E5 - Acid-Base Homeostasis Flashcards
(31 cards)
How is H+ expressed as pH?
Inverse relationship. pH= -log[H+]
High H+ = Low pH
Low H+ = High pH
What to Hydrogen ions combine to in a liquid state?
Combine to H2O forming Hydronium ions
What is an acid & how does it affect pH?
Acids are capable of releasing [H+]
High acid in body = High [H+] = Lower pH
What is a base?
A base is any substance that is capable of binding/combining with a [H+].
What main organs are in charge of acid-base balancing/ pH homeostasis?
Lungs and the Kidneys
What is our body’s main buffer system & its role?
The blood and it plays a protective role. Preventing large changes in pH
How does the body excrete acids?
Through lungs & kidneys
Lungs are major in acid elimination. Lungs can excrete 13000 mEq/day of carbonic acid
Kidneys only eliminate 40-80 mEq/day of acid
What group of acid do lungs excrete?
Volatile acids. They can be converted to gaseous form to easily excrete acid.
Carbonic acid is the ONLY volatile acid.
What group of acids do kidneys excrete?
Fixed acids:
Sulfuric & Phosphoric acid
these cannot convert to gaseous form, hence can only be excreted through urine in liquid form.
What are kidneys responsible for and what is the most important base that it takes care of?
Regulating bases in the blood in the nephrons of the kidneys.
Plasma bicarbonate [HCO3-]
What are the 4 chemical principles for H2CO3 elimination to occur?
1) Chemical equilibrium
2) Law of Mass Action
3) Hydrolysis Reaction
4) Direct relationship between dissolved CO2 & H2CO3
What is chemical equilibrium and what is the name of a reaction that can go in both direction?
Balance of products & reactants
H2O + CO2 <=> H2CO3
Reverse reaction in a closed system
What is Law of Mass Action?
When an additional component is added or even removed to the reaction, a new equilibrium will occur until balance is restored. Can cause the shift to the left OR the right depending on what is added/removed
What is a Hydrolysis Reaction?
It is when H2O is broken down to react with another compound to form a larger molecule. In this case: CO2 to form carbonic acid.
H2O + CO2 <=> H2CO3
Explain the Direct relationship between CO2 and H2CO3.
In the blood, an increase in PCO2 levels will lead to a blood H2CO3 increase as well. Due to this direct relationship, PCO2 is a marker of blood volatile acid (carbonic acid) levels.
Note:
Venous blood is more acidotic than ABG
For each H2CO3, there are 340 CO2 molecules
How is Carbonic Acid excreted by the lungs?
Once the blood has picked up the increased CO2 at the tissue level and more carbonic acid is formed, the blood will make its way to the lungs to be excreted. A forced hydrolysis reaction will occur causing the reaction shift to the left. H2CO3 will be broken down, CO2 will enter the alveolus and be expelled. [H+] will reduce and H2O restored. HENCE, excretion of H2CO3
Do Alveolar Minute Ventilation & PaCO2 have a directly proportional or inverse relationship?
Inverse
What is CO2 homeostasis?
Maintaining constant PCO2 levels in the arterial blood
What is the normal CO2 production?
200 ml/min
Note:
CO2 production = VCO2
What equation can be used to determine PaCO2 leves?
PaCO2 (mmHg) = (VCO2*0.863)/VA (alveolar minute ventilation)
What factors can affect the rate of metabolism and why is the rate of metabolism important?
1) body temperature = increase rate
2) Types of foods (ex: carbs produce more CO2)
* VCO2 is extremely dependent on metabolism. High metabolic rate = high CO2 production
What factors can increase in CO2 production?
1) high metabolic rate
2) exercise
3) NaHCO3 administration
What can cause a person to be unable to increase their alveolar minute ventilation?
Not having an intact respiratory drive or no/no proper brainstem function. Trauma, injury, mass, stroke, lesion.
Note:
Increase in alveolar minute ventilation = decrease in PaCO2
How to assess if the ventilation is adequate?
ABG & verify PaCO2 levels
