39.1 Systems of Gas Exchange

The primary function of the respiratory system is to deliver oxygen to the cells of the body's tissues and remove carbon dioxide, a cell waste product.

The human respiratory system has three main structures.

Aerobic organisms need oxygen to function.

Different organisms have different ways of getting oxygen from the atmosphere.

The environment in which the animal lives affects how it respires.

The complexity of the respiratory system is related to the size of the organisms.
In unicellular organisms, it is possible to get oxygen to the cell.
Slow, passive transport is what Diffusion is.
In order to provide oxygen to the cell, the rate of oxygen absorption must match the rate of diffusion.
If the cell was large or thick, it would not be possible for diffusion to provide enough oxygen to the inside of the cell.
For small organisms or those with highly-flattened bodies, dependence on diffusion as a means of obtaining oxygen and removing carbon dioxide remains feasible.

To transport oxygen throughout their entire body, larger organisms had to evolve specialized respiratory tissues, such as gills, lungs, and respiratory passages.

The cell of the unicellular alga Ventricaria ventricosa is five centimeters in diameter and one of the largest known.

Small multicellular organisms are able to meet their oxygen needs with the help of the outer membrane.

For organisms less than 1mm in diameter, gas exchange by direct diffusion is efficient.
Every cell in the body is close to the outside environment in simple organisms.
Their cells are moist and diffuse quickly.
Flatworms are small, literally flat worms, which 'breathe' through the outer layer of the cell.
The flat shape of these organisms ensures that each cell in the body has access to oxygen.
The cells in the center of the flatworm wouldn't be able to get oxygen if it had a cylindrical body.

Amphibians use their skin as a respiratory organ.

A dense network of capillaries lies just below the skin and facilitates gas exchange between the external environment and the circulatory system.
The respiratory surface needs to be moist in order for the gases to diffuse.

Organisms need to get oxygen from the water.

The atmosphere has a small amount of oxygen.
The water's oxygen concentration is lower than that.

The gills on fish and other aquatic organisms take up dissolved oxygen from the water.

Gills are highly branched and folded.
The dissolved oxygen in water quickly diffuses across the gills into the bloodstream when it passes over the gills.
The oxygenated blood can be carried to other parts of the body.
In animals with coelomic fluid, oxygen diffuses across the gill surfaces into the fluid.

Gills can be found in mollusks, annelids, and crustaceans.

The common carp has gills that allow it to get oxygen from water.

The large surface area of the gills ensures that the fish gets enough oxygen.

When equilibrium is reached, the material travels from high concentration to low concentration.
The blood has a low concentration of oxygen in it.
The concentration of oxygen in the water is higher than in the gills.
The carbon dioxide in the blood diffuses from the high concentration to the low concentration.

Oxygen is transferred from the water to the blood through the veins.

The blood does not play a direct role in the transport of oxygen.

The tracheal system is a specialized type of respiratory system that insects have.

The most efficient respiratory system in animals is the tracheal system.
The tracheal system is made of tubes.

There are openings in the insect bodies called spiracles.

The openings allow oxygen to pass into the body and regulate the flow of CO2 and water.
Air leaves the tracheal system through the spiracles.
Some insects can move their bodies.

In mammals, breathing occurs via inhalation.

The air is humidified as it passes through the nose.
mucus is used to seal the respiratory tract from air.
The water is high.
Water is picked up by the air as it crosses the surfaces.
Cold, dry air can cause damage to the body, so these processes help equilibrate the air.
mucus and cilia are used to remove particulate matter from the air.
The processes of warming, humidifying, and removing particles are important protective mechanisms that prevent damage to the trachea and lungs.
Inhaling brings oxygen into the respiratory system.

Air enters the respiratory system through the nose and pharynx, and then goes through the trachea and ends up in the lungs.

Air travels from the pharynx to the trachea when we breathe in.

The bronchioles are part of the body.

The main function of the trachea is to get the air out of the body.

The human trachea is a cylinder about 10 to 12 cm in length and 2 cm in diameter that sits in front of the esophagus and extends into the chest where it divides into the two primary bronchi at the midthorax.

