Shier, Butler, and Lewis:  Hole’s Human Anatomy and Physiology, 12th ed.    

Chapter 19:  Respiratory System

I.  Introduction

A.  The respiratory system consists of passages that filter incoming air and transport it to the body, into the lungs, and to the many microscopic air sacs where gases are exchanged.
B.  Respiration is the entire process of exchanging gases between the atmosphere and body cells.
C.  Respiration consists of ventilation, external respiration, transport of gases by the blood between lungs and body cells, internal respiration, and cellular respiration.
D.  Ventilation is the movement of air in and out of the lungs.
E.  External respiration is the exchange of gases between the air in the lungs and the blood.
F.  Internal respiration is the exchange of gases between the blood and the body cells.
G.  Cellular respiration is oxygen utilization and production of carbon dioxide in body cells.

II.  Why We Breathe

A.  Respiration enables cells to harness the energy held in chemical bonds of nutrient molecules.
B.  Without oxygen as a final electron acceptor, much energy remains locked in nutrients.
C.  A metabolic waste of respiration is carbon dioxide.
D.  Carbon dioxide, when it reacts with water, forms carbonic acid which contributes to the pH of blood.
E.  Too much carbon dioxide will lower blood pH.
F.  Cellular respiration and control of blood pH explain why we must obtain oxygen and get rid of carbon dioxide.

