essay on respiratory system in human

• Biology Article

Human Respiratory System

Respiratory system of humans.

Breathing involves gaseous exchange through inhalation and exhalation. The human respiratory system has the following main structures – Nose, mouth, pharynx, larynx, trachea, bronchi, and lungs. Explore in detail.

Table of Contents

• What Is Respiratory System

Respiratory Tract

Respiratory system definition.

“Human Respiratory System is a network of organs and tissues that helps us breathe. The primary function of this system is to introduce oxygen into the body and expel carbon dioxide from the body.”

What is the Respiratory System?

As defined above, the human respiratory system consists of a group of organs and tissues that help us to breathe. Aside from the lungs, there are also muscles and a vast network of blood vessels that facilitate the process of respiration.

Also Read:  Mechanism of Breathing

Human Respiratory System Diagram

To gain a clearer understanding, we have illustrated the human respiratory system and its different parts involved in the process.

Human Respiratory System Diagram showing different parts of the Respiratory Tract

Features of the Human Respiratory System

The respiratory system in humans has the following important features:

• The energy is generated by the breakdown of glucose molecules in all living cells of the human body.
• Oxygen is inhaled and is transported to various parts and are used in the process of burning food particles (breaking down glucose molecules) at the cellular level in a series of chemical reactions.
• The obtained glucose molecules are used for discharging energy in the form of ATP- (adenosine triphosphate)

Also Read:  Difference between trachea and oesophagus

Respiratory System Parts and Functions

Let us have a detailed look at the different parts of the respiratory system and their functions.

Humans have exterior nostrils, which are divided by a framework of cartilaginous structure called the septum. This is the structure that separates the right nostril from the left nostril. Tiny hair follicles that cover the interior lining of nostrils act as the body’s first line of defence against foreign pathogens . Furthermore, they provide additional humidity for inhaled air.

Two cartilaginous chords lay the framework for the larynx. It is found in front of the neck and is responsible for vocals as well as aiding respiration. Hence, it is also informally called the voice box. When food is swallowed, a flap called the epiglottis folds over the top of the windpipe and prevents food from entering into the larynx.

Also check: What is the role of epiglottis and diaphragm in respiration?

The nasal chambers open up into a wide hollow space called the pharynx. It is a common passage for air as well as food. It functions by preventing the entry of food particles into the windpipe. The epiglottis is an elastic cartilage, which serves as a switch between the larynx and the oesophagus by allowing the passage of air into the lungs, and food in the  gastrointestinal tract .

Have you ever wondered why we cough when we eat or swallow?

Talking while we eat or swallow may sometimes result in incessant coughing. The reason behind this reaction is the epiglottis. It is forced to open for the air to exit outwards and the food to enter into the windpipe, triggering a cough.

The trachea or the windpipe rises below the larynx and moves down to the neck. The walls of the trachea comprise C-shaped cartilaginous rings which give hardness to the trachea and maintain it by completely expanding. The trachea extends further down into the breastbone and splits into two bronchi, one for each lung.

The trachea splits into two tubes called the bronchi, which enter each lung individually. The bronchi divide into secondary and tertiary bronchioles, and it further branches out into small air-sacs called the alveoli. The alveoli are single-celled sacs of air with thin walls. It facilitates the exchange of oxygen and carbon dioxide molecules into or away from the bloodstream.

Lungs are the primary organs of respiration in humans and other vertebrates. They are located on either side of the heart, in the thoracic cavity of the chest. Anatomically, the lungs are spongy organs with an estimates total surface area between 50 to 75 sq meters. The primary function of the lungs is to facilitate the exchange of gases between the blood and the air. Interestingly, the right lung is quite bigger and heavier than the left lung.

Also Read:  Respiration

The respiratory tract in humans is made up of the following parts:

• External nostrils – For the intake of air.
• Nasal chamber – which is lined with hair and mucus to filter the air from dust and dirt.
• Pharynx – It is a passage behind the nasal chamber and serves as the common passageway for both air and food.
• Larynx – Known as the soundbox as it houses the vocal chords, which are paramount in the generation of sound.
• Epiglottis – It is a flap-like structure that covers the glottis and prevents the entry of food into the windpipe.
• Trachea – It is a long tube passing through the mid-thoracic cavity.
• Bronchi – The trachea divides into left and right bronchi.
• Bronchioles – Each bronchus is further divided into finer channels known as bronchioles.
• Alveoli – The bronchioles terminate in balloon-like structures known as the alveoli.
• Lungs – Humans have a pair of lungs, which are sac-like structures and covered by a double-layered membrane known as pleura.

Air is inhaled with the help of nostrils, and in the nasal cavity, the air is cleansed by the fine hair follicles present within them. The cavity also has a group of blood vessels that warm the air. This air then passes to the pharynx, then to the larynx and into the trachea.

The trachea and the bronchi are coated with ciliated epithelial cells and goblet cells (secretory cells) which discharge mucus to moisten the air as it passes through the respiratory tract. It also traps the fine bits of dust or pathogen that escaped the hair in the nasal openings. The motile cilia beat in an ascending motion, such that the mucus and other foreign particles are carried back to the buccal cavity where it may either be coughed out (or swallowed.)

Once the air reaches the bronchus, it moves into the bronchioles, and then into the alveoli.

Respiratory System Functions

The functions of the human respiratory system are as follows:

Inhalation and Exhalation

The respiratory system helps in breathing (also known as pulmonary ventilation.) The air inhaled through the nose moves through the pharynx, larynx, trachea and into the lungs. The air is exhaled back through the same pathway. Changes in the volume and pressure in the lungs aid in pulmonary ventilation.

Exchange of Gases between Lungs and Bloodstream

Inside the lungs, the oxygen and carbon dioxide enter and exit respectively through millions of microscopic sacs called alveoli. The inhaled oxygen diffuses into the pulmonary capillaries, binds to haemoglobin and is pumped through the bloodstream. The carbon dioxide from the blood diffuses into the alveoli and is expelled through exhalation.

Also read: Exchange Of Gases in Plants

Exchange of Gases between Bloodstream and Body Tissues

The blood carries the oxygen from the lungs around the body and releases the oxygen when it reaches the capillaries. The oxygen is diffused through the capillary walls into the body tissues. The carbon dioxide also diffuses into the blood and is carried back to the lungs for release.

