Question

Which region of the kidney has the lowest solute concentration? A. Nephron B. Cortex C. Medulla D. Pelvis

Short answer

The cortex has the lowest solute concentration.

Step-by-step solution

Identify the regions of the kidney

The kidney has different regions including the cortex, medulla, pelvis, and the nephron which is a structural unit within these regions.

Understand the function of each region

The cortex is the outer part of the kidney and is where ultrafiltration occurs. The medulla contains the renal pyramids where urine is concentrated. The pelvis is a funnel-shaped cavity that collects urine before it moves to the ureter. The nephron includes structures in both the cortex and the medulla.

Determine solute concentration in each region

The medulla has a high solute concentration due to the counter-current mechanism. The pelvis also has a relatively high concentration as it stores concentrated urine. Solute concentration is generally lower in the cortex.

Choose the correct region with the lowest solute concentration

Given the functions and solute concentration in each region, the cortex typically has the lowest solute concentration.

Key concepts

kidney cortex

The kidney cortex is the outermost layer of the kidney. It is crucial for filtering blood and beginning the process of urine formation. The cortex houses the glomeruli, where blood filtration occurs, extracting wastes and excess substances. This part of the kidney has a low solute concentration because it is the initial site for filtrate formation.
In the cortex:

• Blood is filtered in the glomeruli.
• The filtrate starts as almost pure water, with low solute levels.

This makes the cortex vital for maintaining low solute concentration before the filtrate moves deeper into the kidney.

renal function

Renal function refers to the kidneys' capacity to filter blood, remove wastes, balance electrolytes, and regulate blood pressure. The kidneys perform several key roles:

• Filtration: Blood is filtered to remove waste and produce urine.
• Reabsorption: Essential substances like glucose, sodium, and water are reabsorbed back into the blood.
• Secretion: Additional wastes and excess ions are secreted into the urine.

Proper renal function is essential for homeostasis and overall health. Any impairment in these functions can lead to serious health issues, including electrolyte imbalance and toxin accumulation.

nephron structure

The nephron is the functional unit of the kidney. It plays a pivotal role in filtering blood and forming urine. Each kidney contains around a million nephrons:

• Glomerulus: A cluster of capillaries where filtration begins.
• Bowman's Capsule: Encases the glomerulus and collects the filtered substances.
• Proximal Convoluted Tubule: Where reabsorption of water, ions, and nutrients occurs.
• Loop of Henle: Concentrates the urine through a counter-current mechanism.
• Distal Convoluted Tubule: Further adjusts the composition of urine.
• Collecting Duct: Delivers urine to the renal pelvis.

This elaborate structure ensures efficient blood filtration and urine formation, contributing to the kidneys' regulatory functions.

medulla solute concentration

The medulla is the inner part of the kidney, organized into pyramids. It has a high solute concentration, crucial for urine concentration. This is achieved through a counter-current exchange mechanism:

• Thick and thin limbs of the Loop of Henle: Facilitate solute and water exchange, increasing medullary osmolarity.
• Vasa Recta: Capillary network that maintains the solute gradient in the medulla.

The high solute concentration in the medulla is pivotal for concentrating urine and conserving water, hence supporting the body's fluid and electrolyte balance.