Pulmonary 3 Gas Exchange

Summary

This lecture delves into the fundamentals of pulmonary physiology, focusing on oxygen supply's dependency on ambient air concentration and pressure. It explains the constant composition of ambient air, the concept of partial pressure, and Dalton's law. The script further explores gas behavior, Henry's law, and the passive diffusion of gases between the lungs, blood, and body tissues, emphasizing the role of pressure gradients and gas solubility in efficient gas exchange, crucial for understanding respiratory processes and maintaining life.

Takeaways

• 🌍 Oxygen supply to the body is critically dependent on the concentration of oxygen in the ambient air and the pressure it exerts.
• 📊 Ambient air composition is remarkably constant, with oxygen at about 20.93%, nitrogen at 79.4%, and carbon dioxide at 0.03%, with trace amounts of water vapor.
• 💨 Gas molecules are in constant rapid motion, causing collisions that generate pressure, which is essential for the diffusion of gases across respiratory surfaces.
• 🌡 Partial pressure of a single gas is a product of its concentration and the total pressure, exemplified by oxygen's partial pressure at sea level being 150.9 mm of mercury.
• 🔍 Dalton's law states that the total pressure of a gas mixture is the sum of the partial pressures of the individual gases.
• 🌬 The partial pressure of oxygen decreases as it moves down the respiratory tract due to the saturation with water vapor.
• 🔄 Henry's law explains that the amount of gas dissolved in a fluid is directly proportional to the pressure of the gas over the fluid, influenced by the pressure differential and solubility of the gas.
• 🔄 Gas solubility varies, affecting the amount transported; for instance, carbon dioxide is approximately 25 times more soluble than oxygen under the same conditions.
• 🌀 Gas diffusion occurs only when there is a pressure difference, with the partial pressure gradient being the driving force.
• 🏃‍♂️ During exercise, the pressure of oxygen in active muscle can drop significantly, creating a larger pressure differential for oxygen to diffuse into cells and carbon dioxide to move out.
• 🔄 Gas exchange in the body occurs passively by diffusion, with pressure gradients determining the direction of gas movement between the lungs and blood, and at the tissue level.

Q & A

What are the two critical factors for oxygen supply to the body?

The two critical factors for oxygen supply to the body are the concentration of oxygen in the ambient air and the pressure that this air exerts.

What are the approximate percentages of the main components in the ambient air?

Oxygen makes up about 20.93%, nitrogen is the most abundant at 79.4%, and carbon dioxide is present at a much lower concentration of 0.03%. There are also small quantities of water vapor.

What is the concept of partial pressure in relation to gases?

Partial pressure refers to the pressure exerted by a single gas in a mixture of gases. It is a combination of the gas's concentration and the total pressure of the mixture.

How does the partial pressure of oxygen at sea level compare to the total atmospheric pressure?

At sea level, the total atmospheric pressure is approximately 760 mm of mercury. The oxygen partial pressure is calculated as 760 mm * 20.93%, which equals about 150.9 mm of mercury.

What is Dalton's law and how does it relate to the total pressure of the atmosphere?

Dalton's law states that the total pressure of a mixture of gases is the sum of the partial pressures of the individual gases. It helps to calculate the total pressure of the atmosphere at sea level.

How does the humidification of air affect the partial pressure of oxygen in the tracheal air?

Humidification of air, which occurs as air enters the nasal cavities and mouth and passes down the respiratory tract, decreases the partial pressure of oxygen in tracheal air by about 10 mm of mercury, from 159 mm to 149 mm.

What is Henry's law and how does it explain the movement of gases between air and fluids?

Henry's law states that the amount of a specific gas dissolved in a fluid at a given temperature is directly proportional to the pressure of the gas over the liquid. It explains how the pressure differential and the solubility of the gas affect the gas movement between air and fluids.

How does the solubility of a gas affect the efficiency of gas exchange processes?

The solubility of a gas affects the efficiency of gas exchange processes by determining how much of the gas can be transported. A gas with greater solubility will have a higher concentration in the fluid at a given pressure, leading to more efficient gas exchange.

