Respiratory Physiology PDF

 Alveoli  Structure of alveoli  Alveolar duct  Alveolar sac  Alveolus  Gas exchange Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Respiratory Membrane (Air-Blood Barrier)  Thin squamous epithelial layer lining alveolar walls  Pulmonary...

 Alveoli  Structure of alveoli  Alveolar duct  Alveolar sac  Alveolus  Gas exchange Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Respiratory Membrane (Air-Blood Barrier)  Thin squamous epithelial layer lining alveolar walls  Pulmonary capillaries cover external surfaces of alveoli Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Respiratory Membrane (Air-Blood Barrier) Figure 13.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Events of Respiration  Pulmonary ventilation – moving air in and out of the lungs  External respiration – gas exchange between pulmonary blood and alveoli Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Events of Respiration  Respiratory gas transport – transport of oxygen and carbon dioxide via the bloodstream  Internal respiration – gas exchange between blood and tissue cells in systemic capillaries Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Mechanics of Breathing (Pulmonary Ventilation)  Completely mechanical process  Depends on volume changes in the thoracic cavity  Volume changes lead to pressure changes, which lead to the flow of gases to equalize pressure Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Mechanics of Breathing (Pulmonary Ventilation)  Two phases  Inspiration – flow of air into lung  Expiration – air leaving lung Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Inspiration  Diaphragm and intercostal muscles contract  The size of the thoracic cavity increases  External air is pulled into the lungs due to an increase in intrapulmonary volume Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Inspiration Figure 13.7a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Exhalation  Largely a passive process which depends on natural lung elasticity  As muscles relax, air is pushed out of the lungs  Forced expiration can occur mostly by contracting internal intercostal muscles to depress the rib cage Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Exhalation Figure 13.7b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Pleural fluid produced by pleural membranes  Acts as lubricant  Helps hold parietal and visceral pleural membranes together  Movement of air into and out of lungs  Air moves from area of higher pressure to area of lower pressure  Pressure is inversely related to volume  Tidal volume  Volume of air inspired or expired during a normal inspiration or expiration  Inspiratory reserve volume  Amount of air inspired forcefully after inspiration of normal tidal volume  Expiratory reserve volume  Amount of air forcefully expired after expiration of normal tidal volume  Residual volume  Volume of air remaining in respiratory passages and lungs after the most forceful expiration  Inspiratory capacity  Tidal volume plus inspiratory reserve volume  Functional residual capacity  Expiratory reserve volume plus the residual volume  Vital capacity  Sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume  Total lung capacity  Sum of inspiratory and expiratory reserve volumes plus the tidal volume and residual volume  Minute ventilation: Total amount of air moved into and out of respiratory system per minute  Respiratory rate or frequency: Number of breaths taken per minute  Anatomic dead space: Part of respiratory system where gas exchange does not take place  Alveolar ventilation: How much air per minute enters the parts of the respiratory system in which gas exchange takes place  Oxygen  Carbon dioxide  Moves from alveoli into  Moves from tissues blood. Blood is almost into tissue capillaries completely saturated  Moves from pulmonary with oxygen when it leaves the capillary capillaries into the alveoli  P02 in blood decreases because of mixing with deoxygenated blood  Oxygen moves from tissue capillaries into the tissues  Oxygen is transported by hemoglobin (98.5%) and is dissolved in plasma (1.5%)  Oxygen-hemoglobin dissociation curve shows that hemoglobin is almost completely saturated when P02 is 80 mm Hg or above. At lower partial pressures, the hemoglobin releases oxygen.  A shift of the curve to the left because of an increase in pH, a decrease in carbon dioxide, or a decrease in temperature results in an increase in the ability of hemoglobin to hold oxygen  A shift of the curve to the right because of a decrease in pH, an increase in carbon dioxide, or an increase in temperature results in a decrease in the ability of hemoglobin to hold oxygen  The substance 2.3-bisphosphoglycerate increases the ability of hemoglobin to release oxygen  Fetal hemoglobin has a higher affinity for oxygen than does maternal  Carbon dioxide is transported as bicarbonate ions (70%) in combination with blood proteins (23%) and in solution with plasma (7%)  Hemoglobin that has released oxygen binds more readily to carbon dioxide than hemoglobin that has oxygen bound to it (Haldane effect)  In tissue capillaries, carbon dioxide combines with water inside RBCs to form carbonic acid which dissociates to form bicarbonate ions and hydrogen ions  In lung capillaries, bicarbonate ions and hydrogen ions move into RBCs and chloride ions move out. Bicarbonate ions combine with hydrogen ions to form carbonic acid. The carbonic acid is converted to carbon dioxide and water. The carbon dioxide diffuses out of the RBCs.  