Structure And Function Of Skin Flashcards
What does the integumentary system refer to?
→ skin, hair and nails
What are the 5 main skin functions?
→ Barrier
→ Thermoregulation
→ Sensation
→ Repair
→ Vitamin D production
What does the skin act as a barrier against?
→ Dehydration
→ Infection
→ Injury/abrasion
→ solar radiation
What are the 3 layers of the skin?
→ Epidermis
→ Dermis
→ Hypodermis
What is the first layer of the epidermis called?
→ Stratum basale
Describe the stratum basale
→ Contains stem cells and is attached to the dermis
→ daughter cells are constantly moving up distally through the epidermis
→ They differentiate as they go until they are shed from the outer surface
What are the characteristics of the stratum spinosum?
→ Cells have many desmosomes that are visible as spines between the cells
What does the stratum granulosum contain?
→ 1-4 layers of cells containing prominent granules of ‘keratohyalin’ - precursor of keratin
→ Lamellar bodies containing lipids
→ differentiating cells to form the outer layer
What does the stratum corneum contain?
→ Squamous cells which have lost their nuclei
→ horn-like keratin
→ non polar lipids are between the cells
What are the 4 main layers of the epidermis?
→ Stratum basale
→ Stratum Spinosum
→ Stratum Granulosum
→ Stratum corneum
What is the stratum corneum constantly doing?
→ Flaking off and being constantly replaced
What is keratin the main component of?
→ horns, hair, nails, claws, hooves
What are other 3 types of epidermal cells?
Melanocytes
→ Langerhans cells
→ Merkel cells
What do melanocytes do?
→ Synthesizes melanosomes
→ transfers them to basal keratinocytes through long dendrites (downwards)
Where are the stem cells found and why?
→ Basal Keratinocytes
→ Need to be protected from UV damage
Where is the melanin pigment mostly found?
→ Basal epidermis
Where do keratinocytes arrange melanin and how?
→ They arrange melanin pigment in a cap distal to the nucleus
→ Especially in the basal layer
What is the function of Langerhans cells?
→ Antigen presenting cells
→ they are also dendritic cells that form a network
Where is vitamin D3 made?
→ In the epidermis
→ mostly in the basal cells but also the stratum spinosum
What does the production of vitamin D3 require and how does this change with skin color?
→ UV light
→ more UV light with dark skin
How and where is vitamin D3 converted into its active form?
→ 1,25 dihydroxyvitamin D3
→ In the liver and kidney
Describe the dermis
→ Dense, irregular connective tissue
Why is the dermis dense?
→ Full of collagen fibres produced by fibroblasts
Why is the dermis irregular?
→ Fibres are running in all directions
What is the function of collagen?
→ provides tensile strength
→ protection against abrasion and impact
What does elastin do?
→ A protein complex that provides elasticity
Why is the dermis rich in blood vessels?
→ it carries blood and nerve supply for the epidermis
Why is the dermal-epidermal border wavy?
→ to resist shear forces
What do fibroblasts in the dermis do?
→ Make and maintain the collagen
What is an effect of UV light on skin?
→ Damage and loss of elastic fibres
→ leads to wrinkles
What is the hypodermis composed of?
→ Fat
→ glands
→ hair follicles
→ nerves
→ blood vessels
→often the thickest layer of skin
What is the function of the hypodermis?
→ Provides insulation
→ Cushioning
→ energy storage
Where do subcutaneous injections go?
→ hypodermis
What are the three types of gland?
→ Sebaceous
→ Eccrine sweat glands
→ Apocrine sweat glands
What is the function of sebaceous glands?
→ Secrete oily sebum into the hair follicle
What is the function of sebum?
→ Conditioner for hair and skin
→ Prevents dryness and flaking
What do eccrine sweat glands do?
→ Watery secretion onto skin surface
→ Cool the body by evaporation
What do apocrine sweat glands do?
→ secrete oily fluid into hair follicles
→ source of body odour after bacterial action
Where are apocrine sweat glands found?
→ Armpits
→ anogenital region
What is acne?
→ When a follicle becomes blocked and can get infected
What are the 4 types of acne?
→ Blackhead
→ whiteheads
→ papules
→ infected
Where is the nail formed?
→ The nail matrix
→Contains modifiedkeratinocytesthatreplicateand undergo the process ofkeratinisation
What is the nail plate made from?
→ hard keratin
What are the 4 receptors in the skin?
→ thermoreceptor
→ Meissners corpuscle
→ Nociceptor
→ Pacinian corpuscle
What are Meissners Corpuscles receptive to?
→ Touch
What are Pacinian corpuscles receptive to?
→ Pressure
How does the skin protect against dehydration?
→ Keratin holds water
→ lipids stop it evaporating
How does the skin protect against injury?
→ epidermis is strong, rapid healing, thick where friction occurs
→ Dermis has collagen, tough and leathery
→ hypodermis cushions
How does the dermis repair itself?
→ Fibroblasts fill gaps with new collagen that epidermis can attach to
Describe the stratum lucidium of the epidermis
→only in thick skin e.g. palms and soles of feet
→clear layer
What is keratinisation?
→keratinocytesflatten out and die
→granulosum layer produce keratin precursors and glycolipid which remain within keratohyalin granules and lamellar granules, respectively.
→Keratohyalin granules eventually start to aggregate and cross-link forming enormous bundles of keratin within the keratinocyte.
→Lamellar granules stick to the outer cell surface.
→ forms a sort of cement between the cells, making them more resistant to external forces and water loss.
What are the two layers of the dermis?
→thin papillary
→deeper reticular layer
What are dermal papillae of the dermis?
→Finger-like protrusions of dermal connective tissue into the epidermal layer
What are rete ridges of the dermal-epidermal border?
Extensions of epidermis into the dermal layer
What parts of the body are dermal-epidermal borders more apparent?
thick skin of hands = fingerprints, as well as feet
What is the hair follicle?
epidermal tissue that dips down into thedermis, and interacts with other structures likeapocrine glands
What does the bulb of the hair contain?
the hair matrix – active site of hair growth and pigmentation.
What two cell types does the bulb contain?
follicular keratinocytes and melanocytes
What is root and shaft formation?
→hard keratin flatten out and are slowly pushed up the follicle
What is the process of balding?
→Follicularkeratinocytesat the bulb of the hairreplicateonly a set number of times
Where are the youngest keratinocytes found?
The youngest keratinocytesare in the nail matrix, and older cells keratinize, and form thenail plate.
What is the eponychium of the nail?
→Proximal skin fold that gives rise to the cuticle
→a semi-circular layer of dead skinkeratinocytesthat covers the junction where the nail enters the skin
What is the function of the eponychium?
preventing the entry of pathogens.
Summarise the different encapsulated endings of the sensory receptors
Pacinian corpuscles (rapidly adapting) → vibration or brief touch
Merkel’s discs (slowly adapting) → sustained touch/pressure e.g. skin indentation
Meissner’s corpuscles (rapidly adapting) → moving touch or vibration
Ruffini endings (slowly adapting) → steady pressure
Root hair plexus (rapidly adapting) → hair displacement.
Krause end bulbs → touch/pressure, possibly thermoreceptors.
