Respiration: Videos & Practice Problems

Respiration involves the exchange of oxygen (O₂) and carbon dioxide (CO₂) between the blood and tissues, relying on pressure gradients. External respiration occurs in the alveoli, where O₂ moves into the blood and CO₂ exits. Internal respiration involves the transfer of O₂ from blood to tissues and CO₂ from tissues to blood. The total amount of O₂ exchanged equals the amount of CO₂ exchanged, reflecting cellular respiration's balance. Key principles include Dalton's law of partial pressure and Henry's law regarding gas solubility.

Respiration

Respiration is a vital process involving the exchange of oxygen and carbon dioxide between the blood and the environment. This exchange relies on pressure gradients, which dictate the movement of these gases from areas of high pressure to areas of low pressure. Understanding Dalton's law of partial pressure is crucial, as it explains how individual gases behave in this context.

Respiration can be divided into two main types: external respiration and internal respiration. External respiration occurs in the alveoli, where gases are exchanged between the air and the blood. For oxygen, there is a net movement from the air into the blood, indicating that the partial pressure of oxygen in the air is greater than that in the blood. Conversely, carbon dioxide moves from the blood into the air, meaning the partial pressure of carbon dioxide in the air is less than that in the blood.

Internal respiration takes place in the tissues after the blood has picked up oxygen from the alveoli. Here, oxygen moves from the blood into the tissues, where it is utilized for cellular respiration. This implies that the partial pressure of oxygen in the blood is greater than in the tissues. On the other hand, carbon dioxide, produced as a waste product of cellular respiration, moves from the tissues into the blood, indicating that the partial pressure of carbon dioxide in the tissues is greater than in the blood.

It is important to note that the concept of partial pressure applies not only to gases in the air but also to gases dissolved in liquids, such as blood or cytoplasm. This relationship is governed by Henry's law, which allows for the conversion of gas partial pressures into concentrations of dissolved gases. Thus, throughout the study of respiration, the unit of partial pressure will be consistently used to describe both gaseous and dissolved states.

When determining the directions that molecules will move in external and internal respiration:

• A. Molecules will always move down the pressure gradient according to their individual partial pressures.
• B. Molecules will move up the pressure gradient for internal respiration and down the pressure gradient for external respiration.
• C. CO₂ will always move up the pressure gradient, while O₂ will always move down the pressure gradient.
• D. Molecules will always move from the area of greatest total pressure to the area of lowest total pressure.

Answer: (A)

Internal and External Respiration

Respiration involves the continuous movement of gases, specifically oxygen and carbon dioxide, down their pressure gradients between the air, blood, and tissues. Understanding the differences in gas composition between atmospheric air and alveolar air is crucial for grasping how these gradients function. Atmospheric air contains a variety of gases, but when it reaches the alveoli, the composition changes significantly due to the presence of water vapor, which is more abundant in the lungs. The total pressure in both the alveoli and atmospheric air remains at 760 millimeters of mercury (mmHg), but the partial pressures of oxygen and carbon dioxide differ markedly.

In the alveoli, the partial pressure of oxygen is approximately 104 mmHg, while carbon dioxide has a partial pressure of about 40 mmHg. This difference is essential for gas exchange. During ventilation, the tidal volume (the amount of air inhaled or exhaled in a single breath) is around 500 milliliters, but the residual volume (the air remaining in the lungs after exhalation) is about 2 liters. This means that carbon dioxide accumulates in the alveoli, leading to a much higher partial pressure compared to atmospheric air.

The process of gas exchange can be divided into two main types: external respiration and internal respiration. External respiration occurs in the alveoli, where oxygen moves from the alveoli into the blood due to the higher partial pressure of oxygen in the alveoli compared to the blood plasma, which is around 40 mmHg. Conversely, carbon dioxide moves from the blood (with a partial pressure of approximately 46 mmHg) into the alveoli, where the pressure is lower. This exchange continues until the partial pressures equalize.

