№ 7. Physiology of the Lungs. Exchange of Gases in the Lungs.
The Respiratory System
Among quadrupeds, the respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. A diaphragm pulls air in and pushes it out. Respiratory systems of various types are found in a wide variety of organisms.
In humans and other mammals, the respiratory system consists of the airways, the lungs, and the respiratory muscles that mediate the movement of air into and out of the body. Within the alveolar system of the lungs, molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation. The system also helps to maintain the acid-base balance of the body through the efficient removal of carbon dioxide from the blood.
Anatomy
In humans and other animals, the respiratory system can be conveniently subdivided into an upper respiratory tract (or conducting zone) and lower respiratory tract (respiratory zone), trachea and lungs.
Anatomy of the respiratory system.
Air moves through the body in the following order:
· Nostrils. A nostril (or naris, pl. nares) is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation. Fish do not breathe through their noses, but they do have two small holes used for smelling which may, indeed, be called nostrils.The Procellariiformes are distinguished from other birds by having tubular extensions of their nostrils. In humans, the nasal cycle is the normal ultradian cycle of each nostril’s blood vessels becoming engorged in swelling, then shrinking.The nostrils are separated by the septum. The septum can sometimes be deviated, causing one nostril to appear larger than the other. With extreme damage to the septum, the two nostrils are no longer separated and form a single larger external opening.Humans have two external nostrils with two additional nostrils inside the head. These internal nostrils are called “choanae” and each contain approximately 1000 strands of nasal hair. They also connect the nose to the throat aiding in respiration. Scientists believe they migrated back inside as evidenced by the discovery of “Kenichthys campbelli“, a 395 million-year-old fossilized fish which shows this migration in progress. It has two nostrils between its front teeth, similar to human embryos at an early stage. If these fail to join up it causes a cleft palate.It is possible for humans to smell different olfactory inputs in the two nostrils and experience a perceptual rivalry akin to that of binocular rivalry when there are two different inputs to the two eyes.
· Nasal cavity.
Nasal cavity
Head and neck.
Conducting passages
The nasal cavity (or nasal fossa) is a large air filled space above and behind the nose in the middle of the face.
Function
The nasal cavity conditions the air to be received by the other areas of the respiratory tract. Owing to the large surface area provided by the nasal conchae, the air passing through the nasal cavity is warmed or cooled to within 1 degree of body temperature. In addition, the air is humidified, and dust and other particulate matter is removed by vibrissae, short, thick hairs, present in the vestibule. The cilia of the respiratory epithelium move the particulate matter towards the pharynx where it passes into the esophagus and is digested in the stomach.
Walls
The lateral wall of the nasal cavity is mainly made up by the maxilla, however there is a deficiency that is compensated by: the perpendicular plate of the palatine bone, the medial pterygoid plate, the labyrinth of the ethmoid and the inferior concha.
The nasal cavity is enclosed by the nasal bone above.
The floor of the nasal cavity, which forms the roof of the mouth, is made up by the bones of the hard palate: the horizontal plate of the palatine bone posteriorly and the palatine process of the maxilla anteriorly. To the front of the nasal cavity is the nose, while the back blends, via the choanae, into the nasopharynx. The paranasal sinuses are connected to the nasal cavity through small orifices called ostia.
The nasal cavity is divided in two by a vertical fin called the nasal septum. On the sides of the nasal cavity are three horizontal outgrowths called nasal conchae (singular “concha“) or turbinates. These turbinates disrupt the airflow, directing air toward the olfactory epithelium on the surface of the turbinates and the septum. The vomeronasal organ is located at the back of the septum and has a role in pheromone detection.
Cilia and mucus
Cilia and mucus along the inside wall of the nasal cavity trap and remove dust and pathogens from the air as it flows through the nasal cavity. The cilia move the mucus down the nasal cavity to the pharynx, where it can be swallowed.
Segments
The nasal cavity is divided into two segments: the respiratory segment and the olfactory segment.
The respiratory segment is lined with ciliated pseudostratified columnar epithelium (also called respiratory epithelium). The conchae are located in this region. The respiratory segment has a very vascularized lamina propria allowing the venous plexuses of the conchal mucosa to engorge with blood, restricting airflow and causing air to be directed to the other side of the nose. This cycle occurs approximately every 20–30 minutes. Nose bleeds [epistaxis] in the inferior concha are common in this region.
The olfactory segment is lined with a specialized type of pseudostratified columnar epithelium, known as olfactory epithelium, which contains receptors for the sense of the smell. This segment is located along the dorsal roof of the nasal cavity. Histological sections appear yellowish-brown due to the presence of lipofuscin pigments. Olfactory mucosal cell types include bipolar neurons, supporting (sustentacular) cells, basal cells, and Bowman’s glands. The axons of the bipolar neurons form the olfactory nerve (cranial nerve I) which enters the brain through the cribiform plate. Bowman’s glands are serous glands in the lamina propria, whose secretions trap and dissolve odoriferous substances.
Blood supply
There is a rich blood supply to the nasal cavity. In some animals, such as dogs, the capillary beds flowing through the nasal cavity help cool the blood flow to the brain.
Blood supply comes from branches of both the internal and external carotid artery, including branches of the facial artery and maxillary artery. The named arteries of the nose are:
Sphenopalatine and Greater palatine arteries, branches of the maxillary artery.
Anterior ethmoidal artery, a branch of the ophthalmic artery
Branches of facial artery supplying the vestibule of the nasal cavity.
Innervation
Innervation of the nasal cavity responsible for the sense of smell is via the olfactory nerve, which sends microscopic fibers from the olfactory bulb through the cribiform plate to reach the top of the nasal cavity.
General sensory innervation is by branches of the trigeminal nerve (V1 & V2):
Nasociliary nerve (V1)
Nasopalatine nerve (V2)
Posterior nasal branches of Maxillary nerve (V2)
There are two passages in the nasal cavity, not to be confused with nostrils.The entire nasal cavity is innervated by autonomic fibers. Sympathetic innervation to the blood vessels of the mucosa causes them to constrict, while the control of secretion by the mucous glands is carried on postganglionic parasympathetic nerve fibers originating from the facial nerve.
Diseases
Diseases of the nasal cavity include viral, bacterial and fungal infections, nasal cavity tumors, both benign and much more often malignant, as well as inflammations of the nasal mucosa.
Nasal cavity
Nose and nasal cavities
Normal Nose CT Front cross section
Coronal section of nasal cavities
Anatomy of the nasal cavity
Left orbicularis oculi, seen from behind
Lateral wall of nasal cavity
Nerves of the wall of the nasal cavity
· Pharynx (naso-, oro-, laryngo-)
The human pharynx (plural: pharynges) is the part of the throat situated immediately inferior to (below) the mouth and nasal cavity, and superior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx (epipharynx), the oropharynx (mesopharynx), and the laryngopharynx (hypopharynx). The pharynx is part of the digestive system and also the respiratory system; it is also important in vocalization.
