General description
Skin completely covers the body and joins onto membranes covering
orifices. It protects the underlying tissues against injury and attack by
microbes.
Sensory nerve receptors perceive pain, cold, heat, touch and pressure,
while motor fibres produce the required reaction.
Skin plays a vital role in the maintenance of normal body temperature,
formation of Vitamin D, and is capable of absorption. The appearance
of skin is quite different in various body sites; smooth and soft or rough
and furrowed. There is also a wide variation in skin thickness. Skin of
the eyelid is paper thin, while the soles of the feet are 10 to 20 times
thicker.
The Skin
Skin colour is affected by three main factors:
- Melanin, a dark pigment secreted by melanocytes in the deep layer of the epidermis.
The amount of colour depends upon the amount of melanin secreted e.g. sunlight promotes secretion of melanin.
- The level of oxygenation and of the amount of blood circulating in
the dermis gives skin a reddish colour.
- Bile pigments in blood and carotene in subcutaneous fat gives the
skin a yellowish colour.
Epidermis
The outer layer of skin or epidermis contains stratified epithelial tissue. The surface consists
of several layers of cornified dead cells that are constantly being rubbed off.
Sweat gland ducts and hairs pass through the epidermis.
Dermis
The dermis is a tough layer of skin located below the epidermis, comprising
connective tissue with elastic and collagen fibers. A network of blood vessels
and lymph vessels permeate the dermis, assisting the regulation of body
temperature. Sensory nerve endings, sweat glands and ducts, hair, hair
follicles and sebaceous glands are also in this layer of skin.“Goose pimples”,
the raising or “standing out” of skin around the hair, resulting from fear or
cold, is caused by the action of involuntary muscles attached to the base of
the hair.
Nails
Nails consist of clear, horn-like cells forming a solid plate and are derived from the same
cells as the epidermis and hair. They grow upon the dermal layer of the and take
their nourishment from it. Nails protect the tips of fingers and toes.
Hair
Hair is formed by the multiplication of cells at the base of the follicle.
As they are pushed up the follicle away from their source of nutrition,
the cells die and are converted into keratin.
Hair follicle
Hair follicles are tubes lined with epidermal cells, in which hair grows. The follicle
begins in the dermis or subcutaneous tissue and lead to the surface of the skin
Sebaceous glands are joined to the hair follicle.
Sebaceous gland
Sebaceous glands are located in the dermis. They secrete an oily fluid
(sebum) to lubricate and protect the skin and hair.
Subcutaneous tissue
The tissue directly beneath the dermis is the subcutaneous tissue
Sweat glands
Sweat glands are located in the dermis. They release sweat onto the skin via sweat gland
ducts, through tiny depressions – pores. Other sweat glands open onto the hair follicles.
Sweat is important for the maintenance of normal body temperature.
Glossary of Terms Skin and Subcutaneous Tissue
Cutaneous
Pertaining to the skin.
Dermis
(der’mis) Lower layer of skin; (also called corium).
Epidermis
(ep-i-der’mis) Superficial layer of skin.
Hair follicles
(fol’likls) Tube-like structures in the dermal layer of skin which produce hairs.
Integumentary system
(in-teg-u-men’tar-e) Skin and its appendages – hair, nails, sweat glands, oil glands and ducts.
Sebaceous glands
(se-ba’shus) Glands which secrete oil (sebum).
Sensory perception
Recognition of sensation such as pain, touch, pressure or temperature change.
Skin
The body covering.
Exercises on the Skin and Subcutaneous Tissue
A. Write in the table below the medical terms for the numbered items in the diagram. Then check your answers against the fully labelled diagram in this section.
B. Read the definitions of the terms below. Each describes a part or
function of the integumentary system. You may refer to the previous
text to fill in the appropriate word or phrase.
Definition
- The skin and its appendages–hair, nails, oil, and sweat
glands– make up this system.
- A vital role of the skin. It also protects the underlying
tissue from injury and infection.
- The outer layer of the skin consisting of several layers of
cornified dead cells that are constantly being rubbed off.
- The tough layer of skin located below the epidermis,
consisting of connective tissue with elastic and collagen fibres
- Derived from the same cells as skin, are clear and
form a solid plate
- Formed by the multiplication of cells at the base of
its follicle.
- Tubes in which hair grows, which is lined with
epidermal cells.
- One of two types of glands located in the dermis.
This gland secretes an oily fluid called sebum.
- Glands which produce a secretion which is released
onto the skin through pores and hair follicles.
- Sensations perceived by sensory nerve receptors
located under the skin.
- The tissue directly beneath the dermis.
- This network permeates the dermis and assists
with the regulation of body temperature.
- These happen when involuntary muscles
attached to hairs contract, causing the hairs to “stand
out” from the skin when we are cold or afraid.
- Two body sites where the skin varies in thickness.
C. Use a medical dictionary to look up the meaning of these terms
which are commonly used in describing conditions related to the
integumentary system.
acne
alopecia
burns of first, second and third degree
carbuncle
cellulitis
Debridement
decubitus ulcer
dermatitis
ecchymosis
eczema
erythema
gangrene
onychomalacia
pedicle graft
z-plasty