Chapter 23 Respiratory System

Transcription

1 Chapter 23 Respiratory System I. Functions of the Respiratory System: 1. Gas Exchange 2. Regulatory (blood ph) 3. Voice Production 4. Olfaction 5. Protection II. Anatomy & Histology of the Respiratory System. a). respiration system consists of the 1. Nasal cavity 2. Pharynx 1-3 Upper Respiratory tract 3. Larynx 4. Trachea 5. Bronchi 4-6 Lower Respiratory Tract 6. Lungs b) Diaphragm and muscles of the thoracic abdominal walls are responsible for respiratory movement. A. Nose 1) Consists of the external nose and the nasal cavity. i) Largest part of the external nose is composed of cartilage plates 2) Nasal cavity extends from the nares to the choanae i) Nares (nostrils) are the external openings of the nasal cavity and the choanae are the openings into the pharynx; the anterior part of the nasal cavity is the vestibule. ii) Hard palate - is a bony plate covered by a mucous membrane that forms the floor of the nasal cavity. (Separates nasal cavity from the oral cavity) iii). nasal septum is a partition dividing the nasal cavity into right and left parts a) Nasal septum - anterior part is cartilage, posterior part is vomer bone; and the perpendicular plate is ethmoid bone. iv) Lateral walls of nasal cavity are 3 bony ridges (conchae). a) Beneath each conchae is a passageway (meatus) b) Functions of the nasal cavity: 1. Passageway for air 2. Cleans air a) Nasal septum & conchae increase the surface area of the nasal cavity 3. Humidifies & warms the air 4. Olfactory epithelium, the sensory organ for smell is located in the most superior part of the nasal cavity 5. Nasal cavity & paranasal sinuses are resonating chambers for speech.

2 v) Figure 23.2 B. Pharynx: 1) Is the common opening of both the digestive & respiratory systems. a) Connected to respiratory system at the larynx & to the digestive system at the esophagus. 2) Divided into 3 regions a) nasopharynx - is the superior part of the pharynx & extends from the conchae to the soft palate (an incomplete muscle & C.T. partition separating the nasopharynx from the oropharnyx) i) Uvula (grape) is the posterior extension of the soft palate ii) Soft palate prevents swallowed mater from entering the nasopharynx & nasal cavity iii) Posterior surface of nasopharynx contains the pharyngeal tonsil (adenoid) which aids in defending the body against infection b) Oropharnyx from the uvula to the epiglottis. i) Oral cavity opens into the oropharnyx through the fauces. a) Palatine tonsils the lingual tonsils are located in fauces. (i) Lining protects against abrasion. c) Laryngopharynx extends from the tip of the epiglottis to the esophagus & passes to the larynx. 3) Cartilages support the anterior and lateral sides; posterior wall is devoid of cartilage and contains an elastic ligamentous membrane and bundles of smooth muscles (trachealis muscle) 2

3 4) Figure ) Trachea divides to form 2 smaller tubes (primary bronchi) a) the most inferior tracheal cartilage forms a ridge (carina) which separates the openings into the primary bronchi C. Larynx: 1. Consists of an outer casing of nine cartilages a) 6 of the 9 are paired; 3 are unpaired b) Largest of the cartilages is the unpaired thyroid cartilage (Adam s apple) c) Most inferior cartilage is the unpaired cricoid cartilage d) 3rd unpaired cartilage is the epiglottis (consists of elastic rather than hyaline cartilage) e) the paired arytenoids cartilage articulate with the posterior, superior border of the ericoid cartilage and the paired corniculate cartilage are attached to the superior tips of the arytenoid cartilage; the paired cuneiform cartilage are contained in a mucous membrane 2. There are two pairs of ligaments: a) Superior ligaments (vestibular folds or false vocal cords) come together and prevent food and liquids from entering the Larynx during swallowing and prevent air from leaving the lungs. b) Inferior ligaments (vocal folds or true vocal cords) i) laryngitis- inflammation of the mucosal epithelium of the vocal folds 3. 3 functions: a) Thyroid and cricoid cartilages maintain an open passageway for air movement b) Epiglottis and vestibular folds prevent swallowed material from moving into the larynx c) Vocal folds are the primary source of sound production 3

