The Trachea (Human Anatomy): Picture, Function, Conditions, and More Human Anatomy Picture of the Trachea © 2014 WebMD, LLC. All rights reserved. The trachea, commonly known as the windpipe, is a tube about 4 inches long and less than an inch in diameter in most people. The trachea begins just under the larynx (voice box) and runs down behind the breastbone (sternum). The trachea then divides into two smaller tubes called bronchi: one bronchus for each lung. The trachea is composed of about 20 rings of tough cartilage. The back part of each ring is made of muscle and connective tissue. Moist, smooth tissue called mucosa lines the inside of the trachea. The trachea widens and lengthens slightly with each breath in, returning to its resting size with each breath out. Trachea Conditions Tracheal stenosis: Inflammation in the trachea can lead to scarring and narrowing of the windpipe. Surgery or endoscopy may be needed to correct the narrowing (stenosis), if severe.

Tracheoesophageal fistula : An abnormal channel forms to connect the trachea and the esophagus. Passage of swallowed food from the esophagus into the trachea causes serious lung problems. Tracheal foreign body: An object is inhaled (aspirated) and lodges in the trachea or one of its branches. A procedure called bronchoscopy is usually needed to remove a foreign body from the trachea. Tracheal cancer: Cancer of the trachea is quite rare. Symptoms can include coughing or difficulty breathing. Tracheomalacia: The trachea is soft and floppy rather than rigid, usually due to a birth defect. In adults, tracheomalacia is generally caused by injury or by smoking. Tracheal obstruction: A tumor or other growth can compress and narrow the trachea, causing difficulty breathing. A stent or surgery is needed to open the trachea and improve breathing. Trachea Tests Flexible bronchoscopy : An endoscope (flexible tube with a lighted camera on its end) is passed through the nose or mouth into the trachea. Using bronchoscopy, a doctor can examine the trachea and its branches.

Rigid bronchoscopy : A rigid metal tube is introduced through the mouth into the trachea. Rigid bronchoscopy is often more effective than flexible bronchoscopy, but it requires deep anesthesia. Computed tomography ( CT scan ): A CT scanner takes a series of X-rays, and a computer creates detailed images of the trachea and nearby structures. Magnetic resonance imaging ( MRI scan ): An MRI scanner uses radio waves in a magnetic field to create images of the trachea and nearby structures. Chest X-ray : A plain X-ray can tell if the trachea is deviated to either side of the chest. An X-ray might also identify masses or foreign bodies. Trachea (Windpipe) Home > Respiratory System > Lungs and Respiratory System of the Chest > Trachea (Windpipe) Trachea (Windpipe) The trachea (or windpipe) is a wide, hollow tube that connects the larynx (or voice box) to the bronchi of the lungs. It is an integral part of the body’s airway and has the vital function of providing air flow to and from the lungs for respiration.

The trachea begins at the inferior end of the larynx in the base of the neck. It is located along the body’s midline, anterior to the esophagus and just deep to the skin, so that it is possible to feel the larynx through the skin of the neck. From its origin at the larynx, the trachea extends inferiorly into the thorax posterior to the sternum.... Move up/down/left/right: Click compass arrows Rotate image: Click and drag in any direction, anywhere in the frame Identify objects: Click on them in the image 2D Interactive 3D Rotate & Zoom Change Anatomical System Change View Angle Full Trachea (Windpipe) Description [Continued from above] . . . In the thorax, the trachea ends where it splits into the left and right bronchi, which continue onward toward the lungs. Viewed in cross section, the trachea is about one inch (2.6 cm) in diameter. It has a thin, membranous wall with C-shaped rings of cartilage embedded into it.

Between sixteen and twenty cartilage rings are stacked along the length of the trachea, with narrow membranous regions spaced between the cartilage rings. The open ends of the cartilage rings face the posterior of the trachea near the esophagus. Four layers of tissues make up the walls of the trachea: The mucosa is the innermost layer and consists of ciliated pseudostratified columnar epithelium with many goblet cells. Goblet cells produce sticky mucus to coat the inner lining of the trachea and catch any debris present in inhaled air before it reaches the lungs. On the surface of the columnar cells, long, hair-like cilia beat together to push mucous away from the lungs like a microscopic conveyor belt. Mucus from the trachea, along with any trapped contaminants, makes its way to the larynx, where it is either expelled during coughing or swallowed and digested in the stomach. Deep to the mucosa is the submucosa layer, which is made of areolar connective tissue containing blood vessels and nervous tissue.

Many collagen, elastin and reticular protein fibers give soft support and elasticity to the wall of the trachea, while blood vessels and nerves support the other layers of the tracheal wall. Longitudinal smooth muscle fibers are present in the posterior trachea between the ends of the cartilage rings. This smooth muscle tissue allows the trachea to adjust its diameter as needed. Surrounding the submucosa is a layer of hyaline cartilage that forms the supportive rings of the trachea. Hyaline provides a strong, yet flexible structure that maintains an open airway and is resistant to external stresses. The outermost layer of the trachea is the adventitia, a layer of areolar connective tissue that loosely anchors the trachea to the surrounding soft tissues. While the trachea plays a vital role as a passive air passageway, it also performs several other important functions as well. The trachealis muscle in the posterior wall allows the trachea to contract and reduce its diameter, which makes coughs more forceful and productive. During the process of swallowing food, the esophagus expands into the space normally occupied by the trachea.

