Can you give examples of upper respiratory and lower respiratory infections? Answers might include the common cold, pharyngitis, and laryngitis as examples of upper respiratory infections; bronchitis and pneumonia are examples of lower respiratory infections.
The paranasal sinuses drain into the nasal cavities. Infected paranasal sinuses have increased and purulent drainage. The oropharynx and the laryngopharynx are part of both the digestive and respiratory systems. The pharynx also contains the opening to the tonsils and the eustachian tubes; the latter can be a pathway for otitis media. The thyroid cartilage (part B) is called the Adam’s apple and can be seen in swallowing. The cartilaginous rings of the trachea prevent its collapse, helping maintain an open airway.
Most importantly, these structures conduct air to the lower respiratory tract. As air is exhaled from the lower respiratory tract, it passes through the glottis, causing the true vocal cords to vibrate and produce sounds. The epiglottis is located just above the glottis so it can prevent food from entering respiratory tubes. Mouth and tongue positions form sounds. Sound quality is modulated by the sinuses, so people sound different with sinusitis. A boy’s voice changes at puberty because the vocal cords thicken and lengthen.
The alveoli form the terminal end of the respiratory tract. The purpose of the entire respiratory system is to move air to the alveoli so that gas exchange can occur with the capillaries. Cartilaginous rings around the trachea gradually disappear. They are no longer needed to keep the trachea patent; moreover, their thick structure makes them unsuited for gas exchange. A tracheoesophageal (TE) fistula is an opening between the trachea and esophagus found in some newborns. It must be corrected with surgery to prevent aspiration, severe respiratory distress, and death.
The right and left bronchi are created when the trachea splits at the carina. Each bronchus enters a lung. Touching the carina during suctioning causes vigorous coughing. Why is the left bronchus narrower and positioned more horizontally than the right bronchus? This is because of the heart’s location toward the left side of the chest. Small particles are more apt to lodge in the right brochus because it is more vertical.
Bronchiolar constriction (e.g., asthma) decreases the flow of air to the alveoli. Drugs called bronchodilators are helpful in relaxing the bronchioles and improving air flow. The name bronchiole should remind students of the name arteriole. Both structures are made of smooth muscle and regulate flow. The alveoli have very thin membranes and are located very close to the pulmonary capillaries. This short diffusion distance favors gas (O2 and CO2) exchange. The word emphysema means “puffed=up alveoli” and it results from difficulty in exhaling air.
There are so many alveoli that their collective surface area is about the size of a third of a tennis court. This favors gas exchange. Any condition that decreases the number of alveoli decreases gas exchange. O2 and CO2 move across the alveoli by diffusion. Atelectasis refers to collapsed and airless alveoli. Anything that blocks the movement of air into alveoli (e.g., mucus or a tumor) will cause atelectasis. Deep breathing by postoperative patients helps prevent this condition.
The lungs occupy most of the space in the thoracic cavity. The left lung has only two lobes because of the position of the heart within the mediastinum. Removal of a lung is called a pneumonectomy.
The intrapleural space is the space between the two pleural membranes; ask students to point it out. Negative pressure in the intrapleural space is crucial for keeping the lungs expanded.
To function properly, lungs need to be expanded. Therefore, negative intrapleural pressure must exceed the elastic recoil and surface tension.
Elastic recoil opposes lung expansion. The analogy of the balloon with the lung illustrates how elastic recoil makes the lung “want” to collapse.
A second force favoring the collapse of the lung is the high surface tension within the alveoli. Normally, surfactants decrease surface tension. Preterm infants may not secrete surfactant and so may have difficulty inflating their lungs. If a preterm birth seems imminent, the mother may be treated with steroids, which increase the production of surfactants. This treatment lowers surface tension and lessens the likelihood of breathing problems in a preterm infant. After birth, a pre-term infant with respiratory distress can also be given surfactants by inhalation.
The most important factor for lung expansion is a negative intrapleural pressure. The intrapleural pressure remains negative when no holes exist in the chest wall or the lung. The left and right intrapleural spaces are not in communication. As a result, a collapse of one lung fortunately does not cause a collapse of the second lung.
Anything that collects in the intrapleural space can collapse the lung. Examples include blood, air, and drainage. On the slide, panel B illustrates how a hole in the chest wall allows air to enter the intrapleural space, eliminating the negative intrapleural pressure and collapsing the lung. Panel C shows how pumping out the air restores negative intrapleural pressure. Panel D shows the expansion of the lung in response to restored negative intrapleural pressure. This is the reason for the use of chest tubes following thoracic surgery.
A knife wound eliminates negative intrapleural pressure, collapsing the lung. A hole in the lung (a ruptured bleb) can eliminate negative intrapleural pressure and collapse the lung. To maintain its negative pressure, the intrapleural space must be airtight, closed off from the inside of the lung and the room air. In these conditions, a chest tube and drainage will be used to restore negative intrapleural pressure.
