Questions and Answers
What is the primary function of the kidney in regards to body fluid tonicity?
What is the threshold value of blood osmolality that triggers an increase in vasopressin secretion?
What is the name of the hormone that plays a crucial role in regulating renal water excretion?
What is the result of an increase in plasma osmolality on vasopressin secretion?
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What is the mechanism that allows the kidney to excrete different volumes of water without perturbing other homeostatic functions?
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Study Notes
Kidney Functions in Homeostasis
- The kidney maintains body fluid tonicity by regulating water excretion.
- It controls extracellular fluid volume through the regulation of NaCl excretion.
- Systemic acid–base balance is achieved by managing net acid excretion.
- K+ balance is regulated through its excretion by the kidneys.
- Urea excretion supports the maintenance of body nitrogen balance.
Independent Regulation of Water and Solute Excretion
- The kidney can independently regulate the excretion of water and solutes.
- It can adjust water excretion based on water intake without altering solute excretion significantly.
- This capability is crucial for performing simultaneous homeostatic functions of the kidney.
Role of Arginine Vasopressin (AVP)
- Arginine vasopressin (AVP), also known as antidiuretic hormone (ADH), tightly regulates renal water excretion.
- Osmoreceptors in the hypothalamus control the release of vasopressin from the posterior pituitary gland in response to blood osmolality exceeding approximately 292 mOsm/kg H2O.
- Factors like arterial underfilling, severe fatigue, or physical stress can modulate vasopressin secretion, overriding osmotic control.
Urine Production Variation
- In response to varying vasopressin levels, the kidney alters urine flow and water excretion.
- During extreme antidiuresis (high vasopressin), water excretion can decrease by over 100 times compared to major water diuresis (low vasopressin).
- Notable changes in water excretion occur without significant changes in steady-state solute excretion.
Kidney's Concentrating and Diluting Mechanisms
- The kidney can concentrate urine when circulating vasopressin levels are high, resulting in urine osmolality much greater than plasma.
- Conversely, during low vasopressin levels, urine osmolality remains below that of plasma, demonstrating the kidney's diluting function.
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Description
Learn about the kidney's role in regulating water and salt excretion, controlling fluid volume, acid-base balance, and maintaining electrolyte and nitrogen balance.
