The Integumentary System

This system protects the body from damage from the outside world and the harmful substances. It consists of the skin, hair, nails and sweat glands. The word integument comes from the Latin word integumentum, meaning “cover” or “enclosure. It is the most visible organ system and one of the most complex.

The Skin

The Skin Structure

Skin makes up around 12% of an adult’s body weight and is the largest organ in the body. It’s very adaptable and able to mold into different shapes, covering bones and muscles to perform various functions of the body’s make up.

The functions of skin (remember the word Shapes) are: Sensation – Main sensory organ for temperature, pressure, touch and pain. Pain and pressure receptors in the skin send messages to the brain to help prevent potential damage or injury.
  • Heat Regulation – Controls the body temperature by sweating to cool the body down when it overheats, allowing the sweat onto the surface of the skin where it evaporates, and shivering when the body is cold. Shivering occurs due to the arrector pili muscle contracting.
  • Absorption – Some creams, fatty substances, essential oils and some medication can be absorbed through the hair follicles.
  • Protection – Too much UV light may harm the skin, so the skin protects itself by producing a pigment, seen in a tan, called Melanin. Bacteria and germs (invading antigens) are prevented from entering the skin by a protective barrier called the Acid Mantle. This barrier also helps protect against moisture loss.
  • Excretion – Waste products and toxins are eliminated from the body through the sweat glands onto the skins surface.
  • Secretion – Sebum, a waxy substance and sweat are secreted onto the skins surface. The sebum keeps the skin lubricated and soft and the sweat combines with the sebum to form the acid mantle.

Another function of the skin:

  • Vitamin D production – Absorption of UV rays from the sun helps formation of vitamin D, which the body needs for the formation of strong bones and good eyesight.

There are 3 major layers of the skin, the Epidermis, Dermis and the Subcutaneous (adipose):

The Epidermis Layer

The outermost layer of the skin is called the epidermis layer. There are no blood vessels in the epidermis but it’s the deepest layer and is supplied with lymph fluid. It is at its thickest in the palms of the hands and on the bottom of the feet.

There are various layers of cells within the epidermis, the outermost of which is called the stratum corneum (or horny layer). The layers may be clearly seen in the diagram of the skin. The surface layer is composed of twenty-five to thirty sub-layers of flattened scale-like cells, which are continually being cast off by friction and replaced by the cells of the deeper epidermal layers. The surface layer is considered the real protective layer of the skin. The cells are commonly called keratinised cells because the living matter within the cell is changed to a protein (keratin) which helps to give the skin its protective properties.

New skin cells are formed in the deepest layer within the epidermis. This area is called the stratum germinative. The new cells will gradually move towards the outer layers of the skin as the stratum corneum is shed. The new cells gradually change in form as they move upward to the outer layers, becoming keratinized in the process.

Names of the Layers of the Epidermis

English NameLatin Name
Horny LayerStratum Corneum
Clear LayerStratum Lucidum
Granular LayerStratum Granulosum
Prickle Cell LayerStratum Spinosum
Basal/Germinative LayerStratum Basale

The Dermis Layer

The dermis is a tough and elastic layer containing white fibrous tissue interlaced with yellow elastic fibres and is found beneath the epidermis. Many structures are embedded in the dermis including: · Blood vessels – form a fine network with capillary branches · Lymphatic capillaries and vessels – form a network throughout the dermis · Sweat glands and their ducts – eccrine and apocrine glands · Sebaceous glands – secrete sebum (oil) · Sensory nerve endings – send messages via the nervous system.  The arrector pili muscle – involuntary muscle sometimes activated in cold weather to give ‘goose bumps’ · Hair follicles, hair bulbs and hair roots

The Subcutaneous Layer (Adipose)

This is the deepest of the layers of skin and is located on the bottom of the skin diagram. It lies below the dermis and above the muscle layer and connects the dermis above it to the underlying organs. The subcutaneous layer is mainly composed of loose fibrous connective tissue made up of fat cells, interlaced with blood vessels. The hypodermis is generally about 8% thicker in females than in males. The main functions of the hypodermis are insulation, storage of lipids, cushioning of the body and temperature regulation.

Below the dermis and above the muscle layer

Diagram of the Skin

Diseases and Disorders of the skin

There are some common diseases and disorders of the skin that affect many people. They can be troublesome and some of them can even be dangerous. They are broken down into different categories; bacterial, viral, fungal, infestations, sebaceous gland disorders, sweat gland disorders, pigmentation disorders, malignant tumours and allergies.

