Guyton and Hall Physiology Chapter 19 - Role of the Kidneys in Long-Term Control of Arterial Pressure and in Hypertension

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Questions and Answers

What characterizes the second stage in volume-loading hypertension?

High blood pressure and high total peripheral resistance (correct)

Low blood pressure and high cardiac output

High blood pressure and elevated cardiac output

Normal blood pressure and low total peripheral resistance

In volume-loading hypertension, what happens to total peripheral resistance after hypertension develops?

It increases as a secondary response to hypertension (correct)

It fluctuates randomly without a clear trend

It remains normal and unaffected

It decreases as a direct cause of hypertension

What measurement may often fail to detect in the second stage of volume-loading hypertension?

Abnormally elevated cardiac output (correct)

Total blood volume

Decreased peripheral resistance

Normal blood pressure ranges

Which factor is primarily secondary to hypertension in volume-loading hypertension?

Total peripheral resistance Signup and view all the answers

What mechanism is indicated to be ineffective in managing blood pressure in patients maintained with an artificial kidney?

Renal blood flow autoregulation Signup and view all the answers

How does renal function relate to hypertension in the context of volume-loading?

Renal function deteriorates leading to higher sodium retention Signup and view all the answers

What is a significant effect of elevated salt intake on arterial pressure?

Increases peripheral resistance and blood pressure Signup and view all the answers

What occurs in the initial weeks of volume-loading hypertension as indicated by the provided data?

Progressive changes in circulatory system variables Signup and view all the answers

What is the initial cause of hypertension in volume-loading hypertension?

Increased fluid volume causing increased cardiac output Signup and view all the answers

Which of the following is a consequence of elevated arterial pressure on kidney function?

Excretion of excess fluid Signup and view all the answers

After several weeks of volume loading, what change occurs to the extracellular fluid volume?

It returns almost completely to normal Signup and view all the answers

What effect does volume loading have on total peripheral resistance after several weeks?

It shows a marked increase Signup and view all the answers

What primarily mediates hypertension in the first stage of volume-loading hypertension?

Increased cardiac output Signup and view all the answers

Which of the following mechanisms is involved in renal autoregulation?

Regulation of glomerular filtration rate Signup and view all the answers

How does increased salt intake affect arterial pressure in the context of volume loading?

It contributes to increased fluid volume and subsequently hypertension Signup and view all the answers

During the progression of volume-loading hypertension, what happens to cardiac output?

It returns to normal levels Signup and view all the answers

Which statement accurately reflects a physiological adaptation in volume-loading hypertension?

Cardiac output and blood volume return to normal while total peripheral resistance remains elevated Signup and view all the answers

What role does increased cardiac output play in the context of hypertension?

It is a direct cause of hypertension Signup and view all the answers

What is the primary mechanism through which renal autoregulation influences blood flow?

Constriction of blood vessels when metabolic needs are exceeded Signup and view all the answers

How does increased salt intake primarily affect arterial pressure in the absence of impaired kidney function?

It usually does not significantly increase arterial pressure as kidneys eliminate excess salt Signup and view all the answers

What condition is characterized by chronic hypertension due to excess extracellular fluid accumulation?

Volume-loading hypertension Signup and view all the answers

What happens to total peripheral resistance when autoregulation mechanisms constrict blood vessels?

Total peripheral resistance increases as a response to reduced blood flow Signup and view all the answers

Which physiological process is disrupted when renal function is impaired, leading to chronic hypertension?

Impaired ability to eliminate excess salt and water Signup and view all the answers

What is the primary initial cause of hypertension related to body fluid volume?

Excess volume accumulation Signup and view all the answers

How does the autoregulation mechanism affect cardiac output in hypertension?

It returns cardiac output toward normal levels Signup and view all the answers

What is secondary to the initial increase in cardiac output during the development of hypertension?

Increase in total peripheral resistance Signup and view all the answers

What triggers the release of renin from the JG cells during low arterial pressure?

Pressure-sensitive baroreceptor response Signup and view all the answers

What is a consequence of allowing extracellular fluid volume to increase without intervention?

Hypertension inevitably develops Signup and view all the answers

What type of hypertension is characterized by excess aldosterone?

