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PSK4U The Respiratory System Composed of structures that allow: Passage of air from outside the body to the lungs Gas exchange to occur The Respiratory System Three main functions: 1. Supply O2 to the blood 2. Remove CO2 from the blood 3. Regulate blood pH (acid-base balance) The Respiratory System External Respiration Internal Respiration Cellular Respiration Divided into two zones: Conductive zone Respiratory zone Respiratory System Structure Nasal cavity Pharynx Larynx Right and left primary bronchi Secondary bronchi Tertiary bronchioles Pulmonary venule Pulmonary arteriole Mouth Epiglottis Trachea Smooth muscle Terminal bronchiole Respiratory bronchiole Alveolar sacs Respiratory System Structure The Conductive Zone The conductive zone is composed of structures that transport air to the lungs: Mouth and nose Larynx Trachea Primary and secondary bronchi Tertiary and terminal bronchioles Filters, warms and humidifies air taken in with each breath Filtration by nasal hairs and mucus membranes 37oC and saturated The Respiratory Zone The respiratory zone is composed of structures involved with the exchange of gases between inspired air and blood: Respiratory bronchioles Alveolar ducts The Respiratory Zone Alveolar sacs (alveoli) Grape like structures Large surface area for diffusion of gas into and out blood Surrounded by capillaries and elastic fibers Walls are only one cell thick Mechanisms of Breathing Inspiration: Contraction of diaphragm Stimulation from brain Thoracic cavity expands Air pressure in thoracic cavity is lower than air pressure outside the body •Air rushes in to lungs to restore balance •Lung pressure = atmospheric pressure •Active process •Require respiratory muscles See diagram on page 250 Mechanisms of Breathing Expiration: Alveolar sacs recoil as diaphragm relaxes Air is expelled Thoracic cavity reduces Lung pressure>atmospheric pressure Passive Quiet breathing Alveolar sacs recoil passively Active Forced Breathing Muscles of the thoracic and abdominal cavity contract actively Decreasing the volume of the thoracic cavity and increase pressure in lungs Ventilation Ventilation (VE) is the volume of air moved by the lungs in 1 minute Combination of inspiration and expiration Influenced by two factors: 1. Tidal volume (V T) Volume of air in each breath At rest 0.5L/breath Exercise 3-4L/breath Ventilation 2. Respiratory frequency (f) Number of breaths taken per minute At rest 12 breaths/minute Exercise 30-40 breaths per minute VE = V T x f Respiratory Control Centers Breathing is result of contraction and relaxation of inspiratory and expiratory muscles Stimulate by CNS-special areas of brain and feedback loops Associated with overall need of O2, metabolic processes, muscle activity and CO2 production Respiratory Control Centers Respiratory control centres found within brain stem (not under conscious control) Medulla oblongata Inspiratory centre Sends messages to respiratory muscles, diaphragm and external intercostals-rhythmic pattern 15-20 breaths per minute at rest During exercise the rate is increases do to feedback mechanism Expiratory centre Two main functions: Ensure the inspiratory muscles never completely relax Stimulate forceful expiration when required (during exercise) Respiratory Control Centres Pons Pneumotaxic and apneustic centres Ensure smooth transition of inhalation to exhalation Fine-tune the breathing pattern Other areas of brain can influence ventilation Stimulation of skeletal muscle also leads to stimulation of breathing control centres Specialized sensory systems in order to provide feedback to control centres For example monitor blood pH level Lung Volumes Lung Volumes are divided into two categories: Static lung volumes Determined by the actual structure of the lung Not influenced by breathing or flow of air Dynamic lung volumes Dependent on volume as well as movement/flow of air Static Lung Volume Three important static lung volumes: 1. Total lung capacity (TLC) Maximum volume of air that lungs can hold Sum of vital capacity and residual volume Static Lung Volume Three important static lung volumes: 2. Vital capacity (VC) Maximum amount of air that can be exhaled following a maximal inhalation Measured using a Forced Vital Capacity (FVC) Static Lung Volume Three important static lung volumes: 3. Residual volume (RV) Air that remains in lungs following a maximal exhalation TLC = VC + RV Dynamic Lung Volume Tests that involve the measurement of the movement of air by breathing Forced Expiratory Volume (FEV) Over 1 or 3 seconds of FVC Dynamic Lung Volume Tests that involve the measurement of the movement of air by breathing Maximal Voluntary Ventilation (MVV) Amount of air an individual can move over 15 seconds Inhale and exhale Multiply value to give value for 1 minute Gas Exchange Diffusion mediates gas exchange Diffusion is the movement of a gas, liquid, or solid from a region of high concentration to low concentration Can only occur if a difference in concentration exists Concentration gradient Gas Exchange Concentration for specific gases involved in respiration are measured using partial pressure Fractional Concentrations and Partial Pressures of Main Gasses Found in Air Gas Exchange Diffusion pathway Area through which gases move from the lungs into the blood; from the blood into the tissue, and back Rates of diffusion depend on: Size of concentration gradient Increase gradient, increase rate Governed by Henry’s Law Thickness of barrier between two areas Gas will dissolve into a liquid until equilibrium has been reached Decrease thickness, increase rate Alveoli and capillary is only 2 cells thick Surface area between two areas Increase surface area, increase rate Alveoli have large surface area, folded on top of another Oxygen Transport Oxygen (O2) transport within the blood achieved in two ways: 1. O2 dissolved within the plasma Represents 2% of O2 found in the blood 0.05 mL O2/100 mL of blood Oxygen Transport Oxygen (O2) transport within the blood achieved in two ways: 2. Binds to Hemoglobin 1.34 mL of O2 for each gram of Hgb 16g Hgb/100 mL of blood 21.4 mL O2/100 mL blood Oxygen Transport Amount of O2 that can be carried by Hgb is termed percent saturation of hemoglobin Sb%O Main factor that determine % saturation is PO2 within the blood Carbon Dioxide Transport Carbon dioxide (CO2) Moved from tissues back to lungs Moved into alveoli and then exhaled and removed from body Transport achieved in three ways: 1. Trace amounts of CO2 dissolved within the plasma (5- 10%) Carbon Dioxide Transport 2. Binds to hemoglobin (20%)-binds to globin rather than heme Forming carbaminohemoglobin when [O2] is low, depends on PCO2 Once it arrives at the lungs the high [O2] stimulate the exchange CO2 then diffuses into alveoli and is exhaled Carbon Dioxide Transport Transport achieved in three ways: 3. Bicarbonate system (70-75%) Chemical reaction with H2O in RBCs forming carbonic acid (H2CO3) Carbonic anhydrase is enzyme responsible H2CO3 H+ + HCO3- where proton is carried by Hgb and bicarbonate is in the plasma At lungs the process is reversed because the PCO2 reduced H+ + HCO3H2CO3 CO2 + H2O CO2 then diffuses from blood to alveoli to be exhaled Carbon Dioxide Transport Transport achieved in three ways: 3. Bicarbonate system (70-75%) At lungs the process is reversed because the PCO2 reduced H+ + HCO3H2CO3 CO2 + H2O CO2 then diffuses from blood to alveoli to be exhaled Ventilation and Control of Blood pH Measure of how acidic or basic the blood is Usually maintain at 7.4 Lactic acid release during exercise will result in a decline in blood pH Due to increase in H+ Ventilation and Control of Blood pH Ventilation helps regulate the amount of H+ ions in the blood Bicarbonate system Increase in ventilation, expel extra amounts of CO2 Cause H+ to combine with HCO3 Lowers the H+ therefore increases the pH level back to normal
