Skin structure and function Flashcards
What are the layers of skin?
-Epidermis
-Dermis
-Hypodermis
What is the epidermis?
-Stratified squamous epithelial layer
What is the epidermis made of?
-Keratinocytes: Changes shape
What is the dermis?
Supportive connective tissue matrix
What is the dermis made of?
Fibroblasts: Forms connective tissue
Immune cells: WBCs
What is the hypodermis?
Fat layer
What is the hypodermis made of?
-Adipocytes: stores energy as fat
In what layers are your nerve endings and blood vessels?
Dermis and hypodermis
What are rete ridges in the skin layers?
-Increase surface area
-Increases cell contact with the basement membrane
-Hold epidermis in place to prevent blisters
When does the epidermis form?
By 1 month of gestation
When does the dermis form?
In week 11 of gestation
What are the functions of skin?
-Prevents mechanical abrasion
-Prevents dessication or water absorption
-Prevents injury by chemicals
-Barrier to pathogens
-Mechanism of sensation
-Metabolic functions
-Thermoregulation
What are the components of the skin structure?
-Hair
-Hair follicles
-Sebaceous gland
-Arrector pill muscle
-Pore
-Blood vessel
-Sensory nerve endings
-Sweat glands
What is the role of the hypodermis?
-Acts as a cushion
-Stabilises structures above
-Insulation
-Absorbs blows
-Energy reserve
Where are rete ridges in the epidermis highly developed?
Areas exposed to stress, i.e hands and feet
What is present in the epidermis to produce pigment?
melanocytes
Why is the epidermis stratified?
-Stem cell population protected deep inside
-Upper cells provide protection
-Monolayer is more difficult to replace if abraded
Where are stem cells in the epidermis?
At the rips of rete ridges
What makes up the rest of the basal layer of the epidermis?
Transit amplifying cells
What does the basal layer consist of?
Columnar cells anchored to the basement membrane
What are the properties of the cells in the basal layer?
-Proliferative: Grow and increase in no. rapidly
-Undifferentiated: No specialised functions
What is the spinous layer of the epidermis?
-Cells are larger and flattened
-Differentiation of cells start
What is the name of the cells in the basal layer?
Hemidesmosomes
What is the name of the cells in the spinous layer?
Desmosomes
What is the granular layer of the epidermis?
Contains:
-Keratohyalin granules with profilaggrin
-Lipid-filled lamellar granules
What is the transition zone in the epidermis?
-Layer between granular (live) and cornified (dead) layers
-Cells are recycled
-Cornified envelope forms
What happens to organelles in the transition zone?
Destroyed by proteases, DNase, RNase
What is the cornified layer of the epidermis?
-Terminally differentiated
-Forms corneocytes
What are corneocytes?
-Flattened cells
-Forms a protective surface
What does the cornified layer consist of?
-80% keratin encased in cornified envelope
-Remnants of organelles, melanin pigment
-Interstitial fluid
How is damage from radiation prevented?
Melanocytes synthesise melanin
What is the role of melanin?
-Absorbs UV radiation
-Scavenges free radicals
What are the 2 types of melanin?
-Eumelanin (Brown/black)
-Phaemelanin (Yellow/red)
How is infection prevented?
-Langerhan’s cells migrate from bone marrow to spinous layer
What do langerhan’s cells do?
-Take up and process microbial antigens
-Become antigen-presenting cells
-Present antigens to T-cells (lymphocytes)
What does the dermis contain?
-Mast cells (immune cells)
-Dermal appendages (hair follicles,sweat glands, blood vessels)
-Fibroblasts
What is the function of fibroblasts?
-Produce chemicals to control proliferation
-Produce collagen for strength
-Produce elastin for stretch and recoil
-Make extracellular matrix
What is the superficial papillary layer of the dermis?
Contains sensory nerves and loose connective tissue
What is the mechanism of sensation?
Nerves
What are the sensors in the epidermis and dermis?
Merkel cells in the basal layer
What are the touch sensors?
Meissner’s corpuscles
What are the pressure/vibration sensors?
paccinian corpuscles
What are the pain/temperature sensors?
Myelinated and non-myelinated sensory nerve endings
What are the metabolic functions of the dermis?
-Synthesis of vitamin D3
-Lipid metabolism storage
-Lipid soluble vitamins storage
Where does hair emerge from?
Hair follicles from deep in the dermis
What are the 3 layers of hair?
-Inner medulla containing keratin
-Outer cortex with hard keratin
-Cuticle coated in keratin
What are the 2 layers of the epithelial wall?
-internal root sheath surrounding roots
-External root sheath covers length of follicle
What is the dermal papilla?
-Formed from connective tissue
-Hold capillaries and nerves
How is hair colour produced?
Melanocytes at the base of hair produce melanin pigment
What are lanugo hairs?
-Form week 20 of gestation
-Shed before birth
-Fine and long
What are vellus hairs?
-Common hair type over body surface
-Short, fine, light colour
What are terminal hairs?
-Thick and long
-On scalp, eyebrows, eyelashes, beard, pubic area
Where does hair growth stem from?
Hair root firmly attached to the matrix
When does hair growth stop?
When the follicle becomes inactive, shrinks and attachment breaks down
What drugs can alter hair growth?
-Cytotoxins, heparin, warfarin, vitamin A, poisons
What are your nails?
Dense plates of cells packed with hardened keratin
What is the role of the nail?
Protects fingernails and help grasping
Where does the blood supply in the skin come from?
-Deep vessels in subcutaneous layer
-Superficial vessels in reticular dermis
What is body temperature maintained at?
37 degrees
What is the role of blood vessels in the skin?
Controls dilation and contraction to regulate flow and control heat loss
What is the relation between body temperature and forensics?
-Body temp rises and releases sweat
-Leaves latent fingerprints
Where are there no sebaceous glands?
Hair less skin like soles or palms
What are exocrine glands?
Secrete products into ducts leading to the environment, e.g. sweat
What are sebaceous glands?
-Derived from epithelial cells
-Associated with hair follicles
-Found on scalp, face, chest, back
What pH is the skin kept at and why?
6-7, discourages microbial growth
What is the role of sebaceous glands?
-Produces an oily sebum protects hair and skin from drying
-Toxic to bacteria to stop infection
What are sweat glands?
-Within the dermis
-Coiled tubes that secrete watery substance
What are the 2 types of sweat glands?
-Eccrine
-Apocrine
What are eccrine sweat glands?
-On palms, soles, forehead, armpits
-Not in mucous membrane
-Under thermal control
What is the composition of sweat?
-Mostly water
-Minerals: Calcium, Potassium, Calcium, Magnesium
-Fatty acids
-Urea
How is sweat analysis conducted?
-Take sweat swab
-Remove water by sublimation (freeze dry)
-Leaves amino acids and proteins
-Analyse by chromatography
What are the problems with sweat analysis?
-No biomarkers
-Difficult to locate
-Heterogeneity of composition between samples
What are the uses of sweat analysis?
-Detect incidental impurities, e.g. drugs
-New biomarkers found identified with antibodies
What are apocrine sweat glands?
-Large sweat glands
-Empty into hair follicles
-Active at puberty
-Produces sticky odourless protein rich secretion
