3-2. COVERINGS OF THE HUMAN BODY
The entire body is surrounded by three layers or envelopes, one inside the other.
These coverings separate the body from the external environment. These envelopes
include (from outside inward)--the skin (the integument proper), the subcutaneous layer,
and the investing deep fascia.
Section II. THE HUMAN INTEGUMENTARY SYSTEM
3-3. THE INTEGUMENT PROPER
The integument proper is the outermost layer of the human body. It is usually
known as the skin. The skin has two layers--the superficial or outer layer called the
epidermis and the deeper or inner layer called the dermis.
a. The Epidermis. The epidermis is a stratified squamous epithelium. This
means that it is made up of several layers of cells, the outermost being flat-type
(1) The outer layers of the epidermis include cells which are transparent,
flattened, dead, and without nuclei. These hardened cells of the outermost layers are
completely filled with keratin and are known as cornified cells. These dead flat cells in
the outermost layers resemble scales. Day by day, these cells are scraped away or just
fall away from the body. They are replaced by cells from the intermediate layers.
(2) In the intermediate layers of the epidermis, the cells change their shapes.
As the cells move towards the surface, they gain granules, begin to manufacture a
hardening material called keratin, and lose their nuclei.
(3) The innermost layer of the epidermis is especially important because it is
the source of all the other layers of the epidermis. It is known as the basal or germina-
tive layer. The cells of this layer are capable of multiplication (mitosis). Its basic
structure is a single layer of columnar-type epithelial cells.
b. The Dermis (Dermal Layer). The dermis is the layer of the skin lying just
beneath the epidermis. It is dense FCT consisting of white and yellow fibers. This layer
in animal hides is used to make leather. The dermis has finger-like projections called
papillae. These papillae extend into the epidermis and keep the dermis and epidermis
from sliding on each other. The dermal layer includes blood vessels, lymph vessels,
nerve endings, hair follicles, and glands.