Several hormones tightly regulate fluid balance in the body, ensuring proper hydration and electrolyte concentrations. These include renin-angiotensin-aldosterone, natriuretic peptides, arginine vasopressin, and parathyroid hormone.
Key Hormones Involved in Fluid Balance
These hormones work together in complex feedback loops to maintain homeostasis.
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Renin-Angiotensin-Aldosterone System (RAAS): This system is activated when blood pressure or sodium levels are low.
- Renin: Released by the kidneys in response to low blood pressure or sodium.
- Angiotensin II: Formed by the conversion of angiotensin I and stimulates vasoconstriction and the release of aldosterone.
- Aldosterone: Secreted by the adrenal cortex and increases sodium reabsorption in the kidneys, leading to increased water retention and potassium excretion. Ultimately this increases blood pressure.
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Natriuretic Peptides (ANP and BNP): These are released in response to high blood volume and atrial stretching.
- Atrial Natriuretic Peptide (ANP): Released by the heart's atria.
- Brain Natriuretic Peptide (BNP): Released by the heart's ventricles.
- Function: They promote sodium and water excretion by the kidneys, lower blood pressure, and counteract the effects of aldosterone.
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Arginine Vasopressin (AVP), also known as Antidiuretic Hormone (ADH): Released by the posterior pituitary gland in response to dehydration or increased blood osmolarity (concentration of solutes in the blood).
- Function: ADH increases water reabsorption in the kidneys, concentrating urine and reducing water loss.
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Parathyroid Hormone (PTH): While primarily involved in calcium regulation, PTH indirectly influences fluid balance by affecting kidney function. It promotes calcium reabsorption in the kidneys and indirectly impacts sodium and water handling.
Summary Table
| Hormone | Source | Stimulus for Release | Primary Action | Effect on Fluid Balance |
|---|---|---|---|---|
| Aldosterone | Adrenal Cortex | Low blood pressure, low sodium, high potassium | Increases sodium reabsorption in kidneys | Increases water retention, increases blood volume |
| ANP/BNP | Heart (Atria/Ventricles) | High blood volume, atrial/ventricular stretching | Increases sodium and water excretion in kidneys, vasodilation | Decreases blood volume, decreases blood pressure |
| Vasopressin (ADH) | Posterior Pituitary | Dehydration, increased blood osmolarity | Increases water reabsorption in kidneys | Decreases water loss, increases blood volume, concentrates urine |
| Parathyroid Hormone (PTH) | Parathyroid Glands | Low blood calcium | Increases calcium reabsorption in kidneys, affects sodium and water handling indirectly | Indirect influence on fluid balance due to effects on kidney function and electrolyte levels |
These hormones maintain the delicate balance of fluids, electrolytes, and blood pressure within the body, crucial for overall health and survival.
