Skin, hair and nails Flashcards
The skin
- The skin is the largest organ
- Covers the whole body
- Water resistant
- Protects and shapes the body
- Three layers
- Epidermis
- Dermis
- Hypodermis
Epidermis
- The visible layer of skin
- Varies in thickness depending on the part of the body
- Thickest on the soles of the feet and palms of the hand
- Thinnest on eyelids and nipples
- The cells on the surface are constantly shed
- Desquamation
- They are constantly replaced from below
- Cells in the basal layer multiply and are pushed up to the surface
- The basal layer of the epidermis receives its blood supply, nutrients and fluids from the dermis
Structure of the Epidermis 5 layers of epithelial cells
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum germinativum
Stratum corneum
- Most superficial layer of the epidermis
- Layer exposed to the outside environment
- Usually 15 to 30 layers of cells
- Prevent the penetration of microbes and the
dehydration of underlying tissues - The entire layer is replaced during a period of
about 4 weeks - Cells are hardened and flattened (highly keratinized- cornification )
- Cells are shed periodically (desquamation) and replaced by cells pushed up from the stratum granulosum
Stratum lucidum
- A smooth clear layer
- Cells contain the clear protein eleiden giving cells a transparent (lucid) appearance
- Eleiden provides barrier to water
- Cells dead and flattened
- Cells are denucleated but not completely hard
- Cell membranes becoming less visible
- Found only in the thick skin of the palms, soles and digits
Stratum granulosum
- Cells have a distinct nucleus but cell membranes are dying
- Contains granules of keratohyalin which are visible in healing tissue after trauma
- Cells generate large amounts of keratin
Stratum spinosum
- Spiny in appearance
- Composed of 8-10 layers of cells
- Cells are living
- Cell membranes are intact
- Cells have protruding processes where they join to other cells
- Capable of mitosis under friction or pressure e.g. soles of the feet and palms of hands
- Langerhans cells also found in this layer
- Macrophages that engulf bacteria, foreign particles and damaged cells
Stratum germinativum/basale
- The basal layer
- Primary site of cell division
- Cells are living
- Cuboidal shaped cells
- Cells take 28-30 days to move from here through the 5 layers of the epidermis before being shed
- Contains melanin pigment
- Melanin produced by melanocytes
- Merkel cells act as receptors (tactile)
Dermis
- Known as the true skin
- Connected to the blood, lymph supply and nerves
- Contains sweat and sebaceous glands
- Made of connective tissue (areolar) that is tough and elastic
- Contains white collagen fibres and yellow elastic tissue (elastin)
- Collagen plumps the skin
- Elastin keeps skin supple and elastic
- Collagen and elastin diminish with age
Dermis 8 main types of structures present
- Specialised cells
- Sweat glands
- Nerve endings
- Sebaceous glands
- Hair follicles
- Blood supply
- Lymphatic capillary
- Papilla
Specialised cells
Fibroblasts
Mast cells
Histiocytes
Leukocytes
Fibroblasts
- Responsible for the production of areolar tissue, collagen and elastin
- Responsible for generating connective tissue and allowing the skin to recover from injury
- Can be damaged by UV light
Histiocytes
- Produce histamine
- Phagocytic cells
- Develop into Langerhans cells
Mast cells
- Produce histamine as an allergic response
- Produce the anticoagulant heparin
Leukocytes
- White blood cells
- Help fight infection and disease
Nerve endings
Sweat glands
- Stretch from deep in the dermis to the outer layer of the epidermis
- Sweat contains mainly water, urea and salts. Produced by 2 glands
- Eccrine glands
- Excrete watery sweat
- Control body temperature
- Found all over the body
- Apocrine glands
- Found in the groin and armpits
- Excrete a milky fluid
- Fluid mixes with bacteria on the skin surface = body odour
Hair follicle
- Travel through the epidermis and dermis
- Erector pili muscles are attached to each hair – goose pimples
Sebaceous gland
- Connected with hair follicles
- Produce sebum
- Fatty acid which keeps the skin moist
- Lubricates the hair shaft
- Found in hairy areas but not on the palms of the hands and soles of
the feet - Sweat and sebum combine on the skin surface
- Form the acid mantle
- Control bacterial levels
- Acts as a natural moisturiser
- Skin pH = 4.5-5.6
Blood supply
- A system of blood vessels including microscopic capillaries
Plexus = network of vessels
Lymphatic capillary
- Works in conjunction with
the blood supply - Carries waste products away
from the area
Papilla
- Small conical projections at the base of the hair
- Contain blood vessels and nerves which supply
the hair with nutrient
Functions
of the skin
Secretion
Heat regulation
Absorption
Protection
Elimination
Sensation
Vitamin D formation
Melanin formation
Secretion