What factors account for the dilution of oxygen in inspired air as it passes into the alveola chambers?

The dilution of oxygen in inspired air as it passes into the alveola chambers is accounted for by three factors: water vapor saturation of the dry inspired air, oxygen continually leaving the alveola, and carbon dioxide continually entering the alveola.

How does the pressure gradient of gases facilitate the passive exchange of gases between the lungs and blood?

The pressure gradient of gases facilitates the passive exchange of gases between the lungs and blood by creating a diffusion gradient. Oxygen diffuses from areas of higher pressure in the alveola air to areas of lower pressure in the blood, and carbon dioxide diffuses in the opposite direction.

What changes occur in the gas pressures of arterial blood and tissues during vigorous exercise?

During vigorous exercise, the pressure of oxygen molecules in active muscle can drop to as low as 3 mm of mercury, while carbon dioxide pressure can approach 90 mm of mercury, creating a substantial pressure differential that drives the diffusion of oxygen to the cells and carbon dioxide away from the cells.

Outlines

00:00

🌪️ Oxygen Supply and Gas Behavior in the Respiratory System

This paragraph introduces the fundamental concepts of pulmonary physiology, focusing on the oxygen supply to the body and the factors that affect it. It explains the composition of ambient air, emphasizing the constant percentages of oxygen, nitrogen, and carbon dioxide, and the impact of water vapor. The behavior of gases, particularly the importance of pressure in driving the diffusion of gases across respiratory surfaces, is discussed. The concept of partial pressure is introduced, and how it is calculated at sea level using Dalton's law is explained. The paragraph also details how the partial pressure of oxygen changes as it moves down the respiratory tract and how gas composition is altered by the humidification process. The role of Henry's law in gas movement between the external environment and body tissues is highlighted, illustrating the principles of gas solubility and pressure differentials.

05:02

🌊 Principles of Gas Diffusion and Solubility

The second paragraph delves into the principles of gas diffusion, using the example of oxygen dissolving in water to demonstrate how gas molecules move from an area of higher pressure to an area of lower pressure until equilibrium is reached. It explains the concept of net diffusion, which only occurs when there is a pressure difference, and how gas solubility affects the amount of gas that can be dissolved in a fluid. The paragraph provides a comparative analysis of the solubility of different gases, particularly the significantly higher solubility of carbon dioxide compared to oxygen, and its implications for gas exchange efficiency. It also discusses the passive diffusion of gases between the lungs and blood, and at the tissue level, driven by pressure gradients, and how these gradients change during rest and exercise.

10:05

🏃‍♂️ Gas Exchange Dynamics During Rest and Exercise

The final paragraph examines the dynamics of gas exchange during rest and exercise. It describes the pressure gradients that favor gas transfer in the body, focusing on the differences in gas pressures between arterial blood and tissues. The paragraph explains how the partial pressure of oxygen in the alveoli is reduced due to the saturation of inspired air with water vapor and the continuous exchange of gases with the blood. It contrasts this with the situation during vigorous exercise, where the pressure of oxygen molecules in active muscle can drop significantly, creating a large pressure differential that drives oxygen towards metabolizing cells and carbon dioxide away from them. The paragraph concludes by emphasizing the importance of understanding these dynamics for maintaining the body's metabolic needs.

Keywords

💡Oxygen Supply

Oxygen supply refers to the process by which oxygen is made available to the body, which is essential for life. In the video, it is described as being critically dependent on the concentration of oxygen in the ambient air and the pressure exerted by this air. The script emphasizes the importance of understanding oxygen supply for maintaining life, especially at different altitudes where the composition of ambient air can change.

💡Ambient Air

Ambient air is the air surrounding us, which typically has a consistent composition under most conditions. The script mentions that the composition of ambient air remains remarkably constant at sea level and even at altitude, which is crucial for sustaining life. Ambient air is composed of approximately 20.93% oxygen, 79.4% nitrogen, and 0.03% carbon dioxide, with small quantities of water vapor.

