12-10-21 - Structure and Function of Skin Flashcards
What are the 3 layers of the skin from top to bottom?
What does each layer contain?
What do some of the layers do?
- The Epidermis
- Consist of avascular keratinised stratified squamous epithelium (lacking blood vessels)
- This undergoes proliferation and synthesises Keratin
- The Dermis (vascular, tough – where leather of animals is found leather)
- Contains blood vessels, lymphatics and cutaneous nerves
- Contains collagen and elastic fibres, which are not replaced with age.
- Hypodermis (aka subcutaneous or superficial fascia layer – varies in thickness)
- Contains blood vessels, nerves, and lymphatics
- Contains fatty adipose tissue
- Contains skin ligaments, loose skin
What are the 3 main functions of the skin?
What are these areas broken down into?
How does it function?
- Protection
- Provides Melanin for protection against UV
- Immune cells are in the skin and can generate an immune response against foreign bodies
- Keratin protects the body from chemicals and water
- Homeostasis
- Metabolic – Vitamin D in skin is used for synthesis and metabolism. The skin can absorb vitamin C from the sun to keep the body healthy. The skin also acts as stored energy (fat)
- Temperature regulation – through vasodilation/constriction, sweating, fat stores, hair
- Internal homeostasis - can regulate water, electrolyte and macromolecule balance
- Sensory information
- Sensation (into the brain) – pain, temperature, touch, pressure, vibration
- Psychosocial signals (out of brain) – Visual signals (face turning red), chemical signals (pheromones secreted from glands in genitals and armpits)
What happens to skin when it is burned?
What are the dangers?
- When the skin is burned, this leads to loss of the skin barrier function
- The dangers are fluid loss, loss of macromolecules, and infection
- A macromolecule is a single molecule that consists of many covalently linked subunits, such as protein
How does it take cells to move from the bottom to the top of the epithelium?
How long does it take these cells to be replaced?
What is the type of epithelium in the epidermis?
What is the type of skin with a thick top layer?
Where is it found?
- It takes cells (keratinocytes) 30-50 days to go from the Stratum basale (bottom layer) to the stratum corneum (top layer)
- It is 40-56 days between the cell being a stem cell, to desquamation (shedding of skin)
- The epidermis consists of Keratinized stratified squamous epithelium
- Glabrous skin is hairless skin, with a thick top layer, that can be found on the palms or soles of feet (anywhere there is abrasion)
What are the different layers of the epidermis from bottom upwards?
What occurs to cells at these stages?
• S= stratum
S. Basale (basal layer)
• This is where the basal lamina (basement membrane) of the epithelium is located
• This is the site of asymmetric division of stem cells.
• One cell begins to move upwards through the layers of epithelium.
S. Spinosum (spiney layer)
• There is expression and production of Keratin 1 and 10 (K1 and K10), which form intermediate filaments (these cells are now keratinized, as they have formed keratin)
• These intermediate filaments (keratin) link via desmosomes at this layer.
• The expression of filaggrin also begins in the Stratum Spinosa.
• This is where programmed cell death is initiated
S. Granulosum (granulated layer)
• The first signs of cell death are seen here.
• Ketohyaline granules form in the cell, which are used to generate filaggrin
• Filaggrin orchestrates condensation, organisation and aggregation of keratin filaments to form layers, which aids in the cornification process.
S. Lucidum (glass like layer – not present in thin skin (majority of body skin)
• Specialised cell death programme occurs here
S. corneum (cornification layer)
• This layer is made from dead cells full of organised/aggregated keratin
• These cells have lost all their organelles.
• These cells are known as cornified cells (corneocytes)
• It is a waterproof layer.
What are keratinocytes?
Where do they originate?
Where do they go?
- Keratinocytes are the major cell type of the epidermis, making up 90% of the cells there
- Keratinocytes originate in the deepest layer of the epidermis (stratum basal) and move up to the final barrier layer of the skin (stratum corneum)
What is cornification?
What does it allow?
- Cornification is a keratinocyte differentiation programme that occurs in the upper layer of the epidermis
- It allows the formation of a dead cells (corneocytes) layer to create a physical barrier for the skin
How are cells attached to the basal lamina?
How is the dermis attached to the basal lamina?
What condition does it cause if there is a mutation in this protein?
- Hemi-desmosomes (junction complex) anchors basal cells to the basal lamina
- The dermis is anchored to the basal lamina by Collagen VII (7), which builds anchoring fibrils.
- If the Collagen 7 becomes mutated, this causes Dystrophic epidermolysis bullosa, which causes major blistering in the skin.
Where are filaggrin proteins found?
What is its precursor?
What are their 3 main functions?
- Filaggrin proteins are found as the main component of the keratohyaline granules in the Stratum granulosum
- The precursor to filaggrin is profilaggin
- Their main functions are:
- To maintain the optical skin barrier
- Aid keratin filament aggregation
- Inhibit water loss (filaggrin cleaves into amino acids that aid in maintaining moisture)
What expressions are seen in the stratum spinosum?
What are the functions of these proteins?
- In the stratum spinosum, proteins K1 and K10 begin to be expressed and produced (K = Keratin)
- K1 and K10 form intermediate filaments
- These Keratin intermediate filaments are connected to each other via desmosomes.
