Respiratory Mechanism

The main function of your respiratory system is to pull in oxygen for your body's cells and get rid of carbon dioxide, a waste product. You do this by breathing in and out and through gas exchange between the small air sacs of your lungs (alveoli) and the nearby blood vessels.

Recall the steps involved in the respiration mechanism:

• Pulmonary ventilation drawns in atmospheric air and exchanges it for CO2 rich alveolar air is released out.
• Diffusion of gases (O2 and CO2) across the alveol membrane.
• Transport of gases by blood.
• Diffusion of O2 and CO2 between blood and tissues

We use two types of cellular respiration;  aerobic respiration that slowly releases a lot of energy in the presence of oxygen and anaerobic respiration that quickly release smaller amounts when oxygen is depleted.

CO2 is a by-product of aerobic metabolism. As long as the cells are functioning properly, they will produce CO2.

• CO2 takes several forms in the blood.
  • Like oxygen, some is dissolved directly into the plasma.
  • The PaCO2 is the measurement of the partial pressure of carbon dioxide dissolved in the plasma. It is measured in mm Hg (millimeters of mercury).
  • When combined with the water in plasma, carbon dioxide becomes carbonic acid (H2CO3):

    CO2 + H2O <--> H2CO3

  • The rest is bound to the hemoglobin in erythrocytes.
• The respiratory mechanism is a way of controlling how much carbon dioxide is in the blood. Elevating arterial CO2 or decreasing pH and increases the rhythmic stimulation of the respiratory muscles by the medulla.
• Normally control of CO2 is based on the rate and depth of ventilation.
• Ventilation is however not synonymous with oxygenation. Ventilation refers only to air moving in and out of the lungs.
  • If everything else is working the way it should, then oxygenation happens.
  • However, adequate ventilation, even mechanical ventilation, does not insure adequate oxygenation if pulmonary circulation or O2 carrying capacity of the blood is insufficient.

Key Points (ventilation)

• The dorsal respiratory group (nucleus tractus solitarius) primarily controls the rhythm and timing of inspiration.
• Ventilation rate (minute volume) is influenced by several factors, with blood CO2 levels being a major one. Changes in blood pH can also be detected by chemoreceptors and influence breathing.
• The medulla oblongata sends signals to respiratory muscles for inspiration and expiration, and controls non-respiratory reflexes like coughing and sneezing.
• The ventral respiratory group is mainly responsible for expiration, including forced exhalation.
• The brainstem, including the apneustic and pneumotaxic centers in the pons, works together to regulate the rate and depth of breathing. The pneumotaxic center plays a more prominent role in limiting inspiration and controlling breathing rate compared to the apneustic center. (Boundless, 2024).

Instant Feedback:

When combined with water, carbon dioxide becomes carbonic acid (H2CO3):

CO2 + H2O <--> H2CO3

CO2's affinity for hemoglobin is much less than oxygen's.

• So, when both are available, hemoglobin will accept oxygen rather than CO2.
• In the oxygen rich environment of the alveoli, hemoglobin carries oxygen.
• Oxygenated blood then travels through the body.

There is less oxygen and more CO2 near the cells.

• Remember that CO2 in solution is an acid.
  • Therefore, in the capillaries, the blood is more acidic.
  • The lower pH changes the affinity of oxygen for hemoglobin (see Oxyhemoglobin Dissociation curve) and oxygen is released to the tissues.
• In this oxygen depleted environment, the CO2 is now able to ride the hemoglobin back to the lungs and out of the body.

CLICK HERE TO VIEW ANIMATED DESCRIPTION OF THIS PROCESS!

As we learned above, acid lowers the pH.

• So, a high PaCO2 means a lower pH.
  • Notice I said "lower" not "low."
• CO2 will "move" the pH, but other factors may still cause an alkalosis.

Instant Feedback:

1. Respiratory mechanism (depth and rate of breathing) controls CO2
2. CO2 in solution is an acid.
3. Higher PaCO2 causes acidosis (lower pH), or neutralizes alkalosis.
4. Lower PaCO2 causes alkalosis (raises pH.), or neutralizes acidosis.

https://openoregon.pressbooks.pub/mhccbiology112/chapter/an-overview-of-cellular-respiration/

References

Bartee, Dr. L., & Brook, J. (n.d.). An overview of cellular respiration. MHCC Biology 112 Biology for Health Professions. https://openoregon.pressbooks.pub/mhccbiology112/chapter/an-overview-of-cellular-respiration/

Boundless. (n.d.). Gas exchange. Boundless Anatomy and Physiology. https://university.pressbooks.pub/test456/chapter/gas-exchange/

https://openoregon.pressbooks.pub/mhccbiology112/chapter/an-overview-of-cellular-respiration/

© RnCeus.com