Nasopharynx
The most cephalad portion of the pharynx. It extends from the base of the skull to the upper surface of the soft palate. It includes the space between the internal nares and the soft palate and lies superior to the oral cavity. The pharyngeal tonsils, more commonly referred to as the adenoids, are lymphoid tissue structures located in the posterior wall of the nasopharynx.
Anterior
In front it communicates through the choanae with the nasal cavities.
Lateral
On its lateral wall is the pharyngeal ostium of the Eustachian tube, somewhat triangular in shape, and bounded behind by a firm prominence, the torus tubarius or cushion, caused by the medial end of the cartilage of the tube which elevates the mucous membrane.
Two folds arise from the cartilaginous opening:
· vertical fold of mucous membrane, the salpingopharyngeal fold, stretches from the lower part of the torus; it contains the Salpingopharyngeus muscle.
· second and smaller fold, the salpingopalatine fold, stretches from the upper part of the torus to the palate; it contains the levator veli palatini muscle. The tensor veli palatini is lateral to the levator and does not contribute the fold, since the origin is deep to the cartilaginous opening.
Behind the ostium of the Eustachian tube is a deep recess, the pharyngeal recess (fossa of Rosenmьller).
Posterior
On the posterior wall is a prominence, best marked in childhood, produced by a mass of lymphoid tissue, which is known as the pharyngeal tonsil.
Above the pharyngeal tonsil, in the middle line, an irregular flask-shaped depression of the mucous membrane sometimes extends up as far as the basilar process of the occipital bone; it is known as the pharyngeal bursa.
Human pharynx.Posterior view.
The nasopharynx, oropharynx, and laryngopharynx or larynx can be seen clearly in this sagittal section of the head and neck.
Polyps or mucus can obstruct the nasopharynx, as can congestion due to an upper respiratory infection. The Eustachian tubes, which connect the middle ear to the pharynx, open into the nasopharynx. The opening and closing of the Eustachian tubes serves to equalize the barometric pressure in the middle ear with that of the ambient atmosphere.
The anterior aspect of the nasopharynx communicates through the choanae with the nasal cavities. On its lateral walls are the pharyngeal ostia of the auditory tube, somewhat triangular in shape, and bounded behind by a firm prominence, the torus tubarius or cushion, caused by the medial end of the cartilage of the tube that elevates the mucous membrane. Two folds arise from the cartilaginous opening:
the salpingopharyngeal fold, a vertical fold of mucous membrane extending from the inferior part of the torus and containing the salpingopharyngeus muscle
the salpingopalatine fold, a smaller fold extending from the superior part of the torus to the palate and containing the levator veli palatini muscle. The tensor veli palatini is lateral to the levator and does not contribute the fold, since the origin is deep to the cartilaginous opening.
Behind the ostium of the auditory tube is a deep recess, the pharyngeal recess (also referred to as the fossa of Rosenmьller). On the posterior wall is a prominence, best marked in childhood, produced by a mass of lymphoid tissue, which is known as the pharyngeal tonsil. Superior to the pharyngeal tonsil, in the midline, an irregular flask-shaped depression of the mucous membrane sometimes extends up as far as the basilar process of the occipital bone; it is known as the pharyngeal bursa.
Oropharynx
The oropharynx or mesopharynx lies behind the oral cavity, extending from the uvula to the level of the hyoid bone. It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the Palatoglossal arch and the Palatopharyngeal arch, is the palatine tonsil. The anterior wall consists of the base of the tongue and the epiglottic vallecula; the lateral wall is made up of the tonsil, tonsillar fossa, and tonsillar (faucial) pillars; the superior wall consists of the inferior surface of the soft palate and the uvula. Because both food and air pass through the pharynx, a flap of connective tissue called the epiglottis closes over the glottis when food is swallowed to prevent aspiration.The oropharynx is lined by non keratinised squamous stratified epithelium.
The HACEK organisms (Haemophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella) are part of the normal oropharyngeal flora, which grow slowly, prefer a carbon dioxide-enriched atmosphere, and share an enhanced capacity to produce endocardial infections, especially in young children. Fusobacterium is a pathogen.
Normal oropharyngeal flora
Fusobacterium
Although older resources have stated that Fusobacterium is a common occurrence in the human oropharynx, the current consensus is that Fusobacterium should always be treated as a pathogen.
HACEK organisms
The name is formed from their initials:
· Haemophilus
· Actinobacillus actinomycetemcomitans
· Cardiobacterium hominis
· Eikenella corrodens
· Kingella
All of these organisms are part of the normal oropharyngeal flora, which grow slowly, prefer a carbon dioxide–enriched atmosphere and share an enhanced capacity to produce endocardial infections, especially in young children.
Actinomyces
Actinomyces species that cause human disease do not exist freely iature but are normal flora of the oropharynx.
Laryngopharynx
Laryngopharynx labeled at bottom right
The hypopharynx or laryngopharynx or (Latin: pars laryngea pharyngis) is the caudal part of the pharynx; it is the part of the throat that connects to the esophagus. It lies inferior to the epiglottis and extends to the location where this common pathway diverges into the respiratory (larynx) and digestive (esophagus) pathways. At that point, the laryngopharynx is continuous with the esophagus posteriorly. The esophagus conducts food and fluids to the stomach; air enters the larynx anteriorly. During swallowing, food has the “right of way”, and air passage temporarily stops. Corresponding roughly to the area located between the 4th and 6th cervical vertebrae, the superior boundary of the laryngopharynx is at the level of the hyoid bone. The laryngopharynx includes three major sites: the pyriform sinus, postcricoid area, and the posterior pharyngeal wall. Like the oropharynx above it, the laryngopharynx serves as a passageway for food and air and is lined with a stratified squamous epithelium. It is innervated by the pharyngeal plexus.
The superior boundary of the hypopharynx is at the level of the hyoid bone with the inferior border being the lower level of the cricoid cartilage.
It can be divided into three sub-sites:
· piriform sinus
· postcricoid area
· posterior pharyngeal wall
The vascular supply to the hypopharynx includes the Superior Thyroid Artery, the Lingual Artery and the Ascending Pharyngeal Artery. The primary neural supply is from both the vagus and glossopharyngeal nerves. The vagus nerve provides a branch termed “Arnolds Nerve” which also supplies the external auditory canal, thus hypophayrngeal cancer can result in referred otalgia. This nerve is also responsible for the ear-cough reflex in which stimulation of the ear canal results in a person coughing.
Organs of the digestive system
The entrance to the larynx, viewed from behind
The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind
Acute catarrhal pharyngitis. The oropharynx is swollen and red
· Larynx (voice box)
The larynx, commonly called the voice box, is an organ in the neck of amphibians, reptiles, and mammals (including humans) involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume. The larynx houses the vocal folds (commonly but improperly termed the “vocal cords”), which are essential for phonation. The vocal folds are situated just below where the tract of the pharynx splits into the trachea and the esophagus.
