Randi, a 24 year old, reports that "I have been urinating two to three times an hour, and it burns and itches and smells awful. My belly feels "yucky." When you ask Randi about pain, she states: "I don't have any pain at the back of my waist." Her temperature is 99.8°F. A clean voided urine sample is positive for leukocytes and the bacterium E. coli. Randi's UTI is most likely to be a(n):

A. The liver metabolizes most components of food (protein, carbohydrates and fats) and also cleans the blood of bacteria and drugs: The liver plays a central role in metabolism, including converting nutrients into energy or storage forms, breaking down toxins, metabolizing drugs, and filtering bacteria from the blood via Kupffer cells.

B. The liver maintains a balanced level of electrolytes and pH in the body and stores glucose, minerals and vitamins: While the liver stores glycogen and some vitamins and minerals, it does not directly regulate electrolyte or pH balance, which is primarily the function of the kidneys and respiratory system.

C. The liver is responsible for the absorption of most dietary nutrients as well as the production of growth hormones: Nutrient absorption is mainly the role of the small intestine. Growth hormone is produced by the pituitary gland, not the liver, making this statement inaccurate.

D. The liver contributes to the metabolism of ingested food and provides the fluids that the GI tract requires: Although the liver produces bile, which aids in fat digestion, it does not supply most of the fluids needed by the GI tract. Salivary glands, gastric glands, pancreas, and intestines contribute the majority of GI fluids.

A. Proteus mirabilis: While Proteus mirabilis is a recognized cause of UTIs, especially in catheterized patients or those with structural abnormalities, it is not the most common pathogen overall.

B. Escherichia coli: E. coli is by far the most common pathogen responsible for urinary tract infections, accounting for approximately 80–90% of uncomplicated UTIs due to its ability to adhere to the uroepithelium with fimbriae.

C. Staphylococcus saprophyticus: This organism is a common cause of UTIs in sexually active young women, but overall it is much less prevalent than E. coli across all age groups and sexes.

D. Klebsiella pneumoniae: Although K. pneumoniae can cause UTIs, particularly in hospitalized or immunocompromised patients, it is not as frequently encountered as E. coli in community-acquired cases.