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After studying this chapter, you should be able to:

  • List the major functions of blood.

  • Describe the principal functions of serum albumin.

  • Explain how haptoglobin protects the kidney against formation of damaging iron precipitates.

  • Describe the roles of ferritin, transferrin, and ceruloplasmin in iron homeostasis.

  • Describe the mechanism by which transferrin, transferrin receptors, and HFE protein regulate the synthesis of hepcidin.

  • Explain how iron homeostasis can be perturbed by dietary deficiencies or certain disorders.

  • Describe the general structures and functions of the five classes of immunoglobulins.

  • Explain how up to a million different immunoglobulins can be generated utilizing fewer than 150 human genes.

  • Describe the activation and mode of action of the complement system.

  • Compare and contrast the adaptive and innate immune systems.

  • Define the term lectin.

  • Outline the key differences between polyclonal and monoclonal antibodies.

  • Describe the salient features of autoimmune and immunodeficiency disorders.


The proteins that circulate in blood plasma play important roles in human physiology. Albumins facilitate the transit of fatty acids, steroid hormones, and other ligands between tissues, while transferrin aids the uptake and distribution of iron. Circulating fibrinogen serves as a readily mobilized building block of the fibrin mesh that provides the foundation of the clots used to seal injured vessels. Formation of these clots is triggered by a cascade of latent proteases, or zymogens, called blood coagulation factors. Plasma also contains several proteins that function as inhibitors of proteolytic enzymes. Antithrombin helps confine the formation of clots to the vicinity of a wound, while α1-antiproteinase and α2-macroglobulin shield healthy tissues from the proteases that destroy invading pathogens and remove dead or defective cells. Circulating immunoglobulins called antibodies form the front line of the body’s immune system.

Perturbances in the production of plasma proteins can have serious health consequences. Deficiencies in key components of the blood clotting cascade can result in excessive bruising and bleeding (hemophilia). Persons lacking plasma ceruloplasmin, the body’s primary carrier of copper, are subject to hepatolenticular degeneration (Wilson disease), while emphysema is associated with a genetic deficiency in the production of circulating α1-antiproteinase. More than one in every 30 residents of North America suffer from an autoimmune disorder, such as type 1 diabetes, asthma, and rheumatoid arthritis, resulting from the production of aberrant immunoglobulins (Table 52–1). Insufficiencies in the production of protective antibodies, such as occur in many persons infected by the human immunodeficiency virus (HIV) or patients administered immunosuppressant drugs, render them immunocompromised, extremely susceptible to infection by microbial and viral pathogens. While the root causes of plasma protein–related diseases such as hemophilia are relatively straightforward, others—in particular many autoimmune disorders—arise due to the complex and cryptic interplay of genetic, dietary, nutritional, environmental, and medical factors.

TABLE 52–1Prevalence of Selected Autoimmune Diseases Among U.S. Population

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