The Vibration of the Vocal Cords

While speaking, the muscles in the larynx move the arytenoid cartilage. These cartilages push the vocal cords together. During exhalation, when the air passes through the vocal cords, it makes them vibrate and creates sound.

Olfaction or Smelling

During inhalation, when the air enters the nasal cavities, some chemicals present in the air bind to it and activate the receptors of the nervous system on the cilia. The signals are sent to the olfactory bulbs via the brain.

Also Read:  Respiratory System Disorders

Respiration is one of the metabolic processes which plays an essential role in all living organisms. However, lower organisms like the unicellular do not “breathe” like humans – intead, they utilise the process of diffusion. Annelids like earthworms have a moist cuticle which helps them in gaseous exchange. Respiration in fish occurs through special organs called gills. Most of the higher organisms possess a pair of lungs for breathing.

Also Read:  Amphibolic Pathway

To learn more about respiration, check out the video below:

Frequently Asked Questions

What is the human respiratory system.

The human respiratory system is a system of organs responsible for inhaling oxygen and exhaling carbon dioxide in humans. The important respiratory organs in living beings include- lungs, gills, trachea, and skin.

What are the important respiratory system parts in humans?

The important human respiratory system parts include- Nose, larynx, pharynx, trachea, bronchi and lungs.

What is the respiratory tract made up of?

The respiratory tract is made up of nostrils, nasal chamber, larynx, pharynx, epiglottis, trachea, bronchioles, bronchi, alveoli, and lungs.

What are the main functions of the respiratory system?

The important functions of the respiratory system include- inhalation and exhalation of gases, exchange of gases between bloodstream and lungs, the gaseous exchange between bloodstream and body tissues, olfaction and vibration of vocal cords.

What are the different types of respiration in humans?

The different types of respiration in humans include- internal respiration, external respiration and cellular respiration. Internal respiration includes the exchange of gases between blood and cells, external respiration is the breathing process, whereas cellular respiration is the metabolic reactions taking place in the cells to produce energy.

What are the different stages of aerobic respiration?

Aerobic respiration is the process of breaking down glucose to produce energy. It occurs in the following different stages- glycolysis, pyruvate oxidation, citric acid cycle or Krebs cycle, and electron transport system.

Why do the cells need oxygen?

Our body cells require oxygen to release energy. The oxygen inhaled during respiration is used to break down the food to release energy.

What is the main difference between breathing and respiration in humans?

Breathing is the physical process of inhaling oxygen and exhaling carbon dioxide in and out of our lungs. On the contrary, respiration is the chemical process where oxygen is utilized to break down glucose to generate energy to carry out different cellular processes.

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High school biology

Course: high school biology   >   unit 8.

• Meet the heart!
• Circulatory system and the heart
• The circulatory system review
• Meet the lungs!
• The lungs and pulmonary system

The respiratory system review

• The circulatory and respiratory systems

The respiratory system

Common mistakes and misconceptions.

• Incorrect : Physiological respiration and cellular respiration are the same thing.
• Correct : People sometimes use the word "respiration" to refer to the process of cellular respiration, which is a cellular process in which carbohydrates are used to generate usable energy. Physiological respiration and cellular respiration are related processes, but they are not the same.
• Incorrect : We breathe in only oxygen and breathe out only carbon dioxide.
• Correct : Often the terms "oxygen" and "air" are used interchangeably. It is true that the air we breathe in has more oxygen than the air we breathe out, and the air we breathe out has more carbon dioxide than the air that we breathe in. However, oxygen is just one of the gases found in the air we breathe. (In fact, the air has more nitrogen than oxygen!)
• Incorrect : The respiratory system works alone in transporting oxygen through the body.
• Correct : The respiratory system works directly with the circulatory system to provide oxygen to the body. Oxygen taken in from the respiratory system moves into blood vessels that then circulate oxygen-rich blood to tissues and cells.

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8.1: Introduction to the Respiratory System

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Learning Objectives

By the end of this section, you will be able to:

• List the structures of the respiratory system
• List the major functions of the respiratory system
• Outline the forces that allow for air movement into and out of the lungs
• Outline the process of gas exchange
• Summarize the process of oxygen and carbon dioxide transport within the respiratory system
• Create a flow chart illustrating how respiration is controlled
• Discuss how the respiratory system responds to exercise
• Describe the development of the respiratory system in the embryo

Hold your breath. Really! See how long you can hold your breath as you continue reading. . . . How long can you do it? Chances are you are feeling uncomfortable already. A typical human cannot survive without breathing for more than 3 minutes, and even if you wanted to hold your breath longer, your autonomic nervous system would take control. This is because every cell in the body needs to run the oxidative stages of cellular respiration, the process by which energy is produced in the form of adenosine triphosphate (ATP). For oxidative phosphorylation to occur, oxygen is used as a reactant and carbon dioxide is released as a waste product.

You may be surprised to learn that although oxygen is a critical need for cells, it is actually the accumulation of carbon dioxide that primarily drives your need to breathe. Carbon dioxide is exhaled and oxygen is inhaled through the respiratory system, which includes muscles to move air into and out of the lungs, passageways through which air moves, and microscopic gas exchange surfaces covered by capillaries. The circulatory system transports gases from the lungs to tissues throughout the body and vice versa. A variety of diseases can affect the respiratory system, such as asthma, emphysema, chronic obstruction pulmonary disorder (COPD), and lung cancer. All of these conditions affect the gas exchange process and result in labored breathing and other difficulties.

Contributors and Attributions

• Anatomy & Physiology. Provided by : OpenStax CNX. Located at : http://cnx.org/contents/[email protected] . License : CC BY: Attribution . License Terms : Download for free at http://cnx.org/contents/[email protected]

Home — Essay Samples — Nursing & Health — Anatomy & Physiology — Respiratory System

Essay Examples on Respiratory System

The respiratory system is an essential part of the human body, responsible for the intake of oxygen and the release of carbon dioxide. It plays a crucial role in maintaining the body's overall health and well-being. Writing an essay about the respiratory system can help to increase awareness and understanding of its importance.

When choosing a topic for an essay on the respiratory system, it is important to consider the different types of essays that can be written. For an argumentative essay, topics could include the impact of air pollution on respiratory health or the benefits of regular exercise for lung function. In a cause-and-effect essay, topics could explore the relationship between smoking and lung disease or the effects of air quality on respiratory health. For an opinion essay, topics could focus on the importance of clean air for respiratory health or the role of government policies in promoting lung health. Finally, for an informative essay, topics could cover the anatomy and function of the respiratory system or the common respiratory disorders and their treatments.

