Respiratory System PDF

ANATOMY AND PHYSIOLOGY CHAPTER X. THE RESPIRATORY SYSTEM The respiratory system plays an important role in maintaining homeostasis. It maintains the optimum level of oxygen in our body which is very important in all bodily processes because it is needed for the me...

ANATOMY AND PHYSIOLOGY CHAPTER X. THE RESPIRATORY SYSTEM The respiratory system plays an important role in maintaining homeostasis. It maintains the optimum level of oxygen in our body which is very important in all bodily processes because it is needed for the metabolic reactions that generate adenosine triphosphate (ATP). Together with the cardiovascular system, it helps supply the needed oxygen to all parts of the body. However, unlike the cardiovascular system, the respiratory system is an open system which means it is exposed to the external environment. The good thing is, the different organs and systems of the body is made exactly for its purpose. As you go on with the discussion in this module regarding the respiratory system, you will find out how the respiratory system defends itself from the influences of the external environment. LESSON 1. OVERVIEW OF THE RESPIRATORY SYSTEM INTRODUCTION OF THE LESSON AND PRESENTATION OF OUTCOMES You may already have an idea on how important the respiratory system is. For you to be able to understand the intricate details on the vitality of the respiratory system, it is best that you should learn its structures. After studying the lesson, you must have: 1. discussed the steps that occur during respiration 2. defined the respiratory system 3. explained how the respiratory organs are classified structurally and functionally. WARM-UP ACTIVITY Growing up you have probably experienced respiratory infections. Remember what was mentioned earlier in this module that unlike the cardiovascular system which is a close system, the respiratory system is an open system. Reflect on that statement and present your insights using your prior knowledge and even experiences in less than 10 sentences. Post your responses in the discussion forum provided for this purpose using your MVLE portals.  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM PRESENTATION OF LEARNING INPUTS Primary Functions of the Respiratory System The respiratory system’s main function is gas exchange. When we say gas exchange it is not only the process of taking in oxygen from the environment and giving out carbon dioxide but it also involves the diffusion of oxygen from the lungs into the blood vessels in exchange of carbon dioxide for excretion. While maintaining the levels of oxygen and carbon dioxide in the body, the respiratory system also helps in maintaining acid-base balance. If there is an increase in carbon dioxide level in the blood, the respiratory system works with the nervous system by increasing the rate of respiration so that carbon dioxide will be eliminated. This prevents the accumulation of carbonic acid which makes the blood acidic which means that the cells and tissues of our body will not be able to function properly because of the decrease in blood pH. And while the respiratory system is performing both of the above functions, it is also responsible for looking out for itself. Remember that the respiratory system is an open system which means it is exposed to insults form the external environment that includes irritants and microorganisms. The respiratory system has its defense mechanisms to ward of irritants and microorganisms. It filters the air that enters the lungs so that problems will not arise in the lower respiratory tract which could impair its primary function which is gas exchange. Other functions of the respiratory system include containing receptors for sense of smell, production of vocal sounds also known as phonation and excretion of small amount of water and heat. Steps Involved in Respiration After knowing the primary function of the respiratory system, it is time to know how it performs its function. Respiration is the process of supplying the body with oxygen and eliminating carbon dioxide. It involves three steps as follows: Pulmonary ventilation is the inflow of oxygen and the outflow of carbon dioxide. This step is simply called breathing. So this involves the exchange of gases between the alveoili of the lungs and the atmosphere. The main goal in this step is to take in oxygen and eliminate carbon dioxide. External (pulmonary) respiration on the other hand involves the alveoli and the capillaries of the pulmonary circulation. It involves the diffusion of oxygen from the alveoli into the pulmonary capillaries while carbon dioxide diffuses form the pulmonary capillaries into the alveoli for excretion. Internal (tissue) respiration is the last step which involves the body tissues and the capillaries. In this step the blood losses its oxygen by giving it off to the tissues in exchange of carbon dioxide which is one of the byproduct of cellular metabolism. This process is also known as cellular respiration. Mariano Marcos State University College of Health Sciences Department of Nursing 2  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM WRAP-UP ACTIVITY Reflect on our current situation today, since COVID-19 is a disease that affects the respiratory and knowing that the respiratory system is in constant exposure to the environment, how can you protect your respiratory system? ASSESSMENT (POST-ASSESSMENT) A 20-item quiz will be administered to you via MVLE. You are required to get 60% of the items to pass the exam. REFERENCES Marieb, E. (2014). Essentials of Human anatomy and physiology (11th ed.). Pearson Education South Asia. Tortora, G., & Derrickson. B. (2014). Principles of anatomy and physiology (14th ed.). John Wiley & Sons, Inc. LESSON 2. COMPONENTS OF THE RESPIRATORY SYSTEM INTRODUCTION OF THE LESSON AND PRESENTATION OF OUTCOMES After learning the basic function of the respiratory system and how respiration occurs, go ahead and proceed with studying the structures of the respiratory system. It is time for you to learn the anatomy of the respiratory system. After studying the lesson, you must have: 1. described the anatomy of the respiratory system 2. identified the functions of the structures of the respiratory system Mariano Marcos State University College of Health Sciences Department of Nursing 3  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM WARM-UP ACTIVITY Solve the crossword puzzle then take a screenshot and upload it on the discussion forum in the MVLE. 8 4 2 9 10 3 1 6 5 7 1. The three mucosa-covered projections into the nasal cavity that greatly increase surface area of mucosa exposed to air are called __________. 2. The mucosa-lined windpipe that extends from the larynx to the level of the fifth thoracic vertebra is called the __________. 3. Clusters of lymphatic tissue in the pharynx are referred to as __________. 4. The opening between the vocal folds is called the __________. 5. The C-shaped rings that reinforce the trachea are constructed of __________ cartilage. 6. The serous membrane that surrounds each lung is created by a parietal and visceral __________. 7. The division of the trachea produces two tubes called the right and left main (primary) __________. 8. "Dust cells" that wander in and out of the alveoli, picking up bacteria, carbon particles, and other debris, are actually __________. 