Week 4 Flashcards
What are the functions of skin
Physical protection -acts as a barrier
Thermoregulation
Sensation - lots of sensory receptors in skin
Metabolic functions- fat, adipose tissue, Vit D production
Indicator of general health
Shock absorption
Maintenance of fluid balance
What are the three main layers of skin
Epidermis
Dermis
Hypodermis/ subcutis
What is the epidermis
Keratinised stratified squamous epithelium
Mostly filled with keratinocytes
Four/five discrete layers
Cuboidal cells at the basal layer (stratum basale)
Squamous layer at top
What is the stratum basale/basal layer
Cuboidal cells
Most deep layer
Sat on the basement membrane
Mitosis occurs to replenish above layers
Melanocytes present
What is the stratum spinosum/ prickle layer
8-10 cell layers- biggest layer in epidermis
Connected by desmosomes
Gives prickly appearance on dehydration
Produces cytokeratin- intermediate filament of cytoskeleton
What is the stratum granulosum/ granular layer
3-5 cell layers
Become squamous cells
Granules contain keratohyalin- one of steps in keratin maturation
Stains deeply with H&E
Keratin maturation
Keratin is produced as intermediate filaments- cytokeratin, which matures into packed extracellular keratin
The epidermis is constantly being replenished every 25-30 days in normal skin
Process of keratin maturation in layers
Stratum corneum- keratin
Stratum granulosum- keratohyaline granules
Stratum spinosum- cytokeratin- tonofibrils
Stratum basale- mitosis, some cytokeratin
What is the stratum lucidum
Layer between the stratum granulosum and corneum
Only present in thick skin
What is the stratum corneum/cornified layer
Mature keratin= cytokeratin & keratohyaline
Dead/dying keratinocytes cells ‘squames’
No cytoplasm/nucleus/organelles
what aremelanocytes
Produce melanin
Found in basal layer
Can’t see with H&E
UV protection
Pigment
What are Merkel cells
In stratum basale
Associated with free nerve endings
Sensory- light touch
What are Langherhan’s cells
Found in all layers and dermis
Immune cell, like a macrophage
Specialised immune cell
Antigen presenting cell
Involved in immune and allergic reactions
What is the papillary layer
In dermis
Above the reticular dermis
The dermal papillae (elevations) increase surface area, diffusion nutrients
What is the reticular layer
Dense irregular collagenous tissue- more collagen
Elastin present throughout dermis
This elastic reduces age
Neurovascular supply in the dermis
Complex of vessels present
Subpapillary and cutaneous plexus with shunting vessels between
Important in thermoregulation
Controlled by ANS
Types of skin mechanoreceptors
Meissner corpuscle - papillary layer
Pacinian corpuscle - dermis & hypodermis
Ruffini’s corpuscles
Merkels disks
Free nerve endings
What are free nerve endings for
Pain, nociception (feeling pain)
Merkel disks
Perception of shape , texture
Meissners corpuscle
Motion detection
Grip control
Ruffini ending
Skin stretch
Tangential force
Pacinian corpuscle
Perception of distant events through vibrations
What are the unencapsulated mechanoreceptors
Merkel
Free nerve endings
What are encapsulated mechanoreceptors
Pacinian
Ruffinis
Meissners
What type of skin are hairs found
Thin skin
What is hair made of
Keratin, densely packed
What are sabaceous glands
Secrete oily sebum on upper part of hair follicle
Sweat glands
Found in the superficial hypodermis
Watery fluid
Secrete sweat through exocytosis- termed merocrine secretion
Sebaceous glands
Attached to hair follicles
Secrete sebum
Cells fill with secretory vesicles then dissociates- termed Holocrine secretion
What are the two types of sweat glands
Eccrine
Apocrine
Both are merocrine secretion
Eccrine sweat glands
Directly on skin
Function in heat loss (ANS)
Less viscous
Found everywhere
Apocrine sweat glands
Open into hair follicle
Regulated by hormones
More viscous
Limited to axilla/ genitals and areola
Secrete through merocrine secretion
burns classification
Superficial epidermal
Partial thickness- superficial dermal
Partial thickness- deep dermal
Full thickness- burn extends through all layers of skin to subcutaneous tissue
What is an autograft
Layer of own skin used
What is a allograft
Donor skin cadaver
What does central dogma mean
A theory stating that genetic info flows only in one direction from DNA to RNA to protein
Structure DNA
Double stranded
High molecular weight
Structure RNA
Single stranded
Heterogeneous in size, smaller, vary in size
What does a nucleotide consist of
Phosphate group
Pentose sugar
Base
Sugar used in RNA
B-D-ribose
Sugar used in DNA
B-D-2-deoxyribose
What bonds join nucleotides
Phosphodiester bonds between phosphate group and sugar
Comparison of RNA and DNA
RNA has a OH group at ribose C2 DNA doesn’t
RNA uses uracil where DNA used thymine
Why is RNA unstable
Because the lone pair of electrons on OH group on C2 can react with phosphate
What are purines
Adenine and guanine
Pyrimidines
Cytosine and thymine