Question

The primary function of the nephron is to create urine that is A. hypertonic to the blood. B. hypotonic to the blood. C. hypertonic to the filtrate. D. hypotonic to the vasa recta.

Short answer

The urine created by the nephron is hypertonic to the blood. The correct answer is A.

Step-by-step solution

Understanding the Function of the Nephron

The nephron is the basic structural and functional unit of the kidney. Its primary function is to filter blood, reabsorb necessary substances, and excrete waste products in the form of urine.

Analyzing Urine Osmolarity

Consider the osmolarity of urine compared to the blood and filtrate. Osmolarity refers to the concentration of solutes in a solution.

Identifying Urine Compared to Blood

Urine is typically hypertonic to both blood and the filtrate. This means urine has a higher concentration of solutes compared to blood, allowing for the excretion of excess salts and waste while conserving water.

Choosing the Correct Answer

Based on the information, the urine created by the nephron would be hypertonic to the blood. Therefore, the correct option is A. hypertonic to the blood.

Key concepts

Urine Osmolarity

Urine osmolarity is a crucial concept when understanding kidney function. Osmolarity is the measure of solute concentration in a solution. In the body, solutions include blood, urine, and the filtrate in the nephron. The nephron adjusts the osmolarity of urine depending on the body's hydration levels. Typically, urine is hypertonic compared to blood. This means that it has a higher concentration of solutes, such as salts and waste products.

When your body needs to conserve water, the kidneys make urine more concentrated. Conversely, when excess water needs to be excreted, the kidneys produce diluted urine with lower osmolarity. This balance ensures that essential nutrients are reabsorbed while unnecessary substances are excreted.

Monitoring urine osmolarity is important for diagnosing various health conditions, such as dehydration, kidney diseases, and electrolyte imbalances.

Kidney Filtration

Understanding kidney filtration is key to grasping how the nephron functions. The process begins in the glomerulus, a network of capillaries located at the beginning of each nephron. Here, blood pressure forces water, salts, glucose, amino acids, and waste products out of the blood and into the Bowman's capsule of the nephron.

This initial filtrate is similar in composition to blood plasma but lacks larger proteins and cells, which are too large to pass through the glomerular filter. The filtrate then moves through different parts of the nephron - the proximal tubule, loop of Henle, distal tubule, and collecting duct.

The specific structure of these segments allows for the selective reabsorption and secretion of various substances. Water and essential nutrients are reabsorbed back into the bloodstream, while waste products and excess ions are concentrated into urine for excretion. This meticulous filtration system is essential for maintaining the body's chemical balance.

Solute Concentration

Solute concentration in the body is maintained through the processes carried out by the nephron. Solutes include electrolytes, waste products, and other dissolved substances in the body's fluids. The renal system plays a vital role in managing these concentrations to ensure homeostasis.

The nephron regulates solute concentration by selectively reabsorbing some solutes back into the bloodstream while allowing others to be excreted in the urine. For example, important electrolytes like sodium, potassium, and calcium are closely regulated through reabsorption and secretion mechanisms. This regulation is controlled by various hormones, including aldosterone and antidiuretic hormone (ADH).

As the filtrate moves through the nephron, its solute concentration changes. By the time it becomes urine, it will have a carefully balanced concentration of water and solutes. If the body is dehydrated, the kidneys will reabsorb more water, making the urine more concentrated and increasing its solute concentration.

This sophisticated process allows the kidney to maintain proper solute levels in the blood, supporting overall health.