is also known as the integumentary system, and serves a waterproof, elastic covering for the body, as well as its first line
of defense. The skin is also the body’s
largest organ, and has many important functions, including the prevention of heat loss, the excretion of urea and uric acid
through sweating, and synthesizing vitamin D. The skin also protects the inner tissues of the body from physical damage, such
as falls, from chemical damage, bacterial invasions, ultraviolet radiation, heat or cold damage, and from drying out.
is made up of two primary layers. The outermost layer, called the epidermis, is made of five sub-layers of squamous epithelium
cells, which secrete keratin. Keratin causes the outer layers of the epidermis to harden, and because these cells receive
no blood supply, they flatten and die, eventually forming the skin that is seen on the body. These cells continually flake
off and die, being replaced by dead or dying cells underneath.
layer of the skin, called the dermis, is the thicker part of the skin which is made of a thick connective tissue, and holds
the body together as a whole. The dermis is composed of living cells which receives its own blood supply, and can be divided
into two parts. The first is the papillary layer, which houses the pain and touch receptors, and forms the ridges and whorls
on the hands and feet that allow for better grip.
deeper part of the dermal layer is called the reticular layer. Within the layer are found the sweat and oil glands, the blood
vessels that supply the dermis with nutrients, deep pain receptors, and large amounts of phagocytes, which prevent bacteria
from getting deeper into the body. A layer of adipose tissue, called the hypodermis, connects the skin to the underlying tissues
underneath the skin, and also serves as a shock absorber and insulator for the organs.