Anatomically , the respiratory system consists of an upper respiratory tract and a lower respiratory tract . Functionally , it can be divided into a conducting portion (“the pipes”) and a respiratory portion (tiny air sacs where gas exchange occurs.
The primary function most of us associate with the respiratory tract is breathing, which consists of inhalation (inspiration) and exhalation (expiration).
The inhaled air is “conditioned” prior to reaching the tiny air sacs of the lungs. The gases are warmed, humidified, and cleansed of particulate matter through contact with the respiratory epithelium.
The respiratory system not only allows gas exchange, it also promotes vocalization.
Cranial nerve I (olfactory nerve) relies upon chemoreceptors in upper nasal mucous membranes.
The structure of the respiratory system protects the body by trapping foreign debris in mucus and destroying microbes with lysozyme.
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The upper respiratory tract consists of the nose and nasal cavity , the paranasal sinuses, the pharynx (throat), and structures associated with all of the above . All of these are part of the conducting portion of the respiratory tract.
The external portion of the nose consists of cartilage and bone
Pliable cartilage forms the distal portions of the nose. Paired nostrils (external nares) open on the inferior surface of the nose
The roof of the nose consists of the nasal bones, the frontal bone , the cribriform plate of the ethmoid bone, and the sphenoid bone . The floor of the nose consists of the horizontal plate of the maxillae and the horizontal portions of the palatine bones .
The anterior region of the nasal cavity, near the nostrils, is called the vestibule . Near the vestibule are coarse hairs called vibrissae to help trap large particles.
The maxillary sinuses are quite large and drain high on their medial side.
Because the drainage of the maxillary sinuses is so high, fluid has a tendency to accumulate and result in an infection (sinusitis). Region of drainage Maxillary sinus
The pharynx (throat) for most of its length (except for the nasopharynx) is a common pathway for both inhaled and exhaled air and for ingested food.
There are three regions to the pharynx (throat).
The nasopharynx, which is lined with cilia, is the portion of the throat behind the nose. The Eustachian tubes from the middle ear open into this region and the uvula is in the lower portion of this region.
The uvula , which is the most posterior portion of the soft palate, rises upward with the soft palate during swallowing to block food or liquids from entering the nasopharynx.
Note the soft palate and uvula preventing food or liquids from entering the nasopharynx during swallowing.
The palatine tonsils are the masses of lymphatic tissue you see at the back of the oropharynx while the pharyngeal tonsils (adenoids) are not apparent and are located in the nasopharynx . (Adenoids)
This is a posterior view of the nasopharynx showing the pharyngeal tonsils (adenoids). Note also the conchae (turbinates), soft palate, uvula, and nasal septum. Conchae
The oropharynx is the portion of the throat behind the mouth. The visible palatine tonsils can be seen at this location.
This small snake has navigated the nasal cavity, the nasopharynx, the oropharynx, and the mouth (buccal cavity). Head Tail
Usually, there are several groups of tonsils found in the pharynx: pharyngeal tonsils (adenoids), palatine tonsils , and lingual tonsils .
The laryngopharynx is the lowest portion of the throat. It allows food or liquids into the esophagus and air in and out of the trachea.
The most common location for large pieces of food to get stuck is the laryngopharynx .
The lower respiratory tract is made up of conduction airways (larynx, trachea, bronchi, bronchioles, and associated structures) as well as the respiratory portion of the respiratory system (reparatory bronchioles, alveolar ducts, and alveoli).
The larynx (voice box) connects the laryngopharynx to the trachea. Inferior to the vocal cords, the larynx is lined with cilia.
The larynx , despite being called the “voice box” is shaped more like a shield. It is open posteriorly. Note the epiglottis, thyroid cartilage (Adam’s apple), and the circular cricoid cartilage .
The laryngeal prominence is created by the thyroid cartilage and is commonly called the Adam’s apple.
Note thyroid cartilage, cricothyroid ligament, and cricoid cartilage .
The cricoid cartilage is a complete circle and connects the thyroid cartilage above with the trachea below. An emergency airway ( cricothyrotomy) can be made by cutting through the cricothyroid ligament.
Note the spoon-shaped epiglottis that is pivoted shut when the larynx rises superiorly during swallowing.
The epiglottis closes posteriorly (towards the spine) when the larynx moves superiorly during swallowing.
Posterior view showing the epiglottis in an open position
Note epiglottis closing posteriorly to cover the entrance to the larynx during swallowing so the mass of blue food can only enter the esophagus.
