BL Skin Structure And Function Flashcards
What are the layers of the skin?
Epidermis
Dermis
Hypodermis
Structure of the epidermis
- made of epithelial cells - keratinocytes
- keratinised stratified squamous epithelium
- thick skin - 5 layers
- thin skin - 4 layers
- adherens junctions
- desmosomes
- avascular
Function of the epidermis
Prevents water loss
Protection against bacteria + parasites
Presents pathogens to immune cells
Prevents underlying tissue loss from abrasion
Keratin synthesis
Temperature regulation
Sensation
Layers of the epidermis
Come, Let’s Get Sunburnt
Stratum Corneum - corny/horny later
Stratum Lucidum - only in palms + sole of feet
Stratum Granulosum - granular layer
Stratum Spinosum -spinous layer
Stratum Basale - basal cell layer
Outline the structure of the stratum corneum
Made of squames: dead keratinocytes
Thick on palms + soles of feet - prone to injury
Continuously shed
Outline the structure of the stratum granulosum
Very darkly stained
Stratified squamous epithelium
Many Golgi apparatus for vesicles
Lamellar granules + keratohyalin granules
Tonofibrils
What are lamellar granules?
Where are they found?
Filament associated proteins that assemble keratin fibrils + release it
Stratum granulosum
What are tonofibrils?
Where are they found?
Bundles of keratin filaments + keratohyalin granules
Stratum granulosum
Outline the structure of the stratum spinosum
Cuboidal epithelium arranged in 3 layers - held together by desmosomes
Producer of lamellar bodies - lipid production
- keratohyalin factories
Keratohyalin granules
Outline the structure of stratum basalt
Columnar epithelium
Keratinocytes are constantly dividing by mitosis
Melanocytes
What are do melanocytes release and what stimulates this?
Melanin
MSH - melanocyte stimulating hormone
Outline the structure of the dermis
Loose connective tissue - upper papillary layer
Dense irregular connective tissue - lower reticular layer
Collagen
Elastin
Contains blood vessels
0.6mm-10mm thick
Functions of the dermis
- thermoregulation - contains hairs and sweat glands
- touch - contain sensory structures
- structure + body shape
What causes skin wrinkling?
Thinning of the dermis
Less collagen and elastin
Structure of the hypodermis
Mainly adipose tissue
Loose connective tissue - fibroblasts, macrophages
Functions of the hypodermis
- provides energy store - generate heat
- insulator for underlying muscle heat generation
- shock absorber
- makes hormones
- connects skin to underlying muscles + bones
What is the varying thickness of the hypodermis based on?
Location
Person - men vs women
Hypodermis thickness in men
Thick in abdomen - white adipose - energy storage
Thick in back of shoulders - brown adipose
Hypodermis thickness in women
Thick in hips, thigh and buttock
What part of the body has a thick hypodermis in both sexes?
Palms of the hand
Function of the skin
- protection and repair
- temperature regulation + excretion of waste products
- lubrication
- storage
- vitamin D synthesis
- absorption
- aesthetics
- sensations
How does the skin provide protection?
Epidermis of keratinocytes - abrasion
UV protection by melanocytes
Outline vitamin synthesis in the skin
1- cholecalciferol produced in the skin
2- converted into 25-hydroxyl cholecalciferol by liver
3- converted into 1,25-hydroxyl cholecalciferol VitD3 - active vitamin by kidneys
What is desquamation?
Shedding of the outer layer of the skin
Describe the process of keratinocyte differentiation
- upwards maturation of basal keratinocytes into cornified cells with the progressive flattening of cells, loss of nuclei + other organelles
. - stranum basale - keratinocytes are made via cell division - one cell remains + others move up layers. Tonofibrils are synthesised
- stranum spinosum - where keratohyalin granules + lamellar bodies begin in form - start of cornifying cells + aggregating keratin filaments
- stratum granulosum - more keratohyalin granules + lamellar bodies produced. Tonofibrils act as water barrier
- stranum corneum - progressive flattening + lose of organelles to form the corny layer
What hormone does the hypodermis produce?
What does it do?
Leptin
Involved in regulating food intake
Where is soft and hard keratin found?
Soft - skin
Hard - horns, hair + nails
Location of langerhan’s cells
Stratum spinosum
What is a merkel cell?
What does it look like in H+E staining?
