Balance WK2 LG 3 Regulation of Arterial Pressure- Hormones, Pressure Natriuresis and Diuretics

What is the overall goal of blood-pressure regulation in this lecture?

Answer: Maintain effective circulating volume and blood pressure.

Extra Information:

• Multiple systems act over different time scales to accomplish this.

What equation relates blood pressure to cardiac output and total peripheral resistance?

Answer: BP = CO × TPR.

Extra Information:

• Cardiac output and vascular resistance are the major determinants of arterial pressure.

What determines cardiac output?

Answer: Heart rate × stroke volume.

Extra Information:

• CO = HR × SV.

What two major factors determine stroke volume in the BP review?

Answer: Preload and afterload.

Extra Information:

• Changes in circulating volume can therefore affect stroke volume and cardiac output.

What organ acts as the master controller of cardiovascular regulation?

Answer: Brain.

Extra Information:

• The autonomic nervous system regulates the heart, blood vessels, and kidneys.
• It influences heart rate, stroke volume, and total peripheral resistance.

What blood vessels are major determinants of total peripheral resistance?

Answer: Resistance arteries.

Extra Information:

• Their constriction increases resistance.
• Their dilation decreases resistance.

What factors regulate resistance arteries according to the lecture?

Answer: ANS, angiotensin II, and endothelial nitric oxide.

Extra Information:

• Remodeling or hypertrophy can also narrow the vascular lumen.

Which organs provide long-term control of blood volume and pressure?

Answer: Kidneys.

Extra Information:

• They regulate sodium and water balance.
• They respond to ANS, RAAS, ANP, and other signals.

How does vascular remodeling or hypertrophy affect blood pressure?

Answer: It can narrow the vascular lumen and increase resistance.

Extra Information:

• Resistance arteries are major determinants of total peripheral resistance.

What is the basic division of labor in blood-pressure regulation?

Answer: Neural mechanisms act rapidly, while renal-fluid mechanisms provide long-term control.

Extra Information:

• Hormonal and vascular mechanisms operate between these time scales.

What controls blood pressure within seconds to minutes?

Answer: Neural control.

Extra Information:

• Examples include the baroreflex, autonomic nervous system, and CNS ischemic response.

What mechanisms dominate BP control over minutes to hours?

Answer: Hormonal and vascular mechanisms.

Extra Information:

• RAAS, ADH, catecholamines, and vasoconstriction provide sustained support.

What mechanisms dominate BP regulation over hours to days and long term?

Answer: Renal sodium and water balance.

Extra Information:

• Pressure natriuresis and diuresis control blood volume.

What is the main purpose of rapid neural BP regulation?

Answer: Rapidly defend arterial pressure.

Extra Information:

• It does not necessarily replace lost circulating volume.

What ultimately replaces volume lost during hemorrhage?

Answer: Long-term renal and hormonal mechanisms.

Extra Information:

• Neural reflexes initially defend pressure.
• Sodium and water retention restore volume.

What is the CNS ischemic response?

Answer: An extreme sympathetic response to severe cerebral ischemia.

Extra Information:

• It is described as a “last-ditch” pressure-control mechanism.

At approximately what blood pressure does the CNS ischemic response become important in this lecture?

Answer: Below about 60 mm Hg.

Extra Information:

• Severe cerebral ischemia triggers an emergency survival response.

What happens to sympathetic activity during the CNS ischemic response?

Answer: It greatly increases.

Extra Information:

• The goal is to rapidly raise mean arterial pressure.

How does the CNS ischemic response affect heart rate?

Answer: Heart rate increases.

Extra Information:

• Sympathetic stimulation also increases contractility and stroke volume.

How does the CNS ischemic response affect cardiac contractility?

Answer: Contractility increases.

Extra Information:

• This helps increase stroke volume and cardiac output.

How does the CNS ischemic response affect systemic vascular resistance?

Answer: Systemic vascular resistance increases.

Extra Information:

• Strong sympathetic vasoconstriction produces this effect.

Trace the CNS ischemic response to increased MAP.

Answer: Severe cerebral ischemia → increased sympathetic activity → increased HR, contractility, CO, and SVR → increased MAP.

Extra Information:

• MAP rises because MAP = CO × SVR.

How does hypercapnia stimulate cardiovascular compensation?

Answer: It activates the central chemoreceptor pathway and increases sympathetic activity.

