Question

When a person is suffering from poor renal reabsorption, which one of the following will not help in the maintenance of blood volume? (a) Increased ADH secretion (b) Decreased glomerular filtration (c) Increased arterial pressure in kidneys (d) Decreased arterial pressure in kidneys

Short answer

The option that will not help in maintaining blood volume when a person is suffering from poor renal reabsorption is (c) Increased arterial pressure in kidneys.

Step-by-step solution

Analysis of Option A

ADH or Antidiuretic Hormone is involved with water retention. When ADH secretion increases, it causes the kidneys to retain more water, thereby reducing urine output and helping in maintaining the blood volume.

Analysis of Option B

Glomerular filtration is the first step in urine formation. Therefore, if glomerular filtration decreases, the amount of urine produced will decrease, resulting in the retention of more fluid in the body which helps maintaining the blood volume.

Analysis of Option C

An increase in arterial pressure in the kidneys could lead to a increase in the volume of blood filtered, if the renal autoregulation does not compensate. This could potentially increase the urine output, which may not help in maintaining the blood volume.

Analysis of Option D

A decrease in arterial pressure in the kidneys will lead to a decrease in glomerular filtration rate and thus, less urine output, resulting in more fluid in the body which in turn helps in maintaining the blood volume.

Key concepts

Antidiuretic Hormone (ADH)

The Antidiuretic Hormone (ADH), also known as vasopressin, plays a pivotal role in regulating water balance within the body. Its main function is to control the amount of water reabsorbed by the kidneys. When ADH levels rise, the kidney's collecting ducts become more permeable to water, allowing for greater water reabsorption back into the bloodstream. This process not only decreases urine volume but also concentrates the urine, effectively conserving water and helping to maintain blood volume—an essential aspect in the overall fluid balance.

For individuals facing poor renal reabsorption, an increase in ADH secretion would help to mitigate the conditions of excess urine output by promoting water retention, thereby contributing to maintaining blood volume. ADH's intricate balance and its impact on renal physiology underscore its importance as a therapeutic target in conditions such as diabetes insipidus, where ADH secretion is abnormal.

Glomerular Filtration Rate (GFR)

Glomerular Filtration Rate (GFR) is a critical indicator of kidney function and reflects how well the kidneys are filtering the blood. GFR measures the amount of plasma filtered through the glomeruli — tiny filters in the kidneys — per unit of time. Normal GFR ensures that waste products are efficiently removed from the body. A decreased GFR means fewer toxins are filtered, and less urine is produced. Conversely, a high GFR could indicate that the kidneys are over-filtering, potentially leading to the loss of too many electrolytes and an imbalance in body fluids.

In the context of maintaining blood volume, a decreased GFR aids in fluid retention since it leads to lower urine production. Understanding GFR is vital for healthcare professionals to diagnose and manage kidney-related disorders and for maintaining the delicate equilibrium of the body's internal environment.

Kidney Arterial Pressure

Kidney arterial pressure refers to the blood pressure within the renal arteries that supply blood to the kidneys. This pressure is crucial for the kidneys to filter blood and form urine properly. When the arterial pressure is high, it can potentially increase the GFR, resulting in more fluid being filtered and an increased urine output, which may be counterproductive when trying to maintain blood volume. Conversely, a low arterial pressure can reduce GFR, leading to less urine production and improved blood volume retention.

The kidney possesses an incredible capacity for autoregulation, which allows it to maintain a relatively constant GFR despite fluctuations in systemic blood pressure. However, when the ability to autoregulate is compromised or when extreme changes in arterial pressure occur, there can be significant implications for both renal function and one's overall health.

Renal Physiology

Renal physiology encompasses the study of kidney function and its contributions to the homeostasis of the body. One of its integral roles is the regulation of electrolyte balance, acid-base balance, and blood pressure — all through various processes such as filtration, reabsorption, secretion, and excretion of numerous substances. In maintaining blood volume, the kidneys adjust their function in response to various hormones and signals, including those from the renin-angiotensin-aldosterone system, natriuretic peptides, and the sympathetic nervous system.

Additionally, the kidneys are not merely passive filters; they actively reabsorb fundamental electrolytes and nutrients while secreting waste products. An understanding of renal physiology is essential when examining the effects of various factors like ADH, arterial pressure, and GFR on kidney health and disease states. Effective management and treatment of renal pathologies require a thorough grasp of these complex interactions.