Physiology of Respiratory System PDF

RNB10603 BASIC ANATOMY AND PHYSIOLOGY 1 RESPIRATORY SYSTEM RESPIRATORY SYSTEM RNB10603  Learning Outcomes At the end of this session, students should be able to: ▪ describe the lung volumes and capacities of respiratory system ▪ explain the pulmonary vent...

RNB10603 BASIC ANATOMY AND PHYSIOLOGY 1 RESPIRATORY SYSTEM RESPIRATORY SYSTEM RNB10603  Learning Outcomes At the end of this session, students should be able to: ▪ describe the lung volumes and capacities of respiratory system ▪ explain the pulmonary ventilation in respiratory system ▪ explain the external and internal respiration ▪ describe the transport of respiratory gases ▪ explain the control of respiration  Lung Volumes And Capacities ❑A healthy adult breath about 12 times a minute with each inhalation and exhalation moving about 500 mL of air into and out of lungs ❑Measurement of lung volumes provides a tool for understanding normal function of the lungs as well as disease states ❑ In normal breathing at rest, approximately one- tenth of the total lung capacity is used. Greater amounts are used as needed (i.e., with exercise).  Lung Volumes And Capacities The following terms are used to describe lung volumes : ❑Tidal volume (TV) ❑Inspiratory reserve volume (IRV) Volume ❑Expiratory reserve volume (ERV) ❑Residual volume (RV) ❑Total Lung Capacity(TLC) ❑Vital capacity (VC). Capacity ❑Functional residual capacity (FRC) ❑Inspiratory capacity (IC) Lung Volumes And Capacities ❑Tidal Volume (TV) ❖The amount of gas inspired or expired with each normal breath. ❖About 500 ml Lung Volumes And Capacities ❑Inspiratory Reserve Volume (IRV) ❖ Maximum amount of additional air that can be inspired from the end of a normal inspiration Lung Volumes And Capacities ❑Expiratory Reserve Volume (ERV) ❖The maximum volume of additional air that can be expired from the end of a normal expiration. Lung Volumes And Capacities ❑Residual Volume (RV) ❖The volume of air remaining in the lung after a maximal expiration. Lung Volumes And Capacities ❑Total Lung Capacity(TLC) ❖The volume of air contained in the lungs at the end of a maximal inspiration. ❖Called a capacity because it is the sum of the 4 basic lung volumes ❖TLC= RV+IRV+TV+ERV Lung Volumes And Capacities ❑Vital Capacity (VC) ❖The maximum volume of air that can be forcefully expelled from the lungs following a maximal inspiration. ❖Called a capacity because it is the sum of inspiratory reserve volume, tidal volume and expiratory reserve volume. ❖VC= IRV+TV+ERV = TLC - RV Lung Volumes And Capacities ❑Functional residual capacity (FRC) ❖The volume of air remaining in the lung at the end of a normal expiration. ❖Called a capacity because it equal residual volume plus expiratory reserve volume. ❖FRC= RV+ERV Lung Volumes And Capacities ❑Inspiratory Capacity (IC) ❖Maximum volume of air that can be inspired from end expiratory position. ❖Called a capacity because it is the sum of tidal volume and inspiratory reserve volume. ❖This capacity is of less clinical significance than the other three. ❖IC= TV+IRV Lung Volumes And Capacities  Understanding Gases To understand how this mechanical coupling between the lungs, the pleural cavities and the chest wall results in breathing, we first need to discuss some physics of gases called the gas laws.  Understanding Gases The respiratory system depends on the medium of the earth’s atmosphere to extract the oxygen necessary for life. The atmosphere is composed of these gases: – Nitrogen (N2) 78% – Oxygen (O2) 21% – Carbon Dioxide (CO2) 0.04% – Water Vapor variable, but on average around 1%  Understanding Gases Gases obey laws of physics called the gas laws. – These laws apply equally to the gases of the atmosphere, the gases in our lungs, the gases dissolved in the blood, and the gases diffusing into and out of the cells of our body. – To understand the mechanics of ventilation and respiration, we need to have a basic understanding of 4 common gas laws.  