The incomplete cartilage rings of the trachea allow it to narrow and permit the esophagus to expand into its space. Finally, the loose connection of the adventitia allows the trachea to move within the neck and thorax, aiding the lungs in their expansion and contraction during breathing. Prepared by Tim Taylor, Anatomy and Physiology Instructor Trachea: Function, Meaning & System - Video & Lesson Transcript | Study.com Trachea: Function, Meaning & System Watch short & fun videos Start Your Free Trial Today An error occurred trying to load this video. Try refreshing the page, or contact customer support. You must create an account to continue watching Register for a free trial Are you a student or a teacher? I am a student Start Your Free Trial To Continue Watching As a member, you'll also get unlimited access to over lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed. Coming up next: Bradypnea: Definition, Causes & Symptoms You're on a roll. Keep up the good work!

Your next lesson will play in 10 seconds 0:00 Getting Oxygen to Your Tissues 1:25 The Respiratory Tree Add to Add to Add to Want to watch this again later? Log in or sign up to add this lesson to a Custom Course. Custom Courses are courses that you create from Study.com lessons. Use them just like other courses to track progress, access quizzes and exams, and share content. Teachers Organize and share selected lessons with your class. Make planning easier by creating your own custom course. Students Create a new course from any lesson page or your dashboard. From any lesson page: Click "Add to" located below the video player and follow the prompts to name your course and save your lesson. From your dashboard: Click on the "Custom Courses" tab, then click "Create course". Next, go to any lesson page and begin adding lessons. Edit your Custom Course directly from your dashboard. Personalize: Name your Custom Course and add an optional description or learning objective. Organize: Create chapters to group lesson within your course. Remove and reorder chapters and lessons at any time. Share your Custom Course or assign lessons and chapters.

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Some highly active organs, such as your brain and heart, can be irreversibly damaged if their oxygen supply is interrupted for only a few minutes. Most of your cells, tissues, and organs lie far beneath the surface of your body and don't have access to the oxygen in the atmosphere. Therefore, they must have oxygen delivered to them from some distance away. Fortunately, nature has devised a way to address this problem. Your body relies on two closely intertwined organ systems to provide the oxygen your cells require. Your respiratory system is responsible for drawing oxygen into your body, while your circulatory system is charged with delivering the oxygen to your tissues. These two systems overlap in your lungs, where oxygen from inhaled air is absorbed into your bloodstream. At the same time, carbon dioxide, a waste product of cellular metabolism, is removed from your bloodstream and transferred to the air you exhale with every outward breath. The Respiratory Tree Much of your respiratory system is composed of simple conduits, or pipes, that conduct gases between the atmosphere and your lungs. As you inhale, air is drawn through your nose and mouth, funneled into your throat, and routed through your larynx, or voice box.

Your Adam's apple, which is formed by a broad, tough ring of cartilage surrounding your larynx, is a surface landmark showing the location of your larynx. As inhaled air passes through your larynx, it enters your trachea (from the Greek word for rough). Your trachea extends downward into the center of your chest, where it divides into two separate tubes called bronchi. (Bronchi is the plural form of bronchus.) Your bronchi then divide into progressively smaller tubes that deliver air to each segment of your lungs. The overall structure of your major airways resembles an upside-down tree. (In fact, doctors often refer to this system of tubes as the respiratory tree.) If you imagine your larynx as the root of the up-ended tree, you can see how your trachea would represent the tree's trunk, and the bronchi and smaller airways would represent the progressively smaller branches of the tree. External Anatomy of the Trachea Many of the tubes in your body - your arteries, veins, and intestine, for example - are at least partially collapsible. Your trachea and bronchi are specifically designed to resist squashing, making them unlike these other structures.

If the trachea wasn't a rigid tube, every time you tried to exhale the pressure in your chest would collapse the trachea's walls - much like pinching the end of an inflated balloon - and trap the air within your lungs. Your trachea maintains its rigidity by virtue of a series of cartilaginous rings arranged along its length, called C-shaped cartilage rings. The open part of each 'C' is found at the back of your trachea, which rests directly against your esophagus. The esophagus is the collapsible tube leading from the back of your throat to your stomach. If the cartilage rings in your trachea completely encircled it, they would press against your esophagus and you would have difficulty swallowing your food. The gaps between the trachea's cartilage rings are bridged by strong elastic membranes. Thus, while your trachea is very resistant to compression, it does have the ability to stretch slightly along its length, like a long, tubular accordion. This permits it to lengthen and shorten somewhat during breathing.

× Trachea Definition, Functions and Parts Know Symptoms And Signs Of Heart Attack In Men Trachea Definition, Functions and Parts Concerning trachea definition, it is an important anatomical structure that is an integral part of respiratory system in humans and other higher animals. Allowing the passage of air (respiratory gases) it connects larynx (voice box) and pharynx with lungs. The trachea location can be traced in the chest region, and it is made of soft bony material, called cartilage that allows great amount of flexibility for the efficient performance of its essential tasks. However, as the age progresses, it becomes rigid and hard, and is converted into bone. Apart from just gaseous exchange, it is also involved in the production of vocal sounds as one of the secondary trachea functions. As with other organs of your body, trachea is also vulnerable to a number of diseases that are commonly known as respiratory disorders, viz. tracheal stenosis, tracheobronchomalacia, and so on.

