WINDSOR UNIVERSITY SCHOOL OF MEDICINE

1. WINDSOR UNIVERSITYSCHOOL OF MEDICINE RespiratoryPhysiology Dr.Vishal Surender.MD.

2. Respiratory System Introduction • As they function, our cells use oxygen and produce carbon dioxide. • The respiratory system brings the needed oxygen into and eliminates carbon dioxide from the body by working closely with the cardiovascular system. • The blood transports these gases, carrying oxygen to the tissues and carbon dioxide to the lungs.

3. An Overview of Key Steps in Respiration • Ventilation: Movement of air into and out of lungs • Gas exchange between air in lungs and blood • Transport of oxygen and carbon dioxide in the blood • Internal respiration: Gas exchange between the blood and tissues

4. Respiratory System Functions • Gas exchange: Oxygen enters blood and carbon dioxide leaves • Regulation of blood pH: Altered by changing blood carbon dioxide levels • Voice production: Movement of air past vocal folds makes sound and speech • Olfaction: Smell occurs when airborne molecules drawn into nasal cavity • Protection: Against microorganisms by preventing entry and removing them • Metabolism: Synthesize and metabolize different compounds (Nonrespiratory Function of the Lung)

5. Anatomy Review: Respiratory Structures nasal cavity pharynx nares, or nostrils. larynx trachea Rt.bronchus Lt. bronchus lung diaphragm

6. Demonstration of Pleurae and the Lungs visceral pleura parietal pleura pleural cavity mediastinum, the diaphragm, and the thoracic wall pleural fluid pleural cavity is an extremely thin, slit-like space between the pleurae, separating them by a thin layer of pleural fluid. The pleural fluid assists in breathing movements by acting as a lubricant.

7. Bronchial Tree • The lungs contain many branching airways which collectively are known as the bronchial tree. main bronchi cartilage which keeps the airways open. Lobar bronchi/secondary Smooth muscle allows airflow regulation by altering the diameter of the bronchioles. Smooth muscle segmental Bronchi/ter. bronchioles The airways from the nasal cavity through the terminal bronchioles are called the conducting zone. The air is moistened, warmed, and filtered as it flows through these passageways Terminal bronchioles respiratory zone the region of the lung where gas exchange occurs.

8. Respiratory Zone terminal bronchiole alveolar sacs. Respiratory bronchioles alveolar ducts scattered alveoli in their walls alveolar ducts alveoli Respiratory bronchioles alveoli tiny thin-walled sacs where gas exchange occurs. alveolar sacs.

9. Alveoli and Pulmonary Capillaries • The pulmonary arteries carry blood which is low in oxygen from the heart to the lungs. • • These blood vessels branch repeatedly, eventually forming dense networks of capillaries that completely surround each alveolus. • • This rich blood supply allows for the efficient exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries. • • Blood leaves the capillaries via the pulmonary veins, which transports the freshly oxygenated blood out of the lungs and back to the heart. Branch of pulmonary vein Branch of pulmonary arterY capillaries

10. Structure of an Alveolus • helps removing debris • and microbes alveolar macrophages • Gas exchange occurs • easily across this very • thin epithelium. simple squamous epithelium, or Type I Pneumocyte cell. surfactant-secreting, or Type II Pneumocyte.

11. Role of Surfactant • • The inside surface of the alveolus is lined with alveolar fluid. • • The water in the fluid creates a surface tension. • Surface tension is due to the strong attraction between water molecules at the surface of a liquid, which draws the water molecules closer together. • • this force pulls the alveolus inward and reduces its size. If an alveolus were lined with pure water, it would collapse. • • Surfactant, which is a mixture of phospholipids and lipoproteins, lowers the surface tension of the fluid by interfering with the attraction between the water molecules, preventing alveolar collapse. • • Without surfactant, alveoli would have to be completely reinflated between breaths, which would take an enormous amount of energy.

12. simple squamous epithelium of alveolar mem basement membrane of alveolous. basement membrane of Pulmr. Capr. simple squamous epithelium of pulm.capr. no interstitial fluid

13. Pulmonary Ventilation • Pulmonary ventilation, or breathing, is the exchange of air between the atmosphere and the lungs. • As air moves into(Inspiration) and out of the lungs(Expiration), it travels from regions of high air pressure to regions of low air pressure

14. Boyle's Law: Relationship Between Pressure and Volume • In order to understand ventilation, we must first look at the relationship between pressure and volume. • Pressure is caused by gas molecules striking the walls of a container. • The pressure exerted by the gas molecules is related to the volume of the container.

15. The large sphere contains the same number of gas molecules as the original sphere. Notice that in this larger volume, the gas molecules strike the wall less frequently, thus exerting less pressure. • • In the small sphere, the gas molecules strike the wall more frequently, thus exerting more pressure. Notice that the number of gas molecules has not changed.

