BIOL1XX8 2024 L13 Circulation Study Notes (PDF)

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

Human circulatory system Dr Melissa Cameron School of Medical Sciences [email protected] https://images.app.goo.gl/5oJpV3GFFYmQPUyd8  What’s to come J We will take a tour on the motor highway of the circulatory system, including the pulmonary and systemic circuits and how the heart drives blood around our body. Your body contains around 100,000 km of vessels. They would go around the world twice if all laid out! Within them there are 75 million blood cells (red, white, platelets) to keep alive. Your heart beats 3.5 billion times if you live until you are 80 years old! Blood flows unidirectionally in your body and through the heart – You will learn the process of exchange at the tissues and we will trace fluid through our lymphatic system where it completes the circuit back to the heart. The University of Sydney Photo by Unknown Author is licensed under CC BY-SA Human Circulatory System – Humans have a closed circulatory system – Physically separated from the rest of the body – Consists of vessels and pump http://clickmypicture.com – Humans have a “double” circulatory system as our heart is divided completely into right and left sides The University of Sydney  Different types of blood vessels https://images.app.goo.gl/coxQM12c7H92DEWo9 The University of Sydney Let’s label! Annotate this image with me The University of Sydney  What is Blood? – One of the main components of the cardiovascular system (and probably most underrated!) – It is a connective tissue made up of cellular elements, suspended in a fluid matrix – Plasma – Makes up a quarter of the ECF – Acts as buffer between the cells and the external environment – Circulating portion The University of Sydney  Blood composition 92% Water 7% Protein 1% Dissolved organic molecules The University of Sydney  Erythropoiesis Controlled by the glycoprotein erythropoietin (EPO) + some cytokines – Produced by the kidneys The trigger for EPO release is hypoxia Kidney Erythropoietin Reduced oxygen- carrying capacity Developing erythrocytes in red bone Relieves marrow Increased oxygen- carrying capacity Erythrocytes The University of Sydney  Blood doping Used to improve athletic performance by artificially improving the body’s ability to transport O2 to the tissues/muscles Three common types: – Blood transfusion – Injection of EPO – Injection of synthetic O2 carriers https://images.app.goo.gl/57zvWH2RsWDRJ3UZA The University of Sydney  The Heart “Workhorse” of the body – Generates a pressure to force blood continuously around the body – Composed predominantly of cardiac muscle The University of Sydney  How does the heart contract? – Specialised cells within the heart generate an electrical signal to coordinate contraction – Autorhythmic cells – Depolarises the membrane, spreading rapidly through conducting pathway – This electrical activity is what you see on an ECG!! – Let’s explore this closer The University of Sydney  Mechanical events of the heart The University of Sydney  Alterations to our heart rate Importantly, our heart rarely contracts to its maximum force – At rest, after each beat blood remains in the heart (65mL) For each contraction of the heart, the volume ejected is known as the stroke volume (SV) Changing SV directly correlates to alterations in heart rate (HR), therefore altering the performance of the heart – Performance is measured by cardiac output (CO) CO = SV x HR CO = 70 mL/beat x 72 bpm = 5.4 L/min HR is altered by the autonomic nervous system by changes to the depolarisation of the autorhythmic cells The University of Sydney  How does blood flow? Driving Blood Pressure Arteries Arterioles From veins To capillaries (a) Heart contracting and emptying Arteries Arterioles From veins To capillaries (b) Heart relaxing and filling The University of Sydney  Blood flow around the body Blood (fluid) flows from an area of high to low pressure – Arterial system is under high pressure, venous system is under low pressure – Why does blood pressure decrease the further blood flows away from the heart? The University of Sydney  Blood pressure Blood pressure is often recorded as: – 120/80 mmHg – What do these numbers actually mean? https://images.app.goo.gl/kToBr4ibxgZEiLG26 As the heart oscillates between contraction and relaxation, measurements are taken at these points: – 120 mmHg is the systolic pressure – 80 mm Hg is the diastolic pressure Systole is the pressure in the arteries when the heart has contracted Diastole is the pressure in the arteries when the heart is fully relaxed The University of Sydney The case of the fainting soldier Standing at attention can cause soldiers to faint after a period of time Unique physiological response Caused by postural hypotension The University of Sydney  Postural hypotension If we don’t move our legs, the blood cannot return to the heart – Why? Fluid-filled – Standing causes blood to “pool” in our tube Open venous valve permits flow of feet blood toward heart Point of Vein constriction Contracted skeletal – If not enough blood is returning to the muscle heart we faint to “rectify” the problem Closed venous valve prevents backflow of blood (a) Fluid moving (b) Action of venous valves, in both directions permitting flow of blood toward on squeezing a heart and preventing backflow fluid-filled tube of blood The University of Sydney  Capillary transport – Three mechanisms of exchange – Movement between endothelium – Transcytosis – Bulk flow https://images.app.goo.gl/Fb1XKvynXpHfNcfT8 The University of Sydney  Lymphatic System Three key functions: Return filtered fluid to circulatory system Fat reabsorption from gut into circulation Destroy foreign pathogens 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