Respiratory physiology 2023(1).pptx

OFFICI AL An introduction to the respiratory system Physiology OFFICI AL Lesson Objectives By the end of the lesson, students will be able to: State Boyles law State Daltons law Identify how these laws relate to respiration Describe the chemical and neurological control of respiration Describe the m...

OFFICI AL An introduction to the respiratory system Physiology OFFICI AL Lesson Objectives By the end of the lesson, students will be able to: State Boyles law State Daltons law Identify how these laws relate to respiration Describe the chemical and neurological control of respiration Describe the mechanical control of respiration Understand the normal parameters relating to the partial pressure of each gas Discuss the oxyhaemoglobin dissociation curve OFFICI AL Introduction Respiration’ is a term that refers to the utilisation of oxygen The actual oxygen requirement of individual tissues varies according to their energy needs. For example, cardiac muscle is very active and uses about 30 times as much oxygen per minute than does the relatively inactive skin. Maintaining an adequate supply of oxygen therefore is essential to the metabolic homeostasis of cells and tissues. Tissue oxygenation occurs through four stages: 1 Oxygen is taken in from the air by blood. 2 Oxygen is carried by the blood. 3 Tissues receive adequate perfusion with blood. 4 Oxygen passes from the blood to cells. OFFICI AL Key Terms Hypoxia : a lack of oxygenation in tissues Hypoxaemia : poor oxygenation of arterial blood (‘-aemia’ = of blood). However, hypoxaemia will induce hypoxia and so this latter term tends to be more widely used, even if the problem stems from poor blood oxygenation; Hypercapnia : excess carbon dioxide in arterial blood. The production of carbonic acid when carbon dioxide combines with water means that hypercapnia is often associated with increased acidity (acidosis) Hypocapnia : deficiency of carbon dioxide in arterial blood. The lack of this important source of acidity means that hypocapnia is often associated with excessive OFFICI AL Carbon Dioxide Carbon dioxide excretion entails more or less the opposite sequence of events from those identified above for oxygen: 1 Uptake of carbon dioxide by blood from cells. 2 Transportation of carbon dioxide by blood. 3 Transfer of carbon dioxide from blood to the air. OFFICI AL Respiration: a general term relating to oxygen uptake and utilisation. Internal respiration: the biochemical reactions taking place within cells that consume oxygen and produce carbon dioxide. External respiration: the processes occurring within the lungs in taking up oxygen from air and releasing carbon dioxide into it. Inspiration: the process of breathing in. Expiration: the process of breathing out. OFFICI AL \ Apnoea: this term refers to cessation of breathing, or breathing that is ineffectual in oxygenating blood. Asphyxia: a physical means, such as choking, that prevents breathing from occurring, leading to anoxia. Dyspnoea: strictly speaking, this term refers to an inadequate ventilation of the lungs. It is similar therefore to the term hypoventilation but it is more widely used in the context of difficulty in breathing (uncomfortable, laboured, even painful) since this more satisfactorily relates the problem to the patient’s experience and to the nurse’s observation. General principles OFFICI AL At rest an adult breathes in about 500 mL of air (7– 8 mL/kg body weight) with each breath. This is referred to as the tidal volume. With a normal breathing rate at rest of about 10– 12 breaths/minute, this means about 5– 6 L of air are breathed in (and out) each minute. This is sufficient to meet the needs of cells of the body at rest, which use about 250 mL of oxygen per minute. Dead space OFFICI AL In normal quiet breathing there are about 15 complete respiratory cycles per minute. The lungs and the air passages are never empty and, as the exchange of gases takes place only across the walls of the alveolar ducts and alveoli, the remaining capacity of the respiratory passages is called the anatomical dead space (about 150 mL). OFFICI AL OFFICI AL OFFICI AL OFFICI AL Key terms spiratory reserve volume piratory reserve volume (IRV) is the extra volume of air that can be inhaled o the lungs during maximal inspiration, i.e. over and above normal TV. spiratory capacity piratory capacity (IC) is the amount of air that can be inspired with maximum effort. onsists of the tidal volume (500 mL) plus the inspiratory reserve volume. OFFICI AL Key