Exam 2 Worksheets Flashcards
What are the primary functions of the respiratory system? You should be able to name 4-5 functions
- Exchange of gases between the atmosphere and the blood
- Helps regulate of body pH
- Protection from inhaled pathogens and irritating substances (dust, pollen, pollutants, bacteria etc)
- Vocalization or production of speech
- Sense of smell
Provide an overview of the 4 processes required for exchange of gases between the atmosphere and the blood. Be sure to include relevant terminology.
There are four important events that need to happen in order for gases to pass from the atmosphere and the blood. These events include – pulmonary ventilation, external respiration, transport of respiratory gases, and internal respiration. Pulmonary ventilation is the processes of breathing, or the cycling between inspiration (bringing air into the lungs) and expiration (moving air out of the lungs). External respiration happens in the alveoli where oxygen diffuses from the alveoli (air spaces) into the blood in the pulmonary capillaries and carbon dioxide diffuses from the blood into the alveoli. Transport of blood is the movement of blood from the lungs to reach the tissues and movement of blood from the tissues back to the lungs. During this transport, the blood moves through both the systemic and pulmonary circuits of the cardiovascular system (and the heart). Internal respiration is the process of gas exchange between the blood and the body’s cells – oxygen leaves the blood and enters the cells while carbon dioxide leaves the cells and enters the blood.
How do the anatomical features of the respiratory system allow humans to live in dry climates?
One of the principal actions of the conducting passageways that make up the respiratory system is to warm, humidify, and filter the air. This action is facilitated by superficial blood vessels that allow for heat exchange, seromucous gland secretions that create a humid environment, and the mucociliary escalator that allow trapped pathogens to be trafficked to the digestive system for destruction. These anatomical features of the respiratory system allow us to live in many different climates because no matter what the surrounding atmosphere looks like, when the air enters the alveoli it is warm, humid, and clean.
Explain what is meant by mucosa or mucous membrane.
A mucosa, or mucous membrane is the name of the lining of all body cavities that open to the outside of the body – such as the hollow organs of the respiratory, digestive and urogenital tracts. These linings are wet or moist and consist of the epithelium that lines the lumen or cavity of the organ, and the connective tissue layer, or lamina propria just deep to the epithelium.
Describe the respiratory mucosa and list where it can be found.
The respiratory mucosa lines most of the upper respiratory tract (nasal cavity, paranasal sinuses, nasopharynx) and some of the lower respiratory tract (larynx below the vocal cords, trachea, upper parts of bronchial tree). The respiratory mucosa is responsible for conditioning the air that comes into the respiratory system through the nasal cavity. The respiratory mucosa consists of ciliated pseudostratified columnar epithelium with goblet cells and a lamina propria that contains seromucous glands and a rich network of blood capillaries. Seromucous secretions include a watery solution, and a sticky mucous; these secretions pass through ducts to reach the lumen surface. Mucous secretions on the surface of the epithelium capture inhaled particles and the gently beating cilia sweep the mucous and trapped particles toward the pharynx for swallowing. Watery secretions from seromucous glands help to humidify the air, Blood vessels in the lamina propria warm incoming air, and help to recapture heat in outgoing air.
Describe the gross anatomy of the nasal cavity. How do these structures facilitate the primary functions of the respiratory system?
The most interesting feature of the nasal cavity is the nasal conchae, which rise like scrolls from the lateral walls. The nasal conchae are made of bone, and they are covered by respiratory mucosa. There are spaces called nasal meatuses between the 3 conchae (superior, middle, and inferior). The conchae increase the surface area of the cavity and create turbulent wind tunnels, maximizing contact of the air with the mucosa lining. This movement of the air ensures efficient conditioning of the air entering the nasal cavity and facilitates the removal of particles from the air.
The nasal cavity contains two different types of mucosa. The
olfactory mucosa and the respiratory mucosa. The olfactory mucosa lines the superior part of the nasal cavity and contains the olfactory neurons that form cranial nerve I and
convey the sense of smell. The respiratory mucosa is a pseudostratified ciliated columnar epithelium with Goblet cells. The cilia beat the mucous toward the back of the throat and toward the digestive system. Seromucous glands produce mucus and enzymes that help trap and kill pathogens found in the air. Blood capillaries in the lamina propria help warm incoming air and reclaim heat in outgoing air.