Three steps move the respiratory gases to and from the lungs and tissues: ventilation, exchange, and transport. Ventilation moves air in and out of the lungs. Exchange moves O2 and CO2 into the blood and tissues. Transport involves the movement of O2 and CO2 by the blood. The next four slides will deal with ventilation and Boyle’s law.
Ventilation is dependent on Boyle’s law. The small and large tubes in the illustration are an analogy for the relationship between volume and pressure. Boyle’s law states that “As volume increases, pressure decreases; as volume decreases, pressure increases.” The finger touching the two tubes represents a measurement of pressure. When the tube is relatively firm, the pressure is high and when the tube is relatively soft, the pressure is lower.
Because of Boyle’s law, as thoracic volume increases, pressure within the lung decreases. The pressure decrease causes air to move through the nose and into the lungs. When the respiratory muscles contract, they increase thoracic volume. How does the boa constrictor suffocate its prey? It wraps its body around the victim’s chest, preventing an increase in thoracic volume; because inhalation is prevented, the prey dies.
Because of Boyle’s law, as thoracic volume decreases, pressure within the lung increases. The pressure increase causes air to move out of the lungs. When the respiratory muscles relax, they decrease thoracic volume.
The diaphragm’s contraction increases thoracic volume vertically. Contraction of the intercostal muscles increases thoracic volume front to back and side to side. Why does a high spinal cord injury (C2) prevent ventilation? This injury will affect the phrenic nerve, which is necessary for contraction of the diaphragm. Curare blocks the receptors (NM) for ACh in skeletal muscles. What effects would you expect? Effects include generalized paralysis, including paralysis of the muscles of respiration.
The top of the diagram shows the diffusion of air from an alveolus to a pulmonary capillary. The amount of O2 in the alveolus (PO2 = 104 mm Hg) is greater than the amount of O2 in the blue pulmonary capillary (PO2 = 40 mm Hg). As a result, O2 diffuses into the capillary, making it red. In a similar mechanism, CO2 diffuses from the pulmonary capillaries to the alveoli for exhalation. The bottom of the diagram illustrates gas exchange at the tissue. The diffusion of gases here follows a similar mechanism.
Why can severe anemia result in hypoxemia? With severe anemia, there is a deficiency of hemoglobin, and therefore diminished oxygen transport; this results in hypoxemia. Explain why CO causes hypoxemia but CO2 does not. CO binds with iron in hemoglobin and displaces oxygen from it. This causes hypoxemia. On the other hand, CO2 binds to an amino group on the globin chain and does not interfere with oxygen binding.
Have students demonstrate tidal volume at rest on the graph and predict it in exercise. Have them demonstrate inspiratory reserve volume. Have them demonstrate expiratory reserve volume.
Have students explain to a partner how to perform a vital capacity test. They should indicate that vital capacity involves three volumes: inspiratory reserve, tidal volume, and expiratory reserve. Why does vital capacity not equal total lung capacity? Residual volume is air that remains in the lungs at all times.
The medulla oblongata fires rhythmically and stimulates the phrenic and intercostal nerves; this action by the inspiratory neurons is the starting point for respiration. When the inspiratory neurons quiet down, the expiratory neurons fire, initiating exhalation. Opioids, such as morphine, depress respiratory function. They are never administered without checking for adequate respiration. The pons controls two centers that affect the rate of respiration. Chemoreceptors regulate the rate and depth of respiration. The primary regulator of respiration is PCO2.
Many factors can affect respiration, both voluntary and involuntary. Emotions are considered voluntary factors. A person may gasp in fear without thinking, but he or she can voluntarily control their breathing. The response of the chemoreceptors is involuntary The CNS chemoreceptors respond to PCO2 and H+. The peripheral chemoreceptors, the carotid and aortic bodies, respond primarily to H+. They only respond to PCO2 when those levels are severely depressed.
Why would a person with pulmonary edema display both dyspnea and orthopnea? Water accumulates within and around the alveoli, decreasing gas exchange. As a result, breathing is impaired (dyspnea).These patients are more comfortable sitting up because some of the fluid settles in the bottom on the lungs, thereby clearing the upper alveoli for better gas exchange.
Why does hyperventilation cause hypocapnia? The increased rate and depth of ventilation blows off excess CO2, lowering the level of CO2 in the blood (hypocapnia). Why does hypoventilation cause hypercapnia? The slowed rate and depth of respiration cause the retention of CO2, raising the level of CO2 in the blood (hypercapnia). Hypoventilation and CO2 retention cause respiratory acidosis; hyperventilation and excess CO2 excretion cause respiratory alkalosis. These mechanisms will be discussed in Chapter 25. Other respiratory terms are found in Table 22-2.
The Human Body in Health and
Illness, 4th edition