Introduction to Dermatology I Flashcards
How does skin arise?
By the juxtaposition of 2 major embryological elements:
epidermis
dermis
Where does the epidermis originate from?
ectoderm
Where does the dermis originate from?
mesoderm that comes into contact with the inner surface of epidermis
What is the mesoderm essential for?
for inducing differentiation of epidermal structures (e.g., hair follicles)
What are the layers of the skin?
starting top:
stratum corneum
stratum lucidum
stratum granulosum
stratum spinosum
stratum germinativum
papillary and reticular layers of the dermis
What is the layer only found in palms and soles?
stratum lucidum
What is lanugo hair?
Lanugo is fine, soft, unpigmented hair that is often present in fetuses, newborns, and certain disease states.
What is the overview of the structure of the skin?
Epidermis
BAsement membrane (dermal-epidermal junction)
Dermis
Subcutaneous fat
What is the epidermis composed of?
keratinocytes
Where does start of cell division initiate?
cells in basal layer
What is the structure of the skin epidermis?
Progressive differentiation / flattening towards surface:
➢ Stratum spinosum
➢ Stratum granulosum
➢ Stratum lucidum (palms and soles only, no nuclei or organelles)
➢ Stratum corneum (no nuclei or organelles)
How long does it take for cells to reach the surface, and when can it accelerate?
roughly 30 days
can accelerate in skin disease (e.g., psoriasis)
What does the filamentous cytoskeleton of keratinocytes in the epidermis comprise of?
➢ Actin-containing microfilaments (7nm)
➢ Tubulin-containing microtubules (20-25nm)
➢ Intermediate filaments (keratins) (7-10nm)
What is the role of keratins? (5)
● Structural properties
● Cell signaling
● Stress response
● Apoptosis
● Wound healing
What are desmosomes?
➢ Major adhesion complex in epidermis
➢ Anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes
➢ Allow cells to withstand trauma
What are the different types of desmosomes? (6)
Desmoglein
Desmocollin
Plakoglobin
Plakophilin
Desmoplakin
Keratin
What are the different types of junctions between cells in the epidermis?
tight junction
adherens junction
desmosomes
gap junction
What are gap junctions?
➢ Clusters of intercellular channels (connexons)
➢ Directly form connections between cytoplasm of adjacent keratinocytes
➢ Essential for cell synchronization, cell differentiation, cell growth and metabolic coordination
What are adherens junctions?
➢ Transmembrane structures
➢ Engage with the actin skeleton
What are tight junctions?
role in barrier integrity and cell polarity
What are cells present in the epidermis of the skin?
Keratinocytes
Melanocytes
Langerhans cells
Merkel cells
Mast cells
What are melanocytes?
➢ Dendritic
➢ Distribute melanin pigment (in melanosomes) to keratinocytes
➢ Number of melanocytes same among all skin types
What are melanosomes?
Melanosomes are intracellular organelles that are uniquely generated by pigment cells in the skin and eye, where they function to synthesize and store melanin pigments.
What are langerhans cells?
➢ Dendritic
➢ Antigen-presenting cells
What are merkel cells?
mechasensory receptors
What are mast cells for?
hypersensitivity and immunity
What is another word for basement membrane?
dermal-epidermal junction
What proteins and glycoproteins are in the basement membrane?
colagens (IV, VII), laminin, integrins
What are the roles of the basement membrane?
Cell adhesion
Gate-keeping functions
- Cell migration
- Diffusion of bioactive molecules
Rete ridges (downward projections)
- Strength
- Niche for epidermal stem cells
Roles in development, morphogenesis, wound healing, and skin remodeling
What are the 2 aspects of the dermis?
Papillary and reticular dermis
What is the dermis?
Supporting (extracellular) matrix- that provides resilience
What is the papillary dermis?
➢ Superficial
➢ Loose connective tissue
➢ Vascular
What is the reticular dermis?
➢ Deep
➢ Dense connective tissue
➢ Forms bulk of dermis
What is the reticular dermis?
➢ Deep
➢ Dense connective tissue
➢ Forms bulk of dermis
What is the structure of the dermis?
- proteins
- glycoproteins
- ground substances
What are the proteins in the dermis?
a) Collagen (80-85% of dermis) – mainly types I and III
b) Elastic fibres (2-4%) – fibrillin, elastin
What are the glycoproteins in the dermis and what do they do?
Glycoproteins – fibronectin, fibulin, integrins
– facilitate cell adhesion and cell motility
What are the ground substances in the dermis?
between dermal collagen and elastic tissue
- glycosaminoglycan/ proteoglycan
What are the cells in the dermis?
➢ Fibroblasts
➢ Histiocytes
➢Mast cells
➢ Neutrophils
➢ Lymphocytes
➢Dermal dendritic cells
What is the primary cell within the dermis?
Fibroblasts
Where are melanocytes derived from?
the neural crest
How would you compare the papillary and reticular dermis?
The reticular dermis is composed of deep dense connective tissue while the papillary dermis is more superficial and composed of loose connective tissue
How would you describe the blood supply of the skin?
Deep and superficial vascular plexus
➢ Does not cross into epidermis
What are the types of innervation of the skin?
➢ Sensory – free, hair follicles, expanded tips
➢ Autonomic
o Cholinergic – eccrine
o Adrenergic – eccrine and apocrine
What other structures are involved in the innervation and vascular supply of the skin?
