Acid Base Balance Flashcards
Small changes in pH have….
pH equation
Most bodily fluids are
1 unit pH change equals
A big effect on bodily function
pH= -log10 H+
7.35-7.45.
Other outliers are 6.8-8.
x10 change in H+
Fluctuations in H+ will affect
Excitability of muscles and nerves
Enzyme activities
K levels.
The pH at the start of a capillary is
And at the end it’s
- 45
7. 35
- 45+ means
7. 35- means
Alkalosis.
Acidosis
Body fluids that are outliers in the normal pH range.
Gastric secretions 0.7
CSF 7.3
Pancreatic secretions 8.1
Final urine 5.4
Sources of acid and alkali
Metabolism produced a large amount of acid.
15 mol is CO2 a day.
40nmol of H+ a day
Protein rich western diet is very high in H+
There is alkali in fruit
Lose 10mmol of OH a day
Net excess acid 70mmol a day.
Buffer systems
Blood and tissue buffers take seconds to respond.
Respiration takes minutes to respond.
Renal takes hours or days to respond. And is the only one for the extrusion of acid or alkali.
Where are buffers present
Examples
Blood
Extracellular fluid
Intercellular fluid
Urine
Haemoglobin
HCO3
Inorganic phosphate
Weak acids and bases on proteins.
The carbonic acid and bicarbonate buffer system.
Eg increase CO2
The reaction is in equilibrium.
CO2+H2O = H2CO3 = H + HC03-
An increase in CO2 will acidify the system and shift the equilibrium to the right.
More CO2 will bind with H20 and make more H2CO3 which will make H and HC03-
This will lower the pH.
Henderson hasselbach equation
pH = pk + log HCO3/H2CO3
pk is a constant at 37 degrees of 6.1.
H2CO3 is equal to CO2. This rule is needed for this equation.
Normally there is x20 more HC03 than CO2.
So 6.1 + log (20/1) = 7.4. Normal pH
What happens when you add acid to the body.
The H conc goes up.
The pH goes down
H binds to HCO3 and makes H2CO3.
Which will make CO2 and H2O.
The HCO3 conc goes down when it makes H2CO3.
Causing metabolic acidosis. Which is low pH and low HCO3.
What happens when you add base to the body.
HCO3 conc goes up.
pH goes up.
H will bind to the extra HCO3.
This will make H2CO3 and then H20 and CO2.
The H conc goes down as it binds to all the extra HCO3.
Causes metabolic alkalosis which is high pH and high HCO3.
Removing CO2 from the body
This will shift the equilibrium to the left.
More H and HCO3 will combine to make H2CO3 and then more CO2 and H2O to replace the lost CO2.
The HCO3 and H conc will go down giving a high pH.
Respiratory alkalosis. High pH but low HCO3
Adding CO2 to the body
The equilibrium shifts to the right.
More CO2 and H2O are making H2CO3.
Which makes more H and HCO3.
This gives a high H and a low pH. And it makes a high HCO3 conc.
Respiratory acidosis.
What does the chemical control of ventilation do
Controls blood gas composition
Negative feedback
Triggered by hypoxia and hypercapnia or acidosis.
This will cause increase in ventilation and lead to correction of the problems.
Peripheral chemoreceptors
Glomus cells
Found in carotid body and aortic arch.
Stimulated by hypoxia mainly.
They send signals through the sinus, vagus and Glossopharyngeal nerve to the medulla and respiratory centre. To regulate respiration.
Glomus cells pick up hypoxia and can fire action potentials to stimulate the vagus, sinus and glossopharyngeal nerve.
Structure of carotid body chemoreceptor.
Small 2mg
High blood flow x40
High metabolic rate
Glomus cells fire potentials
Type 2 cells five structural support.
Symp and para axons regulate flow.
Mechanism of glomus cell action
Low oxygen or high CO2 or pH causes block of BK K channels in glomus cell.
Causes depolarisation and action potential.
Opens Ca channels. And high Ca allows ntm release.
The ntm binds to afferent neurons and activates them.
SIDS babies
Sudden instant death syndrome babies.
Unknown reason.
In carotid bodies have too much NA and dopamine and disrupt the breathing pattern.
What happens if a person has hypoxia hypercapnia and a low pH
Even more impulses are fired
Central chemoreceptors and what they are activated by
CO2 increase from 40 to 45
Activated by hypercapnia. It detects the H levels and not the actual CO2.
Amount of CO2 increases from 40 to 45 will cause doubled ventilation.
They are located in the brain parenchyma and are bathed by brain extra cellular fluid.
They are separated from the blood by the BBB which has poor ion permeability.
H and HCO3 can’t cross but CO2 can.
So high CO2 is detected.
Buffering power in the BECF
There is less buffering capacity in the BECF due to no bicarb and less proteins.
This means they can’t help as much to maintain pH.
A drop in the pH in the plasma will be a lot less than in the BECF due to less buffering power.
This allows the central chemoreceptors to be extremely sensitive to changes in pH.
How can chronic acidosis be helped using the BECF
How do respiratory and metabolic acidosis differ in the BECF
Making the barrier allow more HCO3 into the BECF.
Resp acidosis is caused by high CO2 which can enter the BBB.
Metabolic acidosis is caused by H and HCO3 which cannot enter the BBB.
