Question

Urinary filtration moves ________ and small solutes into kidney tubules. a. Water b. insoluble fiber c. large proteins d. red blood cells

Short answer

Water is filtered into kidney tubules during urinary filtration.

Step-by-step solution

Understand Urinary Filtration

Urinary filtration is the process by which the kidneys filter blood, removing waste and excess substances. The glomerulus, a cluster of capillaries, allows water and small molecules to pass into the renal tubules, while larger molecules like proteins and cells remain in the bloodstream.

Identify Solutes in Filtration

In the context of urinary filtration, we primarily consider substances dissolved in body fluids. These include water, electrolytes, glucose, amino acids, and urea. Larger particles such as cells or large proteins are typically not filtered due to size constraints.

Consider Filtration Mechanism

The glomerular filtration barrier allows passage of small molecules. Water is a major component of the blood that is freely filtered. Insoluble fibers, large proteins, and red blood cells are typically too large to pass through the filtration barrier.

Analyze Answer Options

- Water (a small molecule) is routinely moved into kidney tubules during filtration. - Insoluble fiber is not part of the blood and would not be filtered. - Large proteins are too large and not normally filtered into the tubules. - Red blood cells are kept within the bloodstream and not filtered.

Choose the Correct Answer

Based on the filtration mechanism, water and small solutes like ions and glucose move into the kidney tubules. Among the options given, water is the small solute that undergoes this process.

Key concepts

Kidney Function

The kidneys are vital organs that manage a variety of functions, crucial for maintaining homeostasis in the body. Their primary role is to filter blood, remove waste, and balance fluids and electrolytes. They achieve this through a complex process that involves specialized structures.

• Filtration: Blood enters the kidneys through the renal arteries, where it undergoes a filtration process to remove toxins and waste products. This process takes place mainly in the glomeruli, which are tiny ball-shaped structures consisting of capillary networks.
• Reabsorption: After filtration, essential nutrients like glucose and certain ions are reabsorbed back into the bloodstream, while waste products like urea are excreted.
• Secretion: In the later stages of urine formation, substances like hydrogen ions and potassium are secreted into the kidney tubules from the blood, ensuring these chemicals are efficiently managed.

As a result, the kidneys help regulate blood pressure, produce hormones, and contribute to bone health by activating vitamin D.

Glomerulus

The glomerulus is a key component of the nephron, which is the functional unit of the kidney. Think of the glomerulus as a finely-tuned sieve, filtering blood to produce a fluid called filtrate.

• Structure: Consisting of a network of capillaries, the glomerulus is located within the Bowman's capsule. This unique structure creates a high-pressure environment conducive to effective filtration.
• Function: As blood passes through the glomerulus, water and solutes are filtered into the renal tubules. The glomerulus is designed to retain larger molecules like proteins and blood cells within the bloodstream, allowing only small molecules to pass through.
• Relevance: Proper function of the glomerulus is essential, as any disruption can affect kidney efficiency, leading to conditions like proteinuria, where proteins are found in urine.

Overall, the glomerulus performs a crucial role in maintaining the body's internal equilibrium by filtering out unnecessary components from the blood.

Filtration Barrier

The filtration barrier of the glomerulus is a complex structure crucial for selective filtration. It ensures the proper substances are retained or filtered out during kidney function.

• Components: The filtration barrier is made up of three primary layers:
  • Endothelium: The innermost layer of the capillary wall, which allows water and small solutes to pass through.
  • Basement membrane: A dense layer that prevents larger molecules like proteins from being filtered out.
  • Podocytes: Specialized cells that wrap around the capillaries, forming filtration slits that further ensure only small particles pass through into the tubular system.
• Mechanism: These layers work together to create a highly selective filter, maintaining a balance between preventing an excess loss of crucial molecules while allowing waste and excess substances to be filtered into the renal tubules.
• Importance: A healthy filtration barrier contributes to optimal kidney function, whereas damage to any layer can result in compromised filtration capacity and the potential for systemic health issues.

Therefore, understanding the filtration barrier is key to grasping how kidneys maintain bodily health.

Renal Tubules

Renal tubules play a pivotal role in transforming the initial filtrate produced by the glomerulus into urine. This journey involves multiple steps, ensuring waste is excreted and essential nutrients are reabsorbed.

• Tubular Sections: The renal tubules consist of distinct sections, each responsible for different aspects of urine formation:
  • Proximal Convoluted Tubule: Reabsorbs glucose, amino acids, and a large portion of ions and water from the filtrate back into the bloodstream.
  • Loop of Henle: Establishes concentration gradients that allow for water reabsorption and the concentration of urine.
  • Distal Convoluted Tubule: Fine-tunes ion exchange and plays a role in pH balance.
  • Collecting Duct: Further adjusts the urine composition, concentrating it based on the body's hydration levels and hormonal signals.
• Function: The primary task of the renal tubules is to refine the composition of the glomerular filtrate. Their ability to reabsorb water and essential solutes is crucial for maintaining fluid and electrolyte balance.

Through the operations of the renal tubules, the kidneys efficiently manage the body's fluid, electrolyte, and acid-base balance, proving indispensable for overall homeostasis.