Module 1 Lecture 7

1) it is bound to hemoglobin (Hb) within red blood cells (98% this way) 2) Dissolved in plasma (2% this way) O2 loading and unloading is very rapid and efficient

Haemaglobin is composed of 4 iron-containing heme groups- each haemaglobin molecules can carry 4 oxygen molecules

• Partial pressure of oxygen (PO2) • Temperature • Hydrogen ions (decreased pH) • Partial pressure of carbon dioxide (PCO2) • Blood BPG (2,3-bisphosphoglycerate) concentration

Temperature, blood H+, partial pressure of CO2 (PCO2), blood BPG (2,3-bisphosphoglycerate) concentration all ↑ upon greater metabolic demand (i.e. in systemic capillaries)

increase in oxygen unloading, more oxygen is available for use by local tissues

a decrease in oxygen unloading, meaning less oxygen is available for use by local tissues

• Dissolved in plasma (7-10%) • Bound to haemoglobin (Hb) within red blood cells (20%) • As bicarbonate ions in plasma (70%)

Carbon dioxide is transported to lungs -> diffuses down partial pressure gradient from pulmonary capillaries into alveoli & expired

• ↓ PO2 & Hb oxygen saturation = ↑ CO2 transported • E.g. In systemic tissues, where PO2 is low, CO2 is more readily loaded onto Hb to be carried via venous system to the heart, then lungs. In lungs, where PO2 is high, CO2 is unloaded from Hb & diffused into alveoli

• Respiratory muscles contract only when stimulated by nerves • Rhythmic breathing is established by cyclic neural activity from the brainstem to respiratory muscles (although origin of this rhythm not well understood) • Maintains breathing & reflex adjustments when required • Can be voluntarily modified

Medullary Respiratory Centre and Pons respiratory Centre

Medullary Respiratory Centre has two neuronal clusters: • Ventral respiratory group (VRG) – rhythm generating • Dorsal respiratory group (DRG) – integrates inputs from peripheral stretch receptors, chemoreceptors & higher brain centres à communicates with & modifies VRG neurons

Pons Respiratory Centre fine-tunes breathing during activities such as talking, sleeping, exercise - integrates inputs from peripheral sensory receptors & higher brain centres à communicate & modifies DRG & VRG neurons

Depth is determined by degree of neuronal stimulation from respiratory centres: ↑ stimulation of inspiratory neurons ↑ force of respiratory muscle contraction resulting in greater thoracic expansion

Rate is determined by how long the inspiratory neurons are active

Chemical factors: arterial CO2, H+, O2 via central & peripheral chemoreceptors – Higher brain centres: hypothalamus (emotions & pain) & motor cortex (voluntary control) – Pulmonary irritants: mucus, dust, fumes stimulate bronchiole receptors that communicate with respiratory centres via vagal nerve afferents – reflex constriction, cough, sneeze – Inflation reflex: stretch receptors signal respiratory centres via vagal nerve afferents to end inspiration & lungs recoil

Ventilation ↑ 10-20-fold during vigorous exercise due to ↑ tidal volume & respiratory rate: 4L/min –> 80L/min • Greater force of contraction of respiratory muscles & activation of accessory muscles that further ↑ thoracic volume

• Not due to ↑ PCO2 or ↓ PO2 as ventilation ↑ as soon as exercise begins & arterial PCO2 & PO2 remain relatively constant (although capillary & venous levels change) • Psychological – anticipation of exercise • Simultaneous cortical motor & respiratory centre activation • Proprioceptors in active muscles, tendons, & joints stimulate respiratory centres

Respiratory system susceptible to infections due to open airways

Obstructive: COPD (chronic bronchitis & emphysema usually caused by inhaled irritants & smoking), asthma (acute respiratory episodes caused by immune-mediated inflammation) – Restrictive: TB (infectious disease caused by bacterium), lung fibrosis (e.g. asbestos) – Lung cancer (~90% cases due to smoking)

Sleep Apnea: temporary pause in breathing during sleep – Obstructive: collapse of upper airway & obesity is a risk factor – Central: respiratory centre depressed during sleep