Parietal cells in the stomach release hydrochloric acid, activating pepsin and aiding in digestion. This creates a highly acidic environment in the stomach that could be harmful to other regions of the body. When the stomach contents, or chyme, is transported out of the stomach and enters the small intestine it must be neutralized. The first segment of the small intestine is the duodenum, where digestive enzymes from the pancreas are secreted to help digest fats and proteins.

Along with these enzymes, bicarbonate is secreted by the pancreas into the small intestine. The bicarbonate reacts with the remaining acid, producing water, salt, and carbon dioxide.

The functional unit of the kidney is the nephron. Blood is filtered into the nephron to create filtrate. As the filtrate flows through the nephron tubules, its concentration is tightly regulated and ions and water are added and removed. The end result is a highly-concentrated filtrate that is transported to the bladder for excretion.

Neurons are the functional unit of the nervous system, not the kidney. Sarcomeres are the basic contractile unit of skeletal muscle, and chief cells are specialized stomach cells that secrete digestive enzymes, such as pepsinogen.

Ammonia is highly water-soluble and can be toxic to cells at low concentrations due to presence of its ammonium ion, which can interfere with oxidative phosphorylation. Ammonia is small and can easily diffuse through cell membranes, making it easy to excrete. Essentially, there is a trade off of easy excretion and toxicity levels.

For aquatic animals, however, toxicity is negligible due to the large volume of water available to dilute ammonia wastes. The high solubility of ammonia wastes and the abundance of water solvent allow for the ammonia to be transported out of cells in an very dilute concentration, without harming the organism. This allows aquatic organisms to conserve energy, compared to terrestrial organisms that must convert ammonia wastes to other forms.

Amphibians and mammals convert ammonia to urea, which can be excreted with less water, but must still be relatively dilute. These animals release liquid wastes from the body, resulting in water loss, but conserve energy compared to organisms that continue to convert urea into uric acid. Birds and reptiles excrete uric acid, which requires very little water waste, but uses a larger amount of energy in conversion. This is beneficial to animals that may not have ready access to fresh water.

There is a key trade-off between energy consumption and toxicity in the excretion of nitrogenous wastes. Ammonia is the simplest form of the waste product, and requires very little energy to produce; however, it is highly toxic and must be diluted to extremely low concentrations in order to be safe to the cells. Many aquatic animals excrete ammonia because of their proximity to water. Access to large amounts of water means that these organisms can safely excrete dilute ammonia without needing to use energy in conversions.

Terrestrial animals, with less access to water, excrete urea or uric acid. These wastes are derived from ammonia, but require an input of energy for the conversion. They are less toxic and require less water loss for dilution, making them ideal for animals that must conserve fluids. Uric acid is the least toxic of the nitrogenous wastes, but also requires the greatest energy investment.

Alcohol decreases the activity of antidiuretic hormone (vasopressin). A diuretic increases the production of urine and thus, inhibition of this antidiuretic hormone results in an increase in the production of highly diluted urine.

Alcohol does not block the flow of fluids through the kidney tubules.

Proteins would not be found in the urine because these molecules are too large to pass through the glomerulus of the nephron of the kidney. They would be filtered out and remain in the bloodstream. Meanwhile, all of the other compounds would be present in normal urine.