19 - Skin Flashcards
What are the 4 layers of the epidermis (outermost to innermost)?
Stratum corneum
Stratum granulosum
Stratum spinosum
Stratum basale
What are the three layers of the dermis?
Papillary dermis (upper) Reticular dermis (lower) Dermal Papillae (interdigitating)
What type of connective tissue makes up the dermis?
Irregular dense connective tissue
What structures are found in the dermis?
- Hair follicles
- Arrector pili muscles
- Sweat glands
- Sebaceous glands
- Blood vessels, nerves and lymphatics
What skin layer lies beneath the dermis?
Hypodermis
How does the thickness of the hypodermis vary between men and women?
Men - thickest in abdomen and shoulders
Women - thickest in hips, thighs and buttocks
Thick on palms of hands in both sexes
What is the hypodermis and what does it do?
- Sub-cutaneous layer (not always considered part of skin)
- Mainly adipose tissue (with some neurovascular bundles) and loose connective tissue
- Energy store
- Insulates underlying muscle
- Shock absorber to protect underlying structures
- Connects skin to underlying muscle/bone
- Makes hormones
What are the functions of the dermis?
- Thermoregulation - hairs and sweat glands
- Special senses (touch) - sensory structures
- Gives structure to the skin and so body shape
What type of epithelial cells make up the epidermis?
Keratinised stratified squamous epithelium
What is the structure of the epidermis?
- Keratinised stratified squamous epithelium
- Four or five layers (depends on thickeness)
- Held together laterally by adherens junctions
- Some terminal nerve endings but no blood vessels
What is the structure of the stratum corneum (outermost layer)?
- Made of dead keratinocytes
- Thick on palms and soles of feet
- Continuously shedded
What is the structure of the stratum granulosum (2nd layer down)?
- Stratified squamous epithelium
- Lamellar granules (proteins that assemble keratin fibrils)
- Tonofibrils (bundles of keratin filaments) made by lamellar bodies
What is the structure of the stratum spinosum (3rd layer down)?
- Cuboidal epithelium arranged in 3 layers
- Held together by desmosomes
- Produce lamellar bodies (keratin factories)
What is the structure of the stratum basale (innermost layer)?
- Tall columnar epithelial cells
- Constantly renew keratinocytes by cell division
- As daughter cells differentiate they move away from the epidermis-dermis junction, make keratin filaments and lose ability to divide
- Contains melanocytes
What additional layer of the epidermis is present in thick skin (e.g. palm of the hand)? Between which layers is this found?
Stratum lucidum
Between the stratum corneum and stratum granulosum
What is the normal transit time for a keratinocyte from the basal layer to the stratum corneum?
28-40 days
In psoriasis the transit time of keratinocytes through the epidermis is reduced, how does the skin appear and what is the transit time for the cells?
Stratum corneum is produced in an abundance of silvery scales every 2-3 days
What is hyperkeratosis?
Too much keratin is put on the surface of the skin, especially the hands and feet.
What are melanocytes and what do they do?
- Cells in the basal layer that produce melanin, the pigment that gives skin its colour
- In dark skin, produce more melanin but same number of melanocytes
- Melanocytes can donate pigment to the keratinocytes around them - keratinocytes phagocytose the tips of the dendritic processes of the melanocyte
What are Langerhans cells in the epidermis?
- Highly specialised antigen presenting cells
- Present to T lymphocytes to mediate immune reactions (e.g. allergic contact dermatitis)
What are Merkel cells?
- Mechanoreceptor cells associated with sensory nerve endings
What are the two types of skin? What are the exceptions to the rule?
- Thin (hairy) skin
- Thick (non-hairy) skin
Exceptions: lips, back of ear, some areas of external genetalia
Where can thick (non-hairy) skin be found? What is its function?
- Palmar surface of hand, plantar surface of foot, areas between the fingers and toes
- Prevents tissue loss from abrasion
- Increases friction between skin and surfaces
- Increased sensation
How does the structure of thick (non-hairy) skin differ from thin (hairy) skin?
- Thin skin has hair follicles, sebaceous glands and arrector pili muscles
- Thick skin has more pronounced ridges and furrows on surface
- Thick skin has more regular shaped dermal papillae
- Thick skin often has the stratum lucidum which is absent in thin skin
What are the three types of hair and where are they found?
- Lanugo - covers the developing foetus and sometimes seen at birth
- Vellus - short, thin, light and soft - not connected to sebaceous glands (replaces lanugo)
- Terminal - head, axillae, external genitalia - long, wide, dark and coarse (produced by action of testosterone)
What are the functions of hair?
- Thermoregulation - arrector pili muscles contract in low temperatures or are stimulated by the sympathetic nervous system
- Sexual attraction - apocrine sweat glands secrete pheromones (hairs trap these oils)
- Sensation - hairs have sensory nerve endings in the bulb (sensory awareness)
- Protection - eyelashes and nasal hair prevent entry of dust and pathogens, eyebrows reduce light and sweat entering eyes, axilla hair conducts sweat away from the body
Where does the arrector pili muscle attach and what causes it to contract?
Smooth muscle fibres attached to papillary region of dermis (origin) and hair bulb (insertion)
Involuntary contraction due to sympathetic stimulation or the cold
The end bulbs of neurones in the dermis contain …………………..
Thermoreceptors
Free nerve endings in the epidermis contain ……………… which detect …………….
Nociceptors, pain
What does the tacticle disc in the dermis detect?
Attaches to the basal layer of keratinocytes and senses touch, pressure and texture
What does the Meissner corpuscle detect?
Tapping and flicker movements
What does the Pacinian corpuscle detect?
Vibrations
What does Ruffini’s corpuscle detect?
Joint movements and tissue stretch
Neurones in the dermis can wrap around hairs to form a root hair plexus, what does this detect?
Vibrations in the hair shaft
What is the structure of nails?
- Nail plate with a nail matrix and nail bed below
- Consists solely of alpha keratin
What are the functions of nails?
- Protect the distal phalanx and surrounding soft tissues
- Enhance precise movements of the digits using counter-pressure
- Enhance sensitivity of fingertip
- As a tool (e.g. pulling, cutting or scraping)
What are the primary functions of the skin?
- Protection and repair
- Temperature regulation and excretion of waste products
- Lubrication
- Storage (white adipose cells)
- Vitamin D synthesis
- Absorption (water, oxygen, some drugs)
- Sensation (mechanoreceptors)