What are paranasal sinuses? Where are they found? What do they do?
The paranasal sinuses are air filled spaces in some of the skull bones that surround the nasal cavity. Sinuses form a ring around the nasal cavity and are found in the frontal bone, sphenoid bone, ethmoid bone and maxillary bones. The sinuses are named according to the bone where they are located (i.e. frontal sinus). Sinuses are lined by respiratory mucosa, and they have holes that drain directly into the nasal cavity. Sinuses lighten the skull and may help to warm and humidify the air.
Describe the anatomy of the pharynx. Be sure to compare and contrast the different regions.
The pharynx is muscular tube that serves as a conduit between the nasal, oral cavity and the lower respiratory system. It is the anatomical region commonly known as “the throat.” There are three regions that make up the pharynx – the nasopharynx, the oropharynx, and the laryngopharynx. The nasopharynx is the most superior region and is posterior to the nasal cavity. This region only allows for the movement of air and so has a pseudostratified ciliated epithelium (respiratory mucosa). The oropharynx is posterior to the oral cavity and therefore allows for the passage of both air and food, so we observe a stratified squamous epithelium here. The laryngopharynx is the more inferior region and is posterior to the larynx. The laryngopharynx is where food is directed into the digestive system (esophagus) and air into the respiratory system (larynx). Because food (as well as air) passes through the laryngopharynx, the epithelium is stratified squamous.
Describe the anatomy and primary functions of the larynx, including the vocal ligaments.
The larynx is a composed of a series of cartilages connected by membranes and ligaments. The most prominent cartilage is the thyroid cartilage that can be found on the anterior side of the larynx. The epiglottis is the only elastic cartilage in the larynx; movement of foodstuffs into the pharynx moves the epiglottis over the opening into the larynx, inhibiting the movement of food into the lower respiratory system. The larynx performs three functions – providing a patent airway, inhibiting the entry of food into the lower respiratory system, and voice production. The open space that allows the movement of air between the upper and lower respiratory system is the glottis. Crossing the glottis are two ligaments called the vocal cords (vocal folds). Muscles that draw the
vocal cords together narrows the glottis; muscles that tense the vocal cords raise the pitch of sound produced by air moving through the glottis.
What is the mucociliary escalator? Where is it found? Why is it important for respiratory system function?
The mucociliary escalator is created by the respiratory mucosa, and can be found in any structures lined by respiratory mucosa, such as the nasal cavity, nasopharynx, lower larynx, trachea and upper regions of the bronchial tree. Secretions from the seromucous glands and goblet cells create two layers of fluid that cover the apical surface of the pseudostratified epithelial cells. A deep watery layer allows the cilia to move freely. The superficial mucus layer traps and inhaled particles or pathogens. The constant beating of the cilia moves the mucus and any trapped particles toward the pharynx where they will be swallowed and directed into the esophagus (digestive system). The mucociliary escalator cleans inhaled air and helps ensure that no foreign particles reach the lower delicate parts of the respiratory system (alveoli).
Which of the following is NOT a benefit of breathing through the nose?
Absorption of oxygen into the blood
Where is the olfactory mucosa?
On the upper border of the superior nasal concha
Which of these structures is lined by stratified squamous epithelium instead of the typical respiratory epithelium?
Oropharynx
hich word or phrase describes the movement of air between the atmosphere and the lungs?
Ventilation
High pitched sounds are generated by air movement over _________.
High tension vocal folds
Describe the anatomy of the lungs.
There are two lungs within the thoracic cavity. The lungs are surrounded by the thoracic cage which is formed by the ribs, sternum, and vertebral column posteriorly. The lungs are located on either side of the mediastinum and fill the space between the rib cage, the diaphragm, and the lateral surface of the pericardium. The left lung contains two lobes, a superior lobe and an inferior lobe separated by the left oblique fissure. The right lung contains three lobes, a superior, middle, and inferior lobe. The right superior and right middle lobe are separated be the horizontal fissure, while the right oblique fissure separates the right middle and right inferior lobes. Each lung is served by a primary or main bronchus that enters at the hilum. The hilum is the area on the medial surface of the lung where the blood vessels, bronchi, nerves and lymphatics enter and leave the lungs.
The lungs are surround by the pleurae or pleural sacs which are described below.
