The skin Flashcards by Lisa Clowes

The skin

The largest organ in the body

Known as the integumentary system.

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Three main layers

Epidermis - the outermost layer
Dermis - The true skin
Subcutaneous - fatty layer (adipose tissue)

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The epidermis

5 layers - Corny Lucy’s Gran Spins Germs

Stratum corneum (Corny)
Stratum lucidum (Lucy's)
Stratum granulosum (Gran)
Stratum spinosim (Spins)
Stratum germinativum (Germs)

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Stratum corneum

Horny layer
Outermost layer
Flat overlapping keratinised cells (corneocytes)
Cells are dead

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Stratum lucidum

Lucid / clear layer - cells are transparent
Only on palms & soles
Cells are dead

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Stratum granulosum

Granular layer - keratinisation begins here
Cells begin to fill with keratin granules
Contains living & dead cells

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Stratum spinosum

Spiny layer - cells interlock with spiny tendrils (arms)
Cells are living
Melanin granules are present in this layer

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Stratum germinativum

Germinating layer - new cells are produced here (mitosis)
Deepest layer of the epidermis
New cells push old cells forward
Journey from germinativum to corneum takes 3-6 weeks (average 28 days)

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Key term -Mitosis

Cell division - one cell splits to form 2 identical copies

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Melanocytes

Cells which produce melanin (skin pigment / tan)

Found in the stratum germinativum

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Key term -Keratinisation

The process through with epidermal cells go from living to dead as the move through the layers of the epidermis & fill with keratin granules.

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Keratin

The protein which forms skin, hair & nails

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The dermis

The true skin - fibres, nerves, blood vessels & appendages are found here

Has 2 layers - papillary & reticular

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The papillary dermis

Lies below the stratum germinativum
Supplies the epidermis with blood (containing oxygen & nutrients).
Sensory nerve endings are found here.

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The reticular dermis

Main section of the dermis
Below the papillary layer
Contains collagen & elastin fibres
Skin appendages are found here (sebaceous glands, hair follicles, sweat glands)

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Skin appendage - arrector pili muscle

Attaches to the hair follicle and the base of the epidermis.

Contracts to pull the hair upwards to form a ‘goose bump’.

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Skin appendage - sweat gland (eccrine)

Found all over the body
Secretes sweat onto the surface of the skin.
As the sweat evaporates, it cools the skin.

Skin appendage - sweat gland (apocrine)

Found in the groin & axilla
Secretes pheromones - a milky liquid containing fats & protein.
As this substance is broken down by bacteria, it can cause body odour

Skin appendage - sebaceous gland

Small, sac like structured located in the upper third of the hair follicle.
Secrete SEBUM on to the skin.

Sebum

The skin’s natural moisturiser
Produced by the sebaceous gland
Mixes with sweat to form the acid mantle.

Skin appendage - sensory nerves

Found all over the body and in high numbers in the skin.

Feedback information to the brain about the body’s external environment through the central nervous system.

Skin appendage - blood capillaries

Provide the cells with oxygen & nutrients (arterioles) & remove CO2 & waste products (venules)

Skin appendage - dermal papilla

Supplies the hair root with blood (oxygen & nutrients) to enable it to grow.

Collagen

A fibre found in the dermis which gives the skin strength.

Produced by fibroblast cells.

Elastin

A fibre found in the dermis which gives the skin 'stretch'. | Produced by fibroblast cells.

Fibroblast cells

Cells within the dermis which produce collagen, elastin & 'extra cellular matrix' (ECM)

Extra-cellular matrix

A jelly like substance which holds lots of water - supports the fibres and appendages within the dermis.

Langahans cells

Immune cells found in the epidermis (stratum spinosum) which protect against infection.

Mast cells

Cells found in the dermis which produce histamine when stimulated through skin damage / irritation.

Histamine

A chemical released by mast cells which increases blood flow to the area (erythema) to begin the healing process.

The subcutaneous layer

Lies below the dermis Contains fatty tissue (adipose tissue) Provides protection to the internal organs, insulation and a food source if required.

Skin functions

``` SHAPESV Sensation Heat regulation Absorption Protection Excretion Secretion Vitamin D production ```

Skin function - sensation

Sensory nerve endings provide the brain with information about the body's environment. Can initiate a reflex action to protect the skin / body from harm.

Skin function - heat regulation

Surface capillaries dilate (open) to release excess heat from the body into the environment & cool the body. Surface capillaries constrict (narrow) to restrict the blood flow to the skin & reduce the heat lost to the environment.

Skin function - absorption

The skin can absorb some chemicals (vitamins, hormones, drugs - nicotine).

Skin function - protection

The skin does this in several ways: The stratum corneum forms a protective, waterproof barrier. The acid mantle inhibits bacterial growth on the skin. Nerve endings allow us to respond to danger. Melanin helps to prevent sun damage.

Skin function - Excretion

A minor role - most excretion is carried out by the kidneys. | Waste products are excreted in small amounts through sweating.

Skin function - Secretion

The skin secretes sebum which is the skin's natural moisturiser. Sebum combines with sweat to form the acid mantle.

Skin function - vitamin D production

The skin produces Vitamin D when exposed to UV light. | Vitamin D is essential for strong bones & correct immune function.

Key term - desquamation

The natural shedding of dead skin cells from the epidermis.

Key term - erythema

Reddening of the skin due to vasodilation (opening) of surface blood capillaries.