Respiratory System PDF

The Respiratory System  Learning Objectives Graph or describe a typical spirogram, indicating the four lung volumes (inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV), and residual volume (RV)) and four capacities (inspiratory capacity (IC), functio...

The Respiratory System  Learning Objectives Graph or describe a typical spirogram, indicating the four lung volumes (inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV), and residual volume (RV)) and four capacities (inspiratory capacity (IC), functional residual capacity (FRC), vital capacity (VC), and total lung capacity (TLC)). Diagram or describe the methods of O2 transport in blood (i.e., dissolved, bound to hemoglobin), and state the percentage of total O2 transported by each method. Graph or describe an oxyhemoglobin dissociation curve (O2-Hb saturation curve) explaining the relationship between O2 partial pressure and Hb saturation. Describe how changes in blood temperature, pH, PCO2, and 2,3-BPG (2,3-DPG) affect O2 transport. Diagram or describe the reversible chemical equation for the conversion of CO2 and H2O to hydrogen ion (H+) and bicarbonate ion (HCO3-), then explain the role of carbonic anhydrase in this reaction (i.e., bicarbonate buffer system). Diagram or describe the methods of CO2 transport in blood (i.e., dissolved, as bicarbonate, and as carbaminohemoglobin [Hb-CO2]), and state the percentage of total CO2 transported by each method.  Respiratory Volumes & Pulmonary Function Tests Respiratory volumes and capacities: provide information on a person’s respiratory status Respiratory volumes: are measured using a spirometer Respiratory capacities: are the sum (combinations) of these volumes Respiratory Volumes Respiratory Capacities  Ventilation Rates Minute (total) ventilation: total amount of gas that flows into or out of the respiratory tract in 1 minute. During normal quiet breathing = 6 L/min (500 ml/br X 12 br/min) During vigorous exercise, it may reach 200 L/min Alveolar ventilation rate (AVR): a better index of effective ventilation than minute ventilation AVR = frequency x (TV – dead space) (ml/min) = (br/min) x (ml/br) = 12 x (500 – 150) = 4200ml/mins Slow, deep breathing → ↑ AVR Spirometry Common test is to inspire maximally and then force the air out as quickly as possible FEV1 ≈ 80% FVC  Pulmonary Function Tests Spirometry can distinguish between: – Obstructive pulmonary disease: increased airway resistance (example: bronchitis) TLC, FRC, RV may increase because of hyperinflation of lungs – Restrictive disease: reduced TLC due to disease (example: tuberculosis) or exposure to environmental agents (example: fibrosis) VC, TLC, FRC, RV decline because lung expansion is compromised © 2016 Pearson Education, Ltd.  Pulmonary Function Tests (cont.) Pulmonary functions tests can measure rate of gas movement – Forced vital capacity (FVC): amount of gas forcibly expelled after taking deep breath – Forced expiratory volume (FEV): amount of gas expelled during specific time interval of FVC FEV1: amount of air expelled in 1st second – Healthy individuals can expel 80% of FVC in 1st second – Patients with obstructive disease exhale less than 80% in 1st second, whereas those with restrictive disease exhale 80% or more even with reduced FVC © 2016 Pearson Education, Ltd. 1 0 TRANSPORT OF OXYGEN BY BLOOD Two ways: Bound to the hemoglobin of erythrocytes (RBC’s), 98.5% Dissolved in plasma, only 1.5%  Oxygen Transport (cont.) Association of oxygen and hemoglobin Each Hb molecule is composed of four polypeptide chains, each with a iron-containing heme group So each Hb can transport four oxygen molecules Oxyhemoglobin (HbO2): hemoglobin-O2 combination Reduced hemoglobin (deoxyhemoglobin) (HHb): hemoglobin that has released O2  Oxygen Transport (cont.) Association of oxygen and hemoglobin (cont.) Loading and unloading of O2 is facilitated by a change in shape of Hb As O2 binds, Hb