It is made of incomplete rings of smooth muscle.
The trachea has goblet cells and ciliated epithelia.

Foreign particles are trapped in the mucus.

The passage is kept open by the strength and support of the cartilage.
The smooth muscle can contract, decreasing the trachea's diameter, which causes expired air to rush upwards from the lungs at a great force.
mucus is expelled when we cough.
Smooth muscle can relax or contract depending on stimuli from the outside.

The bronchi and trachea are made of incomplete rings.

The right and left lungs are divided by the end of the trachea.

The lungs are not the same.
The left lung has two lobes, whereas the right lung has three.

The bronchi in the lungs are bifurcated by the trachea.

The right lung is larger than the other two.
The left lung has two lobes and is smaller than the heart.

The bronchi are similar to the trachea.

The elastic fibers are used at the bronchioles.
The parasympathetic and sympathetic nervous systems control muscle contraction and relaxation in the bronchi and bronchioles.
They rely on air to support their shape.

There are many alveoli and alveolar sacs.

The alveolar sacs look like bunches of grapes.
In alveoli, gas exchange occurs.
Alveoli are made of thin-walled parenchymal cells that look like tiny bubbles in the sacs.

Oxygen will diffuse from alveoli into the blood and be distributed to the cells of the body through intimate contact.

The carbon dioxide produced by cells as a waste product will diffuse from the blood into alveoli to be exhaled.
The relationship of the respiratory and circulatory systems is emphasized by the arrangement of capillaries and alveoli.
The lungs have a sponge-like consistency because there are so many alveolar sacs and alveolar duct.
A large surface area is available for gas exchange.
The lungs have a surface area of 75 m2.
The thin-walled nature of the alveolar parenchymal cells allows gases to easily diffuse across the cells.

Respiratory bronchioles connect to alveolar ducts and alveolar sacs.

The alveolar sacs have the appearance of a bunch of grapes.
Air flows into the alveolar sac and then into alveoli, where gas exchange occurs with the capillaries.
The mucus glands keep the airways moist and flexible.

The respiratory system is reviewed in the following video.

The respiratory system has a number of protective mechanisms.

The mucus and hairs in the nose trap small particles to prevent them from entering.

The bronchi and bronchioles of the lungs contain several protective devices if particulates make it beyond the nose or enter through the mouth.

The bronchi and bronchioles have small hair-like projections on their walls.
The mucus and particles are moved from the bronchi to the throat through the cilia.

tar and other substances in cigarette smoke can cause damage to the cilia, making it more difficult to remove particles.

Smoking causes the lungs to produce more mucus, which the damaged cilia can't move.
This causes a persistent cough, as the lungs try to rid themselves of particulate matter, and makes smokers more susceptible to respiratory ailments.

mucus and other particles are moved out of the lungs by the bronchi and bronchioles.

The lung has a structure that maximizes its surface area.

The surface area of the lung is large due to the large number of alveoli.
The amount of gas that can diffuse into and out of the lungs can be increased by having a large surface area.

Transport is driven by a concentration.

A region of high concentration is replaced by a region of low concentration.
Blood with low oxygen concentration and high carbon dioxide concentration undergoes gas exchange with air in the lungs.
The amount of oxygen in the air in the lungs is higher than the amount in the blood and the amount of carbon dioxide.

The concentration allows for gas exchange.

The partial pressures of the components in the mixture are the total pressure exerted by the mixture.

The rate of dispersal of a gas is determined by the partial pressure within the gas mixture.
The concept is discussed in more detail below.

Different animals have different lung capacities.

The lung capacity of the chess is higher than that of humans and it allows them to run very fast.
Elephants have a high lung capacity.
It's not because they run fast but because they have a large body and need to be able to take up oxygen in their body size.

The lung size of a human is determined by their genetics, sex, and height.

Lungs can hold up to six liters of air, but they don't always operate at maximal capacity.
Volume is the amount of air for one function.

Capacity is how much can be exhaled from the end of a maximal exhalation.

The lung volumes and capacities of humans are shown.