Parts of Trachea As you can see in the trachea pictures, the windpipe is structurally composed of incomplete rings, resembling the letter C in English which range from 15 to 20 in number. At the anterior end, the air passage is bound by a membranous structure, called larynx that contains vocal chords running horizontally across its mouth and forming voice apparatus in humans for the production of speech sounds. At the posterior end, it undergoes dichotomous branching, thus dividing into the two smaller tubes, viz. primary bronchi. Each of the primary bronchi runs into either of the lungs (i.e. left or right one) and allows the smooth and efficient passage of air (or the exchange of respiratory gases). Going deeper into lungs, further branching takes place in which bronchi are subdivided into bronchioles ultimately attaining the size of very small air sacs enclosed by respiratory membranes through which exchange of respiratory gases (carbon dioxide & oxygen) virtually takes place. With the help of incomplete rings, the anterior of the tube (lumen) can be narrowed down to accelerate the air passing through it when needed, e.g. while coughing.

Functions of Trachea Though primarily concerned with respiratory function, it also facilitates sound production and protection against the harmful substances or microbes that may get entry into deeper parts of the lungs and induce malfunctioning. For protective purpose, the lumen of windpipe is lined with a layer of mucous that is a sticky material and traps the foreign substances which are then expelled upward and swallowed either into esophagus or excreted out of the body in the form of phlegm. Breathing constitutes both inhalation and exhalation that need alternate rise or lowering of trachea. This very feature is owed to its great flexibility. For the production of sound, the e - gressive or a - gressive airflow causes the vocal chords to vibrate which, however, also requires some deliberate effort on the part of the speaker. The voice thus produced is further modified into various language sounds in the oral cavity involving uvula, palate, tongue, alveolar ridge, teeth and lips, etc. Diseases of Trachea Any ailment of the respiratory system may disturb the overall functioning of your body as it is responsible for the facilitation of the process of energy extraction from food.

Forming front tubular part of the respiratory system, the anatomical structure, if attached by some acute or chronic disorder, results in the partial or complete collapse of airway system and often leads to the death of the individual. It is surprising to know that this is the organ system of your body which is exposed and extremely vulnerable to environmental hazards, especially in this highly polluted atmosphere. A number of tracheal ailments may arise out of various factors, like infectious and hereditary which include inflammation, tumor formation, cancerous outgrowth, obstructive disorders, etc. Tracheal stenosis is characterized by inflammation of the windpipe that may be relieved by endoscopy or surgical therapy. Formation of large tumor (benign or cancerous) in the lumen of trachea may cause the blockage of the air passage and death of the victim due to chocking. Though it is very difficult to avoid contact with respiratory diseases, proper care, preventive measures and early treatment of the abnormalities can save you from life long miseries. trachea | anatomy | Britannica.com Trachea diaphragm Trachea, in vertebrates and invertebrates, a tube or system of tubes that carries air.

In insects, a few land arachnids, and myriapods, the trachea is an elaborate system of small, branching tubes that carry oxygen to individual body cells; in most land vertebrates, the trachea is the windpipe, which conveys air from the larynx to the two main bronchi, with the lungs and their air sacs as the ultimate destination. In some birds, such as the swan, there is an extra length of tracheal tube coiled under the front of the rib cage. The cartilaginous structures that ring most mammalian tracheae are reduced to small irregular nodules in amphibians. The trachea and major bronchi of the human lungs. Encyclopædia Britannica, Inc. In man the trachea is about 15 centimetres (6 inches) long and 2 to 3 centimetres in diameter. The trachea serves as passage for air, moistens and warms it while it passes into the lungs, and protects the respiratory surface from an accumulation of foreign particles. The trachea is lined with a moist mucous-membrane layer composed of cells containing small hairlike projections called cilia .

The cilia project into the channel (lumen) of the trachea to trap particles. There are also cells and ducts in the mucous membrane that secrete mucus droplets and water molecules. At the base of the mucous membrane there is a complex network of tissue composed of elastic and collagen fibres that aid in the expansion, contraction, and stability of the tracheal walls. Also in this layer there are numerous blood and lymphatic vessels; the blood vessels control cellular maintenance and heat exchange, while the lymphatic vessels remove the foreign particles collected by the wall’s surface. Around the tracheal wall there is a series of 16 to 20 horseshoe-shaped cartilage rings. They encircle the front part of the trachea but are open where the trachea lies next to the esophagus. Here the free ends of the cartilage are connected by muscle bands. Since the cartilage is in individual rings, rather than one continuous sheath, the trachea can stretch and descend with the breathing movements. The cartilage bands are replaced with fibrous scar tissue in advanced age. Similar Topics Respiratory System | Interactive Anatomy Guide Female Full Respiratory System Description [Continued from above] . . .

act as the functional units of the respiratory system by passing oxygen into the body and carbon dioxide out of the body. Finally, the muscles of respiration, including the diaphragm and intercostal muscles, work together to act as a pump, pushing air into and out of the lungs during breathing. Anatomy of the Respiratory System Nose and Nasal Cavity The nose and nasal cavity form the main external opening for the respiratory system and are the first section of the body’s airway—the respiratory tract through which air moves. The nose is a structure of the face made of cartilage, bone, muscle, and skin that supports and protects the anterior portion of the nasal cavity. The nasal cavity is a hollow space within the nose and skull that is lined with hairs and mucus membrane. The function of the nasal cavity is to warm, moisturize, and filter air entering the body before it reaches the lungs. Hairs and mucus lining the nasal cavity help to trap dust, mold, pollen and other environmental contaminants before they can reach the inner portions of the body. Air exiting the body through the nose returns moisture and heat to the nasal cavity before being exhaled into the environment.