Volume-loading hypertension Signup and view all the answers

Which of the following factors contributes to the regulation of renin release during low sodium chloride levels?

Decreased sodium chloride delivery to macula densa Signup and view all the answers

In the context of hypertension, what role does the sympathetic nervous system play?

Stimulates renin release Signup and view all the answers

Which of the following is NOT a mechanism that leads to increased renin release?

Increased peripheral resistance Signup and view all the answers

What is the effect of sustained high peripheral resistance in hypertension?

Compensatory drop in cardiac efficiency Signup and view all the answers

What is a key characteristic of volume-loading hypertension?

Accumulation of excess salt in the body Signup and view all the answers

What effect does consuming 0.9% saline solution have on dogs with significant renal tissue removed?

Elevates mean arterial pressure Signup and view all the answers

What primary change occurs in circulatory function during the development of volume-loading hypertension?

Increase in total peripheral resistance Signup and view all the answers

How does excess salt intake influence arterial pressure?

It raises arterial pressure by causing fluid retention Signup and view all the answers

Which mechanism is primarily responsible for renal autoregulation in maintaining stable blood flow to the kidneys?

Myogenic response of the renal vasculature Signup and view all the answers

What initial change occurs in cardiovascular parameters when salt is accumulated in the body?

Increased arterial pressure Signup and view all the answers

Which of the following best describes the changes that occur during the initial phase of volume-loading hypertension?

Acute increase in cardiac output Signup and view all the answers

What influence does removing 35-45% of left kidney tissue have on arterial pressure?

Potentially raises arterial pressure Signup and view all the answers

How does prolonged sodium intake affect peripheral resistance over time?

Progressively increases peripheral resistance Signup and view all the answers

In the development of volume-loading hypertension, which of the following occurs after acute changes?

Secondary changes in circulatory function Signup and view all the answers

What is the response of the kidneys when excess fluid volume is present in the body?

They eliminate excess fluid. Signup and view all the answers

What is the equilibrium point in relation to long-term arterial pressure control?

The point at which water and salt output equals intake. Signup and view all the answers

What happens to the mean arterial pressure when the renal output of salt and water equals the intake?

It remains unchanged. Signup and view all the answers

What occurs when arterial pressure rises above the equilibrium point?

Excess fluid volume is eliminated. Signup and view all the answers

What principle explains the kidneys' capacity to manage long-term arterial pressure?

Near-infinite feedback gain principle. Signup and view all the answers

What physiological phenomenon describes the kidneys excreting excess fluid when arterial pressure rises?

Pressure diuresis Signup and view all the answers

How does the kidney respond to a significant increase in arterial pressure above normal levels?

Excretes excess fluid Signup and view all the answers

At what arterial pressure does the urine output of a hagfish become essentially zero?

50 mm Hg Signup and view all the answers

What is the relationship between blood volume and arterial pressure in hagfish?

Increased blood volume directly increases arterial pressure Signup and view all the answers

What is the primary purpose of the renal urinary output curve?

To describe renal function related to arterial pressure levels Signup and view all the answers

What happens to arterial pressure when total peripheral resistance increases acutely?

It increases immediately. Signup and view all the answers

Why does arterial pressure return to normal within a couple of days after an acute rise?

Renal resistance increases, causing pressure diuresis. Signup and view all the answers

What role do the kidneys play when there is an increase in arterial pressure?

They induce pressure natriuresis and diuresis. Signup and view all the answers

What primarily causes hypertension when total peripheral resistance increases?

Increased renal resistance. Signup and view all the answers

What happens to the equilibrium point for blood pressure control when vascular resistance is increased elsewhere in the body?

It is unaffected by changes in vascular resistance. Signup and view all the answers

Which mechanism is primarily responsible for the kidneys' response to increased arterial pressure?

Pressure diuresis and natriuresis in response to hemodynamic changes. Signup and view all the answers

What occurs immediately after an acute increase in total peripheral resistance?

Immediate increase in arterial pressure. Signup and view all the answers

If vascular capacity does not increase, how can increased extracellular fluid volume affect arterial pressure?

It can elevate arterial pressure primarily through increased cardiac output. Signup and view all the answers

What is the eventual effect of the kidneys' response to a sustained increase in arterial pressure?