4 4. Movement of the arytenoid and other cartilages is controlled by the skeletal muscle D. Trachea 1. is a membranous tube that consists of dense regular C.T. and smooth muscle reinforced with c- shaped pieces of cartilage 2. Figure 23.3 i) It is an important radiologic landmark E. Tracheobronchial Tree: 1. Beginning with the trachea, all the respiratory passageways are called the tracheobronchial tree a) based on function, it can be divided into: ii) Conducting zone- extends from the trachea to terminal bronchioles (1) Functions as a passageway for air movement and helps to remove debris from the air 2. Primary bronchi divide into secondary (lobar) bronchi (2 in the left lung and 3 in the right); these give rise to tertiary (segmental) bronchi, which subdivide to form terminal bronchioles. 3. Figure Asthma attack- contraction of the smooth muscle in the terminal bronchiole results in: a) Decrease diameter b) Increase resistance to airflow c) Greatly reduced airflow d) Death in severe cases ii) Respiratory zone: 1. Extends from the terminal bronchioles to small chambers (alveoli), which are the sites of gas exchange between the air and blood 2. Terminal bronchioles divide from respiratory bronchioles (limited ability for gas 4

5 exchange because of a few attached alveoli); these five rise to alveolar ducts, which end as 2 or 3 alveolar sacs. 3. Figure types of cells form the alveolar wall 1. Type I pneumocytes (90%) - most of the gas exchange takes place in these cells 2. Type II pneumocytes (10%) - are cube shaped secretory cells that produce surfactant a) The respiratory membrane of the lungs is where gas exchange between the air and blood takes place 1. It consists of: a. a thin layer of fluid lining the alveolus b. the alveolar epithelium c. basement membrane (alveolar epithelium) d. interstitial space e. basement membrane (capillary endothelium) f. capillary endothelium composed of simple squamous epithelium F. Lungs: 1. Are the principle organs of respiration, and volume basis they are among the largest organs of the body 2. conical in shape (base on the diaphragm and apex near clavicle) 3. Right lung larger than the left 5

6 4. hilum- is a region on the medial surface of the lung where structures (primary bronchus, blood vessels, nerves and lymphatic vessels) enter or exit the lung; all structures passing through it are referred to as the root of the lung 5. Right lung has 3 lobes, left lung has 2 a) Lobes are subdivided into bronchopulmonary segments, which are supplied by the tertiary bronchi b) 9 segments are present in the left lung and 10 in the right lung c) The segments are subdivided into lobules 6. Figure 23.9 G. Thoracic Wall and Muscles of Respiration: 1. Thoracic wall consists of: a) Thoracic vertebrae b) Ribs c) Costal cartilage d) Sternum e) and associated muscles 2. Thoracic cavity is a space enclosed by the thoracic wall and the diaphragm, which separates the thoracic cavity from the abdominal cavity 3. Muscles of inspiration include: a) Diaphragm (response 2/3 of the increase volume) b) External intercostals c) Pectoralis minor d) Scalenes b,c,d= elevate ribs 4. Muscles of expiration include a) Abdominal muscles b) Internal intercostals a,b= depress rib s and sternum 5. Primary function of the internal and external intercostals is to stiffen the thoracic wall by contracting at the same time 6

