Bio 202 Anatomy & Physiology II Respiration PDF

ARIZONA STATE UNIVERSITY Respiration College of Integrative Sciences & Arts Bio 202 A natomy & Physiology II Tonya A. Penkrot, Ph.D.  Respiratory System Respiration involves four processes...

ARIZONA STATE UNIVERSITY Respiration College of Integrative Sciences & Arts Bio 202 A natomy & Physiology II Tonya A. Penkrot, Ph.D.  Respiratory System Respiration involves four processes 1. Pulmonary ventilation (breathing): movement of air into and out of lungs 2. External respiration: exchange Respiratory of O2 and CO2 between lungs system and blood 3. Transport of O2 and CO2 in blood 4. Internal respiration: exchange of O2 and CO2 between systemic blood vessels and tissues Circulatory system Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.1 The major respiratory organs in relation to surrounding structures. Nasal cavity Oral cavity Nostril Pharynx Larynx Trachea Left main Carina of (primary) trachea bronchus Right main Left lung (primary) bronchus Diaphragm Right lung Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.4b The pharynx, larynx, and upper trachea. Posterior nasal aperture Nasopharynx Pharyngeal tonsil Opening of pharyngotympanic tube Oropharynx Hard palate Palatine tonsil Soft palate Isthmus of the fauces Tongue Lingual tonsil Laryngopharynx Hyoid bone Larynx Epiglottis Vestibular fold Thyroid cartilage Esophagus Vocal fold Cricoid cartilage Trachea Thyroid gland (b) Structures of the pharynx and larynx Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  22.2 Lower Respiratory System Lower respiratory system consists of: – Larynx, trachea, bronchi, and lungs Broken into two zones – Respiratory zone: site of gas exchange Consists of microscopic structures such as respiratory bronchioles, alveolar ducts, and alveoli – Conducting zone: conduits that tranport gas to and from gas exchange sites Includes all other respiratory structures Cleanses, warms, and humidifies air Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.5b The larynx. Epiglottis Body of hyoid bone Thyrohyoid membrane Thyroid cartilage Laryngeal prominence (Adam’s apple) Cricothyroid ligament Cricoid cartilage Cricotracheal ligament Tracheal cartilages Anterior view Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.5d The larynx. Epiglottis Thyrohyoid Body of hyoid bone membrane Thyrohyoid membrane Cuneiform cartilage Fatty pad Corniculate cartilage Vestibular fold Arytenoid cartilage (false vocal cord) Arytenoid muscle Thyroid cartilage Cricoid cartilage Vocal fold (true vocal cord) Cricothyroid ligament Tracheal cartilages Cricotracheal ligament Sagittal section (anterior on the right) Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.7a Tissue composition of the tracheal wall. Posterior Mucosa Esophagus Submucosa Trachealis Lumen of Seromucous gland trachea in submucosa Hyaline cartilage Adventitia Anterior Cross section of the trachea and esophagus Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.7b GobletTissue cell composition of the tracheal wall. Mucosa Pseudostratified ciliated columnar epithelium Lamina propria (connective tissue) Submucosa Seromucous gland in submucosa Hyaline cartilage Photomicrograph of the tracheal wall (320 ) Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.8 Conducting zone passages. Trachea Superior lobe of left lung Left main (primary) bronchus Superior lobe of right lung Lobar (secondary) bronchus Segmental Middle lobe (tertiary) of right lung bronchus Inferior lobe Inferior lobe of right lung of left lung Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.9a Respiratory zone structures. Alveoli Alveolar duct Respiratory Alveolar duct bronchioles Terminal Alveolar bronchiole sac Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.9b Respiratory zone structures. Respiratory bronchiole Alveolar Alveolar duct pores Alveoli Alveolar sac Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.10a Alveoli