9. The primary muscle for respiration is the ___________. 10. Inadequate oxygen delivery to body tissues is called __________. PRESENTATION OF LEARNING INPUTS The respiratory system can be classified according to its structure or function. When talking about the structural classification of the respiratory system, this includes the upper respiratory system and the lower respiratory system. On the other hand, when we talk of the functional classification of the respiratory system, this includes the conducting zone and respiratory zone. You will learn more of these components of the respiratory system as you go on with this lesson. Mariano Marcos State University College of Health Sciences Department of Nursing 4  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM The Upper Respiratory System The upper respiratory system is one of the structural classification of the respiratory system. The components of the upper respiratory system includes the nose, pharynx, larynx, trachea, bronchi and lungs. To illustrate structures of the upper respiratory system refer to figure 1. Figure 1 Structures of the Upper Respiratory System Source: Marieb, E. (2014). Essentials of Human anatomy and physiology (10th ed.). Pearson Education South Asia. Nose. The nose is a specialized organ which serves as the entrance air into the respiratory system. It is comprised of the external nose and the internal nose. The external nose is the only visible part of the respiratory system. It consist of supporting framework of bones which includes the frontal and nasal bones as well as the maxillae. Aside from the bony framework, the external nose also consist of a hyaline cartilage which is covered by muscle and skin. The cartilaginous framework of the nose include the septal nasal cartilage which forms the anterior portion of the nasal septum, the lateral nasal cartilages which is inferior to the nasal bones and the alar cartilages which form a portion of the nostrils which is the opening of the nose also known as the external nares. The nostrils will lead to a cavity known as the nasal vestibule. Just inside the nostrils are hairs, which help block the entry of dust. The two nasal cavities are within the skull, separated by the nasal septum, which is a bony plate made of the ethmoid bone and vomer. The nasal mucosa(lining) is ciliated epithelium, with goblet cells that produce mucus. Three shelf-like or scroll-like bones called conchae project from the lateral wall of each nasal cavity. Just as shelves in a Mariano Marcos State University College of Health Sciences Department of Nursing 5  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM cabinet provide more flat space for storage, the conchae increase the surface area of the nasal mucosa. As air passes through the nasal cavities it is warmed and humidified, so that air that reaches the lungs is warm and moist. Bacteria and particles of air pollution are trapped on the mucus; the cilia continuously sweep the mucus toward the pharynx. Most of this mucus is eventually swallowed, and most bacteria present will be destroyed by the hydrochloric acid in the gastric juice. In the upper nasal cavities are the olfactory receptors, which detect vaporized chemicals that have been inhaled. The olfactory nerves pass through the ethmoid bone to the brain. You may also recall our earlier discussion of the paranasal sinuses, air cavities in the maxillae, frontal, sphenoid, and ethmoid bones. These sinuses are lined with ciliated epithelium, and the mucus produced drains into the nasal cavities. The functions of the paranasal sinuses are to lighten thes kull and provide resonance (more vibrating air) for the voice. Figure 2 Detailed anatomy of the upper respiratory tract. Source: Marieb, E. (2014). Essentials of Human anatomy and physiology (10th ed.). Pearson Education South Asia. Pharynx. The pharynx is a muscular tube posterior to the nasal and oral cavities and anterior to the cervical vertebrae. For descriptive purposes, the pharynx may be divided into three parts: the nasopharynx, oropharynx, and laryngopharynx. The uppermost portion is the nasopharynx, which is behind the nasal cavities. The soft palate is elevated during swallowing to block the nasopharynx and prevent food or saliva from going up rather than down. The uvula is the part of the soft palate you can see at the back of the throat. On the posterior wall of the nasopharynx is the adenoid or pharyngeal tonsil, a lymph nodule that contains macrophages. Opening into the nasopharynx are the two eustachian tubes, which extend to the middle ear cavities. The purpose of the eustachian tubes is to permit air to enter or leave the middle ears, allowing the eardrums to vibrate properly. The nasopharynx Mariano Marcos State University College of Health Sciences Department of Nursing 6  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM is a passageway for air only, but the remainder of the pharynx serves as both an air and food passageway, although not for both at the same time. The oropharynx is behind the mouth; its mucosa is stratified squamous epithelium, continuous with that of the oral cavity. On its lateral walls are the palatine tonsils, also lymph nodules. Together with the adenoid and the lingual tonsils on the base of the tongue, they form a ring of lymphatic tissue around the pharynx to destroy pathogens that penetrate the mucosa. The laryngopharynx is the inferior portion of the pharynx. It opens anteriorly into the larynx and posteriorly into the esophagus. Contraction of the muscular wall of the oropharynx and laryngopharynx is part of the swallowing reflex. Figure 3 Regions of the Pharynx Source: Marieb, E. (2014). Essentials of Human anatomy and physiology (10th ed.). Pearson Education South Asia The Lower Respiratory System The lower respiratory system is comprised of the larynx, trachea, bronchi and the lungs. Larynx. The larynx is often called the voice box, a name that indicates one of its functions, which is speaking. The other function of the larynx is to be an air passageway between the pharynx and the trachea. Air passages must be kept open at all times, and so the larynx is made of nine pieces of cartilage connected by ligaments. Cartilage is a firm yet flexible tissue that prevents collapse of the larynx. In comparison, the esophagus is a collapsed tube except when food is passing through it. The largest cartilage of the larynx is the thyroid cartilage, which you can feel on the anterior surface of your neck. The epiglottis is the upper-most cartilage. During swallowing, the larynx is elevated, and the epiglottis Mariano Marcos State University College of Health Sciences Department of Nursing 7  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM closes over the top, rather like a trap door or hinged lid, to prevent the entry of saliva or food into the larynx. The mucosa of the larynx is ciliated epithelium, except for the vocal cords (stratified squamous epithelium). The cilia of the mucosa sweep upward to remove mucus and trapped dust and microorganisms. The vocal cords (or vocal folds) are on either side of the glottis, the opening between them. During breathing, the vocal cords are held at the sides of the glottis, so that air passes freely into