THE INTEGUMENTARY SYSTEM
Our skin
The components of the integumentary system…
1. Skin – a.k.a. the integument OR cutaneous membrane
2. Accessory organs Sweat glands Oil glands Hairs Nails
Without our skin, we would quickly fall prey to bacteria and perish from water and heat loss!!!
A little more information about our skin…
The skin ordinarily receives very little respect from its inhabitants, but architecturally it is a marvel
Some of its uniqueness includes: It covers the entire body It has a surface area of 1.5 – 2.0 m2
Weighs ~4 kg (9 lbs) Accounts for about 7% of the total body weight Consists of ~1/2 million cells that are
constantly dying and being replaced It is pliable yet tough
The major functions of the skin1. Protection – the skin covers and
protects underlying tissue and organs from impacts, chemicals, and infections, while preventing the loss of body fluids
2. Temperature maintenance – the skin maintains normal body temperature by regulating heat gain or loss to the environment
The major functions of the skin con’t
3. Storage of nutrients – the deeper portions of the dermis typically contains a large reserve of lipids in the form of adipose tissue
4. Sensory reception – receptors in the integument detect touch, press, pain, and temperature stimuli and relay that information to the nervous system
The major functions of the skin con’t…
5. Excretion and secretion – the integument excretes salt, water, and organic wastes (sweat) and produces milk (a specialized exocrine secretion)
Bell Ringer…
1. Why is temperature regulation so important for the body
2. How does our skin protect us – there is more than one way
The skin consists of two distinct regions: The epidermis – the superficial
epithelium The dermis – underlying dense
connective tissue The subcutaneous tissue just below the
skin is known as the hypodermis or superficial fascia but strictly speaking, it is not considered part of the skin – it attaches to deeper structures such as muscles or bones
The epidermis…
The epidermis is composed entirely of stratified squamous epithelium in 5 zones called strata
The epidermis is avascular - no blood supply
Most cells of the epidermis are keratinocytes – produce keratin, a fibrous protein that makes the epidermis a tough protective layer
The strata of the epidermis… There are 5 strata zones – listed from
inside to outside1. Stratum basale – contain epidermal pegs
to help from this layer from slipping2. Stratum spinosum3. Stratum granulosum4. Stratum lucidum – found only in hairless
area such as our palms and soles of feet5. Stratum corneum
Stratum basale…
Deepest cell layer of the epidermis Lies closest to the dermis, separated by
basement membrane Contains the only epidermal cells that
receive adequate nourishment via diffusion from the connective tissue
Constantly undergoing cell division, producing millions of new cells daily, which make their way up to the superficial layer of the skin
Life cycle of a skin cell produced in the basale layer… As the cell moves away from the basale
layer, it moves through the other layers of the skin, picking up more and more keratin along the way
It eventually reaches the outermost strata – stratum corneum, where it dies and is eventually shed
We have totally “new” epidermis every 25 to 45 days
Keratinization…
The cell membranes of older skin cells (the ones nearer the surface) thicken and develop many desmosomes that fasten them to each other
While this is happening, the cells begin to harden due to strands of tough, fibrous, waterproof keratin proteins being synthesized and stored within the cell (keratinization)
Stratum Spinosum
Called this because the keratinocytes in this layer appear “spiny”
Scattered among the keratinocytes are melanin granules and Langerhans’ cells, which are most abundant in this layer Melanin granules – give skin its color and
protects us from UV radiation Langerhans’ cells – help in immune
responses
Stratum Granulosum
Consists of 3 – 5 layers where the keratinocytes appearance changes drastically They become flatten and fill with
waterproofing lamellated granules All cells above this layer are to far from
the capillaries and therefore die
Stratum corneum…
The outermost layer of skin composed of dead, completely keratinized cells
It is 20 – 30 cells layer thick and accounts for ~ ¾ of the epidermal thickness
Keratin is an exceptionally tough protein – its abundance allows this layer to provide a durable “overcoat” for the body, which protects deeper cells from the hostile environment and water loss
This layer rubs and flakes off slowly but is steadily replaced by cell produced by the stratum basale
Bell Ringer…
List the layers of the epidermis in order from deepest to most superficial
What layer is only seen in the palms of our hands and the soles of our feet?
The dermis…
The layer just below the basement membrane of the epidermis
The boundary between the dermis and epidermis is usually uneven
This is because the epidermis has ridges projecting inward and the dermis has conical dermal papillae passing into the spaces between the ridges, prevents the dermis from slipping laterally
The dermis…
The dermis binds the epidermis to the underlying tissues
It is largely composed of irregular dense connective tissue that includes tough collagenous fibers and elastic fibers in a gel-like substance These fibers give the skin toughness and
elasticity On average, the dermis is 1.0 – 2.0 mm thick,
it may be as thin as 0.5 mm or less on the eyelids or as thick as 3.0 mm on our soles
The dermis…
Contains smooth muscle fibers, such as the arrector pili muscle which causes hair to stand on end
Nerve cell processes are scattered through out the dermis, which pick up on sensations from the outer environment
It also contains blood vessels, hair follicles, sebaceous glands and sweat glands
Medicine delivery through our skin… There are several ways medication can be
administered through our skin1. Intradermal injections
Injected within the skin
2. Subcutaneous injections Injected through a hollow needle into the
subcutaneous layer a.k.a hypodermic injections
3. Transdermal patches The patch is attached to the skin where the medication
diffuses through the epidermis and dermis entering the capillaries
Review…
What are the 5 functions of our skin? How would you distinguish a mucous
and a serous membrane? Where is the subcutaneous layer
located? Is it part of the skin?