and the respiratory membrane. Terminal bronchiole Respiratory bronchiole Smooth muscle Elastic fibers Alveolus Capillaries Diagrammatic view of capillary-alveoli relationships Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.10b Alveoli and the respiratory membrane. Scanning electron micrograph of pulmonary capillary casts (300) Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.10c Alveoli and the respiratory membrane. Red blood cell Type I alveolar cell Alveolar pores Capillary O2 Capillary CO2 Macrophage Alveolus Endothelial cell nucleus Alveolus Alveolar epithelium Respiratory Fused basement membranes membrane of alveolar epithelium and capillary endothelium Capillary endothelium Alveoli (gas-filled Red blood cell Type II alveolar cell Type I air spaces) in capillary (secretes surfactant) alveolar cell Detailed anatomy of the respiratory membrane Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.11c Anatomical relationships of organs in the thoracic cavity. Esophagus Vertebra Posterior (in mediastinum) Root of lung at hilum Right lung Left main bronchus Left pulmonary artery Parietal pleura Left pulmonary vein Visceral pleura Left lung Pleural cavity Thoracic wall Pulmonary trunk Pericardial membranes Heart (in mediastinum) Anterior mediastinum Sternum Anterior Transverse section through the thorax, viewed from above. Lungs, pleural membranes, and major organs in the mediastinum are shown. Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Atmospheric pressure (Patm) 0 mm Hg (760 mm Hg) Parietal pleura Thoracic Visceral pleura wall Pleural cavity Transpulmonary pressure 4 mm Hg (the difference between 0 mm Hg and 4 mm Hg) 4 0 Intrapleural pressure (Pip) 4 mm Hg (756 mm Hg) Always Lung negative!! Diaphragm Intrapulmonary pressure (Ppul) 0 mm Hg (760 mm Hg) Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Punctured parietal pleura Ruptured visceral pleura (e.g., knife wound) (often spontaneous) Figure 22.14 Pneumothorax. Parietal pleura Visceral pleura Pleural cavity (Intrapleural pressure  4 mm Hg) 0 0 0 0 4 Intrapulmonary 4 4 pressure (0 mm Hg) 4 Atmospheric pressure 0 mm Hg (760 mm Hg) Pneumothorax (air in pleural cavity): Intrapleural intrapleural pressure pressure becomes equal to 0 (4 mm Hg) atmospheric pressure 0 0 Intrapulmonary Collapsed lung 4 pressure (0 mm Hg) (atelectasis) Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Pulmonary Ventilation (cont.) Boyle’s law: relationship between pressure and volume of a gas – Gases always fill the container they are in If amount of gas is the same and container size is reduced, pressure will increase – So pressure (P) varies inversely with volume (V) Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Slide 11 Changes in anterior-posterior and Changes in lateral dimensions Sequence of events (superior view) superior-inferior dimensions 1 Inspiratory muscles contract (diaphragm descends; rib cage rises). Ribs are elevated and 2 Thoracic cavity volume sternum flares increases. as external intercostals contract. Inspiration 3 Lungs are stretched; intrapulmonary volume increases. External intercostals contract. 4 Intrapulmonary pressure drops (to 1 mm Hg). 5 Air (gases) flows into lungs Diaphragm moves down its pressure gradient until inferiorly during intrapulmonary pressure is 0 contraction. (equal to atmospheric pressure). 1 Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages). Ribs and sternum are 2 Thoracic cavity volume depressed as decreases. external intercostals Expiration relax. 3 Elastic lungs recoil passively; intrapulmonary External volume decreases. intercostals relax. 4 Intrapulmonary pressure rises (to 1 mm Hg). Diaphragm 5 Air (gases) flows out of lungs moves down its pressure gradient superiorly until intrapulmonary pressure is 0. as it relaxes. Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.16 Changes in intrapulmonary and intrapleural pressures during inspiration and expiration. atmospheric pressure (mm Hg) Inspiration Expiration Intrapulmonary Intrapulmonary pressure. Pressure inside 2 pressure lung decreases as lung volume increases during 0 Pressure relative to inspiration; pressure increases during expiration. Trans- 2 pulmonary Intrapleural pressure. pressure 4 Pleural cavity pressure becomes more negative as chest wall expands during 6 Intrapleural inspiration. Returns to initial pressure value as chest wall recoils. 8 Volume of breath. During Volume of breath Volume (L) each breath, the pressure 0.5 gradients move 0.5 liter of air into and out of the lungs. 0 5 seconds elapsed Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Physical Factors Influencing Pulmonary Ventilation Three physical factors influence the ease of air passage and the amount of energy required for ventilation: – Airway resistance – Alveolar surface tension – Lung compliance Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.17 Conducting Respiratory Resistance in zone zone respiratory Medium-sized passageways. bronchi Resistance Terminal bronchioles 1 5 10 15 20 23 Airway generation (stage of branching) Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.18a Respiratory volumes and capacities. 6000 5000 Inspiratory reserve volume Inspiratory 3100 ml capacity Milliliters (ml) 4000 3600 ml Vital Total lung capacity capacity 4800 ml 6000 ml 3000 Tidal volume 500 ml 2000 Expiratory reserve volume Functional 1200 ml residual 1000 capacity Residual volume 2400 ml 1200 ml 0 Spirographic record for a male Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.18b Respiratory volumes and capacities. Adult male Adult female Measurement average value average value Description 500 ml 500 ml Amount of air inhaled or exhaled with each breath under resting Tidal volume (TV) conditions Inspiratory reserve Amount of air that can be forcefully inhaled after a normal tidal volume (IRV) 3100 ml 1900 ml volume inspiration Respiratory volumes Expiratory reserve 1200 ml 700 ml Amount of air that can be forcefully exhaled after a normal tidal volume (ERV) volume expiration Residual volume (RV) 1200 ml 1100 ml Amount of air remaining in the lungs after a forced expiration Maximum amount of air contained in lungs after a maximum Total lung capacity (TLC) 6000 ml 4200 ml inspiratory effort: TLC  TV  IRV  ERV  RV Maximum amount of air that can be expired after a maximum Vital capacity (VC) 4800 ml 3100 ml inspiratory effort: VC  TV  IRV  ERV Respiratory capacities Maximum amount of air that can be inspired after a normal tidal Inspiratory capacity (IC) 3600 ml 2400 ml volume expiration: IC  TV  IRV Functional residual Volume of air remaining in the lungs after a normal tidal volume 2400 ml 1800 ml capacity (FRC) expiration: FRC  ERV  RV Summary of respiratory volumes and capacities for males and females Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Dead Space Anatomical dead space: does not contribute to gas exchange – Consists of air that remains in passageways ~150 ml out of 500 ml TV Alveolar dead space: space occupied by nonfunctional alveoli – Can be due to collapse or obstruction Total dead space: sum of anatomical and alveolar dead space Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Alveolar Ventilation Minute ventilation: total amount of gas that flows into or out of respiratory tract in 1 minute – Normal at rest = ~ 6 L/min – Normal with exercise = up to 200 L/min – Only rough estimate of respiratory efficiency Alveolar ventilation rate (AVR): flow of gases into and out of alveoli during a particular time – Better indicator of effective ventilation Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Basic Properties of Gases Dalton’s law of partial pressures – Total pressure exerted by mixture of gases is equal to sum of pressures exerted by each gas – Partial pressure Pressure exerted by each gas in mixture Directly proportional to its percentage in