Anatomy of the larynx, anterolateral view
Endoscopic image of a human larynx
Anatomical position and description
In adult humans, the larynx is found in the anterior neck at the level of the C3–C6 vertebrae. It connects the inferior part of the pharynx (hypopharynx) with the trachea. The laryngeal skeleton consists of nine cartilages: three single (epiglottic, thyroid and cricoid) and three paired (arytenoid, corniculate, and cuneiform). The hyoid bone is not part of the larynx, though it is connected to it. The larynx extends vertically from the tip of the epiglottis to the inferior border of the cricoid cartilage. Its interior can be divided in supraglottis, glottis and subglottis.
Iewborn infants, the larynx is initially at the level of the C2–C3 vertebrae, and is further forward and higher relative to its position in the adult body. The larynx descends as the child grows.
Function
Sound is generated in the larynx, and that is where pitch and volume are manipulated. The strength of expiration from the lungs also contributes to loudness.
Fine manipulation of the larynx is used to generate a source sound with a particular fundamental frequency, or pitch. This source sound is altered as it travels through the vocal tract, configured differently based on the position of the tongue, lips, mouth, and pharynx. The process of altering a source sound as it passes through the filter of the vocal tract creates the many different vowel and consonant sounds of the world’s languages as well as tone, certain realizations of stress and other types of linguistic prosody. The larynx also has a similar function as the lungs in creating pressure differences required for sound production; a constricted larynx can be raised or lowered affecting the volume of the oral cavity as necessary in glottalic consonants.
The vocal folds can be held close together (by adducting the arytenoid cartilages), so that they vibrate (see phonation). The muscles attached to the arytenoid cartilages control the degree of opening. Vocal fold length and tension can be controlled by rocking the thyroid cartilage forward and backward on the cricoid cartilage (either directly by contracting the cricothyroids or indirectly by changing the vertical position of the larynx), by manipulating the tension of the muscles within the vocal folds, and by moving the arytenoids forward or backward. This causes the pitch produced during phonation to rise or fall. In most males the vocal folds are longer and with a greater mass, producing a deeper pitch.
The vocal apparatus consists of two pairs of mucosal folds. These folds are false vocal folds (vestibular folds) and true vocal folds (folds). The false vocal folds are covered by respiratory epithelium, while the true vocal folds are covered by stratified squamous epithelium. The false vocal folds are not responsible for sound production, but rather for resonance. The exceptions to this are found in Tibetan Chant and Kargyraa, a style of Tuvan throat singing. Both make use of the false vocal folds to create an undertone. These false vocal folds do not contain muscle, while the true vocal folds do have skeletal muscle.
During swallowing, the backward motion of the tongue forces the epiglottis over the glottis’ opening to prevent swallowed material from entering the larynx which leads to the lungs; the larynx is also pulled upwards to assist this process. Stimulation of the larynx by ingested matter produces a strong cough reflex to protect the lungs.
Innervation
The larynx is innervated by branches of the vagus nerve on each side. Sensory innervation to the glottis and laryngeal vestibule is by the internal branch of the superior laryngeal nerve. The external branch of the superior laryngeal nerve innervates the cricothyroid muscle. Motor innervation to all other muscles of the larynx and sensory innervation to the subglottis is by the recurrent laryngeal nerve. While the sensory input described above is (general) visceral sensation (diffuse, poorly localized), the vocal fold also receives general somatic sensory innervation (proprioceptive and touch) by the superior laryngeal nerve.
Injury to the external laryngeal nerve causes weakened phonation because the vocal folds cannot be tightened. Injury to one of the recurrent laryngeal nerves produces hoarseness, if both are damaged the voice may or may not be preserved, but breathing becomes difficult.
Intrinsic muscles associated with the larynx
Cricothyroid muscles lengthen and stretch the vocal folds.
Posterior cricoarytenoid muscles abduct and externally rotate the arytenoid cartilages, resulting in abducted vocal folds.
Lateral cricoarytenoid muscles adduct and internally rotate the arytenoid cartilages, which can result in adducted vocal folds.
Transverse arytenoid muscle adducts the arytenoid cartilages, resulting in adducted vocal folds.
Oblique arytenoid muscles narrow the laryngeal inlet by constricting the distance between the arytenoid cartilages.
Vocalis muscles increase the thickness of the chords changing the tone.
Thyroarytenoid muscles – sphincter of vestibule, narrowing the laryngeal inlet.
Notably, the only muscle capable of separating the vocal cords for normal breathing is the posterior cricoarytenoid. If this muscle is incapacitated on both sides, the inability to pull the vocal folds apart (abduct) will cause difficulty breathing. Bilateral injury to the recurrent laryngeal nerve would cause this condition. It is also worth noting that all muscles are innervated by the recurrent laryngeal branch of the vagus except the cricothyroid muscle, which is innervated by the external laryngeal branch of the superior laryngeal nerve (a branch of the vagus).
Extrinsic muscles associated with the larynx
· Thyrohyoid muscles
· Sternothyroid muscles
· Omohyoid muscles
· Inferior constrictor muscles
· Digastric
· Stylohyoid
· Mylohyoid
· Geniohyoid
· Hyoglossus
Descended larynx
In infant humans and most animals, the larynx is situated very high in the throat—a position that allows it to couple more easily with the nasal passages, so that breathing and eating are not done with the same apparatus. However, some aquatic mammals, large deer, and adult humans have descended larynges. Adult humans cannot raise the larynx enough to directly couple it to the nasal passage. Despite its presence in deer, proponents of the aquatic ape hypothesis claim that the similarity between the descended larynx in humans and aquatic mammals supports their theory.
Pioneering work on the structure and evolution of the larynx was carried out in the 1920s by the British comparative anatomist Victor Negus, culminating in his monumental work The Mechanism of the Larynx (1929). Negus, however, pointed out that the descent of the larynx reflected the reshaping and descent of the human tongue into the pharynx. This process is not complete until age six to eight years. Some researchers, such as Philip Lieberman, Dennis Klatt, Brant de Boer and Kenneth Stevens using computer-modeling techniques have suggested that the species-specific human tongue allows the vocal tract (the airway above the larynx) to assume the shapes necessary to produce speech sounds that enhance the robustness of human speech. Sounds such as the vowels of the words see and do, [i] and [u], (in phonetic notation) have been shown to be less subject to confusion in classic studies such as the 1950 Peterson and Barney investigation of the possibilities for computerized speech recognition. In contrast, though other species have low larynges their tongues remains anchored in their mouths and their vocal tracts cannot produce the range of speech sounds of humans. The ability to lower the larynx transiently in some species extends the length of their vocal tract, which as Fitch showed creates the acoustic illusion that they are larger. Research at Haskins Laboratories in the 1960s showed that speech allows humans to achieve a vocal communication rate that exceeds the fusion frequency of the auditory system by fusing sounds together into syllables and words. The additional speech sounds that the human tongue enables us to produce, particularly [i], allow humans to unconsciously infer the length of the vocal tract of the person who is talking, a critical element in recovering the phonemes that make up a word.
