Human Respiratory System Lecture Notes PDF

Human respiratory system Dr Melissa Cameron School of Medical Sciences [email protected] https://image...

Human respiratory system Dr Melissa Cameron School of Medical Sciences [email protected] https://images.app.goo.gl/jCV56admuLpKqaWh9  What’s to come  Breathe in breathe out. How often do you remember to breathe? Rarely? Always – Take a little breath and hold, then take another, this is how it feels to have lung disease – never the capacity to breathe out. In our life time we take around 600 million breaths. If we could lay out the 750 million little tubes that make up our lungs, they would take up the size of a tennis court. We will learn about the mechanics of breathing and gas exchange, focussing on the movement of oxygen from the environment into our lungs and then into the circulatory system for dispersal to our tissues. We will consider how lung anatomy allows the movement of gases across the respiratory membranes, and how our anatomy changes when we laugh, cry, yawn and hiccup. The University of Sydney Photo by Unknown Author is licensed under CC BY-SA  The Respiratory System The University of Sydney  The Respiratory System The University of Sydney  Gas Exchange AKA respiration – Uptake of O2 from the atmosphere and discharge of CO2 back into the environment A particular gas within a mixture of gases exerts a pressure – Partial pressure Knowing the partial pressure of a gas allows us to predict its movement – Gases always diffuse from a region of high partial pressure to a low partial pressure The University of Sydney Consider the responses you see your body and those around you make The University of Sydney  What happens when we take a deep breath? Air rushes in through the nose/mouth The chest expands The abdomen expands slightly Shoulders may lift up Why do these things occur when we breathe? The University of Sydney  Negative pressure breathing To move O2 from the atmosphere into our lungs, the pressure must be lower in the lungs – Pulling, rather than pushing air into our lungs Achieved by expansion of the chest wall by muscle contraction The University of Sydney  Why do our lungs expand when our chest contracts? A double membrane surrounds the lungs – One side adheres to the outside of the lung, the other to the wall of the thoracic cavity (ribs) – Filled with fluid that creates surface tension Easily stuck, but not easily pulled apart The University of Sydney  Breathing out - Expiration Compared to inspiration, normal expiration usually does not require the contraction of any muscles – Passive process – Relaxation of diaphragm and rib cage reduces the volume of the thoracic cavity driving air OUT of the lungs The University of Sydney  We can alter the volume within our lungs The University of Sydney  Lung volumes and capacities The University of Sydney  Gas exchange at the alveoli Human lungs contain millions of alveoli, creating a huge surface area – This allows O2 to rapidly diffuse across the membrane into the surrounding capillaries for dispersal around the body The University of Sydney  Remember – gas moves from an area of high partial pressure to low partial pressure Let’s annotate  The University of Sydney  Gas transport in the blood Oxygen is predominantly transported around the body bound to haemoglobin within red blood cells – 98% transported this way – Remaining 2% dissolved in the plasma Carbon dioxide is transported by 3 different mechanisms – 7% dissolved in plasma – Remaining 93% within red blood cells, but via two separate mechanisms 23% bound to haemoglobin 70% converted to bicarbonate The University of Sydney  Oxygen transport by haemoglobin Each haemoglobin molecule can carry 4 molecules of O2 Depending on how much O2 is bound will determine the blood’s saturation – If all binding sites are occupied, the blood is 100% saturated This Photo by Unknown Author is licensed under CC BY-NC-ND The University of Sydney  Oxyhaemoglobin saturation curves – At normal PO2 levels, haemoglobin is 98% saturated! – Minor changes in PO2 do not have a significant effect on the saturation – Haemoglobin is a large store for O2 within the body The University of Sydney  What happens when things go wrong? If diffusion of gases between the alveoli and blood is impaired or oxygen transport in the blood is altered this can result in hypoxia – Often goes hand in hand (but not always!) with hypercapnia The University of Sydney What happens when things go wrong? Two general categories of dysfunction: – Obstructive lung disease – Restrictive lung disease Additional conditions affecting respiratory function https://images.app.goo.gl/TQrLffNjHHtFsz1MA – Diseases affecting diffusion of O2 and CO2 across pulmonary membranes – Reduced ventilation due to mechanical failure – Failure of adequate pulmonary blood flow – Ventilation/perfusion abnormalities involving a poor matching of air and blood so that efficient gas exchange does not occur The University of Sydney  Pneumothorax AKA: Collapsed lung Why does a lung collapse? The University of Sydney  Involuntary Responses Sneezing Receptors in nose send signal to brain to close off mouth Forces air out of lungs through nose to expel irritants Coughing Receptors in respiratory tract send signal to brain to close off glottis and vocal cords Builds pressure in lungs where it is then forced out when muscles contract Hiccups Trigger leads to involuntary contraction of the diaphragm This closes off vocal cords briefly, causing air to “bounce” off them, creating the ‘hic’ sound The University of Sydney  I would appreciate your feedback on these lectures – Anonymous/not more than 5 min to complete https://forms.gle/Hp3nwZeo2yEVkVgv8 Log in to Socrative https://b.socrative.com/login/student/ Enter room 8A8TL1XV for some revision questions (Goes live after respiratory lecture) The University of Sydney