- The skin secretes sebum from the sebaceous glands
- Sebum lubricates the hair shafts when combined with perspiration
- Acts as a protective barrier against bacteria
Heat regulation
- Normal body temperature is maintained at 37oC
- Muscles, liver and digestive organs are involved in heat production
- Heat is absorbed and maintained in the subcutaneous layer of adipose tissue
- Cooling
- Vasodilation
- Capillaries dilate allowing more blood to reach the
surface of the skin - Pores dilate allowing heat to be lost from the body
- Hyperaemia
- Sweating occurs simultaneously with the
evaporation of perspiration cooling the body - Warming
- Vasoconstriction
- Moves blood away from the extremities to the
major organs - Capillaries constrict and also pores. Skin appears
pale - Shivering
- Goose pimples
Absorption
- The skin is a waterproof covering
- Some substances e.g. drugs and essential oils can penetrate the skin
- Amount of penetration is affected by the health and condition of the skin
Protection
- The skin is a continuous barrier
- Prevents entry of microorganisms
- The skin surface has an acidic pH which inhibits bacterial production
- Splits, cuts, tears and irregularities increase the risk of infection
- Melanin protects against UV light damage to tissues
- Sensory nerve endings warn of possible trauma
- Reflex action prevents greater damage
Elimination
- Some toxins are eliminated from the body through sweat
- These include waste salts and water
Sensation
- Specialised nerve endings found in the dermis make the body aware of its surroundings
- Pain, cold, heat, pressure, touch
- Found at different levels in the skin
- Help prevent trauma to the skin and underlying structures
Vitamin D formation
- Vitamin D is essential for the formation and maintenance of bone
- Vitamin D production is stimulated by the ultraviolet light * Converts 7 -dehydro - cholesterol in the sebum into vitamin D
- Circulates in the blood * Excess is stored in the liver
- Lack of vitamin D can result in rickets in children
Melanin formation
- Produced by melanocytes in the basal layer of the epidermis
- Production stimulated by the hormone MSH
- Causes darkening of the skin
- Melanin production is increased by exposure of the skin to ultraviolet rays
- Protects against UV light damage to tissues since dark colours absorb
radiation - In people with dark skin, the melanocytes continuously produce large
- amounts of melanin
- The melanocytes of light-skinned people produce less melanin
Hair follicles
- Hair follicles travel through the epidermis and dermis
- Erector pili muscles are attached to each hair
- Goose pimples form when hair is pulled upright to keep the body warm
where does Hair grow
Hair grows in follicles which are in the dermis
Sebaceous glands
- Associated with each hair follicle
- Produce sebum – fatty acid
- Keeps skin moist and lubricates the hair shaft
- Sweat + sebum = acid mantle
- Protective shield which helps to control bacterial levels
Hair layers
Cuticle
* The outer layer which consists of overlapping, transparent keratin scales
Cortex
* Middle layer consists of elongated cells which contain melanin = hair colour
Medulla
* Centre of the hair and is composed of loosely connected keratinsed cells
Hair follicle layers
1-Inner root sheath
* Includes the cuticle which interlocks with the cuticle of the hair
* Huxley’s layer – 2 or more cell thick
* Henle’s layer – 1 cell thick
2-Outer root sheath
* Forms the follicle wall
* A continuation of the growing layer of the epidermis of the skin
3-Vitreous membrane
* Separates the connective tissue from the outer root sheath
4-Connective tissue
* Surrounds both the follicle and the sebaceous gland providing both sensory and blood supply
* Dermal papilla supplies the follicle with the blood and nourishment required for growth
Types of hair
1-Lanugo hair
* A coat of fine soft downy hair develops about 6 months before birth
* Hair grow at the same time and rate
* Normally shed 1 month before birth
2-Vellus hair
* Follicles have no sebaceous glands
* Distributed over most of the body except palms, soles, lips and nipples
* Pale in colour
* 1-2cm
3-Terminal hair
* Produced by hair follicles with sebaceous glands
* Grows on the head, areas of the face, underarms and pubic area
Hair growth cycle
- The hair that we describe as growing is actually mostly dead
- The hair grows at its base, the hair bulb in the follicle
- The hair we see about 1cm from the skin is a dead shaft of keratin
- The hair will grow from its base for many years and then falls out
- The follicle rests for a while and then resumes production of a new hair
- 3 stages
- Anagen → Catogen → Telogen
Anagen
- Growing ohase
- Can last from 2-7 years
- Hair grows vigorously – 1cm/month
- Hair can grow quicker in summer
- Untrimmed hair can grow to 1 m long
Anagen
- Hair bulb generates melanin
- Melanin gives the hair its colour
