Specials - Human Skin Flashcards
What is the thinnest skin?
Eyelids (0.5mm)
What is the thicket skin?
Palms and soles of feet (4mm)
To what does the human skin act as a barrier to ?
Act as a protector/barrier to the: Chemicals Pathogens UV light Heat Environment
How is human skin involved in thermoregulation?
Sweat glands - evaporation of sweat cools the body
Blood vessels:
Constrict = they reduce heat loss (due to reduced blood flow)
Dilate = Increase heat loss (due to more blood flowing)
How is human skin involved in sensation?
Detect touch/pressure, pain and temperature
Also synthesises vitamin D
The vitamin D requires a modification by UV before the active form can be made in the liver
What are the functions of the human skin?
Barrier/protection
Thermoregulation
Sensation
Blood reservoir
What is the human skin structure?
Epidermis, dermis and hypodermis
Describe the structure of the epidermis
Top layer of skin
Provides barrier and continued renewal
No structural strength
Consists of layers of keratinocytes
What are keratinocytes?
Dead keratin cells that make up the surface of the epidermis
How much blood can the skin hold?
8-10% of the total blood volume
Why does the skin have no structural strength
it is mainly made of dead or dying keratinocytes, so there is no connective tissue in the epidermis to provide strength
What and where is thin skin?
the majority of skin is thin skin and it is when the epidermis has 4 layers of keratinocytes (thinNEST is eyelids)
What and where is thick skin?
it is in the fingertips, palms, soles and has 5 layers. The fifth layer is Stratum Lucidum
Does the skin have vasculature?
No it doesn’t, all nutrient supply and waste removal through the dermis
What does stratification refer to?
the different layers in the epidermis
What is the function of stratification?
Crucial for barrier function and continued renewal of the epidermis
What do cells at the bottom of the epidermis do (I.e at the stratum basale)
Keratinocytes proliferate at the bottom of the epidermis (Stratum Basale) which pushes cells up and away from the dermis
What happens to cells as they move away from the dermis?
They undergo programmed cell death (apoptosis)
How long does complete epidermal turnover take?
A month
What is the acronym for the layers of the epidermis?
Come Lets Get Sun-Burnt
What is the bottom layer of the epidermis?
Stratum Basale
What are keratinocyte stem cells and what do they do?
They are the reservoirs of cells (keratinocytes, stem cells) for a lifetime of renewal.
Keratinocyte stem cells can divide so that one cell remains a stem cell and the others become transit amplifying keratinocytes
What occurs in the Stratum Basale?
Transit amplifying keratinocytes proliferate a lot to provide cells for all the top layers
(divide rapidly but for a short period before they die)
What is the layer above the Stratum Basale?
Stratum Spinosum
How thick is the Stratum Spinosum?
8-10 layers of cells/keratinocytes
What happens to keratinocytes in the Stratum Spinosum
Keratinocytes begin to flatten out
What holds keratinocytes together in the Stratum Spinosum and what is this important for?
Keratin intermediate filaments and desmosomes. This is important for the barrier function of the skin
What layer is above the Stratum Spinosum?
Stratum Granulosum
What happens in the Stratum Granulosum
Flattened keratinocytes undergo apoptosis (programmed cell death)
What are lamellar granules?
Organelles in keratinocytes that fuse to the plasma membrane and begin to release lipid rich secretions to help form the barrier in the Stratum Granulosum
What is keratohyalin?
Protein structure in granules of keratinocytes.
These dark granules help form keratin intermediate filaments into keratin (holds keratinocytes together)
What layer is above the Stratum Granulosum
Stratum Lucidum
Where is the Stratum Lucidum found?
ONLY in thick skin (fingertips, palms, soles)
What is the top layer of the epidermis?
Stratum Corneum
How thick is the Stratum Corneum?
25-30 layers of flattened dead keratinocytes
What is the function of the Stratum Corneum
To form a barrier
Keep moisture in and outside world out
What are keratinocytes like in the Stratum Corneum
Have finished undergoing apoptosis and are overlapping like the scales of a snake
What is the interface between the dermis and epidermis
The basement membrane
What are the proteins in the Basement Membrane
Collagen IV, Perlecan, Nidogen, Lamaminin 332
What do keratinocytes in the basal layer attach to?
Proteins in the basement membrane
What is the Basement membrane important for?
It is important for the epidermal attachment to the dermis
What can a mutation in the basement membrane proteins cause?
Epidermolysis Bullosa
It is when the keratinocytes cannot attach to the BM
What are rete ridges/dermal papillae?
Wave-like ridges in the boundary between the epidermis and the dermis
What is the function of rete ridges?
Their contour provides resistance to shear forces
Where do melanocytes reside?
In the epidermal side of the basement membrane
What do melanocytes make?
Melanosomes
What is contained in melanosomes?
Melanin
How are melanosomes transferred to keratinocytes?
Melanosomes are transferred to keratinocytes by dendrites on the melanocytes
36 keratinocytes at a time
What is melanin?
A pigment which gives the skin colour
What is Pheomelanin
Pigment in melanin
Gives skin red + yellow colours
