dermatology 1

Question 1

• The skin arises from the juxtaposition of 2 major embryological elements. Name them and their origin

what is the mesoderm essential for?

Answer 1

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

Question 2

Outline the stages of skin development (include weeks as well)

Answer 2

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

Question 3

• List the layers of superficial strata of the epidermis from deep to superficial
• What are melanocytes derived from?

Answer 3

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).

Question 4

• What are melanocytes responsible for?
• how does its dendritic structure help its function?
• is the number of melanocytes the same in all ethnicities ?

Answer 4

Melanocytes are responsible for melanin (pigment) secretion to keratinocytes

to distribute pigment better

yes, just different amounts of melanin produced

Question 5

• What does the filamentous cytoskeleton of keratinocytes (in epidermis) contain?

Answer 5

(Thin) actin-containing microfilaments (7nm)

(Thick) tubulin-containing tubules (20-25nm) 

Intermediate filaments (keratin) (7-10nm)

Question 6

what type of epithelium is the epidermis composed of

how does cell division and differentiation take place, and what ccelerates the process

Answer 6

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

Question 7

• What are the roles of keratins?

Answer 7

Stress response

Structural properties 

Cellular signalling 

Apoptosis 

Wound healing

Question 8

• What are desmosomes and what are they made of?

Answer 8

Major adhesion complex in epidermis. Anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes. Allow cells to withstand trauma.-

Question 9

What are other junctions are found in the epidermis and what are their functions?

Answer 9

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)

Question 10

what type of cell is the epidermis mainly comprised of

what is its function

• List the cells of the epidermis (not including keratinocytes).

Answer 10

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

Question 11

• What is considered to be the dermal-epidermal junction, what does this structure consist of and what are its roles/functions?

Answer 11

Basement membrane

Consists of glycoproteins, proteoglycans: collagen IV, VII, laminin and integrin.

Roles in cell adhesion and migration.

Question 12

• What is the dermis?

- Outline the structure of the dermis.

Answer 12

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.

Question 13

what are the two layers of the dermis

Answer 13

Papillary layer - superficial layer, formed from loose connective tissue, vascular

Reticular dermis - deep, dense, forms bulk of dermis

Question 14

• What proteins are found in the dermis? (eg types of collagen, glycoproteins) and in what percentages
• what forms ground substance?

Answer 14

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)

Question 15

• 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?

Answer 15

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

Question 16

• Outline the innervation of skin.

- what is the difference between eccrine glands and apocrine glands

Answer 16

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

Question 17

• What are the 2 types of afferent nerve endings from the skin? Give where they’re found, describe their receptors and examples of each.

Answer 17

Corpuscular - Dermis, encapsulated receptors e.g. Pacinian and meissners.

Free - Epidermis, non-encapsulated receptors e.g. Merkel cell

Question 18

what is a pilosebaceous unit

how is it innervated

what does it contain

Answer 18

hair follicle

has its own innervation

Arrector Pilli muscle, arterioles, shunts

Question 19

• What are Meissner’s corpuscles?

- Where are Meissner’s corpuscles most concentrated?

Answer 19

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)

Question 20

• What are Ruffini corpuscles?
• what is their function
• what is their location
• what is their shape

Answer 20

Slow acting mechanoreceptors

sensitive to skin stretch, monitors slippage

deep in dermis, high density around fingernails

spindle-shaped

Question 21

• What are Pacinian corpuscles?
• what is their function
• what is their location
• what is their shape

Answer 21

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

Question 22

• What are Merkel cells?

- Where are Merkel cells found?

Answer 22

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.

Question 23

• What are the nerve endings for the following modalities?
  
  • Light touch
  • Touch, pressure
  • Vibration
  • Temperature
  • Pain

Answer 23

Meissner, Merkel, free

    Merkel, Ruffini, Pacinian, Free 

    Meissner and Pacinian 

    Thermoreceptor 

    Nociceptor (free nerve endings)

Question 24

• 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?

Answer 24

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

Question 25

• What are the functions of the skin?

Answer 25

Immunological barrier 
    Physical barrier 
    Thermoregulation 
    Sensation 
    Metabolism 
    Aesthetic appearance

Question 26

• What are Langerhans Cells?

- where do they reside?

Answer 26

Dendritic APCs, residing within the basal layer within the epidermis. Initiates immune response and also contributes to immune tolerance

Question 27

• What are the functions of Langerhans Cells?

Answer 27

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.

Question 28

• Which cells in the dermis carry out immune surveillance?

Answer 28

Tissue-resident T-cells

Macrophages 

DCs

Question 29

• Outline the immune barrier of the skin?
• what is the expression of cathelicidin enhanced by?
• where are cathelicidins located?

Answer 29

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

Question 30

• 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?

Answer 30

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.

Question 31

• Outline the role of skin in thermoregulation.

Answer 31

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.

Question 32

• List the metabolic functions of the skin.

Answer 32

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