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Questions and Answers
What is the primary function of the kidneys with respect to body fluids?
What is the primary function of the kidneys with respect to body fluids?
Which ion plays the most significant role in determining extracellular fluid volume?
Which ion plays the most significant role in determining extracellular fluid volume?
A patient is in negative sodium balance. Which of the following conditions is most likely to result?
A patient is in negative sodium balance. Which of the following conditions is most likely to result?
What does sodium ion balance refer to?
What does sodium ion balance refer to?
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If sodium ion excretion is less than ingestion, this could lead to which state?
If sodium ion excretion is less than ingestion, this could lead to which state?
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What is the relationship between ECF volume and plasma volume?
What is the relationship between ECF volume and plasma volume?
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Although sodium is the major cation of ECF, what is one thing it does NOT directly affect?
Although sodium is the major cation of ECF, what is one thing it does NOT directly affect?
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What happens to water when excess sodium is lost from the body?
What happens to water when excess sodium is lost from the body?
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Study Notes
Control of Plasma Volume
- The kidneys handle sodium ions to regulate extracellular fluid (ECF) volume.
- Handling sodium ions in the proximal convoluted tubule (PCT) involves glomerulotubular balance and ECF volume effects.
- Sodium ion reabsorption in the loop of Henle is a key process, though not solely through the countercurrent system.
- Sodium ion uptake occurs in both the early and late distal tubules.
- Hormones, sympathetic nerves, dopamine, and Starling forces regulate sodium chloride reabsorption.
- The renin-angiotensin system controls sodium uptake in response to blood pressure changes.
- The body's water is either intracellular or extracellular (composed of interstitial fluid and plasma).
- Extracellular fluid composition influences intracellular fluid.
- Kidneys regulate extracellular fluid composition, influencing intracellular composition.
Proximal Tubule Composition
- 65% of water and 67% sodium are reabsorbed
- 100% of glucose and amino acids are reabsorbed
- 90% of bicarbonate is reabsorbed
Loop of Henle Composition
- 25% of sodium and 15% of water are reabsorbed
Distal and Collecting Ducts Composition
- 20% of water, 8% of sodium, and 10% of bicarbonate are reabsorbed
- These processes maintain sodium ion balance.
Sodium Ion Balance
- Kidneys balance sodium ion excretion and ingestion daily.
- Sodium is the primary cation of ECF.
- Sodium ion concentration dictates ECF volume; this influences plasma, blood volume, and blood pressure.
- An excess of sodium ion excretion leads to negative sodium ion balance, resulting in reduced ECF volume and blood pressure.
ECF Expansion/Contraction
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Increased ECF volume is detected by sensors in the vascular system (volume/baroreceptors).
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Low-pressure baroreceptors in the atria and pulmonary vasculature signal the brainstem via the vagus nerve.
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This signaling reduces sympathetic nerve outflow and increases antidiuretic hormone (ADH) secretion, thus promoting water reabsorption.
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Kidneys increase NaCl and water excretion to reduce ECF volume if it increases. They decrease NaCl and water excretion to increase the ECF volume if it decreases.
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Changes in sodium concentration in the extracellular fluid do not generally affect extracellular fluid osmolarity.
Fluid Compartments
- Fluid is located intracellularly and extracellularly (composed of interstitial fluid and plasma)
- Extracellular fluid composition affects intracellular fluid
- Kidneys control extracellular fluid composition, allowing for changes in intracellular composition
Reference
- Textbook of medical physiology by Guyton & Hall, 9th edition.
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Description
This quiz covers the regulation of plasma volume through sodium ion handling by the kidneys, emphasizing the processes in the proximal convoluted tubule and loop of Henle. It also discusses the role of hormones and the renin-angiotensin system in sodium uptake, as well as the composition of extracellular and intracellular fluids. Test your understanding of these key renal functions.