and out of the trachea. During speaking, the intrinsic muscles of the larynx pull the vocal cords across the glottis, and exhaled air vibrates the vocal cords to produce sounds that can be turned into speech. It is also physically possible to speak while inhaling, but this is not what we are used to. The cranial nerves that are motor nerves to the larynx for speaking are the vagus and accessory nerves. Trachea and Bronchial Tree. The trachea is about 4 to 5 inches (10 to 13 cm) long and extends from the larynx to the primary bronchi. The wall of the trachea contains 16 to 20 C- shaped pieces of cartilage, which keep the trachea open. The gaps in these incomplete cartilage rings are posterior, to permit the expansion of the esophagus when food is swallowed. The mucosa of the trachea is ciliated epithelium with goblet cells. As in the larynx, the cilia sweep upward toward the pharynx. The right and left primary bronchi are the branches of the trachea that enter the lungs. Their structure is just like that of the trachea, with C-shaped cartilages and ciliated epithelium. Within the lungs, each primary bronchus branches into secondary bronchi leading to the lobes of each lung (three right, two left). The further branching of the bronchial tubes is often called the bronchial tree. Imagine the trachea as the trunk of an upside-down tree with extensive branches that become smaller and smaller; these smaller branches are the bronchioles. No cartilage is present in the walls of the bronchioles; this becomes clinically important in asthma. The smallest bronchioles terminate in clusters of alveoli, the air sacs of the lungs. Figure 4 Cross sectional view of the trachea and surrounding structures Source: Marieb, E. (2014). Essentials of Human anatomy and physiology (10th ed.). Pearson Education South Asia Lungs and Pleural Membranes. The lungs are located on either side of the heart in the chest cavity and are encircled and protected by the rib cage. The base of each lung rests on the diaphragm below; the apex (superior tip) is at the level of the clavicle. On the medial Mariano Marcos State University College of Health Sciences Department of Nursing 8  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM surface of each lung is an indentation called the hilus, where the primary bronchus and the pulmonary artery and veins enter the lung. The pleural membranes are the serous membranes of the thoracic cavity. The parietal pleura lines the chest wall, and the visceral pleura is on the surface of the lungs. Between the pleural membranes is serous fluid, which prevents friction and keeps the two mem-branes together during breathing. Figure 5 Anterior view of the lungs flank mediastinal structures laterally. Source: Marieb, E. (2014). Essentials of Human anatomy and physiology (10th ed.). Pearson Education South Asia Mariano Marcos State University College of Health Sciences Department of Nursing 9  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM Figure 6 Transverse section through the thorax, viewed from above. Lungs, pleural membranes, and major organs in the mediastinum are shown. Source: Marieb, E. (2014). Essentials of Human anatomy and physiology (10th ed.). Pearson Education South Asia Alveoli. The functional units of the lungs are the air sacs called alveoli. The flat alveolar type I cells that form most of the alveolar walls are simple squamous epithelium. In the spaces between clusters of alveoli is elastic connective tissue, which is important for exhalation. Within the alveoli are macrophages that phagocytize pathogens or other foreign material that may not have been swept out by the ciliated epithelium of the bronchial tree. There are millions of alveoli in each lung, and their total surface area is estimated to be 700 to 800 square feet (picture a sidewalk two and a half feet wide that is as long as an American football field, or a rectangle 25 feet by 30 feet). Each alveolus is surrounded by a network of pulmonary capillaries. Recall that capillaries are also made of simple squamous epithelium, so there are only two cells between the air in the alveoli and the blood in the pulmonary capillaries, which permits efficient diffusion of gases. Each alveolus is lined with a thin layer of tissue fluid, which is essential for the diffusion of gases, be-cause a gas must dissolve in a liquid in order to enter or leave a cell (the earthworm principle an earthworm breathes through its moist skin, and will suffocate if its skin dries out). Although this tissue fluid is necessary, it creates a potential problem in that it would make the walls of an alveolus stick together internally. Imagine a plastic bag that is wet inside; its walls would stick together because of the surface tension of the water. This is just what would happen in alveoli, and inflation would be very difficult.This problem is overcome by pulmonary surfactant, a lipoprotein secreted by alveolar type II cells, also called septal cells. Surfactant mixes with the tissue fluid within the alveoli and decreases its surface tension, permitting inflation of the alveoli. Normal inflation of the alveoli in turn permits the exchange of gases, but before we discuss this process, we will first see how air gets into and out of the lungs. Mariano Marcos State University College of Health Sciences Department of Nursing 10  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM Figure 7 Diagrammatic view of respiratory bronchioles, alveolar ducts, and alveoli Source: Marieb, E. (2014). Essentials of Human anatomy and physiology (10th ed.). Pearson Education South Asia CENTRAL ACTIVITIES Activity 1 True/False 1) The ciliated cells of the nasal mucosa propel contaminated mucus posteriorly toward the pharynx. Answer: 2) The nasal cavity is separated from the oral cavity by the nasal conchae. Answer: 3) There are only three paranasal sinuses located in the frontal, sphenoid, and parietal bones. Answer: 4) The portion of the pharynx continuous with the mouth is termed the oropharynx. Answer: 5) The tonsils are located in the larynx. Answer: Mariano Marcos State University College of Health Sciences Department of Nursing 11  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM 6) The larynx routes air and food into their proper channel and plays an important role in speech production. Answer: 7) The "guardian of the airways" that prevents food from entering the superior opening of the larynx is the thyroid cartilage. Answer: 8) The function of the C-rings of hyaline cartilage in the trachea is to keep the airway patent or open for breathing. Answer: 9) Each main (primary) bronchus enters the lung at the apex. Answer: 10) The bronchioles are the smallest of the conducting passageways in the lungs. Answer: Activity 2 Match the following structure with its description: A) surfactant 1) Passageway for both food and air; known B) mucous as the "throat" C) nasal conchae 2) Rigid, patent airway reinforced with C- D) bronchioles rings of hyaline cartilage E) larynx 3) Routes air and food into their proper F) diaphragm channels G) trachea 4) Protects the superior opening of the H) pleura larynx during swallowing I) epiglottis 5) Serous membranes surrounding the J) mucus lungs K) main (primary) bronchi 6) Lipid (fat) molecule produced by the L) glottis alveoli to prevent alveoli