Describe the anatomy of the bronchial tree including structural changes that occur in the various branches.
The trachea branches into two primary or main bronchi which enter each lung on their medial surface. The primary bronchus quickly branches into secondary or lobar bronchi that serve each lobe (2 on the left and 3 on the right). Secondary bronchi branch into tertiary or segmental bronchi. Bronchi continue dividing into smaller divisions. Larger bronchi are lined by the typical respiratory mucosa – ciliated pseudostratified columnar epithelium with goblet cells with a lamina propria, which is responsible for conditioning the air entering the lungs. The bronchi also have hyaline cartilage plates in their walls for structural support. The larger bronchi have more cartilage, and the cartilage plates start to get smaller and are replaced by smooth muscle cells in smaller bronchi. Once the cartilage plates disappear, the branching air passageways are called bronchioles. Bronchioles are about 0.5 – 1 mm in diameter, have no cartilage in their walls, but do have smooth muscle cells. There is also a change in the epithelium as the passageways get narrower. The epithelium transitions from a pseudostratified columnar to a cuboidal cell type with fewer mucus secreting cells and cilia. Smooth muscle in the walls of the bronchioles
help control air flow by constricting (bronchoconstriction) or dilating (bronchodilation) the lumen of the bronchiole
What is the functional difference between the conducting and respiratory zone? What is the anatomical feature that delineates the transition from conducting to respiratory zone?
The conducting zone structures primarily are responsible for moving air from the atmosphere toward the respiratory zone. Along the way the air is humidified, warmed, and cleaned (filtered). The respiratory zone is where gas exchange occurs. The respiratory zone is defined by the presence of the alveoli. So, the presence of the first alveolus marks the transition from conducting to respiratory zone.
Describe the anatomical features of the respiratory zone.
The respiratory zone contains respiratory bronchioles, alveolar ducts, alveolar sacs, and individual alveoli. By definition, the respiratory zone is where the alveoli are located because this is where gas exchange can occur.
The respiratory bronchiole is the smallest type of bronchiole and it is the first part of the bronchial tree where we start to see alveoli – it’s actually the last part of the bronchial tree too, because bronchioles will transition into alveolar ducts. Bronchioles are considered respiratory bronchioles if they have alveoli in their walls. Respiratory bronchioles transition into alveolar ducts, which are long hallways lined by alveoli. Alveolar sacs are clusters of alveoli at the ends of alveolar ducts. The alveolar sacs are analogous to a cluster of grapes, while an individual alveolus is analogues to a single grape. The alveoli are surrounded by elastic fibers which impart elasticity to the air spaces – the elastic fibers allow them to inflate easily when they fill with air, and they recoil to their original shape during exhalation. The alveoli are also surrounded by pulmonary capillaries which carry blood that needs to be oxygenated.
List the cell types that are found in the alveoli, and describe their functions.
Type I alveolar cell – flat squamous cells that form most of the wall of the alveolus. It forms part of the respiratory membrane across which gas exchange occurs.
Type II alveolar cell – cuboidal shaped cell that secretes surfactant which coats the inner surface of the alveoli and decreases surface tension.
Alveolar macrophage – these cells are phagocytes that keep the respiratory zone of the lung free from debris. They clean up and dust or pieces of dead cells that end up in the alveoli. Some textbooks call them “dust cells”
What is the respiratory membrane and how is it formed? Where do we observe this membrane?
The respiratory membrane is formed by the very thin wall of the alveolus and wall of the capillary across which respiratory gases cross. The respiratory membrane is typically about 0.5 um and is formed by a squamous Type I alveolar cell, the endothelial cell of the pulmonary capillary and the fused basement membranes (or basal lamina) between these two cells. This ultra-thin membrane allows for diffusion of gases between the alveolar air space and the blood. The respiratory membrane is found in the respiratory zone structures in between the walls of the alveoli and the pulmonary capillaries that surround the alveoli.
Describe the relationship between the pleurae and the lungs.
