Which statement describes phantom pain?

Choice A rationale

Antidiuretic hormone, also known as vasopressin, is secreted by the posterior pituitary gland in response to high blood osmolality. Its primary function is to act on the collecting ducts of the kidneys to increase their permeability to water. This promotes the reabsorption of water back into the bloodstream, which concentrates the urine and increases blood volume. By conserving water, ADH plays a critical role in maintaining fluid balance and preventing systemic dehydration. +1.

Choice B rationale

ADH does not promote the excretion of potassium; that function is primarily regulated by the hormone aldosterone and the acid-base status of the body. Aldosterone works in the distal tubules to exchange sodium for potassium, leading to potassium loss in the urine. ADH is focused strictly on the movement of water molecules through aquaporin channels. Therefore, its primary mechanism of action is independent of the direct active secretion or excretion of potassium ions.

Choice C rationale

ADH actually inhibits the excretion of urine by promoting water reabsorption, hence its name "antidiuretic.”. When ADH levels are high, the volume of urine produced decreases significantly as the water is reclaimed by the body. This is a survival mechanism to prevent the loss of essential fluids during states of high plasma osmolality or low blood pressure. Promoting the excretion of urine would be the function of a diuretic substance, not ADH. +1.

Choice D rationale

The reabsorption of sodium is the primary task of the hormone aldosterone, not ADH. While water often follows sodium osmotically, ADH specifically provides a mechanism for the reabsorption of free water regardless of sodium transport. Aldosterone acts on the sodium-potassium pumps to pull sodium back into the blood, whereas ADH works on water channels. Maintaining the balance between these two hormones is essential for regulating both the volume and the concentration of body fluids.

Choice A rationale

Kidney stones, or nephrolithiasis, cause acute kidney injury by creating a physical obstruction in the urinary tract, either in the ureters or the urethra. This blockage prevents the outflow of urine, leading to increased retrograde pressure within the renal pelvis and parenchyma, which impairs glomerular filtration. Because the problem occurs after the urine has already been formed and is located within the collecting system, it is classified as a post-renal cause of injury.

Choice B rationale

Fluid volume deficit, such as that caused by severe dehydration or hemorrhage, leads to decreased systemic blood volume. This reduction in volume results in decreased renal perfusion pressure, which prevents the kidneys from receiving enough blood to maintain an adequate glomerular filtration rate. Since the injury is caused by factors that reduce blood flow to the kidneys before it reaches the renal vasculature itself, it is categorized as a pre-renal acute kidney injury.

Choice C rationale

Low blood pressure, or hypotension, directly diminishes the mean arterial pressure required to drive blood through the renal arteries and into the glomeruli. Without sufficient pressure, the kidneys cannot effectively filter waste products from the blood, leading to a rise in blood urea nitrogen and creatinine. Similar to fluid volume deficit, the underlying issue is a lack of adequate perfusion to the kidney, which defines this as a pre-renal cause of acute kidney injury.

Choice D rationale

Benign prostatic hypertrophy involves the enlargement of the prostate gland, which can compress the urethra and obstruct the normal flow of urine out of the bladder. This urinary retention creates back-pressure that can eventually damage the kidneys and impair their function if the obstruction is bilateral or sufficiently severe. Like kidney stones, this is an obstructive issue occurring distal to the kidney itself, making it a classic example of a post-renal acute kidney injury.

Choice E rationale

Glomerulonephritis is an inflammatory condition that directly damages the glomeruli, the filtering units within the kidney. This inflammation can be caused by autoimmune reactions or infections and leads to the destruction of the basement membrane and capillary endothelium. Because the pathological process is occurring within the actual tissue and functional units of the kidney, it is classified as an intra-renal, or intrinsic, cause of acute kidney injury, as the damage is internal.