collapse M) alveoli 7) Smallest conducting passageways in the N) pharynx lungs 8) Part of the respiratory zone, these air sacs are the sites of gas exchange WRAP-UP ACTIVITY Essay question: Explain the roles of mucus and cilia in the respiratory system. Mariano Marcos State University College of Health Sciences Department of Nursing 12  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM ASSESSMENT (POST-ASSESSMENT) A 20-item quiz will be administered to you via MVLE. You are required to get 60% of the items to pass the exam. REFERENCES Marieb, E. (2014). Essentials of Human anatomy and physiology (11th ed.). Pearson Education South Asia. Scanlon, V. C., Sanders, T. (2019). Essentials of anatomy and physiology. Philadelphia, PA: F. A. Davis Company. Tortora, G., & Derrickson. B. (2014). Principles of anatomy and physiology (14th ed.). John Wiley & Sons, Inc. Mariano Marcos State University College of Health Sciences Department of Nursing 13  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM LESSON 3. MECHANISM OF BREATHING INTRODUCTION OF THE LESSON AND PRESENTATION OF OUTCOMES As a future nurse, it is important that we recognize abnormalities of breathing in a patient. Ineffective breathing pattern is one of the priority problems often encountered by a professional nurse therefore, it is important that as future nurses, you should be able to describe the mechanism of breathing. After studying the lesson, you must have: 1. explained the mechanism of breathing 2. identified the three types of pressure necessary in breathing WARM-UP ACTIVITY Word Hunt. Find the 6 terms that are related to the next lesson. If you are patient enough you might find my secret message too. G R I N H A L A T I O N H D S Q F O O F N Y T P Q T Q Y U J G F A W G P D E T T V O S M A T J K F G Q E H L L E R R E I A O A H M L D H W X J K O R A E N U D S Z N I M S J E H K J V R P W T Y F P W B K N A K R A L H E F L Q I T G H S G K B Q L T L M G S G E D L P V E Z Y V U W K Y A N F Y D U S A R H R X T O V E O U T B D O W R D T E J I C V L C R I I I V S U E A H I W K C E F O X T U I O C A D R L Z O I N T R A P U L M O N I C C F K L N Q L C D R P Z Y Y O P X Z Mariano Marcos State University College of Health Sciences Department of Nursing 14  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM PRESENTATION OF LEARNING INPUTS Ventilation is the term for the movement of air to and from the alveoli. The two aspects of ventilation are inhalation and exhalation, which are brought about by the nervous system and the respiratory muscles. The respiratory centers are located in the medulla and pons. Their specific functions will be covered in a later section, but it is the medulla that generates impulses to the respiratory muscles. These muscles are the diaphragm and the external and internal intercostal muscles. The diaphragm is a dome-shaped muscle below the lungs; when it contracts, the diaphragm flattens and moves downward. The intercostal muscles are found between the ribs. The external intercostal muscles pull the ribs upward and outward, and the internal inter-costal muscles pull the ribs downward and inward. Ventilation is the result of the respiratory muscles producing changes in the pressure within the alveoli and bronchial tree. With respect to breathing, three types of pressure are important: 1. Atmospheric pressure—the pressure of the air around us. At sea level, atmospheric pressure is 760 mmHg. At higher altitudes, of course, atmospheric pressure is lower. 2. Intrapleural pressure—the pressure within the potential pleural space between the parietal pleura and visceral pleura. This is a potential rather than areal space. A thin layer of serous fluid causes the two pleural membranes to adhere to one another. Intrapleural pressure is always slightly below atmospheric pressure (about 756 mmHg), and is called a negative pressure. The elastic lungs are always tending to collapse and pull the visceral pleura away from the parietal pleura. The serousfluid, however, prevents actual separation of the pleural membranes. 3. Intrapulmonic pressure—the pressure within the bronchial tree and alveoli. This pressure fluctuates below and above atmospheric pressure during each cycle of breathing. Inhalation, also called inspiration, is a precise sequence of events that may be described as follows: Motor impulses from the medulla travel along the phrenic nerves to the diaphragm and along the intercostal nerves to the external intercostal muscles. The diaphragm contracts, moves downward, and expands the chest cavity from top to bottom. The external intercostal muscles pull the ribs up and out, which expands the chest cavity from side to side and front to back. As the chest cavity is expanded, the parietal pleura expands with it. Intrapleural pressure becomes even more negative as a sort of suction is created between the pleural membranes. The adhesion created by the serous fluid, however, permits the visceral pleura to be expanded too, and this expands the lungs as well. As the lungs expand, intrapulmonic pressure falls below atmospheric pressure, and air enters the nose and travels through the respiratory passages to the alveoli. Entry of air continues until intrapulmonic pressure is equal to atmospheric pressure; this is a normal inhalation. Of course, inhalation can be continued beyond normal, that is, a deep breath. This requires a more forceful contraction of the respiratory muscles to further expand the lungs, permitting the entry of more air. Mariano Marcos State University College of Health Sciences Department of Nursing 15  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM Exhalation may also be called expiration and begins when motor impulses from the medulla decrease and the diaphragm and external intercostal muscles relax. As the chest cavity becomes smaller, the lungs are compressed, and their elastic connective tissue, which was stretched during inhalation, recoils and also compresses the alveoli. As intrapulmonic pressure rises above atmospheric pressure, air is forced out of the lungs until the two pressures are again equal. Notice that inhalation is an active process that requires muscle contraction, but normal exhalation is a passive process, depending to a great extent on the normal elasticity of healthy lungs. In other words, under normal circumstances we must expend energy to inhale but not to exhale. We can, however, go beyond a normal exhalation and expel more air, such as when talking, singing, or blowing up a balloon. Such a forced exhalation is an active process that requires contraction of other muscles. Contraction of the internal intercostal muscles pulls the ribs down and in and squeezes even more air out of the lungs. Contraction of abdominal muscles, such as the rectus abdominis, compresses the abdominal organs and pushes the diaphragm upward, which also forces more air out of the lungs. Pulmonary Volumes The capacity of the lungs varies with the size and age of the person. Taller people have larger lungs than do shorter people. Also, as we get older our lung capacity diminishes as lungs lose their elasticity and the respiratory muscles become less efficient. For the following pulmonary volumes, the values given are those for healthy young adults. 