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INTRODUCTION

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OBJECTIVES

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 interact to regulate synthesis of hepcidin, a key regulator of iron homeostasis.

  • 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 and the uses of monoclonal antibodies.

  • Explain how our bodies are able to synthesize up to a million different immunoglobulins utilizing fewer than 150 genes.

  • Describe the how the complement system becomes activated and subsequently lyses invading microorganisms.

  • Explain how the body’s adaptive immune system differs from its innate immune system.

  • Define the term lectin.

  • Outline the key differences between polyclonal and monoclonal antibodies.

  • Explain the salient features of autoimmune and immunodeficiency disorders.

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BIOMEDICAL IMPORTANCE

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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. Transferrin aids the uptake and distribution of iron, a component of many critically important metalloproteins. 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. Clot formation is triggered by a cascade of blood coagulation factors, latent proteases that normally circulate as inactive proproteins, or zymogens. 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 prevent the proteases used to destroy invading pathogens and dead or defective cells from damaging healthy tissue. Circulating immunoglobulins called antibodies form the front line of the body’s immune system.

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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. Aberrant production of immunoglobulins characterizes the numerous autoimmune disorders, such as type-1 diabetes, asthma, and rheumatoid arthritis, that affect more than one in every thirty residents of North America (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, renders them immunocompromised, extremely susceptible to infection by microbial and viral pathogens, and vulnerable to their spread. While the root causes of plasma protein-related diseases such as hemophilia are relatively straightforward, others—in particular many autoimmune disorders—arise due to ...

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