Respiratory Function PDF

RESPIRATORY FUNCTION  OBJECTIVE ✦ By the end of this section, you will be able to: The function of the Respiratory system Explain the muscular requirement for ventilation Understand the elasticity of the lungs Describe how breathing is increased during exercise Explain dyna...

RESPIRATORY FUNCTION  OBJECTIVE ✦ By the end of this section, you will be able to: The function of the Respiratory system Explain the muscular requirement for ventilation Understand the elasticity of the lungs Describe how breathing is increased during exercise Explain dynamic compression can narrow the airways and limit airflow. INTRODUCTION Respiratory function The primary function of the respiratory system is the exchange of gases 02 and CO2 between the blood and environment Structurally divided into − Upper airways: Nares, Nasal passage, Larynx, Trachea − Lower airways: Bronchi, Bronchioles − Trachea and Bronchi contain cartilages that keeps them from collapsing, and contain goblet cells and bronchial glands whose secretions contribute to the mucous lining − Cartilage, goblet cells and bronchial glands are absent from the bronchioles. Instead Club cells (Clara cells) line the epithelium and secrete Functionally divided into − Conducting airways/ Zone: Nares, Nasal passage, Larynx, Trachea, Bronchi, Bronchioles. Function is to conduct air from environment to respiratory airways, filter the air, humidify and warm the air. − Respiratory airways/ Zone: Terminal bronchiole, Respiratory bronchiole, Alveolar ducts, Alveolar sac, Alveoli. Are responsible for gas exchanget  Respiratory function The conducting airways, from the nares to the bronchioles, serve to conduct air from the environment to the gas exchange regions of the lungs, as well as condition it by filtering out particles, warming it to body temperature, and humidifying it to saturation with water vapor. At the periphery of the lungs, the terminal bronchioles branch into respiratory bronchioles, then alveolar ducts, alveolar sacs, and finally alveoli. These peripheral structures are the site of gas exchange as oxygen (O2) moves from the alveolar air to the pulmonary capillaries and carbon dioxide (CO2) moves in the reverse direction.  INSPIRATION VS EXPIRATION Inspiration/ Inhalation: Is a product of respiratory muscle contraction resulting in expansion of the thorax and the lungs within it. This creates a negative (sub-atmospheric) pressure which pulls air from the environment into the lungs. It is an active process i.e requires muscular efforts Expiration/ Exhalation: Elastic energy stored by the stretched lungs and thorax drives exhalation. It is a passive process in all resting animals with horses being the only exception. During exercise or in some diseased states, exhalation becomes an active process  RESPIRATORY MUSCLES I Muscle Action Diaphragm Inspiratory muscle Pulls thorax caudally External intercostal Inspiratory muscle Pulls ribs rostrally and outward Neck muscles (SCM) Inspiratory muscle Pulls sternum rostrally Internal intercostal Expiratory muscle Pulls ribs caudally and ventrally Abdominal muscles Expiratory muscle Increase intra-abdomnal (Rectus abdominus, pressure which pushes Internal abdominal oblique, diaphragm upward, External abdominal reducing the size of the oblique, Transversus thoracic cavity abdominus)  Inhalation occurs when the respiratory muscles contract to expand the thorax, stretch the lung, and create a subatmospheric pressure within the alveoli, which causes air to enter the respiratory system as it moves down the pressure gradient During exhalation, the elastic energy stored in the stretched lungs and thorax causes them to decrease in volume, leading to an increase in alveolar pressure (above atmospheric pressure) that drives air out of the respiratory system. In most resting mammals, exhalation is passive in that it does not require muscular effort. Horses are an exception because they have an active phase to exhalation, even at rest. In all species during exercise or in the presence of some respiratory diseases, exhalation has an active phase during which it is assisted by muscle contraction.  During quiet inspiration, diaphragm is the predominant muscle used. During exercise, diaphragm, external internal muscles and neck muscles are responsible for inspiration. External intercostal muscles and abdominal muscles are responsible for expiration In cursorial (running) mammals, ventilation and gats are synchronized when at canter and gallop. Inhalation occurs as the forelimbs are extended and exhalation occurs when the forelimbs are flexed and in contact with the ground. Expansion of the thorax is brought about mostly by elongation of the trunk as the spine extends  COMPLIANCE AND ELASTICTY Compliance C : A measure of the distensibility of an elastic structure Mathematically, C = Change in lung volume Change in transpulmonary pressure Healthy lungs are very compliant as little change in transpulmonary pressure causes a large change in lung volume Elasticity E: A measure of the ability of a stretched structure to return to its original shape. Mathematically, E = Change in transpulmonary pressure Change in lung volume Elasticity is the reciprocal of compliance  PRESSURE-VOLUME CURVE Graph representing the relationship between the lung volume and its distending pressures (Elastance and compliance) at normal resting breathing The steel of the curve is fairly steep in the middle (indicating the small changes in the tranpulmonary pressure will result in large change in lung volume), but at extreme volumes (RV, TLC), the slope is less steep (indicating that a larger transpulmonary pressure is required to cause a change in lung volume)  Sulfactant Lipids composed mostly of dipalmitoyl phosphatidylcholine and proteins, lines the inner surface of alveoli. Its function is to prevent surface tension on the surface of the alveoli that will otherwise cause alveoli to collapse. Sulfactant is produced late in the neonatal period by type 2 pneumocytes within the alveoli epithelium. After birth, deep inspiration aids release of sulfactant. Sulfactant has a hydrophobic portion and a hydrophilic portion. This enables it to bind to the fluid that lines the alveolar and he breaks up the cohesive forces that is present.  