Download Acid-Base Balance in the Human Body

pH of Body Fluids
I.
A.
Remember that to an extent water ionizes to
form protons (H+) and proton acceptors (OH-)
H 2O
1.
H+ + OH-
The pH of a solution is determined by the
measure of the solution’s H+ ion concentration.
a.
When a solution is acidic it has a higher H+
concentration than OH- concentration
b.
When a solution is basic it has a higher
concentration of OH- concentration than H+
concentration
2.
In our bodies, many different changes,
both internal and external, effect pH.
Controlling pH in our Bodies
II.
A.
1.
2.
The pH of the blood needs to be within a
narrow pH range of 7.35-7.45.
There are three ways that the blood pH is
maintained: the buffer system, the
respiratory system, and the urinary
system.
The pH of blood differs in arteries and
veins: because of (carbon dioxide) CO2
level differences and filtering in the
kidneys.
The blood in veins is slightly more acidic
because of a chemical reaction that occurs
between CO2 and water (H2O).
B.
1.
CO2 is released into the veins from all of
the cells undergoing cellular respiration
around the blood capillaries.
a.
CO2 (from cellular respiration) will combine with
water in the veins (from plasma) to produce
carbonic acid (H2CO3).
𝑯𝟐 𝑶 + 𝑪𝑶𝟐
𝒄𝒂𝒓𝒃𝒐𝒏𝒊𝒄
𝒂𝒏𝒉𝒚𝒅𝒓𝒂𝒔𝒆∗
𝐇𝟐𝐂𝐎𝟑
*Carbonic anhydrase is an
enzyme necessary to
speed up the rate of this
reaction.
b.
H2CO3 will then travel in venous
blood back to the lungs where the
reverse reaction takes place.
𝑯𝟐 𝑪𝑶𝟑
𝒄𝒂𝒓𝒃𝒐𝒏𝒊𝒄
𝒂𝒏𝒉𝒚𝒅𝒓𝒂𝒔𝒆
𝑯𝟐 𝑶 + 𝑪𝑶𝟐
𝑯𝟐 𝑶 + 𝑪𝑶𝟐
𝒄𝒂𝒓𝒃𝒐𝒏𝒊𝒄
𝒂𝒏𝒉𝒚𝒅𝒓𝒂𝒔𝒆
𝑯𝟐 𝑪𝑶𝟑
2.
If you hold your breath the amount
of carbonic acid in the blood will
decrease the pH of the blood.
Acidosis – condition in which there is
an excessive proportion of acid in the
blood
Alkalosis – condition in which there is
an excessive proportion of alkali
(base) in the blood
C.
Buffers in the blood work to make sure the pH remains at
homeostasis.
Buffer – compound that combines with an acid or with a
base to form a weaker acid or base, thereby lessening the
change in hydrogen-ion concentration that would occur
without the buffer
1.
The strength of an acid depends on the amount of H+
ions in the solution. The higher the concentration
of H+ ions, the stronger the acid.
The strength of a base depends on the amount of
*OH- ions in the solution. The higher the
concentration of OH- ions in the solution, the
stronger the base.
*Or any proton-accepting compound
2.
Sodium bicarbonate (NaHCO3) buffers extreme
acids by buffering the strong acid (i.e.
Hydrochloric acid, HCl) to make a much weaker
acid and sodium chloride.
Carbonic acid buffers extreme bases by buffering
the strong base (i.e. Sodium hydroxide, NaOH) to
make NaHCO3 and water.
Sodium bicarbonate buffers weak acids by
buffering the weak acid to form a weaker acid
and sodium lactate.
D.
1.
2.
The kidneys are the most efficient organs for
regulating blood pH because they can
remove both excess acids and excess base.
Kidneys usually acidify urine to a pH of
approximately 4.8.
The kidneys conserve sodium bicarbonate
(NaHCO3) in 2 ways. (While still excreting acid)
III.
pH Imbalances
In humans the acid-base balance needs to be
maintained at the proper ratio of 20 NaHCO3 to 1
H2CO3.
A.
1.
2.
CO2 is expelled in the respiratory and urinary
systems so that the levels of H2CO3 can drop,
raising the pH of the blood to normal levels.
Proteins that contain an –NH2 group are expelled
in the urinary system so that protons from the
NH2 will not raise the acid (lower pH) level of
the blood.
Metabolic disturbances in acid-base balance result
in metabolic acidosis and metabolic alkalosis.
B.
1.
2.
Metabolic acidosis can be caused by a bicarbonate
deficiency caused by renal failure/disease,
uncontrolled diabetes, prolonged diarrhea, or
the ingestion of toxic chemicals like antifreeze
(ethylene glycol) or wood alcohol (methanol).
Metabolic alkalosis can be caused by bicarbonate
excess. This can be the result of diuretic
therapy, loss of gastric juice due to vomiting or
suction or from certain diseases.
Respiratory disturbance
C.
1.
2.
Respiratory acidosis can be caused by an excess
of H2CO3 resulting from slow breathing that will
increase the concentration of CO2 in the
arteries. This can happen due to depressed
breathing due to anesthesia, drugs, or
pulmonary disease.
Respiratory alkalosis can be caused by an H2CO3
deficit resulting from excessive loss of CO2 due
to hyperventilating. Hyperventilation can occur
due to nervousness, overinflation of patients on
ventilators, or a hepatic coma.
a.
1.
2.
3.
4.
The removal of CO2 occurs when:
CO2 leaves the blood and enters the distal
tubules of the kidneys
In the kidneys it reacts with H2O to form
H2CO3
A proton leaves H2CO3 and enters the urine
leaving HCO3- to bind with a Na+ ion to form
NaHCO3
The H+-ion makes a weak acid (NaH2PO4) and
is excreted with urine.
b.
1.
The removal of amino groups (-NH2) when:
Breaking down proteins result in the release of
amino acids into blood.
2.
-NH2 leaves the blood and enters the distal tubules
of the kidneys
3.
A proton joins –NH2 to form NH3. NH3 then goes
into urine.
4.
In urine, NaCl dissociates and a Cl- ion joins NH3 to
make NH3Cl- (a base)
5.
H2CO3 releases a H+ ion that enters the urine to
join NH3Cl- to form NH4Cl to be excreted with the
urine
6.
HCO3 in the kidneys bonds with Na+ to make
NaHCO3