For example, a thesis statement for an essay on the respiratory system could be "The respiratory system is a vital organ system that is essential for human survival and overall health." This statement provides a clear focus for the essay and sets the tone for the rest of the paper.

In the paragraph of an essay on the respiratory system, one could start with a thought-provoking question such as "Have you ever stopped to think about how important your breathing is to your overall health?" This can help to engage the reader and draw them into the topic. Another approach could be to provide a brief overview of the respiratory system and its functions, setting the stage for the rest of the essay.

In the paragraph of an essay on the respiratory system, one could summarize the key points discussed in the essay and reiterate the importance of maintaining respiratory health. One could also encourage readers to take proactive steps to care for their respiratory system, such as avoiding exposure to air pollutants and practicing good respiratory hygiene. This can help to leave a lasting impression on the reader and reinforce the significance of the topic.

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Respiratory System - Essay Samples And Topic Ideas For Free

The respiratory system is a biological system consisting of organs that facilitate the inhalation of oxygen and exhalation of carbon dioxide. Essays on the respiratory system could delve into its anatomy and physiology, common diseases and conditions affecting it, and the impact of environmental factors like pollution on respiratory health. We have collected a large number of free essay examples about Respiratory System you can find at Papersowl. You can use our samples for inspiration to write your own essay, research paper, or just to explore a new topic for yourself.

Respiratory System Function

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The Anatomy of the Respiratory System and Asthma

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Respiratory and Circulatory System

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The Respiratory System

The functions of the respiratory system are; inhalation and exhalation, External Respiration exchanges gases between the Lungs and the bloodstream, Internal Respiration Exchanges gases between the bloodstream and body tissues and generates sound with speech. The respiratory system includes the nose, pharynx, larynx, trachea, bronchi and lungs. The respiratory system has two important functions: it brings oxygen into our bodies, which we need for our cells to live and function properly; and it helps us get rid of carbon dioxide, […]

Breathing is Main of the Respiratory System

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Pathophysiology and Etiology of the Asthma

Asthma, a chronic disease process, affects approximately 18 million people in the United States. While asthma can be reversible, failure to control symptoms and provide adequate and timely treatment can lead to a decrease in respiratory function, which ultimately increases the risk of death (Durham, Fowler, Smith, & Sterrett, 2017). Accurate and timely nursing care can help patients manage their symptoms and increase their quality of life while decreasing hospitalizations and related costs (Keep, Reiffer, & Bahl, 2016). Disease Condition […]

Respiratory System Research Paper

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Organs of the Respiratory System

This system consists of "the nose, pharynx, larynx, trachea, bronchi and their smaller branches, and the lungs which contain the alveoli" IMarieb, 2015). The nose is superior to the mouth. The pharynx is posterior to the nasal and oral cavities. The larynx is inferior to the pharynx and connects the pharynx to the trachea. The (main) bronchi are medial to the arms and are formed by the division of the trachea. The lungs are superior to the diaphragm and occupy […]

A Chronic Inflammatory Disease Asthma

Asthma is a chronic inflammatory disease of the airways which occurs in genetically predisposed individuals. Asthma is a reactive airway disease. This common disease has an epidemic progression in western countries (Wenzel, 2003). Environmental factors are likely to be the cause of the progression of this disease. Asthma can be triggered by various stimuli and can result in either a bacterial or viral infection. Asthma occurs when inflammation constricts the airways when the lungs are reacting to physical activities, respiratory […]

Respiratory System – a Group of Respiratory Organs

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Pulmonary System: Anatomy, Function, and Diseases

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The Respiratory System Functions and Varieties Across the Animal Kingdom

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The mortal frame comprises a labyrinthine interconnection of mechanisms harmonizing to sustain existence. Amidst these, the circulatory and respiratory mechanisms enact pivotal roles in upholding the organism's operations. These duad systems intricately intertwine, operating synchronously to ensure the conveyance of oxygen to the tissues and the expulsion of carbon dioxide from the entity. Comprehending the interplay between these mechanisms proves pivotal to grasp the manner in which the entity preserves its intrinsic milieu and sustains its diverse endeavors. The respiratory […]

The Essential Role of the Respiratory System

The respiratory mechanism assumes a pivotal role in the sustenance of life, orchestrating functions of paramount importance for our existence. At its essence, this intricate apparatus facilitates gas interchange, bestowing oxygen upon the corpus while expelling carbon dioxide, a metabolic byproduct. This foundational process underpins cellular respiration, a cornerstone of energy generation and bodily homeostasis. Beyond its rudimentary function, the respiratory ensemble assumes critical responsibilities in blood pH modulation, immunological defense, and speech facilitation. Oxygen, the lifeblood of cellular metabolism, […]

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14.2: Organs and Structures of the Respiratory System

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Learning Objectives

• List the structures that make up the respiratory system
• Describe how the respiratory system processes oxygen and CO 2
• Compare and contrast the functions of upper respiratory tract with the lower respiratory tract

The major organs of the respiratory system function primarily to provide oxygen to body tissues for cellular respiration, remove the waste product carbon dioxide, and help to maintain acid-base balance. Portions of the respiratory system are also used for non-vital functions, such as sensing odors, speech production, and for straining, such as during childbirth or coughing (Figure \(\PageIndex{1}\)).

Functionally, the respiratory system can be divided into a conducting zone and a respiratory zone. The conducting zone of the respiratory system includes the organs and structures not directly involved in gas exchange. The gas exchange occurs in the respiratory zone .

Conducting Zone

The major functions of the conducting zone are to provide a route for incoming and outgoing air, remove debris and pathogens from the incoming air, and warm and humidify the incoming air. Several structures within the conducting zone perform other functions as well. The epithelium of the nasal passages, for example, is essential to sensing odors, and the bronchial epithelium that lines the lungs can metabolize some airborne carcinogens.

The Nose and Its Adjacent Structures

The major entrance and exit for the respiratory system is through the nose. When discussing the nose, it is helpful to divide it into two major sections: the external nose, and the nasal cavity or internal nose.

