Respiratory system

pH , Acidity , and Alkalinity
The degree of acidity or alkalinity of a solution is determined
by its hydrogen ion [H ⁺].
Increase [H ⁺] acidic , decrease [H ⁺] basic .
[H ⁺] in the body fluids is very small = 0.0000001 mol/L = 10
mol/L .
Acidity and Alkalinity is expressed as the negative logarithm
of the hydrogen ion [H ⁺] , which is referred to as pH
pH , Acidity , and Alkalinity
To express hydrogen ion concentration as a pH , we use the role :
pH= -log [H ⁺]
e.g. : if [H ⁺] is 10 ⁻ ⁷ mol/L . To calculate the pH we dropped the negative sign
and the pH is indicated as 7 :
pH=-log[10 ⁻ ⁷ ]= 7
pH , Acidity , and Alkalinity
There is an inverse relationship between pH and the [H ⁺].As the [H ⁺] increases , the pH
decreases , and vice versa .
Acidic solution → low pH & high [H ⁺] .
Alkaline solution → high pH & low [H ⁺].
Importance of Acid-Base Balance
Normal metabolic function can occur only if the
composition of the body cells and their surrounding
environment are kept relatively constant .
Necessary metabolic activities can only proceed if the
balance between acidic and basic substances in body fluids
kept within proper limis .
The activities of virtually all enzymes within the cells are to
some extent pH-dependant .
Importance of Acid-Base Balance
Cont ;
In acidic or basic environment , some reactions
are accelerated while others are slowed don or
stopped completely .
Hydrogen Ion Production And Excretion
Acid-Base balance refer to homeostasis or [H⁺] in the body fluids .
Products of the body’s metabolic reactions are acidic →the body produce large
excess of acid under physiological conditions .
If acids accumulate → the pH of blood and other component would be dramatic
and lethal .
Continual production of acids →need mechanisms to minimize the pH changes
→ these mechanisms must be able to respond to pH variation and accordingly .
Mechanisms of pH Regulation and Hydrogen Ion
The mechanisms are : respiratory system , renal system , and
the chemical buffer system.
Buffer system
Buffer: chemical solution prevent excessive
change in pH and hydrogen ion concentration
when acid or base is added to the solution.
Specifically buffer is mixture of a weak acid
and alkali salt or weak base and acidic salt.
Buffer can be take up any excess H+ that can
produced in same way that sponge soaks up
Buffering is only a short term solution
To the problem of excess H+ , the body must get rid of
the H+ by renal excretion or by lung without pH of
blood dropped.
Four main buffer systems in the body :
• Bicarbonate/carbonic acid buffer system .
• Phosphate buffer system
• Protein buffer system
• Hemoglobin buffer system .
Bicarbonate \carbonic acid buffer
-it is the most important and major one .
-it buffers 70% of the fixed acid in plasma and 30% of fixed acid in RBCs .
-it can be regulated by both kidney and lung.
-Carbonic acid (H₂CO₃) can be retained or exhaled as CO₂ (by the lung).
-bicarbonate (HCO₃) can be retained or excreted by the kidney tubules as
The normal ratio in blood between
HCO₃\H₂CO₃= 20\1 , so the system is
easly buffered against excess acid
of acids
• Volatile acids: that can
be excreted as gases
by the lung.
• Non volatile acids :
that can be excreted
by the kidney , for
example : lactic acid ,
keton bodies,
phosphoric acid ,
sulfuric acid.
Respiratory system:
CO₂ is the major end product of metabolism, formed
continuously in the cell .
From the cell diffuse in to interstitial fluid to the blood
stream where it form H₂CO₃ and dissolve it . RBCs
transport CO₂ to the lung as H₂CO₃ (which it is in the
blood stream now.
RBCs transport CO₂ to the lung as H₂CO₃ (which it is in
the blood stream now.
The Respiratory System
In the lung : CO₂ is reformed and diffuse in to alveoli ,
to be exhaled.