The adult male has six liters of lung capacity.
The volume of air in a single breath is called tidal volume.
Residual volume is the amount of air left in the lungs after a deep breath.

The average volume is around one-half liter, which is less than a 20-ounce bottle.

The reserve amount can be exhaled beyond what is normal.
There is always some air left in the lungs after a maximal exhalation.
The lung tissues would stick together if the lungs did not have residual volume.
There is always some air in the lungs.
Large fluctuations in respiratory gases are prevented by residual volume.
The residual volume can't be measured directly because it's impossible to completely empty the lung of air.
The volume can only be calculated.

Capacities are two or more volumes.

The sum of expiratory reserve volume, tidal volume, and inspiratory reserve volume is what it is.
The sum of the tidal volume and inspiratory reserve volume is what it is.
The amount of air that can be exhaled is measured by the FRC.
It is the total of the residual volume, expiratory reserve volume, tidal volume, and inspiratory reserve volume.

The total amount of air that can be forcibly exhaled is measured.

The lungs are not compliant if the FEV1/FVC ratio is high and the patient has lung fibrosis.
The lung volume is exhaled very quickly by patients.
There is resistance in the lung when the FEV1/FVC ratio is low.
It is hard for the patient to get the air out of his or her lungs, and it takes a long time to reach the maximal exhalation volume.
In either case, breathing is difficult.

Respiratory therapists evaluate and treat patients with lung and cardiovascular diseases.

They are part of a medical team.
Premature babies with underdeveloped lungs, patients with chronic conditions such as asthma, and older patients with lung disease may be treated by respiratory therapists.
They can operate advanced equipment such as compressed gas delivery systems.
A bachelor's degree with a respiratory therapist specialty can be obtained through specialized programs.
Respiratory therapist career opportunities are expected to remain strong because of a growing aging population.

The properties of gases can be looked at to understand the respiratory process.

Gases are moving, but gas particles are hitting the walls of the vessel, causing gas pressure.

Nitrogen (N; 78.6 percent), oxygen (O; 20.9 percent), water vapor (H2O; 0.5 percent), and carbon dioxide (CO2; 0.04 percent) are some of the gases in air.

The mixture exerts pressure on each component.
The partial pressure of the gas in the mixture is what the individual gas pressure is.
Oxygen makes up approximately 21 percent of atmospheric gas.
Carbon dioxide is found in relatively small amounts.
The pressure of oxygen is greater than carbon dioxide.

The pressure at sea level is 760mm Hg.

Patm does not change at high altitudes, but the partial pressure decrease is due to the reduction in Patm.

The air mixture has been humidified when it reaches the lung.

The pressure of the water in the lung does not change the pressure of the air, but it must be included in the partial pressure equation.

The gas exchange is determined by the pressures in the system.

Oxygen and carbon dioxide can flow from high to low.
Understanding how gases move in the respiratory system will be aided by understanding the partial pressure of each gas.

Oxygen and carbon dioxide are produced in the body and used as waste products.

The RQ would equal one if the body was powered by just sugar.
Every mole of oxygen consumed would produce one mole of carbon dioxide.
There are other fuels for the body.
Fuels are also used for the body.
Less carbon dioxide is produced and the RQ is lower because of it.

The partial pressure of oxygen in the lungs was calculated.

The inspired air mixes with the residual air and lowers the pressure of oxygen within the alveoli.
The concentration of oxygen in the lungs is lower than in the air.

The pressure is less than the outside air.

The inspired air in the lung will flow into the bloodstream.

In the lungs, oxygen diffuses out of the alveoli and into the capillaries.

Oxygen is reversibly binding to the respiratory hemoglobin found in red blood cells.
Oxygen diffuses from the hemoglobin into the cells of the tissues when it is carried by the RBCs.

Oxygen diffuses down its pressure gradient, moving out of the alveoli and entering the blood of the capillaries where O2 bind to hemoglobin.

Alveolar is lower than blood by 40mm Hg.
CO2 moves out of the capillaries and into the alveoli.

Oxygen and carbon dioxide have their own pressures.