Mouth The mouth, also known as the oral cavity , is the secondary external opening for the respiratory tract. Most normal breathing takes place through the nasal cavity, but the oral cavity can be used to supplement or replace the nasal cavity’s functions when needed. Because the pathway of air entering the body from the mouth is shorter than the pathway for air entering from the nose, the mouth does not warm and moisturize the air entering the lungs as well as the nose performs this function. The mouth also lacks the hairs and sticky mucus that filter air passing through the nasal cavity. The one advantage of breathing through the mouth is that its shorter distance and larger diameter allows more air to quickly enter the body. Pharynx The pharynx, also known as the throat, is a muscular funnel that extends from the posterior end of the nasal cavity to the superior end of the esophagus and larynx. The pharynx is divided into 3 regions: the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx is the superior region of the pharynx found in the posterior of the nasal cavity.

Inhaled air from the nasal cavity passes into the nasopharynx and descends through the oropharynx, located in the posterior of the oral cavity. Air inhaled through the oral cavity enters the pharynx at the oropharynx . The inhaled air then descends into the laryngopharynx , where it is diverted into the opening of the larynx by the epiglottis. The epiglottis is a flap of elastic cartilage that acts as a switch between the trachea and the esophagus. Because the pharynx is also used to swallow food, the epiglottis ensures that air passes into the trachea by covering the opening to the esophagus. During the process of swallowing, the epiglottis moves to cover the trachea to ensure that food enters the esophagus and to prevent choking. Larynx The larynx , also known as the voice box, is a short section of the airway that connects the laryngopharynx and the trachea. The larynx is located in the anterior portion of the neck, just inferior to the hyoid bone and superior to the trachea.

Several cartilage structures make up the larynx and give it its structure. The epiglottis is one of the cartilage pieces of the larynx and serves as the cover of the larynx during swallowing. Inferior to the epiglottis is the thyroid cartilage , which is often referred to as the Adam’s apple as it is most commonly enlarged and visible in adult males. The thyroid holds open the anterior end of the larynx and protects the vocal folds. Inferior to the thyroid cartilage is the ring-shaped cricoid cartilage which holds the larynx open and supports its posterior end. In addition to cartilage, the larynx contains special structures known as vocal folds, which allow the body to produce the sounds of speech and singing. The vocal folds are folds of mucous membrane that vibrate to produce vocal sounds. The tension and vibration speed of the vocal folds can be changed to change the pitch that they produce. Trachea The trachea, or windpipe, is a 5-inch long tube made of C-shaped hyaline cartilage rings lined with pseudostratified ciliated columnar epithelium.

The trachea connects the larynx to the bronchi and allows air to pass through the neck and into the thorax. The rings of cartilage making up the trachea allow it to remain open to air at all times. The open end of the cartilage rings faces posteriorly toward the esophagus, allowing the esophagus to expand into the space occupied by the trachea to accommodate masses of food moving through the esophagus. The main function of the trachea is to provide a clear airway for air to enter and exit the lungs. In addition, the epithelium lining the trachea produces mucus that traps dust and other contaminants and prevents it from reaching the lungs. Cilia on the surface of the epithelial cells move the mucus superiorly toward the pharynx where it can be swallowed and digested in the gastrointestinal tract. Bronchi and Bronchioles At the inferior end of the trachea, the airway splits into left and right branches known as the primary bronchi. The left and right bronchi run into each lung before branching off into smaller secondary bronchi.

The secondary bronchi carry air into the lobes of the lungs—2 in the left lung and 3 in the right lung. The secondary bronchi in turn split into many smaller tertiary bronchi within each lobe. The tertiary bronchi split into many smaller bronchioles that spread throughout the lungs. Each bronchiole further splits into many smaller branches less than a millimeter in diameter called terminal bronchioles. Finally, the millions of tiny terminal bronchioles conduct air to the alveoli of the lungs. As the airway splits into the tree-like branches of the bronchi and bronchioles, the structure of the walls of the airway begins to change. The primary bronchi contain many C-shaped cartilage rings that firmly hold the airway open and give the bronchi a cross-sectional shape like a flattened circle or a letter D. As the bronchi branch into secondary and tertiary bronchi, the cartilage becomes more widely spaced and more smooth muscle and elastin protein is found in the walls. The bronchioles differ from the structure of the bronchi in that they do not contain any cartilage at all. The presence of smooth muscles and elastin allow the smaller bronchi and bronchioles to be more flexible and contractile.

The main function of the bronchi and bronchioles is to carry air from the trachea into the lungs. Smooth muscle tissue in their walls helps to regulate airflow into the lungs. When greater volumes of air are required by the body, such as during exercise, the smooth muscle relaxes to dilate the bronchi and bronchioles. The dilated airway provides less resistance to airflow and allows more air to pass into and out of the lungs. The smooth muscle fibers are able to contract during rest to prevent hyperventilation. The bronchi and bronchioles also use the mucus and cilia of their epithelial lining to trap and move dust and other contaminants away from the lungs. Lungs The lungs are a pair of large, spongy organs found in the thorax lateral to the heart and superior to the diaphragm. Each lung is surrounded by a pleural membrane that provides the lung with space to expand as well as a negative pressure space relative to the body’s exterior. The negative pressure allows the lungs to passively fill with air as they relax. The left and right lungs are slightly different in size and shape due to the heart pointing to the left side of the body.

