Question

Which one of the following statements is correct with respect to kidney function regulation? (a) When someone drinks lot of water, ADH release is suppressed. (b) Exposure to cold temperature stimulates ADH release. (c) An increase in glomerular blood flow stimulates formation of angiotensin II. (d) During summer when body loses lot of water by evaporation, the release of \(A D H\) is suppressed.

Short answer

(a) When someone drinks a lot of water, ADH release is suppressed, is the correct statement with respect to kidney function regulation.

Step-by-step solution

Understanding ADH Regulation

Anti-diuretic hormone (ADH), also known as vasopressin, is a hormone that regulates the amount of water excreted by the kidneys. When the body is dehydrated or when a person consumes less water, ADH levels increase, making the kidneys reabsorb more water and produce concentrated urine. Conversely, when there's an excess of water in the body, ADH release is suppressed, leading kidneys to excrete more water and thus dilute the urine.

Evaluating Statement (a)

The statement 'When someone drinks a lot of water, ADH release is suppressed' is correct. This is aligned with the body's need to excrete excess water to maintain the fluid balance.

Evaluating Statement (b)

The statement 'Exposure to cold temperature stimulates ADH release' is incorrect. Cold exposure would typically lead to peripheral vasoconstriction and not directly influence ADH release, which responds primarily to changes in plasma osmolality and blood volume.

Evaluating Statement (c)

The statement 'An increase in glomerular blood flow stimulates formation of angiotensin II' is not directly correct. The formation of angiotensin II is stimulated by a decrease in renal blood flow, not an increase. This happens through the activation of the renin-angiotensin-aldosterone system (RAAS), which is triggered when blood flow to the kidneys is reduced.

Evaluating Statement (d)

The statement 'During summer when the body loses a lot of water by evaporation, the release of ADH is suppressed' is incorrect. In fact, during the summer or when the body loses water through evaporation, ADH release would be stimulated to conserve water, not suppressed.

Key concepts

Anti-Diuretic Hormone (ADH)

The anti-diuretic hormone (ADH) plays a crucial role in the regulation of water balance in the body by controlling the concentration of urine. When the body experiences an increase in plasma osmolality, such as when one is dehydrated or has not consumed enough water, ADH is released from the posterior pituitary gland into the bloodstream.

The ADH then acts on receptors in the kidneys, particularly at the collecting ducts, prompting the kidneys to reabsorb more water back into the bloodstream, resulting in less water being lost as urine. This mechanism conserves water and prevents further dehydration. In contrast, an abundance of water intake leads to decreased ADH release, causing the kidneys to excrete more water, thereby diluting urine and reducing plasma osmolality to maintain homeostasis.

Renin-Angiotensin-Aldosterone System (RAAS)

When discussing kidney function regulation, it is essential to highlight the renin-angiotensin-aldosterone system (RAAS), which is another significant regulatory mechanism influencing blood pressure and fluid balance.

Upon sensing a reduction in blood flow or sodium content, specialized cells in the kidney (juxtaglomerular cells) release an enzyme called renin. Renin converts angiotensinogen, a protein made by the liver, into angiotensin I, which is further converted into angiotensin II by angiotensin-converting enzyme (ACE) primarily in the lungs. Angiotensin II is a potent vasoconstrictor that increases blood pressure and stimulates the secretion of aldosterone from the adrenal glands. Aldosterone promotes sodium and water reabsorption and potassium excretion by the kidneys, which ultimately leads to increased blood volume and pressure.

Glomerular Blood Flow

Understanding glomerular blood flow is central to grasping how the kidneys filter blood and regulate its composition. Glomerular blood flow refers to the movement of blood through the tiny blood vessels (glomeruli) of the kidneys.

The rate of blood flow through these capillary networks affects the formation of urine, as it determines how much blood gets filtered. Normally, the kidneys autoregulate blood flow to maintain a consistent glomerular filtration rate (GFR), despite fluctuations in blood pressure. When blood flow is too low, RAAS is activated to construe the blood vessels and raise the blood pressure, increasing the blood flow into the glomeruli. However, contrary to a common misconception, an increase in glomerular blood flow does not stimulate angiotensin II formation; rather, it's the decrease in renal blood flow that triggers this process.

Body Fluid Balance

Body fluid balance is a complex mechanism involving several systems in the body working together to ensure homeostasis, the stability of the internal environment. This balance is primarily maintained by regulating the volume and concentration of body fluids, particularly the extracellular fluid, which includes blood plasma and interstitial fluid.

Key players in this regulatory dance include ADH and RAAS, as well as other factors like atrial natriuretic peptide (ANP), which is released from the heart and acts to reduce blood volume and pressure. The balance is constantly adjusted in response to various stimuli, such as changes in hydration levels, salt intake, and even external temperature. Noteworthy is that the body's response to dehydration or fluid loss through mechanisms such as sweating involves retaining water by increasing ADH secretion, highlighting the body's intuitive ability to preserve equilibrium.