Return of arterial pressure to its normal level. Signup and view all the answers

An increase in arterial pressure can cause the renal output of water to decrease.

False Signup and view all the answers

Pressure natriuresis refers to the increase in salt output in response to increased arterial pressure.

True Signup and view all the answers

The renal-body fluid system for arterial pressure control acts quickly but is less powerful than other mechanisms.

False Signup and view all the answers

Fluid intake and output must be precisely unbalanced for long-term survival.

False Signup and view all the answers

The renin-angiotensin mechanism is a significant refinement added to the renal-body fluid system over evolutionary stages.

True Signup and view all the answers

Drinking 0.9% saline solution instead of water significantly increases mean arterial pressure in dogs with removed renal tissue.

True Signup and view all the answers

In volume-loading hypertension, total peripheral resistance decreases over time.

False Signup and view all the answers

The kidneys play a role in controlling long-term arterial pressure by excreting excess fluid when arterial pressure is high.

True Signup and view all the answers

The removal of 35-45% of left kidney tissue has no impact on arterial pressure.

False Signup and view all the answers

Secondary changes in circulatory function occur immediately after the development of volume-loading hypertension.

False Signup and view all the answers

In the second stage of volume-loading hypertension, cardiac output is significantly lower than normal.

False Signup and view all the answers

Total peripheral resistance is a primary cause of hypertension in volume-loading hypertension.

False Signup and view all the answers

Volume-loading hypertension can occur in patients without any kidney function.

True Signup and view all the answers

In volume-loading hypertension, hypertension is a result of increased cardiac output.

False Signup and view all the answers

The second stage of volume-loading hypertension is characterized by low total peripheral resistance.

False Signup and view all the answers

Hypertension in volume-loading hypertension develops before any peripheral resistance changes occur.

True Signup and view all the answers

The typical techniques used to measure cardiac output are often unable to detect changes during the second stage of volume-loading hypertension.

True Signup and view all the answers

In individuals with volume-loading hypertension, elevated blood pressure and increased peripheral resistance typically occur together.

True Signup and view all the answers

Cardiac output remains chronically elevated in patients experiencing volume-loading hypertension.

False Signup and view all the answers

Progressive changes in circulatory variables during volume-loading hypertension are uncomplicated and linear.

False Signup and view all the answers

Match the following terms related to arterial pressure and kidney function:

Arterial Pressure = The force exerted by circulating blood on the walls of blood vessels Pressure Diuresis = Increased urine output due to elevated arterial pressure Equilibrium Point A = Stable level of arterial pressure when no intake change occurs Renal Output = The amount of fluid excreted by the kidneys Signup and view all the answers

Match the following effects with the corresponding conditions:

Increased Blood Volume = Causes a rise in arterial pressure Urinary Output = Increases dramatically with high arterial pressure Cardiac Output = Returns to normal after fluid loss Fluid Loss = Can lead to a decrease in arterial pressure over time Signup and view all the answers

Match the following concepts in volume-loading hypertension:

Volume-Loading Hypertension = Characterized by increased extracellular fluid volume Renin Release = Stimulated by low arterial pressure Sodium Intake = Directly affects arterial pressure and renal function Cardiac Function = May initially increase before adjusting to hypertension Signup and view all the answers

Match the following terms about renal response to arterial pressure changes:

Excretion of Excess Fluid = Occurs when arterial pressure rises Kidneys' Role = Maintaining long-term arterial pressure control Nervous Control Mechanisms = Block adaptation during fluid loss Salt and Water Intake = Influences equilibrium point A Signup and view all the answers

Match the following points on the arterial pressure–renal urinary output curve:

Point A = Normal arterial pressure level without intake change Point B = Arterial pressure increases to approximately 150 mm Hg Infusion Period = Time during which fluid adjustment occurs Urine Output Increase = Indicated by curve response to arterial pressure rise Signup and view all the answers

Match the following terms with their definitions in the context of arterial pressure control:

Pressure diuresis = Increased renal output of water due to rising arterial pressure Pressure natriuresis = Increased renal output of salt due to rising arterial pressure Renin-angiotensin mechanism = A hormonal system that regulates blood pressure and fluid balance Long-term control = Regulation of arterial pressure over weeks and months Signup and view all the answers