changes shape, increasing its affinity for O2 increases As O2 is released, Hb shape change causes a decrease in affinity for O2 Fully saturated (100%): all four heme groups carry O2 Partially saturated: when only one to three hemes carry O2 © 2016 Pearson  Oxygen Transport (cont.) Influence of PO2 on hemoglobin saturation PO2 heavily influences binding and release of O2 with hemoglobin Percent of Hb saturation can be plotted against PO2 concentrations – Resulting graph is not linear, but an S-shaped curve – Referred to as an oxygen-hemoglobin dissociation curve © 2016 Pearson  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 © 2016 Pearson 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 (2-3 bisphosphoglycerate 2-3 –BPG) or DPG -a unique compound produced by RBC’s  Oxygen Transport (cont.) Influence of other factors on hemoglobin saturation Increases in temperature, H+, PCO2, and BPG can modify structure of hemoglobin – Results in a decrease for Hb’s affinity for O2 – Occurs in systemic capillaries – Enhances O2 unloading, causing a shift in O2-hemoglobin dissociation curve to right Decreases in these factors shift curve to left – Decreases oxygen unloading from blood © 2016 Pearson Percent O2 saturation of hemoglobin 100 10°C 20°C 80 38°C 43°C 60 40 Normal body temperature Increases in temperature 20 - Results in a decrease for Hb’s affinity for O2 - Enhances O2 unloading, - causing a shift in O2-hemoglobin dissociation curve to right 0 Figure 22.22a Effect of temperature on the oxygen- hemoglobin dissociation curve.  Decreased carbon dioxide Percent O2 saturation of hemoglobin (PCO2 20 mm Hg) or H+ (pH 7.6) 100 Increases in CO2 or H+ (pH ) 80 - Results in a Normal arterial decrease for Hb’s carbon dioxide 60 affinity for O2 (PCO2 40 mm Hg) - Enhances O2 or H+ (pH 7.4) unloading, 40 - causing a shift in Increased carbon dioxide O2-hemoglobin (PCO2 80 mm Hg) dissociation curve to or H+ (pH 7.2) right 20 Figure 22.22a Effect of 0 PCO2, and blood pH on the oxygen-hemoglobin 20 40 60 80 100 dissociation curve. PO2 (mm Hg) © 2016 Pearson Education, Ltd. Transport of CO2 by Blood Three forms: Dissolved in plasma, 7-10% Chemically bound to hemoglobin, 20% CO2 + haemoglobin  HbCO2 (carbaminohemoglobin) Binds to globin (not heme) so doesn’t compete with oxygen for Hb In plasma as bicarbonate ion, 70% CO2 + H2O ⇔ H2 CO3 ⇔ H+ + H CO3 – carbon dioxide water carbonic acid hydrogen bicarbonate Bicarbonate ions are carried to lungs & the process is then reversed Transport of CO2 by Blood In systemic capillaries: HCO3– quickly diffuses from RBCs into the plasma The chloride shift occurs: outrush of HCO3– from the RBCs is balanced as Cl– moves in from the plasma Transport of CO2 by Blood In pulmonary capillaries: HCO3– moves into the RBCs and binds with H+ to form H2CO3 H2CO3 is split by carbonic anhydrase into CO2 and water CO2 diffuses into the alveoli  Carbon Dioxide Transport (cont.) Influence of CO2 on blood pH Carbonic acid–bicarbonate buffer system: helps blood resist changes in pH If H+ concentration in blood rises, excess H+ is removed by combining with HCO3– to form H2CO3, which dissociates into CO2 and H2O If H+ concentration begins to drop, H2CO3 dissociates, releasing H+ HCO3– is considered the alkaline reserve of carbonic acid-bicarbonate buffer system © 2016 Pearson  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 © 2016 Pearson Learning Objectives Predict how increasing or decreasing blood PCO2 affects blood pH and the concentrations of bicarbonate and hydrogen ions. Apply knowledge of the equation for the bicarbonate buffer system to predict how changing the bicarbonate concentration or blood pH affects the PCO2 of plasma. Control of pulmonary ventilation Compare and contrast the locations and functions of the central and peripheral chemoreceptors associated with the control of ventilation. Define hyperventilation, and hypoventilation Diagram or describe