LUNG FUNCTION

LUNG FUNCTION

1. MECHANICS OF BREATHING

   • Inspiration
     • External intercostals and diaphragm contract, causing cavity to increase in size
       • This also decreases pressure inside the lungs, causing air to rush in via nose and mouth
     • DURING EXERCISE not only do the external intercostals and diaphragm contract, so do the scaleni and sternocleidomastoids
       • Helps raise first and secnd rib, causing a bigger thoracic activity
   • Expiration
     • External intercostals and diaphragm relaxes, causing them to move back to original positions
       • As ribs move inwards and diaphragm upwards, pressure in lungs is greater than atmosphere outside, forcing air out of lungs
     • DURING EXERCISE internal intercostals and abs contract, moving ribs and diaphragm quicker
   • ALVEOLI - tiny thin-walled air sacs found in large numbers in the lungs
   • INSPIRATION - the act of breathing in
   • EXPIRATION - the act of breathing out

2. LUNG VOLUMES AND CAPACITIES

   • TIDAL VOLUME - amount of air breathed in or out per breath
   • INSPIRATORY RESERVE VOLUME - maximal amount of air forcibly inspired in addition to tidal volume
   • EXPIRATORY RESERVE VOLUME - maximal amount of air forcibly expired in addition to tidal volume
   • VITAL CAPACITY - maximal amount of air exhaled after a maximal inspiration
     • TV + IRV + ERV
   • RESIDUAL VOLUME - amount of air left in lungs after a maximal expiration
   • TOTAL LUNG CAPACITY - vital capacity plus residual volume
     • TV + IRV + ERV + RV
       • VC + RV
   • MINUTE VENTILATION - the amount of air moved in and out of the lungs in one minute. (ml. min-1)
     • Ve = frequency of breathing x tidal volume

3. GASEOUS EXCHANGE

   • DIFFUSION - the movement of gas molecules from an area of high concentration to an area of low concentration
   • PARTIAL PRESSURE - the pressure a gas exerts in a mixture of gases
   • mmHg - mm of mercury
   • OXYGEN IN THE LUNGS Alveoli PO2 = 100mmHg Capillaries PO2 = 40mmHg
     • Diffusion gradient causes O2 to move from alveoli into pulmonary capillaries
   • OXYGEN IN THE MUSCLES Capillaries PO2 = 40mmHg Muscle PO2 = 105mmHg
     • DURING EXERCISE Capillaries PO2=40mmHg Muscle PO2=>40mmHg
       • During exercise, the breakdown of glucose to provide energy for the reformation of ATP increases
   • CARBON DIOXIDE IN THELUNGS Alveoli PCO2 = 40mmHg Capillaries PCO2 45mmHg
     • Diffusion gradient causes CO2 to move from pulmonary capillaries to alveoli
   • CARBON DIOXIDE IN MUSCLES Capillaries PCO2=45mmHg Muscle PCO2=40mmHg
     • Diffuse from capillaries into muscle
     • DURING EXERCISE Capillaries PCO2 =45mmHg Muscle PCO2 = 90mmHg
   • STRUCTURE OF LUNGS TO AID GASEOUS EXCHANGE
     • One-cell thick capillary walls (thin)
       • Semi-permeable membrane
     • Short distance between alveoli and capillary
     • Steep diffusion gradients caused by partial pressures
     • Large surface of alveoli
     • Moisture for enhancing uptake of O2

4. CONTROL OF BREATHING

   • CARBON DIOXIDE 5% dissolved in blood plasma 20% combined with haemoglobin 60-80% combines with water (bicarbonate)
   • CHANGES IN RESPIRATION
     • Controlled by medulla oblongata (found between spial cord and upper brain)
       • Controls depth and rate of breathing
       • At rest inspiratory centre sends nerve impulses to diaphragm and external intercostal muscles to contract
       • During exercise increase in CO2 blood
         • =increased acidity
         • =increase in lactic acid
           • Detected by chemoreceptors, where sympathetic nerve is stimulated (contraction)