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CHAPTER 18 Control Mechanisms in Circulatory Function 291. AUTONOMIC NEURAL CONTROL OF THE thetic nervous system activity parasympathetic activation. CIRCULATORY SYSTEM reduces cardiac contractility, Sympathetic fibers to the heart release NE which binds. Neural regulation of the cardiovascular system involves the to 1 adrenergic receptors in the sinoatrial node the atri. firing of postganglionic parasympathetic and sympathetic oventricular node and specialized conducting tissues and. neurons triggered by preganglionic neurons in the brain cardiac muscle Stimulation of these fibers causes increased. parasympathetic and spinal cord sympathetic and heart rate conduction velocity and contractility. parasympathetic Afferent input influencing these neurons The two divisions of the autonomic nervous system tend. comes from the cardiovascular system as well as from other to oppose each other in their effects on the heart and ac. organs and the external environment tivities along these two pathways usually change in a recip. Autonomic control of the heart and blood vessels was rocal manner. described in Chapter 6 Briefly the heart is innervated by Blood vessels except those of the external genitalia re. parasympathetic vagus and sympathetic cardioaccelera ceive sympathetic innervation only see Fig 18 1 The. tor nerve fibers Fig 18 1 Parasympathetic fibers release neurotransmitter is NE which binds to 1 adrenergic re. acetylcholine ACh which binds to muscarinic receptors ceptors and causes vascular smooth muscle contraction and. of the sinoatrial node the atrioventricular node and spe vasoconstriction Circulating epinephrine released from. cialized conducting tissues Stimulation of parasympathetic the adrenal medulla binds to 2 adrenergic receptors of. fibers causes a slowing of the heart rate and conduction ve vascular smooth muscle cells especially coronary and. locity The ventricles are only sparsely innervated by skeletal muscle arterioles producing vascular smooth mus. parasympathetic nerve fibers and stimulation of these cle relaxation and vasodilation Postganglionic parasympa. fibers has little direct effect on cardiac contractility Some thetic fibers release ACh and nitric oxide NO to blood. cardiac parasympathetic fibers end on sympathetic nerves vessels in the external genitalia ACh causes the further re. and inhibit the release of norepinephrine NE from sym lease of NO from endothelial cells NO results in vascular. pathetic nerve fibers Therefore in the presence of sympa smooth muscle relaxation and vasodilation. Parasympathetic Sympathetic,ACh ACh SA NE,medulla ACh. Most blood,Sacral Blood vessels,of external, FIGURE 18 1 Autonomic innervation of the cardiovascular system ACh acetylcholine NE norepi. nephrine E epinephrine SA sinoatrial node AV atrioventricular node. 292 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY, The Spinal Cord Exerts Control Over Changes in the firing rate of the arterial baroreceptors. Cardiovascular Function and cardiopulmonary baroreceptors initiate reflex re. sponses of the autonomic nervous system that alter cardiac. Preganglionic sympathetic neurons normally generate a output and SVR The central terminals for these receptors. steady level of background postganglionic activity tone are located in the nucleus tractus solitarii NTS in the. This sympathetic tone produces a background level of medulla oblongata Neurons from the NTS project to the. sympathetic vasoconstriction cardiac stimulation and RVL and nucleus ambiguus where they influence the firing. adrenal medullary catecholamine secretion all of which of sympathetic and parasympathetic nerves. contribute to the maintenance of normal blood pressure. This tonic activity is generated by excitatory signals from. Baroreceptor Reflex Effects on Cardiac Output and Sys. the medulla oblongata When the spinal cord is acutely. temic Vascular Resistance Increased pressure in the. transected and these excitatory signals can no longer. carotid sinus and aorta stretches carotid sinus barorecep. reach sympathetic preganglionic fibers their tonic firing. tors and aortic baroreceptors and raises their firing rate. is reduced and blood pressure falls an effect known as. Nerve fibers from carotid sinus baroreceptors join the glos. spinal shock, sopharyngeal cranial nerve IX nerves and travel to the.
Humans have spinal reflexes of cardiovascular signifi. NTS Nerve fibers from the aortic baroreceptors located in. cance For example the stimulation of pain fibers entering. the wall of the arch of the aorta travel with the vagus cra. the spinal cord below the level of a chronic spinal cord. nial nerve X nerves to the NTS, transection can cause reflex vasoconstriction and increased. The increased action potential traffic reaching the NTS. blood pressure, leads to excitation of nucleus ambiguus neurons and inhibi. tion of firing of RVL neurons This results in increased. The Medulla Is a Major Area for Cardiovascular parasympathetic neural activity to the heart and decreased. Reflex Integration sympathetic neural activity to the heart and resistance ves. sels primarily arterioles Fig 18 2 causing decreased car. The medulla oblongata has three major cardiovascular diac output and SVR Since mean arterial pressure is the. functions product of SVR and cardiac output see Chapter 12 mean. Generating tonic excitatory signals to spinal sympa arterial pressure is returned toward the normal level This. thetic preganglionic fibers completes a negative feedback loop by which increases in. Integrating cardiovascular reflexes mean arterial pressure can be attenuated. Integrating signals from supramedullary neural networks Conversely decreases in arterial pressure and decreased. and from circulating hormones and drugs stretch of the baroreceptors increase sympathetic neural. Specific pools of neurons are responsible for elements of activity and decrease parasympathetic neural activity re. these functions Neurons in the rostral ventrolateral nu sulting in increased heart rate stroke volume and SVR this. cleus RVL are normally active and provide tonic excita. tory activity to the spinal cord Specific pools of neurons. within the RVL have actions on heart and blood vessels. RVL neurons are critical in mediating reflex inhibition or. activating sympathetic firing to the heart and blood vessels. The cell bodies of cardiac preganglionic parasympathetic. neurons are located in the nucleus ambiguus the activity. of these neurons is influenced by reflex input as well as in. put from respiratory neurons Respiratory sinus arrhythmia. described in Chapter 13 is primarily the result of the influ. ence of medullary respiratory neurons that inhibit firing of. preganglionic parasympathetic neurons during inspiration. and excite these neurons during expiration Other inputs to. the RVL and nucleus ambiguus will be described below. The Baroreceptor Reflex Is Important in the,Regulation of Arterial Pressure. The most important reflex behavior of the cardiovascular. system originates in mechanoreceptors located in the aorta. carotid sinuses atria ventricles and pulmonary vessels. These mechanoreceptors are sensitive to the stretch of the. walls of these structures When the wall is stretched by in. Baroreceptor reflex response to increased, creased transmural pressure receptor firing rate increases FIGURE 18 2. arterial pressure An intervention elevates ar, Mechanoreceptors in the aorta and carotid sinuses are terial pressure either mean arterial pressure or pulse pressure.
