The human body consists of many interacting systems. Each system contributes to the maintenance of
homeostasis, of itself, other systems, and the entire body. A system consists of two or more organs,
which are functional collections of tissue.
INTEGUMENTARY SYSTEM or Exocrine                        Epidermis
                                                           It is the outermost layer of the skin.
    The human body"s largest organ is the                 It     contains    squamous        cells  or
     integumentary system, which includes the               keratinocytes, which synthesize a tough
     skin, hair, nails, glands and nerve                    protein called keratin. Keratin is a major
     receptors.                                             component of skin, hair and nails.
    Protection: it protects against UV light,             It contains specialized cells called
     mechanical, thermal and chemical stresses,             Langerhans cells that signal the immune
     dehydration and invasion by micro-                     system of an infection.
     organisms.                                            The basal layers of this epithelium are
    Sensation: skin has receptors that sense               folded to form dermal papillae.
     touch, pressure, pain and temperature.
    Thermoregulation: various features of              The epidermis is composed of five sub-layers.
     the skin are involved in regulating
                                                        1. stratum corneum - top layer of dead,
     temperature of the body. For example                   extremely flat cells. Cell nuclei are not
     sweat glands, hair, and adipose tissue.                visible.
    Metabolic      functions:     subcutaneous         2. stratum lucidum - thin, flattened layer of
     adipose tissue is involved in production of            dead cells. Not visible in thin skin.
     vitamin D, and triglycerides.                      3. stratum granulosum - rectangular-shaped
                                                            cells that become increasingly flattened as
                                                            they move to the surface of the epidermis.
It is composed of a layer of epithelial tissue          4. stratum spinosum - polyhedral-shaped
(epidermis) that is supported by a layer of                 cells that flatten as they get closer to the
connective tissue (dermis) and an underlying                stratum granulosum.
subcutaneous layer (hypodermis or subcutis).            5. stratum basale - innermost layer of
                                                            elongated columnar (column-shaped)
                                                            cells. Consists of basal cells that produce
                                                            new skin cells.
                                                           The layer beneath the epidermis is the
                                                           It is the thickest layer of skin composing
                                                            almost 90 percent of its thickness.
                                                           It contains specialized cells that help
                                                            regulate temperature, fight infection, store
                                                            water and supply blood and nutrients to
                                                            the skin.