Skin

Question 1

what are the functions of skin

Answer 1

• physical barrier
• immunological barrier
• thermoregulation
• vitamin D synthesis
• UV protection
• sensory organ
• regulation of H2O loss - waterproof barrier
• endocrine organ

Question 2

3 main layers of the skin

Answer 2

1. Epidermis
2. Demis
3. Subcutis / Hypodermis

Question 3

what features of the skin make it waterproof

Answer 3

• Tight junctions between cells in the stratum granulosum
• keratin in the stratum corneum
• epidermal lipid barrier

Question 4

where does vitamin D synthesis take place

Answer 4

in the epidermis and dermis

Question 5

where is vitamin D stored

Answer 5

in the subcutis adipocytes as it is fat solube

Question 6

name the layers of the epidermis

Answer 6

1. stratum corneum [superficial]
2. stratum lucidum
3. stratum granulosum
4. stratum spinosum
5. stratum basale [deep]

Come Lets Get Sun Burnt

Question 7

what lies within the dermis

Answer 7

glands

connective tissue

Question 8

what lies within the subcutis

Answer 8

fat

connective tissue

Question 9

does the epidermis contain collagen

if so what type

Answer 9

yes

type 4 collagen

Question 10

Where does proliferation of the skin occur?

Answer 10

stratum basale only

Question 11

summarise vitamin D synthesis

Answer 11

1. 7-dehydrocholesterol in skin → Cholecalciferol via UV radiation
2. cholecalciferol transported to teh liver and in the diet → 25-hydroxyvitamin D
3. 25-hydroxyvitamin D in the kidneys → Calcitriol [1,25-dihydroxyvitamin D3] vi 1-alpha hydrolase

Question 12

which hormones can have an effect on the skin

Answer 12

thyroid hormones

androgens

Question 13

how do androgens affect the skin

Answer 13

they act on follicles and sebaceous glands

Question 14

how do thyroid hormones affect the skin

Answer 14

they act on

• kerantinocytes
• follicles
• sebaceous glands
• eccrine glands
• dermal fibroblasts

Question 15

what hormones are produced in the skin

Answer 15

• vitamin D3 - cholecalciferol
• IGF - insulin-like growth factor
• DHT -5α-dihydrotestosterone

Question 16

what is skin colour dependent on

Answer 16

melanin production NOT number of melanocytes

Carotenoids - orange pigment

Oxy/deoxyhaemoglobin

Question 17

what are langerhans cells

Answer 17

macrophages of the skin

Question 18

what are the effects of UV-A and UV-B on the skin

Answer 18

• burns
• suppressed action of Langerhans cells
• photo-aging
• DNA-damage → cancers

Question 19

what is melanin made

where is it produced?

Answer 19

• made from tyrosine
• synthesised in melanosomes within melanocytes in the basal layer

Question 20

where is most melanin found

Answer 20

• Most melanin lies within keratinocytes not melanocytes
• dendritic cells transfer melanin from melanocytes to keratinocytes

Question 21

types of melanin

Answer 21

• Pheomelanin (red/yellow)
• Eumelanin (brown/black)

Question 22

how is melanin photoprotective

Answer 22

it scatters and filters UV light

Question 23

what immune cells can be found in thte skin and where

Answer 23

• dermis
  
  • Langerhans cells
• Epidermis
  
  • NKC
  • T cells
  • Mast cells
  • Dendritic cells
  • Macrophages

Question 24

what happens when a Langerhan cells is challenged

Answer 24

1. the LC migrates from epidermis → dermis and lymph nodes to activate a T-cell response
2. keratinocytes proliferate to increase cytokine secretion
3. leukocytes enter the skin from blood

Question 25

how does the skin detect touch

Answer 25

* via encapsulated *mechanoreceptors* in the _dermis_: * **meissner corpuscles** - touch * **pacinian corpuscles** -pressure and vibration * **Merkle cells** located on the _stratum basal_ for light touch * Myelinated and un-myelinated **sensory nerve endings** in _dermis_ for Pain, Itch, Temperature

Question 26

what's this what's its function

Answer 26

Pacinian corpuscle pressure and vibration

Question 27

what's this what's its function

Answer 27

Meissner Corpuscles fine touch

Question 28

how does skin regulate body temperature

Answer 28

* insulation via subcutaneous fat * heat loss via: * cutaneous blood flow * eccrine sweating

Question 29

describe how cutaneous blood flow regulates body temp

Answer 29

* there is a deep and superficial plexus of blood in the upper and lower reticular **dermis** * loops of blood vessels extend between each plexus * blood is shunted from deep to superficial to lose heat and vice versa to conserve. * **this is regulated by the sympathetic system:** * _sympathetic alpha-noradrenergic_ → vasoconstriction * _sympathetic cholinergic_ nerves → vasodilation

Question 30

which sweat gland is more common

Answer 30

eccrine are more common than apocrine as they are found everywhere in the dermis of the skin apocrine glands are only found in the ear, axilla and groin

Question 30

which sweat gland is more common

Answer 30

eccrine are more common than apocrine as they are found everywhere in the dermis of the skin apocrine glands are only found in the ear, axilla and groin

Question 31

functions of subcutaneous fat

Answer 31

shock absorption insulation energy storage

Question 32

in what layer of skin is keratin formed

Answer 32

stratum granulosum

Question 33

what is the largest layer of the epidermis

Answer 33

stratum spinosum

Question 34

how can you locate the epidermis-dermis junction

Answer 34

the ridged interdigitating pegs that help anchor them together = dermal papillae

Question 35

Answer 35

Question 36

describe the brick wall analogy for the skin

Answer 36

skin cells = brick lipid lamellae = the cement corneodesmosomes = the steel rods that joins the cells together – the adhesion molecules that keep the corneocytes together

Question 37

what is the skin barrier composed of

Answer 37

* lipid lamellae - forms a water barrier that allows the cell to swell * natural moisturising factor [NMF]- maintains pH * corneocytes - cells filled with NMF * corneodesmosomes - link corneocytes * cornified envelope

Question 38

what is the pH of healthy skin

Answer 38

5.5

Question 39

what factors maintain a healthy skin barrier

Answer 39

1. profilaggrin → filaggrin → NMF. * this helps to maintain hydration within the skin by keeping H2O in the corneocytes * it also maintains a slightly acidic environment at the outer surface of the stratum corneum. * a high pH → protease inhibitor not working 2. balance in the introduction of new cells from the basal layer and removal of old cells * desquamation is achieved by protease enzymes breaking down the extracellular corneodesmosomes 3. lipid lamella acts like a barrier: * keeps H2O inside the cell. * irritants and allergens bounce off the skin

Question 40

what is the impact of not having progfilaggrin

Answer 40

* no profilaggrin → no filaggrin → lack of NMF → * less H2O retention in corneocytes * a higher pH - meaning protease inhibitors don't work * damaged corneodesmosomes due to higher pH * breakdown of skin barrier → increased risk of infection