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How do plasma proteins transport substances such as iron and cholesterol?

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Blood plasma — blood Blood sediment in test tubes, showing plasma (clear fluid), red blood cells (red), and the release of hemoglobin into the surrounding plasma (pink).

Plasma proteins facilitate the transport of substances like iron and cholesterol by acting as specialized carriers, as these substances are otherwise insoluble or require specific delivery mechanisms within the bloodstream.123

Iron Transport

Iron is transported in the plasma by a specific metal-binding protein called transferrin. Transferrin binds iron and carries it from tissues and the bloodstream to the bone marrow, where it is utilized in the formation of hemoglobin.42

Cholesterol Transport

Because cholesterol is insoluble in blood, it must be bound to proteins to be transported. This is achieved through lipoproteins, which are complexes of lipids and proteins. Two primary types of lipoproteins manage this process:23
* Low-density lipoproteins (LDLs): These transport cholesterol from the liver to the body's cells.3
* High-density lipoproteins (HDLs): These transport excess or unused cholesterol from tissues back to the liver, where it can be broken down and excreted.3

In addition to these specific carriers, other plasma proteins, such as globulins, also assist in transporting lipids, steroid hormones, and various other substances throughout the body.12