This means that metabolic disorders hardly effect the pH of the BECF and resp acidosis has a big effect.
Resp acidosis will increase the pH 10-35 times more than metabolic.
What is sitting in the BECF
What neural populations does it contain.
Link to SIDS babies
Ventrolateral medulla and other brainstem nuclei.
Acid activated neurons release seratonin
Acid inhibited neurons release GABA.
Some babies lack seratonergic neurons so will have a defect in central chemoreceptors and can stop breathing.
The peripheral and central chemoreceptors responding together.
If there is low oxygen and CO2
If oxygen is normoxic
Which receptors are used in metabolic acidosis
Peripheral do O2
Central do CO2.
Peripheral respond first.
Even larger increase in ventilation.
Central chemoreceptors will do 60-85% if the work.
Acute cases use peripheral.
Chronic cases use central
To increase ventilation.
Kussmaul breathing
Hyperventilation
How do renal mechanisms help
What are the mechanisms
Long term regulation
Removes acid and alkali directly.
HCO3 handling
Urine acidification
Ammonia synthesis
HCO3 handling
Where does it happen
What’s the mechanism
90% happens in the proximal tubule.
10% at the distal tubule.
There is reabsorption of all filtered bicarbonate.
In the proximal cell.
Apical membrane has an Na/H exchanger so Na enters the cell and H leaves.
The H makes H2CO3 with a HCO3.
This splits into H20 and CO2 which can enter the cell. CARBONIC ANHYDRASE
Inside the cell it makes H2CO3 and then HCO3 and H.
The HCO3 can now be reabsorbed into the blood.
In the distal tube it’s the same but there is a H pump instead of the Na\H
Base conservation:
What are the two ways and what percentage of the work do they do.
Urine acidification 25%
Ammonia synthesis 75%
Urine acidification
What molecules are involved
What else is made by proximal cells
Alkaline salt + H = acid salt.
Na2HPO4 = NaH2PO4
The alkaline salt loses a Na which enters the proximal cell and allows a H to leave.
The H combines with the alkaline salt and replaces the Na.
The NaH2PO4 is excreted in the urine.
Acid phosphate, uric acid, creatine
New HCO3
Ammonia production
How is NH3 made in the body
Why is this so effective
NH3 + H = NH4+
Ammonia is permeable and ammonium is not.
Glutamine forms alpha ketoglurarate which makes NH3 and H.
Glutamine in cells makes H and NH3 which both leave the cell through the apical membrane. H uses the transporter and NH3 is permeable.
They combine to make NH4 outside the cell.
This cannot re enter and is excreted.
4 H are gone at once so very effective.
What are the renal responses to acidosis.
H excretion methods are up regulated.
This takes hours or days for new proteins to be made.
Keep the normal 100% HCO3 reabsorption.
The pH of urine will go down and it will help the acidosis
What are the renal responses to alkalosis
H excretion methods are down regulated.
Slight excretion of HCO3
This will help to lower the pH.
What can cause respiratory acidosis.
What are the symptoms and why
What will the renal system do
Problems with CO2 elimination causing high CO2.
Such as lung disease emphysema and chronic bronchitis.
More CO2 means more H2CO3 made which will break down and give off more HCO3 and H.
There will be a low pH and a high HCO3, and a high CO2.
Secretes more H.
pH goes back up.
Reabsorbs more HCO3 and makes more new HCO3 the proximal cells.
What causes respiratory alkalosis
Symptoms and why
What will the renal system do
Too much removal of CO2 due to hyperventilating and fear or stress.
Low CO2 means the equilibrium will shift to make more CO2.
H and HCO3 combine to make H2CO3.
Which makes more CO2 and H2O.
This will use up the H so the pH goes up.
Symptoms are high pH and low HCO3 and CO2.
Secretes less H.
The H combines with HCO3 and makes H2CO3.
This makes more water and CO2.
This will decrease the pH because more CO2 and more H.
What causes metabolic acidosis
Symptoms
How does respiration help
How does the renal system help
Acid ingestion or loss of alkaline fluid. Diarrhoea, cholera, diabetic ketoacidosis.
High H will bind to all the HCO3 and so HCO3 conc will go down. CO2 is normal.
Increase respiration to decrease CO2 and increase the pH. This is because the loss of CO2 will shift the equilibrium to make more CO2 and use up all of the H.
Increase H secretion
More HCO3 reabsorption
What causes metabolic alkalosis
Symptoms
How does respiration help.
What does the renal system do
Ingestion if alkaline fluid or loss of acid from vomiting.
High pH and high HCO3. Normal CO2.
Decrease respiration to increase CO2 levels and lower the pH.
Nothing and we don’t know why
Mixed disorder-
Respiratory acidosis and metabolic acidosis.
High CO2 and a low HCO3.
Life threatening.
The pH changes add together.
Mixed disorder-
Acidosis and alkalosis
They will cancel eachother out
pH is subtractive.
One will dominate but only slightly.
Alcoholics
Asthma
COPD
Alcohol makes acid.
But it will also make you vomit which causes alkalosis.
This will give acidosis and alkalosis.
Respiratory acidosis can’t remove CO2.
Lack of oxygen causes anaerobic respiration which makes lactic acid.
This gives two acidosis disorders.
They are treated with diuretics which cause met alkalosis.
And their lungs cause resp acidosis.
