Skin

Question 1

List the three layers of the basic structure of the skin

Answer 1

Epidermis - avascular (without blood vessels) epithelium; synthesises keratin

Dermis - vascular, tough
- contains blood vessels, nerves and limphatics

Hypodermis - superficial fascia, varies in thickness

• contains blood vessels, lymphatics and nerves
• fatty/adipose tissue
• skin ligaments, loose skin or taut skin in scsrring and incision

Question 2

Functions of the skin

Answer 2

Homeostasis

• Metabolic (vitamin D, fat store)
• Temperature regulation (vasodilation, sweating, fat store, hairs)
• Internal homeostasis (water, electrolyes, macromolecules)

Sensory information

• Sensation (pain, temperature, touch, pressure, vibration)
• Psychological signals (visual, chemicals)

Protection

• UV - melanin
• Organisms - immunity
• Chemical, water, mechanical - keratin

Question 3

Layers of the epidermis

Answer 3

Stratum Corneum - cornified layer; water proof cell ghosts

Stratum Lucidium - clear layer; specialised cell death programme

Stratum Granulosum - granules in cells; keratohyaline granules; keratin aggregation

Stratum Spinosum - spine shaped; IF (keratin) linkage via desmosomes

Stratum Basale - base layer; epithelium is generated here; cell division (stem cells)

Question 4

Decribe the Stratum Basale

Answer 4

Hemidesmosomes (junctions) anchor basal cells to basal lamina
Dermis anchored to basal lamina by Collagen VII (binds epidermis to dermis)
Collagen VII mutated in Dystrophic epidermolysis bullosa - blistering

Question 5

Describe the Stratum Spinosum

Answer 5

Intermediate filaments (keratin) K1/K10 expressed
Linked from cell to cell by desmosomes
Hemidesmosomes also link basal cells with basement membrane

Question 6

What is filaggrin?

Answer 6

Filaggrin aid cornification in keratohyline granules

Filaggrin (and its precursor, profilaggrin) maintain the optimal skin barrier

Filaggrin is the main component of S. granulosum

It aids keratin filament aggregation and inhibits water loss (by being cleaved to amino acids)

Question 7

Filaggrin mutations

Answer 7

Most common mutations causes keratinization disorders - icthyosis vulgaris - skin not being able to shed

Also causes reduced filaggrin expression, eczema, and null mutations are associated with asthma

Question 8

What cells are melanin produced by and where is it found?

Answer 8

Melanocytes

Basal layer of epidermis

Question 9

Function of melanin

Answer 9

Absorbs UV-B and prevents DNA damaga to the underlying cells of the hypodermis

The more melanin one has, the lower the chances the might get skin cancer

Question 10

What is the name of the tumour of these cells?

Answer 10

Melanoma - caused by exposure to UV radiation

Question 11

Where are melanocytes derived from?

Answer 11

Neural crest cells (originate from near the developing NS and spread into the embryo)

Question 12

Function of melanocytes

Answer 12

Melanocytes synthesise specialised Lysosomes that contain melanosomes and undergo exocytosis - these melanosomes are transferred to keratinocytes, where they produce melanin that protects against the UV

Question 13

What are keratinocytes?

Answer 13

Cells that undergo karetinisation

Question 14

What are Langerhans cells and what is their function?
What way do these cells migrate to?
What do they express?

Answer 14

They are derived from monocytes and are found mostly in the S. spinosum;

Their function is antigen processing and presentation

They migrate from epidermis to lymph nodes

They express Lingerin which degrade viruses such as HIV in specialised endosomes called Birberick granules

Question 15

What is the dermis like?

What are its two types?

Answer 15

Tough and vascular

Papillary dermis - comprises fine collagen and elastic fibres, small blood vessels and nerves

Reticular dermis - comprises coarser collagen and elastic fibres and larger blood vessels and nerves (leather)

Question 16

What is the hypodermis like?
What does it consist of?
What does it support?
What is it responsible for?

Answer 16

Also named superficial fascia; it is vascular - superficial blood vessels and lymphatics; has cutaneous nerves that provide sensory innervation to the skin

Consists of loose connective tissue and adipose tissue

Supports deepest part of hair follicles, eccrine and apocrine glands

Responsible for vitamin D production

Question 17

What are the skin appendages? Describe them all

Answer 17

Sweat glands

• Coiled part in deep dermis/or hypodermis, where sweat is made; straight duct passing through dermis and epidermis
• Eccrine: fluid water; opens onto skin; controlled by SNS; important in thermoregulation and is also a response to fear
• Apocrine: thicker, milky consistency, containing pheromones; open into hair follicles;

Hairs/follicles

• Anchored to hypodermis
• Hair shaft is composed of keratin, grows from the bulb; associated with subaceous glands that open into the follicle
• Secrete sebum to lubricate the hair and adjacent skin
• Arrector pili contract smooth muscle attached to th papillary dermis; controlled by the SNS
• Hair follicle + subaceous glands + hair shaft + arrector pili = pilosebaceous unit

Mammary glands
- modified apocrine sweat glands; lactation under hormonal control

Nails
- fromed from keratin; growth from the nail root which passes deep into the dermis

Teeth
- enamel of the teeth develops from the epithelium, dentine, pulp and peridontal membrane is mesodermal

Question 18

Describe the sensations originating from the skin

Answer 18

Pain - nocireceptors

Temperature - separate receptors for cold and heat

Touch - Meissner’s corpuscles/fine touch Merkel cells just beneath the epidermis/S. basale

Pressure - Pacinian cospuscles (dermis)

Vibration - Meissner’s corpuscle and Pacinian corpuscles (dermis)

Question 19

What are Merkel cells?

Answer 19

Tactile corpuscles that aggregate and form touch receptors