Disorders of the larynx
There are several things that can cause a larynx to not function properly. Some symptoms are hoarseness, loss of voice, pain in the throat or ears, and breathing difficulties. Larynx transplant is a rare procedure. The world’s first successful operation took place in 1998 at the Cleveland Clinic, and the second took place in October 2010 at the University of California Medical Center in Sacramento.
Acute laryngitis is the sudden inflammation and swelling of the larynx. It is caused by the common cold or by excessive shouting. It is not serious. Chronic laryngitis is caused by smoking, dust, frequent yelling, or prolonged exposure to polluted air. It is much more serious than acute laryngitis.
Presbylarynx is a condition in which age-related atrophy of the soft tissues of the larynx results in weak voice and restricted vocal range and stamina. Bowing of the anterior portion of the vocal folds is found on laryngoscopy.
Ulcers may be caused by the prolonged presence of an endotracheal tube.
Polyps and nodules are small bumps on the vocal folds caused by prolonged exposure to cigarette smoke and vocal misuse, respectively.
Two related types of cancer of the larynx, namely squamous cell carcinoma and verrucous carcinoma, are strongly associated with repeated exposure to cigarette smoke and alcohol.
Vocal cord paresis is weakness of one or both vocal folds that can greatly impact daily life.
Idiopathic laryngeal spasm.
Laryngopharyngeal reflux is a condition in which acid from the stomach irritates and burns the larynx. Similar damage can occur with gastroesophageal reflux disease (GERD).
Laryngomalacia is a very common condition of infancy, in which the soft, immature cartilage of the upper larynx collapses inward during inhalation, causing airway obstruction.
Laryngeal perichondritis, the inflammation of the perichondrium of laryngeal cartilages, causing airway obstruction.
Cartilages
There are nine cartilages, three unpaired and three paired, that support the mammalian larynx and form its skeleton. The unpaired cartilages of the larynx are the thyroid, cricoid and epiglottis. The paired cartilages of the larynx are the arytenoids, corniculate, and the cuneiforms.
Thyroid Cartilage: This forms the Adam’s apple. It is usually larger in males than in females. The thyrohyoid membrane is a ligament associated with the thyroid cartilage that connects the thyroid cartilage with the hyoid bone.
Cricoid cartilage: A ring of hyaline cartilage that forms the inferior wall of the larynx. It is attached to the top of trachea.
Epiglottis: A large, spoon-shaped piece of elastic cartilage. During swallowing, the pharynx and larynx rise. Elevation of the pharynx widens it to receive food and drink; elevation of the larynx causes the epiglottis to move down and form a lid over the glottis, closing it off.
Paired Arytenoid Cartilage: Of the paired cartilages, the arytenoid cartilages are the most important because they influence the position and tension of the vocal folds. These are triangular pieces of mostly hyaline cartilage located at the posterosuperior border of the cricoid cartilage.
Paired Corniculate Cartilage: Horn-shaped pieces of elastic cartilage located at the apex of each arytenoid cartilage.
Paired Cuneiform Cartilage: Club-shaped pieces of elastic cartilage located anterior to the corniculate cartilages.
Non-mammalian larynges
Most tetrapod species possess a larynx, but its structure is typically simpler than that found in mammals. The cartilages surrounding the larynx are apparently a remnant of the original gill arches in fish, and are a common feature, but not all are always present. For example, the thyroid cartilage is found only in mammals. Similarly, only mammals possess a true epiglottis, although a flap of non-cartilagenous mucosa is found in a similar position in many other groups. In modern amphibians, the laryngeal skeleton is considerably reduced; frogs have only the cricoid and arytenoid cartilages, while salamanders possess only the arytenoids.
Vocal folds are found only in mammals, and a few lizards. As a result, many reptiles and amphibians are essentially voiceless; frogs use ridges in the trachea to modulate sound, while birds have a separate sound-producing organ, the syrinx.
Shape
It is tube shaped and is 10.4 centimeters(4.1″) long
· Trachea (wind pipe)
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx and larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus. This mucus lines the cells of the trachea to trap inhaled foreign particles that the cilia then waft upward toward the larynx and then the pharynx where it can be either swallowed into the stomach or expelled as phlegm.
Despite the name, not all vertebrates have a trachea; only non-fish ones. The name is used in contrast with invertebrate trachea, a structure in arthropod anatomy.
Trachea
In humans, the trachea passes ventrally to the esophagus, dorsally to the ascending aortic arch, but the left main bronchus that the trachea gives off passes ventrally to the descending aortic arch.
In humans
In humans, the trachea passes ventrally to the esophagus, dorsally to the ascending aortic arch, but the left main bronchus that the trachea gives off passes ventrally to the descending aortic arch.
The trachea has an inner diameter of about 25 millimetres (1.0 in) and a length of about 10 to 16 centimetres (4 to 6 in). It commences at the lower border of the larynx, level with the sixth cervical vertebra, and bifurcates into the primary bronchi at the vertebral level of thoracic vertebra T5, or up to two vertebrae lower or higher, depending on breathing.
There are about fifteen to twenty incomplete C-shaped cartilaginous rings that reinforce the anterior and lateral sides of the trachea to protect and maintain the airway, leaving a membranous wall (pars membranacea) dorsally without cartilage. The trachealis muscle connects the ends of the incomplete rings and contracts during coughing, reducing the size of the lumen of the trachea to increase the air flow rate. The esophagus lies posteriorly to the trachea. The cartilaginous rings are incomplete to allow the trachea to collapse slightly so that food can pass down the esophagus. A flap-like epiglottis closes the opening to the larynx during swallowing to prevent swallowed matter from entering the trachea. Lined with respiratory epithelium.
Tracheal diseases and conditions
The following are diseases and conditions that affect the trachea:
· Choking
· Tracheotomy, a surgical procedure on the neck to open a direct airway through an incision in the trachea
· Tracheomalacia (weakening of the tracheal cartilage)
· Tracheal collapse (in dogs)
· Tracheobronchial injury (perforation of the trachea or bronchi)
· Mounier-Kuhn syndrome (causes abnormal enlargement of the trachea)
· Thoracic cavity (chest)
· Bronchi (right and left)
Alveoli (site of gas exchange) An alveolus (plural: alveoli, from Latin alveolus, “little cavity”) is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the terminal ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well. Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates. The alveolar membrane is the gas-exchange surface. Carbon dioxide rich blood is pumped from the rest of the body into the alveolar blood vessels where, through diffusion, it releases its carbon dioxide and absorbs oxygen.
Location
The alveoli are located in the respiratory zone of the lungs, at the distal termination of the alveolar ducts and atria. These air sacs are the forming and termination point of the respiratory tract. They provide total surface area of about 100 m2.
