Problem: An 80 year old woman presents with a three-to-four day history of malaise and "generally not feeling well" followed by vomiting. She has a history of atrial fibrillation and takes digoxin (a cardiac glycoside) to help control heart rate and rhythm and to improve cardiac contractility, and rivaroxaban (brand name Xarelto) to reduce her risk of stroke and blood clots. What is likely to be the main age-related physiological change underlying her condition? Group of answer choices Reduced intestinal transit time Reduced hepatic metabolism Reduced glomerular filtration rate Reduced gastric emptying