Respiratory system Respiratory System Ventilation: Movement of air in/out of lungs External respiration: Gas exchange (oxygen and carbon dioxide ) between air in lungs and blood Internal respiration: Gas exchange between the blood and tissuesAnatomy of Respiratory System Upper tract: nose, pharynx and associated structures Lower tract: larynx, trachea, bronchi, lungs and the tubing within the lungsTrachea • Windpipe: from the larynx into the mediastinum • Wall composed of C-shaped rings of hyaline cartilage • Respiratory zone: respiratory bronchioles to alveoli23-4 Surrounded by fine elastic fibers-- contribute to recoil Contain open pores that connect adjacent alveoli Allow air pressure throughout the lung to be equalized Alveoli Type II (surfactant- secreting) cell Type I cell of alveolar wall Endothelial cell nucleus Macrophage Alveoli (gas-filled air spaces) Red blood cell in capillary Alveolar pores Capillary Alveolus Nucleus of type I cell23-5 The Respiratory Membrane • Three types of cells in membrane.  Type I pneumocytes. 90% of surface of alveolus. Gas exchange.  Type II pneumocytes  Produce surfactant.  Dust cells (phagocytes) Type II (surfactant- secreting) cell Type I cell of alveolar wall Endothelial cell nucleus Macrophage Alveoli (gas-filled air spaces) Red blood cell in capillary Alveolar pores Capillary Alveolus Nucleus of type I cell Respiratory Membrane Layers of respiratory membrane23-6 The Respiratory Membrane • Layers of respiratory membrane  Alveolar fluid (w/surfactant)  Alveolar epithelium  Thin interstitial space  Capillary endothelium Capillary Endothelial cell nucleus Capillary endothelium Fused basement membranes of the alveolar epithelium and the capillary endothelium Alveolar epithelium Red blood cell O2 Alveolus CO2 Nucleus of type I cellPleura Lungs • Two lungs • Thoracic cavity; w/in ribcage • Base sits on diaphragm, • Right lung: three lobes. Lobes separated by fissures • Left lung: Two lobes, and an indentation called the cardiac notch • Covered by pleural membraneMuscles of Ventilation • Inspiration: diaphragm, external intercostals, pectoralis minor, scalenes  Abdominal muscles relax  Other muscles: to help elevate ribs and costal cartilages, allow lateral rib movement • Expiration: muscles that depress the ribs and sternum: abdominal muscles and internal intercostals.  relaxation of diaphragm and external intercostals with contraction of abdominal musclesVentilation • Movement of air into and out of lungs • Air moves from area of higher pressure to area of lower pressure (down [] gradient) • Boyle’s Law: P = k/V, where P = gas pressure, V = volume, k = constant at a given temperature • Atmospheric P= Patm • If Patm > Palv (alveolar pressure) air flows into alveoli • @ insprn, thorax expands, V (alveoli size) , Palv  air flows in.Alveolar Volume Lung recoil drives alveoli to collapse resulting from • Elastic recoil: elastic fibers in the alveolar walls • Surface tension: H bonds of water molecules of fluids in lungs drives alveoli to collapse.  Surfactant: Produced by type II pneumocytes. Reduces tendency of lungs to collapse by reducing surface tension.Pleural Pressure Negative pressure, can cause alveoli to expand (inflated) • Alveoli expand when pleural pressure is low (negative) enough to overcome lung recoil • Pleural fluidMeasurement of Lung FunctionMeasurement of Lung Function Spirometer: measures volumes of air that move into and out of respiratory system. Tidal volume: amount of air inspired or expired with each breath. At rest ~500 mL Inspiratory reserve volume: amount that can be inspired forcefully after inspiration of the tidal volume. At rest 3000 mL Expiratory reserve volume: amount that can be forcefully expired after expiration of the tidal volume At rest 100 mL Residual volume: volume still remaining in respiratory passages and lungs after most forceful expiration. At rest 1200 mLPhysical Principles of Gas Exchange Diffusion of gases thru respiratory membrane depends on 4 factors Surface area. Diffusion coefficient of gas --measure of how easily a gas diffuses through a liquid or tissue. CO2> O2 > N2 Membrane thickness. The thicker, the lower the diffusion rate Partial pressure differences. Gas moves from area of higher partial pressure to area of lower partial pressure.Membrane thickness Cardiac pulmonary edema (aka congestive heart failure) — occurs when left ventricle isn't able to pump out enough of the blood it receives from your lungs.  pressure increases inside the left atrium and then in the veins and capillaries in your lungs fluid pushed through the capillary walls into the air sacs (edema)  gasping, wheezing, decreased gas exchangeGas Exchange Oxygen • Moves from alveoli into blood. Blood is almost completely saturated with oxygen when it leaves the pulmonary capillary • PO2 in blood decreases because of mixing with deoxygnt’d blood • Oxygen moves from tissue capillaries into the tissues Carbon dioxide – Moves from tissues into tissue capillaries – Moves from pulmonary capillaries into alveoliTest yourself Gas exchange at pulmonary capillaries is a. Internal respiration b. External respiration c. ventilation.Respiratory gas exchange is a two-way process: CO2 diffuses out of the body as O2 diffuses in. The concentration gradient of CO2 from air-breathers to the environment is always large.Oxygen is transported by hemoglobin (Hb; 98.5%) and is in plasma (1.5%) hemoglobin— a protein with four polypeptide subunits--tetramer. Each polypeptide surrounds a heme group that can bind a molecule of O2. One molecule of hemoglobin can bind up to four molecules of O2. Heme group a Globin chains b Globin chainsHemoglobin will pick up or release O2 depending on the PO2 of the environment. If PO2 is high, as in the lungs, hemoglobin will pick up its maximum of four O2 molecules. As blood circulates through tissues with lower PO2, hemoglobin will release some O2.The relationship between PO2 and the O2 binding is S-shaped. Oxyhemoglobin dissociation curve Low PO2—one subunit binds O2. Positive cooperativity—one subunit binds and changes shape, making it easier for the next one to bind— the affinity for O2 is increased. When three subunits are bound, a larger increase in PO2 is needed.• Effect of pH on oxygen-hemoglobin dissociation curve: as pH of blood declines, amount of