Each lung is surrounded by a double layered serous membrane sac called the pleurae or pleural sac. The pleural sac is like a balloon, and the lungs are like a fist that is pushed into the balloon. The layer of the pleural sac (balloon) that covers the surface of the lung including the fissures separating each lobe is called the visceral pleura. The layer of pleura that lines the inner surface of the thoracic wall, the superior face of the diaphragm, and the lateral wall of the mediastinum is the parietal pleura. The visceral and parietal pleura are continuous with each other at the hilum, the indentation on the medial surface of the lung where bronchi and blood vessels enter and leave the lung. In between the parietal and visceral pleurae is the pleural cavity that contains a small amount of pleural fluid. In addition to creating a slippery surface that allows the pleural layers to move freely during breathing, the surface tension created by this fluid makes the visceral and parietal pleural layers cling closely to each other (like the walls of a wet plastic bag) which is important in the mechanics of breathing (pulmonary ventilation)
Two separate sets of arteries bring blood to the lungs. Name these two arteries and compare and contrast their functions.
The pulmonary arteries (branches of the pulmonary trunk leaving the right ventricle) carry deoxygenated blood to the lungs to pick up fresh oxygen in the pulmonary capillary beds. These pulmonary arteries are part of the pulmonary circuit that brings low pressure, low oxygen blood to the lungs. This circuit is also high volume, because all of the body’s blood has to come to the lungs for re-oxygenating. Because of this, enzymes that need to work on material in the blood can be located in the lungs.
The bronchial arteries are branches of the aorta, and bring freshly oxygenated blood to the lung to supply oxygen to lung tissue cells to use for cellular respiration. The bronchial arteries are part of the systemic circulation which carries oxygenated, high pressure blood to tissues in the body.
What is a bronchopulmonary segment and why is it clinically relevant?
Each lobe of the lung contains a number of pyramid shaped bronchopulmonary segments that are separated from each other by connective tissue septa. These segments correspond to the regions of the lung that are served by tertiary (or segmental bronchi). In addition to receiving air from its own bronchus, each bronchopulmonary segment is served by its own artery and vein. This is important clinically because pulmonary disease is often limited to one or two segments of the lungs. Physicians typically move the stethoscope around when listening to breathing in order to detect abnormal sounds in any of the individual segments of the lung,
What anatomical feature of the trachea ensures that it stays patent (open)?
C-shaped hyaline cartilages
What property of the bronchi increases as the average diameter of the passageways decreases?
Cross-sectional area
What is a function of the pleural fluid?
To hold the lungs to the thoracic wall
Which of the following is a component of the respiratory membrane?
Endothelial cells of pulmonary capillaries
Which of the following correctly describes the transition from bronchi into smaller branches in the bronchial tree?
The amount of smooth muscle increases in the smaller passageways of the bronchial tree
Which of the following statements about the pleurae is NOT true?
The pleurae create one continuous pleural cavity for both lungs
Define and describe the inter-relationship between atmospheric pressure, intrapulmonary pressure and intrapleural pressure. Include how this relates to air movement into the lungs
Atmospheric pressure is the pressure of the air on the body. Intrapulmonary pressure is the air pressure within the lung air spaces, or alveoli, so its sometimes called the intra-alveolar pressure. Intrapleural pressure is the pressure within the pleural cavity.
Relationships: Atmospheric pressure is the same as intrapulmonary pressure in between breaths, because the air in the lungs equilibrates with the outside air. When the intrapulmonary pressure is less than atmospheric pressure, air flows into the lungs. When intrapulmonary pressure is greater than atmospheric pressure, air moves out of the lungs. Intrapleural pressure is ALWAYS less than the intrapulmonary pressure (i.e. is a negative pressure) and this relationship helps keep the lungs (or alveolar spaces) inflated and keeps the lungs from collapsing. The intrapleural pressure is negative due to a combination of factors, including the tendency of the alveoli to recoil and get smaller, the tendency of the thoracic cage to expand, and the suction (or clinginess) created by the pleural fluid which makes the visceral pleura tend to cling to the parietal pleura, and causes the lungs to adhere to the thoracic wall.
What is tranpulmonary pressure and why is it important?
The transpulmonary pressure is the difference between the intrapulmonary pressure and the intrapleural pressure. (Ppul – Pip) It is usually expressed as an absolute value. If the intrapulmonary pressure is 760 mm Hg, and the intrapleural pressure is 756 mm Hg, or -4 mm Hg relative to the intrapulmonary pressure, then the tranpulmonary pressure is 4 mm Hg. The transpulmonary pressure is the pressure that keeps the lungs from collapsing. The size of the transpulmonary pressure will dictate the size of the lungs. The greater the transpulmonary pressure, the more inflated the lungs become. If the transpulmonary pressure falls to zero the lungs will collapse. Sometimes the descriptions of intrapleural pressure and transpulmonary pressure sound similar. They are both critical to preventing lung collapse, but are different ways of expressing the same concept. Because of this, I would never ask you to distinguish between these two on an exam.