Sulfactant Premature newborns tend to have inadequate sulfactant to prevent lungs from collapsing (atelectasis) and this results in respiratory distress. Synthetic sulfactant is needed to treat such newborns. Sulfactant also play a role in defense against pathogens by trapping pathogens and aiding in their ingestion by macrophages. It also aids in mucociliary clearance of pathogens  AIRWAY RESISTANCE The force that impedes airflow along the respiratory passages Mathematically, R = Pressure drop/Flow Pressure drop= Pressure in atmosphere – Pressure in alveolar Resistance is determined primarily by the radius and cross sectional area of the airway R …. 1/r^4 The upper airway is responsible for majority of all the resistance, while the periphery of the lung contributes the least. During exercise, this resistance is decreased by dilation of nares, vasoconstriction of nasal vascular tissue, decreased mucosal thickness and breathing through mouth  VELOCITY OF AIRFLOW Distance traveled per unit time by air within the respiratory system. Is a function of the volume of air and the cross sectional area. Velocity =k Volume Cross sectional area The cross sectional area of the upper airways is low, the velocity is high and it produces a turbulent flow that can be heard through a stethoscope The cross sectional area of the lower airways is higher, the velocity is low and the flow laminar, so it cannot be heard through a stethoscope  Bronchoconstriction The wall of the airways from the trachea to the alveolar duct contains smooth muscles. Contraction of these smooth muscles under the influence of Parasympathetic nervous system via acetylcholine activity on muscarinic receptors on the smooth muscles, alters the cross sectional area of the peripheral airways. Is termed “bronchoconstriction” Bronchoconstriction can be triggered by; inhalation of irritant materials (dust), or release of inflammatory mediators (histamine, leukotrienes) Relaxation of smooth muscles can be brought about by the activity of Epinephrine and Norepinephrine on β2-adrenergic receptors present on the smooth muscles RESPI AND METAB The respiratory system provides O2 for body’s metabolism, this rids the body of CO2 which is the byproduct of metabolism The rate of O2 consumption and CO2 production is dependent on the metabolism rate of the body, which in turn is dependent on the animals level of activity and physical condition. The relationship between body weight and basal metabolism is defined by: kg ^0.75 Smaller animals consume more O2 per body weight than larger animals. Reason being that smaller animals have a larger surface area, hence have greater surface area for heat loss which they need to compensate for by increasing their basal metabolism  RESPI and METAB Maximum O2 consumption VO2max: Is directly proportional to the total mass of mitochondria within the animals skeletal muscles Athletic species (dogs, horse) possess a higher mitochondria density, hence a greater VO2max when compared o non athletic species of similar body size Exercise increases body metabolism. A racing horse has 30 fold increase in body metabolism when compared to its resting state LUNG VOLUMES The ease with which the normal lung expands and contracts with each breath is due to its extremely compliant nature. This allows the dramatic changes in lung volume that occur during the respiratory cycle. The volumes of air within the lung range from total lung capacity (TLC), which is the amount of air the lungs can hold following a maximum inspiration, to residual volume (RV), which is the volume of air that remains in the lungs after maximal, forced expiration LUNG VOLUMES Tidal volume TV: Volume of air moved in or out of the lungs during quiet resting breathing Residual volume RV: Volume of air that remains in the lungs after forced expiration Total lung capacity TLC: Amount of air the lungs can hold after maximum inspiration. Vital capacity VC: Maximum volume of air that can be moved. Functional residual capacity FRC: Volume of air that remains in the lungs at the end of quiet resting exhalation DEAD SPACE VENTILATION VD Dead space: Inhaled air that does not partake in gas exchange Anatomic dead space: “Conducting airway” From nares to bronchioles. Areas of airways not equipped to partake in gas exchange Alveolar dead space: Alveolar that is ventilated, but not perfused with blood. No gas exchange occurs Physiologic dead space: Sum of Anatomic dead space and Physiologic dead space  Cattle, pigs, and mules subjected to heat stress also increase respiratory rate and dead space ventilation in an attempt to lose heat. By the same principle, animals undergoing cold stress alter their pattern of ventilation to reduce dead space ventilation by increasing VT and decreasing f in an attempt to retain heat.  