E5 - Acid-Base Homeostasis Flashcards
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
Name 4 different ways CO2 exists in the body
1) Dissolved CO2
2) Carbonic Acid
3) Bicarbonate
4) Carbamino compounds
What is the solubility coefficient of CO2?
What is the percentage of dissolved CO2 in the body and does it represent the entire CO2 amount in our body?
0.072 vol%/mmHg = 0.03 mEq/L
Dissolved CO2 only represents 8% of CO2 that exists in our body.
What percentage of carbonic acid is available in our body?
0.006%
CO2 to H2CO3 ratio is 340:1
How is bicarbonate formed and name two reasons why it occurs
Some CO2 that enters the blood will form into HCO3. The amount of HCO3 formed in the plasma is very small. 2 reasons:
1. accumulation of the product of hydrolysis reaction ceasing the reactions
2. Hydrolysis reaction is very slow due to a missing enzyme that speeds up the reaction. That enzyme is carbonic anhydrase.
Note:
Bicarbonate is a major mechanism for CO2 transport. About 80%.
Explain the chloride shift in general.
Also at tissues & in lungs.
Bicarbonate has a negative charge, when it goes into the plasma from the RBC, it creates an electrostatic gradient which causes the chloride anion to shift into the RBC from the plasma.
A.K.A. Hamburger phenomenon
Tissues: Chloride shifts to RBC from plasma
Lungs: Chloride shifts back to plasma from RBC (reverse chloride shift) and HCO3 into the RBC, dissolved into CO2 and out in the alveoli.
What is plasma carbamino compounds
the small portion of CO2 being transported attached to proteins, will react to the amino acids in that protein. This represents about 2% of CO2 transport
Whats is carbamino-hemoglobin
In hemoglobin is a protein and contains 146 amino acids. Which means CO2 will be able to bind to it.
This is 12% of CO2 transport.
Haldane effect: when the affinity to CO2 is greater if there is no O2 bounds
Bohr effect: when hemoglobin is already carrying CO2 and affinity to O2 is decreased.
