The Integumentary
System –
Epidermis/Dermis
Human Anatomy & Physiology
Integumentary System
O The epidermis is a keratinized stratified
squamous epithelium consisting of four distinct
cell types and five distinct layers. It thickness
varies over most of the body.
O Its surface layer, consisting of dead cells, is rich
in keratin, a protein which renders it dry and
more or less waterproof, thus resisting surface
evaporation and preventing excessive water loss.
It also serves as a protective barrier against
ultra-violet light, bacteria, many chemicals and
abrasion.
Integumentary System –
Epidermis
O The epidermal cells are:
O - 1 - the keratinocytes:
O 2 - the Merkel cells: sensory receptors
(touch). They associate with a disc-like
sensory nerve ending to form the Merkel
disc.
Integumentary System –
Epidermis
O 3 - the melanocytes: synthesize the melanin
pigments which protect the skin against
ultraviolet damage.
O 4 - the Langerhans cells: macrophages
used in the defense against
microorganisms.
Epidermis
O The epidermis consists of several layers of
cells. From the deepest to the most
superficial we have:
“Basic Skin Gets Lots of Care”
Epidermis
O 1 - the stratum basale (or stratum
germinativum): is the deepest epidermal layer.
It consists of one row of cuboidal to columnar
shaped cells. Those cells are mostly stem cells
that divide rapidly to produce new keratinocytes
which push up toward the surface and become
part of the more superficial layers
O 10 to 25% of cells found here are melanocytes
O Melanocytes that synthesize the pigment
melanin.
Epidermis
O 2 - the stratum spinosum: is 8-10 layers thick.
O Stratum basale and stratum spinosum are
adjacent to the dermis and thus, contain the
only epidermal cells that receive adequate
nourishment (by diffusion of nutrients from the
dermis).
Epidermis
O 3 - the stratum granulosum: here the
keratinization process begins and the cells
begin to die.
O 4 - the stratum lucidum: is only found in
thickened areas of the epidermis such as the
sole of the feet.
O 5 - the stratum corneum: is the outermost layer
composed of dead, flat, keratinized cells
Integumentary System Dermis
O The dermis consists of two layers:
O 1 - the Papillary layer - is the outer layer closest
to the epidermis
O Its superior region contains fingerlike
projections called dermal papillae
O Dermal papillae contain capillaries, Meissner
corpuscles (pain and touch receptors: make us
feel light touching)
Integumentary System Dermis
O 2 - the Reticular layer is the deeper layer and
the thickest layer. It is made of dense
connective tissue
O The collagen fibers in the reticular region
provides the skin with strength and extensibility
O and elastic fibers provide its elasticity
O The reticular layer is richly supplied with blood
vessels and nerves, and contains sensory
endings for touch (Pacinian corpuscle for
sensing deep pressure
Integumentary System Hypodermis
O The Hypodermis (= subcutaneous tissue
= superficial fascia) is NOT part of the
skin. It consists mainly of adipose tissue
plus some areolar tissue. "Beer belly" in
man and thick thights and buttocks in
female are due to too much fat stored in
the hypodermis of these regions of the
body.
Integumentary System Hypodermis
O Hypodermis shares the skin protective
functions: it stores fat and thus helps
prevent heat loss and acts as a shock
absorber; it anchors the skin to the
underlying structures allowing the skin to
slide almost freely over them. This
feature ensure that blows just glance of
the body without injuring the tissues
below.