16. These demonstrations illustrate Boyle's Law, which states that the pressure of a gas is inversely proportional to the volume of its container. Thus, if you increase the volume of a container, the pressure will decrease, and if you decrease the volume of a container, the pressure will increase

17. Quiet Inspiration: Muscle Contraction • The volume of the thoracic cavity is changed by muscle contraction and relaxation. • During quiet inspiration, the diaphragm and the external intercostal muscles contract, slightly enlarging the thoracic cavity. • As we learned from Boyle's Law, increasing the volume decreases the pressure within the thoracic cavity and the lungs. • diaphragm flattens and moves inferiorly while the external intercostal muscles elevate the rib cage and move the sternum anteriorly. These actions enlarge the thoracic cavity in all dimensions. • As we learned from Boyle's Law, increasing the volume decreases the pressure within the thoracic cavity and the lungs.

18. Quiet Expiration: Muscle Relaxation • Quiet expiration is a passive process, in which the diaphragm and the external intercostal muscles relax, and the elastic lungs and thoracic wall recoil inward. • This decreases the volume and therefore increases the pressure in the thoracic cavity. • As the diaphragm relaxes, it moves superiorly. As the external intercostal muscles relax, the rib cage and sternum return to their resting positions. These actions decrease the size of the thoracic cavity in all dimensions, and therefore increase the pressure in the thoracic cavity.

19. Muscles of Deep Inspiration and Expiration scalenes internal intercostal muscles Sternocleidomastoid external intercostal muscles Diaphragm external oblique, rectus abdominis internal oblique transversusabdominis

20. Movement of the Rib Cage during Inspiration

21. Movement of the Rib Cage during Inspiration

22. Intrapulmonary Pressure Changes • pressure changes that occur in the lungs during breathing, the lungs closely follow the movements of the thoracic wall. • The pressure within the lungs is called the intrapulmonary, or intra-alveolar, pressure. • Between breaths, it equals atmospheric pressure, which has a value of 760 millimeters of mercury at sea level. When discussing respiratory pressures, this is generally referred to as zero. • During inspiration, the volume of the thoracic cavity increases, causing intrapulmonary pressure to fall below atmospheric pressure. This is also known as a negative pressure. Since air moves from areas of high to low air pressure, air flows into the lungs. Notice that at the end of inspiration, when the intrapulmonary pressure again equals atmospheric pressure, airflow stops. • During expiration, the volume of the thoracic cavity decreases, causing the intrapulmonary pressure to rise above atmospheric pressure. Following its pressure gradient, air flows out of the lungs, until, at the end of expiration, the intrapulmonary pressure again equals atmospheric pressure.

23. Pressure Changes during Quiet Breathing

24. • Intrapleural pressure is the pressure within the pleural cavity. • Intrapleural pressure is always negative, which acts like a suction to keep the lungs inflated. Intrapleural Pressure • The negative intrapleural pressure is due to three main factors: • The surface tension of the alveolar fluid. • 2. The elasticity of the lungs. • . The elasticity of the thoracic wall thoracic wall lung Visceral pleura Parietal pleura alveoli the pleural cavity • 2. The elasticity of the lungs. • • The abundant elastic tissue in the lungs tends to recoil and pull the lung inward. As the lung moves away from the thoracic wall, the cavity becomes slightly larger. The negative pressure this creates acts like a suction to keep the lungs inflated. • • The elastic thoracic wall tends to pull away from the lung, further enlarging the pleural cavity and creating this negative pressure. • The surface tension of pleural fluid resists the actual separation of the lung and thoracic wall. • 1. The surface tension of the alveolar fluid. • • The surface tension of the alveolar fluid tends to pull each of the alveoli inward and therefore pulls the entire lung inward. Surfactant reduces this force

25. Intrapleural Pressure Changes Intrapleural pressure changes during breathing: • As the thoracic wall moves outward during inspiration, the volume of the pleural cavity increases slightly, decreasing intrapleural pressure. • As the thoracic wall recoils during expiration, the volume of the pleural cavity decreases, returning the pressure to minus 4, or 756 millimeters of mercury.

26. What do you think will happen if you cut through the Thoracic wall? A. The Lung will collapse B. Lung will expand. Effect of Pneumothorax • If you cut through the thoracic wall into its pleural cavity, air enters the pleural cavity as it moves from high pressure to low pressure. This is called a pneumothorax. • Normally, there is a difference between the intrapleural and intrapulmonary pressures, which is called transpulmonary pressure. The transpulmonary pressure creates the suction to keep the lungs inflated. In this case, when there is no pressure difference there is no suction and the lung collapses. • The lungs are completely separate from one another, each surrounded by its own pleural cavity and pleural membranes. Therefore, changes in the intrapleural pressure of one lung do not affect the other lung.

