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The lungs are the central organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the air and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. The pleurae, which are thin, smooth, and moist, serve to reduce friction between the lungs and chest wall during breathing, allowing for easy and effortless movements of the lungs.
The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that carries sensory fibers that create a pathway that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right vagus nerves—but they are typically referred to collectively as a single subsystem.
The larynx, commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about 4–5 centimeters in diameter. The larynx houses the vocal cords, and manipulates pitch and volume, which is essential for phonation. It is situated just below where the tract of the pharynx splits into the trachea and the esophagus. The word 'larynx' comes from the Ancient Greek word lárunx ʻlarynx, gullet, throat.ʼ
The respiratory system is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies greatly, depending on the size of the organism, the environment in which it lives and its evolutionary history. In land animals, the respiratory surface is internalized as linings of the lungs. Gas exchange in the lungs occurs in millions of small air sacs; in mammals and reptiles, these are called alveoli, and in birds, they are known as atria. These microscopic air sacs have a very rich blood supply, thus bringing the air into close contact with the blood. These air sacs communicate with the external environment via a system of airways, or hollow tubes, of which the largest is the trachea, which branches in the middle of the chest into the two main bronchi. These enter the lungs where they branch into progressively narrower secondary and tertiary bronchi that branch into numerous smaller tubes, the bronchioles. In birds, the bronchioles are termed parabronchi. It is the bronchioles, or parabronchi that generally open into the microscopic alveoli in mammals and atria in birds. Air has to be pumped from the environment into the alveoli or atria by the process of breathing which involves the muscles of respiration.
The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.
Swallowing, also called deglutition or inglutition in scientific contexts, is the process in the body of a human or other animal that allows for a substance to pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. Swallowing is an important part of eating and drinking. If the process fails and the material goes through the trachea, then choking or pulmonary aspiration can occur. In the human body the automatic temporary closing of the epiglottis is controlled by the swallowing reflex.
The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.
Exhalation is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing. This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. 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 control of ventilation is the physiological mechanisms involved in the control of breathing, which is the movement of air into and out of the lungs. Ventilation facilitates respiration. Respiration refers to the utilization of oxygen and balancing of carbon dioxide by the body as a whole, or by individual cells in cellular respiration.
The pharyngeal reflex or gag reflex is a reflex muscular contraction of the back of the throat, evoked by touching the roof of the mouth, back of the tongue, area around the tonsils, uvula, and back of the throat. It, along with other aerodigestive reflexes such as reflexive pharyngeal swallowing, prevents objects in the oral cavity from entering the throat except as part of normal swallowing and helps prevent choking, and is a form of coughing. The pharyngeal reflex is different from the laryngeal spasm, which is a reflex muscular contraction of the vocal cords.
The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve that supplies all the intrinsic muscles of the larynx, with the exception of the cricothyroid muscles. There are two recurrent laryngeal nerves, right and left. The right and left nerves are not symmetrical, with the left nerve looping under the aortic arch, and the right nerve looping under the right subclavian artery then traveling upwards. They both travel alongside the trachea. Additionally, the nerves are among the few nerves that follow a recurrent course, moving in the opposite direction to the nerve they branch from, a fact from which they gain their name.
The superior laryngeal nerve is a branch of the vagus nerve. It arises from the middle of the inferior ganglion of vagus nerve and additionally also receives a sympathetic branch from the superior cervical ganglion.
The superior ganglion of the vagus nerve is a sensory ganglion of the peripheral nervous system. It is located within the jugular foramen, where the vagus nerve exits the skull. It is smaller than and proximal to the inferior ganglion of the vagus nerve.
The dorsal nucleus of vagus nerve is a cranial nerve nucleus of the vagus nerve situated in the medulla oblongata of the brainstem ventral to the floor of the fourth ventricle. It contains nerve cell bodies of parasympathetic neurons of CN X that provide parasympathetic innervation to the gastrointestinal tract and lungs as well as other thoracic and abdominal organs. These functions include, among others, bronchoconstriction and gland secretion.
The Hering–Breuer inflation reflex, named for Josef Breuer and Ewald Hering, is a reflex triggered to prevent the over-inflation of the lung. Pulmonary stretch receptors present on the wall of bronchi and bronchioles of the airways respond to excessive stretching of the lung during large inspirations.
Pulmonary stretch receptors are mechanoreceptors found in the lungs.
The respiratory system of the horse is the biological system by which a horse circulates air for the purpose of gaseous exchange.
Juxtacapillary receptors, J-receptors, or pulmonary C-fiber receptors are sensory nerve endings located within the alveolar walls in juxtaposition to the pulmonary capillaries of the lung, and are innervated by fibers of the vagus nerve. Although their functional role is unclear, J-receptors respond to events such as pulmonary edema, pulmonary emboli, pneumonia, congestive heart failure and barotrauma, which cause a decrease in oxygenation and thus lead to an increase in respiration. They may be also stimulated by hyperinflation of the lung as well as intravenous or intracardiac administration of chemicals such as capsaicin. The stimulation of the J-receptors causes a reflex increase in breathing rate, and is also thought to be involved in the sensation of dyspnea, the subjective sensation of difficulty breathing. The reflex response that is produced is apnea followed by rapid breathing, bradycardia, and hypotension. The physiologic role of this reflex is uncertain, but it probably occurs in pathologic states such as pulmonary congestion or embolization. These receptors were discovered by Autar Paintal.
The respiratory center is located in the medulla oblongata and pons, in the brainstem. The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. In the medulla they are the dorsal respiratory group, and the ventral respiratory group. In the pons, the pontine respiratory group includes two areas known as the pneumotaxic center and the apneustic center.
The pharynx is the part of the throat behind the mouth and nasal cavity, and above the esophagus and trachea. It is found in vertebrates and invertebrates, though its structure varies across species. The pharynx carries food to the esophagus and air to the larynx. The flap of cartilage called the epiglottis stops food from entering the larynx.
References
- 1 2 Hall, John (2011). Guyton and Hall Textbook of Medical Physiology with Student Consult Online Access (12th ed.). Philadelphia: Elsevier Saunders. p. 473. ISBN 978-1-4160-4574-8.
- ↑ Zhang, Mengru; Morice, Alyn H. (2023-08-29). "Unravelling vagal hypersensitivity in chronic cough: A distinct disease". The Journal of Physiology. doi:10.1113/JP284641. ISSN 0022-3751. PMID 37642341.
- ↑ Dicpinigaitis, Peter V.; Kantar, Ahmad; Enilari, Oladunni; Paravati, Francesco (2018). "Prevalence of Arnold Nerve Reflex in Adults and Children With Chronic Cough". Chest. 153 (3): 675–679. doi:10.1016/j.chest.2017.11.019. ISSN 1931-3543. PMID 29197546.
- ↑ Hegland, K. W.; Bolser, D. C.; Davenport, P. W. (2012). "Volitional control of reflex cough". Journal of Applied Physiology. 113 (1): 39–46. doi:10.1152/japplphysiol.01299.2011. PMC 3774289 . PMID 22492938.
