2.21 - Regulation Of Respiration

Question 1

What are the three basic elements of control in respiration?

Answer 1

Sensors: central and peripheral Central controller: pons, medulla & higher centres Effectors: respiratory mucles

Question 2

What sensors are involved in respiration?

Answer 2

Chemoreceptors, tracheo-brachial receptors (mechanoreceptors) and various other receptors

Question 3

Describe the central chemoreceptors in control of respiration

Answer 3

Most important for control Sense CO2 within the BBB BBB impermeable to H+ & HCO3 but permeable to CO2

Question 4

Describe peripheral chemoreceptors in control of respiration

Answer 4

Glomus cell in carotid body signal changes in the partial pressure of oxygen via cranial nerve 9. Fast response to changes on Po2 Sensors only responsible for <20% of ventilatory drive

Question 5

Describe the response (in changes in ventilation) to CO2 and pH

Answer 5

CO2: an increase in Pco2 leads to an increase in ventilation. pH: A decrease in pH (more acidic) stimulates ventilations

Question 6

Describe the factors resulting in the increased respiratory rate during exercise

Answer 6

The increased ventilation is matched by an increase in O2 uptake and CO2 output (up to a threshold of 90L/min) The driver for this increase is not fully know, but CO2 not thought to play a major role. Instead, movement reflexes and the increased temperature are thought to be involved.

Question 7

Describe the inspiratory and expiratory drives and inputs affecting respiration

Answer 7

Breathing rhythm depends on tonic inspiratory drive from DRG and phasic expiratory input from higher centres & spinal cord.

Question 8

List the locations of controllers of respiration

Answer 8

Spinal cord Brainstem (medulla with CPG) Pons (modulation) Other cortical & spinal areas (modulation)

Question 9

Describe the Medullary Respiratory Nuclei

Answer 9

Dorsal Respiratory Group (DRG): Composed of cells in the solitary tract nucleus (nucleus tractus solotarius; NTS). The DRG is involved in the generation of respiratory rhythm, and is primarily responsible for the generation of inspiration. Composed of Inhibitory and excitatory interneurons. Ventral Respiratory Group (VRG): The VRG contains both inspiratory and expiratory neurons. The VRG is secondarily responsible for initiation of inspiratory activity, after the dorsal respiratory group. The nucleus para-ambiguus is active during inspiration, while the nucleus retrofacialis and the nucleus retroambiguus are active during exhalation. The VRG is responsible for motor control of inspiratory and expiratory muscles during exercise.

Question 10

Describe the hierarchal recruitment of respiratory muscles and why it is important

Answer 10

Hierarchal muscle recruitment required for orderly breathing. Innervation of upper airway muscles (nares, tongue, larynx/pharynx). Diaphragm and muscles of the rib cage. Opening of glottis ahead of decrease in tracheal pressure (inspiration): o If the two occur at the same time, flow ↑ causes upper airway collapse (tongue & pharynx)

Question 11

What is the result of damage to neural structures to breathing?

Answer 11

Damage to neural structures results in the loss of structured and orderly breathing. It then leads to “specific patterns” of breathing. E.g. Cheyne-Stokes: periods of apnoea followed by hyperventilation; seen at high altitude and during sleep, severe heart disease and brain damage. Mechanism ? (delay between peripheral and central chemoreceptors)

Question 12

Steven King, a 32 year-old male, likes cycling. One morning, he ponders, which of the following statements best describes the drive for increased ventilation on moderate exercise?

~ represents no change, ↓ a decrease and ↑ an increase.

Answer 12