called baroreceptors Mechanoreceptors in the atria ven stretches the baroreceptors and initiates the reflex The resulting. tricles and pulmonary vessels are referred to as low pres reduced systemic vascular resistance and cardiac output return ar. sure baroreceptors or cardiopulmonary baroreceptors terial pressure toward the level existing before the intervention. CHAPTER 18 Control Mechanisms in Circulatory Function 293. returns blood pressure toward the normal level If the fall in. mean arterial pressure is very large increased sympathetic. neural activity to veins is added to the above responses. causing contraction of the venous smooth muscle and re. ducing venous compliance Decreased venous compliance. shifts blood toward the central blood volume increasing. right atrial pressure and in turn stroke volume,Baroreceptor Reflex Effects on Hormone Levels The. baroreceptor reflex influences hormone levels in addition. to vascular and cardiac muscle The most important influ. ence is on the renin angiotensin aldosterone system. RAAS A reduction in arterial pressure and baroreceptor. firing results in increased sympathetic nerve activity to the. kidneys which causes the kidneys to release renin activat. ing the RAAS The activation of this system causes the kid. neys to save salt and water Salt and water retention in. creases blood volume and ultimately causes blood, pressure to rise The details of the RAAS are discussed later. in this chapter and in Chapter 24, The information on the firing rate of the baroreceptors Carotid sinus baroreceptor nerve firing rate. FIGURE 18 3, is also projected to the paraventricular nucleus of the hy and mean arterial pressure With normal. pothalamus where the release of arginine vasopressin conditions a mean arterial pressure of 93 mm Hg is near the. AVP by the posterior pituitary is controlled see Chapter midrange of the firing rates for the nerves Sustained hyperten. 32 Decreased firing rate of the baroreceptors results in in sion causes the operating range to shift to the right putting 93. creased AVP release causing the kidney to save water The mm Hg at the lower end of the firing range for the nerves. result is an increase in blood volume An increase in arterial. pressure causes decreased AVP release and increased excre. tion of water by the kidneys mately 40 mm Hg when the receptor stops firing to 180. Hormonal effects on salt and water balance and ulti mm Hg when the firing rate reaches a maximum. mately on cardiac output and blood pressure are powerful Fig 18 3 Pulse pressure also influences the firing rate of the. but they occur more slowly a timescale of many hours to baroreceptors For a given mean arterial pressure the firing. days than ANS effects seconds to minutes rate of the baroreceptors increases with pulse pressure. Baroreceptor Reflex Effects on Specific Organs The Baroreceptor Adaptation An important property of the. defense of arterial pressure by the baroreceptor reflex re baroreceptor reflex is that it adapts during a period of 1 to. sults in maintenance of blood flow to two vital organs the 2 days to the prevailing mean arterial pressure When the. heart and brain If resistance vessels of the heart and brain mean arterial pressure is suddenly raised baroreceptor fir. participated in the sympathetically mediated vasoconstric ing increases If arterial pressure is held at the higher level. tion found in skeletal muscle skin and the splanchnic re baroreceptor firing declines during the next few seconds. gion it would lower blood flow to these organs This does Firing rate then continues to decline more slowly until it re. not happen turns to the original firing rate between 1 and 2 days Con. The combination of 1 a minimal vasoconstrictor effect sequently if the mean arterial pressure is maintained at an. of sympathetic nerves on cerebral blood vessels and 2 a elevated level the tendency for the baroreceptors to initi. robust autoregulatory response keeps brain blood flow ate a decrease in cardiac output and SVR quickly disap. nearly normal despite modest decreases in arterial pressure pears This occurs in part because of the reduction in the. see Chapter 17 However a large decrease in arterial rate of baroreceptor firing for a given mean arterial pressure. pressure beyond the autoregulatory range causes brain mentioned above see Fig 18 3 This is an example of re. blood flow to fall accounting for loss of consciousness ceptor adaptation A resetting of the reflex in the central. Activation of sympathetic nerves to the heart causes 1 nervous system CNS occurs as well Consequently the. adrenergic receptor mediated constriction of coronary ar baroreceptor mechanism is the first line of defense in the. terioles and 1 adrenergic receptor mediated increases in maintenance of normal blood pressure it makes the rapid. cardiac muscle metabolism see Chapter 17 The net effect control of blood pressure needed with changes in posture. is a marked increase in coronary blood flow despite the in or blood loss possible but it does not provide for the long. creased sympathetic constrictor activity In summary when term control of blood pressure. arterial pressure drops the generalized vasoconstriction. caused by the baroreflex spares the brain and heart allow Cardiopulmonary Baroreceptors Are Stretch. ing flow to these two vital organs to be maintained. Receptors That Sense Central Blood Volume, Pressure Range for Baroreceptors The effective range Cardiopulmonary baroreceptors are located in the cardiac.
of the carotid sinus baroreceptor mechanism is approxi atria at the junction of the great veins and atria in the ven. 294 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY, tricular myocardium and in pulmonary vessels Their nerve creased parasympathetic activity to the heart These events. fibers run in the vagus nerve to the NTS with projections lead to increases in cardiac output SVR and mean arterial. to supramedullary areas as well Unloading i e decreasing pressure An example of this reaction is the cold pressor re. the stretch of the cardiopulmonary receptors by reducing sponse the elevated blood pressure that normally occurs. central blood volume results in increased sympathetic when an extremity is placed in ice water The increase in. nerve activity and decreased parasympathetic nerve activ blood pressure produced by this challenge is exaggerated in. ity to the heart and blood vessels In addition the car several forms of hypertension. diopulmonary reflex interacts with the baroreceptor reflex A second type of response is produced by deep pain. Unloading of the cardiopulmonary receptors enhances the The stimulation of deep pain fibers associated with crush. baroreceptor reflex and loading the cardiopulmonary re ing injuries disruption of joints testicular trauma or dis. ceptors by increasing central blood volume inhibits the tension of the abdominal organs results in diminished sym. baroreceptor reflex pathetic activity and enhanced parasympathetic activity. Like the arterial baroreceptors the decreased stretch of with decreased cardiac output SVR and blood pressure. the cardiopulmonary baroreceptors activates the RAAS and This hypotensive response contributes to certain forms of. increases the release of AVP cardiovascular shock, Chemoreceptors Detect Changes Activation of Chemoreceptors in the. in PCO2 pH and PO2 Ventricular Myocardium Causes Reflex. Bradycardia and Vasodilation, The reflex response to changes in blood gases and pH be. gins with chemoreceptors located peripherally in the An injection of bradykinin 5 hydroxytryptamine sero. carotid bodies and aortic bodies and centrally in the tonin certain prostaglandins or various other compounds. medulla see Chapter 22 The peripheral chemoreceptors into the coronary arteries supplying the posterior and inferior. of the carotid bodies and aortic bodies are specialized regions of the ventricles causes reflex bradycardia and hy. structures located in approximately the same areas as the potension The chemoreceptor afferents are carried in the va. carotid sinus and aortic baroreceptors They send nerve im gus nerves The bradycardia results from increased parasym. pulses to the NTS and are sensitive to elevated PCO2 as pathetic tone Dilation of systemic arterioles and veins is. well as decreased pH and PO2 Peripheral chemoreceptors caused by withdrawal of sympathetic tone This reflex is also. exhibit an increased firing rate when 1 the PO2 or pH of elicited by myocardial ischemia and is responsible for the. the arterial blood is low 2 the PCO2 of arterial blood is in bradycardia and hypotension that can occur in response to. creased 3 the flow through the bodies is very low or acute infarction of the posterior or inferior myocardium. stopped or 4 a chemical is given that blocks oxidative. metabolism in the chemoreceptor cells The central, medullary chemoreceptors increase their firing rate prima INTEGRATED SUPRAMEDULLARY. rily in response to elevated arterial PCO2 which causes a CARDIOVASCULAR CONTROL. decrease in brain pH, The increased firing of both peripheral and central The highest levels of organization in the ANS are the.