Extra Information:

• Respiratory abnormalities can therefore alter cardiovascular function.

How does hypoxia contribute to sympathetic activation?

Answer: It stimulates peripheral chemoreceptors.

Extra Information:

• This can further increase sympathetic activity.

Why can blood pressure changes in a hypoxic or hypercapnic patient not be viewed as purely cardiovascular?

Answer: Respiratory abnormalities can drive sympathetic cardiovascular compensation.

Extra Information:

• The lecture emphasizes respiratory failure/hypercapnia and severe hypotension/shock as examples.

What change most directly causes the transient BP increase in the severe-hypotension clinical case?

Answer: Increased stimulation of the medullary vasomotor center.

Extra Information:

• The patient has a BP of 52/30 mm Hg.

• This severe hypotension can activate the CNS ischemic response.

The medullary vasomotor center is a group of neurons in the medulla oblongata of the brain that regulates blood vessel diameter and blood pressure

What happens to blood volume after acute blood loss?

Answer: Blood volume decreases.

Extra Information:

• Arterial pressure also tends to decrease.

Which major hormonal system is activated by acute blood loss?

Answer: RAAS.

Extra Information:

• ANP activity decreases because atrial stretch is reduced.

What happens to renin during acute blood loss?

Answer: Renin increases.

Extra Information:

• Reduced renal perfusion activates the renin-angiotensin-aldosterone system.

What happens to angiotensin II during acute blood loss?

Answer: Angiotensin II increases.

Extra Information:

• Increased renin ultimately increases angiotensin II formation.

What happens to aldosterone during acute blood loss?

Answer: Aldosterone increases.

Extra Information:

• Angiotensin II promotes aldosterone secretion.

What happens to ADH during acute blood loss?

Answer: ADH increases.

Extra Information:

• This promotes water retention.

What happens to norepinephrine during acute blood loss?

Answer: Norepinephrine increases.

Extra Information:

• Sympathetic activation helps support arterial pressure.

What happens to renal Na⁺ reabsorption during acute blood loss?

Answer: It increases.

Extra Information:

• Sodium retention helps restore extracellular fluid and blood volume.

What happens to renal water reabsorption during acute blood loss?

Answer: It increases.

Extra Information:

• Water retention helps restore circulating volume.

What is the overall goal of the response to acute blood loss?

Answer: Restore perfusion.

Extra Information:

• RAAS and other volume-retaining systems increase blood volume and pressure toward normal.

What is the overall effect of RAAS on volume and pressure?

Answer: Volume up, pressure up.

Extra Information:

• RAAS promotes vasoconstriction and sodium and water retention.

What stimulates renin release in the RAAS diagram?

Answer: Decreased renal perfusion pressure.

Extra Information:

• Renin initiates the hormonal cascade.

What does renin act on?

Answer: Angiotensinogen.

Extra Information:

• This produces angiotensin I.

What enzyme converts angiotensin I to angiotensin II?

Answer: Angiotensin-converting enzyme.

Extra Information:

• ACE is one pharmacologic target for RAAS blockade.

How does angiotensin II affect total peripheral resistance?

Answer: It increases TPR through vasoconstriction.

Extra Information:

• This contributes directly to increased arterial pressure.

How does angiotensin II affect thirst?

Answer: It increases thirst.

Extra Information:

• Increased water intake helps restore extracellular fluid volume.

How does angiotensin II affect Na⁺ reabsorption?

Answer: It increases Na⁺ reabsorption.

Extra Information:

• Water follows retained sodium.

How does aldosterone contribute to the RAAS response?

Answer: It increases Na⁺ reabsorption.

Extra Information:

• This increases extracellular fluid volume.

What are the net effects of RAAS activation?

Answer: Increased extracellular fluid volume and increased blood pressure.

Extra Information:

• Both vascular and renal mechanisms contribute.

What are major targets for RAAS-blocking drugs shown in the lecture?

Answer: Renin, ACE, angiotensin II receptors, and aldosterone signaling.

Extra Information:

• Blocking RAAS reduces its volume- and pressure-raising effects.

What happens to blood pressure with RAAS blockade?

Answer: Blood pressure decreases.

Extra Information:

• Reduced vasoconstriction and sodium retention contribute.

What cardiovascular structural benefit is shown for RAAS blockade?

Answer: Reduced cardiac remodeling.

Extra Information:

• This is one of the net effects shown on the RAAS slide.

What renal benefit of RAAS blockade is shown in the lecture?

