Semipermeable Membranes - Significant?

Semipermeable Membranes and Fluid Compartments

The water moves back and forth between a cell, the space surrounding a cell and a small member of the blood circulatory system called a capillary.

The cell's interior water is intracellular water and occupies the Intracellular Fluid Compartment of the body. When the water leaves the cell through its semipermeable cell membrane it enters the Interstitial Fluid Compartment of the Extracellular Fluid Compartment that occupies the space between the cell and the circulatory system. When it enters the capillary of the circulatory system through its single cell layer semipermeable membrane it is now in the Extracellular Fluid Compartment. Remember,, the Extracellular Fluid Compartment is made up of the interstitial fluid compartment and the circulatory system.

Your Digestive System breaks down fluids and food into items that easily (sometimes) pass through the selectively permeable membrane with or without help.

Water is like a stream with all these breakdown products floating in it. This is pretty simplistic but you get the idea. 

The reason water flows is the ability of the body to move particles (solute particles)  to the side of a selectively  permeable membrane where the body needs the water to flow. The cells of the body need the breakdown products of digestion. This is the way the breakdown products make it to the circulatory system for distribution to all the cells in the body.

This is the ultimate purpose of glucose. Food for the manufacture of insulin in the pancreas. These strips test for glucose in the blood.

Now were getting to Act Two. The whole process above is reversed to supply those products of digestion to the destination cells.

Since were talking to interested diabetics the destination products, for us, is going to the Pancreas.

Fluids - Extracellular - Interstitial - Intracellular

Fluid and Electrolytic Balance

Water is a solvent, not a solute molecule or particle. Water does not have a "concentration" if it is a body solvent. Things dissolved in water, in living things form a solution.

Fluid is compartmentalized. The basic structure consists of Extracellular Fluid (Outside the Cell) and Intracellular Fluid (Inside the Cell).

The Extracellular Fluid Compartment consists of all the fluid outside the cells. One compartment is the Blood (contained in blood vessels) and the other compartment of the Extracellular Fluid Compartment is the Interstitial Fluid. It is the fluid that exists between the blood vessels and the cells.

The body controls the changes that occurs in the  fluids (what's dissolved in the water that makes up the fluid) to shift fluid from one compartment to another compartment when needed.

This is Fluid Balance.

When fluid flows from one compartment to another it does this in response to the differing concentrations of solutes dissolved, in the water, of each compartment. 

Before we proceed, we need to understand a workable definition of Osmosis. Remember this definition.

Osmosis is the diffusion of water through a selectively permeable cell membrane from an area of low solute concentration to an area of high solute concentration.

Since a cell membrane is constantly changing, and is selectively permeable, the body breaks down large molecules in the fluid into small, electronically charged particles called ions. Some of these are simple like the positively (+) charged Hydrogen Ion and some are complex like the negatively charged ( - ) Bicarbonate Ion discussed in a post earlier about Buffer Systems.

A good way to look at electrolytes is replacement drinks for athletes after a workout. Heres one product below.

These particles are collectively referred to as Electrolytes. 

The body need to shift these essential electrolytes from compartment to compartment to help balance the concentration of electrolytes throughout the body.

This is Electrolytic Balance.

Respiration Buffering of Acidosis - Bicarbonate

Buffering of an Acid - Bicarbonate Buffering System

There are three systems involved in preventing wide swings in blood pH. Respiration, Circulatory and Renal systems.

A goal in Homeostasis is the prevention of wide swings in chemical imbalance. The free hydrogen ion (H +) is a prime candidate to keep within the pH range of 7.38 and 7.42.

It is important to recognize the ability to have a two way system. This enables the bicarbonate buffering system to act on an acidosis one way and an alkalosis on the other way.

One factor to remember is living cells always produce carbon dioxide as a by product. Therefore there is a constant  source of carbon dioxide being formed.

The Respiratory System can control the amount of free hydrogen ion (H +) by either breathing rapidly or very slowly.

Here is the equation:

If carbon dioxide is allowed to build up in the blood by increasing its concentration from lower than normal respiration rate the equation above moves to the right.

The water (H2O) combines with the excess carbon dioxide to form undissociated carbonic acid (H2CO3) that immediately breaks down (dissociates) into free hydrogen ion (H+) and a bicarbonate ion (HCO3-). The increase in the concentration of free hydrogen ion (H+) lowers the pH (becomes more acidic).

If the acidity of the blood approaches a pH of 7.38 the reversible formula above begins to move to the left.

The excess of free hydrogen ion (H+) combines with the bicarbonate ion (HCO3-) to form carbonic acid (H2CO3) that immediately breaks down into water (H2O) and carbon dioxide (CO2).

This happens because the Respiratory System is breathing at a faster rate than normal and "blows off" the excess carbon dioxide (CO2). 

This temporarily takes free hydrogen ion (H+) out of circulation and the pH moves to a more alkaline pH of 7.42.

In a nutshell this is the Bicarbonate Buffering System.

This process continues without your knowledge as a state of equilibrium is maintained that keeps the pH in the range of 7.38 to 7.42.

Just what is Acidosis and Alkalosis?

Acidosis and Alkalosis

First, in the  human body, an acid is the presence of a free hydrogen ion (H+) in the fluids found in the body. This is an important point.

If the hydrogen ion is chemically combined with some other chemical it is not affecting the pH of the body, at that time.

The normal pH of the human body is 7.42. This is an average pH. The range for pH extends from a pH of zero to a pH of 14. Any pH value near 1 is extremely Acidic (lots of free hydrogen ions). Any pH value near 14 is very Basic (very few free hydrogen ions).

The normal pH value of the human body is slightly Basic. When you look at pH what is the significance of the number 7.42? How do we interpret them?

The definition of pH is meaningless when it come to what is happening to the patient. If the pH falls from a value of 7.42 to 7.41 the increase in the number of free hydrogen ions is 10% (percent).

If it drops to 7.32 the increase in the number of free hydrogen ions is 100% (percent). 

Yes, it has doubled. A patient who has a drop of one tenth of a pH value is in a serious Acidosis. Think trends are important? Using an old Minnesota phrase, "You Betcha!"

Going the other way, if the pH rises to 7.52 the number of free hydrogen ions has declined 100% (percent). The patient is in a serious Alkalosis.

Did we really need a formal definition of pH to understand what its values tell us.?

Remember, with electrolytes, time of decision is critical.