange-yellow pigment that can be obtained from some foods.
• Blood, specifically hemoglobin, also influences skin color. Redder skin indicates increased blood flow, while paler skin indicates less blood flow.
• Jaundice is a yellowing of the skin and whites of eyes due to bilirubin buildup in the blood.
• Bruising results from broken blood vessels beneath the skin's surface and displays a range of colors as hemoglobin breaks down.

Epidermal Cancers

• Basal cell carcinoma is the most common epidermal skin cancer, originating in the stratum basale.
• It generally does not metastasize, and most individuals survive the cancer.
• Malignant melanoma is an extremely dangerous skin cancer arising from melanocytes.
• It is characterized by rapid growth and metastasis through the lymphatic system.
• Squamous cell carcinoma is specific to squamous cells and commonly results from UV exposure.

Sensory Perception

• The skin contains various sensory receptors for different sensations such as heat or cold (thermoreceptors), touch (Meissner's corpuscles), pain (nociceptors), and pressure (Pacinian corpuscles).

Burns

• Burns result from exposure to heat, friction, radiation, electrical shock, or strong chemical agents.
• Depths of burns include first-degree (epidermis only), second-degree (dermis and epidermis), and third-degree (full-thickness).
• Deeper burns also involve the hypodermis.
• Severity of burns include area and depth of injury.
• First-degree burns are superficial, causing redness and pain.
• Second-degree burns extend into the dermis and show blistering and pain.
• Third-degree burns involve complete destruction of skin layers, typically causing little pain, due to destroyed nerve endings.
• Skin grafts repair significant burn damage by transferring undamaged skin from other areas of the body or a cadaver or animal.
• Rule of nines is a method for estimating burn percentages.

Hair

• Hair grows and sheds in a hair growth cycle.
• Hair functions to protect the scalp and regulate heat loss.
• Hair is composed of a hair shaft, hair root, hair follicle, root hair plexus, arrector pili muscle, and sebaceous glands.
• Terminal hairs are coarse, dark hairs found on the scalp, armpits, and face.
• Vellus hairs are fine, short, and delicate and are located over the rest of the body.
• Hair follicles are complex structures composed of epithelial and connective tissue.
• Hair matrix actively divides basal cells in contact with the hair papilla.
• Sebaceous glands produce sebum, an oily secretion that lubricates the hair and skin.
• Arrector pili muscles are smooth muscles that cause hairs to stand on end when they contract.

Exocrine Glands

• Exocrine glands, including sebaceous and sweat glands, secrete substances onto the skin's surface.
• Sebaceous glands secrete sebum, an oil that lubricates and protects the skin and hair.
• Sweat glands secrete sweat, a watery fluid, to regulate body temperature.
• Acne is a common skin condition caused by blocked sebaceous glands.
• Sweat glands include two types, eccrine and apocrine.
• Eccrine glands are responsible for thermoregulation via perspiration.
• Apocrine glands release a sticky secretion involved in body odor and localized hormone activity.

Nails

• Nails are hard, keratinized plates that protect the tips of the fingers and toes.
• Nails are made up of keratinized epidermal cells.

Interactions & Changes

• The skin can change structurally and functionally in response to the environment and age.
• Age-related changes in the skin include fewer melanocytes, drier epidermis, thin epidermis, diminished immune response, thinner dermis, and decreased perspiration.

Integument & Endocrine/Digestive/Skeletal Systems

• Hormones and other components between systems can directly affect the skin's structure and function.
• Sunlight triggers the production of Vitamin D3, which is necessary for calcium and phosphate absorption.
• Insufficient calcitriol can lead to rickets in children or decreased bone density in adults due to reduced Vitamin D3 stimulation.

Integument Injury & Repair

• The skin can be damaged in many ways but can regenerate.
• Skin regeneration follows an inflammatory phase, migration phase, proliferation phase, and scarring phase.
• There are four major phases in skin regeneration: inflammatory, migratory, proliferative, and scarring, each with distinct changes.