1. Tidal volume—the amount of air involved in one normal inhalation and exhalation. The average tidal volume is 500 mL, but many people often have lower tidal volumes because of shallow breathing. 2. Minute respiratory volume (MRV)—the amount of air inhaled and exhaled in 1 minute. MRV is calculated by multiplying tidal volume by the number of respirations per minute (average range: 12 to 20per minute). If tidal volume is 500 mL and the respiratory rate is 12 breaths per minute, the MRV is 6000 mL, or 6 liters of air per minute, which is average. Shallow breathing usually indicates a smaller than average tidal volume, and would thus require more respirations per minute to obtain the necessary MRV. 3. Inspiratory reserve—the amount of air, beyond tidal volume, that can be taken in with the deepest possible inhalation. Normal inspiratory reserve ranges from 2000 to 3000 mL. 4. Expiratory reserve—the amount of air, beyond tidal volume, that can be expelled with the most forceful exhalation. Normal expiratory reserve ranges from 1000 to 1500 mL. 5. Vital capacity—the sum of tidal volume, inspiratory reserve, and expiratory reserve. Stated another way, vital capacity is the amount of air involved in the deepest inhalation followed by the most forceful exhalation. Average range of vital capacity is 3500 to 5000 mL. 6. Residual air—the amount of air that remains in the lungs after the most forceful exhalation; the average range is 1000 to 1500 mL. Residual air is important to Mariano Marcos State University College of Health Sciences Department of Nursing 16  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM ensure that there is some air in the lungs at all times, so that exchange of gases is a continuous process, even between breaths. Figure 8 Pulmonary volumes Source: Scanlon, V. C., Sanders, T. (2019). Essentials of anatomy and physiology. Philadelphia, PA: F. A. Davis Company. Some of the volumes just described can be determined with instruments called spirometers, which measure movement of air. Trained singers and musicians who play wind instruments often have vital capacities much larger than would be expected for their height and age, because their respiratory muscles have become more efficient with “practice.” The same is true for athletes who exercise regularly. A person with emphysema, however, must “work” to exhale, and vital capacity and expiratory reserve volume are often much lower than average. Another kind of pulmonary volume is alveolar ventilation, which is the amount of air that actually reaches the alveoli and participates in gas exchange. An average tidal volume is 500 mL, of which 350 to 400 mL is in the alveoli at the end of an inhalation. The remaining 100 to 150 mL of air is anatomic dead space, the air still within the respiratory passages. Despite the rather grim name, anatomic dead space is normal; everyone has it. Physiological dead space is not normal, and is the volume of non-functioning alveoli that decrease gas exchange. Causes of increased physiological dead space include bronchitis, pneumonia, tuberculosis, emphysema, asthma, pulmonary edema, and a collapsed lung. The compliance of the thoracic wall and the lungs, that is, their normal expansibility, is necessary for sufficient alveolar ventilation. Fractured ribs, scoliosis, pleurisy, or ascites may Mariano Marcos State University College of Health Sciences Department of Nursing 17  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM decrease thoracic compliance. Lung compliance will be decreased by any condition that increases physiologic dead space. Normal compliance thus promotes sufficient gas exchange in the alveoli. CENTRAL ACTIVITIES Activity 1 Match the following definitions with their associated respiratory volume or capacity: A) total lung capacity B) tidal volume C) dead space volume D) vital capacity E) conducting zone volume F) inspiratory reserve volume G) residual volume H) expiratory reserve volume 1. Amount of air that can be forcibly exhaled after a normal tidal expiration 2. Normal, quiet breathing which moves approximately 500 mL of air per breath 3. Air that enters the respiratory tract and remains within the conducting zone passageways 4. Amount of air that can be inhaled forcibly over the tidal volume 5. Total amount of exchangeable air 6. Air that remains in the lungs even after the most strenuous expiration 7. Sum total of tidal volume, inspiratory reserve volume, and expiratory reserve volume WRAP-UP ACTIVITY ASSESSMENT (POST-ASSESSMENT) A 20-item quiz will be administered to you via MVLE. You are required to get 60% of the items to pass the exam. REFERENCES Marieb, E. (2014). Essentials of Human anatomy and physiology (11th ed.). Pearson Education South Asia. Scanlon, V. C., Sanders, T. (2019). Essentials of anatomy and physiology. Philadelphia, PA: F. A. Davis Company. Tortora, G., & Derrickson. B. (2014). Principles of anatomy and physiology (14th ed.). John Wiley & Sons, Inc. Mariano Marcos State University College of Health Sciences Department of Nursing 18  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM LESSON 4. EXCHANGE OF GASES INTRODUCTION OF THE LESSON AND PRESENTATION OF OUTCOMES The purpose of the respiratory system is to perform gas exchange. Pulmonary ventilation provides air to the alveoli for this gas exchange process. At the respiratory membrane, where the alveolar and capillary walls meet, gases move across the membranes, with oxygen entering the bloodstream and carbon dioxide exiting. It is through this mechanism that blood is oxygenated and carbon dioxide, the waste product of cellular respiration, is removed from the body. After studying the lesson, you must have: 1. explained diffusion of gases, 2. explained the transport of gases in the blood. WARM-UP ACTIVITY Identify the terms described. _______________: statement of the principle that a specific gas type in a mixture exerts its own pressure, as if that specific gas type was not part of a mixture of gases _______________: gas exchange that occurs in the alveoli _______________: statement of the principle that the concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas _______________: gas exchange that occurs at the level of body tissues _______________: force exerted by each gas in a mixture of gases _______________: sum of all the partial pressures of a gaseous mixture _______________: movement of air into and out of the lungs; consists of inspiration and expiration Mariano Marcos State University College of Health Sciences Department of Nursing 19  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM PRESENTATION OF LEARNING INPUTS There are two sites of exchange of oxygen and carbon dioxide: the lungs and the tissues of the body. The exchange of gases between the air in the alveoli and the blood in the pulmonary capillaries is called external respiration. This term may be a bit confusing at first, because we often think of “external” as being outside the body. In this case, however, “external” means the exchange that involves air from the external environment, though the exchange takes place within the lungs. Internal respiration is the exchange of gases between the blood in the systemic capillaries and the tissue fluid (cells) of the body. The air we inhale (the earth’s atmosphere) is approximately 21% oxygen and 0.04% carbon dioxide. Although most (78%) of the