27. Events During Inspiration During inspiration, the diaphragm and external intercostal muscles contract intrapulmonary pressure volume of the thoracic cavity increases transpulmonary pressure intrapleural pressure becomes more negative increases the transpulmonary pressure, causing the lungs to expand intrapleural pressure tidal volume* lowers the intrapulmonary pressure below atmospheric pressure Air, following its pressure gradient, now flows into the lungs. *the volume of air which enters and leaves the lungs during quiet breathing

28. Events During Expiration During expiration, the diaphragm and external intercostal muscles relax volume of the thoracic cavity decreases intrapleural pressure becomes less negative deccreasesthe transpulmonary pressure, causing the lungs to recoil raisesthe intrapulmonary pressure above atmospheric pressure Air, following its pressure gradient, now flows out ofthe lungs.

29. Other Factors Affecting Ventilation • Two other important factors play roles in ventilation: 1. The resistance within the airways. 2. Lung compliance.

30. 1.Resistance Within Airways • As air flows into the lungs, the gas molecules encounter resistance when they strike the walls of the airway. Therefore the diameter of the airway affects resistance • This relationship is shown by the equation: •What do you think When the bronchiole Constricts- Will the resistance increase or decrease.? In healthy lungs, the airways typically offer little resistance, so air flows easily into and out of the lungs. As the diameter decreases, and the resistance increases. This is because more gas molecules encounter the airway wall. Airflow is inversely related to resistance.

31. Airway Radius or diameter is KEY. •  radius by 1/2  resistance by 16 FOLD

32. Factors Affecting Airway Resistance • Several factors change airway resistance by affecting the diameter of the airways. They do this by contracting or relaxing the smooth muscle in the airway walls, especially the bronchioles. • Parasympathetic neurons release the neurotransmitter acetylcholine, which constricts bronchioles. As you can see in the equation, increased airway resistance decreases airflow. • Histamine, released during allergic reactions, constricts bronchioles. This increases airway resistance and decreases airflow, making it harder to breathe. • Epinephrine, released by the adrenal medulla during exercise or stress, dilates bronchioles, thereby decreasing airway resistance. This greatly increases airflow, ensuring adequate gas exchange.

33. 2.Lung Compliance: A)Elastic Fibers • • Another important factor affecting ventilation is the ease with which the lungs expand, also known as lung compliance. It is primarily determined by two factors: • 1. The stretchability of the elastic fibers within the lungs. • 2. The surface tension within the alveoli. • • Healthy lungs have high compliance because of their abundant elastic connective tissue. • • Low lung compliance occurs in some pathological conditions, such as fibrosis, in which increasing amounts of less flexible connective tissue develop.

34. Lung Compliance: B) Surface Tension • The second factor affecting lung compliance is surface tension within the alveoli. • Some premature infants do not produce surfactant. Is their lung compliance high or low? • Without surfactant, alveoli have high surface tension, and they tend to collapse. Collapsed alveoli resist expansion, so lung compliance is low. This condition is known as respiratory distress syndrome of the newborn. Natural or synthetic surfactant may be sprayed into the infant's respiratory passageways. Surfactant lowers surface tension and increases lung compliance.

35. Pulmonary Volumes and Capacities—Spirometry A simple method for studying pulmonary ventilation is to record the volume movement of air into and out of the lungs, a process called spirometry. spirogram is a fig.. derived from spirometry indicating changes in lung volume under different conditions of breathing. For ease in describing the events of pulmonary ventilation, the air in the lungs has been subdivided in this diagram into four volumes and four capacities, which are the average for a young adult man.

36. Pulmonary Volumes 1. The tidal volume is the volume of air inspired or expired with each normal breath; it amounts to about 500 milliliters in the adult male. 2. The inspiratory reserve volume is the extra volume of air that can be inspired over and above the normal tidal volume when the person inspires with full force; it is usually equal to about 3000 milliliters. 3. The expiratory reserve volume is the maximum extra volume of air that can be expired by forceful expiration after the end of a normal tidal expiration; this normally amounts to about 1100 milliliters. 4. The residual volume is the volume of air remaining in the lungs after the most forceful expiration; this volume averages about 1200 milliliters.

37. Pulmonary Capacities In describing events in the pulmonary cycle, it is sometimes desirable to consider two or more of the volumes together. Such combinations are called pulmonary capacities. 1. The inspiratory capacity equals the tidal volume plus the inspiratory reserve volume. This is the amount of air (about 3500 milliliters) a person can breathe in, beginning at the normal expiratory level and distending the lungs to the maximum amount. 2. The functional residual capacity equals the expiratory reserve volume plus the residual volume. This is the amount of air that remains in the lungs at the end of normal expiration (about 2300 milliliters). 3. The vital capacity equals the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume. This is the maximum amount of air a person can expel from the lungs after first filling the lungs to their maximum extent and then expiring to the maximum extent (about 4600 milliliters).

38. 4. The total lung capacity is the maximum volume to which the lungs can be expanded with the greatest possible effort (about 5800 milliliters); it is equal to the vital capacity plus the residual volume. All pulmonary volumes and capacities are about 20 to 25 per cent less in women than in men, and they are greater in large and athletic people than in small and asthenic people.