9.THE RESPIRATORY SYSTEM

• The respiratory system consists of the organs of respiration such as the nose, pharynx, larynx, trachea, bronchi, and lungs.
• Within the lungs, air flows along a dead-end pathway consisting of bronchi → bronchioles → alveoli.
• Incoming air stops in the alveoli, exchanges gases with the bloodstream through the alveolar wall, and then flows back out.
• The interior wall of the larynx has two folds on each side that stretch from the thyroid cartilage in front to the arytenoid cartilages in back.
• The superior vestibular folds play no role in speech but close the larynx during swallowing and are supported by the vestibular ligaments.
• The inferior vocal cords produce sound when air passes between them and are covered with the vocal ligaments.
• The trachea, or “windpipe,” is a tube about 12 cm (4.5 in.) long and 2.5 cm (1 in.) in diameter, anterior to the esophagus.
• The trachea is supported by 16 to 20 C-shaped rings of hyaline cartilage and is named for the corrugated texture imparted.
• Hyperventilation is the increased pulmonary ventilation in excess of metabolic demand, often associated with anxiety, which expels CO2 faster than it is produced, thus lowering the blood CO2 concentration and raising the blood pH.
• Orthopnea is dyspnea that occurs when a person is lying down or in any position other than standing or sitting erect, often seen in heart failure, asthma, emphysema, and other conditions.
• Dyspnea is labored, gasping breathing or shortness of breath.
• Tachypnea is accelerated respiration.
• Hypoventilation is reduced pulmonary ventilation, which leads to an increase in blood CO2 concentration if ventilation is insufficient to expel CO2 as fast as it is produced.
• Respiratory arrest is permanent cessation of breathing, unless there is medical intervention.
• Hyperpnea is an increased rate and depth of breathing in response to exercise, pain, or other conditions.
• Apnea is a temporary cessation of breathing, often accompanied by dyspnea.
• Kussmaul respiration is deep, rapid breathing often induced by acidosis, seen in diabetes mellitus.
• Anxiety can trigger a bout of uncontrollable hyperventilation in some people, a state in which breathing is so rapid that it expels CO2 from the body faster than it’s produced.
• Some authorities refer to the respiratory rhythm as an autonomic function.
• The effectors of the autonomic nervous system include the respiratory muscles and the heart.
• Variations in the respiratory rhythm are possible because the respiratory centers of the medulla and pons receive input from several other levels of the nervous system and therefore respond to the body’s varying physiological needs.
• Stretch receptors are found in the smooth muscle of the bronchi and bronchioles and in the visceral pleura and respond to inflation of the lungs.
• Hyperventilation can be brought under control by having a person rebreathe the expired CO2 from a paper bag held over the nose and mouth.
• Central chemoreceptors are brainstem neurons that respond especially to changes in the pH of the cerebrospinal fluid and are concentrated on each side of the medulla oblongata at a point only 0.2 mm beneath its anterior surface.
• Irritant receptors are nerve endings amid the epithelial cells of the airway and respond to smoke, dust, pollen.
• Peripheral chemoreceptors are located in the carotid and aortic bodies of the large arteries above the heart.
• Charles’s law states that the volume of a given quantity of gas is directly proportional to its absolute temperature (assuming a constant pressure).
• Henry’s law states that at the air–water interface, the amount of gas that dissolves in water is determined by its solubility in water and its partial pressure in the air (assuming a constant temperature).
• Boyle’s law states that the pressure of a given quantity of gas is inversely proportional to its volume (assuming a constant temperature).
• Millimeters of mercury (mm Hg) is a measure of blood pressure and is used in respiratory physiology.
• Mercury is used in measuring pressures because it can be measured with a relatively short column of mercury, as in the sphygmomanometer of a doctor’s office.
• Jacques A.C. Charles (1746–1823), French physicist
• Robert Boyle (1627–91), Anglo–Irish physicist and chemist
• John Dalton (1766–1844), English physicist and chemist
• Dalton’s law states that the total pressure of a gas mixture is equal to the sum of the partial pressures of its individual gases.
• Respiratory physiologists traditionally used water columns, which are more sensitive, and measure these pressures in centimeters of water (cm H2O).
• William Henry (1774–1836), English chemist
• Small pressure changes will move a column of water more than a column of mercury; one can see them and measure them more accurately.
• Most of the nasal cavity is occupied by three folds of tissue—the superior, middle, and inferior nasal conchae, or turbinates—that project from the lateral walls toward the septum.
• The nasal cavity begins with a small dilated chamber called the vestibule just inside the nostril, bordered by the ala nasi.