7 6. Figure H. Pleura: 1. Each lung is surrounded by a separate pleural cavity 2. The mediastinum (formed by the heart, trachea, and esophagus and associated structures) is a partition that separates the pleural cavities a) parietal pleura- covers i) Inner thoracic wall ii) Superior surface of the diaphragm iii) Mediastinum b) visceral pleura- covers the surface of the lung 3. Pleural fluid does 2 things e) Acts as a lubricant f) Helps hold the parietal and visceral pleural membranes together I. Blood Supply: 1. Oxygenated blood- is blood that has passed through the lungs and picked up oxygen 2. Blood that has passed through the tissues and released some of its oxygen is called deoxygenated blood 3. Oxygenated blood flows from the thoracic aorta through bronchial arteries to capillaries a) Deoxygenated blood from the proximal part of the bronchi returns to the heart through the bronchial veins and the azygos venous system J. Lymphatic Supply: 1. The lungs have 2 lymphatic supplies: a) Superficial lymphatic vessels- function to drain lymph from the superficial lung tissue and the visceral pleura. b) Deep lymphatic vessels- function to drain lymph from the bronchi and associated tissues 7

8 2. No lymphatic vessels are located in the walls of the alveoli 3. Both vessels exit the lung at the hilum II. Ventilation: A. Pressure Differences and Airflow: 1. Ventilation- is the process of moving air into and out of the lungs. a) Flow of air requires a pressure gradient from outside the body to the alveoli and in reverse 2. Physics of Airflow a) F=P1-P2/R F is flow P1 is pressure at point 1 P2 is pressure at point 2 R is resistance B. Pressure and Volume: 1. General gas law a) P=nRT/V P is pressure n is number of gram moles of gas R is the gas constant T is absolute temperature V is volume b) The law reveals that air pressure is inversely proportional to volume (i) Volume increase, pressure decrease 2. Table

9 C. Airflow into and out of Alveoli: a) 3 conventions to help simplify the numbers used to express pressure: 1. Barometric air pressure (Pb)- is atmospheric air pressure outside the body, with value of zero 2. The small pressure in respiratory physiology are usually expressed in centimeters of water (cm H20) 3. Other pressures are measured in reference to barometric air pressure (i) Alveolar pressure- is the pressure inside the alveolus b) The pressure between barometric air pressure and alveolar pressure results in air movement c) Process (4 steps) 1. End of expiration: (i) Barometric and alveolar pressure are equal 2. during inspiration: (i) Thoracic volume increases and increase in alveolar volume, which causes a decrease in alveolar pressure (air flow in) 3. End of inspiration: (i) Alveolar pressure becomes equal to barometric air pressure (no movement of air) 4. during expiration: (i) The volume of the thorax decreases, which results in a decrease in alveolar volume and an increase in alveolar pressure over barometric air pressure D. Changing alveolar volume: a) Lung recoil and changes in pleural pressure cause changes in alveolar volume 1. Lung Recoil: (i) Causes the alveoli to collapse and it results from: (a) Elastic recoil (b) Surface tension (ii) Surfactant- is a mixture of lipoprotein molecules produced by the type II pneumocytes of the alveolar epithelium (a) Reduces the tendency of the lungs to collapse 2. Pleural Pressure: (i) Is the pressure in the pleural cavity (ii) Pleural pressure is less than alveolar pressure because of a "suction effect" caused by lung recoil b) Pneumothorax- is the introduction of air into the pleural cavity through an opening in the thoracic wall or lung, (i) Most common symptoms are chest pain and shortness of breath (ii) Treatment: a) Mild symptoms- may resolve on its own b) Other cases- aspirating the pleural cavity with a tube and it restores a negative pressure c) Surgery may be required to close the opening into the pleural cavity c) Tension pneumothorax- the pressure with in the thoracic cavity is always higher than barometric air pressure results in: (i) Increase in air and pressure within pleural cavity (ii) Decrease venous return (iii) Low blood pressure (iv) Inadequate delivery of oxygen to tissues (a) Tx.- insertion of a large bore needle 3. Pressure changes during inspiration and expiration: a) At the end of a normal expiration, pleural pressure is -5cmH2O, and alveolar pressure is equal to barometric pressure (0cmH2O) 9

