13 Respiratory Physiology and Gas Exchange

A comprehensive set of 115 flashcards covering respiratory physiology, gas laws, lung volumes, gas exchange, and neural/chemical regulation of breathing based on the BMS 595 lecture.

What are the three main processes of respiratory physiology explored in the lecture?

Pulmonary ventilation, gas exchange (physical principles), and the regulation of respiration.

What is the primary purpose of the respiratory system?

To perform gas exchange.

How is gas exchange defined in the context of the respiratory membrane?

The movement of gases across membranes where $O_2$ enters the bloodstream and $CO_2$ exits.

Which specific structures are included in the respiratory zone?

Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

What occurs to the thoracic cavity volume during inspiration?

The thoracic cavity volume increases.

Which muscles contract during inspiration to elevate the ribs and flare the sternum?

The external intercostals.

What happens to the diaphragm during contraction in the inspiratory phase?

It moves inferiorly (descends).

During inspiration, intrapulmonary pressure drops to what specific value before air flows in?

$$-1 mm Hg$$

Air flows into the lungs during inspiration until intrapulmonary pressure reaches what level?

$0 mm Hg$ (equal to atmospheric pressure).

What causes the passive recoil of the lungs during expiration?

The relaxation of inspiratory muscles and the elasticity of the lungs.

What is the intrapulmonary pressure value during expiration as the thoracic volume decreases?

$$+1 mm Hg$$

Where is the respiratory center located in the central nervous system?

The brain stem, specifically in the medulla oblongata and the pons.

What is the primary function of the Dorsal Respiratory Group (DRG)?

It is mainly responsible for inspiration and the basic respiratory rhythm.

Where is the Ventral Respiratory Group (VRG) located, and what is its role?

Located in the ventrolateral portion of the medulla, it causes inspiration or expiration depending on the nerves stimulated.

What is the primary role of the pneumotaxic center?

It controls the rate and pattern (depth) of breathing by limiting inspiration.

Which part of the respiratory center receives information from chemoreceptors and baroreceptors?

The Dorsal Respiratory Group (DRG).

What type of nervous signal is transmitted to the primary inspiratory muscles?

A ramp signal.

How long does the inspiratory ramp signal typically increase for in a normal cycle?

About $2$ seconds.

How long does the inspiratory ramp signal stop for, allowing for expiration?

$3$ seconds.

What is the secondary effect of the pneumotaxic center limiting the duration of inspiration?

It increases the respiratory rate.

What are the breathing rates associated with strong vs. weak pneumotaxic signals?

A strong signal can increase the rate to $30$ to $40$ breaths/min, while a weak signal can reduce it to $3$ to $5$ breaths/min.

Which two chemical factors directly stimulate the respiratory center?

$H^+$ ions and $CO_2$.

How does oxygen ($O_2$) influence the respiratory center if it does not have a direct effect?

It acts through peripheral chemoreceptors located in the carotid and aortic bodies.

What is the definition of pressure in the context of gas laws?

The force exerted by gas molecules on the surfaces with which they are in contact.

Define the term 'partial pressure'.

The pressure caused by a single gas alone within a mixture of gases.

What is the total atmospheric pressure at sea level used in respiratory physiology?

$760 mm Hg$.

What is the approximate percentage and partial pressure of Nitrogen ($N_2$) in dry atmospheric air?

$78.6\%$ and approximately $597.4 mm Hg$ (often rounded to $600 mm Hg$).

What is the approximate percentage and partial pressure of Oxygen ($O_2$) in dry atmospheric air?

$20.9\%$ and approximately $158.8 mm Hg$ (often rounded to $160 mm Hg$).

How is the total pressure of a gas mixture calculated according to Dalton's Law?

It is the sum of the individual partial pressures of each gas present ($P_{total} = P_1 + P_2 + P_3...$).

The rate of gas diffusion in a specific direction is a direct effect of what factor?

The concentration gradient (pressure difference).

What are the layers that make up the respiratory membrane?

Surfactant/fluid layer, alveolar epithelium, epithelial basement membrane, interstitial space, capillary basement membrane, and capillary endothelium.

What happens to dry atmospheric air as it enters the respiratory passage?

It is humidified before reaching the alveoli.

What is the average surface area of the respiratory membrane in a healthy adult?

$70 m^2$ (range of $50$ to $100 m^2$).

How does emphysema affect the respiratory membrane's surface area?