The tip of the laryngoscope moves the epiglottis anteriorly
The tip of the laryngoscope either pivots the epiglottis anteriorly at its base or actually touches the epiglottis to pull it anteriorly. In both instances the epiglottis moves away from the spine and makes it easier to look down into the larynx.
False vocal cords The false vocal cords (vestibular folds) support the true vocal cords just below. The false cords do not produce sound.
The true vocal cords vibrate when air is passed over them and produce sound. The vocal cords of males are longer, vibrate more slowly than those of females, and produce lower pitches.
The opening between the vocal folds (true vocal cords) is called the rima glottidis . The term glottis refers to the rima glottidis plus the vocal folds. When air is forced through the rima glottidis, the vocal folds vibrate, and this vibration produces sound.
The range of voices is determined by the length of the vocal folds, pitch is determined by the tightness of the vocal folds, and loudness is depends on the force of air passing the vocal folds.
The lips, tongue, oral cavity, nasal cavity, sinuses, and constriction of pharyngeal walls all contribute to the recognizable generation of speech.
Read about laryngitis in the clinical view in the text
The trachea connects the larynx to the primary bronchi. The trachea is located anterior to the esophagus and is held open by C-shaped hyaline cartilage rings with the open part of the C facing posteriorly to allow the esophagus to bulge anteriorly when food is passing down the esophagus.
Internal view of the trachea. Note arches created by C-shaped hyaline cartilage rings that keep the trachea open (patent).
The trachealis muscle , which spans the open end of the C-shaped rings, can contract to narrow the trachea so air moves more rapidly to help expel a foreign object or mucus.
Coughing and sneezing are forced expiration and employ the internal intercostals to force the ribs down and in and the abdominal muscles to force the abdominal organs in and up against the diaphragm. The trachealis muscle narrows the trachea to make this expulsion more forceful.
The trachea is lined with ciliated epithelium and mucus secreting cells . Dust and foreign particles are swept up into the pharynx where the mucus is either coughed out or swallowed .
Note that the right primary bronchus is more vertical while the left primary bronchus leaves at a more acute angle (because of the heart). This means that foreign objects are more likely to lodge in the right lung as it is more of a straight down route.
Internal view of the trachea. Note the internal ridge ( carina ) that divides the origins of the left and right primary bronchi.
This branching of the airways looks like the branches of a tree (respiratory tree) with the trachea as the trunk.
As they branch, the airways ( bronchial tree ) get smaller and smaller until they reach the tiny bronchioles that have NO cartilage rings.
Alveolar macrophages (dust cells) are migratory cells that constantly crawl within the alveoli, engulfing microbes and foreign material that has reached the alveoli.
WHICH OF THE FOLLOWING IS MOST RESPONSIBLE FOR BLOOD FLOW (PERFUSION) OF THE ALVEOLI? A RIGHT VENTRICULAR SYSTOLE B PULMONARY VEINS C BRACHIAL ARTERIES D CAPILLARY REFILL AFTER COMPRESSION E ALL OF THE ABOVE
There is a partial vacuum that holds the pleural membranes together
Note the base and the apex of the lungs. Also note that the left lung only has two lobes , while the right lung has three.
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Blood low in oxygen is pumped from the right ventricle, into the pulmonary trunk , and then into the left and right pulmonary arteries which deliver the blood to the pulmonary capillaries . Blood high in oxygen is then conducted by the pulmonary veins to the left atrium.
Bronchial arteries , from the systemic circulation, also bring blood to the lungs
Lymph nodes and vessels are closely associated with the lungs. The lymphatic drainage of the right lung drains into the right lymphatic duct while the lymphatic drainage of the left lung goes to the thoracic duct.
Breathing (ventilation) is carried out by muscular structures surrounding the lungs
Inspiration is an active process that occurs when the dome-shaped diaphragm contracts downward and the external intercostals pull the ribs up and out .
During inspiration the movement of the diaphragm and ribs pull the parietal pleura out and down and the visceral pleura (with the attached lungs) follows. Air is pulled in by negative pressure.
Expiration is a passive process caused by the elastic recoil of the lung tissues. This causes the ribs to move down and in and the diaphragm to be pulled upward. This reduction of space causes air to be pushed out of the lungs by positive pressure.
In order to passively exhale, all a person needs to do is to stop nervous stimulation of the external intercostals and the diaphragm. The elasticity of the lungs will then pull the ribs down and in and the diaphragm up.