10 b) During normal inspiration, the pleural pressure decreases to -8cmH2O c) Decrease in pleural pressure during inspiration occurs for 2 reasons: (i) Because of the effect of changing volume on pressure (general gas law), when the volume of the thoracic cavity increases, pleural pressure decreases (ii) As the thoracic cavity expands, the lungs expand because they adhere to the inner thoracic wall through the pleurae III. Measuring Lung Function: a) The measurements can be used to: (i) Diagnoses diseases (ii) Track progress of diseases (iii) Track recovery from diseases A. Compliance of the lungs and the thorax: 1. compliance- is a measure of the ease with which the lungs and the thorax expand a) It is the volume by which the lungs and thorax increase for each unit of pressure change in alveolar pressure b) Normally is.13l/cmh2o (liter per centimeter of water) c) The greater the compliance, the easier it is for a change in pressure to cause expansion of the lungs and thorax d) Conditions that decrease compliance: (i) Deposition of inelastic fibers in lung tissue (pulmonary fibrosis) (ii) Collapse of the alveoli (respiratory distress syndrome and pulmonary edema) (iii) Increased resistance to airflow caused by airway obstruction (asthma, bronchitis, and lung cancer) (iv) Deformities of the thoracic wall that reduce the ability of the thoracic volume to increase (kyphosis, scoliosis) B. Pulmonary Volumes and Capacities: 1. Spirometry- is the process of measuring volumes of air that move into and out of the respiratory system a) spirometer- is a device used to measure these pulmonary volumes (4) (i) Tidal volume- is the volume of air inspired or expired during normal inspiration or expiration (about 500 ml) (ii) Inspiratory reserve volume- the amount of air that can be inspired forcefully after inspiration of the normal tidal volume (approx. 300ml) (iii) Expiratory reserve volume- the amount of air that can be forcefully expired after expiration of the normal tidal volume (approx. 1100ml) (iv) Residual volume- is the volume of air still remaining in the respiratory passages and lungs after the most forceful expiration (approx ml) 2. Pulmonary capacities: - are the sum of 2 or more pulmonary volumes (4) (i) Inspiratory capacity- is the tidal volume plus the inspiratory reserve volume, which is the amount of air that a person can inspire maximally after a normal expiration (approx ml) (ii) Functional residual capacity- is the expiratory reserve volume plus the residual volume, which is the amount of air remaining in the lungs at the end of a normal expiration (approx. 2300ml) (iii) Vital capacity- is the sum of the inspiratory reserve volume, the tidal volume, and the expiratory reserve volume, which is the maximum volume of air that a person can expel from the respiratory tract after a maximum inspiration (approx. 4600ml) (iv)total lung capacity- is the sum of the inspiratory and expiratory reserve volumes plus the tidal volumes and the residual volume (approx. 5800ml) 3. Sex, age, body size, and physical conditioning cause variations in respiratory volumes and capacities C. Minute ventilation and alveolar ventilation: 10

