Respiratory System PDF

Learning Objectives : Structure and functional organization of the respiratory system Mechanics of gas exchange between the atmosphere and the lungs Common indices used to measure gas exchange during inspiration and expiration Common obstructive and restrictive airway d...

Learning Objectives : Structure and functional organization of the respiratory system Mechanics of gas exchange between the atmosphere and the lungs Common indices used to measure gas exchange during inspiration and expiration Common obstructive and restrictive airway diseases and their impact on provision of dental care The main function of the lungs is Provide oxygen (O2 ) to the tissues - O2 is needed by the mitochondria for oxidative metabolism, i.e. energy (ATP) production (internal respiration) Remove carbon dioxide (CO2 ) from the tissues - and CO2 is generated as a waste product The primary actions which fulfil this function are: the mechanics of breathing, gas exchange and transport, and the control of breathing. Composition of AIR Organization of the Respiratory System The respiratory system is divided into the: Upper respiratory tracts - includes the nasal cavity, pharynx, and larynx Lower respiratory tracts - comprises the trachea, bronchi, and the bronchial tree terminating in air sacs or alveoli Organization of the Respiratory System The respiratory system is divided into the: Upper respiratory tracts - includes the nasal cavity, pharynx, and larynx Lower respiratory tracts - comprises the trachea, bronchi, and the bronchial tree terminating in air sacs or alveoli Organization of the Respiratory System The right lung has three lobes, while the slightly smaller left lung has only two lobes as space is taken up by the pericardium. Organization of the Respiratory System Within the lungs, each branching sequence of the bronchial tree is given a generation number. The dichotomy of the trachea into two main bronchi is generation number 1. At the last generation number, approximately 23. Organization of the Respiratory System The respiratory zone starts after generation number 17, as these terminal respiratory units allow diffusion of gas across their membranes. The region superior to this is called the conducting zone, as the primary function of these airways is to conduct air Lung Volumes and Capacities Lung Volumes and Capacities Mechanics of Pulmonary Ventilation To understand the movement of air in and out of the lungs, we need to remember that the atmospheric air pressure (barometric pressure, or PB) at sea level is normally 101.325kPa (760mmHg) or 1atm. The pressure exerted by a gas in a mixture of gases (like air) is the partial pressure (P). Although the pressure at the mouth is equivalent to PB, by convention it is 0kPa. Mechanics of Pulmonary Ventilation There are two other pressures to consider: -the pleural pressure (Ppl), which is the pressure in the pleural space between the visceral and parietal pleurae. Ppl is negative at the beginning of resting inspiration. This is due to equal and opposing forces on this membrane, as the lungs have a tendency to recoil or collapse, while the chest wall has a tendency to spring outwards. -the alveolar pressure (Palv, or PA), which is the pressure inside the alveoli. Lung Compliance The extent to which the lungs expand for each unit of pressure is referred to as lung compliance (CL )  Respiratory diseases can be classified as either Obstructive, where bronchoconstriction results in altered airflow and airway resistance (Raw), or Restrictive, where the functional volume of the lungs decrease. COPD COPD refers to a group of conditions characterised by irreversible narrowing of the airways, making expiration difficult. COPD includes conditions such as chronic bronchitis and emphysema and affects approximately three million patients in the UK. The main risk factor is smoking, but others include indoor air pollution (including using biomass fuel for cooking and heating), outdoor air pollution, occupational dusts or chemicals, and alpha‐1 antitrypsin deficiency Asthma Asthma is characterised by attacks of shortness of breath (breathlessness), coughing, and wheezing. Normally, this occurs by reversible airway narrowing and it affects 5.4 million patients in the UK. Most cases are atopic, where patients have a tendency to be sensitised to allergens.  Gas Exchange and Transport In the previous chapter, we discuss how air enters the lungs, now we need to understand how it diffuses across the alveolar‐capillary membrane  The exchange and transport of O2 and CO2 are vital to prevent hypoxia (low O2 ) and hypercapnia (high CO2 ). Various disease states can also affect the exchange and transport of these gases and consequently affect acid–base homeostasis.  Gas exchange across the moist alveolar surfaces in the lungs takes place by passive diffusion, down the partial pressure gradients, i.e. from regions of high pressure to regions of low pressure. Control of Breathing Control of breathing is necessary so we can breathe enough to ensure maximum oxygen saturation of haemoglobin and also keep the work of breathing to a minimum. Additionally, carbon dioxide (CO2 ) levels need close regulation, as changes can affect the pH ̇ E is doubled, CO2 decreases and it causes arterial of blood. If V ̇ E is halved, CO2 levels pH to rise to 7.6, from a normal of 7.4. If V increase, and pH falls to 7.2. Control of Breathing Finally control of breathing allows us to ‘override’ the automatic reflex breathing in certain circumstances such as blowing, breath holding, swimming, and speech, etc. Neural Respiratory Centres The neural respiratory centres are found in the brainstem and are located bilaterally in the medulla oblongata and pons. The main areas which are responsible for automatic control of our breathing.  Peripheral Receptors The airways and lungs are innervated by various receptors. These include : the cough receptors - rapidly adapting receptors and are found in epithelial cells of the upper airways and trachea‐bronchial tree. They are stimulated by irritants such as dust, smoke, or chlorine gas and result in cough, bronchoconstriction, and mucus secretion. stretch receptors - slowly adapting receptors and are found in the smooth muscle of small and large airways. This reflex protects the lung from over‐inflation. C‐fibres - cause cessation of inspiration once stimulated.