Skin Flashcards
Functions of skin
- acts as a protective physical barrier
- moisture control
- thermoregulation
- sensation
- UV protection
- production of vitamin D
3 layers of skin
- epidermis; keratinised stratified squamous epithelium
- dermis; collagenous dense connective tissue
- hypodermis; loose connective tissue (mainly adipose tissue)
Epidermis
- top layer of skin
- keratinised stratified squamous epithelium
- composed mostly of keratinocytes (90%)
- four or five discrete layers
- cuboidal cells at the stratum basale
Layers of the epidermis
- stratum basale
- stratum spinosum
- stratum granulosum
- stratum lucidum (only in thick skin)
- stratum corneum
British and Spanish Grannies Love Cornflakes
Melanocytes
- synthesise and store melanin
- found in the stratum basale and stratum spinosum of the epidermis
- involved in the pigmentation of skin and UV protection.
Keratinocytes
- contain keratin
- comprise 90% of the epidermis
- provide protection against mechanical forces
- superficial layer of dead cells is constantly shed
Merkel cells
- associate with free nerve endings to form sensory mechanoreceptors
- found in the stratum basale
Langerhans cells
- serve as antigen presenting cells
- distributed throughout the stratum spinosum and basale
Dermis
- mainly composed of dense collagenous connective tissue, with elastin present throughout
- comprised of reticular and papillary layers
- blood vessels important for thermoregulation (vasoconstriction/vasodilation)
- nerve supply from the subpapillary and cutaneous plexus controlled by the ANS
- nerve endings may be free or encapsulated
Papillary layer
- thin superficial layer of the dermis
- composed of loosely arranged elastic fibres and thin collagen fibres
- rich in blood vessels
Reticular layer
- thick deep layer of the dermis
- composed of dense irregularly arranged collagen fibres and a small number of elastic fibres
- fewer blood vessels
Pilosebaceous unit
Comprised of a hair follicle, sebaceous glands and an erector pili muscle. Sebaceous glands secrete an oily substance called sebum, which forms a protective layer over the skin. The erector pili is a smooth muscle controlled by the sympathetic division of the ANS.
Hairy skin
Covers most of the body, only on thin skin (not the thick skin of the palmar/plantar surfaces). Hair follicles extend into the dermis, or the hypodermis on the scalp.
Eccrine sweat glands
- present all over the body in large numbers
- secrete watery sweat directly onto the skin surface
- important for thermoregulation
Apocrine sweat glands
- found only in the armpits and genital region
- secrete viscous sweat, which may produce odour
Innervation of the skin
- free nerve endings
- Meissner’s corpuscles
- Pacinian corpuscles
- Ruffini’s corpuscles
Meissner’s corpuscles
Rapidly-adapting, encapsulated neurons that sense touch and vibration. They are prominent in the papillary dermis of the fingers, toes, palms and soles.
Pacinian corpuscles
Rapidly adapting, deep receptors that sense deep pressure and vibration. Usually found deep in the hypodermis.
Pacinian= Pressure
Ruffini’s corpuscles
Slow-adapting, encapsulated neurons that sense temperature, mechanical stimuli and respond to skin stretch.
Merkel’s discs
Slow-adapting receptors associated with free nerve endings that respond to light touch.
Free nerve endings
Unencapsulated neurons found in the upper layers of skin, that sense pain, itch, temperature etc. May associate with Merkel cells or surround hair follicles.
Skin disorders
- psoriasis
- malignant melanoma
- benign skin naexus (mole)
- vitiligo
- allergic contact dermatitis
Dermatitis
Inflammation of the skin, triggered by environmental, chemical or seborrheic factors.
Burns
Injuries to the skin caused by heat, chemicals, radiation, friction or electricity. Classified as superficial, partial thickness or full thickness. Full thickness burns may be painless due to the destruction of nerve endings.
