Skin: Structure & Function Flashcards by aimen n

What is the integumentary system?

Refers to the skin, hair and nails.
Largest and heaviest organ of the body – ~15% of adult weight
Medically significant

How well did you know this?

Not at all

Perfectly

What are the main functions of the skin?

Barrier (protection), against:
- Dehydration
- Infection
- Injury / abrasion
- Solar radiation
Thermoregulation
Sensation
Repair
Vitamin D production

How well did you know this?

Not at all

Perfectly

What is the Integumentary system composed of?

3 layers of the skin 
Epidermis, Dermis, Hypodermis
Hairs
Glands
Sense organs

How well did you know this?

Not at all

Perfectly

What is H&E stain?

Stained with H+E (Haematoxylin and eosin)

How well did you know this?

Not at all

Perfectly

Describe the structure of hypodermis

Hypodermis can be the thickest layer - composed of fat

How well did you know this?

Not at all

Perfectly

Describe the epidermis structure

Thinnest (in abdomen)

Thickest on the heel of your foot

How well did you know this?

Not at all

Perfectly

What are the 4 layers of epidermis?

Basal layer - (Stratum basale)
Stratum spinosum - (spiny layer)
Stratum granulosum - (Granular layer)
Stratum corneum - (cornified layer)

How well did you know this?

Not at all

Perfectly

Outline the features of the basal layer

(Stratum basale)
First single layer, containing stem cells, and attached to dermis.
Stem cells constantly proliferate

How well did you know this?

Not at all

Perfectly

Why is the basal layer referred to as dynamic?

Daughter cells constantly move “up” (distally) through the epidermis, differentiating as they go, until they are shed from the outer surface
This takes ~20-50 days.

How well did you know this?

Not at all

Perfectly

Describe the structure and function of the stratum spinosum

(spiny layer)
Cells have many desmosomes, (junctions) here visible as “spines” between the cells

Strong bonds holding the epidermis together

How well did you know this?

Not at all

Perfectly

Describe the composition of the stratum granulosum layer

(Granular layer)
1-4 layers of cells containing prominent granules of “keratohyalin” (keratin precursor)

Also contain lamellar bodies containing lipids (seen by TEM)

How well did you know this?

Not at all

Perfectly

Describe the function of the stratum granulosum cells

Cells are differentiating to form the outermost layer

How well did you know this?

Not at all

Perfectly

What is the stratum corneum ?

(cornified layer)

The outer protective layer of the epidermis. Many cells thick.

How well did you know this?

Not at all

Perfectly

Outline the composition of the stratum corneum

Squamous cells which have lost their nuclei,

Cornified – full of “horny” keratin (from keratohyalin granules) thus tough and resistant to injury

Nonpolar lipids (waterproof) are between the cells – from lamellar bodies

How well did you know this?

Not at all

Perfectly

Name examples of other epidermal cell types and their roles

Melanocytes  (pigment)
Langerhans cells  (defence)
Merkel cells  (sensation

How well did you know this?

Not at all

Perfectly

What stain is used to view melanocytes?

Special (DOPA) stain for melanin shows their dendritic form

How well did you know this?

Not at all

Perfectly

What is the role of melanocytes?

Melanocytes in the epidermis synthesise melanosomes (pigment granules)
and transfer them to basal keratinocytes through long dendrites

How well did you know this?

Not at all

Perfectly

What is melanin?

Pigment mainly in basal epidermis

How well did you know this?

Not at all

Perfectly

Where in the skin is melanin found?

Keratinocytes arrange melanin pigment in a cap distal to the nucleus (sunny side)
especially in basal layer (stem cells

How well did you know this?

Not at all

Perfectly

Outline the role of melanin in UV protection

UV protection - black-skinned people have only about 10% as many skin cancers as white people with the same lifestyle

How well did you know this?

Not at all

Perfectly

What are Merkel cells?

Oval shaped mechanoreceptors (pale) cells in the basal layer
Touch-sensors
Hard to tell difference with H&E alone in white people

How well did you know this?

Not at all

Perfectly

What is the function of Langerhans cells?

Immune system. Antigen-presenting cells (like macrophages)

Also are dendritic cells, forming a network

How well did you know this?