How does the puncturing of the parietal pleura of one lung result in a pneumothorax in only that lung?
The puncturing of the parietal pleura allows for the intrapleural pressure to equilibrate to the atmosphere. In this situation the intrapleural pressure would be equal to the intrapulmonary pressure and the transpulmonary pressure would drop to zero resulting in a collapsed lung. However, this only effects the lung with the punctured pleura, as each lung is encased in its own pleural cavity allowing each lung to operate somewhat independently
What is Boyle’s Law? How does it relate to pulmonary ventilation?
The pressure of a gas within a container is inversely related to the volume of the container. In a container that contains a gas, if the volume of that container is reduced, the pressure of the gas increases. If the volume of the container increases, the pressure decreases. This law can be described mathematically as P1V1 = P2V2, where P is pressure and V is volume.
In pulmonary ventilation, the thoracic cavity and lungs act like a container. The pressure within the lungs and alveolar air spaces is the intrapulmonary pressure (or intra-alveolar pressure). When the inspiratory skeletal muscles contract, the thoracic cavities and lungs enlarge, so the intrapulmonary pressure decreases. Since intrapulmonary pressure is now less than atmospheric pressure, air flows down its pressure gradient and enters the lungs. When the inspiratory skeletal muscles relax, the thoracic wall and lungs recoil back to their original size (get smaller), and the intrapulmonary pressure increases. Since intrapulmonary pressure is greater than atmospheric pressure, air moves out of the lungs, down its concentration gradient.
Compare and contrast quiet inspiration, quiet expiration, forced inspiration, and forced expiration. Include the role of skeletal muscles involved in each phase.
The repeating pattern of quiet inspiration and quiet expiration is commonly referred to as ventilation or breathing. The amount of air moved during this process is the tidal volume (usually around 500 mL). Quiet inspiration is an active process and requires the contraction of the diaphragm and external intercostal muscles, which cause an increase in the thoracic cavity volume, a decrease in intrapulmonary pressure and air flow into the lungs. Quiet expiration is a passive process and therefore only requires the relaxation of the diaphragm and external intercostal muscles. The natural recoil of the lungs and the thoracic wall cause an increase in intrapulmonary pressure and air flows out of the lungs.
Forced inspiration is an active process that requires the recruitment of additional muscles including the sternocleidomastoid, scalenes, serratus anterior. These muscles help increase the volume of the thoracic cavity beyond what is seen in quiet inspiration, thus allowing for the movement of more air. Forced expiration is also an active process that requires the recruitment of the internal intercoastal muscles and the abdominal wall muscles. Contraction of these muscles help decrease the volume of the thoracic cavity beyond what is achieved with quiet expiration, again allowing for a greater movement of air.
Describe three (3) physical factors that affect the efficiency of pulmonary ventilation.
The three factors that can impact the efficient of pulmonary ventilation include airway resistance, alveolar surface tension, and lung compliance.
• Airway resistance is controlled by smooth muscles that line the bronchioles. Contraction of the smooth muscles causes bronchoconstriction which decreases the diameter of the airway, increases resistance and therefore decreases airflow. Relaxation of the smooth muscles produces bronchodilation, or increased diameter of the airway. Bronchodilation decreases resistance and therefore increases airflow.
• Alveolar surface tension is created by the thin layer of fluid on the inner surface of the alveoli. The molecular attraction between the water molecules creates high surface tension which make the alveoli tend to collapse, just like a plastic bag with a few drops of water in it. Collapsed alveoli are extremely difficult to inflate, limiting gas exchange. However, surfactant secreted by the type II alveolar cells decreases surface tension, keeping the alveoli open.
• Lung compliance refers to how easy it is for the lungs to stretch or expand at a given transpulmonary pressure. Things that can decrease lung compliance are increasing alveolar surface tension (which makes the alveoli hard to inflate), limiting chest wall movement (broken ribs or weak muscles), or inhibiting lung movement within the thoracic cavity. Decreased lung compliance leads to decreased pulmonary ventilation.