The respiratory tract is a common site for infections. Upper respiratory tract infections are probably the most common infections in the world.
Most of the respiratory tract exists merely as a piping system for air to travel in the lungs, and alveoli are the only part of the lung that exchanges oxygen and carbon dioxide with the blood.
Moving down the respiratory tract starting at the trachea, the tubes get smaller and divide into more and more tubes. There are estimated to be about 20 to 23 divisions, ending up at an alveolus.
Even though the cross-sectional area of each bronchus or bronchiole is smaller, because there are so many, the total surface area is larger. This means there is less resistance at the terminal bronchioles. (Most resistance is around the 3-4 division from the trachea due to turbulence.)
The respiratory tract is covered in an epithelium, the type of which varies down the tract. There are glands and mucus produced by goblet cells in parts, as well as smooth muscle, elastin or cartilage.
Most of the epithelium (from the nose to the bronchi) is covered in pseudostratified columnar ciliated epithelial cells, commonly called respiratory epithelium. The cilia beat in one direction, moving mucus towards the throat where it is swallowed. Moving down the bronchioles, the cells get more cuboidal in shape but are still ciliated.
Cartilage is present until the small bronchi. In the trachea they are C-shaped rings, whereas in the bronchi they are interspersed plates.
Glands are abundant in the upper respiratory tract, but there are fewer lower down and they are absent starting at the bronchioles. The same goes for goblet cells, although there are scattered ones in the first bronchioles.
Smooth muscle starts in the trachea, where it joins the C-shaped rings of cartilage. It continues down the bronchi and bronchioles, which it completely encircles.
Instead of hard cartilage, the bronchi and bronchioles are composed of elastic tissue.
Anatomy
The alveoli contain some collagen and elastic fibres. The elastic fibers allow the alveoli to stretch as they are filled with air during inhalation. They then spring back during exhalation in order to expel the carbon dioxide-rich air.
A typical pair of human lungs contain about 700 million alveoli, producing 70mІ of surface area. Each alveolus is wrapped in a fine mesh of capillaries covering about 70% of its area. An adult alveolus has an average diameter of 200 micrometres, with an increase in diameter during inhalation.
The alveoli consist of an epithelial layer and extracellular matrix surrounded by capillaries. In some alveolar walls there are pores between alveoli called Pores of Kohn.
Histology
There are three major cell types in the alveolar wall (pneumocytes):
Type I (Squamous Alveolar) cells that form the structure of an alveolar wall
Type II (Great Alveolar) cells that secrete pulmonary surfactant to lower the surface tension of water and allows the membrane to separate, therefore increasing its capability to exchange gases. Surfactant is continuously released by exocytosis. It forms an underlying aqueous protein-containing hypophase and an overlying phospholipid film composed primarily of dipalmitoyl phosphatidylcholine.
Macrophages that destroy foreign material, such as bacteria.
Reinflation of the alveoli following exhalation is made easier by pulmonary surfactant, which is a phospholipid and protein mixture that reduces surface tension in the thin fluid coating within all alveoli. The fluid coating is produced by the body in order to facilitate the transfer of gases between blood and alveolar air. The surfactant is produced by great alveolar cells (granular pneumonocytes, a cuboidal epithelia), which are the most numerous cells in the alveoli, yet do not cover as much surface area as the squamous alveolar cells (a squamous epithelium).
Great alveolar cells also repair the endotheilium of the alveolus when it becomes damaged. Insufficient pulmonary surfactant in the alveoli can contribute to atelectasis (collapse of part or all of the lung). Without pulmonary surfactant, atelectasis is a certainty; however, there are other causes of lung collapse such as trauma (pneumothorax), COPD, and pleuritis.
Diseases
Acute respiratory distress syndrome (ARDS) is a severe inflammatory disease of the lung. Usually triggered by other pulmonary pathology, the uncontrolled inflammation leads to impaired gas exchange, alveolar flooding and/or collapse, and systemic inflammatory response syndrome. It usually requires mechanical ventilation in an intensive care unit setting.
Infant respiratory distress syndrome (IRDS) is a syndrome caused by lack of surfactant in the lungs of premature infants.
In asthma, the bronchioles, or the “bottle-necks” into the sac are restricted, causing the amount of air flow into the lungs to be greatly reduced. It can be triggered by irritants in the air, photochemical smog for example, as well as substances that a person is allergic to.
Emphysema is another disease of the lungs, whereby the elastin in the walls of the alveoli is broken down by an imbalance between the production of neutrophil elastase (elevated by cigarette smoke) and alpha-1-antitrypsin (the activity varies due to genetics or reaction of a critical methionine residue with toxins including cigarette smoke). The resulting loss of elasticity in the lungs leads to prolonged times for exhalation, which occurs through passive recoil of the expanded lung. This leads to a smaller volume of gas exchanged per breath.
Chronic bronchitis occurs when an abundance of mucus is produced by the lungs. The production of this substance occurs naturally when the lung tissue is exposed to irritants. In chronic bronchitis, the air passages into the alveoli, the broncholiotes, become clogged with mucus. This causes increased coughing in order to remove the mucus, and is often a result of extended periods of exposure to cigarette smoke.
Cystic fibrosis is a genetic condition. A mutation of the cystic fibrosis transmembrane conductance regulator gene causes defective CFTR proteins, which are transmembrane proteins that function in Cl– transport in wet epithelia. Because wet epithelium is such a ubiquitous and multipurpose tissue type, CF has myriad deleterious effects, some of the most serious of which are severe respiratory problems. Many of the mechanisms by which CF causes damage or inadequate function in the wet epithelia of other tissues, such as the digestive and reproductive tracts, are well-understood. CF’s mechanisms in causing lung disease, however, remain poorly elucidated. One popular hypothesis suggests increased viscosity due to increased salinity of the mucous secreted by glands of the pseudostratified respiratory epithelium, causing difficulty in maintaining normal respiratory tract mucociliary clearance. The frequency of certain specific bacterial infections (Pseudomonas, Haemophilus influenzae, Staphylococcus) has prompted two other popular categories of hypotheses: that the high salt content may interfere with defensins and lysosome, and/or may encourage the growth of the several bacterial species typically infecting the ordinarily-sterile lower lungs of CF patients. Regular treatment is usually required—primarily percussive therapy and antibiotics. Promising research into gene therapies is taking place.
Diffuse interstitial fibrosis
Lung cancer is a common form of cancer causing the uncontrolled growth of cells in the lung tissue. Due to the sensitivity of lung tissue, such malignant growth is often hard to treat effectively.
Pneumonia is an infection of the lung parenchyma, which can be caused by both viruses and bacteria. Cytokines and fluids are released into the alveolar cavity and/or interstitium in response to infection, causing the effective surface area of gas exchange in the lungs to be reduced. If this happens to such a degree that the patient cannot draw enough oxygen from his or her environment to maintain cellular respiration, then the victim may need supplemental oxygen.
