Control of Breathing Rate

Dorsal respiratory group (DRG)

Medulla, mainly inspiration

Ventral respiratory group (VRG)

Medulla, mainly inspiration, inactive during quiet breathing, active during heavy exercise

Pneumotaxic centre

Pons, mainly controls rate and depth of breathing, inhibits drg and inspiration may take .5 seconds only, strongly active = shallow and superficial breathing, less active = low frequency but deep breathing

Neurons in respiratory centres

Neurons in drg connected to motor neurons of inspiratory muscles, phrenic nerve = C345

Respiratory centres and quiet breathing

drg active for two seconds of inhalation and three seconds of exhalation

Respiratory centres and forced breathing

drg active for inhalation and exhalation

Peripheral chemoreceptors

Located at aortic and carotid bodies, stimulation of drg, monitor composition of arterial blood, stimulated by hypoxia when blood PO2 is less than 60mmHg - causes inadequate gas exchange, ischemia and anaemia

Central chemoreceptors

Located in medulla oblongata, monitor composition of cerebrospinal fluid, highly sensitive to hypercapnia and acidosis, stimulation of drg

Baroreceptors

Located in aortic arch and carotid sinus, respiratory rate increases if blood pressure decreases, respiratory rate decreases if blood pressure increases

Mechanoreceptors in the lungs

Hering-Breuer inflation relex, prevents overexpansion of lungs, activity terminates inspiration, decreases tidal volume and increases breathing rate

Major changes that reduce max oxygen uptake

Arthritic changes in costovertebral joints and costal cartilages = stiffen thorax and decrease compliance, elastic tissue replaced with scar tissue = reduces lung compliances and vital capacity, emphysema destroys alveolar surface and reduces surface area available for gas exchange