ACID AND BASE BALANCE Flashcards
proton donor (the substance that liberates hydrogen ion)
acid
proton acceptor (the substance that accepts hydrogen ion)
base
concentration of free hydrogen ion in the body
pH 7.4
normal H+ concentration in the extracellular fluid (ECF)
38 to 42
nM/L.
An increase in H+ ion concentration ____ the pH (acidosis)
decreases
reduction in H+
concentration ____ the pH (alkalosis)
increases
An increase in pH by onefold requires a ____ in H+ concentration
tenfold decrease
indirect method determine the acid-base status in the ECF
Henderson-Hasselbalch equation
bicarbonate ions
𝐻𝐶𝑂3−
𝐻𝐶𝑂3−
bicarbonate ions
pH of plasma is also determined by using
pH meter
Normal acid-base ratio
1:20
1 CO2 (from 𝐻2𝐶𝑂2): 20 𝐻𝐶𝑂3−
two types of acids are produced in the body
- Volatile acids
- Non-volatile acids.
are derived from 𝐶𝑂2
Volatile acids
Large quantity of 𝐶𝑂2 is produced during the
metabolism of carbohydrates and lipids. This 𝐶𝑂2 is not a threat because it is almost totally
removed through expired air by lungs.
produced during the metabolism of other nutritive substances
such as proteins
Non-volatile Acids
real threat
sulfuric acid is produced during the metabolism of sulfur containing amino acids such as
cysteine and methionine
is produced during the metabolism of lysine,
arginine and histidine.
hydrochloric acid
the body has three mechanisms
to regulate acid-base status:
- Acid-base buffer system, which binds free H+
- Respiratory mechanism, which eliminates 𝐶𝑂2
- Renal mechanism, which excretes H+ and conserves the bases (HCO3 –)
the fastest mechanism and it
readjusts the pH within seconds.
acid-base buffer system
mechanism does it in minutes
respiratory mechanism
slower and it takes few hours to few days to bring the pH back to normal
renal mechanism
most powerful mechanism than the other two in
maintaining the acidbase balance of the body fluids
renal mechanism
acid-base buffer system is the combination of a?
weak acid (protonated substance)
and a base – the salt (unprotonated substance).
acts immediately to prevent the changes in pH
Buffer system
Buffer system maintains pH by ____
binding with free
H+.
Body fluids have three types of buffer systems
Bicarbonate buffer system
Phosphate buffer system
Protein buffer system.
buffer system is present in ECF (plasma).
Bicarbonate buffer system
consists of the protonated substance, carbonic acid (H2CO3) which is a weak acid and the unprotonated substance, HCO3 –, which is a weak base. HCO3 – is in the form of salt, i.e. sodium bicarbonate (NaHCO3).
Bicarbonate buffer system
Bicarbonate buffer system prevents the fall of pH in a fluid to which a strong acid like ?
hydrochloric acid (HCl) is added.
This is because the H+ dissociated from HCl combines with H𝐶𝑂3 – of NaH𝐶𝑂3 and
forms a weak H2CO3. This H2CO3 in turn dissociates into 𝐶𝑂2 and 𝐻2𝑂
buffer system also prevents the increase in pH in a fluid to which a strong
base like sodium hydroxide (NaOH) is added
Bicarbonate buffer system
As sodium bicarbonate is a very weak base, its association with H+ is poor. So the rise
in pH of the fluid is very mild.
pK of bicarbonate buffer system
6.1
Bicarbonate buffer system is not powerful like the other buffer systems, large difference between ECF pH of 7.4
Concentration of H𝐶𝑂3 – is regulated by
BBS
kidney
the concentration of 𝐶𝑂3 is
regulated by the
BBS
respiratory system
consists of a weak acid, the dihydrogen phosphate (H2PO4 – protonated substance) in the form of sodium dihydrogen phosphate (NaH2PO4) and the base, hydrogen phosphate (HPO4 – unprotonated substance) in the form of disodium hydrogen phosphate (Na2HPO4)
Phosphate Buffer System
buffer system is useful in the intracellular fluid (ICF), in red blood cells or
other cells, as the concentration of phosphate is more in ICF than in ECF
Phosphate Buffer System
Phosphate buffer system pK
6.8
more powerful than BBS as it is close to the pH of the body fluids, i.e. 7.4
phosphate buffer is useful in ____ also. It is because more phosphate ions are found
in tubular fluid.
tubular fluids of kidneys
In the red blood cells, the potassium ion concentration is higher than the sodium ion concentration.
So, the elements of phosphate buffer inside the red blood cells are in the form of?
potassium dihydrogen phosphate (KH2PO4) and dipotassium hydrogen phosphate
(K2HPO4).
buffer systems are present in the blood; both in the plasma and erythrocytes.
Protein Buffer System
Elements of proteins, which form the weak acids in the plasma are:
a. C-terminal carboxyl group, N-terminal amino group and side-chain carboxyl group of glutamic acid
b. Side-chain amino group of lysine
c. Imidazole group of histidine.
Protein buffer systems in plasma are ____ because of their high concentration in plasma and because of their pK being very close to 7.4.
more powerful
is the most effective protein buffer and the major buffer in blood
Hemoglobin
Due to its high concentration than the plasma proteins, hemoglobin has about ____ more buffering capacity than the plasma proteins.
six times
The ____ hemoglobin is a more powerful buffer
than ____ hemoglobin because of the higher pK.
deoxygenated
oxygenated
When a hemoglobin molecule becomes
deoxygenated in the capillaries, it easily binds with H+, which are released when CO2 enters
the capillaries. Thus, hemoglobin prevents fall in pH when more and more CO2 enters the
capillaries.
play an important role in the maintenance of acid-base balance by removing CO2
which is produced during various metabolic activities in the body
Lungs
H2CO3 splits into
carbonic acid
H+ + HCO3-
CO2 is blown off by
ventilation
When metabolic activities increase, more amount
of CO2 is produced in the tissues and the concentration of H+ increases as seen above.
Increased H+ concentration increases the pulmonary ventilation (hyperventilation) by acting
through the chemoreceptors. Due to hyperventilation, the excess of CO2 is removed from the
body.
maintains the acid-base balance of the body by the secretion of H+ and by the
retention of HCO3
kidney
reduction in pH (increase in H + concentration) below normal range.
Acidosis
Acidosis is produced by
- Increase in partial pressure of CO2 in the body fluids particularly in arterial blood
- Decrease in HCO3 – concentration
is the increase in pH (decrease in H+ concentration) above the normal
range.
Alkalosis
Alkalosis is produced by:
- Decrease in partial pressure of in the arterial blood
- Increase in HCO3 – concentration
Since the partial pressure of CO2 (pCO2) in arterial blood is controlled by lungs, the acid-base disturbances produced by the change in arterial pCO2 are called the?
respiratory
disturbances
the disturbances in acid-base status produced by the change in
HCO3 – concentration are generally called the?
metabolic disturbances.
acid-base disturbances are:
- Respiratory acidosis
- Respiratory alkalosis
- Metabolic acidosis
- Metabolic alkalosis.