HSF Respiratory System Physiology 2025 PDF

Physiology of Respiratory System Assoc. Prof. Dr. Radiah Abdul Ghani Department of Biomedical Science Kulliyyah of Allied Health Sciences 1  Learning Outlines  To describe the importance of respiratory system.  To state the gas laws.  To explain the...

Physiology of Respiratory System Assoc. Prof. Dr. Radiah Abdul Ghani Department of Biomedical Science Kulliyyah of Allied Health Sciences 1  Learning Outlines  To describe the importance of respiratory system.  To state the gas laws.  To explain the process of ventilation.  To describe the gas exchange in the lungs, and in the tissues.  To explain the gas transport in the blood.  To identify the regulation factors of ventilation.  To describe the pulmonary function test.  To relate the system with the routine in our life.  To realize the Greatness of Allah S.W.T 2  Breathing – why bother?  Exchange of gases between atmosphere and blood.  Homeostatic regulation of body pH.  Protection from inhaled pathogens and irritating substances.  Vocalisation 3  2 Types of breathing  Cellular respiration - Intracellular reaction. - Oxygen + organic molecules =➔ CO2 + H2O + ATP  External respiration - Interchange of gases between environment and the body’s cells. 4  External respiration Internal respiration 5 6  External respiration  External respiration describes the exchange of gasses between the external environment and the bloodstream.  The components of external respiration include alveolar surface area, ventilation and perfusion matching, and partial pressure gradients.  Partial pressure gradients allow gasses to flow from areas of high pressure to areas of lower pressure. 7  Internal Respiration  Internal respiration is known as cellular respiration and is the chemical process by which glucose is broken down and energy (ATP) produced.  Most living organisms need aerobic respiration in order to produce enough energy to survive, and thus require the oxygen that enters the body by external respiration. 8 9 The Lungs and Breathing The space between the outer surface of the lungs and inner thoracic wall is known as the pleural space. This is usually filled with pleural fluid, forming a seal which holds the lungs against the thoracic wall by the force of surface tension. This seal ensures that when the thoracic cavity expands or reduces, the lungs undergo expansion or reduction in size 10 accordingly.  Mechanics of Breathing  The mechanics of breathing air moves in and out of the lungs in response to differences in pressure.  When the air pressure within the alveolar spaces falls below atmospheric pressure, air enters the lungs ( inspiration ), provided the larynx is open;  when the air pressure within the alveoli exceeds atmospheric pressure, air is blown from the lungs ( expiration ). 11 Muscle of Breathing 12 Mechanics of Breathing – Focus on Diaphragm 13 Mechanics of Breathing – Focus on intercostal 14  Volume and pressure  During breathing, the contraction and relaxation of muscles acts to change the volume of the thoracic cavity. As the thoracic cavity and lungs move together, this changes the volume of the lungs, in turn changing the pressure inside the lungs. 15  Boyle’s Law  Boyle’s law states that the volume of gas is inversely proportional to pressure (when temperature is constant). Therefore:  When the volume of the thoracic cavity increases – the volume of the lungs increases and the pressure within the lungs decreases.  When the volume of the thoracic cavity decreases – the volume of the lungs decreases and the pressure within the lungs increases. 16 17  Gases movement  Occurs whenever there is pressure gradient.  Higher to lower pressure.  Solubility of a gas in a liquid depends on the pressure of the gas.  Boyle’s Law : Gas pressure in closed container is inversely proportional to volume of container 18  Inspiration  Inspiration is the phase of ventilation in which air enters the lungs. It is initiated by contraction of the inspiratory muscles:  Diaphragm – flattens, extending the superior/inferior dimension of the thoracic cavity.  External intercostal muscles – elevates the ribs and sternum, extending the anterior/posterior dimension of the thoracic cavity.  The action of the inspiratory muscles results in an increase in the volume of the thoracic cavity. As the lungs are held against the inner thoracic wall by the pleural seal, they also undergo 19 an increase in volume.  As per Boyle’s law, an increase in lung volume results in a decrease in the pressure within the lungs. The pressure of the environment external to the lungs is now greater than the environment within the lungs, meaning air moves 20 into the lungs down the pressure gradient.  