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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. 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.
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. 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. 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. 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 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. 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.
Health Issues Affecting the Respiratory System When something impairs our ability to exchange carbon dioxide for oxygen, this is obviously a serious problem. Many health problems can cause respiratory problems, from allergies and asthma to pneumonia and lung cancer. The causes of these issues are just as varied—among them, infection bacterial or viral , environmental exposure pollution or cigarette smoke, for instance , genetic inheritance or a combination of factors.
Review Guide: Respiratory System 1. How can you change the pitch of the sound in the vocal cords? What causes altitude sickness? What is a deviated septum? What happens when the diaphragm is lowered? What is the function of the hyaline cartilage of the trachea? What protein combines with oxygen in the blood for transport? What is the function of the nasal conchae? What is the triangular slit that opens and closes during talking called? Where is the respiratory center located? What structure resembles a bunch of grapes? What is the function of the mucus membrane that lines the nasal cavities? What is the main force for pushing air out of the lungs? Name bone of the skull does NOT have a sinus? What is the Adam's Apple? How does oxygen enter blood capillaries? Why is the first breath of a newborn the most difficult?
How many lobes are in the right lung? What happens to your respiration rate with the level of CO2 rises? What tool would be used to measure "vital capacity"? What is hypoxia? The respiratory membrane at the alveoli is made of what type of cells? What is the function s of the respiratory system? Name the organs of the upper respiratory tract? In what body cavity are the lungs located? What structure prevents food from entering the airway during swallowing? What fluid lubricates the lungs? Where does the trachea lie in relation to the esophagus? What is the main vessel the sends deoxygenated blood from the heart to the lungs? What is internal respiration?
Bronchioles Alveoli The pharynx is a part of the respiratory system and also a part of the gastrointestinal system. The pharynx receives air from the nares or the mouth and it also receives food from the mouth. When people say that their "food has gone down the wrong pipe", they are experiencing an abnormally small amount of food moving from the pharynx into the tracheal windpipe without the help of the epiglottis which, under normal situations, closes off the trachea from food and fluids. The nasopharynx, oropharynx, and laryngopharynx are labeled at right. The epiglottis is the "flap" like projection in the back of the mouth that is attached to the larynx. It goes up during breathing to allow the air to enter into the trachea and it moves down during the swallowing of food and drinking fluids to allow the food to enter the esophagus which is part of the gastrointestinal and digestive system. This part of the respiratory and digestive system also plays a role in the gag and cough reflexes.
The trachea, sometimes referred to as the windpipe connects the pharynx to the larynx. The larynx, which is sometimes referred to as the "Adam's apple and the "voice box", receives inspired air from the trachea and it then is the passage through which the air passes into the bronchi of the lung. As shown in the picture above, the larynx houses the vocal cords which are necessary to produce sounds and speech. Speech occurs because the vocal cords vibrate with speech as exhaled air passes over the vocal cords.
The bronchus, with the pleural of bronchi, is the part of the respiratory system that receives inspired air from the larynx into the lungs. The left and right bronchi are the entry gates of external, environmental air into the lungs. The right bronchus enters the right lung and the left bronchus enters the left lung. The right bronchus is shorter, wider in terms of its inner diameter and straighter anatomically in the body than the left bronchus. Before entering the lung, the right bronchus subdivides into three smaller branches, one for each of the three lobes of the right lung, which are the superior lobe, the middle lobe and the inferior lobe of the right lung.
The left bronchus enters the right lung. The left bronchus is longer, more narrow in terms of its inner diameter and more slanted anatomically in the body than the right bronchus Before entering the lung, the left bronchus subdivides into the two smaller branches that enter into each of the two lobes of the left lung which are the superior lobe and the inferior lobe of that lung. The bronchioles, the smaller portion, and branches of the bronchi connect the bronchi to the alveoli which are the area where the physiological exchange of gases such as carbon dioxide and oxygen occurs.
A lobule of the lung showing r. The alveoli, also referred to as "air sacs", are the anatomical structures that enable and facilitate the exchange of gases in the lungs. The movement of oxygen into the human body from the inspired environmental air occurs in the alveoli of the lung, and the movement of the waste product of carbon dioxide from the human body back into the environment begins in the alveoli of the lung. This movement of gases occurs when the body's blood, with its oxygen and carbon dioxide, passes to the alveolus, which is the singular form of the pleural form of alveoli. These grape-like structures expand and contract with inspiration and expiration.
The Respiratory Cycle The respiratory cycle includes two phases which are an inspiration, or the inhaling, of environmental air which includes oxygen; and the expiration, or exhalation, of carbon dioxide. Each inspiration plus one expiration is one breath. The lungs expand and contract with each breath. The lungs expand with inspiration and the lungs deflate and relax during expiration.
The expansion of the lungs during inspiration is possible because the muscular diaphragm and the muscles between the ribs, which are referred to as the intercostal muscles, actively allow the chest and the lungs to expand when a person breathes in. The intercostal muscles are considered accessory breathing muscles and the diaphragm is considered the major muscle of breathing.
The contraction of the lungs during expiration is possible because the muscular diaphragm and the muscles between the ribs, which are referred to as intercostal muscles and shown in the pictures below, relax, thus allowing the lungs to contract and decrease in size so that the person is able to rid air and carbon dioxide from the respiratory tract during expiration. The lungs do not expand and contract without these muscles because the lungs to not have the muscular tissue to expand and contract.
The effect of the respiratory muscles in expanding the rib cage. Normally, adults breathe 16 to 20 times per minute or from to 1, times per hour. A respiratory rate of less than 16 per minute is referred to as bradypnea or slow breathing and a respiratory rate of more than 20 per minute for an adult is referred to as tachypnea or rapid breathing. Of all the vital signs, which include the cardiac pulse rate, the body temperature, the blood pressure, and the respiratory rate, it is the respiratory rate that is the only vital sign that is able to be controlled with a conscious and voluntary effort.
The other vital signs are involuntary and not controllable with conscious effort. Disorders Affecting the Respiratory System Many disorders and diseases can adversely affect the respiratory system and respiratory functioning. Some of these disorders can be congenital and others can be acquired. Congenital respiratory disorders affect the infant in the uterus before they are born. For example, a neonate, or newborn, can be born with hyaline membrane disease or cystic fibrosis. Acquired respiratory diseases and disorders occur later in life after birth. Some of the most commonly occurring heart diseases and disorders are: Pneumonia.
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