It decreases the surface area (up to $5$-fold) due to the dissolution of alveolar walls.

What is the relationship between the thickness of the respiratory membrane and the rate of diffusion?

Increased thickness (e.g., from edema) decreases the rate of diffusion.

According to Henry's Law, what two factors determine the pressure of a gas in a solution?

Concentration and the solubility coefficient.

How much more soluble is Carbon dioxide ($CO_2$) compared to Oxygen ($O_2$)?

It is $20$ times more soluble.

Define alveolar gas exchange.

The exchange of respiratory gases between the blood in pulmonary capillaries and the alveoli.

Define systemic gas exchange.

The exchange of gases between blood in systemic capillaries and systemic cells.

List three reasons why alveolar air composition differs from atmospheric air.

Partial replacement per breath, constant $O_2$ absorption/$CO_2$ diffusion, and humidification of dry air.

What is the partial pressure of Oxygen ($PO_2$) in the alveoli?

$104 mm Hg$.

What is the $PO_2$ of blood entering the pulmonary capillaries?

$40 mm Hg$.

What is the partial pressure of Carbon dioxide ($PCO_2$) in the alveoli?

$40 mm Hg$.

What is the $PCO_2$ of blood entering the pulmonary capillaries?

$45 mm Hg$.

During systemic gas exchange, what is the $PO_2$ in systemic cells vs. systemic capillaries?

$40 mm Hg$ in cells and $95 mm Hg$ in capillaries.

How is pulmonary ventilation calculated?

Tidal volume $\times$ Respiration rate.

What are the typical values for tidal volume and respiration rate used to calculate a typical pulmonary ventilation of $6 L/min$?

$500 mL$ and $12$ breaths/min.

Define 'anatomic dead space' and its typical volume.

The space in the conducting zone where no gas exchange occurs, typically $150 mL$.

How is alveolar ventilation calculated?

$(\text{Tidal volume} - \text{anatomic dead space}) \times \text{Respiration rate}$.

What is 'physiologic dead space'?

The sum of anatomic dead space and any volume from non-functional/damaged alveoli.

What does a spirometer measure?

Respiratory volumes.

Define Tidal Volume (TV).

The amount of air inhaled or exhaled per breath during quiet breathing ($500 mL$).

Define Inspiratory Reserve Volume (IRV).

The amount of air that can be forcibly inhaled beyond the tidal volume ($3100 mL$).

Define Expiratory Reserve Volume (ERV).

The amount of air that can be forcibly exhaled beyond the tidal volume ($1200 mL$).

What is Residual Volume (RV)?

The amount of air left in the lungs after the most forceful expiration ($1200 mL$).

How is Inspiratory Capacity (IC) calculated?

$TV + IRV$ ($3600 mL$).

How is Functional Residual Capacity (FRC) calculated?

$ERV + RV$ ($2400 mL$).

How is Vital Capacity (VC) calculated?

$TV + IRV + ERV$ ($4800 mL$).

How is Total Lung Capacity (TLC) calculated?

The sum of all volumes ($TV + IRV + ERV + RV$), approximately $6000 mL$.

What is Forced Expiratory Volume (FEV)?

The percentage of vital capacity that can be expelled in a set period of time (e.g., $FEV_1$ in one second).

What is the normal range for $FEV_1$ in a healthy person?

$75$ to $85\%$ of vital capacity.

What is Maximum Voluntary Ventilation (MVV)?

The greatest amount of air that can be taken in and expelled in $1$ minute, potentially as high as $30 L/min$.Header: Ventilation-Perfusion Ratio

What does the 'V' and 'Q' stand for in the V/Q ratio?

'V' stands for Alveolar ventilation and 'Q' stands for Blood flow (perfusion).

What is the ideal V/Q ratio for maximally efficient function?

$1$.

In a standing position, how does the V/Q ratio differ between the apex and the base of the lung?

It is roughly $3.3$ at the apex and $0.63$ at the base.

What is the average overall V/Q value in a human lung?

Approximately $0.8$.

What is the result of a V/Q ratio of $0$?

No ventilation exists (shunt), resulting in gas pressures equal to venous blood ($PO_2 = 40, PCO_2 = 46$).

What is the result of a V/Q ratio of infinity (\infty)?

No perfusion exists (dead space), resulting in gas pressures equal to inspired air ($PO_2 = 159, PCO_2 = 0$).

What is a 'physiologic shunt' in terms of blood flow?