Process of expiration  Expiration is the phase of ventilation in which air is expelled from the lungs. It is initiated by relaxation of the inspiratory muscles:  Diaphragm – relaxes to return to its resting position, reducing the superior/inferior dimension of the thoracic cavity.  External intercostal muscles – relax to depress the ribs and sternum, reducing the anterior/posterior dimension of the thoracic cavity.  The relaxation of the inspiratory muscles results in a decrease in the volume of the thoracic cavity. The elastic recoil of the previously 21 expanded lung tissue allows them to return to their original size.  As per Boyle’s law, a decrease in lung volume results in an increase in the pressure within the lungs. The pressure inside the lungs is now 22 greater than in the external environment, meaning air moves out of the lungs down the pressure gradient. 23  Force Breathing  Forced breathing involves active inspiratory and expiratory movements. During forced breathing, the accessory muscles assist with inhalation. Exhalation involves contraction of the internal intercostal muscles. The abdominal muscles are involved during the maximum levels of forced breathing. 24 25 Determinants of Airway Resistance 26  Ventilation  Upper airways – more than serve as passageway. - Warming air to 37 C. - Adding water vapour until air reaches 100% humidity. - Filtering out foreign material – mucus secreted by goblet cells..contains immunoglobulin. Can you reach all these criteria if breathing through mouth? 27  Ventilation  Function of mucus: - Traps most inhaled particles. - Its layer continuously move towards pharynx by the upward beating of cilia – mucus escalator. - When mucus reach pharynx, will be swallowed, acid and enzymes in stomach will kill the remaining bacteria. - Secretion of watery layer beneath the mucus – crucial. What happen if there is no watery layer? 28  Blood Flow rate and pressure in lungs  Rate of blood flow is high compared to other tissue.  Blood pressure is low. Why?  The net hydraulic pressure is also low.  Filtered fluid remove by lymphatic system. 29  Ohm’s law usually refers to electrical circuits, in which current = voltage/resistance. However, it can be applied to describe the relationship between airflow, pressure gradient and resistance.  The equation is:  Flow = Pressure gradient / Resistance  This demonstrates that as resistance increases, the pressure gradient must also increase to maintain the same rate of into the alveoli. 30  Clinical relevant: Athsma In an asthma exacerbation, the already narrowed airways (due to mucosal inflammation and smooth muscle hypertrophy) are further constricted due to increased smooth muscle tone. This can decrease the diameter of the airways significantly, causing resistance to airflow to become very high. This means the patient must work harder to overcome the increased resistance. This can lead to turbulent flow, causing the characteristic wheeze of an asthma attack. 31 Gas Exchange 32  What is it?  Gas exchange is the process by which oxygen and carbon dioxide move between the bloodstream and the lungs. This is the primary function of the respiratory system and is essential for ensuring a constant supply of oxygen to tissues, as well as removing carbon dioxide to prevent its accumulation. 33 34 Gas Exchange - Single layer thin exchange epithelium. - Type I & II alveolar 35 cells - Intimate with CV shown here. Gas exchange in the lungs: Alveoli to Red Blood Cell The diffusion of gases between the alveoli and the blood obeys the rules for simple diffusion 36 Surfactant decreases the work of breathing Detergent like fluid produced by Type II Alveolar cells Reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse Increases lung compliance (distensibilty) Reduces lung’s tendency to recoil Makes work of breathing easier Is more effective in small alveoli than large 37 38 39  Surface Tension  Lung collapse  Need to be compliance – ability to stretch.  Surface tension tends to oppose alveoli expansion  Pulmonary surfactant reduces surface tension and decrease the work/force of breathing.  Begins to synthesize at 25 weeks and completed at 32 weeks. - Newborn respiratory disease syndrome. 40 41 Diffusion Barrier Alveolar epithelium Tissue fluid Capillary endothelium Plasma Red cell membrane 42  Factors that Affect the Rate of Diffusion  Membrane thickness – the thinner the membrane, the faster the rate of diffusion. The diffusion barrier in the lungs is extremely thin , however some conditions cause thickening of the barrier, thereby impairing diffusion.  Diffusion will take more time and gas exchange is inhibited.  Eg: Fluid in the interstitial space (pulmonary oedema).  Eg: Thickening of the alveolar membrane (pulmonary fibrosis). 43 44  Membrane surface area – the larger the surface area, the faster the rate of diffusion. The lungs normally have a very large surface area for gas exchange due to the alveoli.  