Capítulo 3 Arquitectura de los teléfonos celulares
3.6. Estructura de la Red
c.F– Post-exercise hyperaemia lasts several minutes, as the metabolic debt is repaid and vasodilator metabolites, lactate, etc., are cleared from the muscle(Figures 13.4 and 13.12).
d.T– The sustained intramuscle tension during an isometric contraction compresses the blood vessels within the muscle. Consequently, lactate accumulates quickly and the static compression cannot be maintained for a very long period.
13.11 a.T– This is called reactive or post-ischaemic hyperaemia(Figure 13.12). It is caused by the myogenic response and the accumulation of vasodilator metabolites in the tissue during the period without blood flow.
b.T– Clamping an artery for a long period during surgery can lead to poor reperfusion.
c.T– After a prolonged obstruction of flow, the ischaemic endothelium expresses leukocyte-binding selectins (Figure 9.7). Leukocytes are stiff and, when bound to the wall of small vessels, they act as obstacles to flow.
d.F– Oxygen radicals are highly toxic.They are generated from the reperfused O2by leukocyte NADPH oxidase and, in some tissues, xanthine oxidase.
e.F– Cardiac myocytes become overloaded with Ca2⫹during ischaemia.This is due to reduced Na⫹–K⫹–ATPase pumping, and hence reduced Ca2⫹extrusion by the Na⫹–Ca2⫹exchanger(Figure 6.18).The rise in Ca2⫹can lead to cardiac myocyte contracture and cell damage during reperfusion.
13.12 a. From Darcy’s law, flow⫽ arterio-venous pressure difference/resistance ⫽ pressure difference⫻ conductance.Therefore conductance is flow/pressure difference, namely 9 ml min⫺1/(95⫺ 5) mmHg.The answer is 0.1 ml min⫺1mmHg⫺1.
b. If the circulation consisted of non-expandable plastic tubes, flow would increase linearly with pressure, moving up the line of fixed conductance in Figure 1.5. A 50% increase in pressure difference would raise flow by 50% to 13.5 ml min⫺1. From Darcy’s law,
flow⫽ pressure difference ⫻ conductance ⫽ (140 ⫺ 5) mmHg ⫻ 0.1 ml min⫺1mmHg⫺1⫽ 13.5 ml min⫺1.
c. From Darcy’s law, the actual conductance of the resting muscle at 140 mmHg ABP was flow/pressure difference⫽ 10 ml min⫺1/(140⫺ 5) mmHg ⫽ 0.074 ml min⫺1mmHg⫺1. The conductance (slope of line in Figure 13.5a) has fallen substantially, greatly limiting the rise in flow.The reduced slope of the dashed lines in Figure 13.9are an example of this.
The fall in conductance is caused by the myogenic response of resistance vessels to a rise in ABP, resulting in autoregulation (stabilization) of blood flow.
d. In the exercising muscle, conductance⫽ flow/pressure difference ⫽ 135 ml min⫺1/ (140⫺ 5) mmHg ⫽ 1.0 ml min⫺1mmHg⫺1. Flow has increased because resistance vessel vasodilatation has raised the vascular conductance.This phenomenon is called metabolic hyperaemia (exercise hyperaemia, active hyperaemia).
88 Cardiovascular physiology Answers
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14.1 The sympathetic vasoconstrictor system
a. has short preganglionic fibres that release acetylcholine. 䊐 䊐
b. has long postganglionic fibres that release adrenaline. 䊐 䊐
c. has preganglionic neurons located chiefly in the cervical spinal cord. 䊐 䊐
d. is tonically excited by bulbospinal fibres originating in the ventrolateral medulla. 䊐 䊐
e. innervates the inner tunica media of arterial blood vessels. 䊐 䊐
14.2 Sympathetic postganglionic vasomotor fibres
a. terminate in motor-end plates, similar to those in skeletal muscle. 䊐 䊐
b. are normally quiescent in a resting subject. 䊐 䊐
c. activateα-adrenoceptors on blood vessels. 䊐 䊐
d. activate P2xpurinergic receptors on some blood vessels. 䊐 䊐
e. ‘spill’ some noradrenaline into the circulation. 䊐 䊐
14.3 A rise in human sympathetic vasomotor fibre activity
a. can raise arterial blood pressure. 䊐 䊐
b. enhances local blood flow through a tissue. 䊐 䊐
c. increases the capillary filtration rate. 䊐 䊐
d. reduces the splanchnic venous blood volume. 䊐 䊐
e. in skin can occur at the same time as sympathetic activity falls in skeletal muscle. 䊐 䊐
14.4 Neurally mediated vasodilatation
a. can be achieved by reducing sympathetic vasomotor activity. 䊐 䊐