💡Partial Pressure

Partial pressure is the pressure exerted by a specific gas within a mixture of gases. In the context of the video, it is used to describe the pressure of oxygen in the air, which is calculated by multiplying the total atmospheric pressure by the percentage of oxygen in the air. The script explains that the partial pressure of oxygen at sea level is approximately 150.9 mm of mercury, which is vital for driving the diffusion of oxygen across respiratory surfaces.

💡Dalton's Law

Dalton's Law, as mentioned in the script, states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases. This law is fundamental in understanding how the partial pressures of different gases, such as oxygen and carbon dioxide, contribute to the total atmospheric pressure and how they behave in the respiratory system.

💡Diffusion

Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. The video script discusses how the pressure of gas molecules drives diffusion across respiratory surfaces, which is essential for the transport of oxygen into the body and carbon dioxide out of the body.

💡Humidification

Humidification is the process by which water vapor is added to the air as it passes through the nasal cavities and mouth, and down the respiratory tract. The script explains that this process affects the partial pressure of oxygen in tracheal air, causing it to decrease by about 10 mm of mercury, which is an important factor in the respiratory process.

💡Alveoli

Alveoli are small air sacs in the lungs where the exchange of oxygen and carbon dioxide between the air and the blood takes place. The script describes how the partial pressure of oxygen in the alveoli is influenced by the saturation of the air with water vapor and the continuous exchange of gases with the blood, which is crucial for understanding gas exchange in the body.

💡Henry's Law

Henry's Law, as explained in the script, states that the amount of a specific gas dissolved in a fluid is directly proportional to the pressure of the gas over the fluid. This law is important for understanding how gases dissolve in the blood and other body fluids, which is essential for the transport and exchange of gases in the body.

💡Gas Solubility

Gas solubility refers to the ability of a gas to dissolve in a fluid. The script uses the example of carbon dioxide being approximately 25 times more soluble in fluids than oxygen, which highlights the impact of solubility on the efficiency of gas exchange processes in the body.

💡Gas Exchange

Gas exchange is the process by which oxygen is taken up by the body and carbon dioxide is expelled. The video script describes how this process occurs passively by diffusion, depending on the pressure gradients of the gases. It is a fundamental concept in understanding how the body maintains metabolic needs by exchanging gases between the lungs and the blood.

💡Metabolic Needs

Metabolic needs refer to the body's requirement for oxygen and the production of carbon dioxide during cellular respiration. The script explains how the pressure differential between arterial blood and tissues, especially during exercise, creates a diffusion gradient that facilitates the movement of oxygen to cells and carbon dioxide from cells to the blood, which is essential for meeting the body's metabolic demands.

Highlights

Oxygen supply to the body is critically dependent on the concentration of oxygen in the ambient air and the pressure it exerts.

The composition of ambient air remains remarkably constant under most conditions, crucial for maintaining life.

Oxygen makes up about 20.93% of the ambient air, while nitrogen is the most abundant at 79.4%, and carbon dioxide is present at just 0.03%.

Gas molecules are in constant rapid motion, causing them to collide with surfaces and each other, exerting pressure which drives the diffusion of gases.

Partial pressure of a single gas is a combination of the gas concentration and the total pressure.

At sea level, the oxygen partial pressure is 150.9 mm of mercury, calculated by multiplying the oxygen concentration by the total pressure of 760 mm mercury.

Dalton's law states that the total pressure of a gas mixture is the sum of the partial pressures of the individual gases.

Oxygen partial pressure decreases by about 10 mm of mercury due to humidification as air passes down the respiratory tract.

Carbon dioxide continually enters the alveoli from the blood, while oxygen moves in the other direction, affecting the gas composition.

The average pressure exerted by oxygen against the alveolar capillary membrane decreases to about 103 mm of mercury due to carbon dioxide entry.

Understanding gas behavior in air and fluids is crucial for comprehending the mechanisms of gas movement between the external environment and body tissues.

Henry's law states that the amount of a specific gas dissolved in a fluid at a given temperature varies directly with the pressure of the gas over the liquid.

Gas solubility in a fluid plays a significant role in determining the amount of gas that can be transported.

Different gases dissolve to different extents in fluids, affecting the efficiency of gas exchange processes.