The external nose consists of the surface and skeletal structures that result in the outward appearance of the nose and contribute to its numerous functions (Figure \(\PageIndex{2}\)). The root is the region of the nose located between the eyebrows. The bridge is the part of the nose that connects the root to the rest of the nose. The dorsum nasi is the length of the nose. The apex is the tip of the nose. On either side of the apex, the nostrils are formed by the alae (singular = ala). An ala is a cartilaginous structure that forms the lateral side of each naris (plural = nares), or nostril opening. The philtrum is the concave surface that connects the apex of the nose to the upper lip.

Underneath the thin skin of the nose are its skeletal features (see Figure \(\PageIndex{2}\), lower illustration). While the root and bridge of the nose consist of bone, the protruding portion of the nose is composed of cartilage. As a result, when looking at a skull, the nose is missing. The nasal bone is one of a pair of bones that lies under the root and bridge of the nose. The nasal bone articulates superiorly with the frontal bone and laterally with the maxillary bones. Septal cartilage is flexible hyaline cartilage connected to the nasal bone, forming the dorsum nasi. The alar cartilage consists of the apex of the nose; it surrounds the naris.

The nares open into the nasal cavity, which is separated into left and right sections by the nasal septum (Figure \(\PageIndex{3}\)). The nasal septum is formed anteriorly by a portion of the septal cartilage (the flexible portion you can touch with your fingers) and posteriorly by the perpendicular plate of the ethmoid bone (a cranial bone located just posterior to the nasal bones) and the thin vomer bones (whose name refers to its plough shape). Each lateral wall of the nasal cavity has three bony projections, called the superior, middle, and inferior nasal conchae. The inferior conchae are separate bones, whereas the superior and middle conchae are portions of the ethmoid bone. Conchae serve to increase the surface area of the nasal cavity and to disrupt the flow of air as it enters the nose, causing air to bounce along the epithelium, where it is cleaned and warmed. The conchae and meatuses also conserve water and prevent dehydration of the nasal epithelium by trapping water during exhalation. The floor of the nasal cavity is composed of the palate. The hard palate at the anterior region of the nasal cavity is composed of bone. The soft palate at the posterior portion of the nasal cavity consists of muscle tissue. Air exits the nasal cavities via the internal nares and moves into the pharynx.

Several bones that help form the walls of the nasal cavity have air-containing spaces called the paranasal sinuses, which serve to warm and humidify incoming air. Sinuses are lined with a mucosa. Each paranasal sinus is named for its associated bone: frontal sinus, maxillary sinus, sphenoidal sinus, and ethmoidal sinus. The sinuses produce mucus and lighten the weight of the skull.

The nares and anterior portion of the nasal cavities are lined with mucous membranes, containing sebaceous glands and hair follicles that serve to prevent the passage of large debris, such as dirt, through the nasal cavity. An olfactory epithelium used to detect odors is found deeper in the nasal cavity.

The conchae, meatuses, and paranasal sinuses are lined by respiratory epithelium composed of pseudostratified ciliated columnar epithelium (Figure \(\PageIndex{4}\)). The epithelium contains goblet cells, one of the specialized, columnar epithelial cells that produce mucus to trap debris. The cilia of the respiratory epithelium help remove the mucus and debris from the nasal cavity with a constant beating motion, sweeping materials towards the throat to be swallowed. Interestingly, cold air slows the movement of the cilia, resulting in accumulation of mucus that may in turn lead to a runny nose during cold weather. This moist epithelium functions to warm and humidify incoming air. Capillaries located just beneath the nasal epithelium warm the air by convection. Serous and mucus-producing cells also secrete the lysozyme enzyme and proteins called defensins, which have antibacterial properties. Immune cells that patrol the connective tissue deep to the respiratory epithelium provide additional protection.

The pharynx is a tube formed by skeletal muscle and lined by mucous membrane that is continuous with that of the nasal cavities (see Figure \(\PageIndex{3}\)). The pharynx is divided into three major regions: the nasopharynx, the oropharynx, and the laryngopharynx (Figure \(\PageIndex{5}\)).

The nasopharynx is flanked by the conchae of the nasal cavity, and it serves only as an airway. At the top of the nasopharynx are the pharyngeal tonsils. A pharyngeal tonsil , also called an adenoid, is an aggregate of lymphoid reticular tissue similar to a lymph node that lies at the superior portion of the nasopharynx. The function of the pharyngeal tonsil is not well understood, but it contains a rich supply of lymphocytes and is covered with ciliated epithelium that traps and destroys invading pathogens that enter during inhalation. The pharyngeal tonsils are large in children, but interestingly, tend to regress with age and may even disappear. The uvula is a small bulbous, teardrop-shaped structure located at the apex of the soft palate. Both the uvula and soft palate move like a pendulum during swallowing, swinging upward to close off the nasopharynx to prevent ingested materials from entering the nasal cavity. In addition, auditory (Eustachian) tubes that connect to each middle ear cavity open into the nasopharynx. This connection is why colds often lead to ear infections.

The oropharynx is a passageway for both air and food. The oropharynx is bordered superiorly by the nasopharynx and anteriorly by the oral cavity. The fauces is the opening at the connection between the oral cavity and the oropharynx. As the nasopharynx becomes the oropharynx, the epithelium changes from pseudostratified ciliated columnar epithelium to stratified squamous epithelium. The oropharynx contains two distinct sets of tonsils, the palatine and lingual tonsils. A palatine tonsil is one of a pair of structures located laterally in the oropharynx in the area of the fauces. The lingual tonsil is located at the base of the tongue. Similar to the pharyngeal tonsil, the palatine and lingual tonsils are composed of lymphoid tissue, and trap and destroy pathogens entering the body through the oral or nasal cavities.

The laryngopharynx is inferior to the oropharynx and posterior to the larynx. It continues the route for ingested material and air until its inferior end, where the digestive and respiratory systems diverge. The stratified squamous epithelium of the oropharynx is continuous with the laryngopharynx. Anteriorly, the laryngopharynx opens into the larynx, whereas posteriorly, it enters the esophagus.

The larynx is a cartilaginous structure inferior to the laryngopharynx that connects the pharynx to the trachea and helps regulate the volume of air that enters and leaves the lungs (Figure \(\PageIndex{6}\)). The structure of the larynx is formed by several pieces of cartilage. Three large cartilage pieces—the thyroid cartilage (anterior), epiglottis (superior), and cricoid cartilage (inferior)—form the major structure of the larynx. The thyroid cartilage is the largest piece of cartilage that makes up the larynx. The thyroid cartilage consists of the laryngeal prominence , or “Adam’s apple,” which tends to be more prominent in males. The thick cricoid cartilage forms a ring, with a wide posterior region and a thinner anterior region. Three smaller, paired cartilages—the arytenoids, corniculates, and cuneiforms—attach to the epiglottis and the vocal cords and muscle that help move the vocal cords to produce speech.