b. in skin may be brought about by increased sympathetic cholinergic activity. 䊐 䊐
c. in skin may be brought about by a C-fibre axon reflex. 䊐 䊐
d. in salivary glands is associated with parasympathetic activity and secretion. 䊐 䊐
e. by parasympathetic fibres contributes to vasodilatation in exercising muscle. 䊐 䊐
f. by parasympathetic fibres can cause penile erection. 䊐 䊐
14.5 An intravenous infusion of adrenaline
a. causes active constriction of resistance vessels in skeletal muscle. 䊐 䊐
b. causes active constriction of resistance vessels in the skin. 䊐 䊐
c. raises total peripheral resistance. 䊐 䊐
d. raises systolic blood pressure more than diastolic pressure. 䊐 䊐
e. elicits tachycardia, whereas intravenous noradrenaline causes bradycardia. 䊐 䊐
f. reduces plasma glucose concentration. 䊐 䊐
CHAPTER 14
Control of blood vessels:
II. Extrinsic control by nerves
and hormones
14.6 Noradrenaline
a. is stored in the vesicles of sympathetic varicosities. 䊐 䊐
b. is formed from adrenaline by methyltransferase. 䊐 䊐
c. raises mean blood pressure. 䊐 䊐
d. increases cutaneous blood flow. 䊐 䊐
e. has a greater affinity for α- than β-adrenoceptors. 䊐 䊐
14.7 Vasopressin
a. is a peptide synthesized by the posterior pituitary gland. 䊐 䊐
b. is mainly a stimulus for water excretion. 䊐 䊐
c. release is triggered by a rise in plasma osmolarity. 䊐 䊐
d. release is reduced following a haemorrhage. 䊐 䊐
e. secretion during nausea contributes to the grey pallor of skin. 䊐 䊐
14.8 The renin–angiotensin system
a. is activated by angiotensinogen secreted by juxtaglomerular cells. 䊐 䊐
b. is stimulated following a loss of blood. 䊐 䊐
c. depends on endothelium to generate angiotensin II. 䊐 䊐
d. can induce vasoconstriction. 䊐 䊐
e. generally shows reduced activity in patients with hypertension. 䊐 䊐
14.9 Aldosterone secretion
a. promotes NaCl reabsorption in the distal renal tubule. 䊐 䊐
b. is stimulated by a fall in plasma angiotensin II concentration. 䊐 䊐
c. is increased following a major haemorrhage. 䊐 䊐
d. falls in response to a low salt diet. 䊐 䊐
e. rises during pregnancy. 䊐 䊐
14.10 The natriuretic peptide
a. ANP (atrial natriuretic peptide) is secreted by atrial myocytes when cardiac
filling pressure falls. 䊐 䊐
b. ANP lowers blood pressure by both natriuresis and resistance vessel
dilatation. 䊐 䊐
c. ANP increases plasma volume by reducing capillary and venular
filtration rates. 䊐 䊐
d. BNP (brain natriuretic peptide) is produced in the brain, but not the heart. 䊐 䊐
e. BNP can increase 200-fold in the circulation during heart failure. 䊐 䊐
14.11 Regarding the control of veins,
a. peripheral venoconstriction can enhance cardiac filling pressure. 䊐 䊐
b. splanchnic veins are poorly innerved by sympathetic vasoconstrictor fibres. 䊐 䊐
c. skeletal muscle veins are well innervated by sympathetic vasoconstrictor
fibres. 䊐 䊐
d. cutaneous veins are reflexly constricted during moderate exercise. 䊐 䊐
e. veins dilate markedly in response to glyceryl trinitrate. 䊐 䊐
90 Cardiovascular physiology Questions
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Here, for a change, is a data interpretation problem.The question is based on a true experiment.
14.12 Regarding the human alerting response, a resting student had a heart rate of 70 minⴚ1, brachial artery blood pressure 125/80 mmHg, forearm blood flow 8 ml minⴚ1(100 g)ⴚ1and hand blood flow 10 ml minⴚ1(100 g)ⴚ1. The sly experimenter then deliberately frightened the student. Within 120 seconds the parameters had changed to 140 minⴚ1, 150/90 mmHg, forearm 48 ml minⴚ1(100 g)ⴚ1and hand 7 ml minⴚ1(100 g)ⴚ1.
a. How might forearm blood flow have been measured, and what tissue does the flow mainly represent?
b. What were the mean arterial blood pressures at rest and when the student was alarmed?
c. How do you explain the failure of blood pressure to increase as much as the heart rate, which doubled?
d. What mechanism is most likely to account for the 6-fold increase in forearm blood flow?
e. How do you account for the fall in hand blood flow at a time when arterial pressure and forearm flow were increasing?