Problem 166 - Objective Biology for NEET

Question

Assertion: Urine produced (1 to \(1.5 \mathrm{~L}\) ) per day is far less than the volume of filtrate occur per day (18L). Reason: \(99 \%\) of filtrate is reabsorbed by the renal tubules.

Step-by-Step Solution

Answer

Yes, the assertion is correct, and the reason provided is valid. Although large volumes of filtrate are produced, 99% is reabsorbed, resulting in only 1 to 1.5 liters of urine being excreted daily.

Step 1: Understanding the Renal System

The renal system, which includes the kidneys, is responsible for filtering blood and generating waste in the form of urine. This process begins when blood enters the kidneys and is filtered. This filtered substance is referred to as the filtrate.

Step 2: Acknowledging the Volume of Filtrate Produced

Approximately 180 liters of filtrate are produced in the kidneys each day. This filtrate contains water, glucose, and other useful substances, as well as waste products.

Step 3: Considering Filtrate Reabsorption

Although a large volume of filtrate is initially produced, most of this is reabsorbed by the renal tubules. During the reabsorption process, the required and helpful substances are extracted from the filtrate and re-enter the bloodstream. About 99% of the filtrate is reabsorbed, meaning only a minor fraction is excreted as urine.

Step 4: Comparing Filtrate and Urine Volumes

Given the high reabsorption rate of 99%, only about 1% of the original filtrate volume becomes urine. Thus, even though 180 liters of filtrate are produced daily, only about 1 to 1.5 liters of urine are excreted.

Key Concepts

Filtrate Reabsorption

Our kidneys are incredible organs that handle the task of filtrate reabsorption. Each day, our kidneys filter vast amounts of blood, forming a substance called filtrate. This filtrate initially totals around 180 liters daily! However, nearly 99% of this filtrate gets reabsorbed. The renal tubules skillfully take back necessary nutrients and water, allowing only the waste materials and excess substances to be expelled. This reabsorption process ensures that vital components like glucose, amino acids, and ions are conserved. By effectively reabsorbing these substances, our bodies maintain homeostasis and ensure that we don't dehydrate or lose essential nutrients.
Understanding filtrate reabsorption is key to appreciating how the kidneys maintain the balance of fluids and electrolytes, a fundamental part of our overall health.

Kidney Function

The primary role of the kidneys is to filter blood and help in waste removal. They act as our body's natural filtration system. Blood carrying waste enters each kidney, where tiny structures called nephrons take charge. There are about a million nephrons in each kidney, and each nephron has two parts: a glomerulus and a renal tubule. As blood passes through the glomerulus, waste products and small molecules are filtered into the renal tubule to form filtrate.
Filtration isn't the only role of the kidneys. They also regulate blood pressure, balance electrolytes, and play a part in red blood cell production by releasing a hormone called erythropoietin. This hormone encourages the production of red blood cells in the bone marrow. Through these essential functions, kidneys contribute significantly to the stability and health of our body systems.

Urine Production

Urine production is the final step in the filtration process carried out by the kidneys. After 99% of the 180 liters of filtrate is reabsorbed, the remainder—around 1 to 1.5 liters—is converted into urine. This urine collects in the renal pelvis and travels down the ureters to the bladder, where it is stored until it's convenient to be expelled.
This entire process is crucial for removing waste and excess substances from our blood. Additionally, urine production helps maintain fluid balance within the body, preventing conditions like dehydration or fluid overload. By adjusting the volume and concentration of urine, our bodies can adapt to different levels of water and solute intake, ensuring that we remain in optimal health even when external factors change.