Answer: Reduced renal injury and slower progression of kidney disease.

Extra Information:

• This accompanies its blood-pressure-lowering effects.

What happens to atrial stretch after blood or fluid transfusion?

Answer: Atrial stretch increases.

Extra Information:

• Increased circulating volume stretches the atria.

Which hormone is released in response to increased atrial stretch?

Answer: ANP.

Extra Information:

• ANP is released from atrial myocytes.

What is the overall effect of ANP on volume and pressure?

Answer: Volume down, pressure down.

Extra Information:

• ANP opposes the major actions of RAAS.

Where are the low-pressure baroreceptors highlighted in the ANP slide?

Answer: Veins, atria, and pulmonary arteries.

Extra Information:

• Atrial stretch is especially important for ANP release.

Where is ANP produced?

Answer: Atrial myocytes.

Extra Information:

• Increased atrial stretch stimulates ANP release.

How does ANP affect vascular smooth muscle?

Answer: It causes vasodilation.

Extra Information:

• ANP binds NPR1 on vascular smooth muscle.

How does ANP affect total peripheral resistance?

Answer: It decreases TPR.

Extra Information:

• Vasodilation produces this effect.

How does ANP affect the afferent arteriole?

Answer: It dilates the afferent arteriole.

Extra Information:

• This contributes to increased GFR.

How does ANP affect the efferent arteriole?

Answer: It constricts the efferent arteriole.

Extra Information:

• Together with afferent dilation, this increases GFR.

How does ANP affect GFR?

Answer: It increases GFR.

Extra Information:

• This promotes greater sodium and water excretion.

How does ANP affect renal Na⁺ reabsorption?

Answer: It decreases Na⁺ reabsorption.

Extra Information:

• This occurs in the late distal tubule and collecting duct in the lecture diagram.

What is natriuresis?

Answer: Increased urinary Na⁺ excretion.

Extra Information:

• ANP promotes natriuresis.

What is diuresis?

Answer: Increased urinary water excretion.

Extra Information:

• ANP promotes both natriuresis and diuresis.

What is the net effect of ANP on extracellular fluid volume?

Answer: ECF volume decreases.

Extra Information:

• Increased Na⁺ and water excretion lowers blood volume.

What happens to RAAS after blood/fluid transfusion?

Answer: RAAS activity decreases.

Extra Information:

• Renin and aldosterone decrease as circulating volume increases.

What happens to ADH after volume expansion in the ANP-vs-RAAS comparison?

Answer: ADH decreases.

Extra Information:

• This favors water excretion.

What is the overall relationship between ANP and RAAS?

Answer: They are complementary opposing systems that return blood volume and pressure toward normal.

Extra Information:

• Low volume favors RAAS.
• High volume favors ANP.

What happens to ANP during acute blood loss?

Answer: ANP decreases.

Extra Information:

• Reduced volume produces less atrial stretch.

What happens to ANP during volume expansion?

Answer: ANP increases.

Extra Information:

• Increased atrial stretch is the major stimulus.

What is BNP primarily used to help evaluate clinically?

Answer: Acute heart failure in patients with dyspnea.

Extra Information:

• BNP is interpreted along with the rest of the clinical picture.

What does a low BNP suggest in a dyspneic patient?

Answer: Acute heart failure is less likely.

Extra Information:

• Increasing BNP levels support the diagnosis and tend to reflect greater severity.

What does pressure natriuresis mean?

Answer: Increased arterial pressure causes increased renal Na⁺ excretion.

Extra Information:

• This is a major mechanism of long-term BP control.

How do kidneys provide long-term stability of arterial pressure?

Answer: By controlling body-fluid and Na⁺ balance.

Extra Information:

• The lecture emphasizes that pressure natriuresis can function independently of hormonal influence.

How does a normal kidney respond to high salt intake?

Answer: Na⁺ excretion increases with almost no change in blood pressure.

Extra Information:

• Normal kidneys have excellent salt-excreting ability.

What characterizes a hypertensive but salt-resistant patient?

Answer: A higher baseline pressure is required, but salt causes relatively little additional BP increase.

Extra Information:

• This corresponds to Patient 1 on the pressure-natriuresis graph.

What characterizes salt-sensitive hypertension?

Answer: An impaired pressure-natriuresis response.

Extra Information:

• Salt loading causes a substantial increase in blood pressure.