The internal intercostal muscles can depress the ribs and diminish the volume of the thoracic cavity. However, this only occurs during forceful exhalation (exercise or coughing/sneezing.
Read about asthma in the clinical view in the text
Sympathetic innervation opens up airways while parasympathetic innervation narrows them. The respiratory control centers are located in the pons and in the medulla oblongata .
Smoking an pollution can lead to emphysema and lung cancer . Read the clinical view in your text.
Putting babies to sleep on their backs will reduce risk of suffocation and Sudden Infant Death Syndrome (SIDS). Read the clinical view in your text.
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Preparation for a tracheotomy , which is the surgery to open this airway in the trachea.
Contraction of the trachealis muscle, and narrowing of the trachea , can allow air to move more forcefully to expel mucus and debris
If the cartilage of the larynx or trachea were crushed by trauma , these airways would collapse and death would quickly occur by asphyxiation.
The lungs are separated by the mediastinum which contains the heart, trachea, esophagus, thymus, and major blood vessels.
All structures of the respiratory tract beyond the primary bronchi are contained in the lungs. Note the right lung has three lobes while the left lung has only two lobes because of the space taken up by the heart on that side.
WHICH OF THE FOLLOWING HAS BEEN LINKED TO THE DEVELOPMENT OF EMPHYSEM A? A CHEWING TOBACCO B AIR POLLUTION C STIFFLING A SNEEZE D COCAINE ABUSE E PREMATURE BIRTH
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The serous membranes associated with the lungs are the outer parietal pleura and the inner visceral pleura .
The pleural cavity is actually a “potential space” that is mostly occupied by the spongy tissues of the lungs. Normally the two pleural membranes are close together like two pieces of Saran wrap with a small amount of lubricating pleural fluid between them.
If outside air entered the space between the pleural membranes (pleural space) the elastic lung tissue would collapse inward and the chest wall would expand outward.
WHICH OF THE FOLLOWING OCCURS DURING RESTFUL INSPIRATION ? A THE DIAPHRAGM MOVES SUPERIORLY B THE PHRENIC NERVE IS ACTIVATED C THE EPIGLOTTIS MOVES TOWARDS THE SPINE D THE INTERNAL INTERCOSTAL MUSCLES CONTRACT E THE MESENCEPHALON SENDS STIMULATORY IMPULSES TO THE CENTRAL TENDON
A blow to the abdomen, or a sudden fall onto one’s back, can stretch the diaphragm and its associated nerves . It will then spasm for a brief period of time and fail to contract. This temporary reduction in ventilatory ability is referred to as “getting the wind knocked out of you”.
Outside air between the pleural membranes (pneumothorax) allows the elastic lung to collapse inward and the chest wall to expand outward. The pleural cavity becomes obvious. Once the lung is collapsed, the person has only the one lung to survive on.
Ventilation (breathing) is the movement of gases in and out of lungs
Loudness is determined by the force of the air passed over the vocal cords and the amount of vibrating.
Valsalva’s maneuver also increases abdominal pressure to aid in childbirth (parturition).
Breathing (ventilation) External respiration , which occurs in the alveoli, and internal respiration , which occurs in active tissues throughout the body. Cellular respiration , which is metabolism in cells.
External respiration occurs between alveoli and pulmonary capillaries
Internal respiration occurs between tissue capillaries throughout the body and nearby cells.
Cellular respiration is the use of oxygen and generation of carbon dioxide by cell metabolism.
Brain damage and death can occur if breathing stop, or is cut off, for 7-8 minutes so that the body’s store of oxygen is depleted.
Valsalva’s maneuver increases thoracic and abdominal pressure to help stabilize the spine while lifting heavy objects.
Coughing and sneezing also keep the airways free of obstruction and help remove irritants.
WHAT DRAINS FROM AN OPENING JUST INFERIOR TO THE INFERIOR NASAL CONCHAE? A SALIVARY GLAND B FLUID FROM ORBIT C ETHMOIDAL SINUSES D PHEROMONES E JUICE FROM THE “SMALL GRAPE” KNOWN AS THE UVULA
WHAT IS CONNECTED BY THE EUSTACHIAN TUBE ? A MASTOID AIR CELLS AND NOSE B TEMPORAL BONE AND NASOPHARYNX C CRANIAL CAVITY AND MIDDLE EAR D EXTERNAL EAR AND EAR DRUM E EYE AND NOSE
Epiglottitis is inflammation of the epiglottis typically caused by a bacterial infection that may cause it to swell and block the airway.