19 - Skin Flashcards by James Hobson

What are the 4 layers of the epidermis (outermost to innermost)?

Stratum corneum
Stratum granulosum
Stratum spinosum
Stratum basale

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What are the three layers of the dermis?

Papillary dermis (upper)
Reticular dermis (lower)
Dermal Papillae (interdigitating)

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What type of connective tissue makes up the dermis?

Irregular dense connective tissue

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What structures are found in the dermis?

Hair follicles
Arrector pili muscles
Sweat glands
Sebaceous glands
Blood vessels, nerves and lymphatics

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What skin layer lies beneath the dermis?

Hypodermis

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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

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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

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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

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What type of epithelial cells make up the epidermis?

Keratinised stratified squamous epithelium

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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

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What is the structure of the stratum corneum (outermost layer)?

Made of dead keratinocytes
Thick on palms and soles of feet
Continuously shedded

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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

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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)

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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

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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

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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)