THE RESPIRATORY SYSTEM CHAPTER 15 Introduction To continue functioning, body cells must obtain oxygen and eliminate carbon dioxide. The Functions of the Respiratory System 1. Moving air to and from exchange surfaces where diffusion can occur between air and circulating blood 2. Defending the respiratory system and other tissues from pathogens 3. Permitting vocal communication 4. Helping control body fluid pH. Organization The respiratory system includes the nose, nasal cavity, and sinuses as well as the pharynx, larynx, trachea, and conducting passageways leading to the surfaces of the lungs. Respiratory Tract The respiratory tract consists of the conducting passageways that carry air to and from the alveoli The Nose Air normally enters the respiratory system via the external nares, which open into the nasal cavity. The vestibule is guarded by hairs that screen out large particles. The hard palate separates the oral and nasal cavities. The soft palate separates the superior nasopharynx from the rest of the pharynx. The internal nares connects the nasal cavity and nasophaarynx. Much of the respiratory epithelium is ciliated and produces mucus that traps incoming particles. Pharynx and Larynx The pharynx is a chamber shared by the digestive and respiratory systems. Inhaled air passes through the glottis en route to the lungs. The larynx surrounds and protect the glottis. The epiglottis projects into the pharynx Exhaled air passing through the glottis vibrates the true vocal cords and produces sound. The Trachea The wall of the trachea (windpipe) contains C-shaped tracheal cartilages, which protect the airway. The posterior tracheal wall can distort to permit large masses of food to pass. The Bronchi The trachea branches within the mediastinum to form the right and left primary bronchi The primary bronchi, secondary bronchi,and their branches form the bronchial tree. As the tertiary bronchi branch within the lung, the amount of cartilage in their walls decreases and the amount of smooth muscle increases. The Bronchioles Each terminal bronchiole delivers air to a single pulmonary lobule. Within the lobule, the terminal bronchiole branches into respiratory bronchioles. The Alveolar Ducts and Alveoli The respiratory bronchioles open into alveolar ducts, which end at alveolar sacs. Many alveoli are interconnected at each alveolar sac. The Respiratory Membrane The 1. respiratory membrane consists of A simple squamous alveolar epithelium 2. A capillary endothelium 3. Their fused basement membranes. Surfactant cells produce an oily secretion that keeps the alveoli from collapsing. Alveolar macrophages engulf foreign particles. The Lungs and Pleural Cavities The lungs are made up of five lobes; three in the right lung and two in the left lung. Each lung occupies a single pleural cavity lined by a pleura (serous membrane) Respiratory Physiology Respiratory physiology focuses on a series of integrated processes: Pulmonary ventilation or breathing. Gas exchange or diffusion between the alveoli and circulating blood and between the blood and interstitial fluids Gas transport between the blood and interstitial fluids. Pulmonary Ventilation A single breath, or respiratory cycle, consists of an inhalation (inspiration) and exhalation (expiration) The relationship between the pressure inside the respiratory tract and atmospheric pressure determines the direction of airflow. The diaphragm and the external intercostal muscles are involved in quiet breathing, in which exhalation is passive. Accessory muscles become active during the active inspiratory and expiratory movement of forced breathing in which exhalation is active. The vital capacity includes the tidal volume plus the expiratory reserve volume and the inspiratory reserve volume. The air left in the lungs at the end of maximum expiration is the residual volume. Gas Exchange Gas exchange involves external respiration, the diffusion of gases between the blood and alveolar air across the respiratory membrane, Internal The respiration diffusion of gases between blood and interstitial fluid across the single endothelial cells of capillary walls. Gas Transport Blood entering peripheral capillaries delivers oxygen and absorbs carbon dioxide. The transport of oxygen and carbon dioxide in the blood involves reaction that are completely reversible. Over the range of oxygen pressures normally present in the body, a small change in plasma PO2 will mean a large change in the amount of oxygen bound or released by hemoglobin Aerobic metabolism in peripheral tissues generates carbon dioxide. Roughly 7 percent of the CO2 transported in the blood is dissolved in the plasma 23% is bound as carbaminohemoglobin The rest is converted to carbonic acid which dissociates into a hydrogen ion and a bicarbonate ion. The Control of Respiration Large-scale changes in oxygen demand require the integration of cardiovascular and respiratory responses. Local Control of Respiration Arterioles leading to alveolar capillaries constrict when oxygen is low and bronchioles dilate when carbon dioxide is high The Respiratory Centers of the Brain The respiratory center include three pairs of nuclei in the reticular formation of the pons and medulla oblongata. These nuclei regulate the respiratory muscles and control the respiratory rate and the depth of breathing. The respiratory rhythmicity centers in the medulla oblongata set the basic pace for respiration. The Reflex Control of Respiration The inflation reflex prevents overexpansion of the lungs during forced breathing. The deflation reflex stimulates inspiration when the lungs are collapsing. Chemoreceptor reflexes respond to changes in the pH PO2 and PCO2 of blood and cerebrospinal fluid. Control by Higher Centers Conscious and unconscious thought processes can affect respiration by affecting the respiratory centers or the motor neurons controlling respiratory muscles. Respiratory Changes at Birth Before delivery, the fetal lungs are fluidfilled and collapsed. After the first breath, the alveoli normally remain inflated for the life of the individual. Aging and the Respiratory system The respiratory system is generally less efficient in the elderly because: Elastic tissue deteriorates, lowering the vital capacity of the lungs Movements of the chest cage are restricted by arthritic changes and decreased flexibility of costal cartilages Some degree of emphysema is normal in the elderly.