NameAppearanceCauseCategories i. e fungal, bacterial etc
Contact DermatitisInflammation of the skin, swelling & rednessAllergic reaction to contact with allergen (always wear protective clothing)Allergy
Seborrheic WartsFlat top/warty looking lesionAgeingFungal
Herpes simplexRed sore/scab usually on side of the mouth also none as a cold soreViral infection transmitted by contact with another infected area. Highly contagiousViral
WartsSmall solid growthSame as Herpes simplexViral
ScabiesItchy white spotsMite transmitted by direct skin to skin contact typically from itchy infected area and transporting mite to someone else under fingernails.Infestation by a mite, fungal
PsoriasisRed itchy scaly patches erupting on skinThe immune system sends out a faulty signal that speeds up the growth cycle of skin cellsChronic recurring skin disease which can be pustular or non-pustular
Acne RosaceaRedness on nose and cheeksDilation of minute capillaries in the skinSkin disorder
ImpetigoRed spot which blisters then discharges developing a yellow crustHighly contagious. Spread through direct contact and itchingBacterial
MiliaSmall harmless pinhead cysts also called milk spotsManifestation of immature sebaceous glands and become blocked with keratinBenign cyst
EczemaSame as dermatitis: Redness is due to dilated blood vessels and as fluid accumulates itching and swelling occurs. Weeping skin can then become infectedAllergic reaction StressAllergy

The Hair

There are roughly 5 million hairs that cover the body and with the exception of the palms, soles, the lips, the sides of the fingers and toes and some parts of the genitals, the whole body is covered in hair.

  • Hair originates from a structure called a hair follicle. This tube-like structure extends into the dermis layer and is fed by capillaries and nerves which are attached to it.
  • Epithelial cells grow and divide inside the base of the follicle, which forms the hair bulb.
  • Keratin, a protein which is found in the epithelial cells coats the hair which causes it to stiffen as it grows up through the follicles. Whilst the hair is in the follicle, it is called the root, but once exposed from the scalp it is called the hair shaft.

Structure of the Hair Root

Below the surface of the skin is the hair root, which is enclosed within a hair follicle. At the base of the hair follicle is the dermal papilla. The dermal papilla is feed by the bloodstream, which carries nourishment to produce new hair. The dermal papilla is a structure very important to hair growth because it contains receptors for male hormones and androgens. Androgens regulate hair growth and in scalp hair, Androgens may cause the hair follicle to get progressively smaller and the hairs to become finer in individuals who are genetically predisposed to this type of hair loss.

Each strand of hair consists of three layers.

1. An innermost layer or medulla, which is a core of loosely arranged cells and air spaces and only present in large thick hairs.

2. The middle layer known as the cortex. The cortex provides strength and both the colour and the texture of hair and is made up of densely packed keratinized cells.

3. The outermost layer is known as the cuticle, made up of a single layer of scaly cells that overlap. The cuticle is thin and colourless and serves as a protector of the cortex.

As the newly formed cells grow and push up from the follicle base, the older epithelial cells die.

The colour of the hair is determined by pigmented cells called melanocytes, which contain melanin. The amount of melanin will determine the colour of hair.

Hair Types and Textures

Straight Hair

With this type of hair, there is absolutely no curl pattern, and it is completely straight and sleek. The hair tends to be shiny because of the lack of curl pattern which allows the light to reflect off of the hair, giving it a shiny finish.

If straight hair appears dull is may be because it has become damaged. It is essential to care for the hair carefully to maintain its shine.

Wavy Hair

Wavy Hair can either be fine, or medium textured which looks coarser and thicker. It is possible to style and straighten the hair for a sleek look, but tighter curls can also be added.

Medium Curly Hair

This hair has a tighter curl pattern and can either be loose curl or a tighter curl pattern. There is a lot of body in this hair which gives it versatility and it can be styled in many different styles, although it may be hard to straighten. The hair easily absorbs water when wet, but then it shrinks.

Kinky, Coily Hair

Tightly coiled hair has a lot more kink and appears thicker than other curly hair, but it can be fairly fine. This type of hair is found in Afro styles and should not be brushed when dry as it can cause damage and breakage.

Texture

Hair texture is the measure of the circumference of the hair strand and is classified as either being “coarse”, “fine”, or “medium”.

  • Coarse hair has the largest circumference and is strong as it has more substance. It can be resistant to colouring and perming.
  • Medium texture indicates a middle-range size circumference of the hair shaft, it’s considered normal and poses no special considerations regarding processing and chemical services.
  • Fine hair has the smallest circumference and is often very easy to process. It is easily damaged from chemicals and heat.

Hair texture varies from individual to individual, and the same head of hair can have different textures in different places.

Hair Density

Hair density is the amount of hair strands on the head and is measured by counting the number of hair strands found in one square inch (2.5cm) of scalp. Generally, the classifications of hair density are thick, medium, and thin, and are unrelated to the texture of the hair. The average head has approximately 2,200 strands of hair per square inch, and a total of approximately 100,000 hairs.

Hair Growth Cycle

Hair follicles grow in repeated cycles. One cycle can be broken down into three phases.

1. Anagen – Growth Phase

2. Catagen – Transitional phase

3. Telogen – Resting Phase

Each hair passes through the phases independent of the neighbouring hairs.

We are constantly losing around 30,000 to 40,000 dead skin cells form the surface of the skin every day, with the epidermis constantly replacing old skin cells and shedding them. The germinativum layer (Basale) has cells that are shaped liked columns that divide and push new cells into the layer above. This process continues through each layer with the final layer – the corneum being made up of dead, flat cells that shed around every 2 weeks.