terms esidual volume esidual volume (RV) cannot be directly measured but is the olume of air remaining in the lungs after forced expiration. olar ventilation s the volume of air that moves into and out of the alveoli per minute. qual to the tidal volume minus the anatomical dead space, multiplied e respiratory rate: General principles OFFICI AL Uptake of oxygen into blood, and removal of carbon dioxide from it, takes place by simple diffusion, and so is based on the respective concentration gradients of the gases in the alveoli and dissolved in blood. The air we breathe in is composed of approximately 21% oxygen and only 0.03% (physiologically, this effectively is 0) carbon dioxide. The remaining proportion (approximately 79%) is almost entirely nitrogen. OFFICI AL Inspiration and expiration Breathing movements are referred to as inspiration (breathing in) and expiration (breathing out). Inspiration requires inflation of the lungs, expiration requires deflation. Although this appears a simple process, inflation or deflation can only occur if the appropriate air pressure gradients are generated which will move gases in and out of the lungs Inspiration OFFICI AL If the volume of a container is increased then the pressure of gas within it will decrease. Lung inflation works on this principle, and occurs because the thoracic cavity is expanded, literally sucking air into the airways down the pressure gradient that is generated. OFFICI AL Boyle’s law OFFICI AL https://www.youtube.com/watch? v=RcLnzU6Pk_Q Inspiration OFFICI AL Expansion of the cavity is achieved by: contraction of external intercostal (‘inter-‘ = between; ‘-costal’ = rib) muscles, which raise the rib cage upwards and outwards; Contraction of the muscular diaphragm, which flattens the ‘dome’ of this muscle sheet Expansion of the thoracic cavity lowers the pressure within the lung. OFFICI AL Expiration OFFICI AL In contrast to the active, muscle-involving process of inspiration, expiration at rest is passive and utilises the natural elasticity of the lungs and chest wall. Thus, when inspiration stops, and the inspiratory muscles relax, the lungs simply recoil like a piece of stretched elastic, and so expel the gases. OFFICI AL OFFICI AL OFFICI AL OFFICI AL OFFICI AL Lying in the alveolar wall between the squamous cells are septal cells that secrete surfactant, a phospholipid fluid that stops the alveoli drying out and reduces surface tension, preventing alveolar collapse during expiration. OFFICI AL OFFICI AL External Respiration: This happens in the lungs. It's the process where oxygen from the air we breathe moves into the bloodstream, and carbon dioxide from the bloodstream moves into the air in the lungs. So, during external respiration, oxygen goes into our body, and carbon dioxide leaves our body through breathing. Internal Respiration: This occurs in the body's tissues. It's the process where oxygen from the bloodstream moves into the cells of the body, and carbon dioxide produced by the cells moves into the bloodstream. So, in internal respiration, oxygen is delivered from our blood to our body's cells, and carbon dioxide made by the cells is taken away by the blood to be eventually breathed out. OFFICI AL V/Q OFFICI AL In respiration, V/Q stands for ventilation-perfusion ratio. It's a measure that compares two important aspects: Ventilation (V): This refers to the amount of air reaching the alveoli (tiny air sacs in the lungs) where gas exchange occurs. It's about how much fresh air gets to the parts of the lungs where oxygen and carbon dioxide are exchanged. Perfusion (Q): This represents the blood flow through the capillaries surrounding the alveoli. It's about how well blood circulates through the lungs and picks up oxygen while releasing carbon dioxide. The V/Q ratio essentially tells us if the amount of air getting to the alveoli (ventilation) matches the blood flow around these same areas (perfusion). A balanced V/Q ratio ensures efficient gas OFFICI AL OFFICI AL OFFICI AL OFFICI AL OFFICI AL Partial pressure Partial pressures are those pressures generated by individual gases within a gas mixture. Each gas exerts its own pressure, determined by the relative proportions of the gases; the sum of all of the partial pressures must be equal to the total pressure of the gas mixture. OFFICI AL As indicated earlier, 21% of air is oxygen. At normal atmospheric pressure (at sea level) the total air pressure is about 101 kPa (equivalent to 760 mmHg) and so the partial pressure of oxygen will be 21% of this, which is about 