Understanding Gases Boyle’s law applies to containers with flexible walls – like our thoracic cage. – It says that volume and pressure are inversely related. If there is a decrease in volume – there will be an increase in pressure. V ∝ 1/P  Understanding Gases ❑Henry's law: quantity of gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility ❑Charles' law: as temperature increases the pressure increases therefore as temperature decreases the pressure decreases ❑Dalton's law: each gas in a mixture of gases exerts its own pressure as if no other gases were present.  Gases Exchange Gas Exchange  Understanding Gases ❑Gas will always move from a region of high pressure to a region of low pressure. Applying Boyle's law: If the volume inside the thoracic cavity , the pressure .  Pulmonary Ventilation Mechanics of Breathing What is breathing / ventilation? A process of moving air in and out of the lungs There are 2 phases: i) Inspiration/inhalation –air in to lungs ii) Expiration/exhalation – air out of lungs Air movement is due to changes in the volume of the thorax, which influence the air pressure in the lungs  Pulmonary Ventilation ❑Cycle of Breathing 3 phases are involved: ▪ inspiration ▪ expiration ▪ pause  Ventilation and Respiration Pulmonary ventilation is the movement of air between the atmosphere and the alveoli, and consists of inhalation and exhalation. – Ventilation, or breathing, is made possible by changes in the intrathoracic volume.  Pulmonary Ventilation ❑ Inspiration / Inhalation External intercostals muscles contract during inspiration Diaphragm contracts (downwards and flattens) This pulls the rib cage upwards and outwards These actions cause the thoracic cavity size to increase This decreases the pressure inside the thoracic cavity Gases move from areas of high pressure to low pressure areas Therefore oxygen moves from the atmosphere (higher pressure) into the lungs (now low in pressure) During exercise, a more forceful inspiration is required so extra muscles are involved in this process – sternocleidomastoid and pectoralis minor  Pulmonary Ventilation ❑ Expiration/ Exhalation Usually a passive process As the intercostals muscles relax the rib cage moves downwards The diaphragm relaxes and returns to its dome shape This decreases the size of the thoracic cavity This causes the pressure to increase in the thoracic cavity (smaller volume) Therefore gases move out of the lungs (high pressure) into the atmosphere (lower pressure) During exercise breathing rate is increased, expiration is aided by the internal intercostal muscles and the abdominal muscles, This pulls the rib cage down more quickly and with greater force  Pulmonary Ventilation Inpiration Expiration Pulmonary Ventilation  Pulmonary Ventilation ❑Muscles of Respiration ❖Inspiratory muscles – Diaphragm. – External intercostals. – Accessory muscles. Include sternomastoids, scalene muscles ❖Expiratory muscles – Abdominal muscles. – Internal intercostals.  Pulmonary Respiration Also called external respiration Exchange of oxygen (O2) and carbon dioxide (CO2) between the alveoli of the lungs and pulmonary blood capillaries Deoxygenated blood from the heart is converted into oxygenated blood returning to the heart  Pulmonary Respiration ❑External Respiration Pulmonary Respiration Gas Exchange During Respiration 35  Tissue Respiration Also called internal respiration Exchange of oxygen (O2) and carbon dioxide (CO2) between blood in the capillaries and the body cells. Blood arriving at the tissues has been cleansed of its CO2 and saturated with O2 Tissue Respiration Pulmonary And Tissue Respiration Pulmonary And Tissue Respiration Movement of Oxygen and Carbon Dioxide 40  Transport Of Respiratory Gases ❑Blood transport gases between lung and body tissue ❑Oxygen and carbon dioxide in the blood will have physical and chemical changes throughout the transport and exchange.  