Sect. 8.1 - Acid/Base Balance and Buffers

Acid

a chemical that can donate a H+ ion in solution; proton donor

or a hydronium ion (H3O+) may also accept a pair of electrons

strong acid

has low affinity for H+ and therefore readily dissociates in water to give up H+

Hydrochloric acid (HCl) and Sulfuric acid (H2SO4)

2 examples of strong acids

weak acid

has high affinity for H+ and therefore releases its H+ ion less readily in solution

Acetic acid (CH3COOH) and Ammonium ion (NH4+)

2 examples of weak acids

base

a chemical that can accept a H+ ion; proton acceptor

or a hydroxyl group (OH-) may be formed by donating a pair of electrons

conjugate base

the product of an acid that can react with water

- it can accept H+ ions and act as a base

strong base

readily dissociated to give up hydroxyl ions (OH-)

weak base

has high affinity for OH-

pH

hydrogen ion activity expressed as a negative log of the activity of the solution

7.35 - 7.45

pH reference range

7.4

optimal pH

acidic pH

high concentration of H+

pH < 7..35

basic/alkaline pH

low concentration of H+

pH > 7.45

acid-base balance

the maintenance of homeostasis of the H+ ion concentration of body fluids

buffer

a solution that protects the body by minimizing changes in pH and is the body's first line of defense when body's pH deviates form normal (pH 7.4)

1. bind H+ ions in acidic solutions

2. donate/release H+ ions in basic solutions

What two functions can a buffer perform to maintain the body's pH?

HCO3-

Bicarbonate

H2CO3

Carbonic Acid

CO2

Carbon Dioxide

Bicarbonate buffer system

Hemoglobin buffer system

Phosphate buffer system

Protein buffer system

Four types of buffer systems

Bicarbonate buffer system

Out of the 4 buffer systems, which is the most important?

Bicarbonate-Carbonic acid buffer system

Bicarbonate buffer system is also known as:

Bicarbonate buffer system

this buffer system accounts for the majority of the total buffering capacity in the extracellular spaces of the body

has low buffering capacity, but is the most important

bicarbonate (HCO3-)

Conjugate base in the bicarbonate buffer system

carbonic acid (H2CO3)

Weak acid in the bicarbonate buffer system

Respiratory and Metabolic

2 components of the Bicarbonate buffer system

Respiratory Component

plays a role in CO2 exchange between the blood and the lungs by controlling respiratory rate

helps regulate Carbonic acid (H2CO3)

Metabolic Component

kidneys alter the HCO3- concentration with the amount of substances that are reabsorbed or filtered through renal tubules

immediate, but not sustainable

Regulation of CO2/H2CO3 (carbonic acid) is under the control of the pulmonary system (lungs)

This control is _______________

**hint: can't hyperventilate or decreased breathing forever

slow, but more sustainable

Regulation of HCO3- (bicarb) is under the control of the kidneys.

This control is _______________

faster breathing

How do the lungs get rid of CO2 to balance pH?

slower breathing

How do the lungs retain CO2 to balance pH?

filtered through the renal tubules

How do the kidneys get rid of HCO3- to balance pH?

reabsorbed through renal tubules

How do the kidneys retain HCO3- to balance pH?

20:1

What is the ratio of bicarbonate to carbonic acid when the body pH is normal?

need much more due to high production of CO2 as a by-product through various cellular functions

Why do we need more bicarbonate (20) compared to carbonic acid (1)?

dissolved CO2 (dCO2)

carbonic acid (H2CO3)

bicarbonate (H2CO3-)

hydrogen (H+)

the concentration of total CO2 (tCO2) is made up of (4):

dCO2

more concentrated in the tissues & easily diffuses out into plasma & RBCs

pulmonary system

In the plasma, the regulation of H2CO3 (carbonic acid) is under the control of which system?

kidneys

Plasma HCO3 (bicarb) is under the control of which organ?

Henderson-Hasselbalch equation

important in understanding how bicarb-carbonic acid buffer system regulates acid-base balance

pKa: equilibrium constant

What does pKa represent in the Henderson-Hasselbalch equation?

6.103

What is pKa (equilibrium constant)?

a x PCO2: concentration of carbonic acid (H2CO3)

What does a x PCO2 represent in the Henderson-Hasselbalch equation?

PCO2: partial pressure of CO2 in the plasma when it is in a gaseous state

What does PCO2 represent in the Henderson-Hasselbalch equation?

a: solubility constant

What does a represent in the Henderson-Hasselbalch equation?

0.0306 mmol/L Hg

What is a (constant)?

Hemoglobin buffer system

this buffer system is an internal mechanism in RBC that helps keep blood pH stable by reversibly binding or releasing H+ ions

allows for large amounts of CO2 without changing pH

carbonic anhydrase found in RBC membrane

What is the enzyme responsible for the conversion of PCO2 and water to form carbonic acid in the RBC, and the location of this enzyme?

H+ and HCO3-

Once inside the RBC, the majority of PCO2 forms H2CO3 and then quickly dissociates to:

H+ out (a build-up would increase acidity)

What is the isohydric shift of the hemoglobin buffer system?

HCO3- out, chloride in (a build-up would increase alkalinity)

What is the chloride shift of the hemoglobin buffer system?

carbaminohemoglobin

PCO2 that does not get converted to H2CO3 will attach to the amino acid chains of hemoglobin forming

Phosphate buffer system

this system is important in order to maintain the equilibrium between concentration of H+ ion and OH- (hydroxide) ions within RBCs

internal fluid of all cells

Where does the phosphate buffer system operates?

Dihydrogen phosphate (H2PO4-)

What is the chemical buffer of the phosphate buffer system?

Proteins

make excellent buffers

typically has hundreds of amino acids with functional side groups which allows them to act as buffers

intracellular buffers

The majority of protein buffers are _________ buffers, with a small percentage occuring in the plasma

terminal groups of amino acids

The buffering capacity of proteins comes from

Carboxyl and Amino groups

What are the 2 terminal groups of amino acids found on proteins that allows them to act as buffers?

carboxyl group (O=C-OH)

weak acid of protein buffer system

amino group (NH2)

weak base of protein buffer system

the amino group (NH2) will bind H+ in order to raise pH

How does the protein buffer system respond to an acidic (low pH) environment?

the carboxyl group (O=C-OH) will dissociate to release H+ in otder to lower pH

How does the protein buffer system respond to an basic/alkaline (high pH) environment?

albumin

protein that contributes the majority of the protein buffering capability

albumin has 16 side groups

Why is albumin a great buffer?

CO2

major source of acid in the body

HCO3- (bicarb) will accept H+ to form H2CO3 (carbonic acid) (left shift)

What occurs when acid is added to the body?

To compensate, the body will try to balance acidity by donating H+ ions (right shift)

What is the compensation if body fluid becomes too acidic (low pH)?

H2CO3 (carbonic acid) will donate H+ to form HCO3- (bicarb) (right shift)

What occurs when base is added to the body?

To compensate, the body will try to balance alkalinity accepting H+ (left shift)

What is the compensation if body fluid becomes too basic (high pH)?