11 a) Minute ventilation- is the total amount of air moved into and out of the respiratory system each minute, and it is equal tidal volume times the respiratory rate (i) Respiratory rate or frequency- is the number of breaths taken per minute (approx. 6L/min) b) The part of the respiratory system where gas exchange does not take place is called the dead space. (i) Anatomical dead space- is formed by the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles (ii) Physiologic dead space- is the anatomic dead space plus the volume of any alveoli in which gas exchange is less than normal c) Alveolar ventilation- is the volume of air available for gas exchange per minute IV. Physical Principles of gas exchange: a) One measurement of the concentration of gases is: A. Partial Pressure: 1. Dalton's Law- in a mixture of gases, the part of the total pressure resulting from each type of gas is determined by the percentage of the total volume represented by each gas type 2. Partial pressure- is the pressure exerted by each type of gas in a mixture 3. Water vapor pressure- when water molecules in gaseous form also exert a partial pressure B. Diffusion of gases through liquids: a) When a gas comes into contact with a liquid it tends to dissolve in the liquid b) Henry s Law- the concentration of a gas dissolved in a liquid is equal to the partial pressure of the gas over the liquid times the solubility coefficient of the gas (1) Solubility coefficient is a measure of how easily the gas dissolves in the liquid (2) Partial pressure of a gas in a liquid (in a gaseous state) is a measure of concentration (i) Gas moves from areas of higher concentration to areas of lower partial pressure C. Diffusion of gases through the respiratory membrane: a) Factors that influence the rate of gas diffusion: (i) Thickness of the membrane (ii) Diffusion coefficient (iii) Surface area (iv) Partial pressure difference (I) Respiratory Membrane Thickness: a) Increasing the thickness of the membrane decreases the rate of diffusion b) Diseases can cause an increase c) Most common cause is pulmonary edema caused by failure of the left side of the heart. causes accumulation of fluid (i) TB, pneumonia, or advanced scoliosis also cause accumulation (II) Diffusion Coefficient: a) It is a measure of how easily a gas diffuses through a liquid or tissue, taking into account the solubility of the gas in the liquid, and the size of the gas molecules (molecular weight) (III) Surface area: a) The total surface area of the respiratory membrane is approx. 70 m2 of the size of a 25' x 30' room b) Emphysema and lung cancer cause a decrease in surface area; also surgical removal of lung tissue; destruction of lung tissue by cancer; degeneration of the alveolar walls by emphysema; replacement of lung tissue by C.T. caused by T.B. and pneumonia, and pulmonary edema (IV) Partial Pressure Difference: a) It is the difference between the partial pressure of the gas in the alveoli and the partial pressure of the gas in the blood of the pulmonary capillaries b) The greater volume of atmospheric air exchanged with the residual volume raises alveolar PO2, lowers PCO2, and promotes gas exchange 11

12 D. Relationship between ventilation and pulmonary capillary blood flow: a) The normal relationship between ventilation and pulmonary capillary blood flow can be disrupted in 2 ways: 1. When ventilation exceeds the ability of the blood to pick up oxygen, due to inadequate cardiac output 2. When ventilation is not great enough to provide the oxygen need to oxygenate the blood flow (ex. asthma) b) Blood that isn't completely oxygenated is called shunted blood (i) 2 sources: 1. Anatomic shunt- results when deoxygenated blood from the bronchi and bronchioles mixes with blood in the pulmonary veins 2. Is blood that passes through pulmonary capillaries but doesn't become fully oxygenated. Physiologic shunt is the combination of deoxygenated blood from the anatomic shunt and the pulmonary capillaries c) Gravity is the major factor affecting regional blood flow in the lung, and sometimes PO2 can have an effect V. Oxygen and carbon dioxide transport in the blood: 1. Once oxygen diffuses into the blood, most of it combines reversibly with hemoglobin, and a smaller amount dissolves in the plasma 2. Hemoglobin transports oxygen from the pulmonary capillaries to the tissue capillaries where it is used in aerobic respiration 3. Cells produce CO2 during aerobic metabolism, and it diffuses from the cells into the tissue capillaries. It is transported dissolved in the plasma, in combination with hemoglobin, and in the form of bicarbonate ions A. Oxygen Diffusion Gradients: a) Oxygen diffuses from the alveoli into the pulmonary capillary blood because the PO2 is greater in the alveoli than in the capillary blood b) Blood leaving the pulmonary capillaries has a higher PO2 than blood leaving the lungs in the pulmonary veins; the decrease occurs because the blood from the pulmonary capillaries mixes with deoxygenated (shunted) blood from the bronchial veins c) Due to oxygen usage, a constant diffusion gradient exists B. Carbon Dioxide Diffusion Gradients: a) CO2 is produced as a by-product of cellular respiration, and a diffusion gradient is established from tissue cells to the blood within the tissue capillaries C. Hemoglobin and Oxygen Transport: a) approx. 98.5% of the oxygen transported in the blood from the lungs to the tissues is transported in combination with hemoglobin in RBC's and the remaining 1.5% is dissolved in the water part of the plasma (I.) Effect of PO2: (i) The oxygen-hemoglobin dissociation curve describes the percentage of hemoglobin saturated with oxygen at any given PO2 (a) approx. 23% of the oxygen bound to hemoglobin is released into the blood (II) Effect of ph, PCO2, and Temperature: (a) The increase or decrease of the ph of blood, accounts for the increase or decrease of oxygen binding to hemoglobin (i) Decrease ph - decrease O2 binding to hemoglobin due to increase in hydrogen ions and vise-versa (ii) The effect of ph in the oxygen-hemoglobin dissociation curve is called the Bohr Effect 12

