SL 7: Pulmonary dynamics

Where does gas exchange take place in the respiratory system?

In the respiratory system, Alveoli are the exclusive place where gas exchange occurs. Respiratory bronchioles are the first location that air passes through that is able to exchange gases, this is because there are occasional alveoli budding directly off the walls

Conduction zone

• Nose

• Pharynx

• Larynx

• Trachea

• Bronchi

• Bronchioles (up to terminal bronchioles)

Respiratory zone

• Respiratory bronchioles

• Alveolar ducts

• Alveolar sacs

CO2 is exchanged between the capillaries and alveoli. Is this internal, external, or cellular respiration

Ventilation - Air moving in and out of the lungs

External respiration - gas exchange between alveoli and pulmonary capillaries

Internal respiration - gas exchange between blood capillaries to tissues

Cellular respiration - Gas exchange within the cell

Describe how the pressure differences between the atmospheric and chest cavity air dictate air movement into and out of the lungs. Reference Boyle’s law

As with all pressures the movement goes from high pressure to low pressure. Boyle’s law states that the pressure of gas is inversely proportional to its volume. At rest the pressure in the lungs is the same as atmospheric pressure. When you are inhaling the lungs are expanded by respiratory muscles, increasing volume in the lungs and therefore decreasing pressure, this drives air into the lungs as the pressure is now less in the lungs compared to the atmosphere. During passive exhale, the respiratory muscles relax, decreasing volume in the lungs, increasing pressure and causing the movement of air out of the lungs.

Describe the differences between FVC and FEV1?

FVC (Forced vital capacity) - The capacity of the lungs during max inhalation to max exhalation, shows the “boundaries” of what your lungs can hold during a situation like strenuous exercise

FEV1 (Forced expiratory volume in 1 second) - This shows how much air you can expire from your lungs in a 1 second span. This is compared to FVC to show how much of your lung capacity (percentage) you can exhale in 1 second.

An individual has a severely reduced FEV1:FVC. Is this predictive of exercise performance?

Yes I do believe this will be indicative of exercise performance. The limiter of exercise is rarely hypoxia but rather hypercapnia, FEV1 measures how much air you are able to exhale in 1 breath. If you have a reduced FEV1:FVC it means your capacity to expel CO2 is hindered, this makes your tissues more prone to acidosis as they aren’t able to get rid of CO2 as fast as they are producing it

Is residual volume or functional residual capacity larger in volume?

Functional residual capacity (FRC) is always going to be larger than residual volume (RV) as it adds Expiratory reserve volume (ERV) and RV together

FRV: ERV + RV

ERV = expiratory volume - Vt - RV

RV = air left in lungs (always)

Barometric pressure is 700mmHG. The air mixture contains 20% CO2 and 55% N. What are PCO2 and PN?

PCO2 = 700 × 0.20 = 140mmHg

PN = 700 × 0.55 = 385mmHg

What is the primary role of O2 and CO2 dissolved in the liquid portion of the blood?

When CO2 and O2 are bound to hemoglobin they don’t give off a partial pressure, this allows gas exchange to occur until hemoglobin are saturated. After this point gas exchange continues to enter the blood until an equilibrium is met. This dissolved O2 and CO2 in blood plasma set the concentration gradient for gas exchange

Describe how pressure gradients dictate gas exchange between tissues

Pressure gradients like to move from high pressure to low pressure. In the tissues, you are using O2 and creating CO2, this creates a high PCO2 and a low PO2. In the capillaries the PO2 is much higher and the PCO2 is relatively lower, these partial pressure cause a drive of moving oxygen into the tissues (high PO2 in capillaries, low in tissues) and moving CO2 out of the tissue and into the blood (high PCO2 in tissues, low PCO2 in capillaries)

What is the primary method of CO2 transport in the blood? how does this differ from O2?

About 70% of CO2 transport in the blood is as bicarbonate

When CO2 enters the RBC, a chloride ions leaves (to maintain pH). Carbonic Anhydrase forces it to react with water

CO2 + H20 = H2CO3 → HCO3 + H+

bicarbonate is pumped out into the plasma to act as a buffer and chloride enters the RBC (to maintain ion balance). In the lungs, oxygen has a much higher affinity for hemoglobin than H+ does. Oxygen binds to hemoglobin and it changes shape, this kicks H+ off.

At the lungs a chloride ion leaves (allowing bicarbonate to re-enter). H+ finds a bicarbonate (HCO3) molecule that just re-entered the cell, then join to become Carbonic acid (H2CO3). Carbonic anhydrase reverses the reaction, releasing CO2 and H2O to be expired via external respiration

During the initial phase of exercise, what is the key contributor to increases in V_E?

Since CO2 and H+ haven’t accumulated in the muscle yet the drive to get rid of them isn’t there. The main driver during this initial phase is Neural and proprioceptive which is due to the anticipation of the event, because of this you see a rise in VE because the brain is anticipating oxygen demand to increase (because of exercise), the proprioceptive stimulus is due to joint movement, and mechanoreceptors detecting tension in the muscle

During exercise, is a reduction in PO2 a common stimulus for increased V_E? Explain why or why not?

Your body is incredibly efficient at loading oxygen. Even during intense exercise, your lungs are so good at their job that your arterial PO2 stays almost exactly at 100mmHg

• Because the pressure stays stable in the arteries, the peripheral chemoreceptors never sense a “drop” in oxygen

• Since they never sense a drop, they don’t send a signal to the brain to increase breathing based on O2 levels

The real drivers: CO2 and H+.

Your brain is much more sensitive to waste than it is to fuel.

Are pulmonary adaptations to exercise key determinants of aerobic performance? Explain why or why not

In kinesiology, the pulmonary system is described as being “overbuilt”. It is so efficient that it is rarely the “bottleneck” or the limiting factor for how much oxygen you can use.

The main bottleneck to performance is almost always going to be the cardiovascular system (delivery system)

What is Boyle’s law?

Boyle’s law states that as you decrease the volume of air in a container, the gas molecules are squished together, and they hit the walls more often, which increases pressure. If you increase the volume, the molecules have more room, and pressure changes