skin lecture 2

Question 1

on a cold day

Answer 1

blood vessels near skin constrict to reduce heat loss
blood vessels further down dilate
warm blood enters from arteries
Blood leaves in veins, retaining most of its heat

Question 2

on a hot day

Answer 2

heat lost when vessels near skin dilate
Vessels further down constrict to shunt blood to the skin surface
Warm blood enters from arteries
Blood leaves in veins, having lost some of its heat

Question 3

Vitamin D3 production

Answer 3

Produced in the skin form 7-dehydrocholesterol by UV irridation. which breaks the B ring to form pre-D3. Pre-D3 isomerizes to D3 by thermal conversion
Liver and other tissues metabolise Vitamin D3 from ingestion into 25(OH)2D3, then further metabolised to 1,25(OH)2D3 in the kidney
Enzymes that act in the liver are 25-hydroxylase and ones in the kidney 1alpha-hydroxylase

Question 4

1,25(OH)2D3 systemic effects

Answer 4

calcium and phosphate regulation

Question 5

1,25(OH)2D3 local effects

Answer 5

reduced cell proliferation
incr cell differentiation
immune targets: dendritic cells, T cells, monocytes, macrophages and B cells

Question 6

barrier function of the skin

Answer 6

stratum corneum has 15-20 layers w
Use bricks (corneocytes) and mortar (intercellular lipid) model of the stratum corneum
Corneodesmosomes link adjacent corneocytes

Question 7

function of stratum corneum

Answer 7

permeability barrier than minimises trans-epidermal water loss (loss of water from epidermal layer to surrounds)

Question 8

what is the epidermis colonised by

Answer 8

wide variety of microorganisms

Question 9

commensal relationship

Answer 9

one of partners benefits, other suffers no harm

Question 10

mutualstic

Answer 10

both benefit

Question 11

pathogenic

Answer 11

one causing or capable of causing disease

Question 12

Demodex folliculorum

Answer 12

mite- type of parasite that lives on humans

Question 13

Other ways skin can act as a barrier

Answer 13

intact skin physical barrier to invasion
Acidity of skin surface and stratum corneum (pH 4.5-5.5): secretion of sebum from sweat glands, enzymatic breakdown of epidermal phospholipids to produce free fatty acids, extrusion of H+ in exchange for Na+ by cells in stratum granulosum and release of acidic metabolic by-products by microorgansims (skin flora)
Production of antimicrobial peptides: potent, broad spectrum and produced quickly in response to invading pathogens (innate immune response)

Question 14

What do keratinocytes and Langerhans cells do

Answer 14

cooperate in mobilization and targeting of cells of the adaptive immune system

Question 15

how do they (langerhans and keratinocytes) do this

Answer 15

release of intercellular chemical messengers: cytokines, chemokines
And dynamic adjustment of tight junctions which allows Langerhan’s cells to sample antigens in the stratum corneum

Question 16

What does rapid activation of innate immunity lead to

Answer 16

delayed activation of adaptive immunity

Question 17

what is loss of cells from stratum corneum matched by

Answer 17

proliferation and upward migration and differentiation of cells from the stratum basale

Question 18

What happens in atopic dermatits, or eczema

Answer 18

The balnace homestasis which usually maintains a functional barrier is disrupted
Desquamation accelerates and the barrier is weakened, so more facile penetration of irridating chemicals is now possible. Exacerbates the disruption

Question 19

What happens in atopic dermatits, or eczema

Answer 19

The balance homestasis which usually maintains a functional barrier is disrupted
Desquamation (natural process of shedding of cells from stratum corneum) accelerates and the barrier is weakened, so more facile (effortless) penetration of irridating chemicals is now possible. worsens the disruption

Question 20

innate vs adaptive immune response

Answer 20

innate: short lived, no memory, include physical barriers and macrophages, natural killers
Adaptive: memory,specificity, long lasting
in skin initiated by Langerhans’ (APC) and executed by T cells, B cells and antibodies

Question 21

fibroblasts function

Answer 21

secrete elastin and collagen fibres, from ECM