lecture 3 hydrogen ion homeostasis and disorders Flashcards
Excess of CO2 is removed through ——– , excess of hydrogen ions is excreted by the ———
exhalation (lungs), kidneys
I
Reference interval for our body’s pH
7.35-7.45
Importance of buffering hydrogen ions
Allows to maintain a constant pH→ essential for our body to work at optimal conditions
* Excess of hydrogen ions needs to be buffered with a specific system
Buffer system
A buffer system is made up of a weak acid (incompletely dissociated) and its conjugate base
How does the body buffer hydrogen ions?
The body’s buffer system is the bicarbonate-carbonic acid system
𝑯 + +𝑯𝑪𝑶𝟑− ⇋ 𝑯𝟐𝑪𝑶𝟑
* The bicarbonate system is the most important buffer system in the ECF
Metabolic component of the bicarbonate buffer system
This process happens in the kidneys and it’s essential to regenerate bicarbonate ions lost during the buffering process of hydrogen ions
Respiratory component of the bicarbonate buffer system
Carbon dioxide in the blood is mostly present as bicarbonate
Carbon dioxide is converted into bicarbonate in the red blood cells
to measure carbon dioxide concentration in the
blood?
Expressed as partial pressure (P)
How are hydrogen ions and PCO2 related?
[𝐻 + ]= 𝐾 [𝑃𝐶𝑂2]/[𝐻𝐶𝑂3−]
Hydrogen ion concentration is directly proportional to PCO2 and
inversely proportional to bicarbonate concentration
How do we assess acid-base homeostasis in the blood?
Arterial blood gas (ABG) test
* Performed in arterial blood as it helps us to assess the PCO2 and PO2
* The typical site for arterial blood is the radial/brachial artery
* Analysis is typically performed using point-of-care testing
What happens when the acid-base homeostasis is altered?
Changes in [H+] can be due to changes in either the Respiratory or
the Metabolic component of the Bicarbonate Buffering system
* [H+] > 40 nmol/L (pH < 7.35 ) ACIDOSIS
* [H+] < 40 nmol/L (pH > 7.45) ALKALOSIS
Acidosis or Alkalosis can be Respiratory or Metabolic
Metabolic acidosis
Abnormal increase of hydrogen ions concentration
* The abnormal increase in hydrogen ions can be due to:
➢Increased hydrogen ion formation (i.e. diabetic ketoacidosis, ethanol poisoning)
➢Decreased hydrogen ion excretion (i.e. kidney failure)
➢Loss of bicarbonate (i.e. diarrhea)
The excess hydrogen ions concentration is buffered by bicarbonate
𝐻 + +𝐻𝐶𝑂3
− ⇋ 𝐻2𝐶𝑂3
Reduction of bicarbonate concentration is a feature of metabolic
acidosis
* Carbonic acid dissociates so that CO2 is lost through exhaled air
𝐶𝑂2 + 𝐻20 ⇌ 𝐻2𝐶𝑂3
* Hyperventilation is a compensatory mechanism
Respiratory acidosis
Abnormal increase of PCO2
* Can be caused by
➢Airway obstruction (i.e. COPD, asthma)
➢Depression of respiratory centre (i.e. sedatives, tumours)
➢Neuromuscular diseases (i.e. tetanus, botulism, neurotoxins)
➢Pulmonary disease (i.e. pulmonary fibrosis, severe pneumonia)
* The compensation can be activated by increasing the bicarbonate production and
increasing the excretion of hydrogen ions in the urine → slow process,
bicarbonates are within range in the early stages!
* Corrected by improving ventilation
Metabolic alkalosis
Increase in the ECF bicarbonate concentration causing a reduction in hydrogen ions concentration
* Causes:
➢Related to volume depletion (i.e. vomiting)
Respiratory alkalosis
Reduction of PCO2
* Causes:
➢Increased respiratory drive following hypoxia (i.e. high altitude, severe
anemia, pulmonary embolism)
➢Other: sepsis, cerebral trauma, liver failure
* Compensation: reducing renal hydrogen ion excretion
Respiratory compensation is
quick (minutes to hours) but can not compensate completely
Metabolic compensation
is slow (hours to days) but given enough time it will compensate almost completely