III.  Organs of the Respiratory System

A.  Introduction
1.  The upper respiratory tract includes nose, nasal cavity, sinuses, and pharynx.
2.  The lower respiratory tract includes larynx, trachea, bronchial tree, and lungs.
B.  Nose
1.  The nose is supported internally by muscle, bone, and cartilage.
2.  Nostrils are openings through which air can enter and leave the nasal cavity.
3.  Internal hairs of nostrils prevent entry of large particles carried in air.
C.  Nasal Cavity
1.  The nasal cavity is a hollow space behind the nose.
2.  The nasal septum is a structure that divides the nasal cavity into left and right halves.
3.  The nasal cavity is separated from the cranial cavity by the cribiform plate of the ethmoid bone and from the oral cavity by the hard palate.
4.  Nasal conchae are located on the lateral walls of the nasal cavity and divide the nasal cavity into superior, inferior, and middle meatuses.
5.  Nasal conchae function to support the mucous membranes that line the nasal cavity and to increase the surface area of the nasal cavity.
6.  The lining of the upper portion of the nasal cavity contains olfactory receptors.
7.  Most of the nasal cavity conducts air to and from the nasopharynx.
8.  The mucous membrane lining the nasal cavity contains pseudostratified ciliated epithelium that is rich in mucous-secreting goblet cells.
9.  The functions of the mucous membrane of the nasal cavity are to warm the air, to moisten the air, and to trap small particles entering the nasal cavity.
10.  Cilia of the nasal cavity function to move mucous and any entrapped particles toward the pharynx.
D.  Sinuses
1.  Sinuses are air-filled spaces located within the maxillary, frontal, ethmoid, and sphenoid bones of the skull.
2.  The functions of sinuses are to reduce the weight of the skull and to serve as resonant chambers that affect the quality of the voice.
E.  Pharynx
1.  The pharynx is located posterior to the oral cavity and between the nasal cavity and the larynx.
2.  Functions of the pharynx are to move food into the esophagus, to move air into the larynx, and to aid in the production of sound.
F.  Larynx
1.  The larynx is an enlargement in the airway superior to the trachea and inferior to the pharynx.
2.  The functions of the larynx are to move air into the trachea, prevent foreign objects from entering the trachea, and to house vocal cords.
3.  The larynx is composed of a framework of muscles and cartilages bound by elastic tissue.
4.  The cartilages of the larynx are thyroid, cricoid, and epiglottic.
5.  The thyroid cartilage is located just superior to the thyroid gland.
6.  The cricoid cartilage is located inferior to the thyroid cartilage.
7.  The epiglottic cartilage is located attached to the upper border of the thyroid cartilage.
8.  The epiglottis is flaplike structure supported by the epiglottic cartilage.
9.  The functions of the epiglottis are to prevent foods and liquids from entering the air passages and to allow air to pass into the trachea.
10.  The arytenoid cartilages are located superior to and on either side of the cricoid cartilage.
11.  The corniculate cartilages are attached to the tips of the arytenoid cartilages.
12.  The arytenoids and corniculate cartilages are attachments sites for muscles that help regulate tension on the vocal cords during speech and aid in closing the larynx during swallowing.
13.  The cuneiform cartilages are located between the epiglottic and arytenoid cartilages and function to stiffen soft tissue in this region.
14.  False vocal cords are located inside the larynx and are composed of muscle tissue and connective tissue with a covering of mucous membrane.
15.  The function of the false vocal cords is to help close the larynx during swallowing.
16.  The true vocal cords are located inferior to the false vocal cords and are composed of elastic fibers.
17.  The functions of the true vocal cords are to produce sounds of speech.
18.  A higher pitch of the voice is produced by increasing tension on true vocal cords and a lower pitch is produced by decreasing the tension on the cords.
19.  The loudness of a vocal sound depends on upon the force of air passing over the vocal cords.
20.  The glottis is the opening between vocal cords.
21.  The mucous membrane that lines the larynx continues to filter incoming air by entrapping particles and moving them toward the pharynx by ciliary action.
G.  Trachea
1.  The trachea is a flexible cylindrical tube and is located anterior to the esophagus in the thoracic cavity.
2.  The trachea splits into right and left bronchi.
3.  The inner wall of the trachea is lined with a ciliated mucous membrane that contains many goblet cells.
4.  The mucous membrane of the trachea functions to filter incoming air and to move entrapped particles upward into the pharynx where the mucous can be swallowed.
5.  The wall of the trachea is composed of C shaped pieces of hyaline cartilage, smooth muscle, and connective tissues.
6.  The cartilaginous rings of the trachea prevent the trachea from collapsing and blocking the airway.
7.  The soft tissues that complete the rings in the back of the trachea allow the esophagus to expand as food moves through it on the way to the stomach.
8.  A blocked trachea causes asphyxiation.
9.  A tracheostomy is the production of a temporary hole in the trachea.
H.  Bronchial Tree
1.  Introduction
a.  The bronchial tree consists of branched airways leading from the trachea to the microscopic air sacs in the lungs.
b.  Primary bronchi are the first branches of the trachea.
c.  The carina is a ridge of cartilage that separates the primary bronchi.
d.  Each bronchus, accompanied by blood vessels and nerves, enters its respective lung.
2.  Branches of the Bronchial Tree
a.  Primary bronchi branch into secondary bronchi.
b.  Secondary bronchi branch into tertiary bronchi.
c.  Tertiary bronchi branch into intralobular bronchioles.
d.  A bronchopulmonary segment is a portion of a lung supported by a tertiary segment.
e.  Intralobular bronchioles branch into terminal bronchioles.
f.  Terminal bronchioles branch into respiratory bronchioles.
g.  Respiratory bronchioles branch into alveolar ducts.
h.  Alveolar ducts give rise to alveolar sacs.
i.  Alveolar sacs are thin-walled, closely packed outpouchings of the alveolar ducts.
j.  Alveoli are thin-walled, microscopic air sacs that open to an alveolar sac.
3.  Structure of the Respiratory Tubes
a.  The structure of a bronchus is similar to that of the trachea except the C shaped cartilaginous rings are replaced with cartilaginous plates where the bronchus enters the lung.
b.  Finer branches of the respiratory tree have decreased amounts of cartilage and increased amounts of smooth muscle.
c.  Elastic fibers are scattered throughout the lungs.
d.  Other changes in the tubes of the respiratory tree as they get smaller are the changes in cells types that line the airways.
4.  Functions of the Respiratory Tubes and Alveoli
a.  The branches of the bronchial tree function to filter incoming air and distribute it to the alveoli in all parts of the lungs.
b.  The alveoli function to provide a large surface area of thin epithelial cells through which gas exchanges can occur.
I.  Lungs
1.  The lungs are cone shaped and located in the thoracic cavity.
2.  The right and left lungs are separated by the heart and the mediastinum and enclosed by the diaphragm and thoracic cage.
3.  Tubular structures enter the lung on its medial surface through a region called the hilum.
4.  Visceral pleura are serous membranes attached to the surfaces of the lungs.
5.  Parietal pleura are serous membranes that line the thoracic cavity.
6.  The pleural cavity is the potential space between the visceral pleura and parietal pleura.
7.  The functions of serous fluid in the pleural cavity are to lubricate serous membranes, reduce friction during lung movements, and hold pleural membranes together.
8.  The lobes of the right lung are superior, middle, and inferior.
9.  The lobes of the left lung are superior and inferior.
10.  Lobules of the lungs are divisions of lung lobes.

