Which structures are the functional units within the kidneys that form urine?
glomerulus
nephrons
The correct answer and explanation is :
The functional units within the kidneys that form urine are called nephrons. Each kidney contains approximately 1 million nephrons, and these structures are responsible for filtering blood, reabsorbing essential substances, and excreting waste products as urine.
Structure of a Nephron
A nephron consists of several key parts, each with a specific role in the urine formation process:
- Glomerulus: The glomerulus is a network of tiny blood capillaries located within a structure called the Bowman’s capsule. It serves as the initial filtration site. The glomerulus filters blood, allowing water, ions, glucose, and waste products to pass into the Bowman’s capsule while retaining larger molecules like proteins and blood cells. This filtered fluid is called glomerular filtrate.
- Proximal Convoluted Tubule (PCT): After the glomerulus, the filtrate moves into the PCT, where a significant amount of water, glucose, and essential ions (like sodium, potassium, and chloride) are reabsorbed back into the bloodstream.
- Loop of Henle: The filtrate then enters the loop of Henle, which has a descending and an ascending limb. In the descending limb, water is reabsorbed, concentrating the filtrate. In the ascending limb, sodium and chloride ions are reabsorbed, helping to create a high osmolarity in the surrounding tissue, essential for the kidney’s ability to concentrate urine.
- Distal Convoluted Tubule (DCT): In the DCT, further regulation of ions and water takes place. Hormones like aldosterone and antidiuretic hormone (ADH) influence the reabsorption of sodium and water, helping to regulate blood pressure and fluid balance.
- Collecting Duct: The filtrate from several nephrons enters the collecting duct, where final adjustments in water and electrolyte balance are made, and urine is concentrated.
Conclusion
The nephron, with its glomerulus and other segments, plays a crucial role in filtering blood, reabsorbing needed substances, and excreting waste to form urine. This process is essential for maintaining homeostasis in the body.