Once the blood is oxygenated, it travels to the arterial system, where the partial pressure of oxygen drops slightly to about 100 mmHg due to the binding of oxygen to hemoglobin. As the blood reaches the tissues, the gradients shift again. The partial pressure of oxygen in the blood is higher than in the tissues, allowing oxygen to diffuse into the tissues. Meanwhile, carbon dioxide produced by cellular metabolism accumulates in the tissues, creating a higher partial pressure than in the blood, prompting carbon dioxide to diffuse back into the blood.

It is important to note that the partial pressures of gases can vary depending on the metabolic activity of the tissues. For instance, during intense exercise, the partial pressure of oxygen in active muscle tissues may drop below 40 mmHg, while the partial pressure of carbon dioxide may rise above 46 mmHg due to increased metabolic activity.

This cycle of gas exchange continues as blood returns to the venous system, where it carries carbon dioxide back to the lungs for exhalation and picks up fresh oxygen, maintaining the vital process of respiration.

Respiration Example 1

Understanding the partial pressures of oxygen (O₂) and carbon dioxide (CO₂) in different areas of the body is crucial for grasping respiratory physiology. The partial pressure of a gas is the pressure that gas would exert if it occupied the entire volume alone. This concept is essential in determining gas exchange efficiency in the lungs and tissues.

Starting with the partial pressure of oxygen, the highest value is found in the external air, where the concentration of O₂ is greatest. Following this, the air in the alveoli has a slightly lower partial pressure of oxygen due to the mixing with carbon dioxide and the uptake of oxygen by the blood. The arterial blood then equilibrates with the alveolar air, but as oxygen is absorbed by hemoglobin, its partial pressure decreases slightly, making it lower than that in the alveoli. Next, the partial pressure of oxygen in the body tissues is lower than in the arterial blood, as oxygen is utilized for cellular respiration. Finally, the venous blood, which has given up some of its oxygen to the tissues, has the lowest partial pressure of oxygen, equal to that in the tissues.

In summary, the order from highest to lowest partial pressure of oxygen is: external air > air in the alveoli > arterial blood > body tissues = venous blood.

When considering the partial pressure of carbon dioxide, the scenario is reversed. The highest partial pressure of CO₂ is found in the body tissues, where it is produced during cellular respiration. As blood flows through the capillaries in the tissues, it equilibrates with the high CO₂ levels, resulting in venous blood having a similar partial pressure. The blood then travels to the alveoli, where the partial pressure of CO₂ is lower due to its exhalation. The arterial blood, which has just passed through the alveoli, has a partial pressure of CO₂ that is equal to that in the alveoli. Finally, the external air has the lowest partial pressure of carbon dioxide, as it contains minimal CO₂ compared to the other areas.

Thus, the order from highest to lowest partial pressure of carbon dioxide is: body tissues = venous blood > air in the alveoli > arterial blood > external air.

This understanding of gas exchange dynamics is fundamental for studying respiratory function and the physiological processes that maintain homeostasis in the body.

What is the approximate partial pressure of oxygen in the blood as it enters and leaves the capillaries of the alveoli?

• A. Enters: 40 mm Hg, Leaves: 46 mm Hg.
• B. Enters: 46 mm Hg, Leaves: 40 mm Hg.
• C. Enters: 100 mm Hg, Leaves: 46 mm Hg.
• D. Enters: 40 mm Hg, Leaves: 100 mm Hg.

Answer: (D)

What is one difference between air in the alveoli compared to air in the atmosphere?

• A. The total pressure of air in the alveoli will be greater than the total pressure of air in the atmosphere.
• B. The partial pressure due to water vapor is much greater in the alveoli than in the atmosphere.
• C. The partial pressure due to carbon dioxide is greater in the atmosphere than in the alveoli.
• D. The partial pressure of oxygen is equal to the partial pressure of carbon dioxide in the alveoli, but not in the atmosphere.

Answer: (B)

External Respiration

External respiration involves the exchange of gases between the blood and the air in the alveoli, rather than just the external atmosphere. This process is crucial for maintaining the proper partial pressures of oxygen (O₂) and carbon dioxide (CO₂) in the blood. During external respiration, oxygen moves from the alveolar air into the blood, while carbon dioxide moves from the blood into the alveoli. The movement of these gases is driven by their respective partial pressures, which dictate how they dissolve in the blood plasma.