So the result : CO₂ exhaled by the lung , H₂O will
dissipated into the general water pool of the body.
NOTE: the equilibrium reaction can be shifted to the left : to retain more H ⁺
, and can be shifted to the right : to eliminate acid as CO₂ as required by the
If H+ concentration is imbalanced : the
respiratory center will stimulated;
• if [H+] is high (acidic pH)  increase in the
rate of respiration  .hyperventilation (
that mean: eliminate more acid as CO₂)
• if [H+] is low (alkaline pH)  decrease rate
of respiration  hypoventilation ( that
mean retain more acid as CO₂)
in the lung equilibrium reaction can be shifted to the
left or to the right .
Respiratory center can respond to the changes in
hydrogen ion concentration and blood pH very rapid .
The lung can adjust the [H ⁺] with second after a
sudden changes.
The lung alone can’t return the pH to its normal level
of 7.4 so the kidney must act to restore the balance.
Renal system:
Any imbalance in [H ⁺]  kidney tubules cells are
stimulated to adjust the excretion or reabsorption
(retention) of acid as H ⁺ ions , or buffer as HCO3 ions .
If pH is acidic (low)  kidney respond by excreting
more H ⁺ and retain more HCO₃ to neutralize excess
acid .
pH is alkaline  kidney will retain H ⁺ ion and excrete
HCO₃ .
Renal response to [H ⁺] changes and blood pH is slow in
comparison to the respiratory system.
Renal system work alone so need more time
(days or more ) to adjust [H ⁺] .
Kidney is more powerful of the control mechanisms and
100% efficiency rate.
By themselves : kidney are able to retain pH to completely
normal given adequate time .
Acid – Base Disturbances
Acidosis and Alkalosis
Acidosis and alkalosis occur when an imbalance in the normal
blood pH of the body occurs. An increase in blood pH level
results to alkalosis and a decrease results in acidosis.
The organs which work to restore
Homeostasis :
• Kidney >>> H ⁺ and HCO₃⁻
• Lungs >>> CO₂
The importance of H₂CO₃ and HCO₃⁻ .
PH is directly proportional to the
ratio HCO₃⁻ / H₂CO₃ .
Acidosis / Alkalosis
CO ₂ + H₂O
H ⁺ + HCO₃⁻
Acidosis : is a condition in which there is excessive acid in the
body fluids .
The PH < 7.35 / increase in [ H+ ]
causes :
• Certain diseases like
emphysema or kidney failures
• If you starve yourself or if you
have uncontrolled diabetes
• If your protein intake is in
• Ingestion of a large amount of
acidic substances
Alkalosis : is a condition in which the body fluids have excess
base (alkali).
• Severe diarrhea causes excessive
loss of body fluid.
• Loss of carbonic acid due to rapid
breathing ( hyperventilation ).
• Excessive vomiting leads to loss of
hydrochloric acid.
• Excessive intake of sodium
bicarbonate, to relieve the acid in
Respiratory / Metabolic
kidney >>>>>>
Arterial Blood Gas (ABG)
is a blood test that is performed using blood from
an artery .
involves puncturing an artery with a thin needle
and syringe and drawing a small volume of blood.
The radial artery.
is used to
• PH
• PCO₂
• PO₂
• HCO₃⁻ level
• Concentration of lactate
, HB , electrolytes ,
oxyHB , carboxyHB and
In human anatomy, the radial
artery is the main blood vessel
, with oxygenated blood , of
the lateral aspect of the
Arterial Blood
Gas analyzing
Respiratory or Metabolic
The most two effective systems in
regulating pH:
• Respiratory system: volatile
• Renal system :non-volatile substances(e.g. :
lactate ,ketone bodies ,phosphoric acid and
sulfuric acid).
Metabolic Disturbances
Problem either in the excretion or retaining of H ⁺and HCO₃⁻ in the kidneys
It might be either acidosis or alkalosis
This occurs due to excess of non-volatile acids or loss base.