IV.  Breathing Mechanism

A.  Introduction
1.  Breathing or ventilation is the movement of air from outside the body into the bronchial tree and alveoli, followed by a reversal of this air movement.
2.  Inspiration is inhalation.
3.  Expiration is exhalation.
B.  Inspiration
1.  The force that moves air into the lungs is atmospheric pressure.
2.  If the pressure inside the lungs and alveoli decreases, outside air will flow into the airways.
3.  The diaphragm is located just inferior to the lungs and is composed of skeletal muscle.
4.  The nerves that stimulate the diaphragm are the phrenic nerves.
5.  When the diaphragm contracts it moves inferiorly and the thoracic cavity enlarges.
6.  When the thoracic cavity enlarges, the intra-alveolar pressure decreases.
7.  The action of external intercostal muscles is to raise the ribs and elevate the sternum, which increases the size of the thoracic cavity.
8.  When intra-alveolar pressure falls, air is moved into the airways.
9.  When intercostal muscles move the thoracic wall upward and outward, the parietal pleura and visceral pleura move.
10.  Movement of the parietal and visceral pleura upward and outward expands the lungs in all directions.
11.  Surface tension is the attraction of certain molecules to each other.
12.  Surfactant is located in alveolar spaces and functions to reduce the alveoli’s tendency to collapse.
13. If a person needs to take a deeper than normal breath, the diaphragm and external intercostal muscles may contract to a greater extent.
14.  Other muscles that can be used to enlarge the thoracic cavity are the pectoralis minors and sternocleidomastoids.
15.  Compliance is the ease at which the lungs can expand as a result of pressure changes occurring during breathing.
16.  In a normal lung, compliance decreases as lung volume increases because an inflated lung is more difficult to expand that a lung at rest.
17.  Factors that lead to a decrease in lung compliance are conditions that obstruct air passages, destroy lung tissue, or impede lung expansion in other ways.
C.  Expiration
1.  The forces responsible for normal expiration come from elastic recoil of lung tissues and from surface tension.
2.  As the diaphragm and external intercostals muscles relax, the elastic tissues cause the lungs to recoil.
3.  Air is forced out of respiratory passageways because intra-alveolar pressure rises above atmospheric pressure.
4.  Muscles that aid in a more forceful exhalation than normal are internal intercostal muscles and abdominal wall muscles.
D.  Respiratory Volumes and Capacities
1.  Spirometry is the measure of air volumes.
2.  A respiratory cycle is one inspiration plus the following expiration.
3.  Tidal volume is the amount of air that enters of leaves during a respiratory cycle.
4.  Inspiratory reserve volume is the additional quantity of air, after the resting tidal volume that can enter the lungs.
5.  Expiratory reserve volume is the additional quantity of air that can exit the lungs after a resting tidal volume.
6.  Residual volume is the amount of air that remains in the lungs after a forceful expiration.
7.  Vital capacity is the maximum amount of air that can be exhaled after taking the deepest breath possible.
8.  Inspiratory capacity is the maximum volume of air that can be inhaled following exhalation of tidal volume.
9.  Functional residual capacity is volume of air that remains in the lungs following exhalation of tidal volume.
10.  Total lung capacity is total volume of air that the lungs can hold.
11.  Anatomic dead space is the space in airways.
12.  Alveolar dead space is space in alveoli that do not carry out gas exchange due to poor blood flow.
13.  Physiologic dead space is anatomical dead space plus alveolar dead space.
14.  A spirometer measures respiratory air volumes.
15.  Respiratory volumes and capacities are used to evaluate the course of respiratory illnesses.
E.  Alveolar Ventilation
1.  Minute ventilation is the amount of new atmospheric air that is moved into the respiratory passages each minute and equals the tidal volume multiplied by the breathing rate.
2.  The volume of air that reaches alveoli is calculated by subtracting the physiologic dead space from the tidal volume.
3.  Alveolar ventilation rate is the volume of air that reaches alveoli multiplied by breathing rate and is a major factor affecting the concentrations of oxygen and carbon dioxide in alveoli.
F.  Nonrespiratory Air Movements
1.  Nonrespiratory air movements are air movements that occur in addition to breathing.
2.  Examples of nonrespiratory air movements are coughing, sneezing, crying, and laughing.
3.  Nonrespiratory air movements usually result from reflexes.
4.  Coughing involves taking a deep breath, closing the glottis, and forcing air upward from the lungs against the closure.  Then the glottis is suddenly opened, and a blast of air is forced upward from the lower respiratory tract.
5.  The function of a sneeze is to clear the upper respiratory passages.
6.  Laughing involves taking a deep breath and releasing it in a series of short expirations.
7.  A hiccup is caused by sudden inspiration due to a spasmodic contraction of the diaphragm while the glottis is closed.
8.  The function of a yawn may be rooted in primitive brainstem mechanisms that maintain alertness.

