dermatology 1 Flashcards
- The skin arises from the juxtaposition of 2 major embryological elements. Name them and their origin
what is the mesoderm essential for?
Epidermis - Originates from the ectoderm
Dermis - Arises from the mesoderm that comes into contact with inner surface of epidermis
Mesoderm is essential for inducing differentiation of epidermal structures, e.g. hair follicles
Outline the stages of skin development (include weeks as well)
Epidermis forms by week four as a layer of squamous cells
by week five, secondary layer of non keratinising cuboidal cells have formed- periderm
generates the vernix caseosa- a white waxy protective layer
week 11- basal layer of cuboidal cells (stratum germinativum) proliferate to 4 more superficial layers
deep to superficial- (stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum)
epidermal troughs protrude as troughs into the developing dermis beneath neurovascular supply
by week 9-13- development of hair follicles in the stratum germinativum and appearance of lanugo hair
- List the layers of superficial strata of the epidermis from deep to superficial
- What are melanocytes derived from?
Stratum germinativum → Stratum spinosum → Stratum granulosum → Stratum lucidum (found on palms of hands and soles of feet) → Stratum corneum
Neural crest → Melanosomes. (Migrate dorsally between week 6-8 to developing epidermis, dermis and hair follicles).
- What are melanocytes responsible for?
- how does its dendritic structure help its function?
- is the number of melanocytes the same in all ethnicities ?
Melanocytes are responsible for melanin (pigment) secretion to keratinocytes
to distribute pigment better
yes, just different amounts of melanin produced
- What does the filamentous cytoskeleton of keratinocytes (in epidermis) contain?
(Thin) actin-containing microfilaments (7nm)
(Thick) tubulin-containing tubules (20-25nm) Intermediate filaments (keratin) (7-10nm)
what type of epithelium is the epidermis composed of
how does cell division and differentiation take place, and what ccelerates the process
keratinised, stratified squamous epithelium, avascular
division begins in the basal layer
progressive differentiation and flattening as you move upwards
Cellular progression from basal layer to surface takes ~30 days.
accelerated by skin diseases eg psoriasis
- What are the roles of keratins?
Stress response
Structural properties Cellular signalling Apoptosis Wound healing
- What are desmosomes and what are they made of?
Major adhesion complex in epidermis. Anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes. Allow cells to withstand trauma.-
What are other junctions are found in the epidermis and what are their functions?
Gap junctions - clusters of intercellular channels (connexons) , which directly connect cytoplasm of adjacent keratinocytes. Essential for cell synchronisation, differentiation, growth and metabolic coordination.
Adherens - Transmembrane structures which engage with the actin skeleton. Tight junctions - Role in barrier integrity and cell polarity. (seals gaps bewteen cells)
what type of cell is the epidermis mainly comprised of
what is its function
- List the cells of the epidermis (not including keratinocytes).
keratinocytes- arranged into the four layers
produce keratin
Melanocytes - Dendritic, distribute melanin pigment (melanosomes) to keratinocytes.
Langerhans cells - Dendritic, APCs
Merkel cells - Mechanosensory receptors
Mast cells
- What is considered to be the dermal-epidermal junction, what does this structure consist of and what are its roles/functions?
Basement membrane
Consists of glycoproteins, proteoglycans: collagen IV, VII, laminin and integrin. Roles in cell adhesion and migration.
- What is the dermis?
- Outline the structure of the dermis.
Layer of connective tissue and subcutaneous fat, deep to epidermis and separated by BM.
Dermis consists of 2 layers of connective tissue that compose of interconnected mesh of elastin and collagenous fibres produced by fibroblasts. Provides resilience.
what are the two layers of the dermis
Papillary layer - superficial layer, formed from loose connective tissue, vascular
Reticular dermis - deep, dense, forms bulk of dermis
- What proteins are found in the dermis? (eg types of collagen, glycoproteins) and in what percentages
- what forms ground substance?
Collagen (type I and II) - 80-85% of dermis.
Elastic fibres (2-4%) - fibrillin + elastin GPs - Fibronectin, fibulin, integrins - facilitates cell adhesion and motility. Ground substance - Dermal collagen and elastic tissue (Glycosaminoglycan/ proteoglycan)
- What is the main cell present in the dermis and also what are the other cells present?
- What is the vascular supply of the skin?
Fibroblasts
Histiocytes, mast cells, neutrophils, lymphocytes and dermal dendritic cells.
Deep and superficial vascular plexus, doesn't cross into epidermis. papillary dermis is more vascular than reticular dermis
- Outline the innervation of skin.
