Question
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Arrange the organs of the human excretory system in the correct order, based on the passage of urine.
Ureter, Urethra, Kidney, Urinary bladder

Answer Verified Verified
Hint: Filtration of blood through a system of fine tubules forms urine. It is a toxic metabolic nitrogenous waste that needs to be transported, stored temporarily and finally pushed out of the body.

Complete answer:
The excretory system performs the function of removal of metabolic nitrogenous wastes from the body. It includes a pair of kidneys where urine is formed. This urine is carried by a pair of ureters from each kidney to the urinary bladder. The single urethra finally discharges urine from the body.

Additional Information:
Kidneys- The paired kidneys are bean-shaped and reddish-brown. The right kidney is slightly lower than the left kidney because the liver seizes considerable space on the side above the right kidney. Both the kidneys bear a notch known as hilum from which blood vessels, lymph vessels, nerves and ureters enter or leave. It not only excretes wastes but also regulates blood volume and pressure. It also secretes erythropoietin - a hormone to induce red blood cells’ production.
Ureter- They are paired, narrow, tubular structures which open into the urinary bladder. Ureters are composed of stratified transitional epithelium.
Urinary bladder- It is a pear-shaped muscular sac found in the pelvic cavity. It temporarily stores urine. Urine exerts pressure on the inner walls of the urinary bladder when its volume exceeds 200-400 mL. This activates the stretch receptors on the wall of the urinary bladder and urges a person to urinate.
Urethra- It is a canal-like structure which extends from the floor of the bladder to the exterior. The male urethra is much longer than female urethra as it carries both urine and semen while female urethra discharges only urine.

So, the correct order of the organs of the human excretory system is Kidneys, ureters, urinary bladder and urethra.

Note: The opening of the urethra is controlled by specialised muscles known as sphincters. They are of two types- external sphincter and internal sphincter. The internal sphincter is present at the junction site of the urethra and urinary bladder. It is involuntary. The external sphincter is present inferior to the internal sphincter. It is voluntary. Micturition or urination occurs via a combination of voluntary and involuntary muscle contractions.