BIO 378 Respiration Show Respiratory System:
The exchange of gases (O2 & CO2) between the alveoli & the blood occurs by simple diffusion: O2 diffusing from the alveoli into the blood & CO2 from the blood into the alveoli. Diffusion requires a concentration gradient. So, the concentration (or pressure) of O2 in the alveoli must be kept at a higher level than in the blood & the concentration (or pressure) of CO2 in the alveoli must be kept at a lower lever than in the blood. We do this, of course, by breathing - continuously bringing fresh air (with lots of O2 & little CO2) into the lungs & the alveoli. Breathing is an active process - requiring the contraction of skeletal muscles. The primary muscles of respiration include the external intercostal muscles (located between the ribs) and the diaphragm (a sheet of muscle located between the thoracic & abdominal cavities). The external intercostals plus the diaphragm contract to bring about inspiration:
To exhale:
Intra-alveolar pressure during inspiration & expiration As the external intercostals & diaphragm contract, the lungs expand. The expansion of the lungs causes the pressure in the lungs (and alveoli) to become slightly negative relative to atmospheric pressure. As a result, air moves from an area of higher pressure (the air) to an area of lower pressure (our lungs & alveoli). During expiration, the respiration muscles relax & lung volume descreases. This causes pressure in the lungs (and alveoli) to become slight positive relative to atmospheric pressure. As a result, air leaves the lungs (check this animation by McGraw-Hill). Exchange of gases:
Partial Pressures of O2 and CO2 in the body (normal, resting conditions): (check this animation by McGraw-Hill)
While in the alveolar capillaries, the diffusion of gasses occurs: oxygen diffuses from the alveoli into the blood & carbon dioxide from the blood into the alveoli.
How are oxygen & carbon dioxide transported in the blood?
2 - dissolved in the plasma (1.5%) Because almost all oxygen in the blood is transported by hemoglobin, the relationship between the concentration (partial pressure) of oxygen and hemoglobin saturation (the % of hemoglobin molecules carrying oxygen) is an important one. Hemoglobin saturation:
The relationship between oxygen levels and hemoglobin saturation is indicated by the oxygen-hemoglobin dissociation (saturation) curve (in the graph above). You can see that at high partial pressures of O2 (above about 40 mm Hg), hemoglobin saturation remains rather high (typically about 75 - 80%). This rather flat section of the oxygen-hemoglobin dissociation curve is called the 'plateau.' Recall that 40 mm Hg is the typical partial pressure of oxygen in the cells of the body. Examination of the oxygen-hemoglobin dissociation curve reveals that, under resting conditions, only about 20 - 25% of hemoglobin molecules give up oxygen in the systemic capillaries. This is significant (in other words, the 'plateau' is significant) because it means that you have a substantial reserve of oxygen. If you become more active, & your cells need more oxygen, the blood (hemoglobin molecules) has lots of oxygen to provide When you do become more active, partial pressures of oxygen in your (active) cells may drop well below 40 mm Hg. A look at the oxygen-hemoglobin dissociation curve reveals that as oxygen levels decline, hemoglobin saturation also declines - and declines precipitously. This means that the blood (hemoglobin) 'unloads' lots of oxygen to active cells - cells that, of course, need more oxygen.
The oxygen-hemoglobin dissociation curve 'shifts' under certain conditions. These factors can cause such a shift:
CO2 + H20 -----> H2CO3 -----> HCO3- + H+ & more hydrogen ions = a lower (more acidic) pH. So, in active tissues, there are higher levels of CO2, a lower pH, and higher temperatures. In addition, at lower PO2 levels, red blood cells increase production of a substance called 2,3-diphosphoglycerate. These changing conditions (more CO2, lower pH, higher temperature, & more 2,3-diphosphoglycerate) in active tissues cause an alteration in the structure of hemoglobin, which, in turn, causes hemoglobin to give up its oxygen. In other words, in active tissues, more hemoglobin molecules give up their oxygen. Another way of saying this is that the oxygen-hemoglobin dissociation curve 'shifts to the right' (as shown with the light blue curve in the graph below). This means that at a given partial pressure of oxygen, the percent saturation for hemoglobin with be lower. For example, in the graph below, extrapolate up to the 'normal' curve (green curve) from a PO2 of 40, then over, & the hemoglobin saturation is about 75%. Then, extrapolate up to the 'right-shifted' (light blue) curve from a PO2 of 40, then over, & the hemoglobin saturation is about 60%. So, a 'shift to the right' in the oxygen-hemoglobin dissociation curve (shown above) means that more oxygen is being released by hemoglobin - just what's needed by the cells in an active tissue! Carbon dioxide - transported from the body cells back to the lungs as:
Review questions: What is the primary function of the respiratory system? What are the components of the conducting zone or division of the respiratory system? What makes up the respiratory zone or division? What muscles are involved in inspiration, expiration? What is caused by contraction of the inspiratory muscles, by relaxation of the inspiratory muscles? How & why does intra-alveolar pressure change during inspiration & expiration? What is external respiration & why is it so efficient? What is internal respiration? How does the exchange of gases occur in external respiration? What is partial pressure? What are the partial pressures of CO2 & O2 in the alveoli, alveolar capillaries (both coming in & going out), body cells, tissue capillaries (both going in & coming out)? How is oxygen transported in the blood? How does the partial pressure of oxygen affect hemoglobin saturation? What is the significance of the plateau in the oxygen-hemoglobin dissociation curve? What is the significance of the steep portion of the oxygen-hemoglobin dissociation curve? How do pH, temperature, 2,3-diphosphoglycerate, & CO2 affect hemoglobin molecules & the oxygen-hemoglobin dissociation curve? What is the significance of these effects? How is carbon dioxide transported in the blood? What happens in the lungs when the diaphragm and external intercostal muscles relax is quizlet?Terms in this set (26) What happens in the lungs when the diaphragm and external intercostal muscles relax? Air is forced out of the lungs.
What happens in the lungs when the diaphragm relaxes?When the lungs exhale, the diaphragm relaxes, and the volume of the thoracic cavity decreases, while the pressure within it increases. As a result, the lungs contract and air is forced out.
What happens when external intercostal muscles relax?When you exhale: the external intercostal muscles relax and the internal intercostal muscles contract, pulling the ribcage downwards and inwards. the diaphragm relaxes, moving back upwards. lung volume decreases and the air pressure inside increases.
What happens to the diaphragm and external intercostal muscles?The diaphragm is drawn down and the ribs flared by the external intercostal muscles to increase the thoracic volume. The negative pressure created draws air into the lungs through the upper respiratory tract. In expiration the relaxing muscles allow the ribs to fall back and the diaphragm rises.
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