At the same temperature and pressure differential, approximately 25 times more carbon dioxide than oxygen will diffuse into or out of a fluid.

The exchange of gases between the lungs and blood and gas movement at the tissue level progresses passively by diffusion depending on their pressure gradients.

During vigorous exercise, the pressure of oxygen molecules in active muscle can drop significantly, while carbon dioxide pressure can approach high levels.

The substantial pressure differential between gases in plasma and tissue during exercise creates a diffusion gradient for efficient gas exchange.

Gas exchange in the lungs facilitates oxygen diffusion into the blood and carbon dioxide diffusion out, maintaining the body's metabolic needs.

Transcripts

welcome to the third of the pulmonary

physiology lectures this short video

will provide you with the information to

be able to address the following

learning

objectives let's begin with the basics

oxygen supply to the body is critically

dependent on two factors the

concentration of oxygen in the ambient

ear and the pressure that this ear

exerts now the composition of ambient a

remains remarkably constant under most

conditions with your sea level or

heading up to altitude which is crucial

for maintaining

life now here are the specific

percentages you should remember oxygen

makes up about 20.93% of the ambient a

nitrogen is the most abundant component

at

79.4% and carbon dioxide is present at a

much lower

concentration just

0.03% and additionally there are small

quantities of water vapor which can vary

by based on humidity and other

environmental

factors now let's talk about the

behavior of these gases gas molecules

are in constant rapid motion and it's

this movement that causes the molecules

to collide with surfaces and with each

other exerting what we call

pressure this pressure is vital because

it drives the diffusion of gases

including oxygen across respiratory

surfaces when we we speak about a single

gas Like Oxygen we refer to the pressure

as a partial pressure now the partial

pressure is a combination of the

concentration of the gas and the total

pressure in this situation that would be

at C Level the pressure is approximately

760 mm of mercury so the oxygen partial

pressure is 760 multiplied by

2093 which equals 150 9 mm of

mercury now summing all the partial

pressures of the gases gives us the

total pressure of the mixture in this

case our atmosphere at sea level and

this is what is known as Dalton's

law looking at this table we can see not

only the partial pressure of oxygen and

the other major gases but also the

volume that they would contribute to a

given liter of gas for example oxy

providing 209 mL of

gas now the oxygen partial pressure

changes as we move down the respiratory

tract and other factors are added to

change the composition of the

gas firstly we completely saturate the

ear with water vapor this occurs as the

ear enters the nasal cavities and the

mouth and passes down the respiratory

tract as a result of this humidification

the effect of partial pressure of oxygen

in tracheal air decreases by about 10 mm

of mercury from the ambient value of 159

mm of mercury to 149 mm of

mercury carbon dioxide makes little

contribution to inspired air this means

humidification exerts a negligible

effect on inspired partial pressure of

CO2 however alviola air composition

differs from incoming breath of moist

ambient here because carbon dioxide

continually enters the alvil from the

blood and oxygen moves in the other

direction continually entering the blood

from the

elvoline so the average pressure is

exerted by oxygen against the lvol side

of the alviola capillary membrane

decreases to about 103 mm of mercury

because of the entry of carbon

dioxide understanding how gases behaving

air and fluids is crucial for

comprehending the mechanisms of gas

movement between the external

environment and the body's

tissues this concept is governed by

Henry's law which states that the amount

of a specific gas dissolved in a fluid

at a given temperature varies in direct

proportion to the pressure of the gas

over the

liquid and that this depends on two key

factors first there's the pressure

differential between the gas above the

fluid and the gas dissolved in the fluid

now this differential drives the gas

into the fluid or out of it depending on

the direction of the pressure

gradient and second the solubility of

the gas in the fluid plays a significant

role different gases dissolve to

different extents in fluids and this

solubility affects how much of the gas

can be

transported this figure here illustrates

three examples of gas movement between

air and FL fluid in each of the three

chambers oxygen molecules continually

strike the water surface in chamber a we

start with pure water that contains no

oxygen and because of this a large