ALVEOLAR VENTILATION Alveolar ventilation VA is the volume of air that reaches perfused alveoli VA is the most important respiratory parameter. Is tightly regulated by the body to match its O2 uptake and CO2 elimination. Minute ventilation: total volume of air breathed per minute. Is a product of the Tidal volume (VT) and breathing frequency (f) When the metabolic demand for O2 increases, the body increases minute ventilation by an increase in Tidal volume, or breathing frequency, or both Mathematically, VE = VT X f VE= VA + VD ROLE OF DEAD SPACE VENTILATION IN THERMOREGULATION Air is entering the respiratory system is cooler than body temperature and less saturated. Within the conducting airways, heat and water vapor diffuses from the mucosa surface of the conducting system. When the air is exhaled, heat and vapor escapes from the body. When animals are heat-stressed, they pant (increased breathing frequency f) which increases ventilation of the anatomic dead space, hence increases loss of heat and water vapor When animals are cold-stressed, the reverse occurs. Breathing frequency decreases Control of respiration Control of respiration  CLINICAL CORRELATION History A 3-year-old English Setter in respiratory distress is presented at a teaching hospital. The owner first noticed reluctance of the dog to exercise 3 weeks ago. Since then, the animal has had progressive difficulty in breathing. It appears hungry but cannot eat because it “gets out of breath.” Clinical Examination Inspection reveals a thin dog breathing through its mouth. The respiratory rate is elevated, but the dog seems to be moving little air despite strong inspiratory efforts during which the intercostal spaces sink. Exhalation presents no difficulty; the ribs collapse rapidly and there is no accentuated abdominal effort. Examination reveals slightly blue-colored mucous membranes. Lung sounds are not remarkable. All other systems are normal. Radiographs of the thorax show diffuse miliary density (whiteness) over the parts of the lung that are normally air-filled. The bronchi are normal. An elevated change in pleural pressure during breathing, normal R, and decreased lung compliance are the key findings on lung function testing. VT is greatly reduced.  CLINICAL CORRELATION Treatment This dog has pulmonary fibrosis, which is a diffuse disease of the gas exchange area of the lung. It is characterized by decreased compliance, which increases the work of breathing. The blue tinge to the mucous membranes indicates increased desaturated hemoglobin as a result of impaired O2 exchange in the diseased lung. A biopsy reveals diffuse fibrosis around mineral particles in the walls of the alveoli. The prognosis for the dog is poor.  MCQ Which of the following is true? a. O2 consumption per kilogram body weight is greater in a 50-g mammal than in a 50-kg mammal. b. Maximal O2 consumption in mammals is directly related to the volume of mitochondria in the skeletal muscles. c. O2 consumption increases when metabolic rate increases. d. O2 consumption can increase up to thirtyfold during intense exercise. e. All of the above are true.  MCQ Which of the following lists includes only structures that compose the anatomic dead space? a. Respiratory bronchioles, alveoli, trachea, nasal cavity b. Pharynx, bronchi, alveolar ducts, larynx c. Capillaries, respiratory bronchioles, trachea, bronchi d. Pharynx, nasal cavity, trachea, bronchi e. Capillaries, respiratory bronchioles, alveolar ducts, alveoli Anatomic dead space refers to the parts of the respiratory system where air is conducted but no gas exchange occurs.  MCQ Pulmonary surfactant: a. Can be deficient in premature newborns. b. Is produced in type II alveolar epithelial cells. c. Is in part composed of dipalmitoyl phosphatidylcholine. d. Decreases surface tension of the fluid lining the alveoli. e. All the above.  MCQ The most powerful control of alveolar ventilation in a healthy resting animal is: a. pH of extracellular fluid b. Pco2 of extracellular fluid c. pH of cerebrospinal fluid d. Pco2 of cerebrospinal fluid Carbonic acid changes in Pco2 directly affect the pH of the CSF, which is detected by central chemoreceptors in the brain. These chemoreceptors then regulate the respiratory rate to maintain homeostasis. medulla carbonic anhydrase H2O + CO2 HCO3  MCQ The major part of airway resistance is attributable to the: a. nasal passages b. Alveoli c. trachea d. bronchi e. bronchioles they have a relatively small cross-sectional area compared to other parts of the respiratory system, and they are lined with structures like turbinates that increase resistance to airflow.  MCQ Pressure within the pleural cavity is negative: a. only during inspiration b. during coughing c. at all times during eupnea d. during vomiting e. only during expiration During eupnea, which is normal, quiet breathing, the pressure within the pleural cavity remains negative. This negative pressure is essential for keeping the lungs inflated and allowing for the passive flow of air into the lungs during inspiration. It helps maintain the lungs' expansion against the chest wall.  MCQ Elastic recoil of lung tissue is primarily attributable to: a. connective tissues b. pneumocytes c. bronchiolar walls d. surface tension e. blood vessels This surface tension is created by the thin layer of fluid that coats the alveoli and is reduced by pulmonary surfactant, which helps prevent the alveoli from collapsing