chemoreceptors via the NTS and RVL leads to profound supramedullary networks of neurons with way stations in. peripheral vasoconstriction Arterial pressure is signifi the limbic cortex amygdala and hypothalamus These. cantly elevated If respiratory movements are voluntarily supramedullary networks orchestrate cardiovascular corre. stopped the vasoconstriction is more intense and a striking lates of specific patterns of emotion and behavior by their. bradycardia and decreased cardiac output occur This re projections to the ANS. sponse pattern is typical of the diving response discussed Unlike the medulla supramedullary networks do not. later As in the case of the baroreceptor reflex the coro contribute to the tonic maintenance of blood pressure nor. nary and cerebral circulations are not subject to the sympa are they necessary for most cardiovascular reflexes al. thetic vasoconstrictor effects and instead exhibit vasodila though they modulate reflex reactivity. tion as a result of the combination of the direct effect of. the abnormal blood gases and local metabolic effects. In addition to its importance when arterial blood gases The Fight or Flight Response Includes. are abnormal the chemoreceptor reflex is important in the Specific Cardiovascular Changes. cardiovascular response to severe hypotension As blood Upon stimulation of certain areas in the hypothalamus cats. pressure falls blood flow through the carotid and aortic demonstrate a stereotypical rage response with spitting. bodies decreases and chemoreceptor firing increases clawing tail lashing back arching and so on This is ac. probably because of changes in local PCO2 pH and PO2 companied by the autonomic fight or flight response de. scribed in Chapter 6 Cardiovascular responses include ele. Pain Receptors Produce Reflex Responses vated heart rate and blood pressure. The initial behavioral pattern during the fight or flight. in the Cardiovascular System, response includes increased skeletal muscle tone and gen. Two reflex cardiovascular responses to pain occur In the eral alertness There is increased sympathetic neural activ. most common reflex pain causes increased sympathetic ac ity to blood vessels and the heart The result of this cardio. tivity to the heart and blood vessels coupled with de vascular response is an increase in cardiac output by. CHAPTER 18 Control Mechanisms in Circulatory Function 295. increasing both heart rate and stroke volume SVR and ar and peripheral vasoconstriction sympathetic of the ex. terial pressure When the fight or flight response is con tremities and splanchnic regions when his or her face is. summated by fight or flight arterioles in skeletal muscle di submerged in cold water With breath holding during the. late because of accumulation of local metabolites from the dive arterial PO2 and pH fall and PCO2 rises and the. exercising muscles see Chapter 17 This vasodilation may chemoreceptor reflex reinforces the diving response The. outweigh the sympathetic vasoconstriction in other organs arterioles of the brain and heart do not constrict and there. and SVR may actually fall With a fall in SVR mean arterial fore cardiac output is distributed to these organs This. pressure returns toward normal despite the increase in car heart brain circuit makes use of the oxygen stored in the. diac output blood that would normally be used by the other tissues es. Emotional situations often provoke the fight or flight pecially skeletal muscle Once the diver surfaces the heart. response in humans but it is usually not accompanied by rate and cardiac output increase substantially peripheral. muscle exercise e g medical students taking an examina vasoconstriction is replaced by vasodilation restoring nu. tion It seems likely that repeated elevations in arterial trient flow and washing out accumulated waste products. pressure caused by dissociation of the cardiovascular com. ponent of the fight or flight response from muscular exer. cise component are harmful Behavioral Conditioning Affects. Cardiovascular Responses, Fainting Can Be a Cardiovascular Cardiovascular responses can be conditioned as can other. Correlate of Emotion autonomic responses such as those observed in Pavlov s fa. mous experiments Both classical and operant condition. Vasovagal syncope fainting is a somatic and cardiovascu ing techniques have been used to raise and lower the blood. lar response to certain emotional experiences Stimulation pressure and heart rate of animals Humans can also be. of specific areas of the cerebral cortex can lead to a sudden taught to alter their heart rate and blood pressure using a. relaxation of skeletal muscles depression of respiration variety of behavioral techniques such as biofeedback. and loss of consciousness The cardiovascular events ac Behavioral conditioning of cardiovascular responses has. companying these somatic changes include profound significant clinical implications Animal and human studies. parasympathetic induced bradycardia and withdrawal of indicate that psychological stress can raise blood pressure. resting sympathetic vasoconstrictor tone There is a dra increase atherogenesis and predispose to fatal cardiac ar. matic drop in heart rate cardiac output and SVR The re rhythmias These effects are thought to result from an in. sultant decrease in mean arterial pressure results in uncon appropriate fight or flight response Other studies have. sciousness because of lowered cerebral blood flow shown beneficial effects of behavior patterns designed to. Vasovagal syncope appears in lower animals as the playing introduce a sense of relaxation and well being Some clini. dead response typical of the opossum cal regimens for the treatment of cardiovascular disease. take these factors into account,The Cardiovascular Correlates of Exercise Require. Integration of Central and Peripheral Mechanisms Not All Cardiovascular Responses Are Equal. Exercise causes activation of supramedullary neural net Supramedullary responses can override the baroreceptor re. works that inhibit the activity of the baroreceptor reflex flex For example the fight or flight response causes the. The inhibition of medullary regions involved in the barore heart rate to rise above normal levels despite a simultaneous. ceptor reflex is called central command Central command rise in arterial pressure In such circumstances the neurons. results in withdrawal of parasympathetic tone to the heart connecting the hypothalamus to medullary areas inhibit the. with a resulting increase in heart rate and cardiac output baroreceptor reflex and allow the corticohypothalamic re. The increased cardiac output supplies the added require sponse to predominate Also during exercise input from. ment for blood flow to exercising muscle As exercise in supramedullary regions inhibits the baroreceptor reflex pro. tensity increases central command adds sympathetic tone moting increased sympathetic tone and decreased parasym. that further increases