the reflex control of ventilation, including the major stimuli, sensors, neural control pathways, and targets. Application of homeostatic mechanisms Provide specific examples to demonstrate how the respiratory system responds to maintain homeostasis in the body. Explain how the respiratory system relates to other body systems to maintain homeostasis Predictions related to homeostatic imbalance Given a factor or situation (e.g., pulmonary fibrosis), predict the changes that could occur in the respiratory system and the consequences of those changes (i.e. given a cause, state a possible effect). Factors that Influence Rate & Depth of Breathing Respiratory centres located in medulla & pons Lungs contain receptors → impulses sent via vagus nerves to respiratory centres Breathing is normally regulate by respiratory centres involuntarily High brain centres Hypothalamic control: Strong emotions, pain & temperature modify respiratory rate and depth Cortical controls: conscious control over the rate & depth of breathing. Involves direct signals from cerebral motor cortex → motor neurons → stimulates respiratory muscles (bypassing respiratory centres) Figure 22.24 Respiratory centers in the brain stem. Pons Medulla Pontine respiratory centers interact with the medullary respiratory centers to smooth the respiratory pattern. Ventral respiratory group (VRG) contains rhythm generators whose output drives respiration. Pons Medulla Dorsal respiratory group (DRG) integrates peripheral sensory input and modifies the rhythms generated by the VRG. Phrenic nerve (from C3, C4, C5) innervates the diaphragm. Intercostal nerves Diaphragm External intercostal muscles Factors influencing rate and depth Arterial pH Arterial partial pressure of oxygen Arterial partial pressure of carbon dioxide Higher brain centres Reflexes  Factors Influencing Breathing Rate and Depth (cont.) Chemical factors Most important of all factors affecting depth and rate of inspiration Changing levels of PCO2, PO2, and pH are most important Levels of these chemicals are sensed by: Central chemoreceptors: located throughout brain stem Peripheral chemoreceptors: found in aortic arch and carotid arteries © 2016 Pearson  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 © 2016 Pearson  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 PCO2 levels drop abnormally low – Swimmers sometimes voluntarily hyperventilate to enable them to hold their breath longer » Causes a drop in PCO2, which causes a delay in respiration, as PCO2 levels need to build back up » Can cause dangerous drops in PO2 levels © 2016 Pearson  Clinical – Homeostatic Imbalance 22.15 Hyperventilation: increased depth and rate of breathing that exceeds body’s need to remove CO2 – May be caused by anxiety attacks – Leads to decreased blood CO2 levels (hypocapnia) Causes cerebral vasoconstriction and cerebral ischemia, resulting in dizziness, fainting Early symptoms include tingling and involuntary muscle spasms in hands and face – Treatment: breathing into paper bag increases CO2 levels being inspired © 2016 Pearson Education, Ltd. Hyperventilation What changes will occur if a person hyperventilates, that is, breathes ↓ ↑ deeper and faster than necessary for normal gas exchange? During hyperventilation, carbon dioxide is exhaled, lowering the PCO2. This drives the chemical reaction to the ↓ ↓ left, decreasing the hydrogen ion concentration, and increasing pH: CO2 + H2O ←H2CO3← H+ + HCO3- Since the PCO2 is low, the central ↓ chemoreceptors send fewer impulses ↓ to the respiratory centers. Since the pH is high, the peripheral chemoreceptors also send fewer ↓ impulses to the respiratory centers, which send fewer nerve impulses to the ↓ respiratory muscles, thereby further decreasing breathing rate and depth and returning the arterial gases and pH to normal levels.  