Blood, Sweat and Buffers

Buffers in Biological Systems

Biological Buffers*

*A buffer resists changes in pH when small quantities of an acid or base are added to it.

Every life form is extremely sensitive to slight pH changes. Human blood for example needs to remain within the pH range of 7.38 to 7.42.

How do buffer solutions work?

A buffer solution has to “remove” any hydrogen ions or hydroxide ions you might add - otherwise the pH will change.

A buffer contains a weak acid and a weak base.

They do not react with each other or the water

But will react with strong acids or bases

If a strong base is added to a buffer, the weak acid will give up its H+ in order to transform the base (OH-) into water (H2O). Since the added OH- is consumed by this reaction, the pH will change only slightly.

If a strong acid is added to a buffer, the weak base will react with the H+ to form the weak acid HA: H+ + A- → HA. The H+ gets absorbed by the A- instead

of reacting with water to form H3O+ (H+), so the pH changes only slightly.

H2CO3 H+ + HCO3-

Carbonic acid bicarbonate ion

Two especially important biological buffers are the phosphate and bicarbonate systems.

Living systems have built in biological buffers.

You can also find chemical (artificial) buffers.

Examine the buffering ability of substances

Problem: How well do different compounds buffer against changes in pH?

Goal: Complete the experiment testing the buffering ability of the model buffer to changes in pH compared to water alone.

Conclusion: How is this a good model for the function of a buffer in a biological system?

Experimental materials:

0.10 M HCl (acid)

0.10 M NaOH (base)

droppers

pH indicator/paper

Small test tubes

stirring rod

distilled water

Sodium bicarbonate solution (model base)

Seltzer water solution (model acid)

Why is it important to maintain a constant blood pH of about 7.4?

Hemoglobin’s ability to carry oxygen is modified by altered blood pH

Oxygen absorption at the cellular level decreases in acidic environments.

The products of cellular respiration, Carbon Dioxide and Water, affect the pH of blood

Q2: Do you agree or disagree with this statement:

respiration?

Think about what is needed for respiration and the products of respiration.

What happens to the pH of blood during cellular respiration?

Example: blood buffering system

Quick review of cellular respiration:

How do the products of respiration (CO2 and H2O) affect blood pH?

• Carbon Dioxide combines with water and produces Carbonic acid , therefore pH of blood decreases

CO2 + H2O H2CO3 - Uh oh! Blood is acidic!

Carbonic Acid

Blood is acidic! What next?

Hemoglobin

- Component of blood- Large capacity to carry oxygen- Works as a buffer to maintain stable pH in blood

How does hemoglobin buffer blood pH?

• In response to decrease in pH, Hemoglobin gives up oxygen to support respiration (remember, oxygen is needed for respiration)

• Then, Hemoglobin acts as a buffer

and takes H+ ions from Carbonic acid.

Hemoglobin + H2CO3 HCO3- +(Hemoglobin(H+))

• Bicarbonate ions raise the pH of the blood

bicarbonateCarbonic acid

In the lungs, bicarbonate ions form carbon dioxide and water (with the help of hemoglobin) and are expelled from lungs

HCO3- + Hemoglobin(H+) CO2 + H2O

To more clearly show the two equilibrium reactions in the carbonic-acid-

bicarbonate buffer, the equation below is rewritten to show the direct

involvement of water:

The equilibrium on the left is an acid-base reaction. Carbonic acid (H2CO3) is the acid and water is the base. The conjugate base for H2CO3 is HCO3

- (bicarbonate ion).

If buffers in the blood stopped working, what would happen?

• Proteins require a specific three-dimension shape to function, and their shapes are affected by the tiniest changes in pH of your bodily fluids.

• Changes in pH affect the functionality of some enzymes

• Changes in pH affect the assimilation of certain minerals

• Most harmful bacteria and viruses prefer acidic environments.

Do your activities affect your blood pH?some examples

example: Exercise

When we exercise, our heart rate,

systolic blood pressure, and cardiac

output (the amount of blood pumped per

heart beat) all increase. Blood flow to the

heart, the muscles, and the skin increase.

The body's metabolism becomes more

active, producing CO2 and H+ in the

muscles. We breathe faster and deeper

to supply the oxygen required by this

increased metabolism.

Exercise has many short-term (acute) and long-term effects that the body must

be capable of handling for the exercise to be beneficial.

Some of the major acute effects of exercising.

As we develop a long-term habit of exercise, our cardiac output and lung

capacity increase, even when we are at rest, so that we can exercise longer

and harder than before. Over time, the amount of muscle in the body

increases, and fat is burned as its energy is needed to help fuel the body's

increased metabolism.

Eventually, with strenuous exercise, our body's metabolism exceeds the

oxygen supply and begins to use alternate biochemical processes that do not

require oxygen. These processes generate lactic acid, which enters the

blood stream.

Blood buffering during exercise.

During exercise, muscles use up oxygen as they convert glucose to mechanical energy. The production and removal of CO2

and H+, together with the use and transport of O2, cause chemical changes in the blood. These chemical changes, cause the pH of the blood to drop.

If the pH drops below 6.8 (or

rises above 7.8), death may occur. Fortunately, we have buffers in the blood to protect against large changes in pH.

O2 is supplied by hemoglobin in the blood. CO2 and H+ are produced during the breakdown of glucose, and are removed from the muscle via the blood.

The kidneys and the lungs work together to help maintain a blood pH of 7.4 by affecting the components of the buffers in the blood.

This figure shows the major organs that help control the blood concentrations of CO2

and HCO3-, and thus help

control the pH of the blood.

Removing CO2 from the blood helps increase the pH.

Removing HCO3- from the

blood helps lower the pH.

Q3: Do you agree or disagree with this statement:

The body’s buffering system is there to protect the body from damage.

Can you think of something you eat or drink that affects your blood pH?

Q4: Do you agree or disagree with this statement:

Teenagers are at risk of osteoporosis due to the buffering system in the body

Look at the 3rd ingredient of most soda.

Phosphoric Acid H3PO4

Researchers at Tufts University, studying several thousand men and women, found that women who regularly drank cola-based sodas -- three or more a day -- had almost 4% lower bone mineral density in the hip, even though researchers controlled for calcium and vitamin D intake. But women who drank non-cola soft drinks, like Sprite or Mountain Dew, didn't appear to have lower bone density.

webMD

How does the body respond when someone drinks soda?

• Stomach counteracts acidity and carbonation

(irritation) by secreting antacid, Calcium , taken from the blood into the stomach

• Body buffers blood by taking from Calcium from

bones in process called bone resorption to increase pH and calcium levels in blood

Research suggests:

What happens when Calcium is taken from bones?

Osteoporosis – thinning of bone tissue, loss of bone density

What is a consequence of osteoporosis?WEAK/BROKEN BONES

Another possible culprit is caffeine, which experts have long known can interfere with calcium absorption. In the Tufts study, both caffeinated and non-caffeinated colas were associated with lower bone density. But the caffeinated drinks appeared to do more damage.

This study isn't the last word on the subject. Some experts point out that the amount of phosphoric acid in soda is minimal compared to that found in chicken or cheese. And no one's telling women to stop eating chicken. webMD

Review

Where are buffers found in the body?

How do buffers work in the blood?

Why are buffers important?