Physiology of the Skin Flashcards
What are the two main compartments of the skin?
the dermis and the epidermis
What are the embryologic origins of the dermis and epidermis?
Epidermis = ectoderm Dermis = mesoderm
What are the 4 layers of the epidermis? What is their composition?
- Stratum basale: single cell later of dividing keratinocytes
- Stratum spinosum: the spinous layer in which the desmosomal attachments between keratinocytes are prominent
- Stratum granulosum: granular cell layer where terminal keratin and lipid organization occurs and lysosomes are prominent
- Stratum corneum: 15-20 layers of flattened, non-nucleated cells called corneocytes
Keratinization (cornification) refers to…
The process by which the principle fibrous proteins of the keratinocyte are formed. Begins in the basal layer where dispersed keratin filaments are synthesized and as the cell matures, thicker filaments are deposited that increase structural integrity and UV filtration
What layer of the epidermis forms the main diffusion barrier of the skin?
the stratum corneum
What 2 compartments of the stratum corneum are vital for maintaining the diffusion barrier of the skin?
- protein rich corneocytes
2. lipid rich intercellular material
How is the diffusion barrier of the skin formed?
- proteins and lipids are synthesized by keratinocytes
- proteins and lipids are modified as keratinocytes mature
- keratolyalin is formed in the granular layer from keratin and profilaggrin
- an envelope of highly cross-linked proteins forms a corneocyte exoskeleton with the intercellular cement produced by lamellar bodies (Odland bodies) which are lipid rich lysosomal bodies secreted into the intercellular space.
What can occur if there are abnormalities in the formation of the skin barrier?
ichthyosiform = “scaly” disorders like atopic dermatitis!
What separates the epidermis and the dermis?
The basement membrane
What are 2 functions of the basement membrane?
- Scaffold for tissue organization and repair
2. physical barrier between cell types
What components make up the basement membrane of the skin?
- Type IV collagen
- Laminin
- Heparin sulfate proteoglycans
- hemidesmosomes/anchoring filaments/anchoring fibrils
- these are unique and required for the skin BM
Alterations in the formation of the basement membrane can lead to what type of disorders?
blistering disorders
What are the the two types of UV light that can damage the skin? How do they cause damage?
- UVA: penetrates the skin more deeply that UVB and causes formation of cytotoxic free radicals
- causes wrinkling and aging of skin - UVB: “sunburn” UV light that damages both proteins and nucleic acids
What are the two primary barriers the skin has to UV radiation?
- Protein barrier in the stratum corneum (keratins)
- Melanin barrier dispersed throughout the epidermis
* both melanin and keratin absorb UV photons
What are the 4 pigments that contribute to skin colour? Where are they?
- brown: melanin in epidermis
- red: oxygenated Hbg in dermis
- Blue: reduced Hbg in dermis
- Yellow: carotenoids in the epidermis
What is melanin?
A high molecular weight polymer produced by melanocytes and localized in subcellular membrane bound organelles called melanosomes
What are the 3 functions of melanin?
- protection against UV radiation
- Scavenging of cytotoxic radicals
- Participating in neurologic development
Where do melanocytes originate from?
neural crest cells that migrate to the epidermal/dermal junction