The left lung is therefore slightly smaller than the right lung and is made up of 2 lobes while the right lung has 3 lobes. The interior of the lungs is made up of spongy tissues containing many capillaries and around 30 million tiny sacs known as alveoli . The alveoli are cup-shaped structures found at the end of the terminal bronchioles and surrounded by capillaries. The alveoli are lined with thin simple squamous epithelium that allows air entering the alveoli to exchange its gases with the blood passing through the capillaries. Muscles of Respiration Surrounding the lungs are sets of muscles that are able to cause air to be inhaled or exhaled from the lungs. The principal muscle of respiration in the human body is the diaphragm, a thin sheet of skeletal muscle that forms the floor of the thorax. When the diaphragm contracts, it moves inferiorly a few inches into the abdominal cavity, expanding the space within the thoracic cavity and pulling air into the lungs. Relaxation of the diaphragm allows air to flow back out the lungs during exhalation.

Between the ribs are many small intercostal muscles that assist the diaphragm with expanding and compressing the lungs. These muscles are divided into 2 groups: the internal intercostal muscles and the external intercostal muscles. The internal intercostal muscles are the deeper set of muscles and depress the ribs to compress the thoracic cavity and force air to be exhaled from the lungs. The external intercostals are found superficial to the internal intercostals and function to elevate the ribs, expanding the volume of the thoracic cavity and causing air to be inhaled into the lungs. Physiology of the Respiratory System Pulmonary Ventilation Pulmonary ventilation is the process of moving air into and out of the lungs to facilitate gas exchange. The respiratory system uses both a negative pressure system and the contraction of muscles to achieve pulmonary ventilation. The negative pressure system of the respiratory system involves the establishment of a negative pressure gradient between the alveoli and the external atmosphere. The pleural membrane seals the lungs and maintains the lungs at a pressure slightly below that of the atmosphere when the lungs are at rest. This results in air following the pressure gradient and passively filling the lungs at rest.

As the lungs fill with air, the pressure within the lungs rises until it matches the atmospheric pressure. At this point, more air can be inhaled by the contraction of the diaphragm and the external intercostal muscles, increasing the volume of the thorax and reducing the pressure of the lungs below that of the atmosphere again. To exhale air, the diaphragm and external intercostal muscles relax while the internal intercostal muscles contract to reduce the volume of the thorax and increase the pressure within the thoracic cavity. The pressure gradient is now reversed, resulting in the exhalation of air until the pressures inside the lungs and outside of the body are equal. At this point, the elastic nature of the lungs causes them to recoil back to their resting volume, restoring the negative pressure gradient present during inhalation. External Respiration External respiration is the exchange of gases between the air filling the alveoli and the blood in the capillaries surrounding the walls of the alveoli. Air entering the lungs from the atmosphere has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than does the blood in the capillaries.

The difference in partial pressures causes the gases to diffuse passively along their pressure gradients from high to low pressure through the simple squamous epithelium lining of the alveoli. The net result of external respiration is the movement of oxygen from the air into the blood and the movement of carbon dioxide from the blood into the air. The oxygen can then be transported to the body’s tissues while carbon dioxide is released into the atmosphere during exhalation. Internal Respiration Internal respiration is the exchange of gases between the blood in capillaries and the tissues of the body. Capillary blood has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than the tissues through which it passes. The difference in partial pressures leads to the diffusion of gases along their pressure gradients from high to low pressure through the endothelium lining of the capillaries. The net result of internal respiration is the diffusion of oxygen into the tissues and the diffusion of carbon dioxide into the blood. Transportation of Gases The 2 major respiratory gases, oxygen and carbon dioxide, are transported through the body in the blood. Blood plasma has the ability to transport some dissolved oxygen and carbon dioxide, but most of the gases transported in the blood are bonded to transport molecules.

Hemoglobin is an important transport molecule found in red blood cells that carries almost 99% of the oxygen in the blood. Hemoglobin can also carry a small amount of carbon dioxide from the tissues back to the lungs. However, the vast majority of carbon dioxide is carried in the plasma as bicarbonate ion. When the partial pressure of carbon dioxide is high in the tissues, the enzyme carbonic anhydrase catalyzes a reaction between carbon dioxide and water to form carbonic acid. Carbonic acid then dissociates into hydrogen ion and bicarbonate ion. When the partial pressure of carbon dioxide is low in the lungs, the reactions reverse and carbon dioxide is liberated into the lungs to be exhaled. Homeostatic Control of Respiration Under normal resting conditions, the body maintains a quiet breathing rate and depth called eupnea. Eupnea is maintained until the body’s demand for oxygen and production of carbon dioxide rises due to greater exertion. Autonomic chemoreceptors in the body monitor the partial pressures of oxygen and carbon dioxide in the blood and send signals to the respiratory center of the brain stem. The respiratory center then adjusts the rate and depth of breathing to return the blood to its normal levels of gas partial pressures.