atmosphere is nitrogen, this gas is not physiologically available to us, and we simply exhale it. This exhaled air also contains about 16% oxygen and 4.5% carbon dioxide, so it is apparent that some oxygen is retained within the body and the carbon dioxide produced by cells is exhaled. Diffusion of Gases –Partial Pressures Figure 9 Partial pressures and oxygen saturation Source: Scanlon, V. C., Sanders, T. (2019). Essentials of anatomy and physiology. Philadelphia, PA: F. A. Davis Company. Within the body, a gas will diffuse from an area of greater concentration to an area of lesser concentration. The concentration of each gas in a particular site (alveolar air, pulmonary blood, and so on) is expressed in a value called partial pressure. The partial pressure of a gas, measured in mmHg, is the pressure it exerts within a mixture of gases, whether the mixture is actually in a gaseous state or is in a liquid such as blood. The abbreviation for partial pressure is “P,” which is used, for example, on hospital lab slips for blood gases and will be used here. Mariano Marcos State University College of Health Sciences Department of Nursing 20  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM Because partial pressure reflects concentration, a gas will diffuse from an area of higher partial pressure to an area of lower partial pressure. The air in the alveoli has a high PO2 and a low PCO2. The blood in the pulmonary capillaries, which has just come from the body, has a low PO2 and a high PCO2. Therefore, in external respiration, oxygen diffuses from the air in the alveoli to the blood, and carbon dioxide diffuses from the blood to the air in the alveoli. The blood that returns to the heart now has a high PO2 and a low PCO2 and is pumped by the left ventricle into systemic circulation. The arterial blood that reaches systemic capillaries has a high PO2 and a low PCO2. The body cells and tissue fluid have a low PO2 and a high PCO2 because cells continuously use oxygen in cell respiration (energy production) and produce carbon dioxide in this process. Therefore, in internal respiration, oxygen diffuses from the blood to tissue fluid (cells), and carbon dioxide diffuses from tissue fluid to the blood. The blood that enters systemic veins to return to the heart now has a low PO2 and a high PCO2 and is pumped by the right ventricle to the lungs to participate in external respiration. Disorders of gas exchange often involve the lungs, that is, external respiration. Figure 10 Pulmonary gas exchange Source: Marieb, E. (2014). Essentials of Human anatomy and physiology (10th ed.). Pearson Education South Asia Mariano Marcos State University College of Health Sciences Department of Nursing 21  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM Transport of Gases in the Blood Although some oxygen is dissolved in blood plasma and does create the PO2 values, it is only about 1.5% of the total oxygen transported, not enough to sustain life. As you already know, most oxygen is carried in the blood bonded to the hemoglobin in red blood cells (RBCs). The mineral iron is part of hemoglobin and gives this protein its oxygen-carrying ability. The oxygen–hemoglobin bond is formed in the lungs where PO2 is high. This bond, however, is relatively unstable, and when blood passes through tissues with a low PO2, the bond breaks, and oxygen is released to the tissues. The lower the oxygen concentration in a tissue, the more oxygen the hemoglobin will release. This ensures that active tissues, such as exercising muscles, receive as much oxygen as possible to continue cell respiration. Other factors that increase the release of oxygen from hemoglobin are a high PCO2 (actually a lower pH) and a high temperature, both of which are also characteristic of active tissues. Another measure of blood oxygen is the percent of oxygen saturation of hemoglobin (SaO2). The higher the PO2, the higher the SaO2, and as PO2 decreases, so does SaO2, though not as rapidly. A PO2 of 100 is an SaO2 of about 97% , as is found in systemic arteries. A PO2 of 40, as is found in systemic veins, is an SaO2 of about 75%. Notice that venous blood still has quite a bit of oxygen. Had this blood flowed through a very active tissue, more of its oxygen would have been released from hemoglobin. This venous reserve of oxygen provides active tissues with the oxygen they need. Carbon dioxide transport is a little more complicated. Some carbon dioxide is dissolved in the plasma, and some is carried by hemoglobin (carbaminohemoglobin), but these account for only about 20% of total CO2 transport. Most carbon dioxide is carried in the plasma in the form of bicarbonate ions (HCO3-). Let us look at the reactions that transform CO2 into a bicarbonate ion. When carbon dioxide enters the blood, most diffuses into red blood cells, which contain the enzyme carbonic anhydrase. This enzyme (which contains zinc) catalyzes the reaction of carbon dioxide and water to form carbonic acid: CO2 + H2O → H2CO3 The carbonic acid then dissociates: H2CO3 → H+ + HCO3- The bicarbonate ions diffuse out of the red blood cells into the plasma, leaving the hydrogen ions (H+) in the red blood cells. The many H+ ions would tend to make the red blood cells too acidic, but hemoglobin acts as a buffer to prevent acidosis. To maintain an ionic equilibrium, chloride ions (Cl–) from the plasma enter the red blood cells; this is called the chloride shift. Where is the CO2? It is in the plasma as part of HCO3- ions. When the blood reaches the lungs, an area of lower PCO2, these reactions are reversed, and CO2 is re-formed and diffuses into the alveoli to be exhaled. Mariano Marcos State University College of Health Sciences Department of Nursing 22  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM CENTRAL ACTIVITIES Activity 1 Fill-in the blanks 1. Most oxygen attaches to ___________ molecules on the RBCs to form _____________. 2. A small amount of oxygen dissolves in the ___________ for transport. Carbon dioxide is also transported in two ways: 1. Most carbon dioxide dissolves in the plasma as the ____________. 2. A small amount of carbon dioxide is carried inside the ________ bound to hemoglobin (bound to a different site from oxygen). Activity 2 Critical thinking questions: 1. Compare and contrast Dalton’s law and Henry’s law. 2. A smoker develops damage to several alveoli that then can no longer function. How does this affect gas exchange? WRAP-UP ACTIVITY EVERYDAY CONNECTIONS: HYPERBARIC CHAMBER TREATMENT A type of device used in some areas of medicine that exploits the behavior of gases is hyperbaric chamber treatment. A hyperbaric chamber is a unit that can be sealed and expose a patient to either 100 percent oxygen with increased pressure or a mixture of gases that includes a higher concentration of oxygen than normal atmospheric air, also at a higher partial pressure than the atmosphere. There are two major types of chambers: monoplace and multiplace. Monoplace chambers are typically for one patient, and the staff tending to the patient observes the patient from outside of the chamber. Some facilities have special monoplace hyperbaric chambers that allow multiple patients to be treated at once, usually in a sitting or reclining position, to help ease feelings of isolation or claustrophobia. Multiplace