lab assignment respiratory system

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Lab 6: Respiratory System

Measurable outcomes.

• Understand and identify the anatomical structures of the respiratory system on available models.
• Deduce the pathway of air through the respiratory system.
• Determine the pathway of pulmonary circulation.
• Identify the various muscles involved in respiration.
• Recognize the hallmarks of lung histology.
• Demonstrate an adequate understand of the material in this section.

The respiratory system is responsible for the gas exchange of oxygen and carbon dioxide. The main specialized organs of this process are the lungs which house clusters of sac-like structures known as alveoli . There are from 480 to 790 million alveoli which increase the efficiency of gas exchange by increasing surface area to around 118m 2  in men and 91m 2 in women. The respiratory system consists of the nasal cavity, pharynx, larynx, trachea, lungs, bronchi, bronchioles , and alveoli , along with their accessory structures. These structures are divided into the upper and lower respiratory systems , with the lower portion beginning at the larynx. The primary function of this system is to exchange oxygen and carbon dioxide between the body and the environment. Functionally, the respiratory system can be divided into the conducting zone , terminating at the terminal bronchioles; then air flows into the respiratory zone,  where the actual gas exchange occurs.

Though we view each system individually in this lab, it is important to keep in mind that all organ systems overlap and work together in such a way that scientist are constantly discovering new connections. One such example is the nose . Not only is it the primary entrance and exit for respiration, but it also contains the olfactory epithelium, the primary structure of one of the special senses, olfaction. Likewise, the pharynx is a structure shared by both the respiratory and digestion systems.

Although both lungs functionally participate in respiration, they differ physically in various ways. The right lung is shorter and wider than the left lung, and the left lung occupies a smaller volume than the right. Another distinction between the two lungs is that the left lung contains the cardiac notch , which makes space for the heart. Furthermore, whereas the right lung has three lobes, the left lung has only two.

Though not visible on every model, each lung is surrounded by the pleura, which consists of two layers called the visceral and parietal pleurae. They are important because they lubricate the lungs and reduce friction during inhalation and exhalation.

Vocabulary for Respiratory System can be found on page(s) 169 .

Human Anatomy Lab Manual Copyright © 2018 by Malgosia Wilk-Blaszczak is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Respiratory system

Author: Gordana Sendić, MD • Reviewer: Roberto Grujičić, MD Last reviewed: October 30, 2023 Reading time: 16 minutes

The respiratory system , also called the pulmonary system , consists of several organs that function as a whole to oxygenate the body through the process of respiration (breathing) . This process involves inhaling air and conducting it to the lungs where gas exchange occurs, in which oxygen is extracted from the air, and carbon dioxide expelled from the body. The respiratory tract is divided into two sections at the level of the vocal cords ; the upper and lower respiratory tract.

• The upper respiratory tract includes the nasal cavity , paranasal sinuses , pharynx and the portion of the larynx above the vocal cords.
• The lower respiratory tract includes the larynx below the vocal cords, the trachea , bronchi , bronchioles and the lungs.

The lungs are most often considered as part of the lower respiratory tract, but are sometimes described as a separate entity. They contain the respiratory bronchioles , alveolar ducts , alveolar sacs and alveoli . 

This article will discuss the anatomy and function of the respiratory system.

Nasal cavity

Paranasal sinuses, lower respiratory tract, microanatomy, upper respiratory tract infections, lower respiratory tract infections.

Upper respiratory tract

The upper respiratory tract refers to the parts of the respiratory system that lie outside the thorax , more specifically above the cricoid cartilage and vocal cords. It includes the nasal cavity , paranasal sinuses , pharynx and the superior portion of the larynx . Most of the upper respiratory tract is lined with the pseudostratified ciliated columnar epithelium, also known as the respiratory epithelium . The exceptions are some parts of the pharynx and larynx.

The upper respiratory tract begins with the nasal cavity . The nasal cavity opens anteriorly on the face through the two nares, and posteriorly into the nasopharynx through the two choana e. The floor of the nasal cavity is formed by the hard palate , while the roof consists of the cribriform plate of the ethmoid bone posteriorly, and the frontal and nasal bones anteriorly. The nares and anterior portion of the nasal cavity contain sebaceous glands and hair follicles that serve to prevent any larger harmful particles from passing into the nasal cavity. 