The amount of blood per minute (approx $2\%$ of cardiac output) that is not oxygenated because it bypasses alveoli or passes through areas with abnormal V/Q ratios.

Why is the slow replacement of alveolar air important?

It prevents sudden changes in blood gas concentrations, making respiratory control more stable.

Approximately how much oxygen is transported bound to hemoglobin in the blood?

$98\%$.

Define oxyhemoglobin and deoxyhemoglobin.

Oxyhemoglobin ($HbO_2$) has oxygen bound; deoxyhemoglobin ($HHb$) is without bound oxygen.

In what three ways is Carbon Dioxide ($CO_2$) transported in the blood?

Dissolved in plasma ($7\%$), as carbaminohemoglobin ($23\%$), and as bicarbonate in plasma ($70\%$).

What enzyme facilitates the conversion of $CO_2$ and water to bicarbonate and hydrogen ions in erythrocytes?

Carbonic anhydrase (implied via the transport mechanism).

What is the 'chloride shift'?

The exchange of a newly synthesized bicarbonate ion out of the RBC for a chloride ion ($Cl^-$) to maintain electrical balance.

How many oxygen molecules can a single hemoglobin molecule bind?

Up to $4$ oxygen molecules (one per iron atom).

What is the 'cooperative binding effect' in hemoglobin?

Each oxygen molecule that binds increases the affinity of hemoglobin for the next oxygen molecule.

Describe the shape of the oxygen-hemoglobin saturation curve.

It is S-shaped (sigmoidal) and nonlinear.

What effect does increased temperature have on the oxygen dissociation curve?

It shifts the curve to the right, reducing hemoglobin's affinity for oxygen.

What effect does increased $PCO_2$ or increased acidity (lower pH) have on the oxygen dissociation curve?

It shifts the curve to the right (Bohr effect).

What is 2,3-BPG and how does it affect hemoglobin?

2,3-Bisphosphoglycerate; it shifts the curve to the right by promoting the low-oxygen-affinity state of hemoglobin.

What is the typical oxygen saturation of arterial blood when $PO_2$ is approximately $95 mm Hg$?

$97\%$.

What are the two hereditary diseases mentioned that decrease the blood's oxygen-carrying capacity?

Thalassemia and Sickle cell anemia.

Compare the partial pressure of Oxygen ($PO_2$) in venous blood vs. inspired air.

Venous blood is $40 mm Hg$; inspired air is $159 mm Hg$.

What happens to bicarbonate when blood reaches the lungs?

It is transported back into the RBC in exchange for $Cl^-$, binds with $H^+$, and is converted back into $CO_2$ and water to be exhaled.

Where is the pneumotaxic center specifically located?

Dorsally in the superior portion of the pons.

Which part of the medulla is primarily responsible for causing expiration?

The Ventral Respiratory Group (VRG).

What is the target intrapulmonary pressure after air flows out of the lungs during expiration?

$0 mm Hg$ (equal to atmospheric pressure).

If Alveolar ventilation ($V_a$) is normal and perfusion ($Q$) is normal, the V/Q ratio is said to be…?

Normal.

In emphysema, why is ventilation considered 'wasted'?

Because there is more $O_2$ available in certain alveoli than can be transported due to low perfusion ($Q$).

What percent of the initial $500 mL$ tidal volume actually reaches the alveoli for exchange in a typical breath?

Approximately $70\%$ ($350 mL$).

What constitutes the 'respiratory membrane'?

The layers through which gases must diffuse between the alveolus and the blood.

What determines the duration of expiration in a normal breathing cycle?

The duration of inspiration.

Increased levels of ventilation are achieved by stimulating which center to increase signal frequency?

The respiratory center via $H^+$ and $CO_2$ levels.

According to the solubility table, what is the solubility coefficient of Oxygen ($O_2$) in water?

$0.024$.

According to the solubility table, what is the solubility coefficient of Carbon dioxide ($CO_2$) in water?

$0.57$.

What are the symbols used to designate the partial pressures of individual gases?

$PO_2$, $PCO_2$, and $PN_2$.

What is the partial pressure of Water ($H_2O$) in dry atmospheric air at sea level?

$3.0 mm Hg$.

What is the partial pressure of Carbon dioxide ($CO_2$) in dry atmospheric air at sea level?

$0.3 mm Hg$.

Which gas has the lowest solubility coefficient among Oxygen, Nitrogen, Carbon Dioxide, and Helium?

Helium ($0.008$).