Transport Of Respiratory Gases ❑Oxygen Transport Molecular oxygen is carried in the blood: ❖Bound to hemoglobin (Hb) within red blood cells (98.5%) ❖Dissolved in plasma(1.5%)  Transport Of Respiratory Gases ❑Oxygen Transport Each Hb molecule binds four oxygen atoms in a rapid and reversible process The hemoglobin-oxygen combination is called oxyhemoglobin (HbO2) Hemoglobin that has released oxygen is called reduced hemoglobin (HHb) Lungs HHb + O2 HbO2 + H+ Tissues  Transport Of Respiratory Gases ❑Oxygen Transport When blood Po₂ is high, hemoglobin binds with large amount of O₂ and it is saturated When blood Po₂ is low, hemoglobin releases O₂ Systemic capillaries has low Po₂ Hemoglobin release oxygen Oxygen diffuse from blood plasma to interstitial fluid and to tissue cells  Transport Of Respiratory Gases ❑Other factors influence the amount of oxygen release by hemoglobin Carbon dioxide ❖Pco₂ rises in any tissue ,hemoglogin release more O₂ into the blood flow (muscular tissues during exercise ) Acidity ❖Acidic environment ,hemoglobin release more O₂ into the blood flow. During exercise ,muscles produce lactic acid which promote release of O₂  Transport Of Respiratory Gases ❑Other factors influence the amount of oxygen release by hemoglobin Temperature ❖Temperature increase the release of O₂ from hemoglobin.Active tissues produce more heat, which elevates the local temperature and promotes release of O₂  Transport Of Respiratory Gases ❑Carbon Dioxide Transport Carbon dioxide is transported in the blood in three forms ❖Dissolved in plasma – 7 to 10% ❖Chemically bound to hemoglobin – 20% is carried in RBCs as carbaminohemoglobin ❖Bicarbonate ion in plasma – 70% is transported as bicarbonate (HCO3–) + - CO2 + H2O H2CO3 H + HCO3  Transport Of Respiratory Gases ❑Carbon Dioxide Transport Carbon dioxide diffuses into RBCs and combines with water to form carbonic acid (H2CO3), which quickly dissociates into hydrogen ions and bicarbonate ions CO2 + H2O  H2CO3  H+ + HCO3– Carbon Carbonic Hydrogen Bicarbonate Water dioxide acid ion ion In RBCs, carbonic anhydrase reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid Transport and Exchange of Carbon Dioxide  Transport Of Respiratory Gasses ❑Carbon Dioxide Transport At the tissues: ❖Bicarbonate quickly diffuses from RBCs into the plasma ❖The chloride shift – to counterbalance the outrush of negative bicarbonate ions from the RBCs, chloride ions (Cl–) move from the plasma into the erythrocytes  Transport Of Respiratory Gasses ❑Carbon Dioxide Transport At the lungs, these processes are reversed ❖Bicarbonate ions move into the RBCs and bind with hydrogen ions to form carbonic acid ❖Carbonic acid is then split by carbonic anhydrase to release carbon dioxide and water ❖Carbon dioxide then diffuses from the blood into the alveoli Transport and Exchange of Carbon Dioxide  Control of Respiration ❑Regulation of breathing Voluntary – Somatic motor neurons controlled by centers in medulla oblongata and pons Involuntary – Feedback from receptors that detect changes in blood chemistry Control of Respiration  Control of Respiration The medulla rhythmicity area, located in the brainstem, has centers that control basic respiratory patterns for both inspiration and expiration. – The inspiratory center stimulates the diaphragm via the phrenic nerve, and the external intercostal nerve  Control of Respiration Exhalation is mostly a passive process, caused by the elastic recoil of the lungs. Usually, the expiratory center is inactive during quiet breathing (nerve impulses cease for about 3 sec). – During forced exhalation, however, impulses from this center stimulate the internal intercostal and abdominal muscles to contract.  