13 (b) An increase in PCO2 also decreases the ability of hemoglobin to bind oxygen because of the effect of CO2 on ph (i) Carbonic anhydrase is an enzyme within RBC's that catalyzes the reversible effect (ii) CO2 + H20 - (carbonic an hydrase) = H2CO3 - H+HCO2) bicarbonate ion) (iii) As Co2 increases, more hydrogen ions are produced, and the ph declines (c) An increase in temperature also decreases the tendency for oxygen to remain bound to hemoglobin ph down, CO2 up, temp up) (d) When the affinity of hemoglobin for oxygen decreases, the curve is shifted to the right (ph up, CO2 down, Temp down) (i) In the lungs, the curve shifts to the left because of the lower CO2 levels, lower temperatures, and lower lactic acid levels (III) Effect of BPG: a) BPG (2, 3- bisphosphoglycerate) binds to hemoglobin and increases its ability to release O2 (IV) Fetal Hemoglobin: a) Fetal blood is very efficient at picking up oxygen because: 1. The concentration of fetal hemoglobin is approx. 50% greater than maternal's hemoglobin 2. Fetal hemoglobin is different from maternal hemoglobin (i) It has a curve to the left of the mother's - can hold more O2 3. BPG has little effect on fetal hemoglobin 4. Movement of CO2 out of the fetal blood causes the fetal curve to shift to the left (i) Movement of CO2 into mother's blood causes her curve to shift to the right (ii) Double Bohr effect- mother's blood releases more oxygen and the fetal blood picks up more oxygen D. Transport of Carbon Dioxide: a) Transported in blood in 3 ways: 1) approx. 7% is dissolved in the plasma 2) approx. 23% is transported in combination with blood proteins 3) approx. 70% is transported in the form of bicarbonate ions b) Most abundant protein that CO2 binds to in the blood is hemoglobin c) Haldane effect- hemoglobin that has released its oxygen binds more readily to CO2 than hemoglobin that has O2 bound to it (I) Chloride Shift: 1. CO2 binds to hemoglobin, but most of it reacts with water inside the RBC's to form carbonic acid, a reaction catalyzed by carbonic anhydrase 2. Chloride shift- bicarbonate ion concentrations inside RBC's are lowered by exchanging them for chloride ions 3. Hemoglobin functions as a buffer and resists an increase in ph within the RBC's 4. In the lungs, the reverse occursi) CO2 in RBC's decrease; carbonic acid is converted to CO2 and water; bicarbonate ions join with hydrogen ions to form carbonic acid; as bicarbonate and hydrogen ions decrease, they are replaced; bicarbonate ions enter RBC's in exchange for chloride ions and hydrogen ions are released from hemoglobin (II) Carbon Dioxide and Blood ph: 1. Plasma CO2 levels increase, hydrogen ion levels increase and blood ph decreases 2. An important function of the respiratory system is to regulate blood ph by changing plasma CO2 levels 3. Hyperventilation decreases plasma CO2 (III) Rhythmic ventilation: 13