chambers are large enough for multiple patients to be treated at one time, and the staff attending these patients is present inside the chamber. In a multiplace chamber, patients are often treated with air via a mask or hood, and the chamber is pressurized. Hyperbaric chamber treatment is based on the behavior of gases. As you recall, gases move from a region of higher partial pressure to a region of lower partial pressure. In a hyperbaric chamber, the atmospheric pressure is increased, causing a greater amount of oxygen than normal to diffuse into the bloodstream of the patient. Hyperbaric chamber therapy is used to treat a variety of medical problems, such as wound and graft healing, anaerobic bacterial infections, and carbon monoxide poisoning. Exposure to and poisoning by carbon monoxide is difficult to reverse, because hemoglobin’s affinity for carbon monoxide is much stronger than its affinity for oxygen, causing carbon monoxide to replace oxygen in the blood. Hyperbaric chamber therapy can treat carbon monoxide poisoning, because the increased atmospheric pressure causes more oxygen to diffuse into the bloodstream. At this increased pressure and increased concentration of oxygen, carbon monoxide is displaced from hemoglobin. Another example is the treatment of anaerobic bacterial infections, which are created by bacteria that cannot or prefer not to live in the presence of oxygen. An increase in blood and tissue levels of oxygen helps to kill the anaerobic bacteria that are responsible Mariano Marcos State University College of Health Sciences Department of Nursing 23  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM for the infection, as oxygen is toxic to anaerobic bacteria. For wounds and grafts, the chamber stimulates the healing process by increasing energy production needed for repair. Increasing oxygen transport allows cells to ramp up cellular respiration and thus ATP production, the energy needed to build new structures. ASSESSMENT (POST-ASSESSMENT) A 20-item quiz will be administered to you via MVLE. You are required to get 60% of the items to pass the exam. REFERENCES Marieb, E. (2014). Essentials of Human anatomy and physiology (11th ed.). Pearson Education South Asia. Scanlon, V. C., Sanders, T. (2019). Essentials of anatomy and physiology. Philadelphia, PA: F. A. Davis Company. Tortora, G., & Derrickson. B. (2014). Principles of anatomy and physiology (14th ed.). John Wiley & Sons, Inc. OpenStax, L. (n.d.). Anatomy and Physiology II. Retrieved November 27, 2020, from https://courses.lumenlearning.com/ap2/chapter/gas-exchange/ Mariano Marcos State University College of Health Sciences Department of Nursing 24  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM LESSON 5. REGULATION OF RESPIRATION INTRODUCTION OF THE LESSON AND PRESENTATION OF OUTCOMES The respiratory system is controlled by two mechanism. In this lesson you will be able to understand the role of the nervous system and the chemical reactions in our blood and how they affect an individual’s breathing pattern. After studying the lesson, you must have: 1. explained nervous regulation of the respiratory system, 2. explained the chemical regulation of the respiratory system. WARM-UP ACTIVITY Thought-provoking question: Is breathing voluntary or involuntary? Reflect on the question and try to answer it briefly. Mariano Marcos State University College of Health Sciences Department of Nursing 25  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM PRESENTATION OF LEARNING INPUTS Two types of mechanisms regulate breathing: nervous mechanisms and chemical mechanisms. Because any changes in the rate or depth of breathing are ultimately brought about by nerve impulses, we will consider nervous mechanisms first. Nervous Regulation Figure 11 Nervous regulation of respiration. (A) Midsagittal section of brain. (B) Respiratory centers in medulla and pons. (C) Respiratory muscles. Source: Scanlon, V. C., Sanders, T. (2019). Essentials of anatomy and physiology. Philadelphia, PA: F. A. Davis Company. The respiratory centers are located in the medulla and pons, which are parts of the brain stem. Within the medulla are the inspiration center and expiration center. The inspiration center automatically generates impulses in rhythmic spurts. These impulses travel along nerves to the respiratory muscles to stimulate their contraction. The result is inhalation. As the lungs inflate, baroreceptors in lung tissue detect this stretching and generate sensory impulses to the medulla; these impulses begin to depress the inspiration center. This is called the Hering-Breuer inflation reflex, which also helps prevent overinflation of the lungs. As the inspiration center is depressed, the result is a decrease in impulses to the respiratory muscles, which relax to bring about exhalation. Then the inspiration center becomes active again to begin another cycle of breathing. When there is a need for more forceful exhalations, such as during exercise, the inspiration center activates the expiration center, which generates impulses to the internal intercostal and abdominal muscles. Mariano Marcos State University College of Health Sciences Department of Nursing 26  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM The two respiratory centers in the pons work with the inspiration center to produce a normal rhythm of breathing. The apneustic center prolongs inhalation, and is then interrupted by impulses from the pneumotaxic center, which contributes to exhalation. In normal breathing, inhalation lasts 1 to 2 seconds, followed by a slightly longer (2 to 3 seconds) exhalation, producing the normal respiratory rate range of 12 to 20 breaths per minute. What has just been described is normal breathing, but variations are possible and quite common. Emotions often affect respiration; a sudden fright may bring about a gasp or a scream, and anger usually increases the respiratory rate. In these situations, impulses from the hypothalamus modify the output from the medulla. The cerebral cortex enables us to voluntarily change our breathing rate or rhythm to talk, sing, breathe faster or slower, or even to stop breathing for 1 or 2 minutes. Such changes cannot be continued indefinitely, however, and the medulla will eventually resume control. Coughing and sneezing are reflexes that remove irritants from the respiratory passages; the medulla contains the centers for both of these reflexes. Sneezing is stimulated by an irritation of the nasal mucosa, and coughing is stimulated by irritation of the mucosa of the pharynx, larynx, or trachea. The reflex action is essentially the same for both: An inhalation is followed by exhalation beginning with the glottis closed to build up pressure. Then the glottis opens suddenly, and the exhalation is explosive. A cough directs the exhalation out the mouth, while a sneeze directs the exhalation out the nose. Hiccups, also a reflex, are spasms of the diaphragm. The result is a quick inhalation that is stopped when the glottis snaps shut, causing the “hic” sound. The stimulus may be irritation of the phrenic nerves or nerves of the stomach. Excessive alcohol is an irritant that can cause hiccups. Some causes are simply unknown. Yet another respiratory reflex is yawning. Most of us yawn when we are tired, but the stimulus