Final answer:
Unconjugated bilirubin travels in the blood bound to albumin. This albumin-bilirubin complex is transported to the liver, where bilirubin is conjugated and made water-soluble for excretion through feces. Lipoproteins, not bilirubin, primarily carry other lipids such as cholesterol and fats in the blood.
Step-by-step explanation:
Unconjugated bilirubin is a lipophilic substance, and in order to travel within the hydrophilic environment of blood, it must be carried by certain proteins. Primarily, it forms a complex with albumin, a protein found in plasma. This albumin-bilirubin complex facilitates the transportation of unconjugated bilirubin to the liver. Upon reaching the liver, the bilirubin is absorbed, leaving albumin in the plasma. The liver cells then conjugate the bilirubin with glucuronic acid to form bilirubin diglucuronide, which is water-soluble, through the action of the enzyme UDP glucuronyl transferase. This leads to effective excretion of bilirubin from the body via bile into the small intestine, and eventually, waste elimination through feces.
It's important to note that lipoproteins are involved in the transport of other hydrophobic substances through the blood, using their hydrophobic and hydrophilic properties to transport lipids to different parts of the body. However, unlike lipoproteins that carry cholesterol and fats, unconjugated bilirubin primarily uses albumin for its transport.
In pathological conditions, such as in infants with unconjugated hyperbilirubinemia where the enzyme UDP glucuronyl transferase is not fully developed, the ability to conjugate bilirubin is limited, which can lead to excessive unconjugated bilirubin in the blood, potentially causing severe conditions like kernicterus.