The integumentary system is
the organ system that protects the body from damage, comprising the skin and its
appendages (including hair and nails). The integumentary system has a variety of
functions; it may serve to waterproof, cushion and protect the deeper tissues, excrete
wastes, regulate temperature and is the location of receptors for pain, sensation,
pressure and temperature.
The integumentary system is the largest organ system. It distinguishes, separates,
protects and informs the animal or human being with regard to its surroundings.
Small-bodied invertebrates of aquatic or continually moist habitats respire using
the outer layer (integument). This gas exchange system, where gases simply diffuse
into and out of the interstitial fluid, is called integumentary exchange.
The skin is the largest organ in the body and has a surface area of about 1.75 square
meters, approximately 2-3 mm thick. It is part of the integumentary system and covers
the entire skeletal frame. It is made up of multiple layers all of which have an
important function that offers protection to the body’s other systems.
Epidermis
Epidermis, "epi" coming from the Greek meaning "over", is the top layer of the skin
and is made up of epithelial cells. Its main job is protection. Structurally it
consists of a keratinized stratified squamous epithelium comprising four types of
cells.
- Keratinocytes
- Melanocytes
- Merkel cell
- Langerhans' cell
The majority of the epidermis is the keratinocyte which produces keratin. Keratin
is a fibrous protein that aid in protection. Millions of dead keratinocytes rub
off every day. A totally new epidermis is present every 25 to 45 days. Melanocytes
create melanin, the substance that gives our skin colour. These cells are found
deep in the epidermis layer. Accumulations of melanin are packaged in melanosomes
(membrane-bound granules). These granules form a pigment shield against UV radiation
for the keratinocyte nuclei.
This layer is made up of five layers; the stratum corneum (horny lay) which is the
most superficial layer, made up of all dead cells, proteins, and glycolipids which
keep the body waterproof), the stratum lucidum (clear layer) the extra layer that
occurs in places such as palms and soles of the feet, the stratum granulosum (granular
layer), stratum spinosum (prickle cell layer) and the stratum basale (basal layer).
It is in this section that new skin cells and melanin are produced.
The stratum basale is the only layer capable of cell division 'pushing up' cells
to replenish the outer layer which is constantly shedding dead cells. The Epidermis
does not contain blood vessels (non vascular). The pigment melanin gives its skin
colour and allows the skin to tan. An uneven distribution of melanin causes freckles.
The epidermis contains different types of cells, the most common are:
- squamous cells which are flat, scaly cells on the surface of the skin
- basal cells which are round cells
- melanocytes which give the skin its colour.
The epidermis also contains Langerhan's cells, which are formed in the bone marrow
and then migrate to the epidermis. They work in conjunction with other cells to
fight foreign bodies as part of the body's immune defence system. Granstein cells
play a similar role.
Dermis
The dermis is second of the three layers, the thick inner layer of skin, which comprises
of blood vessels, connective tissue, nerves, lymph vessels, sweat glands and hair
shafts. It has two main layers: the papillary and the reticular layer. The upper
layer for touch, pain and heat, which communicate with the central nervous system
and is responsible for the folds (called dermal papillae) of the fingerprints. The
light touch sensors which are in the papillary section of the dermis are called
Meissner's corpuscles. The lower layer house the hair follicles, nerves, gland,
and gives the skin most of its stretchiness and strength. In this layer there are
also touch receptors, these however are for sensing pressure, these sensors are
called Pacinian Corpuscles.
It also contains cells known as fibroblasts which produce collagen and elastin.
These run parallel to the skin surface and help to plump out and prevent the skin
from forming fine lines and wrinkles.
Subcutaneous
The subdermis is the layer of tissue directly underneath the dermis. It is mainly
composed of areolar connective tissue and adipose tissue. Its physiological functions
include insulation, the storage of energy and aiding in the anchoring of the skin.
It also cushions the underlying body for extra protection against trauma