The lateral walls of the nasal cavity contain three bony projections called nasal conchae (superior, middle and inferior), which increase the surface area of the nasal cavity. The nasal conchae also disrupt the laminar flow of air, making it slow and turbulent, thereby helping to humidify and warm up the air to body temperature. 

The roof of the nasal cavity contains the olfactory epithelium which consists of specialized sensory receptors. These receptors pick up airborne odorant molecules and transform them into action potentials that travel via the olfactory nerve to the cerebral cortex , allowing the brain to register them and provide a sense of smell.

Another pathway for the entry of air is the oral cavity . Although it is not classified as a part of the upper respiratory tract, the oral cavity provides an alternative route in the case of obstruction of the nasal cavity. The oral cavity opens anteriorly on the face through the oral fissure, while posteriorly, it opens into the oropharynx through a passage called the oropharyngeal isthmus. 

Several bones that form the walls of the nasal cavity contain air-filled spaces called the paranasal sinuses, which are named after their associated bones; maxillary , frontal , sphenoidal and ethmoidal sinuses .

The paranasal sinuses communicate with the nasal cavity via several openings, and thereby also receive the inhaled air and contribute to its humidifying and warming. In addition, the mucous membrane and respiratory epithelium that lines both the nasal cavity and the paranasal sinuses traps any harmful particles, dust or bacteria.

After passing through the nasal cavity and paranasal sinuses, the inhaled air exits through the choanae into the pharynx. The pharynx is a funnel-shaped muscular tube that contains three parts; the nasopharynx, oropharynx and laryngopharynx . 

• The nasopharynx is the first and superiormost part of the pharynx, found posterior to the nasal cavity. This part of the pharynx serves only as an airway, and is thus lined with respiratory epithelium. Inferiorly, the uvula and soft palate swing upwards during swallowing to close off the nasopharynx and prevent food from entering the nasal cavity.
• The oropharynx is found posterior to the oral cavity and communicates with it through the oropharyngeal isthmus. The oropharynx is a pathway for both the air incoming from the nasopharynx and the food incoming from the oral cavity. Thus, the oropharynx is lined with the more protective non-keratinizing stratified squamous epithelium .
• The laryngopharynx (hypopharynx) is the most inferior part of the pharynx. It is the point at which the digestive and respiratory systems diverge. Anteriorly, the laryngopharynx continues into the larynx, whereas posteriorly it continues as the esophagus . 

Following the laryngopharynx, the next and last portion of the upper respiratory tract is the superior part of the larynx . The larynx is a complex hollow structure found anterior to the esophagus. It is supported by a cartilaginous skeleton connected by membranes, ligaments and associated muscles. Above the vocal cords, the larynx is lined with stratified squamous epithelium like the laryngopharynx. Below the vocal cords, this epithelium transitions into pseudostratified ciliated columnar epithelium with goblet cells ( respiratory epithelium ). 

Besides its main function to conduct the air, the larynx also houses the vocal cords that participate in voice production. The laryngeal inlet is closed by the epiglottis during swallowing to prevent food or liquid from entering the lower respiratory tract.

If you want to learn more about the anatomy and function of the larynx, take a look at the study unit below!

The lower respiratory tract refers to the parts of the respiratory system that lie below the cricoid cartilage and vocal cords, including the inferior part of the larynx , tracheobronchial tree and lungs .

Tracheobronchial tree

The tracheobronchial tree is a portion of the respiratory tract that conducts the air from the upper airways to the lung parenchyma. It consists of the trachea and the intrapulmonary airways (bronchi and bronchioles).The trachea is located in the superior mediastinum and represents the trunk of the tracheobronchial tree. The trachea bifurcates at the level of the sternal angle (T5) into the left and right main bronchi, one for each lung.

• The left main bronchus passes inferolaterally to enter the hilum of the left lung. On its course, it passes inferior to the arch of the aorta and anterior to the esophagus and thoracic aorta.
• The right main bronchus passes inferolaterally to enter the hilum of the right lung. The right main bronchus has a more vertical course than its left counterpart and is also wider and shorter. This makes the right bronchus more susceptible to foreign body impaction.

