Acid base balance I Flashcards by Karla Littleford

Why is acid/base balance so important?

Small changes in pH –> huge impacts on the body

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How is pH calculated?

pH = -log10 [H+]

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What is the normal pH range in the body?

7.35-7.45

BUT, there are SOME tissues which sit outside of this range

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What is the pH scale described as?

What does this mean?

1) A log scale
- For every 1 unit change in pH, theres is a X10 change in [H+]

2) A reciprocal scale
- Increase in pH, decrease in [H+]

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What does a pH of 7.35-7.45 correspond to in [H+]?

45-35 nmoles/litre

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What happens to the pH in the capillary bed?

Drops from 7.45 to 7.35

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What is pH above 7.45 classed as?

Alkalosis

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What is pH below 7.35 classed as?

Acidosis

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What 3 major things can fluctuations in [H+] have an effect on?

1) Excitability of muscles/nerves
2) Enzyme activities
3) K+ levels

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How do changes in [H+] change the excitability of muscles/nerves?

Changes the binding of H+ to the ion channels associated with excitability

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How do changes in [H+] change enzyme activities?

Enzymes are pH sensitive

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How do changes in [H+] change K+ levels?

What does this cause?

Increase in [H+] concentration in the plasma decreases [K+] in the cell as:

Body tries to get rid of H+ in the plasma, by transporting it into the cell
As the expense of K+ - transported out

Causes:

Hyperkalemia
Impact on the excitable cells of the body

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What is the pH of gastric secretions?

0.7

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What is the pH of CSF?

7.3

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What is the pH of pancreatic secretions?

8.1

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What is the pH of the final urine?

5.4

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What are the sources of acid/alkali?

1) Metabolism

2) Diet

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What produces more H+, metabolism or diet?

Metabolism (double at 40mmol/day)

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What is lost in the diet?

10 mmol/day of OH-

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What produces a lot of alkali?

Fruit

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Why is the western diet an excess of H+?

Protein rich - lots of H+

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How much excess of H+ is there per day?

Why must happen to this H+?

Net excess of 70mmol/day

Must be regulated to prevent acidosis

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What are the 3 systems that regulate acid levels in the body?

How long does it take for the 3 systems to act?

1) Blood and tissue BUFFERS
- Takes seconds

2) Respiration
- Takes minutes

3) Renal
- Takes hours/days

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What do buffers do to regulate H+ levels?

Bind to free H+

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How does respiration regulate H+ levels?

Rids of CO2

How does the renal system regulate H+ levels?

By direct excretion

Where are pH buffers present in the body? (4)

- Blood (plasma and RBC) - ECF - ICF - Urine

What are 4 examples of buffers in the body?

1) Heamoglobin 2) HCO3- 4) Inorganic phosphate 5) Weak acids/bases on PROTEINS

What is the equilibrium system involving bicarbonate? What happens if increase CO2? What happens if increase H+?

CO2 + H20 H2CO3 H+ + HCO3- Increase CO2: 1) Shift eq to the RIGHT 2) Extra CO2 bind with H2O and form H2CO3 3) H2CO3 dissociates into H+ + HCO3- 4) pH decreases Increase H+: 1) Shift eq to the LEFT 2) H+ bind with HCO3 to form H2CO3 3) H2CO3 dissociates into H2O and CO2

What is CO2?

An acidifier

What is the Henderson-Hasselbalch equation?

pH = pK + log [HCO3]/[H2CO3] Where: - pK is a constant - H2CO3 ~CO2

What is the value for pK at 37 degrees C?

6.1

What is the normal ratio of [HCO3]/[H2CO3]?

20:1

At pH 7.4, what is the normal [HCO3]?

25mM

What happens to pH and [HCO3-] when acid is added? What is this common of?

Both low Common of metabolic acidosis

What happens to pH and [HCO3-] when base is added? What is this common of?

Both high Common of metabolic alkalosis

What happens when decrease CO2? What is this common of?

High pH and low [HCO3-] Common of respiratory alkalosis

What happens when increase CO2? What is this common of?

Low pH and high [HCO3-] Common of respiratory acidosis

What is 'metabolic acidosis/alkalosis' to do with?

Addition or loss of acid/base from the body

What is 'respiratory acidosis/alkalosis' to do with? What does this highlight a problem with?

Level of CO2 in the body Highlights a problem with the lungs

What is the chemical control of ventilation? How?

Peripheral and central chemoreceptors Regulate the blood gas composition: PO2, PCO2, pH

What 3 things triggers chemoreceptors?

1) Hypoxia (low O2) 2) Hypercapnia (high CO2) 3) Acidosis

What happens when the chemoreceptors are activated? What does this lead to?

Increase in VENTILATION Leads to: - Increase in O2 - Decrease in CO2 - Increase in pH

Where are peripheral chemoreceptors found?

In the carotid and aortic bodies

What do the peripheral chemoreceptors regulate?

Plasma

What is the MAIN stimulus for the peripheral chemoreceptors? What does it cause them to do?

Hypoxia (low PO2) Causes them to increase firing rate

When the peripheral chemoreceptors are activated, where do they send signals through? To where?

Through: - Sinus nerve - Glosso-pharyngeal nerve - Vagus nerve To: - Medulla and respiratory centres - Which feed into the respiratory system to change breathing

What is the main cell type in the peripheral chemoreceptor?

Glomus cell

What is the structure of the carotid body?

Contains: - Glomus cells - Type II supporting cells - Sinusoids - Parasympthetic and sympathetic chemoreceptors

Describe glomus cells?

Neural phenotype - fire action potentials when O2 drops Release NEUROTRANSMITTERS - activate the cranial nerve afferents to the respiratory centres

What are sinosoids?

Enlargement of blood vessel

What do the PS and S ganglion cells do in the carotid body?

- INPUT into the chemoreceptors - Regulate blood flow - Fine-tune activation

How are aortic peripheral chemoreceptors different to carotid body peripheral chemoreceptors?

Small | Less well studied

Describe the action potential firing in the glomus cell

1) Inhibition of BK K+ channels by increase PCO2, decrease O2 or decrease pH 2) Depolarisaion 3) Action potential firing 4) Voltage gated Ca2+ open - increase intracellular Ca2+ 5) Fusion of vesicles containing neuroT - neuroT release 6) Afferent fibre stimulation 7) Signals to the rep centre

What at the neurotransmitters released by the glomus cells onto the cranial afferents?

- Ach - Dopamine - NA - 5-HT - Substance P - ANP

How are hypoxia, hypercaptina and pH linked?

1) Sensitivity to PO2 changes with acid/base status | 2) Sensitivity to PCO2 changes with pH

What happens to sensitivity of the peripheral chemoreceptor to PO2 if pH decrease/CO2 increase?

Increases

What happens to sensitivity of the peripheral chemoreceptor to PO2 if pH increase/CO2 decrease?

Decrease

What happens to sensitivity of the peripheral chemoreceptor to PCO2 if pH increase increase?

Decrease

What happens to sensitivity of the peripheral chemoreceptor to PCO2 if pH increase decrease?

Increase

Acid base balance I Flashcards

(60 cards)