The diagram illustrates two homeostatic and excretory pathways occurring within a mammalian hepatocyte situated between a blood sinusoid (Sinusoid X) and a bile canaliculus (Canaliculus Y).
Based on the diagram and your knowledge of liver function, which of the following statements is correct?
The conversion of ammonia to urea in Pathway 1 is a passive, hydrolytic reaction that allows toxic nitrogenous waste to diffuse freely down its concentration gradient into Sinusoid X.
Pathway 1 is an ATP-requiring process that reduces the concentration of highly toxic ammonia in the body by converting it to a less toxic, soluble substance that is transported in Sinusoid X to the kidneys.
Bilirubin excretion in Pathway 2 represents a form of ultrafiltration, where high hydrostatic pressure in Sinusoid X forces the breakdown products of haemoglobin directly into Canaliculus Y.
Hepatocytes directly engulf senescent red blood cells from Sinusoid X and phagocytose them to initiate Pathway 2, releasing bilirubin as a metabolic waste product.