As they reach the lungs, the main bronchi branch out into increasingly smaller intrapulmonary bronchi. The left main bronchus divides into two secondary lobar bronchi , while the right main bronchus divides into three secondary lobar bronchi that supply the lobes of the left and right lung, respectively.

Each of the lobar bronchi further divides into tertiary segmental bronchi that aerate the bronchopulmonary segments . The segmental bronchi then give rise to several generations of intrasegmental (conducting) bronchioles, which end as terminal bronchioles . Each terminal bronchiole gives rise to several generations of respiratory bronchioles . Respiratory bronchioles extend into several alveolar ducts, which lead into alveolar sacs, each of which contains many grape-like outpocketings called alveoli . Since they contain alveoli, these structures mark the site where gas exchange begins to occur.

The lungs are a pair of spongy organs located within the thoracic cavity. The right lung is larger than the left lung and consists of three lobes (superior, middle and inferior), which are divided by two fissures; oblique and horizontal fissure . The left lung has only two lobes (superior and inferior), divided by one oblique fissure. 

Each lung has three surfaces , an apex and a base . The surfaces of the lung are the costal, mediastinal and diaphragmatic surface, which are named after the adjacent anatomical structure which that surface faces. The mediastinal surface connects the lung to the mediastinum via its hilum . The apex of the lung is where the mediastinal and costal surfaces meet. It is the most superior portion of the lung, that extends into the root of the neck. The base is the lowest concave part of the lung that rests upon the diaphragm.

Each hilum of the lung contains the following:

• Principal bronchus
• Pulmonary artery
• Two pulmonary veins
• Bronchial vessels
• Pulmonary autonomic plexus
• Lymph nodes and vessels

On the microscopic level, the lower respiratory tract is characterized by several changes of epithelial lining, serving different purposes. Beginning from the inferior part of the larynx to the tertiary segmental bronchi, the lower respiratory tract is lined with pseudostratified ciliated columnar epithelium with goblet cells . The goblet cells produce mucus that lubricates and protects the airway by trapping any inhaled harmful particles. These trapped particles are then propelled towards the upper respiratory tract by the cilia of the epithelial cells and eventually expelled by coughing. 

As the larger tertiary segmental bronchi divide into smaller bronchi, the epithelium begins to change from respiratory epithelium to a simple columnar ciliated epithelium . This epithelium is continued in the larger terminal bronchioles, and transitions into a simple cuboidal epithelium in smaller terminal bronchioles. The epithelium of the terminal bronchioles contains exocrine bronchiolar cells called club cells , formerly known as Clara cells. These are non-ciliated cuboidal cells that contribute to the production of surfactant. In addition, the terminal bronchioles contain smooth muscle in their walls, that allows for bronchoconstriction and bronchodilation to occur. 

Terminal bronchioles then branch into respiratory bronchioles, which are also lined by simple cuboidal epithelium . The walls of the respiratory bronchioles extend into alveoli, and the epithelium changes into a simple squamous epithelium composed of type I and type II pneumocytes. Type I pneumocytes are thin, squamous cells that carry out the gas exchange, while type II pneumocytes are larger cuboidal cells that produce surfactant.

The main function of the respiratory system is pulmonary ventilation , which is the movement of air between the atmosphere and the lung by inspiration and expiration driven by the respiratory muscles. The respiratory system works as a whole to extract the oxygen from the inhaled air and eliminate the carbon dioxide from the body by exhalation. The upper respiratory mainly has an air-conducting function, while the lower respiratory tract serves both the conducting and respiratory functions. 

Besides its main function to conduct the air to the lower respiratory tract, the upper respiratory also performs several other functions. As mentioned earlier, the nasal cavity and paranasal sinuses change the properties of the air by humidifying and warming it in order to prepare it for the process of respiration. The air is also filtered from dust, pathogens and other particles by the nasal hair follicles and the ciliary epithelium.  

The portion of the lower respiratory tract, starting from the respiratory bronchioles, is the place where gas exchange begins to occur. This process is also known as external respiration , in which the oxygen from the inhaled air diffuses from the alveoli into the adjacent capillaries , while the carbon dioxide diffuses from the capillaries into the alveoli to be exhaled. The newly oxygenated blood then goes on to supply all the tissues in the body and undergoes internal respiration . This is the process in which the oxygen from the systemic circulation exchanges with carbon-dioxide from the tissues. Overall, the difference between external and internal respiration is that the former represents gas exchange with the external environment and takes place in the alveoli, while the latter represents gas exchange within the body and takes place in the tissues.

