Albumin is the most abundant (about 55%) of the plasma proteins. An important function of albumin is to bind with various molecules in the blood and serve as a carrier protein, transporting these substances throughout the circulation. Substances that bind with albumin include hormones; amino acids; fatty acids; bile salts; and vitamins. Albumin also serves as an osmotic regulator. Because capillary walls are impermeable to plasma proteins, these molecules exert a powerful osmotic force on water in the blood. In fact, the plasma colloid osmotic pressure exerted by plasma proteins is the only force that retains water within the vascular compartment and therefore maintains blood volume (see Chapter 15). Albumin is synthesized in the liver.

The globulins account for about 38% of plasma proteins. The three types of globulins are alpha (a), beta (b), and gamma (g). The alpha and beta globulins are involved with several activities. They transport substances in the blood (hormones, cholesterol, iron), function as clotting factors, and serve as precursor molecules (angiotensinogen). The gamma globulins function as antibodies, which play an important role in the immune response. Alpha and beta globulins are synthesized in the liver; the gamma globulins are made by the lymphocytes (a type of white blood cell).

Fibrinogen also plays a role in the blood clotting process. It serves as a precursor for fibrin, which forms the meshwork of a blood clot. Fibrinogen is synthesized in the liver.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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