Transcript Acid-Base Regulation Modified

ACID - BASE PHYSIOLOGY
PROFESSOR. ASHRAF HUSAIN
DEPT. OF PHYSIOLOGY
COLLEGE OF MEDICINE
KING SAUD UNIVERSITY
RIYADH.
Modified by
The Legendary Genius
Acid Base Physiology
• Definition:
pH is defined as potential of H+ Ion
concentration in body fluid. The amount of
H+ ion concentration is so low in the body
hence it is expressed as –ve logarithm to
base of the H+ ion concentration in
mEq/lit.
pH = log 1/ [H+ ]
= - log [H+ ]
The Acid-Base Balance
• Balance of H conc. In ECF .
• To Achieve Homeostasis .
• Balance Between :
The H Intake or Production
The H Removal
NORMAL VALUE
• Arterial blood = 7.35 – 7.45
Can be explained as follows;
Normal value of H+ ion conc. is about
40nEq/lit.
40 nEq/lit = 0.00000004 Eq/lit.
Therefore pH = - log [0.00000004]
= 7.4
Acid – Base Imbalance
• Acidosis = Decrease in arterial PH ( <7.35 )
Due to excess H+
• Alkalosis = Elevation in Arterial PH ( >7.45)
Due to excess base .
pH and H+ ion concentration
pH
•
•
•
•
6.0
7.0
8.0
9.0
•
•
•
•
H+ ion in nmol/lit
1000
100
10
1.0
Note : one point drop in pH results in a ten
fold decrease in H+ ion conc.
Scale of pH measurement
• The pH scale is between 0 – 14.
Zero onwards below 7 is acidic.
After 7 upto 14 the solution is alkaline.
At 7 (neutral e.g. water) where the amount
o
of H+ and Hydroxyl ion are equal at 23
Examples of pH zero, one & two.
pH 0 = 1 lit. of HCl contains 1gm of H+ = 10o
pH 1 = 10 lit. of N/10 HCl contains 1gm of H+
Therefore 1 lit. will contain 1/10gm of H+ =10-1
pH 2 = 100 lit. of N/100 HCl contains 1gm of H+
Therefore 1 lit. will contain 1/100gm of H+ =10-2
And so on..
It will be noted that a solution of pH 2 does not
have twice the H+ ion conc. at a pH of 4
rather it has 100 times H+ ion conc.
• Since pH is inversely related to H+ ion
conc. so a low pH corresponds to high H+
ion conc. (Acidic) and a high pH
corresponds to low H+ ion conc. (Alkaline)
Acidic
0
Neutral
7
Alkaline
14
The Negative logarithmic relationship between [H+] and pH
About H+
H+ are derived from hydrogen atoms.
Hydrogen atom has proton a positive
electrical charge with a negative charge
electron which is revolving around it. The
hydrogen ion is formed when negative ion
(electron) is lost and it contains only
proton. The H+ is the smallest ionic
particle, highly reactive with a very short
life and unable to survive on its own.
A very tight control is needed for normal
metabolic functions.
eg. Enzymatic activity, blood clotting and
neuromuscular activity.
Hydrogen ions are the toxic end product of
metabolism and they adversely affect all
physical and biochemical cellular process
in our body.
Acid
• Molecules containing H atoms that can
release (donate) H ions in solutions .
• Example , HCL .
• Strong acids :
- Completely dissociate : (HCL , H2SO4 )
• Weak acid :
- Partially dissociate : ( H2CO3)
Base
• An Ion that accept a H ion .
• An example of a base is the Bicarbonate
( HCO3 ) .
Buffers
• Substances that Neutralize acids or bases.
• Chemical Reactions which Reduce the
effect of adding acid or base to a solution
PH .
How the body defends against
fluctuations in PH
• Three Systems in the body :
1) Buffers in blood .
2) Respiration through the lungs .
3) Excretion by the kidney .
Blood Buffer
• These buffer systems serve as a first line
of defense against changes in the acidbase balance :
- HCO3(Regulated by Renal and
Respiratory) .
- Protein
- Phosphate
- Hemoglobin
Protein
• Acidic and Basic Amino acid in plasma
and cell protein act as buffers .
• HB is an important buffer , can’t be
regulated physiological .
Phosphate & Intracellular
Buffers
• Both Intra and Extra cellular phosphate act
as a buffer . But its role is minor compared
to HB or HCO3.
• Intracellular buffers are needed because H
doesn’t cross Plasma Membrane .
• Intracellular PH is more acidic . (7.2)
Hydrogen Ion Excretion in Kidney
Buffering of hydrogen ions in urine
Factors that increase or decrease H secretion and HCO3
Reabsorption by renal tubules :
Increase in H ion secretion
and HCO3 ion reabsorption
Decrease H ion secretion
and HCO3 ion reabsorption
PCO2
PCO2
H ,
H ,
HCO3
HCO3
ECF volume
ECF volume
Angiotensin II
Angiotensin II
Aldosterone
Aldosterone
Hypokalemia
Hyperkalemia
Respiratoy Regulation of PH
• Maintaining Normal PH by maintaining
constant PCO2 .
• Normal gas Exchange and ventilation .
• Controlled by chemoreceptors .
•
PCO2
PH
Renal Regulation
• Tubular Mechanisms of H+
• Tubular Reabsorption of HCO3 .