Hemoglobin, a protein found in red blood cells, plays a vital role in transporting oxygen. It binds to oxygen molecules, allowing the blood to carry a significantly larger amount of oxygen than could be dissolved in plasma alone. The relationship between the amount of oxygen and carbon dioxide exchanged is important; for every molecule of oxygen consumed during cellular respiration, an equivalent amount of carbon dioxide is produced. This balance ensures that the total exchange of gases remains equal during both external and internal respiration.

To visualize this process, consider an analogy where the alveoli are represented as a "lung lounge" and the capillaries as a street. The hemoglobin acts like buses on this street, transporting gases. For instance, if the partial pressure of CO₂ in the blood is higher (46 mmHg) than in the alveoli (40 mmHg), CO₂ will diffuse into the alveoli until equilibrium is reached. Conversely, oxygen has a higher partial pressure in the alveoli (104 mmHg) compared to the blood (40 mmHg), driving oxygen into the blood. This process continues until the pressures equalize, with blood leaving the alveoli saturated with oxygen at approximately 100 mmHg.

Despite the differences in partial pressure gradients—where the CO₂ gradient is only 6 mmHg while the O₂ gradient is 60 mmHg—both gases are exchanged in equal amounts. This is explained by Henry's law, which states that the solubility of a gas in a liquid is proportional to its partial pressure. CO₂ is about 20 times more soluble than O₂, allowing it to diffuse more easily into the blood without requiring as steep a gradient. Consequently, while oxygen needs hemoglobin to facilitate its transport due to its lower solubility, carbon dioxide can travel more freely in the blood plasma.

In summary, external respiration is a complex but efficient process that ensures the body receives the necessary oxygen while removing carbon dioxide, facilitated by the unique properties of hemoglobin and the principles of gas exchange.

Respiration Example 2

Hyperventilation is characterized by an increased rate and/or tidal volume of ventilation, leading to alveolar air that closely resembles atmospheric air. This phenomenon highlights the significant differences in gas composition between alveolar air and the surrounding atmosphere. When hyperventilating, the relative change in the partial pressure of carbon dioxide (CO₂) is greater than that of oxygen (O₂). In the atmosphere, the partial pressure of O₂ is approximately 159 mmHg, while in the alveoli, it is about 104 mmHg. Conversely, the partial pressure of CO₂ in the atmosphere is only 0.3 mmHg, compared to 40 mmHg in the alveoli. This indicates that during hyperventilation, the substantial decrease in CO₂ levels is more pronounced than the relatively minor change in O₂ levels.

In arterial blood, the normal partial pressures are 40 mmHg for CO₂ and 100 mmHg for O₂. As hyperventilation alters the composition of alveolar air, the partial pressure of CO₂ in the blood is expected to decrease, as per Henry's law, which states that the amount of gas dissolved in a liquid is proportional to its partial pressure. Therefore, a down arrow indicates a reduction in CO₂ levels in the blood. In contrast, the partial pressure of O₂ is expected to increase, leading to an up arrow, as more O₂ will dissolve into the blood due to the elevated partial pressure in the alveoli.

When considering hemoglobin saturation, which is typically around 98% for O₂, it becomes evident that hyperventilation has a more significant impact on CO₂ levels than on O₂ levels. Most O₂ in the blood is bound to hemoglobin, and since it is already nearly saturated, the increase in O₂ partial pressure will not substantially affect the amount of O₂ carried by the blood. In contrast, CO₂ is primarily transported in solution, and changes in its partial pressure will greatly influence how much CO₂ can be dissolved in the blood. Thus, hyperventilation predominantly affects the amount of CO₂ in the blood more than it does O₂.

Which gradient most directly determines the direction that oxygen and carbon dioxide molecules will move between the air in the alveoli and the blood:

• A. The pressure gradient between alveolar air and the blood plasma.
• B. The concentration gradient between the hemoglobin and the blood plasma.
• C. The concentration gradient between carbon dioxide and oxygen.
• D. The pressure gradient between the hemoglobin and alveolar air.