Test your knowledge on the respiratory system with this quiz.

To learn more about the complex respiratory system and solidify what you already learned in this article, head over to our respiratory system quizzes and labeled diagrams !

Clinical aspects

Upper respiratory tract infections are contagious infections that can be caused by a variety of bacteria and viruses. The most common causing agents are influenza virus (the flu), rhinoviruses and streptococcus bacteria. Depending on which part of the upper respiratory tract is affected, these infections may have different types, such as rhinitis , sinusitis , pharyngitis , epiglottitis , laryngitis and others. 

The common cold is the most common type of upper respiratory tract infection. It is a viral infection that usually involves the nose and throat, but other parts can be affected as well. The symptoms usually include sore throat,‎ coughing, sneezing, runny nose, headache, and fever.

Lower respiratory tract infections are infections that affect the parts of the respiratory tract below the vocal cords. These infections can affect the airways and manifest as bronchitis or bronchiolitis , or they can affect the lung alveoli and present as pneumonia . These can also occur in conjunction as bronchopneumonia. 

The most common cause of lower respiratory tract infections are bacteria, but they can also occur due to viruses, mycoplasma, rickettsiae and fungi. These agents invade the epithelial lining, causing inflammation, increased mucus secretion, and impaired mucociliary function. The inflammation and build-up of fluid in the lungs and airways may result in symptoms such as coughing, fever, sputum production, difficulty breathing or in severe cases, airway obstruction and impaired gas exchange.

References:

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
• Netter, F. (2019). Atlas of Human Anatomy (7th ed.). Philadelphia, PA: Saunders.
• Standring, S. (2016). Gray's Anatomy (41st ed.). Edinburgh: Elsevier Churchill Livingstone.
• Dasaraju PV, Liu C. Infections of the Respiratory System. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 93.
• Jeremy P. T. Ward; Jane Ward; Charles M. Wiener (2006). The respiratory system at a glance. Wiley-Blackwell.

Illustrators:

• The respiratory system (Systema respiratorium) - Begoña Rodriguez
• Organs of the respiratory system (overview) - Begoña Rodriguez
• Bronchi and alveoli (overview) - Paul Kim
• Medial view of the lung (overview) - Yousun Koh

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Respiratory System Anatomy and Physiology

Breathe life into your understanding with our guide on the respiratory system anatomy and physiology. Nursing students, immerse yourself in the intricate dance of inhalation and exhalation that fuels every living moment.

Table of Contents

Functions of the respiratory system, main bronchi, the respiratory membrane, respiration, mechanics of breathing, respiratory volumes and capacities, respiratory sounds, external respiration, gas transport, and internal respiration, control of respiration, age-related physiological changes in the respiratory system.

The functions of the respiratory system are:

• Oxygen supplier.  The job of the respiratory system is to keep the body constantly supplied with oxygen.
• Elimination.  Elimination of carbon dioxide.
• Gas exchange.  The respiratory system organs oversee the gas exchanges that occur between the blood and the external environment.
• Passageway.  Passageways that allow air to reach the lungs.
• Humidifier.  Purify, humidify, and warm incoming air.

Anatomy of the Respiratory System

The organs of the respiratory system include the nose, pharynx , larynx, trachea, bronchi, and their smaller branches, and the lungs, which contain the alveoli.

The nose is the only externally visible part of the respiratory system.

