19. Skin Flashcards
What are the 3 layers of skin?
Epidermis
Dermis
Hypodermis
What are the 4 layers of the epidermis?
St. Corneum
St. Granulosum
St. Spinosum
St. Basale
What kind of tissue is the dermis made of?
Regular dense connective tissue
What is the role of the dermal papilla and epithelial pegs (rete pegs)?
Hold the structures together and allows movement
What is the structure of the hypodermis?
Contains adipose tissue
Loose connective tissue (fibroblasts, macrophages, fibres, mast cells)
What are the functions of the hypodermis?
Provides energy store - generates heat
Insulator
Shock absorber
Connects skin to underlying muscle and bones
Makes hormones e.g. leptin to control eating habits
What are the 3 layers of the dermis?
Papillary - upper
Reticular - lower
Dermal papillae - interdigitating
What are the functions of the dermis?
Contains hairs and sweat glands (thermoregulation)
Contains sensory structures
Gives structure to skin and so body shape
What cells is the epidermis made up of?
Keratinised stratified squamous epithelium (keratinocytes)
What is the structure of the epidermis?
Four layers of cells in thin skin Five layers of cells in thick skin Held together laterally by adherens junctions Layers held together by desmosomes Has some terminal nerve endings No blood vessels
What are the functions of the epidermis?
Prevents water loss
Prevents entry to bacteria
Specula cells that preset pathogens to immune cells
Synthesis of keratin
Prevents underlying tissue loss due to abrasion
Stratum corneum
Outermost layer made of squames
Thick on palms and soles of feet
Continuously shed
Stratum lucidum
Only on palms and soles of feet
One cell thick but made of keratin
Has water barrier
Stratum granulosum
Stratified squamous epithelium
Lamellar granules
Tonofibrils (bundles of keratin filaments and keratohyalin granules)
Stratum spinosum
Cuboidal epithelium arranged in 3 layers held together by desmosomes
Producers of lamellar bodies
Stratum basale
Tall columnar epithelial cells Constantly renew keratinocytes As daughter cells differentiate they move away from epidermis-dermis junction Make keratin filaments (tonofilaments) Have melanocytes - produce melanin
Keratin synthesis pathway
Tonofilaments (intermediate keratin filaments) in basal cell
Keratin forming factory in spinous cell
Apoptosis first occurs in granular cell
Desmosomes between layers are broken down by proteins
What is the normal transit time of a keratinocyte from basal layer to stratum corneum?
28-40 days
In psoriasis 2-3 days
Melanocytes in epidermis
Occur at intervals
Difficult to see without stains
Produce melanin - not increased in number in people with darker skin
Langerhans cells in epidermis
Difficult to see without stains
Highly specialised capacity to present antigens to T lymphocytes mediate immune reactions
Merkel cells in epidermis
Difficult to see without stain
Mechanoreceptor cells associated with sensory nerve endings
What are the 2 types of skin?
Thin skin - tends to be hairy
Thick skin - tends to be non-hairy
Exceptions: lips, back of ear, some areas of external genitalia
Where is thick non-hairy skin?
Palmar surface of hand
Plantar surface of foot
Area between fingers and toes (webs)
What is the structure of thick non-hairy skin?
No hair No arrector pili muscles No sebaceous glands Thicker starts corneum Thinner dermis Increased density of mechanoreceptors Pronounced ridges and furrows on surface
What are the functions of thick non-hairy skin?
Prevent tissue loss due to abrasion
Increased friction between skin and surfaces
Increased sensation
What are the 3 types of hair?
Lanugo - covers developing fetus
Vellus - replaces lanugo, short, thin, light coloured and soft
Terminal - head, axillae, external genital region, long, wide, dark coloured, coarse
What are the functions of hair?
Thermoregulation
Sexual attraction
Sensation
Protection
Arrector pili muscle
Smooth muscle fibres attached to papillary region of dermis and hair bulb
Fight or flight response or cold causes involuntary contraction
May also induce sebum release from sebaceous gland
What do end bulbs detect?
Thermoreceptors so register temperature
What do free nerve endings detect?
Have nociceptors
Register pain
What do tactile discs detect?
Senses touch, pressure and texture
Merkel in non-hairy skin, meissner in hairy skin
Vertical dimpling of skin
What do meissner corpuscles detect?
Tapping and flicking movements
What do pacinian corpuscle detect?
Vibration
What do Ruffini’s corpuscle detect?
Joint movements and tissue stretch
What do root har plexus detect?
Vibrations in the hair shaft
What are the main functions of skin?
Protection and repair Thermoregulation Excretion of waste products Lubrication Storage Vitamin D synthesis Absorption Aesthetics Sensation
