The Integumentary System Overview

Study Notes

The Integumentary System includes skin, hair, nails, sweat glands, and sebaceous glands
The Integumentary System is 16% of body weight
The system is composed of the cutaneous membrane (skin) and accessory structures
The skin is the most accessible organ and the largest organ
The cutaneous membrane is divided into the epidermis (epithelium) and dermis (connective tissue)
There are accessory structures of the Integumentary system such as hair, nails, sweat glands, and sebaceous glands

Protection of underlying organs from:
- Dehydration
- Infection
- Abrasion
- UV damage
- Cold/Heat
Maintenance of normal body temperature through:
- Insulation
- Evaporative cooling
Synthesis of Vitamin D3 (when exposed to the sun)
Excretion of water, salts, and oils
Production of melanin to protect the underlying tissue from UV radiation
Production of keratin which repels water and protects against abrasion
Sensory Perception at the tactile receptors and free nerve endings
Energy Storage (of lipid) in adipocytes in the dermis and in adipose tissue in the subcutaneous layer
Coordination of immune response to pathogens and cancers in the skin

There are 3 main layers of the skin:
- Epidermis
- Dermis
- Hypodermis (subcutaneous layer)
The cutaneous membrane includes the Epidermis and Dermis
The Epidermis is a keratinised stratified squamous epithelium
The Dermis is composed of loose areolar CT and dense irregular CT proper with accessory structures
The Hypodermis (or subcutaneous layer) is composed of loose CT proper

The cutaneous membrane is the skin
The membrane is thick and relatively waterproof and dry
The Cutaneous membrane is composed of:
- The Epidermis (epithelium) which is supported by the areolar CT of the dermis
- The Dermis (connective tissue) which connects the epithelium to the underlying structures

There are 3 main types of cells in the epidermis:
- Squamous cells: flat cells in the outer portion of the epidermis that shed as new cells form
- Basal cells: located in the deeper portion of the epidermis, called the basal cell layer
- Melanocytes: make melanin, which gives the skin its tan or brown color
- Melanin functions as the body’s natural sunscreen
The epidermis is separated from deeper layers of skin by the basement membrane
Skin cancer becomes more advanced when it moves through the basement membrane and into deeper layers
There are also cells of the immune system and sensory nerve cells in the epidermis

Thick skin is found on the palms of the hand and soles of the feet and has 5 epidermal layers
Thin skin is found on the rest of the body and has 4 epidermal layers
The thickness of the epidermal layer determines thick or thin skin
Thick skin of the palms and soles of the feet is about 0.5mm thick
Thin skin of the rest of the body is about 0.08mm thick

The Epidermis is made up of stratified squamous epithelium (keratinised)
The Epithelial cells of the Epidermis are called keratinocytes
There are 4 or 5 layers of the epidermis, depending on the thickness
The Epidermis is difficult to distinguish with a light microscope
The Epidermis gives the skin properties such as:
- Water resistance
- Protection from microorganisms and abrasion
- Gland secretions
- Support for sensory cells
A blister is water trapped between layers of the epidermis
The fingerprint is a pattern of epidermal ridges, which increase the surface area for contact between the epidermis and the dermis