• Nostrils.  During breathing, air enters the nose by passing through the nostrils, or nares.
• Nasal cavity. The interior of the nose consists of the nasal cavity, divided by a midline nasal septum .
• Olfactory receptors. The olfactory receptors for the sense of smell are located in the mucosa in the slitlike superior part of the nasal cavity, just beneath the ethmoid bone .
• Respiratory mucosa. The rest of the mucosal lining, the nasal cavity called the respiratory mucosa, rests on a rich network of thin-walled veins that warms the air as it flows past.
• Mucus.  In addition, the sticky mucus produced by the mucosa’s glands moistens the air and traps incoming bacteria and other foreign debris, and lysozyme enzymes in the mucus destroy bacteria chemically.
• Ciliated cells. The ciliated cells of the nasal mucosa create a gentle current that moves the sheet of contaminated mucus posteriorly toward the throat, where it is swallowed and digested by stomach juices.
• Conchae.  The lateral walls of the nasal cavity are uneven owing to three mucosa-covered projections, or lobes called conchae, which greatly increase the surface area of the mucosa exposed to the air, and also increase the air turbulence in the nasal cavity.
• Palate. The nasal cavity is separated from the oral cavity below by a partition, the palate; anteriorly, where the palate is supported by bone, is the hard palate; the unsupported posterior part is the soft palate .
• Paranasal sinuses. The nasal cavity is surrounded by a ring of paranasal sinuses located in the frontal, sphenoid, ethmoid, and maxillary bones ; theses sinuses lighten the skull , and they act as a resonance chamber for speech.

• Size. The pharynx is a muscular passageway about 13 cm (5 inches) long that vaguely resembles a short length of red garden hose.
• Function.  Commonly called the throat , the pharynx serves as a common passageway for food and air.
• Portions of the pharynx. Air enters the superior portion, the nasopharynx , from the nasal cavity and then descends through the oropharynx and laryngopharynx to enter the larynx below.
• Pharyngotympanic tube. The pharyngotympanic tubes, which drain the middle ear open into the nasopharynx.
• Pharyngeal tonsil. The pharyngeal tonsil, often called adenoid is located high in the nasopharynx.
• Palatine tonsils . The palatine tonsils are in the oropharynx at the end of the soft palate.
• Lingual tonsils . The lingual tonsils lie at the base of the tongue.

The larynx or voice box routes air and food into the proper channels and plays a role in speech.

• Structure.  Located inferior to the pharynx, it is formed by eight rigid hyaline cartilages and a spoon-shaped flap of elastic cartilage, the epiglottis .
• Thyroid cartilage. The largest of the hyaline cartilages is the shield-shaped thyroid cartilage, which protrudes anteriorly and is commonly called Adam’s apple .
• Epiglottis.  Sometimes referred to as the “guardian of the airways” , the epiglottis protects the superior opening of the larynx.
• Vocal folds. Part of the mucous membrane of the larynx forms a pair of folds, called the vocal folds, or true vocal cords , which vibrate with expelled air and allows us to speak.
• Glottis.  The slitlike passageway between the vocal folds is the glottis.

• Length.  Air entering the trachea or windpipe from the larynx travels down its length (10 to 12 cm or about 4 inches) to the level of the fifth thoracic vertebra , which is approximately midchest.
• Structure.  The trachea is fairly rigid because its walls are reinforced with C-shaped rings of hyaline cartilage; the open parts of the rings abut the esophagus and allow it to expand anteriorly when we swallow a large piece of food, while the solid portions support the trachea walls and keep it patent, or open, in spite of the pressure changes that occur during breathing.
• Cilia.  The trachea is lined with ciliated mucosa that beat continuously and in a direction opposite to that of the incoming air as they propel mucus, loaded with dust particles and other debris away from the lungs to the throat, where it can be swallowed or spat out.
• Structure.  The right and left main (primary) bronchi are formed by the division of the trachea.
• Location.  Each main bronchus runs obliquely before it plunges into the medial depression of the lung on its own side.
• Size.  The right main bronchus is wider, shorter, and straighter than the left.

