CHAPTER 5: The Integumentary System
The integumentary system or integument
is the largest system of the body.
- 16% of body weight; 1.5 to 2 square meters in area
The integument is made up of 2 parts:
1. the cutaneous membrane
, or skin, and
2. the accessory structures
The cutaneous membrane is made up of 2 parts:
1. the outer epidermis
or superficial epithelium (epithelial tissues) and
2. the inner dermis
, composed of connective tissues
The accessory structures include hair, nails, and multicellular exocrine glands. These structures
generally originate in the dermis and extend through the epidermis to the skin’s surface.
The integument interacts with the circulatory system through blood vessels in the dermis, and with the
nervous system through sensory receptors for pain, touch, temperature etc.
Below the dermis is a subcutaneous layer
of loose connective tissue, also known as the superficial fascia
(where hypodermic injections are administered).
The functions of skin and its subcutaneous layer include:
of underlying tissues and organs against shock, abrasion, fluid loss and chemical attack.
of salts, water, and organic wastes by glands.
Maintenance of body temperature
by insulation (heating) and sweat evaporation (cooling).
Synthesis of vitamin D3
(converted to calcitriol for calcium regulation).
of touch, pressure, pain and temperature.
The Epidermis, p. 155
The epidermis is an avascular stratified squamous epithelium that relies on diffusion of nutrients and
oxygen from capillaries in the dermis.
The most abundant cells in the epidermis are the keratinocytes
(so called because they contain large
amounts of the protein keratin).
Most of the body is covered by thin skin
, which has only 4 layers of keratinocytes in the epidermis.
The palms of the hands and soles of the feet are covered with thick skin
, which has 5 layers of
keratinocytes in its epidermis.
Layers of the Epidermis, p. 155
The 5 layers or strata
of keratinocytes in the thick skin of the epidermis are (from the deep basal lamia to the
free surface) the:
1. stratum germinativum
2. stratum spinosum
3. stratum granulosum
4. stratum lucidum
, and the
5. stratum corneum
The stratum germinativum
(“germinative layer”) is attached to the basal lamina by hemidesmosomes,
forming a strong bond between the epidermis and the dermis.
- Stratum germinativum forms epidermal ridges
that determine our fingerprint pattern, and dermal
papillae or tiny mounds.
- Stratum germinativum has many germinative (stem) cells, called basal cells
, which replace
keratinocytes that are shed at the skin’s surface.