How can measuring respiratory volumes and capacities help determine your patient’s respiratory disease status? In your answer, mention the difference between obstructive and restrictive respiratory diseases.
While respiratory volumes and capacities won’t diagnose a specific disease, they can be useful for evaluating loss of respiratory function and following the progression or recovery from a respiratory disease. Knowing which volumes or capacities are impaired or deviate from expected normal can help distinguish between obstructive pulmonary diseases or restrictive pulmonary diseases.
Obstructive pulmonary diseases are often diseases in which patients experience increased airway resistance. In obstructive disease, it’s harder to push air out of the lungs. Obstructive diseases include chronic bronchitis, emphysema, asthma and cystic fibrosis. Patients with obstructive disease might exhibit increased total lung capacity (TLC), increased functional residual capacity (FRC) and increased residual volume (RV). In other words, more air stays in the lungs because it’s hard to push out. The lungs might hyperinflate, but its harder to push air out.
Restrictive pulmonary diseases usually involve a decrease in total lung capacity. Examples of restrictive disease include tuberculosis, pneumonia or fibrosis where there is an increase in non-elastic tissue in the lungs, so its
harder to inflate the lungs. In these diseases, the vital capacity (VC), total lung capacity (TLC), functional residual capacity (FRC) and residual volume may decline (RV). In these diseases, its harder to to expand the lungs – in other words, there is a decrease in overall compliance.
What is the anatomical dead space and why is it important to consider when discussing respiratory efficiency?
The anatomical dead space is the volume of the conducting zone structures. It is important to consider when discussing respiratory efficacy because it means that not all of the air moved in the tidal volume participates in gas exchange. Approximately 150 mL of air moved during the tidal volume is within the anatomical dead space, which means that only 350 mL of air is actually participating in gas exchange. By taking the dead space into account when you consider pulmonary ventilation, you will have a better understanding of how much air is reaching the alveoli for gas exchange.
Define minute ventilation and alveolar ventilation. Explain how understanding the difference between minute and alveolar ventilation can help you predict which types of breathing patterns result in the most effective ventilation.
Minute ventilation is the ventilation rate (number of breaths per minute) times the tidal volume. Alveolar ventilation takes into account the anatomical dead space and is the ventilation rate times the tidal volume minus the anatomical dead space. The alveolar ventilation gives a better indication of the amount of fresh air that is flowing into the alveoli to participate in gas exchange. To get the most effective ventilation, you want to know how much fresh air is reaching the alveoli, and is not stuck in the dead space. Since the anatomical dead space is the same in a given individual, increasing the volume of breathing (i.e. deep breaths) enhances the flow of fresh air to the alveoli more than shallow, fast breathing. In shallow, fast breathing most of the inspired air never reaches the air spaces and is stuck in the dead space. In deep, slow breathing, a greater percentage of each inspired breath reaches the alveoli.
Which of the following correctly describes Boyles Law?
P1V1 =P2V2
Contraction of the muscles of inspiration most directly produces what change?
An increase in thoracic volume
In spirometry, what is the residual volume?
The air remaining in the lungs and alveoli
At which point in during pulmonary ventilation is transpulmonary pressure the greatest?
When the lungs are expanded the most
Which is the best definition of the anatomical dead space?
The volume of the conducting zone
How do Dalton’s law and Henry’s law relate to gas exchange?
Dalton’s law states that the total pressure of a mixture of gases is the sum of the pressures of the individual gases that make up that mixture, and the partial pressure of each gas within a mixture is proportional to the percentage of the gas in the mixture. The air that we breathe is made of a mixture of gases including the respiratory gases, oxygen and carbon dioxide. We can determine the partial pressure of oxygen and carbon dioxide in air based on the percentage they contribute to air.
Henry’s law states that when a gas is in contact with a liquid, the gas will dissolve in the liquid in proportion to its partial pressure and its solubility.