The epiglottis , attached to the thyroid cartilage, is a very flexible piece of elastic cartilage that covers the opening of the trachea (see Figure \(\PageIndex{3}\)). When in the “closed” position, the unattached end of the epiglottis rests on the glottis. The glottis is composed of the vestibular folds, the true vocal cords, and the space between these folds (Figure \(\PageIndex{7}\)). A vestibular fold , or false vocal cord, is one of a pair of folded sections of mucous membrane. A true vocal cord is one of the white, membranous folds attached by muscle to the thyroid and arytenoid cartilages of the larynx on their outer edges. The inner edges of the true vocal cords are free, allowing oscillation to produce sound. The size of the membranous folds of the true vocal cords differs between individuals, producing voices with different pitch ranges. Folds in males tend to be larger than those in females, which create a deeper voice. The act of swallowing causes the pharynx and larynx to lift upward, allowing the pharynx to expand and the epiglottis of the larynx to swing downward, closing the opening to the trachea. These movements produce a larger area for food to pass through, while preventing food and beverages from entering the trachea.

Continuous with the laryngopharynx, the superior portion of the larynx is lined with stratified squamous epithelium, transitioning into pseudostratified ciliated columnar epithelium that contains goblet cells. Similar to the nasal cavity and nasopharynx, this specialized epithelium produces mucus to trap debris and pathogens as they enter the trachea. The cilia beat the mucus upward towards the laryngopharynx, where it can be swallowed down the esophagus.

The trachea (windpipe) extends from the larynx toward the lungs (Figure \(\PageIndex{8}\).a). The trachea is formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue. The trachealis muscle and elastic connective tissue together form the fibroelastic membrane , a flexible membrane that closes the posterior surface of the trachea, connecting the C-shaped cartilages. The fibroelastic membrane allows the trachea to stretch and expand slightly during inhalation and exhalation, whereas the rings of cartilage provide structural support and prevent the trachea from collapsing. In addition, the trachealis muscle can be contracted to force air through the trachea during exhalation. The trachea is lined with pseudostratified ciliated columnar epithelium, which is continuous with the larynx. The esophagus borders the trachea posteriorly.

Bronchial Tree

The trachea branches into the right and left primary bronchi at the carina. These bronchi are also lined by pseudostratified ciliated columnar epithelium containing mucus-producing goblet cells (Figure \(\PageIndex{8}\).b). The carina is a raised structure that contains specialized nervous tissue that induces violent coughing if a foreign body, such as food, is present. Rings of cartilage, similar to those of the trachea, support the structure of the bronchi and prevent their collapse. The primary bronchi enter the lungs at the hilum, a concave region where blood vessels, lymphatic vessels, and nerves also enter the lungs. The bronchi continue to branch into bronchial a tree. A bronchial tree (or respiratory tree) is the collective term used for these multiple-branched bronchi. The main function of the bronchi, like other conducting zone structures, is to provide a passageway for air to move into and out of each lung. In addition, the mucous membrane traps debris and pathogens.

A bronchiole branches from the tertiary bronchi. Bronchioles, which are about 1 mm in diameter, further branch until they become the tiny terminal bronchioles, which lead to the structures of gas exchange. There are more than 1000 terminal bronchioles in each lung. The muscular walls of the bronchioles do not contain cartilage like those of the bronchi. This muscular wall can change the size of the tubing to increase or decrease airflow through the tube.

Respiratory Zone

In contrast to the conducting zone, the respiratory zone includes structures that are directly involved in gas exchange. The respiratory zone begins where the terminal bronchioles join a respiratory bronchiole , the smallest type of bronchiole (Figure \(\PageIndex{9}\)), which then leads to an alveolar duct, opening into a cluster of alveoli.

An alveolar duct is a tube composed of smooth muscle and connective tissue, which opens into a cluster of alveoli. An alveolus is one of the many small, grape-like sacs that are attached to the alveolar ducts.

An alveolar sac is a cluster of many individual alveoli that are responsible for gas exchange. An alveolus is approximately 200 μm in diameter with elastic walls that allow the alveolus to stretch during air intake, which greatly increases the surface area available for gas exchange. Alveoli are connected to their neighbors by alveolar pores , which help maintain equal air pressure throughout the alveoli and lung (Figure \(\PageIndex{10}\)).

The alveolar wall consists of three major cell types: type I alveolar cells, type II alveolar cells, and alveolar macrophages. A type I alveolar cell is a squamous epithelial cell of the alveoli, which constitute up to 97 percent of the alveolar surface area. These cells are about 25 nm thick and are highly permeable to gases. A type II alveolar cell is interspersed among the type I cells and secretes pulmonary surfactant , a substance composed of phospholipids and proteins that reduces the surface tension of the alveoli. Roaming around the alveolar wall is the alveolar macrophage , a phagocytic cell of the immune system that removes debris and pathogens that have reached the alveoli.

The simple squamous epithelium formed by type I alveolar cells is attached to a thin, elastic basement membrane. This epithelium is extremely thin and borders the endothelial membrane of capillaries. Taken together, the alveoli and capillary membranes form a respiratory membrane that is approximately 0.5 mm thick. The respiratory membrane allows gases to cross by simple diffusion, allowing oxygen to be picked up by the blood for transport and CO 2 to be released into the air of the alveoli.

Diseases of the Respiratory System: Asthma

Asthma is common condition that affects the lungs in both adults and children. Approximately 8.2 percent of adults (18.7 million) and 9.4 percent of children (7 million) in the United States suffer from asthma. In addition, asthma is the most frequent cause of hospitalization in children.

Asthma is a chronic disease characterized by inflammation and edema of the airway, and bronchospasms (that is, constriction of the bronchioles), which can inhibit air from entering the lungs. In addition, excessive mucus secretion can occur, which further contributes to airway occlusion (Figure \(\PageIndex{11}\)). Cells of the immune system, such as eosinophils and mononuclear cells, may also be involved in infiltrating the walls of the bronchi and bronchioles.

Bronchospasms occur periodically and lead to an “asthma attack.” An attack may be triggered by environmental factors such as dust, pollen, pet hair, or dander, changes in the weather, mold, tobacco smoke, and respiratory infections, or by exercise and stress.