- The protein Filaggrin also begins to be expressed in the stratum spinosum
- Filaggrin in the ketohyaline granules in the stratum granulosum layer are used for the condensation, organisation and aggregation of keratin filaments to aid in cornification.
How is filaggrin originally made?
How is filaggrin then made?
What also happens during this process?
What conditions can filaggrin mutation lead to?
- Filaggrin is initially made as a multi-component profilaggrin
- This profilaggrin contain 10-12 near perfect filaggrin monomers, and 2 imperfect ones.
- To make filaggrin, these filaggrin monomers are chopped out from the profilaggrin.
- Simultaneously, this generates small molecules which are responsible for retaining water, which moisturizes the skin
- Filaggrin mutations can cause a reduction in filaggrin expression, which reduces the amount of these small molecules generated.
- This leads to disorders of dryness and weakness of the skin, such as eczema
- Filaggrin mutations are the cause of 50% of eczema cases.
Where are melanocytes found?
What is their function?
How does this function vary between races?
What conditions can be caused from melanocytes?
How does this condition vary with different races?
- Melanocytes are found in the basal layer of the epithelium in the epidermis.
- They synthesise and release brown pigment called melanin
- The amount of melanin, varies between races and individuals, with darker races having more melanin
- A melanoma is the tumour that is formed by these cells, and is caused by exposure to UV radiation.
- There is a lower incidence of skin cancer in individuals with more melanin, as they are protected better from UV rays.
What do melanocytes derive from?
What is unique about this?
How do Melanocytes share their pigment with keratinocytes?
- Melanocytes are derived from neural crest cells that originate near the developing nervous system
- They then spread into the embryo and become mesenchymal stem cells with multipotent differentiation capabilities in vitro
- This is unique, as they are naturally occurring cells that make the transition from epithelia to mesenchymal cells, which is typically done by cancerous cells.
- To transfer melanin, melanocytes synthesise specialised lysosomes called melanosomes
- These melanosomes exit the melanocytes via exocytosis, then enter keratinocytes via endocytosis
What are Langerhans cells derived from?
What are their structures like?
Where are they most commonly found?
Where are they activated and where do they go to?
What is their function?
What helps them deal with viruses?
- Langerhans cells are special cells of the skin derived from monocytes
- Langerhans cells are dendritic in form (have branches resembling a tree)
- They are most commonly found in the stratum spinosum
- They are activated in the skin, but migrate to the lymph nodes
- Langerhans are macrophage like cells that capture, process, and present antigens
- Langerhans cells express Langerin, which helps the cells to bind on to, and degrade viruses (such as HIV) in specialised endosomes called Birbeck granules.
What are the 3 different parts of the dermis?
What do each comprise of?
What are functions of the top layer?
- Dermo-epidermal junction
- Joins the dermis to the epidermis via protrusions of dermal connective tissue called pappilae, which form outpokcetings in the dermis
- Prevents shearing
- The pappilae flatten with age, making the skin more vulnerable
- Papillary dermis
- Comprises of final collagen and elastic fibres
- Also contains small blood vessels, nerves and lymphatics
- This layer has looser skin
- Reticular dermis
- Comprised of coarser collagen and elastic fibres, which gives the skin strength
- Contains larger blood vessels and nerves
- This layer is the leather of animals.
What does the hypodermis (superficial fascia) layer consist of?
What does the hypodermis support?
What does it contain in terms of vascularisation and nerves?
- The hypodermis consists of loose connective tissue and adipose tissue, which varies in thickness at different parts of the body.
- The hypodermis supports:
- The deepest part of hair follicles
- Merocrine (eccrine) and apocrine sweat glands (can be found in both dermis and hypodermis)
- Vascularly, the hypodermis contains superficial blood vessels, lymphatics, and cutaneous nerves
What are the 2 different types of sweat gland?
Where can sweat glands be found?
What are the 2 different parts of the sweat gland?
- There are Merocrine (eccrine) sweat glands – these are present from birth
- There are apocrine sweat glands – these developed through puberty
- Sweat glands can be found in the dermis and hypodermis.
- There is the coiled secretory portion of the sweat gland, then a transmitting tubular duct that leads to a pore at the surface of the skin
What is hair made from?
What is the structure of the hair like?
What are the structures of hair follicles like?
Where are they found? How are hairs and follicles linked?
What is also associated with the hair follicle?
How does the hair follicle move?
What is this whole system referred to?
- The hair is composed of keratin
- The hair consists of a bulb root at the bottom, a bulb, and a shaft that grows from root
- The hair follicles are the regions around the root of the hair which generates the hair.
- Hair follicles are cylindrical, epithelial structures which are anchored in the hypodermis
- There is a sebaceous (oil) gland that secretes sebum through the hair follicle in order to lubricate the hair and kin.
- There is smooth arrector pili muscle that attaches to the papillary dermis and the hair follicle (controlled by Nervous system)
- When this muscle contracts, the hair stands upright, which is how we get goose bumps.
- Hair shaft + hair follicle + sebaceous glands + arrector pili =+ pilo-sebaceous unit