• Location.  The lungs occupy the entire thoracic cavity except for the most central area, the mediastinum , which houses the heart, the great blood vessels, bronchi, esophagus, and other organs.
• Apex.  The narrow, superior portion of each lung, the apex, is just deep into the clavicle .
• Base.  The broad lung area resting on the diaphragm is the base.
• Division.  Each lung is divided into lobes by fissures; the left lung has two lobes , and the right lung has three .
• Pleura.  The surface of each lung is covered with a visceral serosa called the pulmonary , or visceral pleura, and the walls of the thoracic cavity are lined by the parietal pleura .
• Pleural fluid. The pleural membranes produce pleural fluid, a slippery serous secretion that allows the lungs to glide easily over the thorax wall during breathing movements and causes the two pleural layers to cling together.
• Pleural space. The lungs are held tightly to the thorax wall, and the pleural space is more of a potential space than an actual one.
• Bronchioles .  The smallest of the conducting passageways are the bronchioles.
• Alveoli.  The terminal bronchioles lead to the respiratory zone structures, even smaller conduits that eventually terminate in alveoli or air sacs.
• Respiratory zone. The respiratory zone, which includes the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli, is the only site of gas exchange .
• Conducting zone structures. All other respiratory passages are conducting zone structures that serve as conduits to and from the respiratory zone.
• Stroma.  The balance of the lung tissue, its stroma, is mainly elastic connective tissue that allows the lungs to recoil passively as we exhale.
• Wall structure. The walls of the alveoli are composed largely of a single, thin layer of squamous epithelial cells.
• Alveolar pores. Alveolar pores connect neighboring air sacs and provide alternative routes for air to reach alveoli whose feeder bronchioles have been clogged by mucus or otherwise blocked.
• Respiratory membrane. Together, the alveolar and capillary walls, their fused basement membranes, and occasional elastic fibers construct the respiratory membrane (air-blood barrier), which has gas (air) flowing past on one side and blood flowing past on the other.
• Alveolar macrophages . Remarkably efficient alveolar macrophages sometimes called “dust cells” , wander in and out of the alveoli picking up bacteria, carbon particles, and other debris.
• Cuboidal cells. Also scattered amid the epithelial cells that form most of the alveolar walls are chunky cuboidal cells, which produce a lipid (fat) molecule called surfactant , which coats the gas-exposed alveolar surfaces and is very important in lung function.

Physiology of the Respiratory System

The major function of the respiratory system is to supply the body with oxygen and to dispose of carbon dioxide. To do this, at least four distinct events, collectively called respiration, must occur.

• Pulmonary ventilation . Air must move into and out of the lungs so that gasses in the air sacs are continuously refreshed, and this process is commonly called breathing.
• External respiration. Gas exchange between the pulmonary blood and alveoli must take place.
• Respiratory gas transport. Oxygen and carbon dioxide must be transported to and from the lungs and tissue cells of the body via the bloodstream.
• Internal respiration. At systemic capillaries, gas exchanges must be made between the blood and tissue cells.
• Rule.  Volume changes lead to pressure changes, which lead to the flow of gasses to equalize pressure.
• Inspiration.  Air is flowing into the lungs; the chest is expanded laterally, the rib cage is elevated, and the diaphragm is depressed and flattened; lungs are stretched to the larger thoracic volume, causing the intrapulmonary pressure to fall and air to flow into the lungs.
• Expiration.  Air is leaving the lungs; the chest is depressed and the lateral dimension is reduced, the rib cage is descended, and the diaphragm is elevated and dome-shaped; lungs recoil to a smaller volume, intrapulmonary pressure rises, and air flows out of the lung.
• Intrapulmonary volume. Intrapulmonary volume is the volume within the lungs.
• Intrapleural pressure. The normal pressure within the pleural space, the intrapleural pressure, is always negative, and this is the major factor preventing the collapse of the lungs.
• Nonrespiratory air movements. Nonrespiratory movements are a result of reflex activity, but some may be produced voluntarily such as coughing , sneezing, crying, laughing, hiccups, and yawning.

