The role of ventilation in acid base balance Flashcards
Why is pH homeostasis important?
- 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.
how does disrupting the pH affect protein structure?
The presence of excessive/deficient levels of H+ disrupts the bonding pattern denaturing the protein and impairing function
do all proteins have maximum function at the same pH level?
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
why is arterial pH is tightly regulated?
to ensure effective protein function
how is arterial pH is tightly regulated?
- the presence of buffering systems
2. regulating the level of molecules associated with acid and base production
How do buffers work?
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
how can the strength of an acid be determined?
determined by the degree to which it ionises (a strong acid completely ionises)
what are buffers used for?
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
can buffering systems become saturated?
yes
although the bicarbonate buffering system, is the most important name some other buffers and how they are classified:
intracellular
- phosphate buffer system
- amino acids/protein
- haemoglobin
extracellular
- (bicarbonate)
- plasma proteins (eg. albumin)
what is CO2 transport important in?
acid-base balance
how does hypoventilation affect CO2 levels?
accumulation of CO2
how does hyperventilation affect CO2 levels?
removal of CO2
how does an increase in CO2 affect pH?
↑CO2 = ↑H+
acidity, ↓pH
what do they lungs contribute to?
acid-base balance (because they play a role in regulating CO2 levels)
explain the relevance of the following fully reversible equation:
CO2 + H2O –> H2CO3 –> H+ + HCO3-
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
an increase [H+] causes what?
acidosis
a decrease in [H+] causes what?
alkalosis
analysing of ABG (arterial blood gas) and pH can be used for what?
diagnosing and interpretating of signs of respiratory and metabolic distress
how can excess CO2 be removed from the lungs?
by increasing ventilation
how does the respiratory system have a key role in maintaining blood pH, eg. an increase in pH
if pH increases, ventilation will be reduced to increase PaCO2 and [H+]
Increasing the levels of HCO3- will remove what from the system?
H+
levels of HCO3- are regulated by which organ?
the kidneys
what is the Henderson-Hasselbach equation and what is it used for?
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.
give an example of how the Henderson-Hasselbach equation is used:
e.g. for the carbonic acid-bicarbonate buffering system, the pH of the blood is dependent on:
- the acid-dissociation constant of carbonic acid
- the concentrations of bicarbonate ions and carbonic acid
how do the lungs regulate pH homeostasis?
by regulating PaCO2
The more you ventilate the more the carbon dioxide you expel
the respiratory system works at much faster reaction time.
how do the kidneys regulate pH homeostasis?
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.
relationship between CO2, HCO3- and pH?
↑ PaCO2 = ↓ pH
↓ PaCO2 = ↑ pH
↑ [HCO3-] = ↑ pH
↓ [HCO3-] = ↓ pH
what is blood pH is proportional to?
ratio of HCO3- to CO2
what may excessive changes in pH result from?
may result from respiratory (CO2) or metabolic (HCO3-) dysfunction
what is a normal pH
7.35 - 7.45
what does an ABG (arterial blood gas measurement) measure?
gives you:
- pH
- partial pressure of co2 and bicarbonate ions
what can cause acidosis?
High PaCO2
a high PaCO2 can indicate what?
indicates that respiration is abnormal (hypoventilation)
what pH is the blood at in acidosis?
less than 7.35
what pH is the blood at in alkalosis?
greater than 7.45
causes of acidosis
Hypercapnia (hypoventilation)
↑ Lactic acid (spesis) and Ketone bodies (diabetes)
↓ Kidney acid excretion (renal failure)
↓HCO3- reabsorption (renal acidosis)
Diarrhoea (loss of HCO3- from gut)
effects of acidosis
Tachypnoea Muscular weakness Headache Confusion, Coma Cardiac arrhythmia Hyperkalaemia
compensatory mechanisms to combat acidosis
Hyperventilation (↓PaCO2, respiratory compensation)
↓ HCO3- excretion (renal compensation)
causes of alkalosis
Hypocapnia (hyperventilation)
Vomiting (loss of H+ in HCl)
↑ kidney acid excretion (diuretics)
↑ alkalotic agent consumption (antacids, NaHCO3)
effects of alkalosis
Bradypnoea Muscular weakness, cramps, tetany Headache, Nausea Lightheadedness, confusion, coma Cardiac arrhythmia Hypokalaemia
compensatory mechanisms to combat alkalosis
Hypoventilation (↑PaCO2, respiratory compensation)
↑ HCO3- excretion (renal compensation)
explain how acidosis-induced hyperkalaemia occurs:
acidosis causes cardiac arrhythmias
- 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
what is the consequence of hyperkalaemia?
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
explain how alkalosis-induced cerebral vasoconstriction occurs:
- 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
summary q, disturbances in pH lead to…
lead to clinical effects such as arrhythmias & muscle weakness (via effects on serum potassium levels) and confusion (via effects on cerebral blood flow)