Match the following physiological processes with their functions:

Fluid intake = Maintains balance in body fluid volume Fluid output = Regulates the excretion of excess salts and water Renal autoregulation = Maintains stable blood flow to the kidneys Arterial pressure regulation = Controls blood pressure through various mechanisms Signup and view all the answers

Match the following consequences with their respective triggers in blood pressure regulation:

Increased arterial pressure = Stimulates pressure diuresis Increased salt intake = Leads to elevated arterial pressure Fluid overload = Triggers the kidneys to excrete excess fluids Low arterial pressure = Stimulates renin release from JG cells Signup and view all the answers

Match the following concepts with their significance in the renal–body fluid system:

Homeostasis = Balance of fluid intake and output Arterial pressure control = Essential for long-term survival Kidneys = Organs responsible for fluid and salt regulation Hormonal control = Affects kidney function and pressure regulation Signup and view all the answers

Match the following mechanisms with their descriptions:

Nervous control = Involves immediate responses to pressure changes Hormonal controls = Involves long-term adjustments in body fluid balance Local control systems = Regulate kidney function based on local conditions Integrated system = Combines various controls for effective pressure regulation Signup and view all the answers

Study Notes

Stages of Volume-Loading Hypertension

Stage 1: Increased blood volume leads to elevated cardiac output, resulting in high blood pressure.
Stage 2: Total peripheral resistance increases after hypertension develops. While cardiac output returns to normal, the increased resistance sustains the high blood pressure.

Volume-Loading Hypertension in Patients with No Kidneys

Artificial Kidney Maintenance: When patients have no kidneys but are maintained with an artificial kidney, the increased blood pressure causes the kidneys to excrete excess fluid.
Consequences: Over time, this leads to:
- Hypertension
- Increased total peripheral resistance
- Return of normal extracellular fluid volume, blood volume, and cardiac output

Volume-Loading Hypertension: Causes and Mechanisms

Increased Fluid Volume: Excess fluid accumulation, potentially from drinking excessive fluids or consuming a salty diet, raises the blood pressure.
Cardiac Output: The increased volume initially causes a rise in cardiac output, which directly contributes to the increased pressure.
Autoregulation: Once the hypertension has developed, the body’s autoregulation mechanisms return the cardiac output to normal.
Total Peripheral Resistance: This shift in cardiac output causes a secondary increase in total peripheral resistance, perpetuating the hypertension.

Consequences of Salt Intake and Renal function

Salt Intake: Excess salt intake in individuals with healthy kidneys typically doesn’t lead to significant blood pressure elevation. This is due to the ability of the kidneys to quickly eliminate the extra salt.
Impaired Renal Function: However, when kidney function is impaired, the excess salt accumulates in the body.
Hormonal Effects: Excessive levels of antinatriuretic hormones, such as aldosterone, can also cause sodium retention and contribute to hypertension.

Renin Release and Pressure Regulation

Renin Release: Renin is an enzyme released by the juxtaglomerular (JG) cells in the kidneys, which plays a key role in regulating blood volume and pressure.
Stimuli for Renin Release:
- Decreased pressure in the kidney
- Decreased sodium chloride delivery to the macula densa cells in the distal tubule
- Increased sympathetic nervous system activity

Role of the Renin-Angiotensin-Aldosterone System (RAAS)

RAAS: This system contributes to blood pressure regulation by influencing salt and water retention.
Aldosterone: The mineralocorticoid hormone aldosterone, produced by the adrenal glands, stimulates sodium retention in the kidneys and plays a critical role in fluid balance.
Hypertension: Excess aldosterone can lead to volume-loading hypertension by increasing blood volume.

Autoregulation and Tissue Blood Flow

Autoregulation: Local tissues regulate their blood flow independently of the body’s overall circulatory needs. When blood flow increases, the tissue constricts blood vessels to maintain a stable flow.
Systemic Effects: Increased blood volume causes increased flow to all tissues. If this flow exceeds the tissues’ metabolic needs, the autoregulation mechanism constricts blood vessels across the entire body. This systemic constriction contributes to increased total peripheral resistance.

