LUNG FUNCTION

MECHANICS OF BREATHING
1. Inspiration
  1. External intercostals and diaphragm contract, causing cavity to increase in size
    1. This also decreases pressure inside the lungs, causing air to rush in via nose and mouth
  2. DURING EXERCISE not only do the external intercostals and diaphragm contract, so do the scaleni and sternocleidomastoids
    1. Helps raise first and secnd rib, causing a bigger thoracic activity
2. Expiration
  1. External intercostals and diaphragm relaxes, causing them to move back to original positions
    1. As ribs move inwards and diaphragm upwards, pressure in lungs is greater than atmosphere outside, forcing air out of lungs
  2. DURING EXERCISE internal intercostals and abs contract, moving ribs and diaphragm quicker
3. ALVEOLI - tiny thin-walled air sacs found in large numbers in the lungs
4. INSPIRATION - the act of breathing in
5. EXPIRATION - the act of breathing out
LUNG VOLUMES AND CAPACITIES
1. TIDAL VOLUME - amount of air breathed in or out per breath
2. INSPIRATORY RESERVE VOLUME - maximal amount of air forcibly inspired in addition to tidal volume
3. EXPIRATORY RESERVE VOLUME - maximal amount of air forcibly expired in addition to tidal volume
4. VITAL CAPACITY - maximal amount of air exhaled after a maximal inspiration
  1. TV + IRV + ERV
5. RESIDUAL VOLUME - amount of air left in lungs after a maximal expiration
6. TOTAL LUNG CAPACITY - vital capacity plus residual volume
  1. TV + IRV + ERV + RV
    1. VC + RV
7. MINUTE VENTILATION - the amount of air moved in and out of the lungs in one minute. (ml. min-1)
  1. Ve = frequency of breathing x tidal volume
GASEOUS EXCHANGE
1. DIFFUSION - the movement of gas molecules from an area of high concentration to an area of low concentration
2. PARTIAL PRESSURE - the pressure a gas exerts in a mixture of gases
3. mmHg - mm of mercury
4. OXYGEN IN THE LUNGS Alveoli PO2 = 100mmHg Capillaries PO2 = 40mmHg
  1. Diffusion gradient causes O2 to move from alveoli into pulmonary capillaries
5. OXYGEN IN THE MUSCLES Capillaries PO2 = 40mmHg Muscle PO2 = 105mmHg
  1. DURING EXERCISE Capillaries PO2=40mmHg Muscle PO2=>40mmHg
    1. During exercise, the breakdown of glucose to provide energy for the reformation of ATP increases
6. CARBON DIOXIDE IN THELUNGS Alveoli PCO2 = 40mmHg Capillaries PCO2 45mmHg
  1. Diffusion gradient causes CO2 to move from pulmonary capillaries to alveoli
7. CARBON DIOXIDE IN MUSCLES Capillaries PCO2=45mmHg Muscle PCO2=40mmHg
  1. Diffuse from capillaries into muscle
  2. DURING EXERCISE Capillaries PCO2 =45mmHg Muscle PCO2 = 90mmHg
8. STRUCTURE OF LUNGS TO AID GASEOUS EXCHANGE
  1. One-cell thick capillary walls (thin)
    1. Semi-permeable membrane
  2. Short distance between alveoli and capillary
  3. Steep diffusion gradients caused by partial pressures
  4. Large surface of alveoli
  5. Moisture for enhancing uptake of O2
CONTROL OF BREATHING
1. CARBON DIOXIDE 5% dissolved in blood plasma 20% combined with haemoglobin 60-80% combines with water (bicarbonate)
2. CHANGES IN RESPIRATION
  1. Controlled by medulla oblongata (found between spial cord and upper brain)
    1. Controls depth and rate of breathing
    2. At rest inspiratory centre sends nerve impulses to diaphragm and external intercostal muscles to contract
    3. During exercise increase in CO2 blood
      1. =increased acidity
      2. =increase in lactic acid
        Detected by chemoreceptors, where sympathetic nerve is stimulated (contraction)

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