Symptoms of an asthma attack involve coughing, shortness of breath, wheezing, and tightness of the chest. Symptoms of a severe asthma attack that requires immediate medical attention would include difficulty breathing that results in blue (cyanotic) lips or face, confusion, drowsiness, a rapid pulse, sweating, and severe anxiety. The severity of the condition, frequency of attacks, and identified triggers influence the type of medication that an individual may require. Longer-term treatments are used for those with more severe asthma. Short-term, fast-acting drugs that are used to treat an asthma attack are typically administered via an inhaler. For young children or individuals who have difficulty using an inhaler, asthma medications can be administered via a nebulizer.

In many cases, the underlying cause of the condition is unknown. However, recent research has demonstrated that certain viruses, such as human rhinovirus C (HRVC), and the bacteria Mycoplasma pneumoniae and Chlamydia pneumoniae that are contracted in infancy or early childhood, may contribute to the development of many cases of asthma.

Chapter Review

The respiratory system is responsible for obtaining oxygen and getting rid of carbon dioxide, and aiding in speech production and in sensing odors. From a functional perspective, the respiratory system can be divided into two major areas: the conducting zone and the respiratory zone. The conducting zone consists of all of the structures that provide passageways for air to travel into and out of the lungs: the nasal cavity, pharynx, trachea, bronchi, and most bronchioles. The nasal passages contain the conchae and meatuses that expand the surface area of the cavity, which helps to warm and humidify incoming air, while removing debris and pathogens. The pharynx is composed of three major sections: the nasopharynx, which is continuous with the nasal cavity; the oropharynx, which borders the nasopharynx and the oral cavity; and the laryngopharynx, which borders the oropharynx, trachea, and esophagus. The respiratory zone includes the structures of the lung that are directly involved in gas exchange: the terminal bronchioles and alveoli.

The lining of the conducting zone is composed mostly of pseudostratified ciliated columnar epithelium with goblet cells. The mucus traps pathogens and debris, whereas beating cilia move the mucus superiorly toward the throat, where it is swallowed. As the bronchioles become smaller and smaller, and nearer the alveoli, the epithelium thins and is simple squamous epithelium in the alveoli. The endothelium of the surrounding capillaries, together with the alveolar epithelium, forms the respiratory membrane. This is a blood-air barrier through which gas exchange occurs by simple diffusion.

Essay Questions

Q. What happens during an asthma attack. What are the three changes that occur inside the airways during an asthma attack?

A. Inflammation and the production of a thick mucus; constriction of the airway muscles, or bronchospasm; and an increased sensitivity to allergens.

Review Questions

Q. Which of the following anatomical structures is not part of the conducting zone?

B. nasal cavity

Q. What is the function of the conchae in the nasal cavity?

A. increase surface area

B. exchange gases

C. maintain surface tension

D. maintain air pressure

Q. The fauces connects which of the following structures to the oropharynx?

A. nasopharynx

B. laryngopharynx

C. nasal cavity

D. oral cavity

Q. Which of the following are structural features of the trachea?

A. C-shaped cartilage

B. smooth muscle fibers

D. all of the above

Q. Which of the following structures is not part of the bronchial tree?

C. terminal bronchioles

D. respiratory bronchioles

Q. What is the role of alveolar macrophages?

A. to secrete pulmonary surfactant

B. to secrete antimicrobial proteins

C. to remove pathogens and debris

D. to facilitate gas exchange

Critical Thinking Questions

Q. Describe the three regions of the pharynx and their functions.

A. The pharynx has three major regions. The first region is the nasopharynx, which is connected to the posterior nasal cavity and functions as an airway. The second region is the oropharynx, which is continuous with the nasopharynx and is connected to the oral cavity at the fauces. The laryngopharynx is connected to the oropharynx and the esophagus and trachea. Both the oropharynx and laryngopharynx are passageways for air and food and drink.

Q. If a person sustains an injury to the epiglottis, what would be the physiological result?

A. The epiglottis is a region of the larynx that is important during the swallowing of food or drink. As a person swallows, the pharynx moves upward and the epiglottis closes over the trachea, preventing food or drink from entering the trachea. If a person’s epiglottis were injured, this mechanism would be impaired. As a result, the person may have problems with food or drink entering the trachea, and possibly, the lungs. Over time, this may cause infections such as pneumonia to set in.

Q. Compare and contrast the conducting and respiratory zones.

A. The conducting zone of the respiratory system includes the organs and structures that are not directly involved in gas exchange, but perform other duties such as providing a passageway for air, trapping and removing debris and pathogens, and warming and humidifying incoming air. Such structures include the nasal cavity, pharynx, larynx, trachea, and most of the bronchial tree. The respiratory zone includes all the organs and structures that are directly involved in gas exchange, including the respiratory bronchioles, alveolar ducts, and alveoli.

Bizzintino J, Lee WM, Laing IA, Vang F, Pappas T, Zhang G, Martin AC, Khoo SK, Cox DW, Geelhoed GC, et al. Association between human rhinovirus C and severity of acute asthma in children. Eur Respir J [Internet]. 2010 [cited 2013 Mar 22]; 37(5):1037–1042.

Kumar V, Ramzi S, Robbins SL. Robbins Basic Pathology. 7th ed. Philadelphia (PA): Elsevier Ltd; 2005.

Martin RJ, Kraft M, Chu HW, Berns, EA, Cassell GH. A link between chronic asthma and chronic infection. J Allergy Clin Immunol [Internet]. 2001 [cited 2013 Mar 22]; 107(4):595-601.

Contributors and Attributions

OpenStax Anatomy & Physiology (CC BY 4.0). Access for free at  https://openstax.org/books/anatomy-and-physiology

Short essay on Respiratory System in Humans (Or Man)

In human beings, many organs take part in the process of respiration. We call them organs of respiratory system. The main organs of human respiratory system are: Nose, Nasal passage (or Nasal cavity), Trachea, Bronchi, Lungs and Diaphragm.

The human respiratory system begins from the nose. Our nose has two holes in it which are called nostrils. There is a passage in the nose behind the nostrils which is called nasal passage (or nasal cavity). The air for respiration is drawn into our body through the nostrils present in the nose. This air then goes into nasal passage.

