The term skin is commonly used to describe the body
covering of any animal but technically it refers only to the coverings of
vertebrates. Then skin which is otherwise known and identified as a cutaneous
membrane is an organ of the integumentary system. It is a vital, diverse,
complex, extensive and one of the most important organs in the body. It is the
largest and one of the more versatile organs of the body with a surface area as
large as individual owner’s body, probably as large as 1.6 -1.9 square metres
(m2) in most adults and in the male adult weighs 4.5-5kg. It covers
the body surface at a thickness of 1.4-4mm.
covering of any animal but technically it refers only to the coverings of
vertebrates. Then skin which is otherwise known and identified as a cutaneous
membrane is an organ of the integumentary system. It is a vital, diverse,
complex, extensive and one of the most important organs in the body. It is the
largest and one of the more versatile organs of the body with a surface area as
large as individual owner’s body, probably as large as 1.6 -1.9 square metres
(m2) in most adults and in the male adult weighs 4.5-5kg. It covers
the body surface at a thickness of 1.4-4mm.
The skin functions are crucial to survival as it plays
vital roles in the maintenance of homeostasis. It is composed of two (2)
distinct layers of tissues i.e. epidermis and dermis.
vital roles in the maintenance of homeostasis. It is composed of two (2)
distinct layers of tissues i.e. epidermis and dermis.
Epidermis: the outer layer is a
tough, water proof, protective layer composed of keratinized stratified
squamous epithelium. It varies in thickness in different parts of the body. It
is thickest on areas of the body that regularly rub against objects such as the
palms of the hands and soles of the feet, thinnest on the lips and eyelids and
there are no blood vessels or nerve endings in the epidermis.It is both
delicate and resilient, constantly renews itself and has a remarkable ability
to repair itself after any injury.
tough, water proof, protective layer composed of keratinized stratified
squamous epithelium. It varies in thickness in different parts of the body. It
is thickest on areas of the body that regularly rub against objects such as the
palms of the hands and soles of the feet, thinnest on the lips and eyelids and
there are no blood vessels or nerve endings in the epidermis.It is both
delicate and resilient, constantly renews itself and has a remarkable ability
to repair itself after any injury.
Dermis: the inner layer is thicker
than the epidermis and gives the skin its strength and elasticity. It includes
a variety of tissues, such as epithelial tissue, tough elastic fibrous
connective tissue, smooth muscle tissue, nerve tissue and blood. It contains
both collagen and elastin protein bundles which gives the skin its strength and
elasticity. They are produced by cells called fibroblasts which are scattered
throughout the dermis.
than the epidermis and gives the skin its strength and elasticity. It includes
a variety of tissues, such as epithelial tissue, tough elastic fibrous
connective tissue, smooth muscle tissue, nerve tissue and blood. It contains
both collagen and elastin protein bundles which gives the skin its strength and
elasticity. They are produced by cells called fibroblasts which are scattered
throughout the dermis.
Underlying the dermis are masses of losses connective
superficial fascia and adipose tissue that bind the skin to underlying organs.
They form the subcutaneous layer. The adipose tissue is otherwise called the
panniculusadiposus which acts as a cushion. In all parts of the body,
except.the palms of the hands and soles of the feet, it has four (4) layers
while in the skin of the palms and soles there are five layers thus providing
maximum wear and tear qualities for areas of maximum stress.
superficial fascia and adipose tissue that bind the skin to underlying organs.
They form the subcutaneous layer. The adipose tissue is otherwise called the
panniculusadiposus which acts as a cushion. In all parts of the body,
except.the palms of the hands and soles of the feet, it has four (4) layers
while in the skin of the palms and soles there are five layers thus providing
maximum wear and tear qualities for areas of maximum stress.
These five (5) layers from
outside are:
outside are:
i.
Stratum corneum (Horny layer)- containing
dead non nucleated cells
ii.
Stratum lucidum- contains ELEIDIN a translucent
compound present only in thick skin of palms and soles of the feet.
iii.
Stratum granulosum – Cytoplasm of cells contain
visible granules and cells die in the layer.
iv.
Stratum spinosum/malphighi (prickle cell
layer)-contains irregularly shaped cells with centrally located large oval
nuclei and developing fibers of keratin.
v.
Stratum germinativum (Basal cell layer) contains
a single row of columnar shaped cells undergoing mitosis and pigment producing
melanocytes. Rupture of eleastic fibres occurs when the skin is over stretched
resulting in permanent stretch marks that may be found in pregnancy and
obesity.
The structures in the
dermis include:
dermis include:
·
Blood vessels
Blood vessels
·
Lymph vessels
Lymph vessels
·
Sensory nerve endings,
Sensory nerve endings,
·
Sweat glands and their ducts (Ecocrine,
Apocrine). The sweat glandssecrete up to 10 litres (2.6 gallons) of fluid in a
day.
Sweat glands and their ducts (Ecocrine,
Apocrine). The sweat glandssecrete up to 10 litres (2.6 gallons) of fluid in a
day.