Prepared by Tim Taylor, Anatomy and Physiology Instructor The Trachea and Bronchi - Human Anatomy Human Body > XI. Splanchnology > The Trachea and Bronchi 1b. The Trachea and Bronchi FIG. 961 Front view of cartilages of larynx, trachea, and bronchi. The trachea or windpipe (Fig. 961) is a cartilaginous and membranous tube, extending from the lower part of the larynx, on a level with the sixth cervical vertebra, to the upper border of the fifth thoracic vertebra, where it divides into the two bronchi, one for each lung. The trachea is nearly but not quite cylindrical, being flattened posteriorly; it measures about 11 cm. in length; its diameter, from side to side, is from 2 to 2.5 cm., being always greater in the male than in the female. In the child the trachea is smaller, more deeply placed, and more movable than in the adult.

Relations.The anterior surface of the trachea is convex, and covered, in the neck, from above downward, by the isthmus of the thyroid gland, the inferior thyroid veins, the arteria thyroidea ima (when that vessel exists), the Sternothyreoideus and Sternohyoideus muscles, the cervical fascia, and, more superficially, by the anastomosing branches between the anterior jugular veins; in the thorax, it is covered from before backward by the manubrium sterni, the remains of the thymus, the left innominate vein, the aortic arch, the innominate and left common carotid arteries, and the deep cardiac plexus. Posteriorly it is in contact with the esophagus.

Laterally, in the neck, it is in relation with the common carotid arteries, the right and left lobes of the thyroid gland, the inferior thyroid arteries, and the recurrent nerves; in the thorax, it lies in the superior mediastinum, and is in relation on the right side with the pleura and right vagus, and near the root of the neck with the innominate artery; on its left side are the left recurrent nerve, the aortic arch, and the left common carotid and subclavian arteries. The Right Bronchus (bronchus dexter), wider, shorter, and more vertical in direction than the left, is about 2.5 cm. long, and enters the right lung nearly opposite the fifth thoracic vertebra. The azygos vein arches over it from behind; and the right pulmonary artery lies at first below and then in front of it. About 2 cm. from its commencement it gives off a branch to the upper lobe of the right lung. This is termed the eparterial branch of the bronchus, because it arises above the right pulmonary artery.

The bronchus now passes below the artery, and is known as the hyparterial branch; it divides into two branches for the middle and lower lobes. The Left Bronchus (bronchus sinister) is smaller in caliber but longer than the right, being nearly 5 cm. long. It enters the root of the left lung opposite the sixth thoracic vertebra. It passes beneath the aortic arch, crosses in front of the esophagus, the thoracic duct, and the descending aorta, and has the left pulmonary artery lying at first above, and then in front of it. The left bronchus has no eparterial branch, and therefore it has been supposed by some that there is no upper lobe to the left lung, but that the so-called upper lobe corresponds to the middle lobe of the right lung. The further subdivisions of the bronchi will be considered with the anatomy of the lung. FIG. 962 Bronchi and bronchioles. The lungs have been widely separated and tissue cut away to expose the air-tubes.

(Testut.) If a transverse section be made across the trachea a short distance above its point of bifurcation, and a birds-eye view taken of its interior (Fig. 963), the septum placed at the bottom of the trachea and separating the two bronchi will be seen to occupy the left of the median line, and the right bronchus appears to be a more direct continuation of the trachea than the left, so that any solid body dropping into the trachea would naturally be directed toward the right bronchus. This tendency is aided by the larger diameter of the right tube as compared with its fellow. This fact serves to explain why a foreign body in the trachea more frequently falls into the right bronchus. (* 157 FIG. 963 Transverse section of the trachea, just above its bifurcation, with a birds-eye view of the interior. Structure (Fig. 964).The trachea and extrapulmonary bronchi are composed of imperfect rings of hyaline cartilage, fibrous tissue, muscular fibers, mucous membrane, and glands.

The cartilages of the trachea vary from sixteen to twenty in number: each forms an imperfect ring, which occupies the anterior two-thirds or so of the circumference of the trachea, being deficient behind, where the tube is completed by fibrous tissue and unstriped muscular fibers. The cartilages are placed horizontally above each other, separated by narrow intervals. They measure about 4 mm. in depth and 1 mm. in thickness. Their outer surfaces are flattened in a vertical direction, but the internal are convex, the cartilages being thicker in the middle than at the margins. Two or more of the cartilages often unite, partially or completely, and they are sometimes bifurcated at their extremities. They are highly elastic, but may become calcified in advanced life. In the right bronchus the cartilages vary in number from six to eight; in the left, from nine to twelve. They are shorter and narrower than those of the trachea, but have the same shape and arrangement. The peculiar tracheal cartilages are the first and the last (Fig. 961).

The first cartilage is broader than the rest, and often divided at one end; it is connected by the cricotracheal ligament with the lower border of the cricoid cartilage, with which, or with the succeeding cartilage, it is sometimes blended. The last cartilage is thick and broad in the middle, in consequence of its lower border being prolonged into a triangular hook-shaped process, which curves downward and backward between the two bronchi. It ends on each side in an imperfect ring, which encloses the commencement of the bronchus. The cartilage above the last is somewhat broader than the others at its center. The Fibrous Membrane.The cartilages are enclosed in an elastic fibrous membrane, which consists of two layers; one, the thicker, passing over the outer surface of the ring, the other over the inner surface: at the upper and lower margins of the cartilages the two layers blend together to form a single membrane, which connects the rings one with another. They are thus invested by the membrane. In the space behind, between the ends of the rings, the membrane forms a single layer. The muscular tissue consists of two layers of non-striated muscle, longitudinal and transverse.

