Circulation 9: Special Circulations III Flashcards
Describe skin blood flow in a normothermic person. (Skin blood flow, CO, how skin blood flow can vary)
In a normothermic person, total skin blood flow is about 300-500 ml/min. or about 5-10% of the cardiac output. However, skin blood flow can vary from near 0 (in cold) to >7 liters/min (heat stress).
The oxygen and nutrient requirements of the skin are relatively small. Skin blood flow far exceeds nutritive requirements.
Which is more important in skin blood flow; neural control or local metabolic control?
neural. almost completely sympathetic
What is the primary function of cutaneous circulation? How is this achieved?
Describe its function in regards to heat loss.
The primary function of the cutaneous circulation is to maintain a constant body temperature. This function is achieved by providing convective transport of heat to the body surface for exchange with the environment. (far more blood flow than you need than to just provide nutrients. its more the regulation of temperature.)
The cutaneous vasculature is more efficient at promoting heat loss than it is in preventing heat loss. Skin blood flow may increase up to 30 times with heat but decrease by only a factor of 10 with cold. Therefore, humans acclimatize better to heat than to cold. (dep. on moisture. if you’re dehydrated you don’t lose heat effectively. if you sweat too much you can lose volume. can also lose your osmolarity bc lose more water than you do Na. )
How does blood flow contribute to skin color? When will someone be pale, cyanotic, reddish, bright pink?
Blood flow contributes to skin color by the volume and degree of oxygenation of blood in the cutaneous vessels.
Low blood flow (pale); desaturated hemoglobin (cyanotic); fully saturated hemoglobin (reddish); carbon monoxide poisoning (bright pink).
Why can skin also appear red in cold weather even though blood flow is low due to vasoconstriction?
(What does low temp do the dissociation of O from hemoglobin)?
In cold climates, the skin may also appear red (nose, ears and rosey cheeks) even though blood flow is low due to vasoconstriction.
Low temperature in the tissues decreases the dissociation (unloading) of oxygen from hemoglobin, resulting in more oxyhemoglobin, which gives arterial blood its red color.
gonna appear more red bc of the O hemoglobin dissociation which is low. have more O associated w hemoglobin in those conditions
apical skin- these are anastomoses-curled area (Slide 7). allows lots of blood flow to skin or prevents heat loss in conservation of heat-whichever way it goes. again this is why these tissues red bc holding onto O more under cold conditions. (nose toes fingertips ears)
What are the two types of resistance vessels that the skin contains?
How are they controlled? Sympathetic/Local metabolic? Basal tone?
arterioles – some basal tone; controlled by both sympathetic nerve activity and local regulatory factors.
arteriovenous (AV) anastomoses - shunts blood from the arterioles to venules and venous plexuses, bypassing the capillary beds. Exclusively under sympathetic neural control (rather than local metabolic control). No basal (non-neural) tone; no metabolic control; no reactive hyperemia or autoregulation.
In terms of blood flow there are 2 types of skin. Describe apical/non-apical.
Where present? Do they contain AV anastomoses? How innervated?
What 2 things distingush nonapical from apical?
Apical - Present on the nose, lips, ears, fingertips, hands, and feet.
High surface-to-volume ratio that favors heat loss.
Contains specialized AV anastomoses called glomus bodies that helps facilitate heat loss. (arteriovenous anastomoses-are basically shunts and they’re either vasodilated, or vasoconstricted. used for heat loss or heat conservation (dep. on if constricted)
Nonapical - Present in the rest of the body. Two features distinguish nonapical from apical skin.
Almost completely lacks AV anastomoses.
Innervated by sympathetic fibers that release acetylcholine (postganglionic) that produce active vasodilation. innervating sweat glands. cause release of bradykinin which is a vasodilator. sweating in non apical skin.
Which type of skin sweats?
nonapical
Compare the basal tone of skin to basal tone of muscle. What are the implications of this?
Graph.
Slide 5.
talking about arterioles, basal tone. basal tone of skin much lower than basal tone of muscle. can vasodilate much more than musculature of skeletal muscle system. Makes sense bc designed to get rid of heat. so can open up more.
(Basal Tone: Theoretical reference point. Amount of vascular contraction found under resting conditions without neural or hormonal (extrinsic) influences. )
Describe neural control of apical skin.