21 kPa (160 mmHg). The air also contains nitrogen, carbon dioxide and small quantities of other gases. Each of these will exert its own partial pressure and the sum of these individual pressures, with oxygen, will equal 101 kPa. Daltons law OFFICI AL A law stating that the pressure exerted by a mixture of gases in a fixed volume is equal to the sum of the pressures that would be exerted by each gas alone in the same volume. OFFICI AL "Pressure exerted" refers to the force applied by a gas on the walls of its container due to the constant collisions of gas molecules with the container's surface. In simpler terms, when gas particles move around in a container, they bump into the walls of that container. The force with which they collide with the walls creates pressure. The more collisions there are per unit area, the higher the pressure exerted by the gas. For instance, in a closed container, if you have more gas molecules bouncing around or if those molecules are moving faster (which increases their collisions OFFICI AL Relevanc e OFFICI AL In practice… OFFICI AL External respiration External respiration is exchange of gases by diffusion between the alveoli and the blood in the alveolar capillaries, across the respiratory membrane. Each alveolar wall is one cell thick and is surrounded by a network of tiny capillaries (the walls of which are also only one cell thick). OFFICI AL Internal respiration OFFICI AL Internal respiration is exchange of gases by diffusion between blood in the capillaries and the body cells. Oxygen OFFICI AL Oxygen is carried in the blood in: chemical combination with haemoglobin as oxyhaemoglobin (98.5%) solution in plasma water (1.5%). Oxyhaemoglobin is unstable and under certain conditions readily dissociates, releasing oxygen. Factors that increase dissociation include low O 2 levels, low pH and raised temperature. In active tissues there is increased production of carbon dioxide and heat, which leads to increased release of oxygen. In this way, oxygen is available to tissues in greatest need. OFFICI AL Carbon dioxide OFFICI AL Carbon dioxide is one of the waste products of metabolism. It is excreted by the lungs and is transported by three mechanisms: As bicarbonate ions (HCO plasma (70%) 3 − ) in the Combined with haemoglobin in erythrocytes as carbaminohaemoglobin (23%) Dissolved in the plasma (7%). OFFICI AL Oxyhaemoglobin dissociation curve Oxygen delivery to the tissues requires the binding of oxygen to haemoglobin in red blood cells (RBCs). Each molecule of haemoglobin can bind four oxygen molecules, which fills (saturates) all of its binding sites. Each RBC normally has millions of haemoglobin molecules. When blood passes through the lung alveoli, where oxygen concentration is the greatest, oxygen diffuses from the alveoli into RBCs and binds to all those haemoglobin molecules. OFFICI AL OFFICI AL OFFICI AL OFFICI AL OFFICI AL OFFICI AL OFFICI AL Right shift OFFICI AL Increased temperature Reduced pH Increased CO2 But why?? These are all metabolic processes OFFICI AL OFFICI AL Increased temperature Increased CO2 Reduced pH OFFICI AL OFFICI AL OFFICI AL OFFICI AL OFFICI AL OFFICI AL OFFICI AL https:// www.youtube.com/watch? v=K1S7STZ2BrA&t=2s Left shift Decreased temperature Increased pH Decreased CO2 OFFICI AL OFFICI AL 2,3-diphosphoglycerate (2,3-DPG) is a molecule found in red blood cells that plays a crucial role in regulating oxygen release from haemoglobin to tissues. OFFICI AL OFFICI AL Why?? OFFICI AL A decreased level of carbon dioxide (CO2) in the blood can cause a left shift in the oxygen dissociation curve due to its impact on blood pH, known as the Bohr effect. Here's how it works: 1. Increased pH (Alkalosis): When there's a decrease in CO2 levels, less carbon dioxide is available to combine with water in the blood, leading to a decrease in carbonic acid formation. As a result, blood pH increases, making the environment more alkaline. 