Importance of Maintaining Normal Fluid Volume

Dialysis Patients: In individuals with no kidneys, regular dialysis is crucial to maintain normal fluid volume and prevent hypertension.
Volume Control: Without proper fluid volume control, these patients experience the same sequence of events as in volume-loading hypertension, starting with increased cardiac output followed by a secondary increase in peripheral resistance.

Blood Pressure and Fluid Volume

Increased blood volume raises arterial pressure unless vascular capacitance also increases.
Kidneys excrete excess volume to maintain normal pressure.
Pressure diuresis: Increased urine output due to rising arterial pressure.
Pressure natriuresis: Increased sodium output as arterial pressure rises.

Renal-Body Fluid System for Pressure Control

Primitive pressure control in hagfish.
Hagfish drink seawater, increasing blood volume and pressure.
Kidneys excrete excess fluid to regulate pressure.
System has evolved to include nervous system, hormones, and local control mechanisms.

Kidney Function and Arterial Pressure Control

Renal output curve: Relates kidney's output of water and salt to arterial pressure.
Equilibrium point: Intersection of renal output curve and intake curve; where output equals intake.
Arterial pressure adjusts to reach the equilibrium point over time.
Increasing total peripheral resistance can temporarily raise pressure, but kidneys will compensate.

Hypertension: Increased Fluid Volume

Hypertension can occur when extracellular fluid volume rises.
Initial cause: Increased cardiac output
Secondary effect: Increased total peripheral resistance.
High peripheral resistance hypertension is often the final result of increased fluid volume.

Hypertension: Excess Aldosterone

Aldosterone excess can lead to hypertension due to sodium and water retention.
Sodium and water retention further increases blood volume and pressure.

Renin-Angiotensin System and Blood Pressure

Renin-Angiotensin System helps regulate blood pressure.
Renin released by the kidneys due to:
- Decreased arterial pressure
- Decreased sodium chloride delivery
- Increased sympathetic nervous system activity
Angiotensin II constricts renal arterioles, leading to:
- Reduced blood flow in kidneys
- Increased fluid reabsorption
Angiotensin II stimulates aldosterone secretion, further increasing sodium and water retention.
Renin-Angiotensin system plays a key role in short-term blood pressure regulation.

Renal-Body Fluid System for Arterial Pressure Control

The renal-body fluid system is a powerful mechanism for long-term arterial pressure control.
It acts slowly but effectively by regulating the balance between fluid intake and output.
This system is crucial for maintaining homeostasis of body fluid volume.
The kidneys, through local control systems, regulate the excretion of salt and water for long-term pressure regulation.
An example of this system in action is the "pressure diuresis" phenomenon.
A small increase in arterial pressure can double the renal output of water and salt.
Humans, similar to hagfish, possess this essential renal-body fluid system for long-term arterial pressure control.
Over time, the system has evolved with refinements, including the renin-angiotensin mechanism, making it more precise.

Quantitation of Pressure Diuresis and Arterial Pressure Control

Studies involving volume-loading hypertension have provided valuable insights into long-term arterial pressure regulation.
In these studies, excess salt and water intake lead to an increase in extracellular ﬂuid volume.
This excess fluid is gradually excreted, raising arterial pressure until the excess salt and water are eliminated.
Experiments using dogs with partial nephrectomy (kidney removal) demonstrate the impact of renal function on arterial pressure.
Removing 35-45% of the left kidney or the entire right kidney results in a significant increase in arterial pressure.
This increase is sustained over several days, indicating the role of the kidneys in regulating long-term arterial pressure.

Sequential Changes in Circulatory Function During Volume-Loading Hypertension

During the development of volume-loading hypertension, specific circulatory changes occur over time.
Initially, there is an increase in extracellular fluid volume, leading to a rise in cardiac output and a slight decrease in total peripheral resistance.
As the hypertension progresses, the cardiac output returns to near-normal levels, while total peripheral resistance progressively increases.
This increase in total peripheral resistance is a secondary response to hypertension, not its cause.

Role of the Renin-Angiotensin System in Arterial Pressure Control

The renin-angiotensin system is another powerful mechanism for regulating arterial pressure, complementing the kidneys' role in fluid balance.
Renin, an enzyme released by the kidneys, activates the renin-angiotensin system when arterial pressure falls.
This system helps restore pressure by increasing blood volume and constricting blood vessels.