The nasal passage is separated from the mouth cavity (buccal cavity or oral cavity) by a hard, bony palate so that we can breathe in air even when we are eating food (and the mouth cavity is filled with food). The nasal passage is lined with fine hair and mucus (Mucus is secreted by the glands inside the nasal passage).

When air passes through the nasal passage, the dust particles and other impurities present in it are trapped by nasal hair and mucus so that clean air goes into the lungs. The part of throat between the mouth and wind pipe is called pharynx. From the nasal passage, air enters into pharynx and then goes into the wind pipe (or trachea).

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The trachea is a tube which is commonly known as wind pipe. The air coming from the nostrils during breathing passes through trachea. Trachea does not collapse even when there is no air in it because it is supported by rings of soft bones called cartilage. The upper end of trachea has a voice box called larynx.

The trachea runs down the neck and divides into two smaller tubes called ‘bronchi’ at its lower end. (The singular of bronchi is bronchus). The two bronchi are connected to the two lungs. The lungs lie in the chest cavity or thoracic cavity which is separated from abdominal cavity by a muscular partition called diaphragm.

The lungs are covered by two thin membranes called pleura. The lungs are enclosed in a ‘rib cage’ made of bones called ‘ribs’. We have not shown the rib cage in Figure 64 to keep the diagram simple.

Each bronchus divides in the lungs to form a large number of still smaller tubes called ‘bronchioles’. The smallest bronchioles have tiny air-sacs at their ends (see Figure 64). The pouch-like air-sacs at the ends of the smallest bronchioles are called ‘alveoli’ (singular alveolus).

The walls of alveoli are very thin and they are surrounded by very thin blood capillaries. It is in the alveoli that oxygen is taken into the body and carbon dioxide is eliminated. In other words, it is in the alveoli that gaseous exchange takes place. The human lungs have been designed to maximise the exchange of gases as follows:

There are millions of alveoli in the lungs. The presence of millions of alveoli in the lungs provides a very large area for the exchange of gases. And the availability of large surface area maximises the exchange of gases. For example, if all alveoli from the two human lungs are unfolded, they would give an area of about 80 square metres (which is nearly the size of a tennis court!). The diaphragm is a sheet of muscle below the lungs. It helps in ‘breathing in’ and ‘breathing out’. The muscles of chest also help in breathing in and breathing out.

When we breathe in air, the diaphragm arid muscles attached to the ribs contract due to which our chest cavity expands. This expansion movement of the chest increases the volume inside the chest cavity. Due to increase in volume, the air pressure decreases inside the chest cavity and air from outside (being at higher pressure) rushes into the lungs through the nostrils, trachea and bronchi.

In this way, during the process of ‘breathing in’ the air sacs or alveoli of the lungs get filled with air containing oxygen. The alveoli are surrounded by very thin blood vessels called capillaries carrying blood in them. So, the oxygen of air diffuses out from the alveoli walls into the blood.

The oxygen is carried by blood to all the parts of the body (This oxygen is carried by a red pigment called hemoglobin present in blood). As the blood passes through the tissues of the body, the oxygen present in it diffuses into the cells (due to its higher concentration in the blood).

This oxygen combines with the digested food (glucose) present in the cells to release energy. Carbon dioxide gas is produced as a waste product during respiration in the cells of the body tissues. This carbon dioxide diffuses into the blood (due to its higher concentration in body tissues).

Blood carries the carbon dioxide back to the lungs where it diffuses into the alveoli. When we breathe oil air, the diaphragm and the muscles attached to the ribs relax due to which our chest cavity contracts ant becomes smaller. This contraction movement of the chest pushes out carbon dioxide from the alveoli of the lungs into the trachea, nostrils and then out of the body into air. In this way the process of gaseous exchange is completed in the human respiratory system.

Please note that during the breathing cycle, when air is taken in (or inhaled) and let out (or exhaled), the lungs always contain a certain residual volume of air so that there is sufficient time ‘for the oxygen tot absorbed’ into the blood and ‘for the carbon dioxide to be released’ from the blood. Another point to be noted is that carbon dioxide is more soluble in water (than oxygen), so it is mostly transported in the dissolved form in our blood.

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Guest Essay

Why the New Human Case of Bird Flu Is So Alarming

By Rick Bright

Dr. Bright is a virologist and the former head of the Biomedical Advanced Research and Development Authority.

The third human case of H5N1, reported on Thursday in a farmworker in Michigan who was experiencing respiratory symptoms, tells us that the current bird flu situation is at a dangerous inflection point.

The virus is adapting in predictable ways that increase its risk to humans, reflecting our failure to contain it early on. The solutions to this brewing crisis — such as comprehensive testing — have been there all along, and they’re becoming only more important. If we keep ignoring the warning signs we have only ourselves to blame.

H5N1 has long been more than a bird problem. The virus has found its way into dairy cattle across nine states , affecting 69 herds that we know about. Of the three human cases of H5N1 that have been identified, all involve farmworkers who were in direct contact with infected cows or milk. The first two cases were relatively mild, involving symptoms like eye irritation, or conjunctivitis. However, the most recent case has shown more concerning signs, including coughing.

The emergence of respiratory symptoms is disconcerting because it indicates a potential shift in how the virus affects humans. Coughing can spread viruses more easily than eye irritation can.

New symptoms should be expected as the virus continues to spread and adapt to humans. Yet our response to this looming danger has been woefully inadequate, particularly in the area of testing.

Testing is our first line of defense in identifying and controlling infectious diseases. It allows health responders to understand the extent of an outbreak, identify who is infected and take measures to prevent further spread.

In the case of H5N1, human testing is crucial not only for diagnosing current infections but also for understanding how the virus is spreading. Serology testing, which looks for antibodies in the blood, can help us determine how many people have been infected with the virus even if they did not develop symptoms.

Despite its importance and repeated calls for its use , serology testing for H5N1 has been virtually non-existent in this outbreak. Without serology testing by state or local health officials, we are most likely missing many cases, particularly among asymptomatic people or those with mild symptoms. This underreporting skews our understanding of the virus’s spread and hampers our ability to respond effectively.

Undetected cases of H5N1 mean that infected people may continue to spread the virus unknowingly. This is especially dangerous in farming communities where close contact with animals and other workers is common. Each missed case is a potential link in a chain of transmission that could lead to a wider outbreak.

Moreover, failing to detect cases undermines the ability to have targeted public health interventions. If we don’t know the full extent of the outbreak, we can’t effectively allocate resources such as vaccines and antiviral treatments to those who need them most.