- what is the difference between eccrine glands and apocrine glands
Sensory - Free, hair follicles, expanded tips
Autonomic - Cholinergic for eccrine; adrenergic for eccrine and apocrine
eccrine- sweat gland responsible for thermal regulation
apocrine- sweat gland acts as a scent gland- primitive function
- What are the 2 types of afferent nerve endings from the skin? Give where they’re found, describe their receptors and examples of each.
Corpuscular - Dermis, encapsulated receptors e.g. Pacinian and meissners.
Free - Epidermis, non-encapsulated receptors e.g. Merkel cell
what is a pilosebaceous unit
how is it innervated
what does it contain
hair follicle
has its own innervation
Arrector Pilli muscle, arterioles, shunts
- What are Meissner’s corpuscles?
- Where are Meissner’s corpuscles most concentrated?
Encapsulated un-myelinated mechanoreceptors, aka tactile corpuscles
lamellated capsule
responds to light touch, slow vibration, senses low-frequency stimulation at level of dermal papilla.
Thick, hairless skin (finger pads and lips)
- What are Ruffini corpuscles?
- what is their function
- what is their location
- what is their shape
Slow acting mechanoreceptors
sensitive to skin stretch, monitors slippage
deep in dermis, high density around fingernails
spindle-shaped
- What are Pacinian corpuscles?
- what is their function
- what is their location
- what is their shape
Encapsulated, phasic (rapidly adapting) mechanoreceptor
deep pressure and vibration; vibrational role (detects surface textual);
Predominantly found in dermal papillae of hands an feet.
ovoid shape
- What are Merkel cells?
- Where are Merkel cells found?
Non-encapsulated mechanoreceptors, detecting light/sustained touch, pressure.
Oval shaped. Modified epidermal cells.
Stratum basale, directly above BM. Most populous in fingertips. Also in palms, soles, oral and genital mucosa.
- What are the nerve endings for the following modalities?
- Light touch
- Touch, pressure
- Vibration
- Temperature
- Pain
Meissner, Merkel, free
Merkel, Ruffini, Pacinian, Free
Meissner and Pacinian
Thermoreceptor
Nociceptor (free nerve endings)
- What bacteria predominates in the microbiome of the skin?
- What is the function of the microbiome of the skin?
- what does the composition of each niche in microbiota depend on?
Predominantly Actinobacteria
role in immune modulation and epithelial health
but also may have a role in disease eg chronic inflammation
composition of bacteria fungi and virus depends on the environment
- What are the functions of the skin?
Immunological barrier
Physical barrier
Thermoregulation
Sensation
Metabolism
Aesthetic appearance- What are Langerhans Cells?
- where do they reside?
Dendritic APCs, residing within the basal layer within the epidermis. Initiates immune response and also contributes to immune tolerance
- What are the functions of Langerhans Cells?
Dendritic processes extends through intercellular tight junctions to sample the stratum corneum.
Interpret microenvironmental context → Determines appropriate quality of immune response. In absence of danger, promote expansion and activation of skin-resident regulatory cells (Tregs). Detection of PAMPs → rapid initiation of innate antimicrobial responses. Induction of adaptive immune response: Power and specific of T-cell.
- Which cells in the dermis carry out immune surveillance?
Tissue-resident T-cells
Macrophages DCs
- Outline the immune barrier of the skin?
- what is the expression of cathelicidin enhanced by?
- where are cathelicidins located?
Keratinocyte-derived endogenous antimicrobial peptides are secreted (Defensins, cathelicidins)- innate immune defence
Expression of cathelicidin is enhanced by keratinocyte activity,
predominantly residing within granules of the superficial epidermis
- Explain the what the physical barrier formed by the skin is and what happens in extensive disease
- What has an important role in cushioning trauma?
- What protects us against UV-induced damage?
Cornified cell envelope and stratum corneum restrict water and protein loss from the epidermis. (High output cardiac failure and renal failure in extensive disease.)
Subcutaneous fat Melanin in basal keratinocytes.
- Outline the role of skin in thermoregulation.
Thermoregulatory centre of the hypothalamus detects temperature of blood.
Increase in blood temperature is identified by central receptors Warm environment - Vasodilation occurs. More blood flows through capillaries, ; less blood flows through deeper shunt vessels. More blood flow close to surface - temperature gradient become steeper; cooling by conduction and radiation increased. Eccrine sweat glands - cooling effect.
- List the metabolic functions of the skin.
Vitamin D synthesis
Subcutaneous fat - Storage - Through lipogenesis, glucose is converted into triglycerides stored within adipocytes. CALORIE RESERVE - Hormonal - skin release Leptin acts on hypothalamus to regulate hunger and energy metabolism- satiety hormone