How these laws help us understand gas exchange: Dalton’s law helps us understand how oxygen and carbon dioxide will behave in a mixture of gases, and how their partial pressures are determined. Henry’s law helps us understand how oxygen and carbon dioxide will move from the air of the alveolus to the blood (dissolve) based on their pressure gradients and their relative solubility. Both oxygen and carbon dioxide will move by simple diffusion and move from an area of high partial pressure to an area of lower partial pressure until they reach equilibrium. This explains how oxygen will diffuse from the alveolus (air) to the blood and carbon dioxide will diffuse from the blood to the alveolus (air) in the lungs and oxygen will diffuse from the blood to the tissue cells and carbon dioxide will diffuse from the tissue cells to the blood in the systemic capillary beds.
What gases make up atmospheric air, and how does this differ from the alveolar air?
Atmospheric air is composed mostly of (in order of greatest percent contribution) nitrogen, oxygen, water, and carbon dioxide. About 99% of atmospheric air is composed of the combination of nitrogen and oxygen, and carbon dioxide contribute less than 1% together.
In alveolar air, the same gases contribute, but the partial pressures of water and carbon dioxide are much higher – because of the moisture added to air in the respiratory passageways, and because of the carbon dioxide produced by the cells during cellular respiration and eliminated in the alveoli (for exhalation).
Why is the partial pressure of oxygen and carbon dioxide in the atmosphere different from the partial pressures of the same gases in the alveoli?
There are three primary explanations for this mismatch. First, gas exchange is constantly occurring in the alveoli, such that oxygen is always diffusing out and carbon dioxide is always diffusing in. This is not an activity normally observed in the atmosphere at large. Second, humidification occurs along respiratory passageways. The
humidification allows for the development of water vapor pressure, which becomes part of the total gas mixture modulating the ratio of each gas partial pressure to the total pressure. Finally, gases mix in the respiratory passageways such that not all of the oxygen inspired enters the alveoli and not all of the carbon dioxide expired escapes the conducting system.
What are the three physiological variables that can affect external respiration? Briefly describe these variables
The variables that can affect the efficiency of external respiration or pulmonary gas exchange, include partial pressure gradients and gas solubility, thinness and surface area of the respiratory membrane, and ventilation- perfusion coupling.
The partial pressure gradients of oxygen and carbon dioxide dictate the direction of gas flow. In external respiration the partial pressure of oxygen is around 104 mm Hg in the alveoli and 40 mm Hg in the pulmonary capillary. Because of this pressure gradient, oxygen will diffuse from the alveolus (air) into the capillary (blood). The partial pressure of carbon dioxide in the alveolus is around 40 mm Hg and 45 mm Hg in the pulmonary capillary. This pressure gradient facilitates the diffusion of carbon dioxide from the capillary into the alveoli.
The respiratory membrane adds to the efficiency of pulmonary gas exchange due to its thinness and the large number of alveoli in the lungs (millions). Simple diffusion is most efficient over short distances and over a large surface area. Any disease that decreases the number of healthy alveoli (surface area available) such as emphysema, or increases the thickness of the respiratory membrane (fibrosis, pneumonia, scarring) will decrease the efficiency of gas exchange.
Ventilation-perfusion coupling is the process by which the ventilation of air into the alveoli is matched to the perfusion of blood through the surrounding pulmonary capillary. For optimal gas exchange, there must be a close match between the amount of gas reaching the alveoli (which we call ventilation), and the amount of blood flow through the pulmonary capillaries (we call perfusion). In other words, you want the blood supply to go to the areas of the lungs that are getting the best air flow to the healthiest alveoli, and you also want the best airflow to go to the areas of the lung that have the healthiest blood supply. This is regulated by PO2 and PCO2 levels.
Describe how the partial pressures of oxygen and carbon dioxide help regulate ventilation-perfusion coupling.
Both the bronchiole diameter (which determines air flow or ventilation) and arteriole diameter (which determines blood flow to the capillary beds) are controlled by local autoregulatory mechanisms that continuously respond to local conditions. The partial pressure of oxygen controls blood perfusion, where an increase in pressure increases perfusion and a decrease in pressure decreases perfusion. The partial pressure of carbon dioxide controls ventilation, where an increase in pressure increases ventilation and a decrease in pressure decreases ventilation.
If the ventilation (air flow) isn’t very good (could be due to blocked bronchioles, buildup of mucus), local O2 is low because the blood carries oxygen away faster than ventilation can replenish it. As a result local arterioles constrict, which redirects blood to capillary beds in other areas of the lung that are getting better airflow. If the air flow is good, the local levels of PO2 increases (fresh air). The high PO2 levels stimulate arteriole dilation, which increases blood flow to the capillary beds in this area with healthy alveoli.
