2.6 The Skin Flashcards
The skin is the biggest organ in the human body, what area and weight is it?
It covers an average area of about 2 square meters and weighs about 4-5 kilograms.
Skin covers the whole body but varies in thickness, where is the thickest found? What is the average thickness?
On parts of the body likely to receive the more wear and tear like the soles of the feet. The average thickness of the skin over most of the body is one - two millimetres.
What is the visible part of the sin and the hair comprised of?
The visible part of the sin and the hair are both comprised of dead cells which are constantly being shed and replaced.
The skin continually renews itself, old skin cells are shed and replaced by new ones with most cells being replaces every how many days?
Every 28 days.
Every minuet, his many dead skin cells do we lose from the surface of our skin?
About 30,000 to 40,000, which is almost 4kg of cells every year.
Like most of the body, skin contains a high percentage of what?
A high percentage of water and if it dries out this can cause skin disorders. The water content of sin needs to be maintained in order to ensure skin health.
Why is the skin at more risk of drying out than any other part of the body?
The skin is exposed to the sun and wind.
What important function does the skin have for the body?
Maintaining internal temperature. It helps the body transfer heat to the environment to cool down or reduce the energy transfers when needed to keep warm, so that under normal circumstances, the internal core temperature of the body varies by no more than 0.1 degrees C.
The structure of the skin has to be strong enough to keep out pathogens and protect the vital organs beneath from physical damage and dehydration, yet be sufficiently flexible to allow movement - it has three layers, what are these?
The epidermis, the dermis and the subcutaneous layer.
What layer of the skin is the epidermis?
The top layer.
What does the epidermis provide?
Protection and prevents micro-organisms from entering the body.
The epidermis is made up of a number of layers - what is the inner most layer made from?
The innermost layer of the epidermis is made up of rapidly dividing cells attached to a basement membrane which separates the dermis from the epidermis.
What cells are found in the basal layer of the epidermis? what do they produce?
Melanocytes are cells found in the basal layer of the epidermis which produce the protective pigment melanin in response to UV light from the sun.
What does melanin reduce the risk of?
Melanin protects the cells from UV radiation and therefore reduces the risk of radiation induced mutations taking place in the DNA of the skin cells. This in turn protects the body from the risk of skin cancers such as melanoma developing as a result of the mutations.
Basement membranes or basal laminae are found beneath sheets of what throughout the body?
Basement membranes are found beneath sheets of epithelial cells throughout the body
In the skin, what is the basal lamina fastened to and by what?
The basal lamina is fastened to connective tissue by collagen molecules - in some diseases these connections are absent and the epidermis becomes detached and blistering occurs.
As these rapidly dividing cells move towards the skins surface, their structure and activity change, they begin forming which protein?
As these rapidly dividing cells move towards the skins surface, their structure and activity change, they begin forming keratin and this continue a they move towards the surface, pushed up by new cells forming beneath them.
After 15-30 days, the cells reach the outer later of the epidermis called what?
Stratum corneum, which is made from dead keratinised cells. these gradually shed from the surface.
Why is the stratum corneum the major barrier to the loss of water from the body?
Largely because it is rich in lipids (oils) which are impermeable to water.
What is the stratum corneum not, despite being water resistant?
It is not waterproof.
What fluid gradually penetrates it and evaporates from the surface into the surrounding air? approx how much water is lost from the body each day in this way?
The interstitial fluid, approx 500cm3
Skin varies on different parts of the body - which skin has relatively thin epidermis and numerous sensory receptors?
Non-hairy skin, like that of the palms of the hand and soles of the feet.
Which skin has a thin epidermis and many sebaceous glands?
Skin with hair follicles such as the scalp.
What do the sebaceous glands excrete?
A wax/oily substance called sebum that helps lubricate and waterproof the skin.
When does dry skin arise?
When there is not enough water in the stratum corneum
What is the normal water content of this later of tissue and when do symptoms of dry skin appear?
The normal water content is between 10% - 20% and when the water content falls below 10% the symptoms of dry skin appear
What are a number of reasons dry skin can occur?
- Ageing = as an individual grows older, the epidermis begins to thin and loses the ability to retain moisture, the skin therefore becomes dryer.
- Over exposure to the sun
- Exposure to cold weather
- Inflammatory conditions such as dermatitis and eczema are associated with dry skin.
What symptoms may people suffering from dry skin experience?
Loss of flexibility, roughness, hyperkeratosis (a thickening of the outer layer of the skin), inflammation and pruritus (itching)
The dermis contains cells in a network made up of which two main types of protein?
Collagen and elision.
What do the collagen fibres and elastin provide?
The collagen fibres provide strength while elastin gives the skin its flexibility.
What other structures are found in the dermis?
Network of blood vessels.
Sweat glands which are found all over the skin and secrete a dilute sale solution onto the skins surface.
Sebaceous glands which are associated with hair follicles and secrete sebum onto the surface of the skin.
Sensory receptors which detect changes in the environment such as pressure and temperature.
All over the skin of mammals there are hairs, each hair grows from its own individual hair follicle. How does new hair form inside the follicle?
Inside the follicle, new hair cells form at the root of the hair shaft, as the cells form, they push older cells out of the follicle, as they are pushed out, the cells die and become the hair we see.
What is the growth phase ?
The period where a follicle will produce new cells for a certain period of time depending on where it is located on the body.
What is the rest phase?
When the follicle stops producing new cells for a period of time, before restarting the growth phase again, at this stage the old hair falls out and is replaced by a new one.
What muscle us the hair follicle attached to?
The arrestor pili (also called erector pili or hair erector muscle).
What do the arrestor pili do? What is an example of this?
They contract to pull the hair shaft erect - in furry animals when the hairs stand on end this traps a later of insulating air to help conserve heat in the body.
What are goose pimples?
We get goose pimples when out hairs stand on end, the goose pimples are the effect on the skin of the contractions of the arrestor pili muscles on the hair follicles.
Why can adult man lose their scape hair?
It is caused by increased sensitivity to male sex hormones (androgens) in certain parts of the scalp - this tendency for male pattern baldness is pass on from generation to generation.
How many sweat gland in the dermis does the average person have?
2.5 million.
What is the watery secretion, sweat very important for?
Maintaining homeostasis, if the core body temperature begins to rise, swear production increases, the sweat cools the body as it evaporates from the surface of the skin.
What re aprocine sweat glands?
They are found adjacent to hair follicles in the hairy areas of the body such as the armpit and the grown - they produce sweat that contains organic chemicals inc. proteins, when these are broken down by the bacteria on the skin, they can produce an unpleasant body odour.
What are the eccrine sweat glands?
The rest of the skin has eccrine sweat glands which basically produce salty water - they are sited between hair follicles.
What do sebaceous glands nearly always connect to?
Hair follicles.
