Why is liver so dark red in living animals?

Liver appears dark red in living animals due to its rich blood supply. The liver receives a dual blood supply from the hepatic artery and the portal vein. The hepatic artery supplies oxygenated blood to the liver, while the portal vein delivers nutrient-rich blood from the digestive organs. This abundant blood supply is essential for the liver to perform its numerous functions, which include detoxification, metabolism, and storage of nutrients.

The dark red color of the liver is mainly attributed to the presence of a high concentration of hemoglobin in the blood vessels within the organ. Hemoglobin is the protein that carries oxygen in red blood cells. When the blood is oxygenated (carrying oxygen from the lungs to the body tissues), it appears bright red. However, the blood in the liver is partially deoxygenated (reduced hemoglobin) as it has been depleted of oxygen during various metabolic processes within the liver. Reduced hemoglobin absorbs more red and yellow light, giving it a darker reddish-brown color. This is why the liver has a darker appearance compared to other organs.