Components of the Renin-Angiotensin System

Renin is produced and stored in the juxtaglomerular cells (JG cells) of the kidneys.
JG cells are specialized smooth muscle cells located in the walls of the afferent arterioles leading to the glomeruli.
The renin-angiotensin system works through a series of steps:
- Renin converts angiotensinogen (a precursor protein) into angiotensin I.
- Angiotensin I is further converted into angiotensin II by an enzyme in the lungs.
- Angiotensin II, the active hormone, causes vasoconstriction, increases renal salt and water retention, and ultimately raises arterial pressure.

Hypertension in Preeclampsia

Preeclampsia, also known as toxemia of pregnancy, is a complex condition characterized by high blood pressure.
It affects 5% to 10% of expectant mothers and typically subsides after delivery.
While the exact causes of preeclampsia are not fully understood, ischemia (lack of blood flow) to the placenta is believed to play a role.
This placental ischemia releases toxic factors that can contribute to endothelial dysfunction.
Endothelial dysfunction, in turn, impairs nitric oxide production, leading to vasoconstriction, decreased renal filtration, and impaired pressure natriuresis, ultimately contributing to hypertension.

Renal-Body Fluid System for Arterial Pressure Control

Increase in arterial pressure above 150mm Hg causes a dramatic increase in renal output
This increase in pressure above the equilibrium point, causes pressure diuresis
Renal-body fluid system controls arterial pressure over long periods
Increase in extracellular fluid volume increases blood volume, mean circulatory filling, venous return, cardiac output, ultimately leading to increased arterial pressure.
Increase in arterial pressure causes increased renal excretion of salt and water
Autoregulation controls blood flow
Increases in cardiac output increase arterial pressure; one is direct increase in pressure; the other is an indirect effect of increasing peripheral vascular resistance.

Quantitation of Pressure Diuresis as a Basis for Arterial Pressure Control

Pressure diuresis is the increase in renal output of water in response to increased arterial pressure
Pressure natriuresis is the increase in renal output of salt in response to increased arterial pressure
When pressure rises above the equilibrium point, renal output increases
This system of pressure diuresis and natriuresis is fundamental to long-term arterial pressure control

Volume-Loading Hypertension

Increasing extracellular fluid volume and blood volume can lead to hypertension
The body regulates salt and water to control extracellular fluid volume
Increasing sodium causes thirst and increases antidiuretic hormone (ADH) secretion
Increases in ADH cause increased water reabsorption in the renal tubules, leading to reduced urine output and increased extracellular fluid volume.
Volume-loading hypertension results from increased blood volume and increased arterial pressure
Increased blood volume directly increases cardiac output, thus increasing pressure
Increased blood volume also causes a rise in total peripheral resistance, which indirectly increases pressure

Hypertension in Preeclampsia (Toxemia of Pregnancy)

Preeclampsia is a condition characterized by hypertension that develops during pregnancy
It occurs in about 5-10% of pregnancies and often subsides after delivery
Placental ischemia may trigger preeclampsia
Placental toxicity may cause dysfunction of the vascular endothelium
Endothelial dysfunction causes vasoconstriction, decreased glomerular filtration rate, impaired renal pressure natriuresis, and hypertension

Sequential Changes in Circulatory Function During Development of Volume-Loading Hypertension

Volume-loading hypertension causes increased blood volume and cardiac output, leading to increased arterial pressure
The kidneys eventually excrete the excess salt and water, returning arterial pressure to normal
Ischemic kidney tissue releases renin, which can initiate a cascade of events, including vasoconstriction and increased arterial pressure
When kidneys are ischemic, arterial pressure increases due to reduced pressure natriuresis and renin release
In later stages of volume-loading hypertension, increased peripheral resistance and structural changes in nephrons are observed
These structural changes contribute to sustained hypertension in these individuals.

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Description

This quiz explores the stages and mechanisms of volume-loading hypertension, particularly in patients without kidneys. Understand how increased blood volume affects blood pressure and the resulting physiological adaptations. Dive into the causes behind elevated total peripheral resistance and cardiac output changes.