The longitudinal fibers are external, and consist of a few scattered bundles. The transverse fibers (Trachealis muscle) are internal, and form a thin layer which extends transversely between the ends of the cartilages. Mucous Membrane.The mucous membrane is continuous above with that of the larynx, and below with that of the bronchi. It consists of areolar and lymphoid tissue, and presents a well-marked basement membrane, supporting a stratified epithelium, the surface layer of which is columnar and ciliated, while the deeper layers are composed of oval or rounded cells. Beneath the basement membrane there is a distinct layer of longitudinal elastic fibers with a small amount of intervening areolar tissue. The submucous layer is composed of a loose mesh-work of connective tissue, containing large bloodvessels, nerves, and mucous glands; the ducts of the latter pierce the overlying layers and open on the surface (Fig. 964). FIG. 964 Transverse section of trachea. Vessels and Nerves.The trachea is supplied with blood by the inferior thyroid arteries.

The veins end in the thyroid venous plexus. The nerves are derived from the vagus and the recurrent nerves, and from the sympathetic; they are distributed to the Trachealis muscles and between the epithelial cells. Note 157. Reigel asserts that the entry of a foreign body into the left bronchus is by no means so infrequent as is generally supposed. See also Med.-Chi. Trans., lxxi, 121. [ back ] SEER Training:Larynx & Trachea Larynx & Trachea Larynx & Trachea Larynx The larynx, commonly called the voice box or glottis, is the passageway for air between the pharynx above and the trachea below. It extends from the fourth to the sixth vertebral levels. The larynx is often divided into three sections: sublarynx, larynx, and supralarynx. It is formed by nine cartilages that are connected to each other by muscles and ligaments. The larynx plays an essential role in human speech. During sound production, the vocal cords close together and vibrate as air expelled from the lungs passes between them.

The false vocal cords have no role in sound production, but help close off the larynx when food is swallowed. The thyroid cartilage is the Adam's apple. The epiglottis acts like a trap door to keep food and other particles from entering the larynx. Trachea The trachea, commonly called the windpipe, is the main airway to the lungs. It divides into the right and left bronchi at the level of the fifth thoracic vertebra, channeling air to the right or left lung. The hyaline cartilage in the tracheal wall provides support and keeps the trachea from collapsing. The posterior soft tissue allows for expansion of the esophagus, which is immediately posterior to the trachea. The mucous membrane that lines the trachea is ciliated pseudostratified columnar epithelium similar to that in the nasal cavity and nasopharynx. Goblet cells produce mucus that traps airborne particles and microorganisms, and the cilia propel the mucus upward, where it is either swallowed or expelled. What is the trachea? | Reference.com What is the trachea?

A: Quick Answer The trachea carries the air necessary for respiration for many types of animals. Both vertebrates and invertebrates possess tracheae, but in many invertebrates, the trachea is often a branching structure that carries gases directly to and from the animal's cells. In many vertebrates, the trachea is a structure that carries air to the lungs, organs that are dedicated specifically to gas exchange. Full Answer Not all animals possess a trachea. Fish, for instance, do not breathe air and conduct oxygen exchange in their gills. Only air-breathing animals have a trachea. In humans, the trachea is about 6 inches long and about 1 inch in diameter. It serves not only to carry air but to moisten and clean the air on its way to the delicate lungs. To clean the air, the trachea has multiple hair-like cilia that secretes mucus and water droplets. These trap contaminants and gradually move them up and out of the airway. The human trachea, as well as that of most other air-breathing vertebrates, is reinforced with rings of cartilage to keep it from collapsing.

Amphibians are the only exception with sparser cartilage reinforcements. This reinforcement structure of multiple rings allows the trachea to stretch as needed during breathing. Chapter 21: The esophagus, trachea and main bronchi Chapter 21: The esophagus, trachea and main bronchi Thoracic part of esophagus The esophagus (figs. 21-1 , 21-2 and 21-3 ) has cervical, thoracic, and abdominal parts, extending from the lower end of the pharynx (C6 vertebrae) to the cardiac opening of the stomach (T11 or 12 vertebral level). When a subject is in the erect position, it is about 25 to 30 cm long. The esophagus is a median structure that lies first behind the trachea and then behind the left atrium. It begins to deviate to the left below the left main bronchus. In the posterior mediastinum it is related to the vertebral column as a string is related to a bow.

Hence there is a (retrocardiac) space between it and the vertebrae, which is visible radiographically in oblique and lateral views. The esophagus has constrictions (1) at its commencement, (2) frequently where it is crossed by the left main bronchus, and (3) commonly where it traverses the diaphragm. These are sites where swallowed objects can lodge notwithstanding the fact that the esophagus is distensible and can accommodate almost anything that can be swallowed, e.g., a denture. The impressions of adjacent structures, and their alterations in disease, can be seen radiographically after barium is swallowed (fig. 21-3 ). The esophagus transports food and liquid and can be replaced successfully by a non-muscular tube. The muscular layer is striated above (supplied by the vagi) and smooth below (supplied by parasympathetic, or vagal, and sympathetic fibers). The process of swallowing may be watched fluoroscopically. A thin barium meal or liquid is "shot down" to the cardiac orifice, whereas a thick meal or a bolus of food travels more slowly.

