lactate produced by skeletal muscles during anaerobic respi-ration (see chapter 9). The blood carries lactate to the liver,where it is converted into glucose.3. Transport of regulatory molecules . The blood carries the hor-mones and many of the enzymes that regulate body processesfrom one part of the body to another.4. Regulation of pH and osmosis . Buffers (see chapter 2), whichhelp keep the blood’s pH within its normal range of 7.35–7.45,are in the blood. The osmotic composition of blood is alsocritical for maintaining normal fluid and ion balance.5. Maintenance of body temperature . Body temperature regula-tion involves several mechanisms, including the movement ofwarm blood from the interior of the body to its surface, whereheat is released.6. Protection against foreign substances . Certain cells andchemicals in the blood make up an important part of theimmune system, protecting against foreign substances, suchas microorganisms and toxins.7. Clot formation . Blood clotting protects against excessiveblood loss when blood vessels are damaged. The blood clotthat forms in damaged tissue is also the first step in tissuerepair and the restoration of normal function (see chapter 4).

19.3 Plasma

LEARNING OUTCOMES

After reading this section, you should be able to

A. Name the components of blood plasma.

B. List the three major plasma proteins and describe theirfunctions.

ASSESS YOUR PROGRESS

1. List the ways that blood helps maintain homeostasis in thebody.

2. What substances are transported by the blood?

3. What is the normal pH range of the blood?

4. How does the blood provide protection?

Plasma (plaz′m ă ) is the liquid part of blood. It is a pale yellow fluidthat consists of about 91% water and 9% other substances, such asproteins, ions, nutrients, gases, waste products, and regulatory sub-stances (table 19.1). Plasma is a colloid (kol′oyd), which is a liquidcontaining suspended substances that do not settle out of solution.Most of the suspended substances are plasma proteins, which makeup about 7% of the volume of plasma (figure 19.1). Based onmolecular size and charge, the plasma proteins can be classified intothree groups: (1) albumin, (2) globulins, and (3) fibrinogen. Almostall of the plasma proteins are produced by the liver or blood cells, anotable exception being protein hormones. Albumin (al-b ū ′min)makes up 58% of the plasma proteins and is important in regulatingthe movement of water between the tissues and the blood. Recallfrom chapter 3 that osmosis, the diffusion of water, occurs whensolutes cannot easily move across a selectively permeable barrierand that osmotic pressure is the tendency for water to move acrossthat barrier. Because albumin does not pass easily from the bloodinto tissues, it plays an important role in maintaining blood colloidosmotic pressure (see chapters 21 and 26). Albumins also bind andtransport other molecules in the blood, such as fatty acids, bilirubin,and thyroid hormones. Globulins (glob′ ū -linz) account for 38% ofthe plasma proteins. The globulins are subdivided into α, β, and γ