In the normal situations kidneys must get rid of H ⁺ in this case in order to
reduce the concentration of acids.
In the abnormal way : the kidneys can’t excrete as much H ⁺ as needed -----Metabolic Acidosis
How to recognize Metabolic Acidosis
The metabolic component in determining the acidity or
alkalinity is HCO₃⁻ .
If [ HCO₃⁻] decreases------drop in pH---- metabolic acidosis
pH=pKa+ log(HCO₃⁻/H₂CO₃)
If HCO₃⁻/H₂CO₃ is less than 20 so we will have metabolic
Metabolic alkalosis
Decrease of non-volatile acids or increase in the
concentration of bases .
The normal situation: the kidneys will retain H+ and
excrete HCO₃⁻
How could we recognize this:
[HCO₃⁻] increases------pH increases-----Metabolic alkalosis
Summary of metabolic disturbances
*If [HCO₃⁻]
*If [HCO₃⁻]
increases---increase in pH--Metabolic Alkalosis.
Determined by the partial pressure of CO₂
These acid -base disturbances occurs due to changes in the [CO₂] which
will change the [H₂CO₃].
It might be either acidosis o alkalosis
1- Acidosis:
Increase in the partial pressure of CO₂-------increase in [H₂CO₃]----increase Acidity ----- decrease pH
Respiratory alkalosis
It occurs due to decrease in the partial
pressure of CO2 ---- decrease in [H2CO3]--increase alkalinity----increase in pH
Respiratory acid – base disturbances
*If PCO₂ increases---increase in
*If PCO₂ decreases--decrease in
[H₂CO₃]-- alkalosis.
Normal values of pH,[HCO₃] and Pressure of CO₂
Normal range
Actual bicarbonate
Standard HCO₃
P O₂
Mixed Disturbances
Mixed disturbances include both respiratory and metabolic ( acidosis and
alkalosis) .
In mixed disturbances we usually have a primary disturbance that causes
the major effect on pH and a compensatory disturbance that tries to
retain the pH to its normal value(runs in the opposite direction).
E.g.: if we have pH=7.10 and we have respiratory acidosis(increase PCO₂)
and metabolic alkalosis ( increase in [HCO₃]).
The major one disturbance: respiratory .
Example on a mixed disturbance caused by
a drug
An overdose of Salicylate ( aspirine)------leads to hyperventilation( excessive
elimination of CO₂)-----respiratory alkalosis.
The metabolism of salicylate---accumulation of acids----metabolic acidosis
Some diseases lead to acid- base disturbances
In the normal situation the systems of the body can keep
up with changes in the acidity or alkalinity of the blood by
its buffering systems and this will keep pH 7.35-7.45 .
Acid-base disturbances that will cause a shift in blood pH
outside its normal range is called uncompensated and
usually result in the cases of some common diseases(due
to accumulation of large amounts of acids or bases) .
Some diseases lead to acidosis
Metabolic acidosis
Respiratory Acidosis
Uncontrolled DM(increase in ketoacids) Lung disease-COPD-retention of CO₂
Starvation or sever reduced carbohydrates Head injury leads to depression in the
diet (increase in ketoacids) respiratory center----retention of CO₂
Sever exercise ( increase in lactic acid)
Sever diarrhea (GI loss of HCO₃)
Renal failure (failure in the excretion of H ⁺
Salicylate overdose
Shock (increase in lactate)
Any condition results in hypoventilation
Common conditions lead to alkalosis
Metabolic alkalosis
Excessive administration of sodium bicarbonate during treatment of cardiac
arrest (increase in HCO₃⁻)
Respirator alkalosis
High fever (stimulation of respiratory
center)------loss of CO₂
Prolonged vomiting (excessive gastric loss Hysteria (hyperventilation ---loss of CO₂)
of H ⁺)
Hyperaldosteronism (renal loss of H ⁺)
Any condition leading to hyperventilation

similar documents