Phys Cuteneous circulation Flashcards
Thermoregulation and the skin
when hot, skin acts as a good radiator and when cold skin acts as a good insulator
importance of the venous plexus in thermoregulation
when we are really hot the venous plexus accumulates a large amount of blood to bring more blood to the surface to disapate heat
what area contains most of the cutaneous blood volume
venous plexus (high capacitance)
Arteriovenous anastamoses (cutaneous circulation)
allows a considerable amount of blood flow to enter the superficial venous plexus (bypassing the superficial capillary beds) and allows us to disapate heat
Anteriovenous anastamoses and cooling
cooling increases SNS activity and closes the AVA shunt to preserve body heat
Anteriovenous anastamoses and warming
warming decreases sympathetic tone resulting in passive vasoconstriction and venodilation to dissipate heat
Deep vs Superficial cutaneous circulation
Superficial cutaneous circulation provide little insulation and radiate heat well (when we are hot) Deep cutaneous circulation parallels the arterial system and are more insulated (when we are cold)
how is core body heat preserved
Counter current heat exchange
Counter Current Heat Exchange
The close association between arteries and veins permits direct transfer of heat to help preserve body heat
Warm environment thermogram
small temperature gradient between core and sufrace
Cold environment thermogram
Large temperature gradient between core and surface due to cutaneous vasoconstriction and counter current exchange (try to maintain core heat)
Control of skin blood flow under resting conditions, whole body heating, and cooling
1.) Resting: 200-500 ml/min (5-10% CO) 2.) Whole Body Heating: up to 40 fold increase in blood flow (8L/min) 3.) Cooling: decrease cutaneous flow to negligible levels
Response to 5C increase in body temp
causes cardiac output to increase markedly to support the increased skin blood flow needed to enhance dissipation of heat. Flow must decrease to other areas (splanchnic organs, kidneys, skeletal muscle) MAP still falls (can get too low causing us to pass out)
Neural Control of Skin Blood Flow
Sympathetic tone (tonic a1 receptro mediated) Note: NO PARASYMPATHETIC INNERVATION (NO B RECEPTORS)
Passive vasodilation
caused by a decrease in sympathetic tone
Acral regions
Hands, feet, nose, ears - Hight sympathetic tone- increases blood flow due to passive vasodilation
Non-actral regions
body, arms, legs - LOW sympathetic tone (only a small amount of passive dilation) PRESENCE OF ACTIVE VASODILATOR SYSTE IN NONACRAL REGIONS OF SKIN
Sympathetic Vasodilation
Neurally mediated cutaneous vasodilation that is coupled to the activation of sweat glands. Results in the release of unidentified cotransmitter from cholinergic nerves resulting is a second rise in flow to nonacral regions
Indirect heating
Increased blood temperature causes a relfex increase in cutaneous blood flow (decreased sympathetic activity - vasodilation to move more heat to the periphery to dissipate) . Thermal sensors in the skin, hypothalamus, and spinal cord are very sensitive to changes in core blood temperature.
Cutaneous Veins
Highly complinat- relax when heating (facilitates more blood to increase heat loss)
Metabolic control of cutaneous blood flow
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