- Length of this stage is an inherited characteristic
Catagen
- Lasts for 2-4 weeks
- The follicle rests
- Also called the intermediate phase
- Bulb produces neither hair cells nor pigment
- Bulb shrinks slightly becoming less deep
Telogen
- Lasts about 3 months
- A new hair begins to grow in the hair follicle
- The old hair will be shed during brushing or washing
- Hair ready to enter into anagen phase after telogen
- Hormonal factors affecting the growth cycle
- Changes in androgens affect the hair, its growth rate and thickness
- Oestrogens slow hair growth and extend the growing phase of the hair growth cycle
- During puberty a rise in androgen levels hair in the pubic area and underarms changes to recognisable terminal hair
- Later in life changes in hormone levels increase face, chest, nose and ear hair growth
- In women hair growth can be affected by hormonal changes during pregnancy and menopause
- Thyroid hormone accelerates hair growth
Diet and environmental factors affecting the growth cycle
- General diet and specific dietary deficiencies affect hair growth
- Poor diet can lead to hair loss
- E.g. crash dieting and anorexia
- Anaemia, alcohol consumption, lack of Vitamin B or Zinc also cause problems
Nails
- Fingernail/nail plate protects the end of the fingertip
- Enhances sensitivity of the nerves in the fingertip
- Made of translucent keratin
Components
of the nail
system
- Free edge – part extending beyond the end of the skin of the fingertip
- Hyponchium- forms a seal between the free edge of the nail and skin of fingertip
- Peronchyium
- Eponchyium
- Nail plate – protective shield of translucent keratin for the nail bed
- Cuticle -layer of skin growing from the base of the nail over the nail plate. Protects the matrix from infection
- Nail bend
- Nail folds
- Matrix – cells of the nail plate and nail bed are produced here. Keratin cells for the nail plate and bed are produced here pushing older cells forward
- Mantle
- Lunula
- Nail wall
- Nail groove
Factors affecting nail growth
Health
*Shape integrity and colour of the nail can be affected by diseases of the lung, heart, kidney, liver or thyroid
Age
*Growth slows with age. Protein in the nail becomes more brittle and prone to splitting
Diet
*Diet does not generally cause abnormal nail changes except in cases of severe Diet malnutrition
Medication
*May affect the rate at which the fast growing cells of the body reproduce
Climate
*Blood increases in hotter climates increasing nail growth
Damage
*If the matrix is damaged nail growth can be affected
Lifestyle
*Environmental factors eg hands in water or chemical solutions
Burns
- A burn is tissue damage
- Burns of the skin may be caused by flames, hot water or steam, sunlight, electricity, or corrosive chemicals
- Bacterial infection is a serious problem for burn patients as pathogens may get into the blood (septicemia) and quickly spread throughout the body
- Dehydration may also be fatal
Squamous and basal cell carcinoma
- The most common forms of skin cancer
- Lesions are visible as changes in the normal appearance of the skin, and a biopsy is used to confirm the diagnosis
- Basal cell carcinomas account for about 78% of all skin cancers
- Tumours arise from cells in the stratum basale of the epidermis and rarely metastasize
- Squamous cell carcinomas account for about 20% of all skin cancers
- Tumours arise from squamous cells of the epidermis, and they have a variable tendency to metastasize.
Malignant melanoma
- Malignant melanoma is a more serious form of skin cancer, which begins in melanocytes
- Any change in a pigmented spot or mole (nevus) should prompt a person to see a doctor
- Melanoma is serious because it may metastasize very rapidly to the lungs, liver, or other vital organ
Psoriasis
- A skin disorder that causes skin cells to multiply up to 10 times faster than normal
- The extra skin cells form scales and red patches that are itchy and sometimes painful
- May cause thickened, pitted or ridged nails
- There is no cure for psoriasis, but symptoms can be managed
Eczema (atopic dermatitis)
- A condition where patches of skin become inflamed, itchy, red, cracked, and rough
- Eczema sometimes precedes asthma and hayfever
Nail white spots (Leuconychia)
- Common condition commonly caused by injury to the nail matrix allowing an air pocket to form
Leukonychia striata - white streaks that appear on the nails due to trauma, manicuring or systemic diseases
Discoloured nails
Yellow nails – most commonly caused by a fungal infection
Blue nails – poor circulation, anaemia or a heart problem
Black nails – usually the result of heavy bruising
Alopecia areata
- Known as spot baldness
- A condition in which hair is lost from some or all areas of the body
- A common autoimmune disorder
*Can lead to the complete loss of hair on the scalp (alopecia totalis) or, in extreme cases, the entire body (alopecia universalis )
