Gas exchange Flashcards
External respiration
exchange of oxygen at the alveoli
exchange of carbon dioxide at the alveoli
Internal respiration
exchange of oxygen at the tissue
exchange of carbon dioxide at the tissue
Air composition
nitrogen- 597 mmHg
oxygen- 159mmHg
water- 2.5mmHg
carbon dioxide- 0.3mmHg
total partial pressure- 760mmHg
Kpa to mmHg
mmHg= Kpa x 7.5
Movement of gases
conducting zone by bulk flow
respiratory zone by diffusion
Alveoli and capillary interface
oxygen dissolves in and diffuses through the surfactant through alveolar wall through capillary wall into plasm into RBC combined with haemoglobin carbon does the reverse
Capillary and tissue interface
Bulk flow of blood to tissue diffusion through RBC wall through plasma through capillary wall through tissue membrane into mitochondria
Dalton’s Law
total pressure of mixture of nonreacting gases is the sum of the partial pressures exerted by each of the gases in the mixture
Henry’s law
the amount of gas in a solution depends on the partial pressure of the gas and it’s solubility
pressure decrease
gas’s ability to dissolve decrease
Carbon dioxide
in air has a low partial pressure but high solubility
Oxygen
in air has a high partial pressure but low solubility
Diffusion
movement of gas from a high partial to a low partial pressure
dependent on
temperature
movement of molecule
diffusion gradient
Ficks law
rate of diffusion is
directly proportional to-
surface area
diffusion gradient
inversely proportional to
-diffusion difference
the higher the surface area, the greater the diffusing ability of the gas, the greater the diffusion gradient and the shorter the diffusion pathway the greater the rate of diffusion
Alveolar oxygen exchange
mixed venous blood contains 40mmHg partial Po2
alveoli air contains 104mmHg partial Po2
movement of oxygen from the alveoli to the venous blood occur
equilibrium reached after 0.25 seconds
Oxygen exchange
oxyhaemoglobin doesn’t contribute to Po2 of capillary blood
once haemoglobin is saturated only oxygen in plasma contributes to partial pressure which the equals the alveolar partial pressure
there transfer of oxygen is perfusion limited
Perfusion
passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissues
oxygen exchange in exercise
blood move more quickly through capillaries
no limit on diffusion or perfusion as capillaries are recruited
partial pressure are maintained
RBC pass through without oxygen being picked up but more capillaries and lung surface are recruited as oxygen demand increases
Disease
patients with abnormal alveolar/ capillary interface thickened barrier of exchange surfaces diffusion of oxygen is reduced suffer from diffusion limitations limits exercise tolerance
application not ficks law
Alveolar carbon dioxide exchange
mixed venous blood contain 45mmHg Pco2
alveolar Pco2 is 40mmHg
small diffusion gradient
as co2 is more soluble reaches equilibrium in 0.25 seconds
Capillary and tissue interface
Bulk flow of blood to tissue diffusion through RBC wall through plasma through capillary wall through tissue membrane into mitochondria
Inspiration
The respiratory centre in the medulla oblongata sends impulses to initiate inspiration, the muscles of inspiration are initiated and contract, Accessory muscles include sternocleidomastoid, scalene, pectorals minor, sertatus anterior. The diaphragm contracts and descends. The rib cage swings up and out, increasing the volume within the thorax. The intrapulmonary pressure starts to drop. The pleural pressure in the pleural space becomes more negative as the rib cage moves up and out. Intrapulmonary pressure becomes less than atmospheric pressure. Air is moved into the lungs down concentration gradient until equilibrium is reached and air movement stops.
Expiration
The respiratory centre in the medulla oblongata stops initiating inspiration, respiratory muscles relax, diaphragm moves up as the ribcage moves down and in. the lungs recoil due to the elastic recoil, intra pulmonary pressure rises, intrapleural pressure becomes less negative air moves down a concentration gradient until equilibrium is reached.
