The role of ventilation in acid base balance

Question 1

Why is pH homeostasis important?

Answer 1

• critical to health
• ensures efficient protein function , because because protein function relies on a 3D structure that is maintained by the presence of inter- and intra-chain bonds between the amino acid groups
• almost all cellular activities rely on the function of proteins, so disruptions of pH are therefore damaging to organs and health.

Question 2

how does disrupting the pH affect protein structure?

Answer 2

The presence of excessive/deficient levels of H+ disrupts the bonding pattern denaturing the protein and impairing function

Question 3

do all proteins have maximum function at the same pH level?

Answer 3

no, different proteins display maximum function at varying pH levels - largely depending on the environment in which they have evolved to exist

e.g. pepsins works best at low pH levels

Question 4

why is arterial pH is tightly regulated?

Answer 4

to ensure effective protein function

Question 5

how is arterial pH is tightly regulated?

Answer 5

1. the presence of buffering systems

2. regulating the level of molecules associated with acid and base production

Question 6

How do buffers work?

Answer 6

buffers are a weak acid (H2CO3) and a conjugate base (HCO3-)

e.g. bicarbonate buffering system, which ‘mops up’ excess H+

Any H+ formed by addition of strong acid, react with conjugate base to form weaker acid, hence pH remains relatively stable

Question 7

how can the strength of an acid be determined?

Answer 7

determined by the degree to which it ionises (a strong acid completely ionises)

Question 8

what are buffers used for?

Answer 8

used to resist sharp changes in pH, so they help maintain pH within a band to keep the tissues and organs working

-so, the otherwise linear relationship between acid concentration and pH decrease is resisted

Question 9

can buffering systems become saturated?

Answer 9

yes

Question 10

although the bicarbonate buffering system, is the most important name some other buffers and how they are classified:

Answer 10

intracellular

• phosphate buffer system
• amino acids/protein
• haemoglobin

extracellular

• (bicarbonate)
• plasma proteins (eg. albumin)

Question 11

what is CO2 transport important in?

Answer 11

acid-base balance

Question 12

how does hypoventilation affect CO2 levels?

Answer 12

accumulation of CO2

Question 13

how does hyperventilation affect CO2 levels?

Answer 13

removal of CO2

Question 14

how does an increase in CO2 affect pH?

Answer 14

↑CO2 = ↑H+

acidity, ↓pH

Question 15

what do they lungs contribute to?

Answer 15

acid-base balance (because they play a role in regulating CO2 levels)

Question 16

explain the relevance of the following fully reversible equation:

CO2 + H2O –> H2CO3 –> H+ + HCO3-

Answer 16

this equation shows that CO2 will naturally react with H2O form H2CO3, which will then dissociate at a natural rate to form H+ and HCO3-

this means that the level of CO2 will ultimately alter the level of acid that’s present, so if we accumulate co2 within the blood (eg. hypoventilate, not breathe sufficiently), there’s more carbonic acid production

Question 17

an increase [H+] causes what?

Answer 17

acidosis

Question 18

a decrease in [H+] causes what?

Answer 18

alkalosis

Question 19

analysing of ABG (arterial blood gas) and pH can be used for what?

Answer 19

diagnosing and interpretating of signs of respiratory and metabolic distress

Question 20

how can excess CO2 be removed from the lungs?

Answer 20

by increasing ventilation

Question 21

how does the respiratory system have a key role in maintaining blood pH, eg. an increase in pH

Answer 21

if pH increases, ventilation will be reduced to increase PaCO2 and [H+]

Question 22

Increasing the levels of HCO3- will remove what from the system?

Answer 22

H+

Question 23

levels of HCO3- are regulated by which organ?

Answer 23

the kidneys

Question 24

what is the Henderson-Hasselbach equation and what is it used for?

Answer 24

describes the relationship between the pH, the acid-dissociation constant of an acid, and the relative concentrations of the ionised and unionised forms of the acid

used to estimated the pH of a biological system in which buffers are present.

Question 25

give an example of how the Henderson-Hasselbach equation is used:

Answer 25

e.g. for the carbonic acid-bicarbonate buffering system, the pH of the blood is dependent on:

1. the acid-dissociation constant of carbonic acid
2. the concentrations of bicarbonate ions and carbonic acid

Question 26

how do the lungs regulate pH homeostasis?