Increased plasma carbon dioxide lowers blood pH. The respiratory system regulates blood pH by regulating plasma carbon dioxide levels  Medullary respiratory center  Dorsal groups stimulate the diaphragm  Ventral groups stimulate the intercostal and abdominal muscles  Pontine (pneumotaxic) respiratory group  Involved with switching between inspiration and expiration  Starting inspiration  Medullary respiratory center neurons are continuously active  Center receives stimulation from receptors and simulation from parts of brain concerned with voluntary respiratory movements and emotion  Combined input from all sources causes action potentials to stimulate respiratory muscles  Increasing inspiration  More and more neurons are activated  Stopping inspiration  Neurons stimulating also responsible for stopping inspiration and receive input from pontine group and stretch receptors in lungs. Inhibitory neurons activated and relaxation of respiratory muscles results in expiration.  Cerebral and limbic  Chemical control system  Carbon dioxide is major regulator  Respiration can be ▪ Increase or decrease in pH voluntarily controlled can stimulate chemo- and modified by sensitive area, causing a emotions greater rate and depth of respiration  Oxygen levels in blood affect respiration when a 50% or greater decrease from normal levels exists  More oxygen is needed for working muscles When we exercise More carbon dioxide must be removed from muscles As a result : 1 the rate of breathing increase 2 the depth of breathing increase up to our vital capacity 3 the flow of blood through the lung increase (cardiac output increase) 4 the oxygen taken up and used by the body increase (metabolic reactions) Oxygen uptake during exercise can be up to twenty times a person’s normal oxygen uptake  The number of breaths taken in 1 minute. At rest, you breathe about 12-15 times each minute. It increases upto 40-45 breaths/minute. When you begin to exercise, the CO2 level in the blood increases, because CO2 is a waste product of energy production. This triggers the respiratory centre in your brain & you breathe faster Energy More oxygen Thus demand intake breathing increas increases required increased es  Detected by Signal the the brain to Higher Change in change the normal the conc. of receptors in breathing Tidal H+ , CO2 the blood depth to suit vessels the demand Volume TV Normal 500 breathing ML Exercise 1000 ML Athletes 2000 ML 3. Increase in Ventilation  Type of exercise Minute Ventilation (L/min) Rest 6 Slow Walking 20 Fast Walking 40 Prolonged Jogging 50 Fast Running 80 How does pulmonary ventilation (breathing) increase during ex 1.During light exercise (walking)? By increasing the tidal volume (Depth) 2.During steady state exercise (jogging)? By increasing both the tidal volume and the frequency of breathing( Depth + Rate) 3.During intense exercise (sprinting)? By increasing the frequency of breathing(Rate) Ventilation= Rate x Depth  Hyperventilation in exercise increases oxygen uptake in the lungs. This helps maintain arterial oxygenation. Maximal O₂ uptake = 20x ( Resting O₂ uptake) Body type VO₂ Moderately Active 35-40ml O₂ /min/kg body wt Strong Athlete 80-90ml O₂ /min/kg body wt 1. Increased 2. Alveolar to Increased arterial perfusion gradient of of pO₂ lungs VO₂ - index of functional 3. capacity of the Increased individual to Diffusion of sustain oxygen exercise across the resp. membrane  Amount of blood flow to the musclesincreases Oxygen release from that blood is also increases REST: 100 ml of arterial blood with 19.4 ml of oxygen= 5ml of oxygen to the tissues EXERCISE: 100ml of blood =15ml of oxygen to the tissues Therefore Oxygen utilisation increases to about 80%  O₂ DEFICIT After the exercise(severe), In the beginning of Amount of excess exercise, O ₂ oxygen consumed consumption < O ₂ during recovery demand phase. Therefore met by Cause: Lactic Acid anerobic pathway removal requires oxygen During strenuous exercise, there is a 3-fold increase in O2 diffusion from the alveoli to the blood because of a massive increase in blood flow to the lungs & dilation of the capillaries surrounding the alveoli. the oxygen The time The curve show how the blood speed increase when it enter the pulmonary capillaries But that requirement cardiac Additional blood remained in the doesn’t affect the saturation of O2 and the blood output capillaries pulmonary capillaries maintain normal PO2 increased 20 becomes less than half times increased open up normal Despite that, the blood is almost completely saturated with oxygen when it leaves the pulmonary capillaries! How? 1The diffusing capacity for oxygen increases almost three fold during exercise, this results mainly from increasing numbers of capillaries participating in the diffusion, and a more even V/Q ratio all over the lung. 2At rest the blood normally stays in the lung capillaries about three times as long as necessary to cause full oxygenation. Therefore, even with shortened time of exposure in exercise, the blood is still fully oxygenated or nearly so.  Normal oxygen consumption for a young man at rest is about 250 ml/min. under maximal conditions It could increase to approximately the Gasping for air after race to repay oxygen debt following average levels: Athletically Untrained average trained average Male marathon male male runner 3600 ml/min 4000 ml/min 5100 ml/min  LC= VC+RV INCREASED VITAL CAPACITY A greater quantity of air needed to Vital Capacity move in and out (VC) is the maximal volume of air that can be expired after maximal Lung Expansion occurs to meet inspiration in one the demand breath Mainly due to the increased strength of intercostal More expansion provides more efficient inhalation muscles. and expiration Diaphragm and intercostal muscles increase in strength Results in an improved ability to breathe in more air, for longer with less fatigue. Aerobic training tends to improve-- the endurance of respiratory muscles Anaerobic training tends to increase --the size and strength of   Increase in the number and size of capillaries leads to more efficient diffusion: Tissues More More Blood Blood Tissues O2 CO2 Therefore, regular training leads to better transportation of O2/CO2 Increase in oxygen diffusion rate  Much higher exercise Due to improved O2 intensities can therefore The athlete can delivery & utilization, a higher lactate be reached and LA and work harder for threshold is longer developed. H+ ion accumulation is delayed.