heart rate and contractility It also re pathetic tone despite an increase in arterial pressure. cruits sympathetic vasoconstriction that redistributes blood Moreover the various cardiovascular response patterns. flow away from splanchnic organs and resting skeletal mus do not necessarily occur in isolation as previously de. cle to exercising muscle Finally afferent impulses from ex scribed Many response patterns interact reflecting the ex. ercising skeletal muscle terminate in the RVL where they tensive neural interconnections between all levels of the. further augment sympathetic tone CNS and interaction with various elements of the local. During exercise blood flow of the skin is largely influ control systems For example the baroreceptor reflex inter. enced by temperature regulation as described in Chapter 17 acts with thermoregulatory responses Cutaneous sympa. thetic nerves participate in body temperature regulation. The Diving Response Maintains Oxygen see Chapter 29 but also serve the baroreceptor reflex At. Delivery to the Heart and Brain moderate levels of heat stress the baroreceptor reflex can. cause cutaneous arteriolar constriction despite elevated. The diving response is best observed in seals and ducks core temperature However with severe heat stress the. but it also occurs in humans An experienced diver can ex baroreceptor reflex cannot overcome the cutaneous vasodi. hibit intense slowing of the heart rate parasympathetic lation as a result arterial pressure regulation may fail. 296 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY, HORMONAL CONTROL OF THE temic vasoconstriction and increases mean arterial pressure. CARDIOVASCULAR SYSTEM The reflex masks some of the direct cardiac effects of NE by. significantly increasing cardiac parasympathetic tone In. Various hormones play a role in the control of the cardio contrast epinephrine causes vasodilation in skeletal muscle. vascular system Important sites of hormone secretion in and splanchnic beds SVR may actually fall and mean arte. clude the adrenal medulla posterior pituitary gland kid rial pressure does not rise The baroreceptor reflex is not. ney and cardiac atrium elicited parasympathetic tone to the heart is not increased. and the direct cardiac effects of epinephrine are evident At. Circulating Epinephrine Has high concentrations epinephrine binds to 1 adrenergic. Cardiovascular Effects receptors and causes peripheral vasoconstriction this level. of epinephrine is probably never reached except when it is. When the sympathetic nervous system is activated the ad administered as a drug. renal medulla releases epinephrine 90 and norepi Denervated organs such as transplanted hearts are very. nephrine 10 which circulate in the blood see Chap responsive to circulating levels of epinephrine and norepi. ter 6 Changes in the circulating NE concentration are nephrine This increased sensitivity to neurotransmitters is. small relative to changes in NE resulting from the direct re referred to as denervation hypersensitivity Several factors. lease from nerve endings close to vascular smooth muscle contribute to denervation hypersensitivity including the. and cardiac cells Increased circulating epinephrine how absence of sympathetic nerve endings to take up circulating. ever contributes to skeletal muscle vasodilation during the norepinephrine and epinephrine actively leaving more. fight or flight response and exercise In these cases epi transmitter available for binding to receptors In addition. nephrine binds to 2 adrenergic receptors of skeletal mus denervation results in up regulation of neurotransmitter re. cle arteriolar smooth muscle cells and causes relaxation In ceptors in target cells During exercise circulating levels of. the heart circulating epinephrine binds to cardiac cell 1 norepinephrine and epinephrine increase Because of their. adrenergic receptors and reinforces the effect of NE re enhanced response to circulating catecholamines trans. leased from sympathetic nerve endings planted hearts can perform almost as well as normal hearts. A comparison of the responses to infusions of epineph. rine and norepinephrine illustrates not only the different. effects of the two hormones but also the different reflex re The Renin Angiotensin Aldosterone System. sponse each one elicits Fig 18 4 Epinephrine and norep Helps Regulate Blood Pressure and Volume. inephrine have similar direct effects on the heart but NE The control of total blood volume is extremely important. elicits a powerful baroreceptor reflex because it causes sys in regulating arterial pressure Because changes in total. blood volume lead to changes in central blood volume the. long term influence of blood volume on ventricular end di. Epinephrine Norepinephrine astolic volume and cardiac output is paramount Cardiac. output in turn strongly influences arterial pressure Hor. monal control of blood volume depends on hormones that. Cardiac output, regulate salt and water intake and output as well as red.
blood cell formation, Reduced arterial pressure and blood volume cause the. 5 5 release of renin from the kidneys Renin release is mediated. 0 4 8 12 16 0 4 8 12 16 by the sympathetic nervous system and by the direct effect. of lowered arterial pressure on the kidneys Renin is a pro. Systemic vascular, 15 19 teolytic enzyme that catalyzes the conversion of an. resistance,giotensinogen a plasma protein to angiotensin I. Fig 18 5 Angiotensin I is then converted to angiotensin. II by angiotensin converting enzyme ACE primarily in. 10 14 the lungs Angiotensin II has the following actions. 0 4 8 12 16 0 4 8 12 16 It is a powerful arteriolar vasoconstrictor and in some. circumstances it is present in plasma in concentrations. pressure mm Hg,150 150 sufficient to increase SVR,Arterial blood. It reduces sodium excretion by increasing sodium reab. 100 Mean 100 sorption by proximal tubules of the kidney. Diastolic It causes the release of aldosterone from the adrenal cor. 0 4 8 12 16 0 4 8 12 16 It causes the release of AVP from the posterior pituitary. Time min Time min gland, A comparison of the effects of intravenous Angiotensin II is a significant vasoconstrictor in some.
FIGURE 18 4 circumstances Angiotensin II directly stimulates contrac. infusions of epinephrine and norepineph, rine See text for details Modified from Rowell LB Human tion of vascular smooth muscle and also augments NE re. Circulation Regulation During Physical Stress New York Ox lease from sympathetic nerves and sensitizes vascular. ford University Press 1986 smooth muscle to the constrictor effects of NE It plays an. CHAPTER 18 Control Mechanisms in Circulatory Function 297. Angiotensinogen Adrenal Aldosterone,cortex release. ACE Renal Decreased blood volume,Angiotensin I Angiotensin II proximal sodium and. tubule excretion arterial pressure,Peripheral Increased. arterioles SVR, FIGURE 18 5 Renin angiotensin aldosterone system This system plays an important role in the regu.