The esophagus is supplied by arteries in the neck (inferior thyroid arteries), thorax (bronchial arteries, direct branches of the aorta, and phrenic arteries), and abdomen (left gastric artery). Veins of the lower part of the esophagus communicate with the left gastric vein, thereby forming an important portal-systemic anastomosis. Portal obstruction (e.g., in the liver with cirrhosis) causes these channels to enlarge, and their varicosities may produce hemorrhage. Pain fibers from the esophagus accompany the sympathetic system. A vague, deep-seated, esophageal pain may be felt behind the sternum or in the epigastrium, and it resembles that arising from the stomach or heart ("heartburn"). In esophagoscopy, measurements are taken from the upper incisor teeth to indicate the beginning of the esophagus (18 cm), the point at which it is crossed by the left bronchus (28 cm), and its termination (43 cm). Trachea The trachea, or windpipe (figs.

21-1 and 21-2 ), which has cervical and thoracic parts, extends from the inferior end of the larynx (C6 vertebra) to its point of bifurcation (between T5 and 7 vertebral level). It is about 9 to 15 cm in length. The trachea descends anterior to the esophagus, enters the superior mediastinum, and divides into right and left main bronchi. The trachea is a median structure but, near its lower end, deviates slightly to the right, resulting in the left main bronchus crossing anterior to the esophagus. Owing to the translucency of the air within it, the trachea is usually visible above the arch of the aorta in radiographs. The trachea has 15 to 20 C-shaped bars of hyaline cartilage that prevent it from collapsing. Longitudinal elastic fibers enable the trachea to stretch and descend with the roots of the lungs during inspiration. When a subject is in the erect position, the trachea divides between the T5 and T7 vertebral levels.

The carina is the upward-directed ridge seen internally at the bifurcation and is a landmark during bronchoscopy. The arch of the aorta is at first anterior to the trachea and then on its left side immediately superior to the left main bronchus. Other close relations include the brachiocephalic and left common carotid arteries. The trachea is supplied mainly by the inferior thyroid arteries. Its smooth muscle is supplied by parasympathetic and sympathetic fibers, and pain fibers are carried by the vagi. Main bronchi Each main bronchus extends from the tracheal bifurcation to the hilus of the' corresponding lung. The right main bronchus may be considered as having (1) an upper (eparterial) part, from which the segmental bronchi for the upper lobe arise, and (2) a lower part, from which the segmental bronchi for the middle and lower lobes emerge (fig. 21-4 ). The left main bronchus divides into two lobar bronchi, one each for the upper and lower lobes.

The upper lobar bronchus may be considered as having (1) an upper division and (2) a lower, or lingular, division. The right main bronchus, about 2.5 cm in length, is shorter, wider, and more nearly vertical than the left. Because it is in almost a direct line with the trachea, foreign objects traversing the trachea are more likely to enter the right main bronchus. The left main bronchus, 5 cm or more in length, crosses anterior to the esophagus (fig. 21-2 ), which it indents. Both bronchi have cartilaginous rings that are replaced by separated plates at the roots of the lungs. The bronchi are supplied by the bronchial arteries and veins, and their innervation is similar to that of the trachea. Additional reading Terracol, J., and Sweet, R. H., Diseases of the Esophagus, W. B. Saunders Company, Philadelphia, 1958. A general reference with an extensive bibliography. Questions 21-1 What lies anterior to the esophagus in the lower part of the thorax?

21-1 The left atrium lies anterior to the esophagus in the lower part of the thorax. Dilatation of the left atrium can be detected radiographically because of compression of a barium-coated esophagus. 21-2 Where does the trachea divide? 21-2 The trachea divides at the level of thoracic vertebrae 5 to 7 in a subject in the erect position. This would be approximately behind the middle of the body of the sternum. 21-3 How does the right main bronchus differ from the left? 21-3 The right main bronchus is shorter, wider, and more nearly vertical than the left, and it is more likely to receive foreign objects. Figure legends Figure 21-1 The trachea and esophagus in relation to vertebral and sternal levels in a subject in the erect position. Figure 21-2 The relations of the trachea, bronchi, esophagus, and aorta to one another. In the right anterior oblique view, the right lobar and segmental bronchi are omitted because they are not clearly visible in radiographs of this view.

For similar reasons, the left lobar and segmental bronchi are omitted from the left anterior oblique view. The horizontal line indicates the level of the carina. Figure 21-3 Oblique (R.A.O.) view of thorax. The esophagus is shown coated with barium. Note the vertical folds of the mucosa and the indentations produced by the arch of the aorta (upper white arrow) and by the left main bronchus (lower white arrow). Note also the right and left domes of the diaphragm (on the left and right sides of the illustration, respectively) and the fluid level in the stomach (black arrow). (From Bassett, D.L., A Stereoscopic Atlas of Human Anatomy, Sawyer's, Portland, Oregon, 1958. Copyright 1958, Sawyer's Inc.) Figure 21-4 The main, lobar, and segmental bronchi. See also table 22-1 . Jump to:

Question: In the human body what is the Trachea?
Answer: Windpipe