Respiratory System - Review Questions

In what two forms is oxygen carried in the blood?

(1) Dissolved in plasma and erythrocyte cytosol (2) reversibly bound to hemoglobin (Hb) molecules within the erythrocytes.

List the physical factors that alter airway resistance.

(1) Transpulmonary pressure exerts a distending force on the airways; a major factor that keeps smaller airways from collapsing. (2) The elastic connective tissue fibers exert a lateral traction on the airways during inspiration, helping them to expand even more.

Describe four functions of the conducting portion of the airways.

(1) provides a low-resistance pathway for airflow (changes in the airway diameter) (2) defends against microbes, toxic chemicals, and other foreign matter (3) warms and moistens the air (4) phonates.

List the functions of the respiratory system.

(1) transfers oxygen from the atmosphere to the blood; (2) eliminates carbon dioxide from the blood to the atmosphere; (3) helps to regulate the blood's H+ concentration (pH); (4) forms speech sounds (phonation); (5) defends against inhaled microbes; (6) influences the arterial concentrations of chemical messengers by removing some from the pulmonary capillary blood and producing and adding others to this blood; and (7) traps and dissolves blood clots.

List four kinds of hypoxemia (low oxygen in blood).

1) Anemic - too few RBCs/abnormal hemoglobin 2) Schemic - blood circulation is impaired 3) Histotoxic - cells can't use O2 4) Hypoxemic - reduced arterial O2

Which two factors determine lung compliance? Which is more important?

1) Stretchability of the lung tissues 2) Surface tension at the air-water interfaces within the alveoli; more important.

What are the 4 pressures in the lungs?

1. Pip 2. Palv 3. Ptp (Palv-Pip) 4. Pcw (Pip-Patm)

List the 4 respiratory volumes and what they are.

1. Tidal Volume (TV) - amount of air inhaled/exhaled in one breath. 2. Inspiratory Reserve Volume (IRV) - amount of air we can inhale after the normal amount. 3. Expiratory Reserve Volume (ERV) - amount of air we can exhale after normal amount. 4. Residual Volume (RV) - amount of air remaining in lungs after expiration.

Reactions carbon dioxide undergoes entering the blood in the tissue capillaries and leaving the blood in the alveoli. What fractions are contributed by dissolved carbon dioxide, HCO3-, and carbaminohemoglobin?

10% of carbon dioxide is dissolved in plasma. 60% is carried as HCO3-. 30% is carried as carbamino hemoglobin.

State the alveolar partial pressures for oxygen and carbon dioxide in a healthy person at rest.

Alveolar PO2 is normally 105 mmHg at rest. Alveolar PCO2 is normally 40 mmHg.

State the formula for calculating alveolar ventilation.

Alveolar ventilation (ml/min) = (Tidal volume - Dead space volume) × Respiratory rate

Describe the effects of increased P CO2, H+ concentration, and temperature on the oxygen-hemoglobin dissociation curve. How are these effects adaptive for oxygen unloading in the tissues?

An increase in any of the above at any given PO2 would cause the curve to shift toward the right, meaning that hemoglobin would have less affinity for oxygen under these conditions. The rightward shift affords a mechanism whereby active tissues have increased oxygen delivery to them because the right shift of the curve in the tissues would unload more oxygen.

Between breaths at the end of an unforced expiration, in what directions do the lungs and chest wall tend to move?

At the end of an unforced expiration, the lungs tend to recoil inward, and the chest wall tends to move inwards.

Describe the sequence of events that cause air to move out of the lungs during expiration.

During expiration, the diaphragm and inspiratory intercostals stop contracting. The chest wall recoils inward, and Pip moves back toward preinspiration value. This causes the transpulmonary pressure to be reduced back toward preinspiration value, and the lungs to recoil back toward preinspiration size. Air in the alveoli becomes compressed; air flows out of the lungs. (Palv>Patm)

Describe the sequence of events that cause air to move into the lungs during inspiration.

During inspiration, the diaphragm and inspiratory intercostal muscles contract, causing the thorax to expand. The thoracic wall moves farther away from the lung surface, causing intrapleural fluid pressure to become more more negative relative to atmosphere. This increases the transpulmonary pressure and causes the lungs to expand. By Boyle's law, an increase in lung volume with no change in the number of gas molecules causes a decrease in pressure. Therefore, air flows into the alveoli. (Palv<Patm).

What is the mechanism of gas exchange between alveoli and pulmonary capillaries?

Gas exchange occurs by diffusion of oxygen from the alveoli to the capillary blood, and diffusion of carbon dioxide from the capillary blood to the alveoli.

In a healthy person at rest, what are the gas pressures at the end of the pulmonary capillaries, relative to those in the alveoli?

In a normal person at rest, the gas pressures at the end of the pulmonary capillaries are nearly identical to those in the alveoli (i.e., PO2 = 100 mmHg; PCO2 = 40 mmHg).

Describe the effects of increased DPG on the oxygen-hemoglobin dissociation curve. What is the adaptive importance of the effects of DPG on the curve?