Bronchioles change their behavior based on local CO2 levels. Bronchioles servicing areas where alveolar PCO2 levels are high will dilate, allowing CO2 to be eliminated from the body more quickly (this corresponds to areas that have good blood supply, so are bringing lots of CO2 for elimination). Bronchioles serving areas where CO2 is low will constrict (corresponds to low blood flow).
What are the partial pressure gradients for oxygen and carbon dioxide that facilitate external respiration?
External Respiration: In the lungs, during external respiration or pulmonary gas exchange, the PO2 of alveolar air is ~104 mm Hg, while the PO2 in the deoxygenated blood arriving at the pulmonary capillary beds is ~40 mm Hg. At the same time, the PCO2 in the blood arriving at the pulmonary capillary beds is ~45 mm Hg (high from the tissues), and is only 40 mm Hg in the alveolar air. These pressure gradients favor the diffusion of oxygen from the alveolus to the blood, and carbon dioxide from the blood to the alveolus. Oxygen will diffuse into the pulmonary capillary until the PO2 in the blood reaches equilibrium with the PO2 in the alveolar air (104 mm Hg), carbon dioxide will diffuse until the PCO2 in the blood reaches equilibrium with the PCO2 in the alveolar air (40 mm Hg)
What are the partial pressure gradients for oxygen and carbon dioxide that facilitate internal respiration?
Internal Respiration: In the tissues, during internal respiration or tissue gas exchange, the PO2 of the blood arriving at the systemic capillary beds is ~100 mm Hg (usually slightly less than at the lungs because of a slight mixing of deoxygenated venous blood added to the oxygenated blood traveling in the pulmonary veins back to the heart). The PO2 in the tissue cells is ~40 mm Hg (and can be even lower in active tissues) because the tissue cells are using oxygen in the process of cellular respiration to make ATP as fast as it arrives. There is a strong gradient for oxygen to move from the blood to the tissue cells. Oxygen will diffuse into the tissue cells until the PO2 of the blood leaving the capillary bed is the same as the PO2 of the tissue cells (at equilibrium = 40 mm Hg). At the same time, the tissue cells are producing CO2 as a waste product of cellular respiration. The PCO2 in the tissue cells is ~45 mm Hg, and is only 40 mm Hg in the blood arriving at the capillary bed. Carbon dioxide will diffuse from the tissues to the blood, until it reaches equilibrium (~45 mm Hg in the blood leaving the capillary bed).
How is oxygen transported in the blood? Why isn’t more transported directly dissolved in plasma?
About 98.5% of oxygen is transported bound to hemoglobin molecules. Each hemoglobin molecule is made up of 4 subunits, each of which has an iron-containing heme group that binds an oxygen molecule. Since there are 4 heme groups, each hemoglobin molecule can carry 4 oxygen molecules if it is fully saturated (100% saturated). Only 1.5% of oxygen is transported dissolved directly in the blood plasma because oxygen is poorly soluble in water (it has low solubility).
What is the relationship between oxygen and hemoglobin? In your answer explain what is meant by saturation.
Each hemoglobin molecule is made up of 4 polypeptide chain subunits, each of which has an iron-containing heme group that binds an oxygen molecule. Since there are 4 heme groups, each hemoglobin molecule can carry 4 oxygen molecules if it is fully saturated (100% saturated). If hemoglobin is partially saturated, 1, 2, or 3 O2 molecules are bound. If 1 oxygen is bound, hemoglobin is 25% saturated, if 2 are bound, hemoglobin is 50% saturated. If 3 oxgyen molecules are bound, hemoglobin is 75% saturated. The binding of oxygen to hemoglobin exhibits cooperativity. This means that after the first oxygen molecule binds to hemoglobin, the hemoglobin changes shape and increases its affinity for oxygen – so the 2nd, 3rd and 4th oxygen molecules bind more easily. The opposite happens when hemoglobin is unloading (releasing) oxygen. After the first oxygen molecule is released, the next oxygen is more easily released, and so on. The affinity (binding strength) of hemoglobin for oxygen changes with the extent of oxygen saturation, and both loading and unloading of oxygen are very efficient.