mixture Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Basic Properties of Gases (cont.) Total atmospheric pressure equals 760 mm Hg Nitrogen makes up ~78.6% of air; therefore, partial pressure of nitrogen, PN2, can be calculated: 0.786  760 mm Hg  597 mm Hg due to N2 Oxygen makes up 20.9% of air, so P O2 equals: 0.209  760 mm Hg  159 mm Hg Air also contains 0.04% CO2, 0.5% water vapor, and insignificant amounts of other gases At high altitudes, partial pressures declines, but at lower altitudes (under water), partial pressures increase significantly Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Basic Properties of Gases (cont.) Henry’s law – For gas mixtures in contact with liquids: Each gas will dissolve in the liquid in proportion to its partial pressure At equilibrium, partial pressures in the two phases will be equal Amount of each gas that will dissolve depends on: – Solubility: CO2 is 20 more soluble in water than O2, and little N2 will dissolve – Temperature: as temperature of liquid rises, solubility decreases – Example of Henry’s law: hyperbaric chambers Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc. Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  External Respiration External respiration (pulmonary gas exchange) involves the exchange of O2 and CO2 across respiratory membranes Exchange is influenced by: – Partial pressure gradients and gas solubilities – Thickness and surface area of respiratory membrane – Ventilation-perfusion coupling: matching of alveolar ventilation with pulmomary blood perfusion Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  External Respiration (cont.) Partial pressure gradient for CO 2 is less steep – Venous blood PCO2 = 45 mm Hg – Alveolar PCO2 = 40 mm Hg Though gradient is not as steep, CO 2 still diffuses in equal amounts with oxygen – Reason is that CO2 is 20 more soluble in plasma and alveolar fluid than oxygen Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.20 Oxygenation of blood in the pulmonary capillaries at rest. 150 PO2 (mm Hg) 100 PO2 104 mm Hg 50 40 0 0 0.25 0.50 0.75 Time in the pulmonary capillary (s) Start of End of capillary capillary Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.21 Ventilation-perfusion coupling. Ventilation less than perfusion Ventilation greater than perfusion Mismatch of ventilation and perfusion Mismatch of ventilation and perfusion  ventilation and/or  perfusion of alveoli  ventilation and/or  perfusion of alveoli causes local  PCO2 and  PO2 causes local  PCO2 and  PO2 O2 autoregulates O2 autoregulates arteriolar diameter arteriolar diameter Pulmonary arterioles Pulmonary arterioles serving these alveoli serving these alveoli constrict dilate Match of ventilation Match of ventilation and perfusion and perfusion  ventilation,  perfusion  ventilation,  perfusion Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.19 Partial pressure P gradients promoting Inspired air: 160 mm Hg P 104gas O2 mm Hg movements in the body. Alveoli of lungs: O2 PCO2 0.3 mm Hg PCO2 40 mm Hg CO2 O2 O2 CO2 O2 CO2 External respiration Pulmonary Alveoli Pulmonary arteries veins (PO2 100 mm Hg) Blood leaving Blood leaving tissues and lungs and entering lungs: entering tissue PO2 40 mm Hg capillaries: PCO2 45 mm Hg PO2 100 mm Hg PCO2 40 mm Hg Heart O2 CO2 O2 CO2 Systemic Systemic veins arteries Internal respiration CO2 O2 Tissues: PO2 less than 40 mm Hg O2 CO2 PCO2 greater than 45 mm Hg Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Oxygen Transport (cont.) Association of oxygen and hemoglobin (cont.) – Rate of loading and unloading of O2 is regulated to ensure adequate oxygen delivery to cells – Factors that influence hemoglobin saturation: PO2 Other factors such as: – Temperature – Blood pH – PCO2 – Concentration of BPG Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Focus Figure 22.1-1 The amount of oxygen carried by hemoglobin depends on the P O2 (the amount of oxygen) available locally. This