Acids and Bases

This week we are investigating pH. It may sound more like a chemistry class lesson, but it really is important to understand pH in order to understand our bodies.

Chapter 25 covers acids and bases (pH) as well as many other topics. This starts on page 897, and continues on through the end of this chapter. This also describes respiratory acidosis and alkalosis, which is helpful for putting this information on pH together with respiration.

On this page, toward the bottom, I have described body fluids and their components. This information is also covered in chapter 25. Understanding body fluids will help you to understand the urinary system. Then, the rest of the unit covers pH. First, you'll read about what pH is. Then, you'll need to understand the strengths of acids and bases. Then we get back into the body, by examining what body processes change pH, and then how to control these changes. The outline for the remaining pages is shown here:

outline23.jpg (10783 bytes)

Body Fluids

All body fluids can be generally separated into two fluid compartments: the fluid found inside of cells, versus the fluid found outside of cells. Your book classifies these fluid compartments as

Intracellular Fluid Compartment

All the fluid inside cells, which includes the dissolved the material in that fluid. Certainly, the fluid in each cell is separated from the fluid in every other cell, but this "compartment" considers the volume of each and every cell as contributing to the total intracellular fluid compartment volume.

This makes up about 63% of all the fluid in our bodies!

Extracellular Fluid Compartment

All the fluid outside of cells, including all the dissolved material in that fluid. This includes interstitial fluid, plasma, lymph, etc.

This makes up about 37% of all the fluid in our bodies.

What is in these fluids?

Generally, the dissolved material in these fluids includes lots of ions because salts dissolve in fluids. For example, if one puts table salt in water, the salt dissolves and dissociates into sodium ions and chloride ions. After the salt dissolves, you have ions in the water. The same thing happens in our own body fluids, so that they have tons of ions in them. The ions in fluids are typically referred to as electrolytes. There are also lots of dissolved organic materials, too, like sugars, amino acids, and proteins.

The intracellular and extracellular fluid compartments have different amounts of many of these dissolved electrolytes and organic materials. Your book represents that with the graph on page 816. Here's a table to represent that as well:

Dissolved Material	Intracellular Fluid Compartment	Extracellular Fluid Compartment
Na⁺	low	high
K⁺	high	low
Ca²⁺	very low	higher
Mg²⁺	high	low
Cl^-	low	high
HCO₃^-	low	high
PO₄^3-	high	low
SO₄^2-	no real difference
Protein	high	high in plasma lower in interstitial fluid and lymph

As you look through this list, you should note that these fluid compartments are extremely different. The membrane around the cells maintains certain items in high concentration inside of the cells (like potassium ions), and prevents other things from entering the cells (like sodium ions). In this manner, the two fluid compartments contain very different electrolytes within them.

One ion that is not listed here is the hydrogen ion. That is because the concentration of the hydrogen ion affects the pH of the fluid compartment. And the pH of the intracellular and extracellular fluid compartments are both near neutral, so there are similar concentrations of hydrogen ions in these compartments. That said, it is time to go on to learn about the pH of these fluids and how it is regulated.

Here are some additional web sites on pH... many of them are found as links in the pages through this unit, but some are just extra. There are some more links embedded throughout the unit.

A simple pH background from Chemistry 4 Kids.

A very simple page from Berkeley on pH.

Two similar pages with a bit more information on pH, but also more terminology than we need:

	A chapter outline
	Acids, bases and the pH scale

� 2011 STCC Foundation Press
written by Dawn A. Tamarkin, Ph.D.