Oxygenation & Blood Gas Regulation

1. Oxygenation & Blood Gas Regulation

2. Respiration 4 distinct processes:  Pulmonary ventilation and lung perfusion  Gas exchange (between blood and alveoli)  Transportation of gases  Gas exchange (between blood and tissue cells)

3. External / internal interface: Alveoli  microscopic  protrude from the end of the smallest bronchioles  groups of alveoli called alveolar sacs  composed of a single layer of cells  alveoli form huge surface area (estimated 70 m2)  surrounded by pulmonary capillaries

4. Diffusion of gases: Blood and alveoli 1. Diffusion occurs across respiratory membrane Respiratory membrane:  composed of alveolar cell wall, interstitial space and cell wall of pulmonary capillary  large surface area and distance very small (0.5 m) disruption of alveoli and respiratory membrane due to lung disease will impair diffusion of gases and lead to health problems

5. 2. Gas concentration difference exists Gas concentration:  amount of a gas expressed as Partial Pressure  unit of measurement for partial pressure varies: clinically use kilopascals (kPa) in physiology use millimetres of mercury (mmHg)  partial pressure of gases vary throughout respiratory system

6.  Diffusion of oxygen Alveolus Pulmonary capillary

7.  Diffusion of carbon dioxide Alveolus Pulmonary capillary

8. Internal environment / intracellular interface: blood and tissue cells:  diffusion of oxygen Tissue capillary Tissue cells

9.  diffusion of carbon dioxide: Tissue capillary Tissue cells

10. Transportation of gases in blood:  Oxygen plasma RBC

11.  carbon dioxide plasma RBC

12. Transportation of gases in blood: Haemoglobin  Haemoglobin is vital in the transportation of oxygen to the tissues  Haemoglobin: large macromolecule composed of: Haem (pigment & iron) and Globin  Anaemia is the term used for a low Hb count  Shortness of breath is associated with anaemia  Haemoglobin (oxygen) saturation: 95 -100%

13. Blood Gas Regulation II

14. Pulmonary ventilation (breathing):  process involved in the exchange of gases between atmosphere and alveoli.  involves inspiration and expiration inspiration - 2 seconds expiration - 3 seconds  tidal volume refers to the volume of air inspired or expired approx. 500 ml but only about 350 ml reaches alveoli

15. Inspiration: mechanical events contraction of external intercostal muscles and diaphragm diaphragm flattens and rib cage moves up and out thoracic cavity expands As ribs move pleural membranes also pulled and lungs expand Gas pressure falls inside lungs relative to atmosphere Air flows into lungs from high to low pressure

16. Expiration (quiet breathing): mechanical events Passive relaxation of external intercostal muscles and diaphragm Rib cage moves downward and diaphragm becomes dome shaped Thoracic cavity and lung volume decreases (aided by elastic recoil of alveolar tissue Gas pressure in lungs increases relative to atmosphere Air flows from alveoli into atmosphere

17. Pulmonary ventilation aided by:  lungs remain partially filled with air at end of expiration residual volume (approx. 1.5 litres)  lower gas pressure in pleural cavity (intrapleural pressure) helps keep alveoli expanded  specialised cells on inner membrane of alveolar wall secrete surfactant - reduces surface tension and prevents collapse of alveoli

18. Receptors chemoreceptors Sensory afferent impulses Integration centre Respiratory centres in Medulla and Pons (Brain stem) Motor efferent outflow Phrenic nerve to diaphragm Intercostal nerve to external intercostal muscles Effector response Rate and depth of ventilation altered

19. Chemoreceptors:  Two types: Central Chemosensitive area in medulla Peripheral Aortic arch and carotid bodies  sensitive to changes in arterial blood PCO2 and PO2  stimulation of chemoreceptors leads to increased activity of inspiratory area in the respiratory centre

20. Chemoreceptors: Central stimulated by  H+ and  pH of ECF & CSF (due to  arterial blood PCO2) Peripheral stimulated by major  in PO2 (from 104 to 50 mmHg)  arterial blood PCO2

21. Respiratory centres:  located in medullaand Pons (areas of brain stem)  Pons: centres co-ordinate the transition between inspiration and expiration.  Medulla: Medullary rhthmicity area controls the basic rhythm of respiration composed of inspiratory area and expiratory area autonomic activity

22. Inspiratory area:  nerve cells have intrinsic excitability  nerve impulses generated and transmitted along: Phrenic nerves and intercostal nerves  inspiration lasts approx. 2 seconds  nerve cells then become inactive and expiration occurs  expiration (during quiet breathing) is passive

23. Other factors which influence breathing: Cerebral cortex  body temperature anxiety pain Stretch receptors in lungs

24. Common terminology: Dyspnoea Tachypnoea Apnoea Orthopnoea Hypoxia Cheyne-Stokes respiration

25. Common terminology: Dyspnoea difficulty in breathing Tachypnoea rapid breathing Apnoea absence of breathing Orthopnoea breathless when lying flat Hypoxia low arterial blood oxygen level Cheyne-Stokes respiration periodic breathing

26. 2. Concentration difference exists  Diffusion of oxygen O2 104 mmHg Alveolus O2 40 mmHg pulmonary capillary Oxygen diffuses along the concentration gradient across the alveolar cell wall, interstitial space and pulmonary capillary wall

27.  Diffusion of carbon dioxide CO2 40 mmHg Alveolus CO2 45 mmHg Pulmonary capillary Carbon dioxide diffuses along the concentration gradient across the pulmonary capillary wall, interstitial space and alveolar cell wall

28. Internal environment / intracellular interface: blood and tissue cells:  diffusion of oxygen Tissue capillary O2 104 mmHg O2 40 mmHg Tissue cells

29.  diffusion of carbon dioxide: CO2 40 mmHg Tissue capillary CO2 45 mmHg Tissue cell