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Table 2–2 Important Electrolytes That Dissociate Chapter 2 The Chemical Level of Organization 67
in Body Fluids
and the molecules do not dissolve. Molecules that do not read-
Electrolyte Ions Released ily interact with water are called hydrophobic (hı.-dro. -FO■ B-
ik; hydro-, water + phobos, fear). Fats and oils of all kinds are
NaCl (sodium chloride) S Na+ + Cl−
KCl (potassium chloride) S K+ + Cl− 2some of the most familiar hydrophobic molecules. For exam-
CaPO4 (calcium phosphate) S Ca2+ + PO42−
NaHCO3 (sodium bicarbonate) S Na+ + HCO3− ple, body fat deposits consist of large, hydrophobic droplets
MgCl2 (magnesium chloride) S Mg2+ + 2Cl− trapped in the watery interior of cells. Gasoline and heating oil
Na2HPO4 (sodium hydrogen phosphate) S 2Na+ + HPO42− are hydrophobic molecules not found in the body. When acci-
Na2SO4 (sodium sulfate) S 2Na+ + SO42− dentally spilled into lakes or oceans, they form long-lasting oil
slicks instead of dissolving.
An aqueous solution containing anions and cations will
conduct an electrical current. When this happens, cations (+) &T i p s T r i c k s
move toward the negative side, and anions (–) move toward To distinguish between hydrophobic and hydrophilic,
the positive side. Electrical forces across plasma membranes r emember that a phobia is a fear of something, and that
affect the functioning of all cells, and small electrical currents -philic ends with “lic,” which resembles “like.”
carried by ions are essential to muscle contraction and nerve
function. In Chapters 10 and 12 we will discuss these processes Colloids and Suspensions
in more detail.
Body fluids may contain large and complex organic molecules,
Electrolytes and Body Fluids such as proteins and protein complexes, that are held in solu-
tion by their association with water molecules (Figure 2–9c).
Soluble inorganic substances whose ions will conduct an A solution containing dispersed proteins or other large mol-
e lectrical current in solution are called electrolytes (e-LEK-tro. - ecules is called a colloid. Liquid Jell-O is a familiar viscous
lı.ts). Sodium chloride in solution is an electrolyte. The disso- (thick) colloid. The particles or molecules in a colloid will re-
ciation of electrolytes in blood and other body fluids releases main in solution indefinitely.
a variety of ions. Table 2–2 lists important electrolytes and the
ions released when they dissociate. In contrast, a suspension contains large particles in solu-
tion, but if undisturbed, its particles will settle out of solution
Changes in the concentrations of electrolytes in body flu- due to the force of gravity. For example, stirring beach sand
ids will disturb almost every vital function. For example, de- into a bucket of water creates a temporary suspension that will
clining potassium levels will lead to a general muscular paral- last only until the sand settles to the bottom. Whole blood
ysis, and rising concentrations will cause weak and irregular is another temporary suspension, because the blood cells are
heartbeats. The concentrations of ions in body fluids are care- suspended in the blood plasma. If clotting is prevented, the
fully regulated, mostly by the coordination of activities at the cells in a blood sample will gradually settle to the bottom of
kidneys (ion excretion), the digestive tract (ion absorption), the container. Measuring that settling rate, or “sedimentation
and the skeletal system (ion storage or release). rate,” is a common laboratory test.
Hydrophilic and Hydrophobic Compounds Checkpoint
14. Explain how the chemical properties of water make life
Some organic molecules contain polar covalent bonds, which
also attract water molecules. The hydration spheres that form possible.
may then carry these molecules into solution (Figure 2–9c).
Molecules that interact readily with water molecules in this See the blue Answers tab at the back of the book.
way are called hydrophilic (hı.-dro. -FIL-ik; hydro-, water +
philos, loving). Glucose, an important soluble sugar, is one 2-7 Body fluid pH is vital
example.
for homeostasis
Many other organic molecules have very few or no polar
covalent bonds. Such molecules do not have positive and neg- Learning Outcome Discuss the importance of pH and the role of buffers
ative ends, and are said to be nonpolar. When nonpolar mol- in body fluids.
ecules are exposed to water, hydration spheres do not form
A hydrogen atom involved in a chemical bond or participating
in a chemical reaction can easily lose its electron, to become a
hydrogen ion, H+. Hydrogen ions are extremely reactive in so-
lution. In excessive numbers, they will break chemical bonds,
change the shapes of complex molecules, and generally disrupt