Cavitary pneumonia is a process in which the alveoli are destroyed and produce a cavity. As the alveoli are destroyed, the surface area for gas exchange to occur becomes reduced. Further changes in blood flow can lead to decline in lung function.
Pulmonary contusion is a bruise of the lung tissue.
Regenerative ability of the human pulmonary alveolus
The following small extracted statement is from a story (taken on Wednesday, November 2, 2011) from the HarvardScience website, a division of the online Harvard Gazette. It had been featured on Harvard University’s homepage. The news release (no author is given) from Harvard Medical School Communications was originally posted on Thursday, October 27, 2011:
“Guided by insights into how mice recover after H1N1 flu, researchers at Harvard Medical School and Brigham and Women’s Hospital, together with researchers at A*STAR of Singapore, have cloned three distinct stem cells from the human airways and demonstrated that one of these cells can form into the lung’s alveoli air sac tissue. What’s more, the researchers showed that these same lung stem cells are rapidly deployed in a dynamic process of lung regeneration to combat damage from infection or chronic disease.
“These findings suggest new cell- and factor-based strategies for enhancing lung regeneration following acute damage from infection, and even in chronic conditions such as pulmonary fibrosis,” said Frank McKeon, professor of cellular biology at Harvard Medical School (HMS).
Upper respiratory tract/conducting zone
The conducting zone begins with the nares (nostrils) of the nose, which open into the nasopharynx (nasal cavity). The primary functions of the nasal passages are to: 1) filter, 2) warm, 3) moisten, and 4) provide resonance in speech. The nasopharynx opens into the oropharynx (behind the oral cavity). The oropharynx leads to the laryngopharynx, and empties into the larynx (voicebox), which contains the vocal cords, passing through the glottis, connecting to the trachea (wind pipe).
Lower respiratory tract/respiratory zone
The trachea leads down to the thoracic cavity (chest) where it divides into the right and left “main stem” bronchi. The subdivision of the bronchus are: primary, secondary, and tertiary divisions (first, second and third levels). In all, they divide 16 more times into even smaller bronchioles.
The bronchioles lead to the respiratory zone of the lungs which consists of respiratory bronchioles, alveolar ducts and the alveoli, the multi-lobulated sacs in which most of the gas exchange occurs.
Ventilation of the lungs is carried out by the muscles of respiration.
Ventilation occurs under the control of the autonomic nervous system from the part of the brain stem, the medulla oblongata and the pons. This area of the brain forms the respiration regulatory center, a series of interconnected neurons within the lower and middle brain stem which coordinate respiratory movements. The sections are the pneumotaxic center, the apneustic center, and the dorsal and ventral respiratory groups. This section is especially sensitive during infancy, and the neurons can be destroyed if the infant is dropped or shaken violently. The result can be death due to “shaken baby syndrome.”
The process of inhalation.
Inhalation
Inhalation is initiated by the diaphragm and supported by the external intercostal muscles. Normal resting respirations are 10 to 18 breaths per minute. Its time period is 2 seconds. During vigorous inhalation (at rates exceeding 35 breaths per minute), or in approaching respiratory failure, accessory muscles of respiration are recruited for support. These consist of sternocleidomastoid, platysma, and the strap muscles of the neck.
Inhalation is driven primarily by the diaphragm. When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This results in a larger thoracic volume, which in turn causes a decrease in intrathoracic pressure. As the pressure in the chest falls, air moves into the conducting zone. Here, the air is filtered, warmed, and humidified as it flows to the lungs.
During forced inhalation, as when taking a deep breath, the external intercostal muscles and accessory muscles further expand the thoracic cavity.
The process of exhalation.
Exhalation is generally a passive process, however active or forced exhalation is achieved by the abdominal and the internal intercostal muscles. During this process air is forced or exhaled out. The lungs have a natural elasticity; as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere reach equilibrium.
During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles, generate abdominal and thoracic pressure, which forces air out of the lungs.
The right side of the heart pumps blood from the right ventricle through the pulmonary semilunar valve into the pulmonary trunk. The trunk branches into right and left pulmonary arteries to the pulmonary blood vessels. The vessels generally accompany the airways and also undergo numerous branchings. Once the gas exchange process is complete in the pulmonary capillaries, blood is returned to the left side of the heart through four pulmonary veins, two from each side. The pulmonary circulation has a very low resistance, due to the short distance within the lungs, compared to the systemic circulation, and for this reason, all the pressures within the pulmonary blood vessels are normally low as compared to the pressure of the systemic circulation loop.
Virtually all the body’s blood travels through the lungs every minute. The lungs add and remove many chemical messengers from the blood as it flows through pulmonary capillary bed . The fine capillaries also trap blood clots that have formed in systemic veins.
The major function of the respiratory system is gas exchange. As gas exchange occurs, the acid-base balance of the body is maintained as part of homeostasis. If proper ventilation is not maintained two opposing conditions could occur: 1) respiratory acidosis, a life threatening condition, and 2) respiratory alkalosis.
Illustration of Gas exchange.
Upon inhalation, gas exchange occurs at the alveoli, the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres), and are permeable to gases. The alveoli are lined with pulmonary capillaries, the walls of which are also thin enough to permit gas exchange. All gases diffuse from the alveolar air to the blood in the pulmonary capillaries, as carbon dioxide diffuses in the opposite direction, from capillary blood to alveolar air. At this point, the pulmonary blood is oxygen-rich, and the lungs are holding carbon dioxide. Exhalation follows, thereby ridding the body of the carbon dioxide and completing the cycle of respiration.
In an average resting adult, the lungs take up about 250ml of oxygen every minute while excreting about 200ml of carbon dioxide. During an average breath, an adult will exchange from 500 ml to 700 ml of air. This average breath capacity is called tidal volume.
The respiratory system lies dormant in the human fetus during pregnancy. At birth, the respiratory system is drained of fluid and cleaned to assure proper functioning of the system. If an infant is born before forty weeks gestational age, the newborn may experience respiratory failure due to the under-developed lungs. This is due to the incomplete development of the alveoli type II cells in the lungs, necessary for the production of surfactant. The infant lungs do not function due to collapse of alveoli caused by surface tension of water remaining in the lungs, which iormal cases would be prohibited by the presence of surfactant. This condition may be avoided by giving the mother a series of steroid shots in the final week prior to delivery, which will enhance the development of type II alveolar cells.
The movement of gas through the larynx, pharynx and mouth allows humans to speak, or phonate. Because of this, gas movement is extremely vital for communication purposes.
