Question

Biologists have been able to produce mice that lack functioning genes for aquaporins. How would the urine of these mice compare to that of mice with normal aquaporins? a. lower volume and lower osmolarity b. lower volume and higher osmolarity c. higher volume and lower osmolarity d. higher volume and higher osmolarity

Short answer

Mice that lack functioning genes for aquaporins would produce urine with a higher volume and lower osmolarity compared to mice with normal aquaporins. This is due to impaired water reabsorption in the collecting ducts of the kidneys, resulting in an increased urine volume and diluted solute concentration. Therefore, the correct answer is c. higher volume and lower osmolarity.

Step-by-step solution

Understanding Aquaporins

Aquaporins are membrane proteins that facilitate the movement of water across cell membranes. In the context of the urinary system, they play a crucial role in regulating the water reabsorption in the collecting ducts of the kidneys. More specifically, aquaporins (especially Aquaporin-2) facilitate the reabsorption of water from the filtrate back into the bloodstream. This helps maintain the balance of fluids and electrolytes within the body.

Effect of Lack of Aquaporins

In mice lacking functional aquaporin genes, the reabsorption of water in the collecting ducts would be impaired. Consequently, the urine produced by these mice would have a higher water content due to less water being reabsorbed into the bloodstream. This would lead to an increase in urine volume. Since the reabsorption of solutes like salts and urea remains unaffected by the absence of aquaporins, the solute concentration in the urine would also be diluted, leading to a lower osmolarity.

Comparing Urine Volume and Osmolarity

With this information, we can make the following comparison: Mice without functioning aquaporins: 1. Higher urine volume (due to less water reabsorption) 2. Lower urine osmolarity (due to dilution of solutes) Mice with normal aquaporins: 1. Lower urine volume (due to greater water reabsorption) 2. Higher urine osmolarity (due to concentration of solutes)

Choosing the Correct Answer

Based on the comparison above, we can conclude that the correct answer is: c. higher volume and lower osmolarity

Key concepts

Membrane Proteins

Membrane proteins are fundamental components of cellular life, acting as gatekeepers and facilitators for the transportation of substances in and out of cells. In particular, membrane proteins such as aquaporins are specialized for water transport.
Aquaporins, a family of water channel proteins, are embedded in the cell membrane and allow water molecules to move through a selective channel. Their function is vital for maintaining water balance in organisms, and they operate based on osmotic gradients. This means water will flow through these proteins from an area with a low concentration of solutes to an area with higher solute concentration, depending on the body's needs.

Roles of Membrane Proteins

• Transport: They regulate substances crossing the cell membrane.
• Receptors: They receive signaling molecules and initiate cellular responses.
• Enzymes: They catalyze reactions at the membrane surface.

Membrane proteins are crucial for the integrity and functionality of cells, and their malfunction can lead to a variety of health issues.

Urinary System

The urinary system is a sophisticated network tasked with filtering blood and removing waste products, maintaining homeostasis in the body. Its primary components are the kidneys, ureters, bladder, and urethra.
A key function of this system is to produce urine, which is created when the kidneys filter waste substances from the bloodstream. The creation of urine involves a delicate balance of reabsorbing necessary molecules and water while excreting unnecessary or toxic substances.

Urinary System Functions

• Excretion: Eliminating waste products and toxins through urine.
• Regulation: Managing body fluid volume, electrolytes, and pH balance.
• Filtering: Clearing the blood of metabolic waste and foreign substances.

Understanding the urinary system is critical for grasping how diseases can affect our body's ability to manage waste and electrolyte balance.

Kidney Function

The kidneys are bean-shaped organs, which are powerhouses in the urinary system, playing several crucial roles. They are primarily responsible for filtering blood and forming urine, by removing waste and extra fluid to balance the body's fluids.
The kidneys use a microscopic system of tubes and blood vessels, including the glomerulus and renal tubules, to process blood. The glomerulus acts as a strainer, keeping blood cells and large proteins in the blood, while smaller molecules, including water, are filtered as a part of the urine.

Stages of Kidney Filtration

• Filtration: Blood plasma is filtered through the glomerulus.
• Reabsorption: Valuable molecules and water are reabsorbed into the bloodstream.
• Secretion: Additional wastes are added into the filtrate.

Disturbances in kidney function can lead to an imbalance of fluids and electrolytes, demonstrating the importance of regulating urine composition for overall health.

Osmolarity

Osmolarity is a measure of solute concentration defined as the total number of solute particles per liter of solution. It is a critical factor in the functioning of cells and the body's management of fluids.
In the kidneys, osmolarity is essential in determining the movement of water in and out of blood and urine. Water moves from areas of lower osmolarity (less solute) to areas of higher osmolarity (more solute) across cell membranes. This regulation is central to the body's ability to concentrate urine and maintain hydration status.
For instance, when we consume a lot of water, urine osmolarity decreases, leading to more dilute urine. Conversely, when dehydrated, the kidneys reabsorb more water to make the urine more concentrated, increasing urine osmolarity.

• Hypotonic: A solution with lower osmolarity than another solution, likely to cause cells to swell as water moves in.
• Isotonic: A solution with the same osmolarity as another solution, leading to no net water movement.
• Hypertonic: A solution with higher osmolarity than another solution, likely to cause cells to shrink as water moves out.

Understanding osmolarity is fundamental in studying how the kidneys respond to the body's needs, thus affecting urine concentration.