lation of arterial blood pressure and blood volume ACE angiotensin converting enzyme. SVR systemic vascular resistance, important role in increasing SVR as well as blood volume cells and released into the bloodstream when the atria are. in individuals on a low salt diet If an ACE inhibitor is given stretched By increasing sodium excretion it decreases. to such individuals blood pressure falls Renin is released blood volume see Chapter 24 It also inhibits renin release. during blood loss even before blood pressure falls and the as well as aldosterone and AVP secretion Increased ANP. resulting rise in plasma angiotensin II increases the SVR along with decreased aldosterone and AVP may be par. One of the effects of aldosterone is to reduce renal ex tially responsible for the reduction in blood volume that. cretion of sodium the major cation of the extracellular occurs with prolonged bed rest When central blood vol. fluid Retention of sodium paves the way for increasing ume and atrial stretch are increased ANP secretion rises. blood volume Renin angiotensin aldosterone and the leading to higher sodium excretion and a reduction in. factors that control their release and formation are dis blood volume. cussed in Chapter 24 The RAAS is important in the normal. maintenance of blood volume and blood pressure It is crit. ical when salt and water intake is reduced Erythropoietin Increases the Production. Rarely renal artery stenosis causes hypertension that of Erythrocytes. can be attributed solely to elevated renin and angiotensin II The final step in blood volume regulation is production of. levels In addition the renin angiotensin system plays an erythrocytes Erythropoietin is a hormone released by the. important but not unique role in maintaining elevated kidneys that causes bone marrow to increase production of. pressure in more than 60 of patients with essential hy red blood cells raising the total mass of circulating red. pertension In patients with congestive heart failure renin cells The stimuli for erythropoietin release include hy. and angiotensin II are increased and contribute to elevated poxia and reduced hematocrit An increase in circulating. SVR as well as sodium retention AVP and aldosterone enhances salt and water retention and. results in an elevated plasma volume The increased plasma. Arginine Vasopressin Contributes volume with a constant volume of red blood cells results. to the Regulation of Blood Volume in a lower hematocrit The decrease in hematocrit stimu. lates erythropoietin release which stimulates red blood cell. Arginine vasopressin AVP is released by the posterior pi synthesis and therefore balances the increase in plasma. tuitary gland controlled by the hypothalamus Three pri volume with a larger red blood cell mass. mary classes of stimuli lead to AVP release increased. plasma osmolality decreased baroreceptor and cardiopul. monary receptor firing and various types of stress such as. physical injury or surgery In addition circulating an COMPARISON OF SHORT TERM AND. giotensin II stimulates AVP release Although AVP is a LONG TERM BLOOD PRESSURE CONTROL. vasoconstrictor it is not ordinarily present in plasma in Different mechanisms are responsible for the short term. high enough concentrations to exert an effect on blood and long term control of blood pressure Short term con. vessels However in special circumstances e g severe trol depends on activation of neural and hormonal re. hemorrhage it probably contributes to increased SVR sponses by the baroreceptor reflexes described earlier. AVP exerts its major effect on the cardiovascular system by Long term control depends on salt and water excretion. causing the retention of water by the kidneys see Chapter by the kidneys Excretion of salt and water by the kidneys. 24 an important part of the neural and humoral mecha is regulated by some neural and hormonal mechanisms. nisms that regulate blood volume most of which have been mentioned earlier in this chapter. However it is also regulated by arterial pressure Increased. Atrial Natriuretic Peptide Helps Regulate arterial pressure results in increased excretion of salt and. water a phenomenon known as pressure diuresis Fig,Blood Volume. 18 6 Because of pressure diuresis as long as mean arterial. Atrial natriuretic peptide ANP is a 28 amino acid pressure is elevated salt and water excretion will exceed the. polypeptide synthesized and stored in the atrial muscle normal rate this will tend to lower extracellular fluid vol. 298 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY,Intervention CARDIOVASCULAR CONTROL. DURING STANDING, Arterial pressure Salt and An integrated view of the cardiovascular system requires an. increase water output understanding of the relationships among cardiac output. decrease venous return and central blood volume and how these re. lationships are influenced by interactions among various. Cardiac output, neural hormonal and other control mechanisms Consid.
Plasma volume eration of the responses to standing erect provides an op. portunity to explore these elements in detail Figure 18 7. Central blood Blood volume compares venous pressures for the recumbent and standing. volume positions When a person is recumbent pressure in the. veins of the legs is only a few mm Hg above the pressure in. 8 the right atrium The pressure distending the veins trans. mural pressure is equal to the pressure within the veins of. the legs because the pressure outside the veins is atmos. Output of salt and water,6 pheric pressure the zero reference pressure. times normal, When a person stands the column of blood above the. lower extremities raises venous pressure to about 50 mm. 4 Hg at the femoral level and 90 mm Hg at the foot This is. 50 100 150 200 250,Arterial pressure mm Hg,FIGURE 18 6. Regulation of arterial pressure by pressure,diuresis A higher output of salt and water in. response to increased arterial pressure reduces blood volume. Blood volume is reduced until pressure returns to its normal. level The curve on the left shows the relationship in a person. with normal blood pressure The curve on the right shows the. same relationship in an individual who is hypertensive Note. that the hypertensive individual has an elevated arterial pres. sure at a normal output of salt and water Modified from Guy. ton AC Hall JE Medical Physiology 10th Ed Philadelphia. WB Saunders 2000 p 203, ume and ultimately blood volume As discussed earlier in.
this chapter and in Chapter 15 a decrease in blood volume. reduces stroke volume by lowering the end diastolic filling. of the ventricles Decreased stroke volume lowers cardiac. output and arterial pressure Pressure diuresis persists until. it lowers blood volume and cardiac output sufficiently to. return mean arterial pressure to a set level A decrease in. mean arterial pressure has the opposite effect on salt and. water excretion Reduced pressure diuresis increases blood. volume and cardiac output until mean arterial pressure is re. turned to a set level, Pressure diuresis is a slow but persistent mechanism for. regulating arterial pressure Because it persists in altering. salt and water excretion and blood volume as long as arte FIGURE 18 7. Venous pressures in the recumbent and,standing positions In this example standing. rial pressure is above or below a set level it will eventually places a hydrostatic pressure of approximately 80 mm Hg on the. return pressure to that level In hypertensive patients the feet Right atrial pressure is lowered because of the reduction in. curve shown in Figure 18 6 is shifted to the right so that central blood volume The negative pressures above the heart with. salt and water excretion are normal at a higher arterial pres standing do not actually occur because once intravascular pressure. sure If this were not the case pressure diuresis would inex drops below atmospheric pressure the veins collapse These are. orably bring arterial pressure back to normal the pressures that would exist if the veins remained open. CHAPTER 18 Control Mechanisms in Circulatory Function 299. the transmural distending pressure because the outside liter of blood It follows that an adequate cardiovascular re. pressure is still zero atmospheric Because the veins are sponse to the changes caused by upright posture or. highly compliant such a large increase in transmural pres thostasis is absolutely essential to our lives as bipeds see. sure is accompanied by an increase in venous volume Clinical Focus Box 18 1. The arteries of the legs undergo exactly the same in The immediate cardiovascular adjustments to upright. creases in transmural pressure However the increase in posture are the baroreceptor and cardiopulmonary recep. their volume is minimal because the compliance of the sys tor initiated reflexes followed by the muscle and respira. temic arterial system is only 1 20th that of the systemic ve tory pumps and later adjustments in blood volume. nous system Standing increases pressure in the arteries and. veins of the legs by exactly the same amount so the added. pressure has no influence on the difference in pressure driv Standing Elicits Baroreceptor. ing blood flow from the arterial to the venous side of the and Cardiopulmonary Reflexes. circulation It only influences the distension of the veins The decreased central blood volume caused by standing in. cludes reduced atrial ventricular and pulmonary vessel. Standing Requires a Complex volumes These volume reductions unload the cardiopul. Cardiovascular Response monary receptors and elicit a cardiopulmonary reflex Re. duced