Conditions of the respiratory system
Disorders of the respiratory system can be classified into four general areas:
· Obstructive conditions (e.g., emphysema, bronchitis, asthma attacks)
· Restrictive conditions (e.g., fibrosis, sarcoidosis, alveolar damage, pleural effusion)
· Vascular diseases (e.g., pulmonary edema, pulmonary embolism, pulmonary hypertension)
· Infectious, environmental and other “diseases” (e.g., pneumonia, tuberculosis, asbestosis, particulate pollutants) coughing is of major importance, as it is the body’s main method to remove dust, mucus, saliva, and other debris from the lungs. Inability to cough can lead to infection. Deep breathing exercises may help keep finer structures of the lungs clear from particulate matter, etc.
The respiratory tract is constantly exposed to microbes due to the extensive surface area, which is why the respiratory system includes many mechanisms to defend itself and prevent pathogens from entering the body.
Disorders of the respiratory system are usually treated internally by a pulmonologist or Respiratory Physician.
Plants use carbon dioxide gas in the process of photosynthesis, and then exhale oxygen gas, a waste product of photosynthesis. However, plants also sometimes respire as humans do, using oxygen and producing carbon dioxide.
Plant respiration is limited by the process of diffusion. Plants take in carbon dioxide through holes on the undersides of their leaves known as stomata(sing:stoma). However, most plants require little air. Most plants have relatively few living cells outside of their surface because air (which is required for metabolic content) can penetrate only skin deep. However, most plants are not involved in highly aerobic activities, and thus have no need of these living cells.
PHYSIOLOGY of RESPIRATION
Respiration (respiratio) is the process in which air passes into and out of the lung with the object of allowing the blood to absorb oxygen and to give off carbon dioxide and water. The exchange of gases takes place in the alveoli of the lungs. Oxygen passes into the blood and carbon dioxide passes into the atmospheric air.
The exchange of oxygen and carbon dioxide is due to the difference of partial pressures of these gases in the alveolar air and in the venous blood. The partial pressure of oxygen in the alveolar air is higher than in the venous blood. The transfer of oxygen from the atmospheric air into the blood is due to this difference of pressures. The partial pressure of carbon dioxide is higher in the venous blood and it enables carbon dioxide to pass from the blood into alveolar air.
The process of transfer of gases into the medium with a lower partial pressure is called diffusion. Hemoglobin is that substance of the blood which transfers oxygen in the blood. The oxygen capacity of the blood averages to 18-20 milliliters (ml) per 100 gr of blood. Carbon dioxide is transferred in combination with hemoglobin and as bicarbonic salts.
The combination of oxygen and hemoglobin is called oxyhemoglobin, that of carbon dioxide and hemoglobin — carbohemoglobin.
Mechanism of respiration. The air passes rhythmically into and out of the air passages, and mixes with the air already in the lungs, these two movements are known as inspiration and expiration.
Inspiration is due to a muscular effort which enlarges the chest in all three dimensions, so that the lungs have to expand in order to fill up the vacuum that would otherwise be left, and the air enters these organs by the air passages. The increase of the chest in size is mainly due to the diaphragm, whose muscular fibers by their contraction reduces its domed shape and causes it to descend, pushing down the abdominal organs beneath it.
The muscles which chiefly provide the process of inspiration are intercostal muscles and levators of the ribs. In forced or extraordinary inspiration, when an especially deep breath is taken, the sternomastoid, serratus magnus, trapezius, and pectoral muscles are also brought powerfully into play.
Expiration is in ordinary circumstances simply an elastic recoil, the diaphragm rising and the ribs sinking into the position that they naturally occupy, when muscular contraction is finished. Expiration occupies a slightly longer period than inspiration. In forced expiration many powerful muscles of the abdomen and thorax are brought into play, and the act may be made a very forcible one, as, for example, in coughing.
When one breathes normally not all the alveoli and capillaries of the lungs are opened. When respiration becomes deep, the number of the opened alveoli and capillaries increases. The flow of blood into the lungs increases when one breathes in and it decreases when one breathes out.
The regulation of the vital capacity of the lungs is of particular importance to the exchange of oxygen and carbon dioxide taking place in the lungs. It is considered that in the adult the vital capacity of the lungs is about 3-4 liters. When the depth of respiration increases the vital capacity may be 6 liters and even more.
The thoracic cavity (or chest cavity) is the chamber of the human body (and other animal bodies) that is protected by the thoracic wall (thoracic cage and associated skin, muscle, and fascia).
The thoracic area includes the tendons as well as the cardiovascular system which could be damaged from injury to the back, spine or the neck.
Components
Structures within the thoracic cavity include:
Fetal thoracic cavity
structures of the cardiovascular system, including the heart and great vessels, which include the thoracic aorta, the pulmonary artery and all its branches, the superior and inferior vena cava, the pulmonary veins, and the azygos vein
structures of the respiratory system, including the trachea, bronchi and lungs
structures of the digestive system, including the esophagus,
endocrine glands, including the thymus gland,
structures of the nervous system including the paired vagus nerves, and the paired sympathetic chains,
lymphatics including the thoracic duct.
It contains three potential spaces lined with mesothelium: the paired pleural cavities and the pericardial cavity. The mediastinum comprises those organs which lie in the centre of the chest between the lungs.
Clinical significance
If the pleural cavity is breached from the outside, as by a bullet wound or knife wound, a pneumothorax, or air in the cavity, may result. If the volume of air is significant, one or both lungs may collapse, which requires immediate medical attention.
Thoracic wall
Body cavities
A transverse section of the thorax, showing the contents of the middle and the posterior mediastinum.
Brief Explanation
The thoracic wall (or chest wall) is the boundary of the thoracic cavity.
The bony portion is known as the thoracic cage. However, the wall also includes muscle, skin, and fascia.
Relation to Apnea
Wheot breathing for long and dangerous periods of time in cold water, your body undergoes great temporary changes to try and prevent death. It achieves this through the activation of the Mammalian diving reflex, which has 3 main properties. Other than Bradycardia and Peripheral vasoconstriction, there is a blood shift which occurs only during very deep dives that affects the thoracic cavity (a chamber of the body protected by the thoracic wall.) When this happens, organ and circulatory walls allow plasma/water to pass freely throughout the thoracic cavity, so its pressure stays constant and the organs aren’t crushed. In this stage, the lungs’ alveoli fill up with blood plasma, which is reabsorbed when the organism leaves the pressurized environment. This stage of the diving reflex has been observed in humans (such as world champion freediver Martin Љtěpбnek) during extremely deep (over 90 metres or 300 ft) free dives.
The human rib cage, also known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic cavity and supports the pectoral girdle, forming a core portion of the human skeleton. A typical human rib cage consists of 24 ribs, the sternum (with Xiphoid process), costal cartilages, and the 12 thoracic vertebrae. It, along with the skin and associated fascia and muscles, makes up the thoracic wall and provides attachments for the muscles of the neck, thorax, upper abdomen, and back.
Respiratory function
The human rib cage is a component of the human respiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular diaphragm, at the floor of the thoracic cavity, contracts and flattens, while contraction of intercostal muscles lift the rib cage up and out.