14 a) the generation of the basic rhythm of ventilation is controlled by neurons within the medulla oblongata that stimulate the muscles of respiration A. Respiratory areas in the Brainstem: 1. Meduallry respiratory center consists of 2 dorsal respiratory groups and 2 ventral respiratory groups a) Dorsal groups are primarily responsible for stimulating contraction of the diaphragm (inspiration) b) Ventral groups primarily stimulate the external intercostal, internal intercostal, and abdominal muscles (action during inspiration and expiration) 2. Pontine respiratory group (pneumotaxic center) in the pons; the precise function is unknown- not essential B. Generation of rhythmic ventilation: a) Exact locations of neurons responsible for rhythmic ventilation is unknown (IV) Modification of Ventilation: A. Cerebral and Limbic System Control: 1. Through the cerebral cortex, its possible to increase or decrease the rate and depth of the respiratory movements 2. Apnea- is the absence of breathing; increases urge to breath primarily associated with increasing PCO2 levels 3. Emotions acting through the limbic system of the brain call stimulate the respiratory center (hyperventilation) B. Chemical Control of Ventilation: (I) Chemoreceptors: (1) Are specialized neurons that respond to changes in chemicals in solution. a) Are responsible for responding to changes in hydrogen ion concentrations or changes in PO2 (2) Central chemorecptors are located bilaterally and ventrally in the chemoreceptive area of the medulla oblongata (3) Peripheral chemorecptors are in the carotid and aortic bodies a) Carotid body chemorecptors connected through the glossopharyngeal nerve (IX) and the aortic body chemorecptors by the vagus nerve (X) (II) Effect of ph: (1) The chemosensitive area is bathed by CSF and is sensitive to changes in the ph of the fluid (2) Blood-brain barrier separates the chemosensitive area from the blood; this area doesn't directly detect changes in blood ph (3) Because changes in CO2 levels can change ph, the respiratory system plays an important role in acid-base balance (III) Effect of Carbon Dioxide: 1. hypercapnia- is a greater-than-normal amount of CO2 in the blood 2. hypocapnia- is a lower than-normal amount of CO2 levels 3. CO2 doesn't directly affect the chemosensitive area- it exerts its effect by changing ph levels 4. Chemosensitive area in the medulla oblongata is more important than carotid and aortic bodies in the regulation of PCO2 and ph; carotid bodies respond more rapidly during intense exercise (IV) Effect of Oxygen: 1. PO2 can affect respiration, but PCO2 are responsible for most changes 2. Hypoxia- is a decrease in oxygen levels below normal valves 3. The carotid and aortic body chemorecptors respond to decreased PO2 by increasing stimulation C. Hering-Breuer Reflex: 1. Limits to degree to which inspiration proceeds and prevents over inflation of the lungs; it depends on 14

15 stretch receptors 2. The reflex in adults important only when the tidal volume is large (exercise); in infants plays a role in regulating basic rhythm of breathing and in preventing over inflation D. Effect of exercise on ventilation: a) Ventilation during exercise is divided into 2 phases: 1. Ventilation increases abruptly: (i) Ventilation may be learned 2. Ventilation increases gradually (i) Despite large changes in oxygen consumption and CO2 production during exercise, the average arterial PO2, PCO2, and ph remain constant and close to resisting levels as long as the exercise is aerobic. 3. The highest level of exercise that can be performed with out causing a significant change in blood ph is called anaerobic threshold E. Other modifications of ventilation: 1. The activation of touch, thermal, and pain receptors can also affect the respiratory center VIII. Respiratory adaptations to exercise: 1) Athletic performance increases because the cardiovascular and respiratory systems become more efficient Disorders of the Respiratory System: IX. Effects of aging on the respiratory system: 1. Almost all aspects of the respiratory system are affected by aging 2. Vital capacity, maximum ventilation rates, and gas exchange decrease with age, but the elderly can engage in light to moderate exercise because respiratory system has a large reserve capacity 3. Lung compliance increases with age, but it is offset by decreased thoracic cage compliance 4. Residual volume increases with age as the alveolar ducts and larger bronchioles increase in diameter 5. The elderly are more susceptible to respiratory infections and bronchitis because the mucus-cilia escalator is less able to move the mucus, move viscous, and cilia and rate of movement decrease 15