intro to derma Flashcards by Anjalin Arora

How does the skin arise?

joining of the epidermis (from ectoderm) and dermis(from mesoderm) touching thinner surface of epidermis *diagram

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What is the mesoderm important for?

induces differentiation of structures in epidermis e.g. hair follicle

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how does the skin develop by week 4?

epidermis is formed: single basal layer of cuboid cells

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In week 5?

a secondary layer of squamous, non-keratinisng cuboidal cells (periderm) developed

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What does the periderm generate?

White, waxy, protective substance == Vernix caseosa

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What does vernix caseosa do?

protects doetus from aminotic fluid during gestation and protects from bacteria at birth

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from week 11 of skin develop?

basal layer of cuboidal cells STRATUM germinativum proliferates and forms multilayered intermediate zone

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By week 20 what happens?

4 more superficial strata:
Spinosum (spinous)
Granulosum(granular)
Lucidium(clear; found on palms and soles)
Corneum (horny) - most super

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between weeks 10-17?

epidermal ridges develop , protrude into dermis beneath. gaps = dermal papillae where neurovascular supply develops

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weeks 9-13?

hair follicles aka pilosebaceous unit ( inc. hair foll, errector pili muscle, sebaceous gland) in stratum germinativum and appearance of lanugo hair (fine)

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What are melanocytes?

pigment cells - give skin and hair colour

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how are melanocytes developed?

melanoblasts (precursor cells) arise from neural crest. they migrate dorsally between week 6-8 to developing epidermis (& dermis) and hair follicles. by weeks 12-13 most at their destination and differentiate into melanocytes

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how are differentiated melanocytes replenished?

subset of melanoblasts form melanocyte stem cells in hair follicle bulge

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Regulation of melanocytes?

Melanocortin 1 receptor (MC1R), a G protein-coupled receptor regulates quantity and quality of melanins produced.

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What is MC1R controlled by?

agonists: alpha melanocyte-stimulating hormone (alphaMSH) and adrenocorticotropic hormone (ACTH) and antagonist, Agouti signalling protein (ASP)

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What does activation of MCR lead to?

agonist activates -> melanogenic cascade (pigment production) -> synthesis of eumelanin

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what does ASP do?

reverses effects of agonists and elicits production of pheomelanin(pale pigment)

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What upregulates the expression of the MC1R gene

ACTH

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what happens to melanocytes when exposed to uv?

increased expression of MITF & downstream melanogenic proteins, inc Pmel 17, MART-1, TYR, TRP1 & DCT

also increases PAR2 in keratinocytes which increases uptake and distribution of melanosomes (pigment packages) by keratinocytes

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what allows melanocytes to distribute melanosomes?

the fact that is a dendritic cell

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Structure of the skin ( overview)

epidermis
basement membrane (dermal-epidermal junction)
dermis: 
-connective tissue
subcutaneous fat

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What is the epidermis made of?

looks like a brick wall:

keratinocytes

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How are cells divided in the basal layer?

Progressive differentiation:

stratum spinosum
stratum granulosum
stratum lucidum (palms and soles only)
stratum corneum ( no nuclei or organelles)

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How long to surface?

cells progress from basal layer to surface in approx 30 days

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When is cell progression accelerated?

in skin diseases such as psoriasis

What is in the cytoskeleton of keratinocytes and sizes?

filamentous cytoskeleton: actin containing microfilaments (7nm) tubulin - containing microfilaments (20-25nm) intermediate filaments (7-10nm)

What are the 5 roles of keratin?

``` structural properties cell signalling stress response apoptosis wound healing ```

What are desmosomes?

Major adhesion complexes in epidermis

What are the functions of desmosomes?

anchors keratin intermediate filaments to cell membrane and bridges adjacent keratinocytes allows cells to withstand trauma

What are gap junctions?

Clusters of intercellular channels (connexons)

What do gap junctions do and why are they important?

directly forms connections between cytoplasm of adjacent keratinocytes essential for cell synchronisation, cell differentiation, cell growth, and metabolic coordination

what are adherens junctions?

transmembrane structures which engage with actin skeleton

What are tight junctions?**

barrier integrity and cell polarity

What are melanocytes?

dendritic cells that distribute melanin pigment in melanosomes to keratinocytes

what are Langerhans cells?

dendritic cells that are antigen-presenting

What are Merkel cells?

mechanosensory receptors

What are the roles of the basement membrane?

Cell adhesion and cell migration

What is the basement membrane also known as ?

dermal-epidermal junction

What proteins are present in the basement membrane?

collagens (IV, VII), laminin and integrins

What does the dermis do?

supports extracellular matrix - provides resistance

What is the papillary dermis?

superficial, vascular, loose areolar tissue

What is the reticular dermis?

deep, dense connective tissue -> forms bulk of dermis

Describe the protein make up of the dermis

80-85% is collagen: mainly type I and III, 2-4% elastic fibres: fibrillin, elastin

What is the function of glycoproteins

facilitate cell adhesion and cell motility : | e.g. fibulin, integrins and fibronectin

Where/what is the ground substance?

glycosaminoglycan and proteoglycan ( maintain hydration) between dermal collagen and elastic tissue

What cells are present in the ground substance?

``` fibroblasts - main primary cells mast cells neutrophils histiocytes lymphocytes dermal dendritic cells ```

Describe the blood supply of the skin

deep and superficial vascular plexus which doesn't cross into epidermis

sensory innervation of skin ?

autonomic innervation

describe the distribution of nerves

1 million afferent nerve fibres, branching network often accompanies blood vessels forms mesh of interlacing nerves in the superficial dermis distribution varies by body site (face, extremities and genitalia)

What are corpuscular nerves?

``` (afferent nerves) encapsulated receptors (dermis e.g. Pacinian, Meissner) ```

What are free nerves?

afferent nerves non-encapsulated receptors (epidermis e.g. Merkel cells)

What is Meissner's corpuscle?

- encapsulated, unmyelinated, mechanoreceptors for light touch and slow vibration senses low-frequency stimulation at level of dermal papilla

Where is the Meissner's corpuscle most concentrated?

thick hairless skin (finger pads and lips)

What is the Ruffini corpuscle?

aka bulbous corpuscle slow-acting mechanoreceptor sensitive to skin stretch deeper in dermis

What shape is the ruffini corpuscle?

spindle

Where is the ruffini corpuscle most dense?

highest density around finger nails - monitors slipage of of objects

What is the Pacinian corpuscle?

encapsulated and ovoid rapidly adapting - phasic mechanoreceptor for deep pressure and vibration - detects surface texture dermal papillae of hands and feet

What are Merkel cells/ discs?

Oval shaped Non-encapsulated mechanoreceptors that sense light, sustained touch/pressure they are a type of modified epidermal cells

WHere are Merkel cells found?

They are in the startum basale, directly above basement membrane most dense in fingertips but also found in palms, soles, oral and genital muscosa

Describe the distribution of bacteria on the skin and what affects this?

~ 1 million bac per cm squared predominantly actinobacteria affected by environment

What is the role of bacteria on skin?

immune modulation and epithelial health

What are the functions of the skin?

``` immunological barrier physical barrier thermoregulation sensation metabolic features aesthetic appearance ```

How does the skin act as an immune barrier?

through Langerhans cells -responds against the microbial threat and contribute to immune tolerance. a dense network is formed for potential invaders to interact.*

Describe the function of Langerhans cells

specialised to sense the environment, they initiate an immune response.

How do Langerhans cells prevent autoimmune response?

by causing the production of t regulatory cells

intro to derma Flashcards

(66 cards)