There’s also a human cost. Farmworkers, often working long hours in proximity to infected animals, bear the brunt of this oversight. They are at higher risk for infection and yet many lack health insurance and paid sick leave, making it difficult for them to seek testing and treatment. They may also be reluctant to report symptoms or seek medical care out of fear of losing their jobs or facing immigration-related repercussions. As a result, many may continue working while infected, further spreading the virus.

This is why we need a robust national testing strategy, coordinated by the Centers for Disease Control and Prevention, that includes both diagnostic and serology testing. This should be coupled with outreach efforts from state and local health departments to ensure that farmworkers have access to testing and feel safe using it. This means providing clear information in multiple languages, ensuring that testing is free and accessible, and offering support for those who test positive, such as paid sick leave and medical care. All health workers should be trained and equipped with tests that can provide a rapid diagnosis that will prompt timely and appropriate treatment.

The United States must also improve surveillance and data collection to get a clearer picture of the outbreak. This includes ramping up testing in areas with known infections, conducting regular screenings of at-risk populations by state and local health departments and using innovative approaches such as wastewater surveillance to detect the virus in communities early.

To further cloud our understanding of the outbreak, the U.S. Department of Agriculture has been slow to share critically important virus sequence data from animals infected with the H5N1 virus. While several states are continually reporting new infections in cows, the U.S.D.A. has not shared a virus sequence collected from a cow in several weeks.

This H5N1 outbreak is a warning. The report of respiratory symptoms is not a good sign, and this is not a good way to prevent a pandemic.

Rick Bright is the chief executive of Bright Global Health, a consulting company that focuses on improving responses to public health emergencies.

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Study of the tumor effect on airflow in human upper airway exhalation using fluid-structure interaction method

• Original Article
• Published: 05 June 2024

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• Golbarg Alsadat Motamedi 1 ,
• Shahrokh Shojaei 2 &
• Kamran Hasani 1  

The present study is able to calculate the effect of tumor presence on the air velocity and relative pressure in the upper respiratory system as in vitro, using fluid-structure interaction method. Three exhaled airflows of 15 L/min, 26 L/min, and 30 L/min were considered to simulate airflow. In this regard, the velocity reaches its maximum in the larynx and oropharynx. The maximum velocities at 15 l/min, 26 l/min, and 30 l/min flow rates are 6.26 m/s, 10.58 m/s, and 12.14 m/s, respectively, which occur in the larynx. The highest relative pressure was experienced in the trachea. So that the maximum relative pressure in the flow rates of 15 l/min, 26 l/min, and 30 l/min was equal to 19.6 Pa, 51.1 Pa, and 65.8 Pa, respectively. Then, by doubling the flow rate, the maximum relative pressure reached more than tripled. The numerical models presented for the respiratory system can be useful for better treatment attitudes.

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Abbreviations

Dynamic viscosity

Fluid stress tensor

Solid stress tensor

Normal vector

Structural displacement

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Acknowledgments

The authors of the manuscript declare that they have no conflict of interest. No organization or University funded the research.

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Department of Biomedical Engineering, College of Medical Science and Technologies, Tehran Science and Research Branch, Islamic Azad University, Tehran, Iran

Golbarg Alsadat Motamedi & Kamran Hasani

Department of Biomedical Engineering, Central Tehran Branch, Islamic Azad University, Tehran, Iran

Shahrokh Shojaei

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Correspondence to Shahrokh Shojaei .

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Golbarg Alsadat Motamedi is a Ph.D. student in the Department of Biomedical Engineering at the Science and Research Branch of Islamic Azad University in Tehran, Iran. Her research interests focus on Fluid-Structure Interaction (FSI) and Computational Fluid Dynamics (CFD), particularly emphasizing the respiratory system. Golbarg’ work aims to enhance the understanding of respiratory mechanics and improve biomedical applications through advanced mathematical modeling techniques.

Shahrokh Shojaei is a faculty member of the Department of Biomedical Engineering, Central Tehran Branch, Tehran, Iran. His research interests focus on Fluid-Structure Interaction (FSI) and Computational Fluid Dynamics (CFD).

Kamran Hassani is a faculty member of the Department of Biomedical Engineering, Science and Research Branch, Tehran, Iran. His research interests focus on Fluid-Structure Interaction (FSI) and Computational Fluid Dynamics (CFD).

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Motamedi, G.A., Shojaei, S. & Hasani, K. Study of the tumor effect on airflow in human upper airway exhalation using fluid-structure interaction method. J Mech Sci Technol (2024). https://doi.org/10.1007/s12206-024-0540-z

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Received : 13 July 2023

Revised : 31 December 2023

Accepted : 11 February 2024

Published : 05 June 2024

DOI : https://doi.org/10.1007/s12206-024-0540-z

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A 3rd human case of bird flu detected, this one with respiratory symptoms

A farmworker exposed to infected cattle has gotten sick with avian flu in Michigan, the third human case in the current U.S. outbreak among dairy cows.

Rich Pedroncelli/AP / AP

Michigan’s health department announced Thursday a human case of bird flu in a dairy worker. It’s the third human case reported to date in the current U.S. avian flu outbreak among dairy cows.

Unlike the previous two cases which only involved eye infection, this patient has respiratory symptoms, according to a statement from Dr. Natasha Bagdasarian, chief medical executive with the Michigan health department. The patient had direct exposure to an infected cow and wasn’t wearing any personal protective equipment.

“This tells us that direct exposure to infected livestock poses a risk to humans,” said Bagdasarian.

The Centers for Disease Control and Prevention said in a statement that its labs tested a sample from the Michigan patient and confirmed it was H5N1 bird flu. The patient had flu-like symptoms, including a cough, fever and eye discomfort. The patient was treated with antivirals and is isolating at home. No other workers or household contacts of the patient have gotten sick so far.

The CDC said that risk to the general public remains low. Like the other two recent cases, this infection came from direct exposure to an infected animal. “There is no indication of person-to-person spread of A(H5N1) viruses at this time,” according to the CDC.

The CDC is monitoring data from influenza surveillance systems , and said "there has been no sign of unusual influenza activity in people."

Both the CDC and Michigan health officials emphasized the importance of protecting farm workers from possible exposure.

Michigan Department of Agriculture and Rural Development director Tim Boring said his department is offering support to dairy farms in need of protective gear. "Proper use of personal protective equipment is the best tool we have to protect farm workers."

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