● Pilosebaceous unit
● Arrector pili muscle / arterioles / shunts
How many nerve fibres involved in skin innervation and how are they distributed?
● One million afferent nerve fibers.
● Form branching network, often accompanying blood vessels, to form a mesh of interlacing nerves in superficial dermis
● Distribution varies by body site
➢Face, extremities & genitalia > rest of skin
What are the types of afferent nerves?
Corpuscular= pacinian, meissner’s
non-encapsulated= merkel cell
What is meissner’s corpuscle?
aka tactile corpuscles
● Encapsulated, unmyelinated mechanoreceptors
● Lamellated capsule
● Superficial dermis
● Most concentrated in thick hairless skin, (fingertips and lips)
● Light Touch (+slow vibration)
What is ruffini corpuscle?
aka bulbous corpuscle
● Slow acting mechanoreceptor
● Deeper in dermis
● Spindle-shaped, encapsulated
● Highest density around fingernails
● Sensitive to skin stretch
● Monitors slippage of objects
What are pacinian corpuscles?
aka lamellar corpuscles
● Encapsulated, ovoid
● Rapidly adapting (phasic) mechanoreceptor
● Deep pressure and vibration (deep touch)
➢ Vibrational role - detects surface texture
● Dermal papillae of hands and feet
What are merkel cells?
● Non-encapsulated mechanoreceptors
● Light / sustained touch, pressure
● Oval-shaped
What are modified epidermal cells?
➢ Stratum basale, directly above basement membrane
➢ Most populous in fingertips
➢ Also in palms, soles, oral & genital mucosa
What are the nerve endings and fibres for light touch?
Meissner, merkel, free
Abeta
What are the nerve endings and fibres for touch and pressure?
merkel, ruffini, pacinian, free
Abeta, Agamma
What are the nerve endings and fibres for vibration?
meissner and pacinian
Abeta
What are the nerve endings and fibres fro temperature?
thermoreceptor
Agamma, C
What re the nerve endings and fibres for pain?
nociceptor (free nerve endings)
Agamma, C
DO ruffini’s corpuscles detect skin stretch?
Yes, they are slow acting mechanoreceptors of touch and pressure, highly concentrated around fingernails, that detect skin stretch and slippage
What is microbiota?
bacteria, fungi, viruses
What is the microbiome?
genome of microbiota
How many bacteria per cm^2 of skin?
roughly 1 million bacteria/ cm^2
What is the microbiota predominantly made of?
Predominantly Actinobacteria (including Propionibacteria and Corynebacteria), Firmicutes (Clostridia and Bacilli [Staphylococcus] , Bacteroidetes & Proteobacteria
What is the composition of each niche dependent on?
environment
What is the role of the skin microbiota?
role in immune-modulation and epithelial health
role in chronic disease
What are the descriptions of niches for the microbiota?
Sebaceous sites
Moist sites
Dry sites
What are the functions of the skin?
● Immunological barrier
● Physical barrier
● Thermoregulation
● Sensation
● Metabolism
● Aesthetic appearance
What the cells involved in the immune barrier of the skin?
langerhans cells
What are langerhans cells?
● Dendritic cell (DC)/macrophage family
● Sentinel cells in epidermis
● Initiate immune response against microbial threats
● Also contribute to immune tolerance
● Form dense network with which potential invaders must interact.
How do langerhans cells work?
● Specialized at “sensing” environment
● Extend dendritic processes through intercellular tight junctions to sample outermost layers of skin (stratum corneum)
● Interpret microenvironmental context → determine appropriate quality of immune response.
● In absence of danger, promote expansion and activation of skin- resident regulatory - cells (Tregs)
● When toll-like receptors (TLRs) sense danger (via pathogen associated molecular patterns [PAMP]) → rapid initiation of innate antimicrobial responses
● Induction of adaptive response - power and specificity of T-cell / B-cell and antibodies (immunoglobulins)
How else is immune surveillance carried out in the dermis?
tissue resident T cells
Macrophages
Dendritic cells
- rapid, effective immunological backup if epidermis is breached
What are antimicrobial peptides?
Keratinocyte-derived endogenous antibiotics (defensins and cathelicidins)–> innate immune defence against bacteria, viruses and fungi
What are the differences between the innate and adaptive immune response?
What is the function of the skin barrier?
Physical barrier against external environment
Cornified cell envelope and stratum corneum restrict water and protein loss from skin
- high cardiac output and renal failure in extensive skin disease
UV barrier
What is the role of subcutaneous fat as a barrier?
cushioning trauma
What is the role of melanin as a barrier?
melanin in basal keratinocytes- protection against UV induced DNA damage
How is the skin involved in thermoregulation?
➢Vasodilation or vasoconstriction in deep or superficial vascular plexuses
→ regulate heat loss
➢Eccrine sweat glands
→ cooling effect
Does the skin have a role in fluid balance?
Yes
How does the thermoregulation work?
What are the metabolic functions of the skin?
● Vitamin D synthesis
● Subcutaneous fat
➢Calorie reserve
➢80% of total body fat (in non-obese)
➢ Hormone (leptin- supresses hunger) release - acts on hypothalamus
→ regulates hunger & energy metabolism
Why does the skin have a aesthetic function?
Psychosexual function
Increased risk of suicide