left ventricular end diastolic volume decreases stroke. When a person stands and the veins of the legs are dis volume and pulse pressure as well as cardiac output and. tended blood that would normally be returned toward the mean arterial pressure leading to decreased firing of aortic. right atrium remains in the legs filling the expanding veins arch and carotid baroreceptors The combined reduction in. For a few seconds after standing venous return to the heart firing of cardiopulmonary receptors and baroreceptors re. is lower than cardiac output and during this time there is sults in a reflex decrease in parasympathetic nerve activity. a net shift of blood from the central blood volume to the and an increase in sympathetic nerve activity to the heart. veins of the legs When a person stands up the heart rate generally in. When a 70 kg person stands central blood volume is creases by about 10 to 20 beats min The increased sympa. quickly reduced by approximately 550 mL If no compen thetic nerve activity to the ventricular myocardium shifts. satory mechanisms existed this would significantly reduce the ventricle to a new function curve and despite the low. cardiac end diastolic volume and cause a more than 60 ered ventricular filling stroke volume is decreased to only. decrease in stroke volume cardiac output and blood pres 50 to 60 of the recumbent value In the absence of the. sure the resulting fall in cerebral blood flow would proba compensatory increase in sympathetic nerve activity. bly cause a loss of consciousness If the individual contin stroke volume would fall much more These cardiac adjust. ues to stand quietly for 30 minutes 20 of plasma volume ments maintain cardiac output at 60 to 80 of the recum. is lost by net filtration through the capillary walls of the bent value An increase in sympathetic activity also causes. legs Therefore quiet standing for half an hour without arteriolar constriction and increased SVR The effect of. compensation is the hemodynamic equivalent of losing a these compensatory changes in heart rate ventricular con. CLINICAL FOCUS BOX 18 1, Hypotension include vasodilation caused by alcohol vasodilating drugs. Baroreceptors volume receptors chemoreceptors and or fever cardiac disease e g cardiomyopathy valvular dis. pain receptors all help maintain adequate blood pressure ease or reduced blood volume secondary to hemorrhage. during various forms of hemodynamic stress such as dehydration or other causes of fluid loss In many patients. standing and exercise However in the presence of certain multiple causative factors are involved. cardiovascular abnormalities these mechanisms may fail The treatment of symptomatic hypotension is to elimi. to regulate blood pressure appropriately when this oc nate the underlying cause whenever possible which in. curs a person may experience transient or sustained hy some cases produces satisfactory results When this ap. potension As a practical definition hypotension exists proach is not possible other adjunctive measures may be. when symptoms are caused by low blood pressure and in necessary especially when the symptoms are disabling. extreme cases hypotension may cause weakness light Common treatment modalities include avoidance of fac. headedness or even fainting tors that can precipitate hypotension e g sudden. Hypotension may be due to neurogenic or nonneuro changes in posture hot environments alcohol certain. genic factors Neurogenic causes include autonomic dys drugs large meals volume expansion using salt supple. function or failure which can occur in association with other ments and or medications with salt retaining volume ex. central nervous system abnormalities such as Parkinson s panding properties and mechanical measures including. disease or may be secondary to systemic diseases that can tight fitting elastic compression stockings or pantyhose to. damage the autonomic nerves such as diabetes or amyloi prevent the blood from pooling in the veins of the legs. dosis vasovagal hyperactivity hypersensitivity of the upon standing Unfortunately even when these measures. carotid sinus and drugs with sympathetic stimulating or are employed some patients continue to have severe de. blocking properties Nonneurogenic causes of hypotension bilitating effects from hypotension. 300 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY, tractility and SVR is maintenance of mean arterial pressure to standing A more powerful activation of the barorecep. In fact mean arterial pressure may be increased slightly tor reflex as occurs during severe hemorrhage is required to. above the recumbent value cause significant venoconstriction However two other. How is increased sympathetic nerve activity maintained if mechanisms return blood from the legs to the central blood. the mean arterial pressure reaches a value near or above that volume The more important mechanism is the muscle. of the recumbent value In other words why doesn t the pump Fig 18 8 If the leg muscles periodically contract. sympathetic nerve activity return to recumbent levels if the while an individual is standing venous return is increased. mean arterial pressure returns to the recumbent value There Muscles swell as they shorten and this compresses adjacent. are two reasons First although the mean arterial pressure re veins Because of the venous valves in the limbs the blood. turns to the same level or even higher pulse pressure re in the compressed veins can flow only toward the heart. mains reduced because the stroke volume is decreased to 50 The combination of contracting muscle and venous valves. to 60 of the recumbent value As indicated earlier the fir provides an effective pump that transiently increases ve. ing rate of the baroreceptors depends on both mean arterial nous return relative to cardiac output This mechanism. and pulse pressures Reduced pulse pressure means the shifts blood volume from the legs to the central blood vol. baroreceptor firing rate is reduced even if the mean arterial ume and end diastolic volume is increased Even mild ex. pressure is slightly higher Second although mean arterial ercise such as walking returns the central blood volume. pressure is returned to the recumbent value central blood and stroke volume to recumbent values Fig 18 9. volume remains low Consequently the cardiopulmonary re The respiratory pump is the other mechanism that acts. ceptors continue to discharge at a lower rate leading to in to enhance venous return and restore central blood volume. creased sympathetic activity Some investigators believe it is Fig 18 10 Quiet standing for 5 to 10 minutes invariably. the decreased stretch of the cardiopulmonary receptors that leads to sighing This exaggerated respiratory movement. provides the primary steady state afferent information for the lowers intrathoracic pressure more than usually occurs with. reflex cardiovascular response to standing inspiration The fall in intrathoracic pressure raises the. The heart and brain do not participate in the arteriolar transmural pressure of the intrathoracic vessels causing. constriction caused by increased sympathetic nerve activity these vessels to expand Contraction of the diaphragm si. during standing therefore the blood flow and supply of oxy multaneously raises intraabdominal pressure which com. gen and nutrients to these two vital organs are maintained presses the abdominal veins Because the venous valves pre. vent the backflow of blood into the legs the raised. Muscle and Respiratory Pumps Help intraabdominal pressure forces blood toward the intratho. racic vessels which are expanding because of the lowered. Maintain Central Blood Volume, intrathoracic pressure The seesaw action of the respiratory.
Although standing would appear to be a perfect situation pump tends to displace extrathoracic blood volume toward. for increased venoconstriction which could return some of the chest and raise right atrial pressure and stroke volume. the blood from the legs to the central blood volume reflex Figure 18 11 provides an overview of the main cardiovascu. venoconstriction is a relatively minor part of the response lar events associated with a short period of standing. During Just after,contraction contraction,Just before. contraction,hydrostatic,Artery Vein,Arterial pressure Venous pressure. 90 93 mm Hg 90 10 mm Hg 90 93 mm Hg 20 10 mm Hg, FIGURE 18 8 Muscle pump This mechanism increases ve static column of blood lowering venous and capillary hydro. nous return and decreases venous volume The static pressure. valves which are closed after contraction break up the hydro. CHAPTER 18 Control Mechanisms in Circulatory Function 301. Prone Erect Walking,Arterial 110,blood pressure,Right atrial. mean pressure 0 2 5 1,Cardiac output,L min 5 SVR 16 21 16.
Stroke volume FIGURE 18 10 Respiratory pump Inspiration leads to an. mL increase in venous return and stroke volume, 50 Small type represents a secondary change that returns variables. toward the original values,blood volume 1 0,0 8 Capillary Filtration During Standing Further. Reduces Central Blood Volume, During quiet minimum muscular movement standing for. Heart rate 10 to 15 minutes the effects of the baroreceptor reflex on. beats min 70 the heart and arterioles are insufficient to prevent a contin. 60 ued decline in arterial pressure The decline in arterial pres. sure is caused by a steady loss of plasma volume as fluid fil. ters out of capillaries of the legs The hydrostatic column of. Forearm Total,blood flow 2 0,mL 100 Muscle,mL 1 min 1. Splanchnic,blood flow 1 0,0 2 4 6 8 10,FIGURE 18 9.