number of oxygen molecules from the ear

dissolve in the water however it's

important to note that some oxygen

molecules also leave the water as the

dissolved molecules are in constant

random

motion now moving on to the Middle

Chamber the pressure gradient between

the air and the water still favors the

net movement or diffusion of oxygen into

the fluid from the gaseous State however

the amount of additional oxygen that

dissolves in the fluid is less than in

the first

chamber this is because there is already

some oxygen dissolved in the water which

reduces the rate at which new oxygen

molecules can

enter in the final chamber the pressures

eventually reach equilibrium and it's at

this point the number of ox oxygen

molecules entering the fluid equals the

number leaving it conversely if the

pressure of the dissolved oxygen

molecules exceeds the oxygen pressure in

the air oxygen will escape from the

fluid until a new pressure equilibrium

is reached now these examples illustrate

a crucial principle a gas's net

diffusion occurs only when there is a

difference in gas pressure the partial

pressure gradient of a specific gas is

the driving force for its

diffusion gas solubility or its

dissolving power reflects the quantity

of gas dissolved in a fluid at a

specific pressure essentially a gas with

greater solubility will have a higher

concentration in the fluid at a given

pressure so when considering two

different gases at identical pressure

differentials it's the solubility of

each gas that determines the number of

Mo ules moving into or out of the

fluid for example in the table here at

the same temperature and pressure

differential approximately 25 times more

carbon dioxide than oxygen will diffuse

into or out of a fluid this significant

difference highlights the impact of gas

solubility on the efficiency of gas

exchange

processes now the exchange of gases

between the lungs and blood and gas

movement at the tissue level progresses

passively by diffusion depending on

their pressure gradients now this figure

illustrates the pressure gradients

favoring gas transfer in the body at

rest and we're going to focus on the top

portion of the figure to begin with the

first step in oxygen transport involves

the transfer of oxygen from the lvi into

the blood and three factors account for

the dilution of oxygen in inspired ear

as it passes into the alveola chambers

first as we know water vapor sorry water

vapor saturates the relatively dry

inspired

air oxygen continually leaves the

alviola air and also carbon dioxide is

continually entering the alviola a so

considering these three factors the

partial pressure of oxygen in the Alvi

averages about 100 mm of

mercury now this value is significantly

though than the 159 mm of mercury found

in the dry ambient

here now despite this reduced P2 the

pressure of oxygen molecules in the

alviola air still averages about 60 mm

of mercury higher than the partial

pressure of oxygen in the Venus blood

that enters the pulmonary

capillaries now this press pressure

difference allows oxygen to diffuse

through the alviola membrane and into

the blood

in Reverse carbon dioxide exits under

slightly greater pressure in the

returning Venus blood than in the

lvi this pressure difference causes

carbon dioxide to diffuse from the blood

into the lungs and although there is

only a small pressure gradient of 6 mm

in Mercury for carbon dioxide diffusion

compared to oxygen carbon dioxide's High

solubility ensures that it transfer

occurs rapidly

gas pressures differ significantly

between arterial blood and the tissues

especially where energy metabolism

consumes oxygen at a rate roughly equal

to carbon dioxide production now if we

look at the bottom part of the figure we

can observe these differences at rest

the average partial pressure of oxygen

within muscle tissue really declines

below 40 mm of mercury in contrast the

intracellular partial pressure of carbon

dioxide averages about 46 mm of mercury

now during vigorous exercise however the

pressure of oxygen molecules in active

muscle can drop to as low as 3 mm of

mercury while carbon dioxide pressure

can approach 90 mm of

mercury this substantial pressure

differential between gases in plasma and

tissue creates a diffusion gradient

oxygen leaves the capillary blood and

flows towards the metabolizing cells or

carbon dioxide moves from the cells into

the blood this Blood now rich in carbon

dioxide and low in oxygen enters the

veins and returns to the heart which

pumps it into the

lungs when Venus blood enters the lung's

dense capillary Network diffusion begins

oxygen diffuses into the blood and

carbon dioxide diffuses out facilitating

gas exchange and maintaining the body's

metabolic needs

hopefully by now you should feel well

prepared to be able to tackle the

following learning objectives