Arterioles, AV anastomoses and venules receive innervation by sympathetic adrenergic nerves.
At rest, reflex stimulation produces vasoconstriction of cutaneous vessels. Withdrawal of sympathetic nerve activity produces passive vasodilation.
neural control of apical skin is actively vasoconstrict or passively vasodilate. by far its pre-capillary arterioles and AV anastomoses.
Describe neural control of nonapical skin.
In addition to sympathetic vasoconstriction (norepinephrine), this tissue exhibits active vasodilation elicited by sympathetic cholinergic fibers through a sweat-dependent release of bradykinin.
nonapical skin. symp. chol. release Ach on post-ganglionic fibers. activates rel. of bradykinin from sweat glands. causes vasodilation.
When someone is completely white during hypovolumic shock, what has happened?
hypovolumic shock..go into baroreceptor vasoconstriction. closes off blood flow to skin. skin is white.. completely vasoconstricted, no blood flow to skin.
not just matter of temp. regulation. skin also responds along w other symp. responses in body
Describe the reflex control as it pertains to temperature regulation.
What controls temperature regulation?
What will increases and decreases in internal temperature lead to?
When does maximum vasodilation occur?
Temperature Regulation – is primarily controlled by major sensory sites in hypothalamus and less by receptors located in the spinal cord. (core body talking about. not temp. on skin that regulates blood flow. its really core body temp. sensed by hypothalamus.)
Increases in internal temperature cause withdrawal of sympathetic nerve activity and vasodilation (increase in blood flow). Maximum vasodilation results from block of sympathetic nerve activity.
Decreases in internal temperature cause activation of sympathetic nerve activity and vasoconstriction (decrease in blood flow).
Why is it that when you exercise, sympathetic activity can be cranked up but also can sweat (vasodilate)?
core body talking about. not temp. on skin that regulates blood flow. its really core body temp. sensed by hypothalamus.
-can be exercising and symp. NS can be cranked up but bc core body temp rising, withdraw of symp. to skin are occurring at same time as rest of symp. being activated. seperate system for controlling symp. to skin.
exercising, increasing symp. nerve activity. temp goes up and want to vasodilate so hypothalamus withdraws symp. nerve activity to vascular system skin causing massive vasodilation.
Describe the effect of moderate changes in local skin temperature.
ambient temperature on skin doesn’t have much of effect.
warmer get a little bit more vasodilation but main regulator is core temp/hypothalamus.
In addition to reflex controls, moderate changes in local skin temperature are accompanied by directionally similar responses in local skin blood flow.
In a normothermic person, how do changes in cutaneous vascular resistance effect total peripheral resistance and blood pressure?
(What induces changes in cutaneous vascular resistance?)
In a normothermic person, total skin blood flow is only 5-10% of cardiac output and therefore changes in cutaneous vascular resistance induced by changes in blood pressure (baroreceptor reflex) exert only a small effect on overall total peripheral resistance and blood pressure.
In heat stress, how can total skin blood flow change?
If someone was in desert, experiencing heat stress and then shot, how will bp be affected?
However, in heat stress, total skin blood flow can approach 8 liters/min. (total cardiac output increases to 13 liters/min) or about 60% of cardiac output. Under these conditions, a decrease in blood pressure (hemorrhage) results in a significant baroreceptor-mediated vasoconstriction of cutaneous vessels (increase in peripheral resistance) that helps maintain blood pressure. However, the competing vasodilation (due to reflex temperature regulation) limits the vasoconstrictor response and blood pressure is not as well maintained compared with normothermic conditions.
if 120 outside max. vasodilated. lots of blood flow to skin, if you get shot and start bleeding have have baroreceptor response to hemorrhage, its more difficult for symp. NS to fight vasodilation that’s occurring bc of temperature to maintain bp. amount of blood to skin in heat stress does have impact to prevent baroreceptors from raising bp.
if losing blood, baroreceptors trying to maintain arterial pressure.
baroreceptors have much harder time if under heat stress.. to maintain bp bc of all blood going to skin
(rel. between diff mechanisms going on. have temp. causing vasodilation. at same time could have baroreceptors trying to cause vasoconstriction. opposing e/o.)