·
Hair roots, hair follicles and hairs.
Hair roots, hair follicles and hairs.
·
Sebacceous glands found all over the body except
on the palms, soles and top of the feet. They are very numerous on the face and
scalp. The sebum they produce inhibits the growth of certain harmful bacteria.
Sebacceous glands found all over the body except
on the palms, soles and top of the feet. They are very numerous on the face and
scalp. The sebum they produce inhibits the growth of certain harmful bacteria.
·
The arrectorespilorum.
The arrectorespilorum.
The maintenance of a
healthy epidemis depends upon the following three (3) processes:
healthy epidemis depends upon the following three (3) processes:
a) Desquamation of the
keratinized cells from the surface.
keratinized cells from the surface.
b) Effective keratinization of
the cells approaching the surface.
the cells approaching the surface.
c) Continual cell division in
the deeper layers with cells being pushed to the surface.
the deeper layers with cells being pushed to the surface.
Note: The complete replacement of the epidermis takes
about 30-40 days.
about 30-40 days.
The surface of the epidermis is ridged by projections
of cells in the dermis called the papillae which is quite different in every
individual. The impression therefore made by them is called the fingerprint.
Passing through the epidermis are the ducts of the sweat glands hairs and
secretions of the sebaceous glands.
of cells in the dermis called the papillae which is quite different in every
individual. The impression therefore made by them is called the fingerprint.
Passing through the epidermis are the ducts of the sweat glands hairs and
secretions of the sebaceous glands.
Pigmentation of the Skin
When no pigment is present the skin, it looks pinkish
white due to the blood in the blood capillaries in the dermis. However, this
colour is modified by varying amounts and proportions of several pigments. The
three most important of the pigments are:
white due to the blood in the blood capillaries in the dermis. However, this
colour is modified by varying amounts and proportions of several pigments. The
three most important of the pigments are:
Melanin: Brown pigment found in the germinative layer
of the epidermis.
of the epidermis.
Melanoid: Brown pigment distributed
widely in the cells of the epidermis.
widely in the cells of the epidermis.
Carotene: Yellow pigment found in
the stratum corneum or horny layer of the epidermis.
the stratum corneum or horny layer of the epidermis.
Collagen: Give the skin its
strength.
strength.
Functions of Skin
·
Determines the aesthetic value (beauty) of an
individual
Determines the aesthetic value (beauty) of an
individual
·
Racial
differentiation
Racial
differentiation
·
Protects the deeper and more delicate organs.
Protects the deeper and more delicate organs.
·
Acts as the main barrier against the invasion of
micro-organisms and other harmful agents, such as, chemicals, physical
agents {trauma, ultra violet rays, and
dehydration.}
Acts as the main barrier against the invasion of
micro-organisms and other harmful agents, such as, chemicals, physical
agents {trauma, ultra violet rays, and
dehydration.}
·
Stimulation of an immune response –by the
specialized cells called Langerhans.cells or phagocytes invading antigens.
Stimulation of an immune response –by the
specialized cells called Langerhans.cells or phagocytes invading antigens.
·
Protective reflex action to unpleasant painful
stimuli thereby preventing further damage.
Protective reflex action to unpleasant painful
stimuli thereby preventing further damage.
·
Protective reflex action to unpleasant
painful stimuli thereby preventing further damage.
Protective reflex action to unpleasant
painful stimuli thereby preventing further damage.
·
Formation of vitamin D by the action of
ultraviolet ray from the sun on a fatty substance 7- dehydrocholesterol in the
skin.
Formation of vitamin D by the action of
ultraviolet ray from the sun on a fatty substance 7- dehydrocholesterol in the
skin.
·
Regulation of body temperature, through
(radiation, convention, conduction and evaporation).
Regulation of body temperature, through
(radiation, convention, conduction and evaporation).
·
Organ of sensation, to touch, pain, temperature
and pressure
Organ of sensation, to touch, pain, temperature
and pressure
·
Absorption of some drugs e.g. Hormone nicotine,
toxic chemical such as mercury bleaching items etc.
Absorption of some drugs e.g. Hormone nicotine,
toxic chemical such as mercury bleaching items etc.
·
Excretion of some substances such as, Na+Cl-,
albumin in sweat, urea when kidney function is impaired, aromatic substances
e.g. garlic and other spices.
Excretion of some substances such as, Na+Cl-,
albumin in sweat, urea when kidney function is impaired, aromatic substances
e.g. garlic and other spices.
·
Personal identification as in finger prints for
legal purposes.
Personal identification as in finger prints for
legal purposes.
·
Therapeutic surgical procedure e.g. skin grafts,
Therapeutic surgical procedure e.g. skin grafts,
·
Prevention of excessive fluid loss
Prevention of excessive fluid loss
·
Storage area for water and fat.
Storage area for water and fat.
·
Fame and economic gains
Fame and economic gains
