Final answer:
An individual running a long distance on a hot day will sweat profusely, leading to a decreased water level in the body. This causes the kidneys to conserve water, resulting in a reduced volume of urine that is darker and possibly has a slight odor. As hydration levels improve, urine volume will increase and color will lighten.
Step-by-step explanation:
When an individual participates in a long-distance run on a hot day, they will often produce large quantities of sweat. This is a natural response to help cool the body but has the effect of reducing the amount of water in the body since sweat is primarily composed of water. As a result, the kidneys, which act as the main organs of the excretory system, will work to conserve water.
Due to the loss of water through sweat, the body will have less water available for urine production. The pituitary gland detects the lower water concentration and releases less antidiuretic hormone (ADH), which leads to the kidneys reabsorbing more water back into the blood. Consequently, the volume of urine will decrease, and the urine produced will appear darker in color, often with a slight odor, as the kidneys concentrate the urine to preserve fluids.
If the body's water levels return to normal, for instance by drinking more water after the run, the kidneys will adjust accordingly. With the increased water intake, the pituitary gland will release less ADH, and the kidneys will produce a larger volume of more dilute urine, which will be lighter in color. Therefore, the characteristics of urine output change depending on body hydration levels, influenced by factors such as exercise intensity, environmental temperature, and water intake.