Integrated Control Of Ventilation

Question 1

What organs regulate blood ph and how

Answer 1

The lungs and kidneys work together to maintain blood pH by regulating the partial pressures of
carbon dioxide and concentration of bicarbonate ions respectively.

Question 2

What happens during respiratory regulation vs renal regulation

Answer 2

Respiratory regulation of carbon
dioxide occurs through varying ventilation rate whilst renal regulation of bicarbonate ion
concentration occurs through controlling reabsorption and excretion in glomerular filtration. The
former process is quicker than the latter process. These two systems can compensate for one
another to maintain blood pH.

Question 3

What controls the level of ventilation

Answer 3

The level of ventilation is controlled by the brainstem that receives
signals various neuronal signals and uses them to regulate ventilation rates. The inputs used include
blood pH.

Question 4

What can abnormalities in the respiratory or renal systems cause

Answer 4

Abnormalities in the respiratory or renal systems can cause respiratory and metabolic
acidosis or alkalosis respectively.

Question 5

What is respiratory acidosis - describe

Answer 5

Respiratory acidosis is a decrease in blood pH caused by dysfunction of the respiratory system
(hypoventilation). This causes acidosis as carbon dioxide accumulates in the body and is not being
removed quick enough (hypercapnia). The result is a decrease in pH as more carbon dioxide means
more carbonic acid that dissociates into hydrogen ions.

Question 6

How does the body respond to respiratory acidosis

Answer 6

The body responds to this by stimulating the

brainstem to increase ventilation rate and remove the excess carbon dioxide.

Question 7

How is the brainstem quickly activated

Answer 7

In particular, central
respiratory chemoreceptors influence the brainstem. This process is usually very quick and blood pH
is restored quite quickly.

Question 8

When does respiratory acidosis cause problems

Answer 8

In order for respiratory acidosis to cause problems, pH must remain low for
an extended period of time. This is caused because the body is unable to ventilate at a sufficient rate
(e.g. caused by obstruction to airways).

Question 9

What happens when the respiratory system is unable to respond to lower ph - and in what case

Answer 9

If the respiratory system is unable to respond to lower pH,
the renal system compensates for this by increasing the reabsorption of bicarbonate ions to increase
their concentration in the body. As mentioned earlier, this only occurs if extended hypoventilation
occurs.

Question 10

Give a cause o hypoventilation

Answer 10

One cause of hypoventilation is airway obstruction that can be caused by increased airway
resistance (asthma and COPD). Airway obstruction can also be caused by asphyxia (strangling) or
choking, as well as obstruction of the upper airways in obstructive sleep apnoea. Hypoventilation can
also be caused by problems with breathing itself.

Question 11

Causes of breathing initiation problems

Answer 11

Breathing initiation problems can be caused by
drug overdose affecting the brainstem, stroke and neuromuscular problems (e.g. motor neuron
disease).

Question 12

What is respiratory alkalosis

Answer 12

Respiratory alkalosis is an increase in blood pH that is also caused by the dysfunction of the
respiratory system but by hyperventilation. This decreases the partial pressure of carbon dioxide in
the blood that causes the conversion of carbonic acid to carbon dioxide and therefore a decrease in
hydrogen ion concentration in the blood.

Question 13

What happens in chronic hyperventilation

Answer 13

Normally, chemoreceptor feedback to the brainstem
decreases initiating it to decrease ventilation rate and therefore decrease ventilation to restore blood
pH. In chronic hyperventilation, the renal system compensates for the decrease carbon dioxide
partial pressure by decreasing the reabsorption of bicarbonate ions to decrease their concentration
in the blood.

Question 14

What causes hyperventilation

Answer 14

Hyperventilation can be caused by anxiety that triggers a panic attack. This causes
higher emotional centres in the brain to influence the brainstem to increase ventilation rate without
increased metabolic demand. Hyperventilation can also be caused by altitude where the partial
pressure of oxygen decreases. This stimulates the brainstem to increase ventilation rate through
hypoxic drive.

Question 15

How does increased ventilation cause respiratory alkalosis

Answer 15

The increased ventilation decreases the partial pressure of carbon dioxide in the body
that results in respiratory alkalosis.

Question 16

What is metabolic acidosis

Answer 16

Metabolic acidosis is a decrease in blood pH caused by a large amount of acid production or
increased excretion of bicarbonate ions.

Question 17

How does the body respond to metabolic acidosis

Answer 17

The respiratory system responds to this change by increasing

ventilation rate to reduce partial pressure of carbon dioxide in the blood.

Question 18

What is the problem with increasing ventilation for metabolic acidosis

Answer 18

This compensatory

mechanism is almost instantaneous however may not be sufficient enough to restore blood pH.

Question 19

What can cause metabolic acidosis

Answer 19

Metabolic acidosis can be caused by infection that triggers a pathological immune response causing
septic shock. This decreases oxygen delivery to tissues that causes them to increase the rate of
anaerobic respiration and therefore increase the rate of lactic acid production (lowers pH). Metabolic
acidosis can also be caused by diabetic ketoacidosis where fatty acid release from the liver is
increased due to insulin deficiency and ketone

is increased. Renal failure can
also decrease the reabsorption of bicarbonate ions into the body and diarrhoea decreases
absorption of bicarbonate ions from the colon. The effect of both of these problems is increased
bicarbonate ion excretion.

Question 20

What is metabolic alkalosis

Answer 20

Metabolic alkalosis is an increase in blood pH caused by the metabolic system. This can in general be
caused by excessive removal of metabolic acid or decreased excretion of bicarbonate ions.

Question 21

How does the body overcome metabolic alkalosis

Answer 21

The
respiratory system reacts to this by decreasing ventilation rate in a compensatory mechanism to try
and restore blood pH.

Question 22

What causes metabolic alkalosis

Answer 22

Metabolic alkalosis can be caused by drugs like diuretics that cause insufficient
excretion of bicarbonate ions and decrease hydrogen ion concentrations. Vomiting causes a loss of
stomach acid that can also lead to increased blood pH. Antacids abuse increases bicarbonate
consumption and therefore concentration in the blood leading to altered blood pH.

Question 23

What can be used to find cause if acidosis or alkalosis

Answer 23

Arterial blood gas readings can be interpreted to find the cause of acidosis or alkalosis.

Question 24

What systems respond to acidosis and alkalosis

Answer 24

Both the
respiratory system and renal systems change carbon dioxide partial pressures and bicarbonate ion
concentrations respectively in response to acidosis and alkalosis. However, one of the changes is the
cause of the acid-base disorder and the other is a compensatory mechanism to try and restore blood
pH.