Mechanorecpetor cells associated with sensory nerve endings - surrounded by Schwann cells
Schwann cell contains lipids > don’t stain in H+E > pale circle around purple dot
Who are at the greatest risk of skin cancer?
People with albinism
Don’t produced melanin
What are the four types of skin?
Hairy skin + non hairy skin
Thin skin + thick skin
Hairy skin tends to be thin
Non-hairy skin tends to be thick
Location of non-hairy/thick skin
Palms of hand
Sole of feet
Area between fingers and toes
Function of non-hairy/thick skin
Prevents tissue loss due to abrasion
Increased friction between skin + surfaces
Increased sensation
Structure of non-hairy/thick skin
No hair
No arrector pili muscles
No sebaceous glands
Thicker startum corneum
Thinner dermis
Increased density of mechanoreceptors
Thick skin vs thin skin in relation to:
- hair follicles
- sebaceous glands
- arrector pili muscles
- ridges + furrows
- dermal papillae
- stranum lucidum
Thick:
- no hair follicles
- no sebaceous glands
- no arrector pili muscles
- pronounced ridges + furrows
- regular shaped dermal papillae
- stratum lucidum present
Thin
- presence of hair follicles
- presence sebaceous glands
- presence of arrector pili muscles
- smaller ridges + furrows
- irregular dermal papillae
- stratum lucidum absent
What are skin appendages derived from?
Examples
Derived from down growths of epidermal epithelium during 3rd month of fetal development
- hairs
- arrector pili
- sebaceous glands
- sweat glands
- nails
What are the types of hair?
Describe them + location
Lanugo - covers developing fetus
Vellum - replaces lanugo
- short, thin, light coloured + soft
Terminal - scalp, eyebrows, nasal passage,
axillae, external genital region
- long, wide, dark coloured, coarse
- produced by the actions of
testosterone
Functions of hair
- Thermoregulation
- Sexual attraction
- Sensation
- Protection
Explain the hair’s function in thermoregulation
Piloerection - when body temp is low
Pilorelaxation - when body temp is normal or raised
Arrector pili muscles contract when stimulated by sympathetic fibres»_space; piloerection
Explain the hair’s function in sexual attraction
Apocrine sweat glands secrete pheromones that attract the opposite sex
Hair traps the pheromones
Explain the hair’s function in sensation
- Hairs have sensory nerve ending within bulb
- Movements sensed by the bulls an transmitted to CNS
- Provide sensory awareness
Explain the hair’s function in protection
- barrier to UV rays - scalp
- eyelashes and nasal hair prevent dust and pathogens
- eyebrows reduce the amount of light and sweat entering the eyes
- axilla hair conducts sweat away from body
Explain the role of arrector pili muscles and how they work
- Consist of smooth muscle fibres attached to papillary region of dermis and hair bulb
- Can induce sebum release from sebaceous gland
- piloerection + pilorelaxation
What are holocrine glands?
Secretions are produced in the cytoplasm
Released by rupture of plasma membrane»_space; destroys the cell
Substance secreted
Functions of sebaceous glands
Produce sebum
- lubricate skin/hair
- reduce water loss
- aid skin flexibility
- protect from UV damage
- reduce friction damage
- facilitate cooling of skin
Where are sebaceous glands found?
Mostly in face and scalp
Eyelids, penis, labia, nipples, lip
List mechanoreceptors and what they detect
- end bulbs: thermoreceptor - temp.
- free nerve endings: nociceptors - pain
- tactile discs: touch, pressure + texture
- meissner corpuscle: tapping + flicker movements - light + touch
- pacinian corpuscle - vibrations/pressure
- ruffini’s corpuscle - joint movements + stretch
- root hair plexus - vibrations in hair shaft
Frequencies used for pacinian corpuscle
Range
Optimum
100 to 1000 Hz
Optimum - 450 Hz
Frequencies used for meissner’s corpuscle
Range
Optimum
10 to 50 Hz
Optimum 35 Hz
Structure of nails
Only made of alpha keratin
Functions of nails
- protection of distal phalanx
- enhances precise delicate movements - extra grip
- enhances sensitivity of the fingertip
- as a tool
What are the epithelium of the layers of epidermis?
- stratum corneum: squames (dead keratinocytes with no organelles)
- stratum granulosum: stratified squamous epithelium
- stratum spinosum: cuboidal epithelium
- startum basale: columnar epithelium