• Tidal volume. Normal quiet breathing moves approximately 500 ml of air into and out of the lungs with each breath.
• Inspiratory reserve volume. The amount of air that can be taken in forcibly over the tidal volume is the inspiratory reserve volume, which is normally between 2100 ml to 3200 ml.
• Expiratory reserve volume. The amount of air that can be forcibly exhaled after a tidal expiration, the expiratory reserve volume, is approximately 1200 ml.
• Residual volume. Even after the most strenuous expiration, about 1200 ml of air still remains in the lungs and it cannot be voluntarily expelled; this is called residual volume, and it is important because it allows gas exchange to go on continuously even between breaths and helps to keep the alveoli inflated.
• Vital capacity. The total amount of exchangeable air is typically around 4800 ml in healthy young men, and this respiratory capacity is the vital capacity, which is the sum of the tidal volume, inspiratory reserve volume, and expiratory reserve volume.
• Dead space volume. Much of the air that enters the respiratory tract remains in the conducting zone passageways and never reaches the alveoli; this is called the dead space volume and during a normal tidal breath, it amounts to about 150 ml.
• Functional volume. The functional volume, which is the air that actually reaches the respiratory zone and contributes to gas exchange , is about 350 ml.
• Spirometer.  Respiratory capacities are measured with a spirometer, wherein as a person breathes, the volumes of air exhaled can be read on an indicator, which shows the changes in air volume inside the apparatus.
• Bronchial sounds. Bronchial sounds are produced by air rushing through the large respiratory passageways (trachea and bronchi).
• Vesicular breathing sounds. Vesicular breathing sounds occur as air fills the alveoli, and they are soft and resemble a muffled breeze.
• External respiration. External respiration or pulmonary gas exchange involves oxygen being loaded and carbon dioxide being unloaded from the blood.
• Internal respiration. In internal respiration or systemic capillary gas exchange , oxygen is unloaded and carbon dioxide is loaded into the blood.
• Gas transport. Oxygen is transported in the blood in two ways: most attaches to hemoglobin molecules inside the RBCs to form oxyhemoglobin, or a very small amount of oxygen is carried dissolved in the plasma ; while carbon dioxide is transported in plasma as bicarbonate ion, or a smaller amount (between 20 to 30 percent of the transported carbon dioxide) is carried inside the RBCs bound to hemoglobin.

Neural Regulation

• Phrenic and intercostal nerves . These two nerves regulate the activity of the respiratory muscles, the diaphragm, and external intercostals.
• Medulla and pons . Neural centers that control respiratory rhythm and depth are located mainly in the medulla and pons; the medulla, which sets the basic rhythm of breathing, contains a pacemaker , or self-exciting inspiratory center, and an expiratory center that inhibits the pacemaker in a rhythmic way; pons centers appear to smooth out the basic rhythm of inspiration and expiration set by the medulla.
• Eupnea.  The normal respiratory rate is referred to as eupnea, and it is maintained at a rate of 12 to 15 respirations/minute .
• Hyperpnea.  During exercise, we breathe more vigorously and deeply because the brain centers send more impulses to the respiratory muscles, and this respiratory pattern is called hyperpnea.

Non-neural Factors Influencing Respiratory Rate and Depth

• Physical factors. Although the medulla’s respiratory centers set the basic rhythm of breathing, there is no question that physical factors such as talking, coughing, and exercising can modify both the rate and depth of breathing, as well as an increased body temperature, which increases the rate of breathing.
• Volition (conscious control). Voluntary control of breathing is limited, and the respiratory centers will simply ignore messages from the cortex (our wishes) when the oxygen supply in the blood is getting low or blood pH is falling .
• Emotional factors. Emotional factors also modify the rate and depth of breathing through reflexes initiated by emotional stimuli acting through centers in the hypothalamus .
• Chemical factors. The most important factors that modify respiratory rate and depth are chemical- the levels of carbon dioxide and oxygen in the blood; increased levels of carbon dioxide and decreased blood pH are the most important stimuli leading to an increase in the rate and depth of breathing, while a decrease in oxygen levels become important stimuli when the levels are dangerously low.
• Hyperventilation.  Hyperventilation blows off more carbon dioxide and decreases the amount of carbonic acid, which returns blood pH to the normal range when carbon dioxide or other sources of acids begin to accumulate in the blood.
• Hypoventilation.  Hypoventilation or extremely slow or shallow breathing allows carbon dioxide to accumulate in the blood and brings blood pH back into normal range when blood starts to become slightly alkaline.

Respiratory efficiency is reduced with age. They are unable to compensate for increased oxygen need and are significantly increasing the amount of air inspired. Therefore, difficulty in breathing is usually common especially during activities.  Expiratory muscles become weaker so their cough efficiency is reduced and the amount of air left in the lungs is increased. Health promotion teaching can include smoking cessation, preventing respiratory infections through handwashing , and ensuring up to date influenza and pneumonia vaccinations.

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• Anatomy and Physiology Nursing Test Banks . This nursing test bank includes questions about Anatomy and Physiology and its related concepts such as: structure and functions of the human body, nursing care management of patients with conditions related to the different body systems.

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