V.  Control of Breathing

A.  Respiratory Center
1.  The respiratory center is composed of groups of neurons in the brainstem which controls breathing.
2.  The functions of the respiratory center are to cause inhalation and exhalation, and to adjust the rate and depth of breathing.
3.  The components for the respiratory center are located widely scattered throughout the pons and medulla oblongata.
4.  The medullary rhythmicity area includes two groups of neurons that extend throughout the length of the medulla oblongata.
5.  The dorsal respiratory group is important in stimulating the muscles of inspiration.
6.  The ventral respiratory group is comprised of neurons that control other respiratory muscles.
7.  Neurons of the pneumotaxic and apneustic center work together to inhibit inspiratory commands for the medulla and may contribute to the basic rhythm of breathing.
B.  Factors Affecting Breathing
1.  Partial pressure of a gas is amount of pressure each gas contributes.
2.  Changes in blood pH are detected by central chemoreceptors.
3.  When carbon dioxide diffuses into the brain, it combines with water to form carbonic acid.
4.  High concentrations of hydrogen ions in blood or cerebrospinal fluid are detected by central chemoreceptors.
5.  In response to high hydrogen ion levels, the respiratory center triggers an increase in alveolar ventilation, which decreases hydrogen ions in blood.
6.  Low concentrations of oxygen in blood are detected by peripheral chemoreceptors.
7.  When blood levels of oxygen are low, ventilation increases and the concentration of oxygen in blood increases.
8.  The inflation reflex helps regulate the depth of breathing.
9.  The inflation reflex occurs when stretch receptors in the visceral pleura, bronchioles, and alveoli are stimulated as lung tissues are stretched.
10.  The inflation reflex prevents overinflation of the lungs.
11.  Hyperventilation is rapid and deep breathing, and it lowers the blood concentration of carbon dioxide.