Answer: (A)

Choose which of the following statements is correct.

• A. The pressure gradient for O₂ is much less than the pressure gradient for CO₂, but because of hemoglobin, more O₂ can be carried in the blood.
• B. Because the pressure gradient for O₂ is greater than the pressure gradient for CO₂, more molecules of O₂ will be exchanged in the alveoli than molecules of CO₂.
• C. Most molecules of O₂ are carried by hemoglobin, but it is the gradient between the plasma and the alveoli that determines the movement of O₂ in and out of the blood.
• D. O₂ is 20 times more soluble than CO₂, meaning that much more O₂ can be carried in the blood plasma than CO₂.

Answer: (C)

Internal Respiration

Internal respiration is a vital process involving the exchange of gases—specifically oxygen (O₂) and carbon dioxide (CO₂)—between the blood and the body's internal tissues. During this process, there is a net movement of CO₂ into the blood and O₂ into the tissues. It's important to note that the total amount of CO₂ exchanged equals the amount of O₂ exchanged, a balance maintained by cellular respiration, which consumes O₂ and produces CO₂ in the tissues.

To visualize this, consider the analogy of a "tissue tower" representing the tissues, with a "street" symbolizing the capillary. The capillary contains blood plasma, while hemoglobin molecules act as buses transporting O₂. The partial pressure of O₂ in the capillary (100 mmHg) is significantly higher than in the tissues (≤40 mmHg), creating a gradient that drives O₂ from the blood into the tissues. As O₂ molecules leave the capillary, the pressure equalizes, halting further movement once both areas reach 40 mmHg.

Despite this exchange, hemoglobin retains a substantial reserve of O₂, with each red blood cell containing approximately 250 million hemoglobin molecules, ensuring that the body has ample oxygen available even after some is delivered to the tissues.

Conversely, the exchange of CO₂ follows a similar gradient principle. The partial pressure of CO₂ is higher in the tissues (46 mmHg) compared to the capillary (40 mmHg), prompting CO₂ to diffuse into the blood. As CO₂ enters the capillary, it binds to hemoglobin at different sites than O₂, facilitating its transport back to the lungs. This process continues until the partial pressures equalize at 46 mmHg in both the capillary and the tissues.

These gradients—60 mmHg for O₂ and 6 mmHg for CO₂—are crucial for understanding gas exchange dynamics. They can vary based on the metabolic activity of the tissues; for instance, during intense exercise, the gradients may increase due to heightened O₂ consumption and CO₂ production. This understanding of internal respiration is essential for grasping how the body maintains homeostasis and meets its metabolic demands.

Respiration Example 3

Respiration involves the exchange of gases, primarily oxygen and carbon dioxide, occurring in two main locations: the alveoli and the tissues. Understanding the differences between these sites is crucial for grasping the respiratory process.

Internal respiration refers to the exchange of gases at the tissue level, where oxygen is delivered from the blood to the tissues, and carbon dioxide is taken from the tissues into the blood. This process is essential for cellular metabolism, as cells utilize oxygen to produce energy and release carbon dioxide as a waste product.

In contrast, external respiration occurs in the alveoli, where oxygen from the external air is exchanged with carbon dioxide in the blood. This exchange is driven by differences in partial pressure, which is a measure of the concentration of a gas in a mixture. For instance, the partial pressure of oxygen in the alveoli is significantly higher than in the blood, facilitating the movement of oxygen into the bloodstream.

Key concepts include:

• The partial pressure of oxygen in the alveoli is approximately 104 mmHg, while the partial pressure of carbon dioxide is around 40 mmHg. This creates a gradient that promotes the diffusion of oxygen into the blood and carbon dioxide out of the blood into the alveoli.
• In the tissues, the partial pressure of carbon dioxide is higher (about 46 mmHg) compared to oxygen (around 40 mmHg), which drives carbon dioxide into the blood and oxygen out of the blood to the tissues.
• Overall, the net movement of oxygen and carbon dioxide molecules is approximately equal in both the alveoli and the tissues, reflecting the stoichiometry of cellular respiration, which consumes 6 molecules of oxygen and produces 6 molecules of carbon dioxide.