Increased DPG also makes the dissociation curve shift to the right. This increase is triggered by a variety of conditions associated with inadequate oxygen supply to the tissues, such as anemia and exposure to high altitude, and the response in the shift helps to maintain oxygen delivery.

Describe the pathways by which increased arterial P CO2 stimulates ventilation. What pathway is more important?

Increased arterial PCO2 stimulates ventilation in 2 ways... 1) Arterial H+ concentration is increased Stimulating the peripheral chemoreceptors to increase their rate of firing. Triggering reflexes that increase the rate of contraction of the respiratory muscles and thus ventilation. Allowing for more carbon dioxide to be eliminated by the lungs, thereby returning arterial PCO2, and thus H+ concentration, toward normal. 2) Involves central chemoreceptors. Increase in brain extracellular-fluid PCO2. Carbonic anhydrase in brain extracellular fluid catalyzes the conversion there of carbon dioxide and water to carbonic acid, which dissociates to HCO3- and H+. Increased H+ concentration stimulates the central chemoreceptors. These receptors trigger the same reflexes described above, resulting in the return of PCO2 and H+ concentration back toward normal. The central chemoreceptors are more important (account for 70% of increased ventilation).

What distinguishes lung capacities, as a group, from lung volumes?

Lung capacities are the sum of two or more lung volumes.

What generates the diffusion gradients for oxygen and carbon dioxide in the tissues?

Metabolic reactions occurring within cells are constantly consuming oxygen and producing carbon dioxide. Therefore, intracellular PO2 is lower and PCO2 higher than in blood. As a result, there is a net diffusion of oxygen from the blood into cells and a net diffusion of carbon dioxide from cells into blood.

State the formula relating minute ventilation, tidal volume, and respiratory rate. Give representative values for each at rest.

Minute ventilation (ml/min) = Tidal volume (ml/breath) × Respiratory rate (breaths/min) At rest, tidal volume is ~500 ml/breath, respiratory rate is 12 breaths/min, and so minute ventilation is 6000 ml/min.

Is respiratory control more sensitive to small changes in arterial P O2 or in arterial P CO2?

Respiratory control is much more sensitive to changes in arterial PCO2.

How does surfactant increase lung compliance? How does surfactant stabilize alveoli by preventing small alveoli from emptying into large alveoli?

Surfactant is a detergent-like substance produced by type II alveolar cells that reduces the cohesive forces between water molecules on the alveolar surface. Therefore, surfactant lowers the surface tension in the fluid lining the alveoli and thus increases lung compliance. Because the molecules of surfactant are closer in smaller spaces, the surface tension is lower in smaller alveoli and, thus, surfactant stabilizes them preventing them from emptying into larger alveoli.

How is airway resistance influenced by airway radii?

The factors that determine airway resistance are the same that determine vascular resistance in the circulatory system: tube length, tube radius, and interactions between moving molecules. The most important factor by far is tube radius: Airway resistance is inversely proportional to the fourth power of the airway radii.

Why does thickening of alveolar membranes impair oxygen movement but have little effect on carbon dioxide exchange?

Thickening increases the distance across which the gases must diffuse. Carbon dioxide diffuses much more readily than oxygen, and so it is not affected as much by such thickening.

What changes stimulate the peripheral chemoreceptors? The central chemoreceptors?

The peripheral chemoreceptors are stimulated mainly by decreased PO2 and increased H+ concentration in the arterial blood. The central chemoreceptors are stimulated by increased PCO2 in the brain extracellular fluid.

Describe the pathway by which a change in arterial H+ concentration independent of altered carbon dioxide influences ventilation. What is the adaptive value of this reflex?

The peripheral chemoreceptors respond to increased (or decreased) arterial H+ concentration, whatever its cause. If it's not respiratory acidosis or respiratory alkalosis, then it is termed metabolic acidosis or alkalosis. For example, during very strenuous exercise, blood concentration of lactic acid can increase (metabolic acidosis), and this increase stimulates the peripheral chemoreceptors to trigger the reflex increase in ventilation, which has the effect of bringing blood H+ concentration back toward normal. Thus, the lungs can help to correct a problem that they did not bring about.

Describe the area of the brain in which automatic control of rhythmical respirations resides?

The respiratory center is located in the medulla oblongata. Neurons in the dorsal and ventral respiratory groups are responsible of controlling respiratory muscles.

Which respiration steps occur by diffusion and which by bulk flow?

Ventilation and the transport of the respiratory gases occur by bulk flow Exchange of O2 and CO2 between alveolar air and blood in the lung capillaries, and the exchange of those gases in tissue capillaries and cells occur by diffusion.

List the 4 respiratory capacities and what they are.

Vital Capacity (VC) = (ERV + IRV + TV) - amount of air exhaled after maximum expiration. Inspiratory Capacity (IC) = (TV + IRV) - max amount of air that can be inhaled after a normal exhale. Functional Residual Capacity (FRC) = (RV +ERV) - amount of air in lungs after a normal expiration. Total Lung Capacity (TLC) = (RV + VC) - max amount of air lungs can hold.