Problem 158 - Objective Biology for NEET

Question

Assertion: Kidneys maintain the osmotic concentration of the blood. Reason: Kidneys eliminate either hypotonic or hypertonic urine according to the need of the body.

Step-by-Step Solution

Answer

The assertion and reason are correctly connected. Kidneys maintain the osmotic balance of blood (Assertion) by altering the concentration of urine - either hypotonic or hypertonic - according to the needs of the body (Reason).

Step 1: Understanding the Assertion

The assertion states that 'Kidneys maintain the osmotic concentration of the blood'. The kidneys play a vital role in maintaining the body's water balance and the concentration of electrolytes in the blood. They do this by filtering out waste and extra fluid from the blood and excreting them as urine.

Step 2: Understanding the Reason

The reason provided is 'Kidneys eliminate either hypotonic or hypertonic urine according to the need of the body'. Depending on the body’s need, kidneys can either eliminate hypertonic urine (more solutes, less water - when the body needs to conserve water) or hypotonic urine (less solutes, more water - when the body needs to get rid of excess water). Thus, kidneys adjust the concentration of urine according to the needs of the body.

Step 3: Connecting the Assertion and Reason

The kidney's ability to produce urine of varying concentration (hypertonic or hypotonic), allows it to maintain the osmotic concentration of blood. Thus, it's clear that the assertion and reason are correctly connected.

Key Concepts

Osmotic Regulation

Osmotic regulation is a critical function that involves maintaining the appropriate balance between water and solutes in the body. The kidneys play a central role in this process by ensuring the osmolarity of body fluids remains constant.
To achieve osmotic regulation, the kidneys filter blood and adjust the concentration of solutes, such as sodium and potassium. These adjustments are made based on bodily requirements and external factors like hydration level and diet.
When blood osmolarity rises, indicating dehydration or increased solute concentration, the kidneys respond by conserving water. They do this by producing hypertonic urine, which contains a higher solute concentration. Conversely, if the body is overhydrated, the kidneys release hypotonic urine, expelling more water compared to solutes.
This remarkable ability allows our bodies to adapt to various conditions and maintain a stable internal environment, which is essential for proper cellular functions.

Urine Concentration

Urine concentration is the process by which the kidneys control the amount of water and solutes eliminated from the body. This mechanism is vital for regulating the body's fluid balance and ensuring that waste is efficiently excreted.
The kidneys achieve urine concentration through a structure called the nephron, which is the functional unit of the kidney. Each nephron filters blood, reclaims needed substances, and excretes waste in the form of urine.
Depending on the body's needs, the nephron can make urine either more dilute (hypotonic) or more concentrated (hypertonic).

• If the body requires water conservation, possibly due to low hydration, the nephron reabsorbs more water, leaving the urine concentrated with solutes.
• If there is excess water in the body, the nephron retains less water, resulting in dilute urine.

Hormones like antidiuretic hormone (ADH) play a crucial role in this process by signaling the kidneys to either conserve or release water, thus manipulating urine concentration.

Body Water Balance

Body water balance is the equilibrium between water intake and water loss in our body, crucial for maintaining health and well-being. The kidneys are pivotal in ensuring this balance through their ability to regulate urine output.
Various factors influence body water balance, such as hydration levels, food intake, and activity level. For example, during intense exercise, the body loses water through sweat, and the kidneys compensate by conserving water and producing less urine.
The regulation of body water balance is adjusted by hormones. Besides ADH, aldosterone helps by signaling the kidneys to retain sodium and water, boosting blood volume. Both hormones work together to correct any imbalance in body water levels.
Additionally, kidneys react to changes in blood pressure and blood volume, modulating how much water is reabsorbed or eliminated, to sustain equilibrium. Thus, the kidneys ensure that every system in the body operates optimally, adapting to each individual's fluid requirements.