Control of Lung Function

Question 1

What are the 4 nuclei found in the medulla oblongata?

Answer 1

Dorsal respiratory group, Ventral respiratory group, Apneustic centre and Pneumotaxic centre

Question 2

What is the function of the dorsal and ventral respiratory groups?

Answer 2

Dorsal respiratory group is the inspiratory centre - main ‘controller’ of inspiration. Sets the ‘rate’ and rhythm of breathing. Ventral respiratory group works synergistically and antagonistically - is the expiratory centre and inactive during quiet breathing as expiratory muscles aren’t usually active. Inhibits apneustic centre.

Question 3

What is the function of the apneustic centre and pneumotaxic centre?

Answer 3

Apneustic centre - Stimulates activity in DRG and is inhibited by pulmonary afferents.
Pneumotaxic centre - Is the ‘inspiratory off switch’.
Regulates depth & frequency.

Question 4

How do the nuclei control one another?

Answer 4

Dorsal respiratory group inhibits ventral.
Ventral respiratory group inhibits dorsal and apneustic centre.
Apneustic centre activates dorsal.
Penumotaxic centre inhibits dorsal.

Question 5

What is the respiratory pacemaker system?

Answer 5

There is a baseline action potential frequency which maintains a certain membrane voltage and frequency of action potentials at apneustic centre increase until pneumotaxic centre is activated. This stops the rhythm hence stopping inspiration. A period of latency occurs until apneustic centre once again stimulates DRG.

Question 6

How does the phrenic nerve arise and what is its purpose?

Answer 6

Arises from C3,C4,C5 which combine to form phrenic nerve - main motor nerve going to diaphragm.

Question 7

What are the features of the blood-brain barrier?

Answer 7

In normal circulation, capillaries are continuous but have small water-filled gap junctions between them whereas the blood-brain barrier has endothelial cells which are packed with tight junctions and hence, have no gaps between them. Between the capillary and the neural tissue lies the CSF.

Question 8

Describe chemosensitivity in the medulla

Answer 8

Protons and bicarbonate cannot diffuse across the endothelial cells as these cells lack the transporters and these molecules are charged, so not lipid soluble. However, carbon dioxide from the bloodstream is very lipid soluble and hence diffuses across bilayer into the CSF. When this reacts with water in the CSF, it dissociates to produce protons and bicarbonate ions. These protons then interact with afferent fibres in the medulla, which uses this information to generate an impulse sent to the dorsal respiratory group. The DRG then generates the rhythm and rate of breathing required.

Question 9

What is the purpose of irritant receptors?

Answer 9

These are afferent receptors embedded within and beneath airway epithelium. Leads to cough: which involves forceful expiration against a closed glottis with sudden glottal opening & high velocity expulsion of air. Found in the upper airways in trachea.

Question 10

What is the purpose of stretch receptors?

Answer 10

Excessive inflation of lungs activates pulmonary stretch receptors. Afferent signals to respiratory centres inhibit DRG and apneustic centre and stimulate pneumotaxic VRG. Inspiration inhibited & expiration stimulated. Found towards ends of respiratory trees.

Question 11

What is the purpose of J-receptors?

Answer 11

These are sensitive to oedema and pulmonary capillary engorgement. Increases breathing frequency. Found in the alveolar region.

Question 12

What is apnoea?

Answer 12

Cessation of breathing - volitional if it is on purpose.

Question 13

What are ventilation triggers during volitional apnoea?

Answer 13

Partial pressure of oxygen and carbon dioxide is relatively constant as ventilation occurs but when stopped, oxygen levels start to drop as carbon dioxide increases. Eventually, carbon dioxide levels increase beyond a certain threshold where there is a high proton concentration in medulla and urge to breathe is overwhelming. If breath still held, eventually oxygen depletes to a level where person blacks out.

Question 14

What is an acid and a base?

Answer 14

An acid is any molecule that has a loosely bound H+ ion that it can donate. H+ ions are also called protons (because an H atom with a +1 valency has no electrons or neutrons). A greater concentration of H+ ions refers to a lower pH. A base is an anionic (negatively charged ion) molecule capable of reversibly binding protons (to reduce the amount that are ‘free’).

Question 15

Why is acid base homeostasis important?

Answer 15

The acidity of the blood must be tightly regulated, marked changes will alter the 3D structure of proteins (enzymes, hormones, protein channels). The acid-base relationship is in an equilibrium. Increasing something on one side will push the equation in the opposite direction

Question 16

What is alkalaemia, acidaemia, alkalosis and acidosis?

Answer 16

Alkalaemia: Refers to high-than-normal pH of blood
Acidaemia: Refers to lower-than-normal pH of blood
Alkalosis: Describes circumstances that will decrease [H+] and increase pH
Acidosis: Describes circumstances that will increase [H+] and decrease pH

Question 17

How is a pH disturbance corrected?

Answer 17

An acidaemia will need an alkalosis to correct while an alkalaemia will need an acidosis to correct. Changes in ventilation can stimulate a RAPID compensatory response to change CO2 elimination and therefore alter pH while changes in HCO3- and H+ retention/secretion in the kidneys can stimulate a SLOW compensatory response to increase/decrease pH.

Question 18

Where are peripheral chemoreceptors positioned?

Answer 18

Positioned near the carotid baroreceptors (sensitive to changes in blood pressure). Carotid and aortic bodies are both found in the aortic arch, next to carotid arteries so measures pH and pressure of the blood going to the brain.

Question 19

How can an emotional need to breathe be created?

Answer 19

Higher brain centres and special senses can create an emotional response, which comes from the limbic system, that act on the respiratory control centre creating a need to breathe.

Question 20

How does breathing change during exercise?

Answer 20

Efferents from primary motor cortex to gross skeletal musculature partly innervate medulla so when impulse sent from primary motor cortex to muscle, branch goes off to medulla and prompts increased ventilation in anticipation of muscle contraction.

However, proprioceptive afferents from muscle spindles & golgi tendon organs innervate medulla on way to brain so even when motor control not involved and if muscle movement is forced by an external force, ventilation is still increased.

Question 21

What is the cold shock response?

Answer 21

When immersed in cold water (below 10 degrees), sensory nerve endings which are very superficial in skin detect this resulting in an inspiratory gasp and resultant hyperventilation. Leads to loss of breath holding control.