Understanding these processes is vital for comprehending how the body maintains homeostasis and meets its metabolic demands through efficient gas exchange.

For internal respiration, which of the following must be true:
I. The total amount of CO₂ exchanged equals the amount of O₂ exchanged.
II. Carbon dioxide will move down its pressure gradient to enter the blood.
III. The partial pressure of O₂ in the tissue before gas exchange is ≥ 40 mm Hg.

• A. I only.
• B. I and II.
• C. III only.
• D. I, II, and III are true.

Answer: (B)

Here’s what students ask on this topic:

What is the difference between external and internal respiration?

External respiration occurs in the alveoli of the lungs, where oxygen (O₂) moves from the air into the blood, and carbon dioxide (CO₂) moves from the blood into the air. This process relies on pressure gradients, with O₂ moving down its gradient from high partial pressure in the alveoli to lower partial pressure in the blood, and CO₂ moving from high partial pressure in the blood to lower partial pressure in the alveoli. Internal respiration, on the other hand, occurs in the tissues of the body. Here, O₂ moves from the blood into the tissues, where it is used for cellular respiration, and CO₂, a waste product of cellular respiration, moves from the tissues into the blood. Both processes ensure that the body receives the necessary O₂ and expels CO₂.

How do Dalton's law of partial pressure and Henry's law apply to respiration?

Dalton's law of partial pressure states that the total pressure of a gas mixture is the sum of the partial pressures of each individual gas. In respiration, this means that O₂ and CO₂ move according to their own partial pressures. For example, O₂ moves from areas of high partial pressure in the alveoli to areas of lower partial pressure in the blood. Henry's law states that the amount of gas that dissolves in a liquid is proportional to its partial pressure and its solubility. This is crucial in respiration because it explains how gases like O₂ and CO₂ dissolve in blood plasma. O₂ has a lower solubility than CO₂, requiring hemoglobin to carry most of the O₂ in the blood.

What are the partial pressures of oxygen and carbon dioxide in the alveoli and blood during respiration?

In the alveoli, the partial pressure of oxygen (P_O2) is approximately 104 mmHg, while the partial pressure of carbon dioxide (P_CO2) is about 40 mmHg. In the venous blood returning to the lungs, P_O2 is around 40 mmHg, and P_CO2 is about 46 mmHg. As blood passes through the alveolar capillaries, O₂ moves into the blood, raising its P_O2 to about 100 mmHg in arterial blood, while CO₂ moves into the alveoli, lowering its P_CO2 to 40 mmHg. These gradients drive the exchange of gases during both external and internal respiration.

Why is the composition of alveolar air different from atmospheric air?

The composition of alveolar air differs from atmospheric air due to several factors. First, alveolar air contains more water vapor because the respiratory tract humidifies the air as it is inhaled. Second, alveolar air has a higher concentration of carbon dioxide (CO₂) and a lower concentration of oxygen (O₂) compared to atmospheric air. This is because CO₂ is constantly being transferred from the blood to the alveoli, while O₂ is being absorbed into the blood. Additionally, the residual volume of air in the lungs, which does not get fully exchanged with each breath, contributes to these differences in gas composition.

How does hemoglobin facilitate the transport of oxygen and carbon dioxide in the blood?

Hemoglobin, a protein in red blood cells, plays a crucial role in transporting oxygen (O₂) and carbon dioxide (CO₂) in the blood. Each hemoglobin molecule can bind up to four O₂ molecules, significantly increasing the blood's oxygen-carrying capacity. This binding occurs in the lungs, where O₂ partial pressure is high. Hemoglobin also helps transport CO₂ from tissues to the lungs. CO₂ binds to hemoglobin at a different site than O₂, forming carbaminohemoglobin. Additionally, CO₂ is converted to bicarbonate (HCO₃^-) in red blood cells, which is then transported in the plasma. This dual role of hemoglobin ensures efficient gas exchange and transport in the body.