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Questions and Answers
What is the primary function of controlling ECF volume?
What is the primary function of controlling ECF volume?
What is the effect of increased osmotic pressure of the plasma on ADH secretion?
What is the effect of increased osmotic pressure of the plasma on ADH secretion?
Where are the osmoreceptors that sense changes in plasma osmolarity located?
Where are the osmoreceptors that sense changes in plasma osmolarity located?
What is the effect of decreased blood volume or blood pressure on ADH secretion?
What is the effect of decreased blood volume or blood pressure on ADH secretion?
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What is the function of angiotensin II in regulating ADH secretion?
What is the function of angiotensin II in regulating ADH secretion?
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What is the effect of ADH on the DCT and collecting ducts?
What is the effect of ADH on the DCT and collecting ducts?
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What is the primary site of ADH synthesis?
What is the primary site of ADH synthesis?
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What is the effect of changes in plasma composition on interstitial fluid composition?
What is the effect of changes in plasma composition on interstitial fluid composition?
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What stimulates the thirst center?
What stimulates the thirst center?
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What happens when the blood volume decreases in the atria and great veins?
What happens when the blood volume decreases in the atria and great veins?
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What is the effect of atrial natriuretic peptide on aldosterone secretion?
What is the effect of atrial natriuretic peptide on aldosterone secretion?
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What is the result of excessive water intake and inappropriate ADH secretion?
What is the result of excessive water intake and inappropriate ADH secretion?
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What is the effect of dehydration on ECF osmolarity?
What is the effect of dehydration on ECF osmolarity?
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What is the purpose of clearance of PAH in renal function tests?
What is the purpose of clearance of PAH in renal function tests?
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What is the result of isotonic fluid gain or loss?
What is the result of isotonic fluid gain or loss?
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What is the effect of atrial natriuretic peptide on Na⁺ reabsorption from renal tubules?
What is the effect of atrial natriuretic peptide on Na⁺ reabsorption from renal tubules?
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What is the result of excess water in the body on the ECF volume?
What is the result of excess water in the body on the ECF volume?
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What stimulates the thirst center in response to changes in plasma osmolarity?
What stimulates the thirst center in response to changes in plasma osmolarity?
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What is the effect of angiotensin II on the distal tubules and collecting ducts?
What is the effect of angiotensin II on the distal tubules and collecting ducts?
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What is the result of decreased ECF volume on the GFR?
What is the result of decreased ECF volume on the GFR?
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What is the role of the angiotensin-converting enzyme (ACE) in the renin-angiotensin-aldosterone system?
What is the role of the angiotensin-converting enzyme (ACE) in the renin-angiotensin-aldosterone system?
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What stimulates the secretion of renin from the juxtaglomerular cells?
What stimulates the secretion of renin from the juxtaglomerular cells?
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What is the effect of ADH on water reabsorption?
What is the effect of ADH on water reabsorption?
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What is the result of dryness of the mouth and pharyngeal mucous membrane on the thirst center?
What is the result of dryness of the mouth and pharyngeal mucous membrane on the thirst center?
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Study Notes
Fluid and Electrolyte Balance
- Body fluid balance is maintained by controlling ECF volume and osmolarity
- Plasma composition can be modified during circulation through the lungs and kidneys, affecting interstitial fluid composition
- Intracellular fluid composition can also be changed according to cell membrane permeability
Antidiuretic Hormone (ADH)
- Synthesized by the hypothalamus and secreted by the posterior pituitary gland
- Controlled by osmotic stimuli, volume stimuli, and the renin-angiotensin system
- Osmotic stimuli:
- Increased osmotic pressure of plasma sensed by osmoreceptors in the hypothalamus
- Significant changes in ADH secretion occur with 1% changes in plasma osmolarity
- Volume stimuli:
- Decreased blood volume or blood pressure stimulate ADH secretion via low-pressure receptors and baroreceptors
- Renin-angiotensin system:
- Angiotensin II acts on the anterior hypothalamus to stimulate ADH secretion
- ADH acts on V2 receptors to increase water permeability in the DCT and collecting ducts
Role of the Kidney in Regulating ECF Volume
- Excess water in the body:
- Increases ECF volume
- Increases arterial blood pressure
- Increases GFR
- Increases urinary excretion of Na+ and water
- Decreased water in the body:
- Decreases ECF volume
- Decreases arterial blood pressure
- Decreases GFR
- Decreases urinary excretion of Na+ and water
Renin-Angiotensin-Aldosterone System
- Decreased ECF volume:
- Stimulates juxtaglomerular cells
- Increases renin secretion
- Renin converts angiotensinogen to angiotensin I
- Angiotensin I is converted to angiotensin II by ACE
- Angiotensin II:
- Stimulates aldosterone hormone secretion
- Increases Na+ reabsorption from distal tubules and collecting ducts
- Stimulates ADH secretion
- Increases thirst
- Causes vasoconstriction
Thirst Mechanism
- Regulated by the hypothalamic thirst center in response to changes in plasma osmolarity and ECF volume
- Stimulated by:
- Changes in plasma osmolarity
- Decreased ECF volume
- Dryness of the mouth and pharyngeal mucous membrane
Volume Receptors
- Present in the atria and great veins
- When blood volume decreases, they cause:
- Increased sympathetic discharge to renal vessels and juxtaglomerular apparatus
- Increased ADH secretion
Atrial Natriuretic Peptide (ANP)
- Secreted from overstretched atrial muscles
- Decreases:
- Aldosterone secretion
- Renin secretion
- Angiotensin II secretion
- Na+ reabsorption from renal tubules
Disorders of ECF Osmolarity
- Overhydration:
- Gain of free water without solutes
- Decreased ECF osmolarity
- Cell swelling (water intoxication)
- Dehydration:
- Loss of free water without solutes
- Increased ECF osmolarity
- Cell shrinkage
- Isotonic fluid gain or loss:
- No water shift between ECF and ICF compartments
Evaluation of Renal Function Tests
- Tests for assessing renal blood flow:
- Whole renal blood flow using clearance of PAH
- Distribution of renal blood flow using radioactive xenon 133
- Tests for assessing GFR:
- Clearance of inulin or creatinine
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Description
Body fluid balance is maintained by controlling extracellular fluid volume and osmolarity to prevent cellular swelling or shrinkage.