Expansion of the thoracic cavity is driven in three planes; the vertical, the anteroposterior and the transverse. The vertical plane is extended by the help of the diaphragm contracting and the abdominal muscles relaxing to accommodate the downward pressure that is supplied to the abdominal viscera by the diaphragm contracting. A greater extension can be achieved by the diaphragm itself moving down, rather than simply the domes flattening. The second plane is the anteroposterior and this is expanded by a movement known as the ‘pump handle.’ The downward sloping nature of the upper ribs are as such because they enable this to occur. When the external intercostal muscles contract and lift the ribs, the upper ribs are able also to push the sternum up and out. This movement increases the anteroposterior diameter of the thoracic cavity, and hence aids breathing further. Finally, you have the transverse. In this situation, it involves mainly the lower ribs (some say it is the 7th-10th ribs in particular) with the diaphragm’s central tendon acting as a fixed point. When the diaphragm contracts, the ribs are able to evert and produce what is known as the ‘bucket handle’ movement, facilitated by gliding at the costovertebral joints. In this way, the transverse diameter is expanded and the lungs can fill.
Breathing may be assisted by other muscles that can raise the ribs, such as sternocleidomastoid, pectoralis major and minor as well as the scalenes. Whilst under most circumstances, individuals respire via eupnea, exercise and other forms of physiological stress can cause the body to require forced expiration, rather than the simple elastic recoil of the thoracic cage, lungs and diaphragm. In this case, muscles are recruited which can help depress the ribs and raise the diaphragm – such as the anterior abdominal wall muscles, excluding the transversus abdominis muscle. Latissimus dorsi can also aid deep, forced expiration.
Another way the thoracic cavity can expand during inhalation is called belly breathing. This also involves a contraction of the diaphragm, but the lower ribs are stabilized so that when the muscle contracts, rather than the central tendon remaining stable and lifting the ribs up, the central tendon moves down, compressing the sub-thoracic cavity and allowing the thoracic cavity and lungs room to expand downward.
These actions produce an increase in volume, and a resulting partial vacuum, or negative pressure, in the thoracic cavity, resulting in atmospheric pressure pushing air into the lungs, inflating them. An exhalation results when the diaphragm and intercostal muscles relax, and elastic recoil of the rib cage and lungs expels the air.
The circumference of the normal adult human rib cage expands by 3 to 5 cm during inhalation.
Rib anatomy
The parts of the rib.
All ribs are attached in the back to the thoracic vertebrae.
Each rib consists of a head, neck, and a shaft. The head typically has two facets on its surface; one for articulation with the corresponding vertebrae, and one for articulation with the immediately superior vertebrae.
The upper seven true ribs(costae verae, vertebrosternal ribs, I-VII). are attached in the head to the sternum by means of costal cartilage. Due to their elasticity they allow movement when inhaling and exhaling.
The 8th, 9th, and 10th ribs are called false ribs (costae spuriae, vertebrochondral ribs, VIII-X), and join with the costal cartilages of the ribs above.The 11th and 12th are also sometimes referred to as false ribs.
The 11th and 12th ribs are known as floating ribs (costae fluitantes, vertebral ribs, XI-XII), as they do not have any anterior connection to the sternum.
The spaces between the ribs are known as intercostal spaces; they contain the intercostal muscles, nerves, and arteries.
Medical issues
Rib fractures are the most common injury to the rib cage. These most frequently affect the middle ribs. When several ribs are injured, this can result in a flail chest.
Abnormalities of the rib cage include pectus excavatum (“sunken chest”) and pectus carinatum (“pigeon chest”). Bifid or bifurcated ribs, in which the sternal end of the rib is cleaved in two, is a congenital abnormality occurring in about 1.2% of the population. The rib remnant of the 7th cervical vertebra on one or both sides is occasionally replaced by a free extra rib called a cervical rib, which can cause problems in the nerves going to the arm.
Rib removal is the surgical excision of ribs for therapeutic or cosmetic reasons.
· Bronchi (right and left)
A bronchus (plural bronchi, adjective bronchial) is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles. No gas exchange takes place in this part of the lungs.
The human trachea (windpipe) divides into two main bronchi (also mainstem bronchi), the left and the right, at the level of the sternal angle and of the fifth thoracic vertebra or up to two vertebrae higher or lower, depending on breathing, at the anatomical point known as the carina. The right main bronchus is wider, shorter, and more vertical than the left main bronchus. The right main bronchus subdivides into three lobar bronchi, while the left main bronchus divides into two. The lobar bronchi divide into tertiary bronchi, also known as segmentalinic bronchi, each of which supplies a bronchopulmonary segment. A bronchopulmonary segment is a division of a lung separated from the rest of the lung by a connective tissue septum. This property allows a bronchopulmonary segment to be surgically removed without affecting other segments. There are ten segments per lung, but due to anatomic development, several segmental bronchi in the left lung fuse, giving rise to eight. The segmental bronchi divide into many primary bronchioles which divide into terminal bronchioles, each of which then gives rise to several respiratory bronchioles, which go on to divide into two to 11 alveolar ducts. There are five or six alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.
The hyaline cartilage forms an incomplete ring in the bronchi, giving them a “D”-shaped appearance in the larger bronchi (as compared with the “O”-shaped complete cartilaginous rings of the trachea), and as small plates and islands in the smaller bronchi. Smooth muscle is present continuously around the bronchi.
In the mediastinum, at the level of the fourth thoracic vertebra, the trachea divides into the right and left primary bronchi. The bronchi branch into smaller and smaller passageways until they terminate in tiny air sacs called alveoli.
The cartilage and mucous membrane of the primary bronchi are similar to those in the trachea. As the branching continues through the bronchial tree, the amount of hyaline cartilage in the walls decreases until it is absent in the smallest bronchioles. As the cartilage decreases, the amount of smooth muscle increases. The mucous membrane also undergoes a transition from ciliated pseudostratified columnar epithelium to simple cuboidal epithelium to simple squamous epithelium.
The alveolar ducts and alveoli consist primarily of simple squamous epithelium, which permits rapid diffusion of oxygen and carbon dioxide. Exchange of gases between the air in the lungs and the blood in the capillaries occurs across the walls of the alveolar ducts and alveoli.
Bronchitis is defined as inflammation of the bronchi. There are two main types: acute and chronic. Acute bronchitis is usually caused by viral or bacterial infections. Chronic bronchitis is a form of COPD, usually associated with smoking or long-term exposure to irritants. Asthma is hyperreactivity of the bronchi with an inflammatory component, often in response to allergens.
While the left mainstem bronchus departs from the trachea at an angle, the right mainstem bronchus is almost a vertical continuation of the trachea. This anatomy predisposes the right lung to several problems:
If food, liquids, or foreign bodies are aspirated, they often will lodge in the right mainstem bronchus. Aspiration pneumonia may result.
If the endotracheal tube used for intubation is inserted too far, it usually lodges in the right mainstem bronchus. This allows ventilation of the right lung, but leaves the left lung useless.
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