Structure & Function of Skin Flashcards
Function of Epithelial tissue
Cover surfaces with sheets cells.
Have function in secretion, barrier & protection,
strength & support
What is the epidermis ?
The most superficial layer of the skin. Avascular.
What are the layers of the epidermis ?
The epidermis comprised of several layers (bottom to top)
- stratum basale
- stratum spinosum
- stratum granulosum
- stratum lucidum
- stratum corneum
What does the number of layers and thickness of the epidermis depend on ?
Location in the body
What are the main cells of the epidermis ?
Keratinocytes
Where do keratinocytes originate ?
In the basal layer and produce the main protein of the epidermis called keratin.
What other cells are found in the epidermis ?
Melanocytes
Langerhan’s cells
Merkel’s cells
What is the function of melanocytes ?
Produce skin pigment
What is the function of Langerhan’s cells ?
Immune, antigen- presenting cells
What is the function of Merkel’s cells ?
Mechanoreceptors for light-touch
Function of the epidermis
Protection, skin regeneration, skin colour
Stratum corneum
Outermost layer
Made up of mature keratinocytes.
Keratinised squamous epithelium.
Stratum Lucidum
Only found in areas of thicker skin.
Clear on histological slides.
Stratum granulosum
Mature keratinocytes, contains granules in the cytoplasm.
No nuclei
Stratum spinosum
Connect by desmosomes
Langerhan’s cells are most abundant here.
Stratum basale
Cells are attached to the basement membrane, hemidesmosomes.
Cell division and grow (mitosis)
Contains melanocytes.
How is the dermis anchored to the basal lamina ?
By Collagen 7
Where is the dermis located ?
Deep the the epidermis.
VASCULAR.
Function of the dermis
To sustain and support the epidermis, as it has blood vessels to supply nutrients and oxygen.
What does the dermis contain ?
Fibroblasts
Collagen
What are the 2 layers of the dermis ?
Papillary dermis
Reticular dermis
What is the papillary dermis ?
The most superficial layer of the dermis.
Function of the papillary dermis
Increases the surface area for the transfer of oxygen and nutrients between the dermis and epidermis.
What is the papillary dermis made up of ?
Fine collagen and elastin fibres.
Small blood vessels and nerves.
i.e. Loose connective tissue
What is the reticular dermis ?
The deep layer of the dermis.
What is the reticular dermis made up of ?
Courses collagen & elastin fibres
Large blood vessels and nerves
i.e. thicker connective tissue
What does the reticular dermis surround ?
Hair follicles
Sweat glands
Sebaceous glands
Nerves
Plexus of blood vessels
Other structures in the dermis
Appendages
Name some appendages
Hair follicles
Glands
Arrector pili muscle
Tactile corpuscles
What is a hair follicle ?
A sac-like down growth of the dermis and epidermis out of which hair grows.
Hair follicle structure
Hair follicles are anchored in the hypodermis.
Hair shaft grows form the bulb and is made of keratin.
What other 2 structures are associated with the hair follicle ?
Sebaceous glands
Arrector pili
What are the components of a Pilo-sebaceous unit ?
Hair follicle
Sebaceous gland
Arrector pili
What is the function of sebaceous glands ?
Exocrine glands that secrete sebum to lubricate hair and adjacent skin.
What is the function of the arrector pili ?
Contraction of smooth muscle attached to the papillary dermis and pulls the hair upright (goosebumps) controlled by the SNS.
What so the sebaceous glands look like ?
Raspberry shaped.
What are exocrine glands ?
Glands which have ducts that open to the outside of the body or to a cavity inside the body.
Sweat gland location
In the dermis and hypodermis.
(ALL over the body)
Function of the sweat glands
Thermoregulation
Also a response to ‘Fight or Flight’ - controlled by the SNS
Tactile corpuscle function (Meissner’s corpuslce)
Facilitate the sensorial capabilities of the skin.
e.g.
Light touch
Vibration
Other sensations
Hypodermis location
Deep to the dermis
Hypodermis composition
Loose connective tissue
Adipose tissue
Blood vessels
Nerve tissue etc.
Function of adipose tissue
Energy storage
Shock absorption
Helps keep in heat
What structures are found in the hypodermis ?
Deepest part of hair follicles
Eccrine and apocrine glands
Subcutaneous vascular plexus function
Series of blood vessels that supply and drain the subcutis.
Subdermal vessel plexus location
Network of blood vessels found at the level of the dermis.
Vascular plexus function
Plays an important role in thermal regulation. These vessels are superficial to the layer of fat in the subcutis.
Why are the vascular plexus vessels superficial to the layer of fat in the subcutis ?
Otherwise the fat which is essential is insulation would prevent those blood vessels from releasing heat.
Cutaneous nerve function
Provide sensory innervation to the skin and have a number of sensory receptors.
What is underneath the hypodermis ?
A layer of fascia which separates the hypodermis from the underlying muscle.
Fascia meaning
Thin layer of fibrous connective tissue.
Function of melanocytes
Synthesise and release brown pigment melanin.
Absorbs UV-B and prevents DNA damage to underlying cells of the hypodermis.
What is melanoma ?
Tumour of melanocytes and is caused by exposure to UV radiation.
- lower incidence in those who have more melanin.
Function of Langerhan’s cells
Express Langerin which helps bind and degrade viruses such as HIV in specialised endosomes called Birbeck granules.
Which intermediate filaments are expressed in the stratum spinosum ?
K1 and K10
What is the function of filaggrin ?
Maintains the optimal skin barrier
Aids keratin filament aggregaation
Inhibits water loss.
What is the precursor of filaggrin ?
Pro-filaggrin
How does filaggrin inhibit water loss ?
Filaggrin cleaved into amino acids which aid in maintaining moisture.
Key functions of the skin
Protection
Sensation
Homeostasis
Lamina densa
Type 4 collagen
Lamina reticulates
Type 7 collagen
Mutation in collagen 7
Dystrophic epidermolysis bullosa = blistering
Tyrosinase
Produced from RER and is responsible for synthesis of melanin
Converts melanocyte into melanin
What is periodontal membrane ?
Periodontal membrane is a fibrous joint between the teeth and the skull.
What is meant by cornification ?
Epidermal keratinocytes undergo a unique form of terminal differentiation and programmed cell death known as cornification.
What happens in cornification ?
Cornification leads to the formation of the outermost skin barrier, i.e. the cornified layer, as well as to the formation of hair and nails
Functions of the cornfied layer of skin
It prevents the penetration of allergens, pathogens (viruses and bacteria), chemical irritants and UV radiation, and the loss of body fluids.
Results of filaggrin mutation
Mutations in the Filaggrin gene can cause absent or reduced filaggrin protein, leading to impaired keratinization and skin barrier defect.