Answer 26

by regulating PaCO2

The more you ventilate the more the carbon dioxide you expel

the respiratory system works at much faster reaction time.

Question 27

how do the kidneys regulate pH homeostasis?

Answer 27

by regulating [HCO3-]

the kidney can choose to excrete or reabsorb bicarbonate ions

if blood becomes too acidic the kidney senses that and excretes less bicarbonate ions to counter the acidosis.

Question 28

relationship between CO2, HCO3- and pH?

Answer 28

↑ PaCO2 = ↓ pH
↓ PaCO2 = ↑ pH
↑ [HCO3-] = ↑ pH
↓ [HCO3-] = ↓ pH

Question 29

what is blood pH is proportional to?

Answer 29

ratio of HCO3- to CO2

Question 30

what may excessive changes in pH result from?

Answer 30

may result from respiratory (CO2) or metabolic (HCO3-) dysfunction

Question 31

what is a normal pH

Answer 31

7.35 - 7.45

Question 32

what does an ABG (arterial blood gas measurement) measure?

Answer 32

gives you:

• pH
• partial pressure of co2 and bicarbonate ions

Question 33

what can cause acidosis?

Answer 33

High PaCO2

Question 34

a high PaCO2 can indicate what?

Answer 34

indicates that respiration is abnormal (hypoventilation)

Question 35

what pH is the blood at in acidosis?

Answer 35

less than 7.35

Question 36

what pH is the blood at in alkalosis?

Answer 36

greater than 7.45

Question 37

causes of acidosis

Answer 37

Hypercapnia (hypoventilation)

↑ Lactic acid (spesis) and Ketone bodies (diabetes)

↓ Kidney acid excretion (renal failure)

↓HCO3- reabsorption (renal acidosis)

Diarrhoea (loss of HCO3- from gut)

Question 38

effects of acidosis

Answer 38

Tachypnoea
Muscular weakness
Headache
Confusion, Coma
Cardiac arrhythmia
Hyperkalaemia

Question 39

compensatory mechanisms to combat acidosis

Answer 39

Hyperventilation (↓PaCO2, respiratory compensation)

↓ HCO3- excretion (renal compensation)

Question 40

causes of alkalosis

Answer 40

Hypocapnia (hyperventilation)

Vomiting (loss of H+ in HCl)

↑ kidney acid excretion (diuretics)

↑ alkalotic agent consumption (antacids, NaHCO3)

Question 41

effects of alkalosis

Answer 41

Bradypnoea
Muscular weakness, cramps, tetany
Headache, Nausea
Lightheadedness, confusion, coma
Cardiac arrhythmia
Hypokalaemia

Question 42

compensatory mechanisms to combat alkalosis

Answer 42

Hypoventilation (↑PaCO2, respiratory compensation)

↑ HCO3- excretion (renal compensation)

Question 43

explain how acidosis-induced hyperkalaemia occurs:

acidosis causes cardiac arrhythmias

Answer 43

• acidosis increase the extracellular [H+]
• this decreases the H+ concentration gradient
• fewer Na+ ions enter the cell
• has a knock-on effect on other transporters
• decreased Na+/K+ exchange
• less K+ absorbed
• build up of K+ in the extracellular space, which leads to hyperkalaemia

Question 44

what is the consequence of hyperkalaemia?

Answer 44

K+ ions are involved in cardiac contraction, so tissue function can be disrupted if the concentration of K+ ions are messed with eg. cardiac arrhythmias, leading to tachy/bradycardia and also muscle weakness

Question 45

explain how alkalosis-induced cerebral vasoconstriction occurs:

Answer 45

• CO2 naturally acts as a vasodilator in blood vessels (cerebral arteries particularly sensitive). Having a certain amount of CO2 helps to maintain open vessels
• If you hyperventilate you reduce CO2 and ↓H+ (alkalosis)
• Alkalosis causes vasoconstriction of cerebral arteries
• ↓ cerebral blood flow = headache, lightheadedness, confusion, seizures

Question 46

summary q, disturbances in pH lead to…

Answer 46

lead to clinical effects such as arrhythmias & muscle weakness (via effects on serum potassium levels) and confusion (via effects on cerebral blood flow)