Question

Which of the following indicates the correct order of the structures through which urine would pass during formation and excretion? a. nephron, renal pelvis, ureter, bladder, urethra b. renal pelvis, ureter, nephron, urethra, bladder C. nephron, renal pelvis, urethra, bladder, ureter d. renal pelvis, nephron, ureter, bladder, urethra

Short answer

a. nephron, renal pelvis, ureter, bladder, urethra

Step-by-step solution

- Understand the function of each structure

Before determining the correct order, it's important to know what each structure does. The nephron filters blood to form urine. The renal pelvis collects the urine from the nephrons. The ureter transports urine from the kidneys to the bladder. The bladder stores urine temporarily. The urethra is the final passage through which urine is excreted from the body.

- Identify the starting point

The formation of urine starts in the nephron. Thus, the correct sequence must start with the nephron.

- Determine the path after nephron

After urine is formed in the nephron, it flows into the renal pelvis. Therefore, the second structure in the sequence should be the renal pelvis.

- Follow the path to excretion

From the renal pelvis, urine travels down the ureter to reach the bladder for storage. The final step is the passage of urine from the bladder through the urethra to be excreted.

- Verify the correct order

The correct order of structures through which urine would pass is: nephron, renal pelvis, ureter, bladder, urethra. This matches option (a).

Key concepts

nephron function

The nephron is the basic functional unit of the kidney. It's responsible for filtering blood and forming urine. Each nephron consists of several parts: the glomerulus, Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and the collecting duct. Blood enters the glomerulus where filtration occurs. The filtered fluid, now called filtrate, passes through the tubule system. Here, essential nutrients and water are reabsorbed, while waste products and excess ions are secreted into the filtrate, forming urine. The nephron is essential for removing waste from the body and maintaining overall fluid and electrolyte balance.

renal pelvis role

The renal pelvis is a funnel-shaped structure in the kidney. It collects urine produced by the nephrons and channels it into the ureter. The renal pelvis is located at the hilum, the central part of the kidney where blood vessels, nerves, and ureters connect. It acts as a reservoir, ensuring smooth and efficient transfer of urine from the kidney to the ureter. Without the renal pelvis, the urine could not be effectively collected and moved forward, potentially leading to backflow and kidney damage.

ureter function

The ureter is a vital tube-like structure that connects the renal pelvis of the kidney to the bladder. It serves as a passageway for urine to travel from the kidneys to the bladder. Each person has two ureters, one for each kidney. The ureters are lined with smooth muscle, which contracts rhythmically to propel the urine down to the bladder through a process called peristalsis. The ureters are equipped with one-way valves at their junction with the bladder to prevent backflow, ensuring that urine only moves in one direction.

bladder storage

The bladder is a muscular, balloon-like organ that stores urine temporarily before it is excreted from the body. It is located in the pelvis and can expand and contract based on the amount of urine it holds. The bladder lining is specialized to stretch and accommodate increasing volumes of urine. When the bladder is full, stretch receptors in its walls send signals to the brain, triggering the urge to urinate. This process allows for controlled urination at convenient times, avoiding constant and uncontrolled urine flow.

urethra excretion

The urethra is the final structure in the urinary pathway, serving as the conduit for urine excretion from the body. In males, the urethra is longer and passes through the penis, while in females, it is shorter and opens just above the vaginal opening. The urethra is surrounded by muscles, including the external urethral sphincter, which provides voluntary control over urination. During urination, the brain signals the sphincter to relax, allowing urine to flow out of the bladder, through the urethra, and finally out of the body.