Hypoventilation Hypoventilation occurs when the breathing rate and depth is too low to maintain normal blood gas levels. During hypoventilation, not enough oxygen is ↓ ↑ ↓ inhaled, so the PO2 decreases. In addition, carbon dioxide builds up in the blood, increasing the PCO2. This drives the chemical reaction to the right, increasing the H+ concentration and decreasing pH. The PO2 drops, but not enough to stimulate the ↑ ↑ peripheral chemoreceptors. The high PCO2 stimulates the central chemoreceptors to send more impulses to ↑ the respiratory centers. A decrease in pH stimulates the peripheral ↑ chemoreceptors, which also send more nerve impulses to the respiratory centers, which stimulate the respiratory muscles, increasing ↑ ↑ the breathing rate and depth. This allows oxygen to be inhaled, carbon dioxide to be exhaled, and drives the chemical reaction to the left, returning the ↑ arterial gases and pH to normal levels.  22.10 Lung Diseases Chronic Obstructive Pulmonary Disease (COPD) Exemplified by chronic emphysema and chronic bronchitis Key feature is irreversible decrease in ability to force air out of lungs © 2016 Pearson Education, Ltd.  Chronic Obstructive Pulmonary Disease (COPD) (cont.) Other common features: – History of smoking in 80% of patients – Dyspnea: labored breathing (“air hunger”) – Coughing and frequent pulmonary infections – Most patients develop hypoventilation accompanied by respiratory acidosis, hypoxemia © 2016 Pearson Education, Ltd.  Chronic Obstructive Pulmonary Disease (COPD) (cont.) Emphysema – Permanent enlargement of alveoli and destruction of alveolar walls result in decreased lung elasticity, with three consequences: 1. Accessory muscles are necessary for breathing, leading to exhaustion from using 10–15% more energy to breathe than normal 2. Trapped air causes hyperinflation, which flattens diaphragm and causes expanded barrel chest, both of which reduces ventilation efficiency 3. Damaged pulmonary capillaries lead to enlarged right ventricle – Hereditary factors for disease include alpha-1 antitrypsin deficiency © 2016 Pearson Education, Ltd.  Chronic Obstructive Pulmonary Disease (COPD) (cont.) Chronic bronchitis – Inhaled irritants cause chronic excessive mucus – Mucosae of lower respiratory passageways become inflamed and fibrosed – Results in obstructed airways that impair lung ventilation and gas exchange – Symptoms include frequent pulmonary infections – Risk factors include smoking and environmental pollutants © 2016 Pearson Education, Ltd.  Chronic Obstructive Pulmonary Disease (COPD) (cont.) COPD symptoms and treatment – Strength of patient’s innate respiratory drive is reason behind different symptoms seen “Pink puffers”: patient usually thin because they burn large amount of energy breathing; near-normal blood gases are maintained, so skin color is normal “Blue bloaters”: patient usually stocky; cyanosis is due to hypoxia, so skin color takes on bluish hue – Treatment: bronchodilators, corticosteroids, oxygen, sometimes lung volume reduction surgery; oxygen must be administered carefully © 2016 Pearson Education, Ltd. Figure 22.28 The pathogenesis of COPD. Tobacco smoke α-1 antitrypsin Air pollution deficiency Continual bronchial Breakdown of elastin in irritation and inflammation connective tissue of lungs Chronic bronchitis Emphysema Excess mucus production Destruction of alveolar Chronic productive cough walls Loss of lung elasticity Airway obstruction or air trapping Dyspnea Frequent infections Hypoventilation Hypoxemia Respiratory acidosis © 2016 Pearson Education, Ltd.  Asthma Sometimes classified as COPD, but episodes are acute, not chronic, with symptom-free periods Characterized by coughing, dyspnea, wheezing, and chest tightness Active inflammation of airways precedes bronchospasms Airway inflammation is an immune response caused by release of interleukins, production of IgE, and recruitment of inflammatory cells Airways thickened with inflammatory exudate magnify effect of bronchospasms © 2016 Pearson Education, Ltd.