relationship ensures optimal oxygen pickup and delivery. The oxygen-hemoglobin dissociation curve will help you understand how the properties of hemoglobin (Hb) affect oxygen binding in the lungs and oxygen release in the tissues. In the lungs, where P O 2 is high (100 mm Hg), Hb is almost This axis tells you how much fully saturated (98%) with O 2. O 2 is bound to Hb. At 100%, each Hb molecule has 4 bound oxygen molecules. Hemoglobin 100 Oxygen If more O 2 is present, Percent O 2 saturation of hemoglobin 80 more O 2 is bound. However, because of Hb’s properties (O 2 binding strength changes with saturation), 60 this is an S-shaped curve. 40 20 0 0 20 40 60 80 100 PO2 (mm Hg) This axis tells you the relative amount (partial pressure) of O 2 dissolved in the fluid surrounding the Hb. In the tissues of other organs, where P O2 is low (40 mm Hg), Hb is less saturated (75%) with O 2. Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Oxygen Transport (cont.) – Influence of PO2 on hemoglobin saturation In arterial blood: – PO2 is 100 mm Hg and contains 20 ml of oxygen per 100 ml blood (20 volume %) – Hb is 98% saturated – Further increases in PO2 (as in deep breathing) produce minimal increases in O2 binding In venous blood, PO2 is 40 mm Hg and contains 15 volume % oxygen – Hb is still 75% saturated – Venous reserve: oxygen remaining in venous blood that can still be used Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Percent O2 saturation of hemoglobin Figure 22.22a Effect of temperature, PCO2, and blood pH on the oxygen-hemoglobin dissociation curve. 100 10°C 20°C 80 38°C 43°C 60 40 Normal body temperature 20 0 Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.22b Effect of temperature, PCO2, and blood pH on the oxygen-hemoglobin dissociation curve. Decreased carbon dioxide Percent O2 saturation of hemoglobin (PCO2 20 mm Hg) or H (pH 7.6) 100 80 Normal arterial carbon dioxide 60 (PCO2 40 mm Hg) or H (pH 7.4) 40 Increased carbon dioxide (PCO2 80 mm Hg) or H (pH 7.2) 20 0 20 40 60 80 100 PO2 (mm Hg) Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Oxygen Transport (cont.) – Influence of other factors on hemoglobin saturation (cont.) As cells metabolize glucose, they use O 2, causing: – Increases in PCO2 and H+ in capillary blood – Declining blood pH (acidosis) and increasing Pco2 cause Hb-O2 bond to weaken » Referred to as Bohr effect= » O2 unloading occurs where needed most – Heat production in active tissue directly and indirectly decreases Hb affinity for O2 » Allows increased O2 unloading to active tissues Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Carbon Dioxide Transport Occurs primarily in RBCs, where enzyme carbonic anhydrase reversibly and rapidly catalyzes this reaction In systemic capillaries, after HCO3– is created, it quickly diffuses from RBCs into plasma – Outrush of HCO3– from RBCs is balanced as Cl– moves into RBCs from plasma » Referred to as chloride shift Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.23a Transport and exchange of CO2 and O2. Tissue cell Interstitial fluid CO2 CO2 (dissolved in plasma) Binds to Slow plasma CO2 CO2  H2 O H2 CO3 HCO3   H  proteins CO2 HCO3  Chloride Cl shift Fast (in) via CO2 CO2  H2 O H2 CO3 HCO3   H  Cl transport Carbonic protein CO2 anhydrase HHb CO2 CO2  Hb HbCO2 (Carbamino- hemoglobin) Red blood cell HbO2 O2  Hb CO2 O2 O2 O2 (dissolved in plasma) Blood plasma Oxygen release and carbon dioxide pickup at the tissues Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.23b Transport and exchange of CO2 and O2. Alveolus Fused basement membranes CO2 CO2 (dissolved in plasma) Slow CO2 CO2  H2 O H2 CO3 HCO3   H  HCO3  Chloride Cl shift Fast (out) via CO2 CO2  H2 O H2 CO3 HCO3   H  transport Carbonic protein anhydrase Cl CO2 CO2  Hb HbCO2 (Carbamino- hemoglobin) Red blood cell O2  HHb HbO2  H  O2 O2 O2 (dissolved in plasma) Blood plasma Oxygen pickup and carbon dioxide release in the