Not at all

Perfectly

Describe the appearance of Langerhans cells in H+E stain

Small, pale cells in non-basal layers of epidermis. Hard to see with H&E only

Where is Vitamin D produced?

Vitamin D3, made in the epidermis. Mostly basal cells, also stratum spinosum

Why is Vit. D deficiency more prevalent in darker skin tones?

Requires UV light. | Requires more UV light in dark skin (melanin barrier)

Where in the body is Vitamin D converted to its active form?

Converted to active form in liver and kidney: 1,25 dihydroxyvitamin D3. Commonly deficient in UK

What is the dermis?

Dense, irregular connective tissue. Dense = full of collagen fibres; Irregular = fibres run in all directions (not parallel)

What are the functions of the dermis?

Collagen provides tensile strength, (strength when pulled), hence protection against abrasion and impact Contains elastin: protein complex providing elasticity Dermis also carries blood and nerve supply for epidermis Rich in blood vessels

Describe the structure of the dermal-epidermal border

The dermal-epidermal border is often wavy, to resist shear forces (rubbing sideways). Especially on hands, = fingerprints, also feet

What are rete ridges?

Epithelial extensions projecting into the underlying connective tissue in skin and mucous membranes

Which layer of the skin contains rete ridges?

Epidermis can have rete ridges | Dermis can have finger-like dermal papillae (sing. = papilla)

What is the hypodermis?

Aka fascia, or subcutis (Cutis = epidermis + dermis) | Where you put a hypodermic syringe, for a subcutaneous injection

Describe the structure of the hypodermis

Composed of fat, containing glands, hair follicles, nerves, blood vessels. Often the thickest layer of skin. Thickness varies with age, body site, nutrition etc

What is the function of the hypodermis?

provides insulation, cushioning and energy storage

Name the 3 types of glands present in the skin

Sebaceous glands Apocrine sweat glands Eccrine sweat glands

What are Sebaceous glands?

Secrete oily sebum (“lanolin”) into hair follicle. Conditioner for hair and skin, prevents dryness and flaking

What are the roles of the Eccrine sweat glands?

These are normal sweat glands. Watery secretion on to skin surface, cools the body by evaporation

What is the function of the apocrine sweat glands?

Secrete into hair follicles Oily fluid in humans, function unclear (contains pheromones in some mammals), but source of body odour after bacterial action Found in armpits and anogenital region - Only after puberty Less in Asian people

What is the role of hair/follicles?

Hair: rudimentary in humans over much of body | Keeps the head warm but can be bald

What infection is associated with hair follicles?

> also site of acne | Acne is when a follicle becomes blocked, and can get infected

What is the nail matrix?

The equivalent to basal layer in rest of epidermis, where cells divide and forming nail

What is the nail plate formed from?

Nail plate is made of keratin | Phalanx is the bone

What is the role of thermoreceptors?

Heat / Cold sensors

What do Meissner's Corpuscle detect?

Senses touch | Merkel cells in basal epidermis also detect light touch

What are nociceptor fibres?

Free nerve endings - sense pain

What is the role of pacinian corpuscles?

Are baroreceptors that sense pressure

Describe the structure of the skin at the fingertip

Paler structure in the middle of the fingertip is the neural structure in a dermal papilla

How does the skin protect us against dehydration?

Epidermis: Keratin holds water, lipids stop it evaporating.

What skin layer helps protect against infection?

Epidermis: Impervious barrier, also immune system

Ho does the skin protect against injury?

All layers Epidermis strong, rapid healing, thick where friction occurs. Dermis has collagen – tough, leathery. Hypodermis cushions.

What layer protects against solar radiation?

Epidermis – stratum corneum and melanin pigment

How does the skin enable thermoregulation?

Hypodermis (insulation); thermoreceptors; blood supply regulation, sweating

What allows sensation in the skin?

Nerve supply and various receptors

How is skin repair enabled?

Epidermis – normal proliferation, and dermis – fibroblasts fill gaps with new collagen that epidermis can attach to

What skin layer is responsible for Vit. D production?

Epidermis

What structures innervate the skin?

- Thermoreceptors - Meissner's Corpuscle - Nocicpetors - Pacinian Corpuscle