for and purpose of yawning are not known with certainty. There are several possibilities, such as lack of oxygen or accumulation of carbon dioxide, but we really do not know. Nor do we know why yawning is contagious, but seeing someone yawn is almost sure to elicit a yawn of one’s own. You may even have yawned while reading this paragraph about yawning. Chemical Regulation Figure 12 Chemical regulation of respiration Source: Scanlon, V. C., Sanders, T. (2019). Essentials of anatomy and physiology. Philadelphia, PA: F. A. Davis Company. Mariano Marcos State University College of Health Sciences Department of Nursing 27  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM Chemical regulation refers to the effect on breathing of blood pH and blood levels of oxygen and carbon dioxide. A decrease in the blood level of oxygen (hypoxia) is detected by the chemoreceptors in the carotid and aortic bodies. The sensory impulses generated by these receptors travel along the glossopharyngeal and vagus nerves to the medulla, which responds by increasing respiratory rate or depth (or both). This response will bring more air into the lungs so that more oxygen can diffuse into the blood to correct the hypoxic state. Carbon dioxide becomes a problem when it is present in excess in the blood, because excess CO2 (hypercapnia) lowers the pH when it reacts with water to form carbonic acid (a source of H+ ions). That is, excess CO2 makes the blood or other body fluids less alkaline (or more acidic). The medulla contains chemoreceptors that are very sensitive to changes in pH, especially decreases. If accumulating CO2 lowers blood pH, the medulla responds by increasing respiration. This is not for the purpose of inhaling, but rather to exhale more CO2 to raise the pH back to normal. Of the two respiratory gases, which is the more important as a regulator of respiration? Our guess might be oxygen, because it is essential for energy production in cell respiration. However, the respiratory system can maintain a normal blood level of oxygen even if breathing decreases to half the normal rate or stops for a few moments. Recall that exhaled air is 16% oxygen. This oxygen did not enter the blood but was available to do so if needed. Also, the residual air in the lungs supplies oxygen to the blood even if breathing rate slows. Therefore, carbon dioxide must be the major regulator of respiration, and the reason is that carbon dioxide affects the pH of the blood. As was just mentioned, an excess of CO2 causes the blood pH to decrease, a process that must not be allowed to continue. Therefore, any increase in the blood CO2 level is quickly compensated for by increased breathing to exhale more CO2. If, for example, you hold your breath, what is it that makes you breathe again? Have you run out of oxygen? Probably not, for the reasons mentioned. What has happened is that accumulating CO2 has lowered blood pH enough to stimulate the medulla to start the breathing cycle again. In some situations, oxygen does become the major regulator of respiration. People with severe, chronic pulmonary diseases such as emphysema have decreased exchange of both oxygen and carbon dioxide in the lungs. The decrease in pH caused by accumulating CO2 is corrected by the kidneys, but the blood oxygen level keeps decreasing. Eventually, the oxygen level may fall so low that it does provide a very strong stimulus to increase the rate and depth of respiration. Mariano Marcos State University College of Health Sciences Department of Nursing 28  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM CENTRAL ACTIVITIES Activity 1 Fill-in the blanks. As carbon dioxide levels__________, the pH of the blood __________ (becomes more acidic). The respiratory centers in the brain stimulate the inspiratory muscles to __________ and ___________ the breathing rate. _____________ is breathing that is deeper and more rapid than _____________ (normal breathing) and removes more ______________ from the blood. If carbon dioxide levels are too low, the blood pH __________ (becomes more alkaline). The breathing rate slows (called ______________) to retain more carbonic acid and __________ the blood pH. WRAP-UP ACTIVITY Key Points:  The motor cortex within the cerebral cortex of the brain controls voluntary respiration (the ascending respiratory pathway).  Voluntary respiration may be overridden by aspects of involuntary respiration, such as chemoreceptor stimulus, and hypothalamus stress response.  The phrenic nerves, vagus nerves, and posterior thoracic nerves are the major nerves involved in respiration.  Voluntary respiration is needed to perform higher functions, such as voice control.  An increase in carbon dioxide concentration leads to a decrease in the pH of blood due to the production of H+ ions from carbonic acid.  In response to a decrease in blood pH, the respiratory center (in the medulla ) sends nervous impulses to the external intercostal muscles and the diaphragm, to increase the breathing rate and the volume of the lungs during inhalation.  Hyperventilation causes alakalosis, which causes a feedback response of decreased ventilation (to increase carbon dioxide), while hypoventilation causes acidosis, which causes a feedback response of increased ventilation (to remove carbon dioxide).  Any situation with hypoxia (too low oxygen levels) will cause a feedback response that increases ventilation to increase oxygen intake.  Vomiting causes alkalosis and diarrhea causes acidosis, which will cause an appropriate respiratory feedback response.  Pulmonary stretch receptors present in the smooth muscle of the airways and the pleura respond to excessive stretching of the lung during large inspirations.  The Hering–Breuer inflation reflex is initiated by stimulation of  stretch receptors. The deflation reflex is initiated by stimulation  of the compression receptors (called proprioceptors) or deactivation of  stretch receptors when the lungs deflate.  Activation of the pulmonary stretch receptors (via the vagus nerve ) results in inhibition of the inspiratory stimlus in the medulla, and thus inhibition of inspiration and initiation of expiration.  An increase in pulmonary stretch receptor activity leads to an elevation of heart rate ( tachycardia ). Mariano Marcos State University College of Health Sciences Department of Nursing 29  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER IX: LYMPHATIC SYSTEM  A cyclical, elevated heart rate from inspiration is called sinus arrhythmia and is a normal response in youth. Inhibition of inspiration is important to allow expiration to occur. ASSESSMENT (POST-ASSESSMENT) A 20-item quiz will be administered to you via MVLE. You are required to get 60% of the items to pass the exam. REFERENCES Marieb, E. (2014). Essentials of Human anatomy and physiology (11th ed.). Pearson Education South Asia. Scanlon, V. C., Sanders, T. (2019). Essentials of anatomy and physiology. Philadelphia, PA: F. A. Davis Company. Tortora, G., & Derrickson. B. (2014). Principles of anatomy and physiology (14th ed.). John Wiley & Sons, Inc. OpenStax, L. (n.d.). Anatomy and Physiology II. Retrieved November 27, 2020, from https://courses.lumenlearning.com/ap2/chapter/gas-exchange/ Mariano Marcos State University College of Health Sciences Department of Nursing 30