2.Effect on Haemoglobin: Higher pH or decreased acidity influences the structure of haemoglobin. In an alkaline environment: Haemoglobin's affinity for oxygen increases. This means that haemoglobin holds onto oxygen more tightly at a given partial pressure of oxygen (PO2). This increased affinity causes the oxygen dissociation curve to shift to the left. Haemoglobin is more likely to bind to oxygen and hold onto it, making it less likely to release oxygen to the OFFICI AL Oxyhaemoglobin dissociation curve https://www.youtube.com/watch? v=wgSUdxrlO8Y https://www.youtube.com/watch? v=ejVMm0VFq5c OFFICI AL Nervous system- The Respiratory centre This is formed by groups of nerves in the medulla, the respiratory rhythmicity centre, which control the respiratory pattern, i.e. the rate and depth of breathing. There are three important groups of neurones here that regulate breathing: an inspiratory group, an expiratory group, and neurones in the pneumotaxic area. Regular automatic firing of the inspiratory neurones sets the basic rhythm of breathing. Expiratory neurones control expiration, and neurones in the pneumotaxic OFFICI AL OFFICI AL Chemoreceptors These are receptors that respond to changes in the partial pressures of oxygen and carbon dioxide in the blood and cerebrospinal fluid (CSF). They are located centrally and peripherally. Central These are located on the surface of the medulla oblongata and are bathed in CSF. When arterial P CO 2 rises (hypercapnia), even slightly, this in turn increases P CO 2 in the CSF. The central chemoreceptors respond by stimulating the respiratory centre, increasing ventilation of the lungs and reducing arterial P CO 2. OFFICI AL Peripheral chemoreceptors These are situated in the arch of the aorta and in the carotid bodies. They respond to changes in blood CO 2 and O 2 levels, but are much more sensitive to carbon dioxide than oxygen. Even a slight rise in CO 2 levels activates these receptors, triggering nerve impulses to the respiratory centre via the glossopharyngeal and vagus nerves. This stimulates an immediate rise in the rate and depth of respiration. An increase in blood acidity (decreased pH or raised [H + ]) also stimulates the peripheral chemoreceptors, resulting in increased ventilation, increased OFFICI AL Inspiration This is initiated by the inspiratory centre in the medulla oblongata, following its activation by the apneustic centre, which is located in the Pons varolii. It ceases because inputs from stretch receptors present in the lung, intercostal muscles and diaphragm (which pass to the brainstem via the vagus nerve), cause the pneumotaxic centre of the pons varolii to inhibit the apneustic centre, and hence deactivate the inspiratory centre. OFFICI AL Expiration In quiet breathing, expiration occurs passively by elastic recoil simply because we stop breathing in. However, part of the apneustic centre will activate the expiratory muscles if we wish to make a more forceful expiration. OFFICI AL Input to the Inspiratory Centre OFFICI AL Classes of inputs to respiration: Chemoreceptors (central and peripheral) Receptors in the lungs peripheral chemoreceptors through the glossopharyngeal nerve mechanoreceptors (stretch receptors) in the lungs through the vagus nerve Joint and muscle receptors. pCO2 receptors in the CSF space send signals through IX and X cranial nerves. Output from the Inspiratory Centre OFFICI AL The signal travels through the phrenic nerve to the diaphragm and intercostal muscles. The signal stops, respiratory muscles relax and expiration takes place. And remember… ‘C3, 4, 5 keep the diaphragm alive.’ OFFICI AL Phrenic nerve and diaphragm OFFICI AL https:// www.youtube.com/watch? v=GqkMzds77f8 OFFICI AL Sensors Control centre Central chemoreceptors -H+ Peripheral chemoreceptors -O2, CO2, H+ Pulmonary receptors -Stretch Effect ors Diaphragm INSPIRATION Respiratory Control Centre External intercostals Accessory muscles EXPIRATION Joint and muscle receptors -Stretch, tension Internal intercostals Abdominal muscles OFFICI AL OFFICI AL Nervous Control Voluntary/Involuntary Sympathetic/parasympathetic Diaphragm = phrenic nerve Intercostal muscles = intercostal nerves OFFICI AL Chemical control OFFICI AL CO2 transportation in the blood and plasma and bicarbonate CO2 + H2O ⇄ H2CO3 ⇄ H+ + HCO370% H2CO3 20% RBC 10% Plasma Chemical Control Oxygen transportation in the blood and plasma 98% O2 binds to the RBC 2% travels in plasma OFFICI AL OFFICI AL Lesson Objectives By the end of the lesson, students will be able to: State Boyles law State Daltons law Identify how these laws relate to respiration Describe the chemical and neurological control of respiration Describe the mechanical control of respiration Understand the normal parameters relating to the partial pressure of each gas Discuss the oxyhaemoglobin dissociation curve OFFICI AL Provide an overview of the events of inhalation and exhalation. Include in your answer time durations, nervous system control, muscle involvement. O2 and CO2 involvement at both the lungs and the tissues. Please explain these processes for both normal and laboured breathing OFFICI AL Questions