Effect of the muscle pump on central blood,volume and systemic hemodynamics The. center section shows the effects of a shift from the prone to the. upright position with quiet standing The right panel shows the. effect of activating the muscle pump by contracting leg muscles. Note that the muscle pump restores central blood volume and. cardiac output to the levels in the prone position The fall in heart. rate and rise in peripheral blood flow forearm splanchnic and. renal associated with activation of the muscle pump reflect the. reduction in baroreceptor reflex activity associated with increased. cardiac output RVEDP right ventricular end diastolic pressure. SVR systemic vascular resistance Modified from Rowell LB Hu. man Circulation Regulation During Physical Stress New York. Oxford University Press 1986,FIGURE 18 11,Cardiovascular events associated with. standing Small type represents compensatory, changes that return variables toward the original values 1 and. 1 refer to adrenergic receptor types,302 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY. blood above the capillaries of the legs and feet raises capil translocation of plasma volume into the interstitial space. lary hydrostatic pressure and filtration During a period of see Chapter 16 These factors together with neural and. 30 minutes a 10 loss of blood volume into the interstitial myogenic responses and the muscle and respiratory pumps. space can occur This loss coupled with the 550 mL dis play a significant role during the seconds and minutes fol. placed by redistribution from the central blood volume into lowing standing Fig 18 12 The combination of all of. the legs causes central blood volume to fall to a level so low these factors minimizes net capillary filtration making it. that reflex sympathetic nerve activity cannot maintain car possible to remain standing for long periods. diac output and mean arterial pressure Diminished cerebral. blood flow and a loss of consciousness fainting result. Arteriolar constriction due to the increased reflex sym Long Term Responses Defend Venous. pathetic nerve activity tends to reduce capillary hydrostatic Return During Prolonged Upright Posture. pressure However this alone does not bring capillary hy In addition to the relatively short term cardiovascular re. drostatic pressure back to normal because it does not affect sponses there are equally important long term adjustments. the hydrostatic pressure exerted on the capillaries from the to orthostasis These are observed in patients confined to. venous side The muscle pump is the most important factor bed or astronauts not subject to the force of gravity In. counteracting increased capillary hydrostatic pressure The people who are bedridden intermittent upright posture. alternate compression and filling of the veins as the muscle does not shift the distribution of blood volume from the. pump works means the venous valves are closed most of the thorax to the legs During the course of a day average cen. time When the valves are closed the hydrostatic column tral blood volume and pressure is greater than in a person. of blood in the leg veins at any point is only as high as the who is periodically standing up in the presence of gravity. distance to the next valve The average increase in central blood volume caused by ex. The myogenic response of arterioles to increased trans. mural pressure also acts to oppose filtration As discussed. earlier raising the transmural pressure stretches vascular. smooth muscle and stimulates it to contract This is espe Blood. cially true for the myocytes of precapillary arterioles The volume. Atrial Arterial, elevated transmural pressure associated with standing causes volume pressure.
a myogenic response and decreases the number of open cap. illaries With fewer open capillaries the filtration rate for a AVP ANP Medullary cardiovascular. center increased, given capillary hydrostatic pressure imbalance is less sympathetic nerve firing. In addition to the factors cited above other safety fac. tors against edema are important for preventing excessive. receptors receptors,vasoconstriction,Sodium load,distal tubules. Stretch of,Renin release afferent,arterioles,Angiotensin I Peritubular. Angiotensin II hydrostatic,Aldosterone Plasma,Sodium excretion. Water excretion Extracellular,fluid volume,Intake of sodium.
FIGURE 18 13 Regulation of blood volume Blood loss in. fluences sodium and water excretion by the, kidney via several pathways All these pathways combined with. an increased intake of salt and water restore the extracellular fluid. FIGURE 18 12 Effects of prolonged standing With pro volume and eventually blood volume These responses occur. longed standing capillary filtration reduces ve later than those shown in Figures 18 10 18 11 and 18 12 The. nous return Without the compensatory events that result in the pathways responsible for stimulating an increased intake of salt. changes shown in small type prolonged standing would in and water are not shown AVP arginine vasopressin ANP atrial. evitably lead to fainting natriuretic peptide GFR glomerular filtration rate. CHAPTER 18 Control Mechanisms in Circulatory Function 303. tended bed rest results in reduced activity of all of the path Aldosterone acts on the distal nephron to cause in. ways that increase blood volume in response to standing creased reabsorption of sodium and thereby decrease its. The reduction in total blood volume begins during the first excretion Aldosterone released from the adrenal cortex. day and is quantitatively significant after a few days At this is increased by among other things angiotensin II Wa. point standing becomes difficult because blood volume is ter intake is determined by thirst and the availability of. not adequate to sustain a normal blood pressure Looking at water. it another way maintaining an erect posture in the earth s The excretion of water is strongly influenced by AVP. gravitational field results in increased blood volume This Increased plasma osmolality sensed by the hypothalamus. increase proportioned between the extrathoracic and in results in both thirst and increased AVP release Thirst and. trathoracic vessels augments stroke volume during stand AVP release are also increased by decreased stretch of. ing If blood volume is not maintained by intermittent erect baroreceptors and cardiopulmonary receptors. posture standing becomes extremely difficult or impossible Consider how these physiological variables are al. because of orthostatic hypotension diminished blood tered by an upright posture to produce an increase in the. pressure associated with standing extracellular fluid volume Renal arteriolar vasoconstric. The long term regulation of blood volume is driven by tion associated with increased sympathetic nerve activ. changes in plasma volume accomplished by sympathetic ity produced by standing reduces the glomerular filtra. nervous system effects on the kidneys hormonal changes tion rate This results in a decrease in filtered sodium and. including RAAS AVP and ANP and alterations in pressure tends to decrease sodium excretion The increased sym. diuresis Figure 18 13 depicts several components of plasma pathetic nerve activity to the kidney also triggers the re. volume regulation by showing their response to a moderate lease of renin which increases circulating angiotensin II. approximately 10 blood loss which is easily compen and in turn aldosterone release The decrease in central. sated for in healthy individuals blood volume associated with standing reduces car. Plasma is a part of the extracellular compartment and is diopulmonary stretch receptor activity causing an in. subject to the factors that regulate the size of that space The creased release of AVP from the posterior pituitary. osmotically important electrolytes of the extracellular fluid Therefore both sodium and water are retained and thirst. are the sodium ion and its main partner the chloride ion The is increased Regulation of the precise quantities of wa. control of extracellular fluid volume is determined by the