lungs Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Carbon Dioxide Transport (cont.) Changes in respiratory rate and depth affect blood pH – Slow, shallow breathing causes an increase in CO2 in blood, resulting in a drop in pH – Rapid, deep breathing causes a decrease in CO2 in blood, resulting in a rise in pH Changes in ventilation can help adjust pH when disturbances are caused by metabolic factors – Breathing plays a major role in acid-base balance of body Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.23a Transport and exchange of CO2 and O2. Tissue cell Interstitial fluid CO2 CO2 (dissolved in plasma) Binds to Slow plasma CO2 CO2  H2 O H2 CO3 HCO3   H  proteins CO2 HCO3  Chloride Cl shift Fast (in) via CO2 CO2  H2 O H2 CO3 HCO3   H  Cl transport Carbonic protein CO2 anhydrase HHb CO2 CO2  Hb HbCO2 (Carbamino- hemoglobin) Red blood cell HbO2 O2  Hb CO2 O2 O2 O2 (dissolved in plasma) Blood plasma Oxygen release and carbon dioxide pickup at the tissues Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.23b Transport and exchange of CO2 and O2. Alveolus Fused basement membranes CO2 CO2 (dissolved in plasma) Slow CO2 CO2  H2 O H2 CO3 HCO3   H  HCO3  Chloride Cl shift Fast (out) via CO2 CO2  H2 O H2 CO3 HCO3   H  transport Carbonic protein anhydrase Cl CO2 CO2  Hb HbCO2 (Carbamino- hemoglobin) Red blood cell O2  HHb HbO2  H  O2 O2 O2 (dissolved in plasma) Blood plasma Oxygen pickup and carbon dioxide release in the lungs Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  Figure 22.27 Location and innervation of the peripheral chemoreceptors in the carotid and aortic bodies. Brain Sensory nerve fiber in cranial nerve IX (pharyngeal branch of glossopharyngeal) External carotid artery Internal carotid artery Carotid body Common carotid artery Cranial nerve X (vagus nerve) Sensory nerve fiber in cranial nerve X Aortic bodies in aortic arch Aorta Heart Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc. Factors Influencing Breathing Rate and Depth (cont.) – Influence of PCO2 Most potent and most closely controlled If blood PCO2 levels rise (hypercapnia), CO2 accumulates in brain and joins with water to become carbonic acid – Carbonic acid dissociates, releasing H+, causing a drop in pH (increased acidity) – Increased H+ stimulates central chemoreceptors of brain stem, which synapse with respiratory regulatory centers – Respiratory centers increase depth and rate of breathing, which act to lower blood PCO2, and pH rises to normal levels Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc. Factors Influencing Breathing Rate and Depth (cont.) – Influence of PCO2 (cont.) If blood PCO2 levels decrease, respiration becomes slow and shallow – Apnea: breathing cessation that may occur when P CO2 levels drop abnormally low – Swimmers sometimes voluntarily hyperventilate to enable them to hold their breath longer » Causes a drop in P CO2, which causes a delay in respiration, as PCO2 levels need to build back up » Can cause dangerous drops in P O2 levels Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc. Factors Influencing Breathing Rate and Depth (cont.) Chemical factors (cont.) – Influence of PO2 Peripheral chemoreceptors in aortic and carotid bodies sense arterial O2 levels Declining PO2 normally has only slight effect on ventilation because of huge O2 reservoir bound to Hb – Requires substantial drop in arterial P O2 (below 60 mm Hg) to stimulate increased ventilation – When excited, chemoreceptors cause respiratory centers to increase ventilation Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.  High Altitude Quick travel to altitudes above 2400 meters (8000 feet) may trigger symptoms of acute mountain sickness (AMS) – Atmospheric pressure and PO2 levels are lower at high elevations – Symptoms: headaches, shortness of breath, nausea, and dizziness – In severe cases, lethal cerebral and pulmonary edema may occur Bio 202 ASU DPC T. Penkrot © 2016 Pearson Education, Inc.