Question

Aldosterone causes all except (a) Reabsorption of electrolyte and water from renal tubule (b) Excretion of \(\mathrm{K}^{+}\) (c) Excretion of \(\mathrm{PO}^{2}\), ion (d) Absorption of \(\mathrm{K}^{+}\)

Short answer

The effect that Aldosterone does not cause is (c) Excretion of \(\mathrm{PO}^{2-}\) ion.

Step-by-step solution

Identify the function of Aldosterone

Aldosterone is a hormone that plays a critical role in the body's control of blood pressure. It does this primarily through the regulation of sodium and potassium levels. It stimulates the reabsorption of salts and water from the renal tubule into the bloodstream which in turn helps in water retention, increasing blood volume and blood pressure. Aldosterone also promotes the excretion of potassium (K+) into the renal tubule.

Analyzing each option based on Aldosterone’s function

Option a) agrees with one of the major functions of Aldosterone, which is the reabsorption of electrolytes and water from the renal tubule. Option b) is also a known function of Aldosterone, which leads to the excretion of \(\mathrm{K}^{+}\). Option c) is false, as Aldosterone doesn't directly lead to the excretion of \(\mathrm{PO}^{2-}\) ions. Aldosterone never interacts with the \(\mathrm{PO}^{2-}\) ion. Option d) is incorrect as Aldosterone promotes the excretion, not the absorption of \(\mathrm{K}^{+}\).

Identify the incorrect option

Upon analyzing the options, it's clear that options (a) and (b) are true effects of Aldosterone. Option (d) is also incorrect but option (c) is the most incorrect one as Aldosterone does not interact with phosphate ions (\(\mathrm{PO}^{2-}\)). Option (c) is the answer.

Key concepts

Hormonal Function

Aldosterone is a hormone produced by the adrenal glands, located above the kidneys. Its primary role is to regulate blood pressure by maintaining sodium and potassium levels in the body. This regulation is part of a system called the renin-angiotensin-aldosterone system (RAAS), which is crucial for fluid balance and blood pressure control.
Aldosterone acts mainly on the kidneys, promoting sodium reabsorption into the blood from the renal tubules. As sodium moves, water follows, which helps to increase blood volume and pressure. This is why aldosterone is directly linked to blood pressure management.
Additionally, aldosterone facilitates the excretion of potassium into the urine, keeping potassium levels within a healthy range. By managing electrolyte balance, aldosterone ensures that cells can function properly. If aldosterone levels are too low or too high, it can lead to conditions like hypoaldosteronism or hyperaldosteronism, affecting blood pressure regulation and electrolyte balance significantly.

Renal Physiology

Renal physiology involves the processes that occur in the kidneys to filter blood, reabsorb necessary substances, and excrete waste. Aldosterone plays a pivotal role in these processes as it acts on specific parts of the nephron, the functional unit of the kidney.
The nephron has several components, with the distal tubule being particularly responsive to aldosterone. When aldosterone binds to receptors in the distal tubule, it activates proteins that increase sodium channels and pumps on the cell surface. This results in enhanced sodium and water reabsorption into the bloodstream, ultimately affecting blood volume and pressure.
Moreover, aldosterone promotes the exchange of sodium ions for potassium ions in the renal tubules. With its action, sodium is reabsorbed, while potassium is secreted into urine. This precise control of electrolytes is vital for maintaining a stable internal environment, necessary for normal physiological functions.

Electrolyte Balance

Electrolytes, like sodium and potassium, are charged ions essential for many bodily functions, including nerve transmission, muscle contraction, and fluid balance. Aldosterone’s role in electrolyte balance is crucial to ensure these processes run smoothly.
By reabsorbing sodium and excreting potassium, aldosterone helps maintain the necessary electrolyte gradients across cellular membranes. This balance is particularly important for nerve impulses and cardiac muscle function. Disturbances in electrolyte levels can lead to severe health issues, including cardiac arrhythmias or neuromuscular dysfunction.
In cases where aldosterone functions improperly, electrolyte imbalances can arise, leading to conditions such as hypertension or hypotension. Maintaining proper aldosterone activity within normal ranges is vital for the body’s electrolyte balance and overall health.