bal ter and sodium that are excreted maintains the correct. ance between the intake and excretion of sodium and water osmolality of the plasma. This topic is discussed in depth in Chapter 24 Sodium excre The distribution of extracellular fluid between plasma. tion is much more closely regulated than sodium intake Ex and interstitial compartments is determined by the balance. cretion of sodium is determined by the glomerular filtration of hydrostatic and colloid osmotic forces across the capil. rate the plasma concentrations of aldosterone and ANP and lary wall Retention of sodium and water tends to dilute. a variety of other factors including angiotensin II plasma proteins decreasing plasma colloid osmotic pres. Glomerular filtration rate is determined by glomerular sure and favoring the filtration of fluid from the plasma into. capillary pressure which is dependent on precapillary af the interstitial fluid However as increased synthesis of. ferent arteriolar and postcapillary efferent arteriolar re plasma proteins by the liver occurs a portion of the re. sistance and arterial pressure Decreased mean arterial pres tained sodium and water contributes to an increase in. sure and or afferent arteriolar constriction tends to result in plasma volume. lowered glomerular capillary pressure less filtration of Finally the increase in plasma volume in the absence of. fluid and lower sodium excretion Changes in glomerular any change in total red cell volume decreases hematocrit. capillary pressure are primarily the result of changes in which stimulates erythropoietin release and erythropoiesis. sympathetic nerve activity and plasma angiotensin II and This helps total red blood cell volume keep pace with. ANP concentrations plasma volume,REVIEW QUESTIONS, DIRECTIONS Each of the numbered B High sensitivity of arterioles to B Lower the heart rate below its. items or incomplete statements in this norepinephrine intrinsic rate. section is followed by answers or by C High sensitivity of arterioles to C Raise and lower the heart. completions of the statement Select the nitric oxide rate above and below its intrinsic. ONE lettered answer or completion that is D Low parasympathetic nerve rate. BEST in each case activity D Neither raise nor lower the heart. E Arterioles insensitive to rate from its intrinsic rate. 1 A person has cold painful fingertips epinephrine 3 The cold pressor response is initiated. because of excessively constricted 2 In the presence of a drug that blocks by stimulation of. blood vessels in the skin Which of all effects of norepinephrine and A Baroreceptors. the following alterations in autonomic epinephrine on the heart the B Cardiopulmonary receptors. function is most likely to be involved autonomic nervous system can C Hypothalamic receptors. A Low concentration of circulating A Raise the heart rate above its D Pain receptors. epinephrine intrinsic rate E Chemoreceptors,304 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY. 4 Which of the following occurs when heart accompanied by a withdrawal of D Lying down. acetylcholine binds to muscarinic sympathetic tone to most of the blood E Living in a space station. receptors vessels of the body is characteristic of. A Heart rate slows A The fight or flight response SUGGESTED READING. B Cardiac conduction velocity rises B Vasovagal syncope Champleau MW Arterial baroreflexes In. C Norepinephrine release from C Exercise Izzo JL Black HR eds Hypertension. sympathetic nerve terminals is D The diving response Primer Baltimore Lippincott Williams. enhanced E The cold pressor response Wilkins 1999, D Nitric oxide release from 8 A patient suffers a severe hemorrhage Dampney RA Functional organization of. endothelial cells is inhibited resulting in a lowered mean arterial central pathways regulating the cardio. E Blood vessels of the external pressure Which of the following vascular system Physiol Rev. genitalia constrict would be elevated above normal levels 1994 74 323 364. 5 Carotid baroreceptors A Splanchnic blood flow Hainsworth R Mark AL eds Cardiovascu. A Are important in the rapid short B Cardiopulmonary receptor activity lar Reflex Control in Health and Dis. term regulation of arterial blood C Right ventricular end diastolic ease London WB Saunders 1993. pressure volume Katz AM Physiology of the Heart 3rd. B Do not fire until a pressure of D Heart rate Ed New York Lippincott Williams. approximately 100 mm Hg is reached E Carotid baroreceptor activity Wilkins 2001. C Adapt over 1 to 2 weeks to the 9 A person stands up Compared with Mohanty PK Cardiopulmonary barore. prevailing mean arterial pressure the recumbent position 1 minute after flexes In Izzo JL Black HR eds Hy. D Stretch reflexively decreases standing the pertension Primer Baltimore Lippin. cerebral blood flow A Skin blood flow increases cott Williams Wilkins 1999. E Reflexively decrease coronary B Volume of blood in leg veins Reis DJ Functional neuroanatomy of cen. blood flow when blood pressure falls increases tral vasomotor control centers In Izzo. 6 Which of the following is true with C Cardiac preload increases JL Black HR eds Hypertension. respect to peripheral chemoreceptors D Cardiac contractility decreases Primer Baltimore Lippincott Williams. A Activation is important in E Brain blood flow decreases Wilkins 1999. inhibiting the diving response 10 Pressure diuresis lowers arterial Rowell LB Human Cardiovascular Con. B Activity is increased by increased pressure because it trol New York Oxford University. pH A Lowers renal release of renin Press 1993, C They are located in the medulla B Lowers systemic vascular resistance Waldrop TG Eldridge FL Iwamoto GA.
oblongata but not the hypothalamus C Lowers blood volume Mitchell JH Central neural control of. D Activation is important in the D Causes renal vasodilation respiration and. cardiovascular response to E Increases baroreceptor firing circulation during exercise In Rowell LB. hemorrhagic hypotension 11 Central blood volume is decreased by Shepherd JT eds Handbook of Physi. E Activity is increased by lowering A The muscle pump ology Section 12 Exercise Regulation. of the oxygen content but not the B The respiratory pump and integration of multiple systems. PO2 of arterial blood C Increased excretion of salt and New York Oxford University Press. 7 Parasympathetic stimulation of the water 1996,CASE STUDIES FOR PART IV. CASE STUDY FOR CHAPTER 11 Answers to Case Study Questions for Chapter 11. 1 The disease chronic granulomatous disease of child. Chronic Granulomatous Disease of Childhood hood results from a congenital lack of the superoxide. An 18 month old boy with a high fever and cough and forming enzyme NADPH oxidase in this patient s neu. with a history of frequent infections was brought to the trophils The lack of this enzyme results in deficient. emergency department by his father A blood examina hydrogen peroxide generation by these cells when they. tion shows elevated numbers of neutrophils but no ingest or phagocytose bacteria resulting in a compro. other defects A blood culture for bacteria is positive mised capacity to combat recurrent life threatening bac. The physician sent a sample of the boy s blood to a labo terial infections. ratory to test the ability of the patient s neutrophils to 2 Normal neutrophil stem cells grown in culture may be in. produce hydrogen peroxide The ability of this patient s fused to supplement the patient s own defective neu. neutrophils to generate hydrogen peroxide is found to trophils In addition researchers are now trying to geneti. be completely absent cally reverse the defect in cultures of a patient s stem. cells for subsequent therapeutic infusion, 1 What cellular defect may have led to the complete absence Reference. of hydrogen peroxide generation in this patient s neu Baehner RL Chronic granulomatous disease of childhood. trophils Clinical pathological biochemical molecular and genetic. 2 How might this disease be treated using hematotherapy aspects of the disease Pediatr Pathol 1990 10 143 153.

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