What happens to blood pressure after salt loading in salt-sensitive hypertension?

Answer: Blood pressure rises substantially.

Extra Information:

• The kidneys require greater pressure to excrete the sodium load.

What does an impaired pressure-natriuresis relationship mean physiologically?

Answer: The kidney requires higher arterial pressure to excrete a given sodium load.

Extra Information:

• This can contribute to chronic hypertension.

What happens to effective circulating volume when sodium is retained?

Answer: It increases because water follows sodium.

Extra Information:

• Sodium balance is therefore closely related to ECF volume.

What do disorders of extracellular fluid volume usually reflect?

Answer: Problems with Na⁺ balance.

Extra Information:

• Edema is an example.

What do hypernatremia and hyponatremia primarily reflect according to the clinical pearl?

Answer: Problems with water balance.

Extra Information:

• Sodium concentration disorders are conceptually different from total-body sodium/ECF-volume disorders.

In bilateral renal artery stenosis, what happens to plasma renin activity?

Answer: It increases.

Extra Information:

• Reduced renal perfusion stimulates renin release.

In renal artery stenosis, what happens to angiotensin II and TPR?

Answer: Both increase.

Extra Information:

• Angiotensin II causes vasoconstriction.

Why does renal artery stenosis cause Na⁺ retention?

Answer: RAAS activation increases renal Na⁺ reabsorption.

Extra Information:

• This contributes to volume expansion and edema.

Why can ANP increase secondarily in renal artery stenosis?

Answer: RAAS-mediated volume expansion increases atrial stretch.

Extra Information:

• ANP acts as a compensatory opposing system.

What is the correct overall pattern in the renal-artery-stenosis case?

Answer: Increased renin, angiotensin II, TPR, Na⁺ retention, and compensatory ANP.

Extra Information:

• This corresponds to option C on the lecture slide.

How do most diuretics reach the renal tubular lumen?

Answer: Active secretion from blood into the proximal tubule.

Extra Information:

• Many diuretics are organic acids.

Which transporter is shown secreting many diuretics into the proximal tubule?

Answer: Organic anion transporter.

Extra Information:

• Active secretion concentrates the drug in tubular fluid.

Why is tubular secretion important for many diuretics?

Answer: It allows them to reach their luminal site of action.

Extra Information:

• Many diuretic targets are located on the luminal membrane.

How are diuretics commonly administered?

Answer: Orally, with IV administration also used.

Extra Information:

• The appropriate route depends on the clinical situation.

What are major clinical uses of diuretics?

Answer: Edema/volume overload, heart failure, hypertension, glaucoma/ICP, and selected other disorders.

Extra Information:

• Additional lecture examples include respiratory alkalosis, nephrolithiasis, and electrolyte disorders.

What is the immediate renal action by which diuretics lower BP?

Answer: Increased Na⁺ and water excretion.

Extra Information:

• Natriuresis and diuresis reduce body-fluid volume.

How does diuresis affect plasma volume?

Answer: Plasma volume decreases.

Extra Information:

• Loss of Na⁺ and water reduces extracellular fluid volume.

How does decreased plasma volume affect preload?

Answer: Preload decreases.

Extra Information:

• Venous return and end-diastolic volume decrease.

How does reduced preload affect stroke volume?

Answer: Stroke volume decreases.

Extra Information:

• This contributes to reduced cardiac output.

How does reduced stroke volume affect cardiac output?

Answer: Cardiac output decreases.

Extra Information:

• CO = HR × SV.

What is the short-term BP-lowering sequence produced by diuretics?

Answer: Na⁺/water loss → decreased plasma volume → decreased preload and SV → decreased CO → decreased MAP.

Extra Information:

• This is the immediate/short-term mechanism emphasized in the lecture.

What additional long-term effect helps diuretics lower BP?

Answer: Decreased peripheral vascular resistance.

Extra Information:

• Reduced arterial stiffness and improved endothelial function further support lower BP.

What is the example carbonic anhydrase inhibitor in the lecture?

Answer: Acetazolamide.

Extra Information:

• It acts in the proximal tubule.

Where do carbonic anhydrase inhibitors act?

Answer: Proximal tubule.

Extra Information:

• Carbonic anhydrase participates in bicarbonate reabsorption there.

What enzyme does acetazolamide inhibit?

Answer: Carbonic anhydrase.

Extra Information:

• This decreases bicarbonate reabsorption and H⁺ secretion.