Cutaneous arterioles

Meta arterioles – resistance vessels

Capillaries – large surface area for heat

exchange

Venules – large sub papillary venous

plexus

AV anastamosis – more prominent in

acral regions

Resting blood flow - 10-15ml/ min/100g of skin

Exposure to cold – falls to one tenth of resting flow i.e 1ml/min/100g

Exposure to heat – increase ten times , produces heavy circulatory load –unconciouness

Regional variation in Cutaneous blood flow

Skin color and blood flow

Skin needs little O2

0.3ml/min/100g (compared to )

So nervous >metabolic control

Nervous control – sympathetic supply

alone

Under resting condition

During exposure to heat – four steps

AV anastomoses dilate

Progressive Cutaneous dilation

sweat gland activation

Bradykinin produces dilation

During exposure to cold

Baroreceptor reflex

Cortical control mechanism

Blanching of skin

Phenomenon of blushing

White reaction – due to vasoconstriction

& appears about 15 sec

Red reaction- within 10 sec , due to

histamine and bradykinn , local response

Flare – spreading redness, after few min,

mediated by axon reflex

diffusely spreading irregular

redness

Wheal - local exudation and edema due

to histamine and substance p

Increased blood flow after a transient

occlusion

Cont’d