Question

In the mammalian urinary system, the urine formed in the kidneys is carried to the urinary bladder by the _____ and from the bladder to the outside of the body by the _____. a. collecting duct, renal pelvis b. nephron, collecting duct c. renal pelvis, urethra d. ureters, urethra e. urethra, ureters

Short answer

The correct answer is (d) ureters, urethra.

Step-by-step solution

Understand the Question

Grasp the content of the question: 'In the mammalian urinary system, the urine formed in the kidneys is carried to the urinary bladder by the _____ and from the bladder to the outside of the body by the _____.' The task asks to choose correct sequence of structures involved in the process.

Recap the Urinary System Structure

In the mammalian urinary system, urine is formed in the kidneys. From there, it is carried to the urinary bladder. This transportation is implemented through tubes called ureters. Urine leaves the body through the tube called the urethra.

Match the Recap with the Choices

Seeing the choices available, let's match the recap with the choices. The correct option should match the sequence, 'kidneys-ureters-urinary bladder-urethra.' It is evident that the correct sequence is given in option (d) 'ureters, urethra.'

Key concepts

Kidney Function

The kidneys play a crucial role in maintaining the body's internal environment. These bean-shaped organs are responsible for filtering blood, removing waste, balancing bodily fluids, and regulating electrolytes. Another important function of the kidneys is to control blood pressure and produce hormones necessary for red blood cell production and strengthening bones.
To achieve these functions, the kidneys make use of specialized structures known as nephrons. Each kidney contains about a million nephrons, which are the functional units where filtration and urine production occur. Nephrons filter out toxins, excess salts, and urea—a nitrogen-based waste created from protein metabolism. The purified blood is then returned to the circulation, while the waste products are excreted as urine.
In summary, the kidney's role is indispensable for detoxification, fluid balance, and overall homeostasis.

Urinary Bladder

The urinary bladder is a hollow, muscular organ situated in the pelvis, serving as a temporary reservoir for urine before it is expelled from the body. Its expandable nature allows it to accommodate varying volumes of urine. As the bladder fills, its walls stretch and the inner lining smoothens out.
The main components of the bladder include the detrusor muscle, which forms the wall of the bladder, and the trigone area, which is a triangular section at the base that remains relatively fixed in place even as the bladder fills and empties.
When the bladder fills to a certain capacity, nerve signals alert the brain, prompting the urge to urinate. During urination, the detrusor muscle contracts while the sphincters at the bladder's opening relax, allowing urine to flow out into the urethra.
Understanding the bladder's function helps highlight its role in urinary storage and the coordinated release process.

Ureters

Ureters are muscular tubes that play the essential role of transporting urine from the kidneys to the urinary bladder. Each kidney is connected to one ureter, and these tubes are typically about 25-30 centimeters long.
The ureters are lined with smooth muscle fibers that undergo rhythmic contractions known as peristalsis. These contractions propel urine downward, regardless of the body's position. The urine enters the bladder in small spurts rather than a continuous stream.
To prevent the backward flow of urine once it reaches the bladder, a one-way valve system is in place. This anatomic feature is crucial for maintaining the unidirectional flow of urine and preventing infections from traveling back into the kidneys.
The role of ureters is vital for efficient urine transport and for maintaining the health of the urinary system by preventing potential infections.

Urethra

The urethra is the final pathway for urine to exit the body from the bladder. It is a narrow tube whose length varies significantly between sexes—being longer in males and shorter in females.
In addition to its primary function of conducting urine out of the body, the male urethra also serves a reproductive role by discharging sperm and seminal fluid during ejaculation. By contrast, the female urethra is solely involved in urination.
The discharge of urine from the urethra is a voluntary process controlled by an external sphincter muscle. This muscle must be relaxed to allow urine flow, illustrating the importance of sphincter control for continence.
Understanding the urethra's function underscores its role in the excretory and, in males, reproductive systems, highlighting the complexity and specialization within the mammalian urinary system.