VI.  Alveolar Gas Exchanges

A.  Alveoli
1.  Alveoli are microscopic air sacs clustered at the distal ends of the finest respiratory tubes.
2.  An alveolus consists of a tiny space surrounded by a thin wall that separates it from adjacent alveoli.
3.  Alveolar pores are tiny openings in the walls of some alveoli.
4.  Alveolar macrophages are phagocytic cells and function to destroy airborne agents that reach alveoli.
B.  Respiratory Membrane
1.  The respiratory membrane is composed of two layers of epithelial cells and two basement membranes.
2.  The respiratory membrane is the site of gas exchange between alveolar air and the blood.
C.  Diffusion Through the Respiratory Membrane
1.  Molecules diffuse from regions where they are in higher concentration toward regions where they are in lower concentration.
2.  Carbon dioxide diffuses from blood in pulmonary capillaries to alveolar air because the partial pressure of carbon dioxide is higher in the blood of pulmonary capillaries than in alveolar air.
3.  Oxygen diffuses from alveolar air to blood in pulmonary capillaries because the partial pressure of oxygen is higher in alveolar air than in the blood of pulmonary capillaries.
4.   Factors that affect diffusion across the respiratory membrane are surface area, distance, solubility of gases, partial pressure gradients, and diseases.
5.  Diseases that harm respiratory membranes are pneumonia and emphysema.
6.  Breath analysis can detect alcohol in the blood because the respiratory membrane is so thin that alcohol can diffuse into alveolar air and be exhaled.
VII.  Gas Transport
A.  Introduction
1.  The blood transports oxygen and carbon dioxide between the lungs and the body cells.
2.  As oxygen and carbon dioxide enter blood, they dissolve in plasma or combine chemically with other atoms or molecules.
B.  Oxygen Transport
1.  Almost all the oxygen carried in blood is bound to hemoglobin.
2.  A small amount of oxygen is carried in blood dissolved in plasma.
3.  Hemoglobin consists of two types of components called heme and globin.
4.  Each heme group contains an atom of iron.
5.  Oxyhemoglobin is the combination of oxygen and hemoglobin.
6.  Factors that promote the release of oxygen from hemoglobin are a decrease in the partial pressure of oxygen, increasing blood concentrations of carbon dioxide, acidity, and increased temperatures.
C.  Carbon Dioxide Transport
1.  Blood flowing through capillaries gain carbon dioxide because the tissues have a high partial pressure of carbon dioxide.
2.  Carbon dioxide is transported to lungs in one of the following three forms:  bound to hemoglobin, dissolved in plasma, or as bicarbonate ions.
3.  Hemoglobin can carry oxygen and carbon dioxide at the same time because they bind at different sites on hemoglobin.
4.  Carbaminohemoglobin is the combination of carbon dioxide and hemoglobin.
5.  The most important carbon dioxide transport mechanism involves the formation of bicarbonate ions.
6.  Carbon dioxide forms carbonic acid when it reacts with water.
7.  Carbonic anhydrase is an enzyme that speeds up the reaction between carbon dioxide and water and is located inside red blood cells.
8.  Carbonic acid dissociates into hydrogen ions and bicarbonate ions.
9.  The chloride shift is the exchange of chloride ions and bicarbonate ions across the red blood cell membrane and functions to maintain the ionic balance between the red blood cells and the plasma.
10.  When blood reaches the pulmonary capillaries, hydrogen ions and bicarbonate ions recombine to form carbonic acid.
11. In the pulmonary capillaries, carbonic acid becomes carbon dioxide and water.
12.  In the lungs, carbon dioxide diffuses out of the blood until equilibrium is established between the partial pressure of carbon dioxide of the blood and that of the alveolar air.
VIII.  Life-Span Changes
A.  Changes in the respiratory system over a lifetime reflect both the accumulation of environmental influences and the effects of aging in other organ systems.
B.  People who have been exposed to foul air are more likely to develop chronic bronchitis, emphysema, or lung cancer.
C.  The factors that change the ability of the respiratory system to clear pathogens from the lungs are a decrease in activity of the cilia, thickening of mucus, and the slowing of swallowing, gagging, and coughing reflexes.
D.  Factors that contribute to an overall increase in effort required to breathe are calcification of cartilage between the sternum and ribs and changes in skeletal structure of the thoracic cavity.
E.  The microscopic changes that occur in the lungs are expansion of alveolar walls, an increase in the amount of collagen, and a decreased amount of elastin.