Three ways to measure acidbase balance in the body :
• Blood PH
• Blood PCO2
• Blood HCO3
Compensation
-If underlying problem is metabolic :
Hyperventilation and Hypoventilation mechanisms
will help through Respiratory Compensation .
-If the problem is Respiratory , Renal mechanisms
, then Renal mechanisms will help through
Metabolic Compensation .
Acidosis
-Principal effect of acidosis is Depression of
the CNS through the decrease in synaptic
transmission .
- Generelized Weakness .
- Deranged CNS is the greatest thread .
- severe acidosis causes :
1- Disorientation
2- Coma
3- Death
Alkalosis
-Causes over excitability of the central and peripheral
nervous systems .
-Numbness
- Lightheadedness
It can cause :
- nervousness .
- muscle spasms or tetany .
- convulsions
- looss of consciousness
- death .
-In the Metabolic(acidosis\alkalosis) the PCO2 is Constant .
- In the Respiratory(acidosis\alkalosis) the HCO3 is Constant .
- Hysterical
- Pneumonia
Loss of excessive alkali
Loss of Gastric acid = Vomiting
Excessive intake of alkali = antiacid
Correction for Respiratory
Alkalosis :
• Correction :
HCO3 reabsorption by kidneys
blood HCO3
normal value .
decreases PH to
- The urine will be excreted with high HCO3.
- In blood : PH= normal
HCO3 = Low , PCO2 = low
Correction for Respiratory
acidosis :
Correction :
HCO3 reabsorption by the kidney
Blood HCO3
PH back to normal .
In blood : PH = normal
PCO2 = high , HCO3 = High
- The urine will be excreted with Low HCO3.
Correction of Metabolic
Alkalosis
• Depress ventilation
Blood PCO2
PH is back to normal .
In blood :
PH=~ Normal
HCO3 = high
PCO2 = high
Correction for Metabolic
Acidosis
• Correction :
- Stimulate ventilation ( Hyperventilation )
PCO2
PH Back to normal .
In blood :
PH =~ normal
HCO3 = Low
PCO2 = Low
The body response to acid-base IMBALANCE
is called
Compensation
If the body is bruoght to
the normal limits then,
It is Complete
If the Range is still outside
the normal then ,
It is Partial
1.
A 44-year – old woman with a long history of indigestion
begins to vomit at home. She becomes unwell after 4
days and is admitted to hospital because of marked
muscle weakness. Her arterial blood gases are [H+]
28nmol/l,
PaCO2 6.5kPa,
[HCO3- 40mmol/l,
PaO210.3kPa,
plasma potassium 2.1 mmol/l.
Q. What is the likely diagnosis and what treatment is
required?
• Metabolic alkalosis is less common than
metabolic acidosis. It is characterized by
an increase in plasma bicarbonate, a fall in
[H+], and a small compensatory rise in
PaCO2.
2. A 32 – year-old man is admitted in a very ill state. He had been
drinking with friends, but had not been seen for some hours. On
admission he is barely conscious and breathing heavily.
His arterial blood gases are;
[H+] 98nmol/l,
PaCO2 2.7kPa,
[HCO3- 6mmol/l,
PaO2 13kPa.
Q. What is likely diagnosis, how should it be confirmed, and what
treatment is required?
• Metabolic acidosis is characterized by a
reduction in plasma bicarbonate and a rise
in [H+]. The PaCO2 is reduced
secondarily by hyperventilation, which
mitigates the rise in [H+].
• 3. a 56-year-old man, who has smoked
heavily for many years, develops a
worsening cough with purulent sputum,
and is admitted to hospital because of
difficulty in breathing. He is drowsy and
cyanosed. His arterial blood gases are
[H+] 65nmol/l,
PaCO2 9.5kPa,
[HCO3- 28mmol/l,
PaO26.2kPa,
Q. What is likely diagnosis and what
treatment is required?
• Respiratory acidosis arises when effective
alveolar ventilation fails to keep pace with
the rate of CO2 production. As a result
PaCO2, blood [HCO3-] and [H+] all rise.
• 4. a 13-year-school boy is brought the
casualty department, having become
acutely unwell in the headmaster’s office.
He is alert and agitated, the respiratory
rate is 35/min, and he complains of tingling
in his hands. His arterial blood gases are;
[H+] 29nmol/l,
PaCO2 2.8kPa,
[HCO3- 22mmol/l,
PaO2 16kPa.
Q. What is the likely diagnosis and what
treatment is required?
• Respiratory alkalosis occurs when there is
excessive loss of CO2 due to overventilation of the lungs. PaCO2 and [H+]
fall. The low PaCO2 results in reduced
renal Na+/H+ exchange.
REASONS FOR METABOLIC ACIDOSIS AND ALKALOSIS
METABOLIC ACID – BASE DISORDERS
COMPENSATION IN PRIMARY METABOLIC DISORDERS
RESPIRATORY AND MIXED ACID – BASE DISORDERS
WHY AN INCREASED PCO2 CAUSES AN ACIDOSIS
RENAL COMPENSATION IN PRIMARY RESPIRATORY ACIDOSIS
CAUSES OF RESPIRATORY ACIDOSIS AND ALKALOSIS
ACID – BASE DISORDERS: DIAGNOSIS AND MANAGEMENT
THE 95% COFIDENCE
INTERVALS FOR
ARTERIAL BLOOD
GASES IN PRIMARY
ACID – BASE
DISORDERS
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