Diseases such as emphysema lead to the destruction of the alveolar architecture, leading to the formation of large air-filled spaces known as bullae. This reduces the surface area available and slows the rate of gas exchange.  Pressure difference across the membrane  Diffusion coefficient of the gas 45 Gas exchange in the alveoli & cells 46  Oxygen Transport in the blood  Either dissolve in plasma  Amount of O2 that binds (1.5%)or within RBC (98.5%)= to Hb depends on: total blood O2 content. - PO2 of plasma  Low solubility of O2 in aqueous surrounding RBC solution, only 3 ml of O2 - Number of potential dissolve in 1 litre of blood. binding site for O2 on  Heavily dependent to Hb. RBC. 47  Carbon dioxide transport When CO2 molecules diffuse from the tissues into the blood, 7% remains dissolved in plasma and erythrocytes, 23% combines in the erythrocytes with deoxyhemoglobin to form carbamino compounds, and 70% combines in the erythrocytes with water to form carbonic acid, which then dissociates to yield bicarbonate and H+ ions. Most of the bicarbonate then moves out of the erythrocytes into the plasma in exchange for Cl- ions & the excess H+ ions bind to deoxyhemoglobin. The reverse occurs in48 the pulmonary capillaries and CO2 moves down its concentration gradient from blood to alveoli. Ventilation Perfussion Matching Ensuring that the ventilation and perfusion of the lungs are adequately matched is vital for ensuring continuous delivery of oxygen and removal of carbon dioxide from the body. 49 Ventilation-Perfusion Relationship Ventilation (air getting to alveoli) Ideally match (compliment) each other Perfusion (local blood flow) 50 Local control of ventilation & perfusion Ventilation in the alveoli is matched to perfusion through pulmonary capillaries. If ventilation decreases in a group of alveoli, PCO2 increases and PO2 decreases. Blood flowing past these alveoli does not get oxygenated. Decreased tissue PO2 around under-ventilated alveoli constricts their arteries and diverts blood to better ventilated alveoli. (Constriction in response to hypoxia is particular to pulmonary vessels due to presence of special enzyme)51 Regulation of Respiration 52 53 54 Phrenic nerve paralysis Phrenic nerve paralysis is where damage to the phrenic nerve results in its dysfunction. This can cause paralysis of the diaphragm, hence breathing problems and inability of patients to regulate their own breathing. Common causes include: spinal cord injury, neck injury and surgical complications. 55 56 57 Control of ventilation: Peripheral Chemoreceptors Carotid and aortic bodies Detect changes in arterial PO2 and [H+] Cause reflex stimulation of ventilation following significant fall in arterial PO2 (consider haemoglobin dissociation) or a rise in [H+] Respond to arterial PO2 not oxygen content Increased [H+] usually accompanies a rise in arterial PCO2 CO2 + H2O  H2CO3  H2CO3- + H+ 58 Transduction mechanism How do you know your lungs are healthy? 59  Pulmonary Function Test  Using a spirometer- measures the volume of air moving with each breath.  Lung Volume divide by: - Tidal volume: the volume of air move in single inspiration or expiration. Average 500 ml.vary with age, sex and height of individu. - Inspiratory reserve volume- additional volume that inspire above tidal volume.(2500 ml). - Expiratory reserve volume – amount of air exhale after the end of inspiration. (1000 ml) - Residual volume- cannot be measured directly.the volume of air remain in respiratory system after maximal exhalation. 60 Lung Volumes & capacities 61 62  Lung Capacities  Capacities - Sum of the two or more volumes. - Represents the maximum of air that can be voluntarily move in and out in one breath. - Vital capacity (VC) = IRV + ERV+ TV - VC + Residual volume = Total Lung capacity (TLC) 63 64 Term Definition Lung Volumes The four nonoverlapping components of the total lung capacity Tidal volume The volume of gas inspired or expired in an unforced respiratory cycle Inspiratory reserve volume The maximum volume of gas that can be inspired during forced breathing in addition to tidal volume Expiratory reserve volume The maximum volume of gas that can be expired during forced breathing in addition to tidal volume Residual volume The volume of gas remaining in the lungs after a maximum expiration Lung Capacities Measurements that are the sum of two or more lung volumes Total lung capacity The total amount of gas in the lungs after a maximum inspiration Vital capacity The maximum amount of gas that can be expired after a maximum inspiration Inspiratory capacity The maximum amount of gas that can be inspired after a normal tidal expiration Functional residual capacity The amount of gas remaining in the lungs after a normal tidal expiration 65 66 End of Lecture 67