Control of Respiration ❑Medullary Rhythmicity Area ❖Medullary Inspiratory Neurons are main control of breathing Pons neurons influence inspiration, with Pneumotaxic area limiting inspiration and Apneustic area prolonging inspiration. The apneustic center in the pons increases the depth and duration of inspiration, whereas the pneumotaxic center decreases depth and duration. Lung stretch receptors limit inspiration from being too deep  Control of Respiration Groups of neurons in the brainstem comprise the respiratory areas that control breathing Impulses travel on cranial nerves and spinal nerves, causing inspiration and expiration Respiratory area also adjust the rate and depth of breathing The respiratory areas include ❖respiratory center of the medulla ❖respiratory group of the pons  Control of Respiration Medullary Respiratory Center ❑The dorsal respiratory group (DRG), or inspiratory center: ❖Is located near the root of nerve IX ❖Appears to be the pacesetting respiratory center ❖Excites the inspiratory muscles and sets eupnea (12-15 breaths/minute) ❖Becomes dormant during expiration ❑The ventral respiratory group (VRG) is involved in forced inspiration and expiration  Control of Respiration Pon Respiratory Centers ❑Pons centers: ❖Influence and modify activity of the medullary centers ❖Smooth out inspiration and expiration transitions and vice versa ❑The pontine respiratory group (PRG) – continuously inhibits the inspiration center Control of Respiration  Control of Respiration Medullary Respiratory Center  Control of Respiration Respiratory Rhythm ❑A result of reciprocal inhibition of the interconnected neuronal networks in the medulla ❑Other theories include ❖Inspiratory neurons are pacemakers and have intrinsic automaticity and rhythmicity ❖Stretch receptors in the lungs establish respiratory rhythm  Control of Respiration Depth and Rate of Breathing Inspiratory depth is determined by how actively the respiratory center stimulates the respiratory muscles Rate of respiration is determined by how long the inspiratory center is active Respiratory centers in the pons and medulla are sensitive to both excitatory and inhibitory stimuli  Control of Respiration Depth and Rate of Breathing :Reflexes Pulmonary irritant reflexes – irritants promote reflexive constriction of air passages Inflation reflex (Hering-Breuer) – stretch receptors in the lungs are stimulated by lung inflation Upon inflation, inhibitory signals are sent to the medullary inspiration center to end inhalation and allow expiration  Control of Respiration Medullary Respiratory Center Control of Respiration  Control of Respiration Depth and Rate of Breathing :Higher Brain Center Hypothalamic controls act through the limbic system to modify rate and depth of respiration Example: breath holding that occurs in anger A rise in body temperature acts to increase respiratory rate Cortical controls are direct signals from the cerebral motor cortex that bypass medullary controls Examples: voluntary breath holding, taking a deep breath  Control of Respiration Depth and Rate of Breathing :Pco₂ Changing PCO2 levels are monitored by chemoreceptors of the brain stem Carbon dioxide in the blood diffuses into the cerebrospinal fluid where it is hydrated Resulting carbonic acid dissociates, releasing hydrogen ions( Respiratory Acidosis) PCO2 levels rise (hypercapnia) resulting in increased depth and rate of breathing  Control of Respiration Depth and Rate of Breathing :Pco₂ Hyperventilation – increased depth and rate of breathing that: ❖Quickly flushes carbon dioxide from the blood ❖Occurs in response to hypercapnia  Control of Respiration Depth and Rate of Breathing :Pco₂ Arterial oxygen levels are monitored by the aortic and carotid bodies Substantial drops in arterial PO2 (to 60 mm Hg) are needed before oxygen levels become a major stimulus for increased ventilation  Control of Respiration Depth and Rate of Breathing :Pco₂  Control of Respiration Depth and Rate of Breathing :Arterial pH Changes in arterial pH can modify respiratory rate even if carbon dioxide and oxygen levels are normal Increased ventilation in response to falling pH is mediated by peripheral chemoreceptors  Control of Respiration Depth and Rate of Breathing :Arterial pH ( pH )  Control of Respiration Depth and Rate of Breathing :Arterial pH and Pco₂ Control of Respiration