Animal Transport

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Open Circulatory System - Insect

  • Fluid is pumped at  arelatively ow pressure from one main long, dorsal (top) tube shaped heart running the length of the body.
  • Fluid called hemolymph bathes the tissues directly enabling the exchange of substances. 
  • When the heart relaxes the hemolymph is sucked slowly back to the heart.
  • There is no respiratory pigment in th insect hemolymph as oxygen is diffused directly to respiratory cells. 
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Closed Circulatory System - Fish and Mammals

  • Blood circulates in a fully enclosed system of tubes (blood vessels)
  • The heart is a muscular pump pushing blood at high pressure with a rapid flow rate. 
  • Organs are not in direct contact with the blood but are bathed in the tissue fluid. 
  • Blood contains a respiratory pigment that carries oxygen. 
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Closed Circulatory System - Earthworms

  • Has dorsal and ventral vessels running the length of the body. These are connected by 5 pairs of pseudohearts. 
  • Blood contains a respiratory pigment that carries oxygen called haemoglobin. 
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Single And Double Circulation (Closed)

  • Single - Blood passes through the heart once in complete circulation
  • Double- Blood passes through the heart twice in one complete circulation. 
  • Pulmonary circulation - All the blood vessels involved in transporting all the blood from the heart to the lungs. 
  • Systematic Circulation - All the blood vessels involved in transporting all the blood from the heart to the rest of the body. 
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Advantages Of Double Circulation

  • Maintains a high blood pressure in systematic circulation which ensures efficient oxygen delivery to respiring cells. 
  • Allows a lower pressure in the pulmonary circulation which prevents the build-up of tissue fluid in the lungs. 
  • Rapid circulation in the systemic circuit is required as fast circulation is needed when pumping blood around the body. 
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Blood Vessels

  • Arteries - Transport blood away from the heart
  • Veins - Transports blood towards to heart. 
  • Capillaries - Small vessels which allow substance exchange e.g. o2 co2 glucose urea amino acids. 
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Blood Vessel Structure

  • Endothelium- This si the innermost layer and is one cell thick. They are the only thing present in capillaries. They are important as they reduce friction which would reduce resistance to the flow of the blood. In capillaries being one cell thick provides a short diffusion pathway for gasses.
  • Elastic Fibres and Smooth Muscle (Tunica Media) - These components make up the middle layer of the vessel. In arteries, this layer is thicker than in veins. The thick smooth muscle in arteries withstands the high blood pressure produced by the heart pumping. It can also redirect blood flow. Also, elastic fibres in arteries stretch and recoil to maintain high blood pressure. 
  • Collagen fibres- Found in the outer layer of the vessels and are resistant to overstretching. 
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Veins

  • Wide diameter lumens so they can deliver blood back to the heart in large volumes. 
  • They also have thin walls as the pressure inside is much lower due to the further distance from the heart. 
  • The thin muscle can be compressed easily allowing contracting skeletal muscles to squeeze veins blood upwards back towards the heart. 
  • Pocket valves ensure blood travels in one direction. 
  • Valves work when blood tries to flow back, it fills the pocket above the valve which forces the valve to shut.  
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Arteries Arterioles and Cappilaries

  • Arteries- Thick layer of smooth muscle to withstand high blood pressure and a thick layer of elastic fibres for recoil to maintain high blood pressure. 
  • Arterioles - Adjust diameter to vary blood supply to the capillary bed. 
  • Capillary- Consist of one cell thick endothelium. Some have pores in their walls. Permeable to dissolved substances. Thin walls allow for efficient exchange as there is a small diffusion pathway and a large SA: V. The narrow lumen restricts blood flow slowing down blood to allow for more time for material exchange at tissues.
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The Heart

  • The heart has 4 chambers and consists largely of cardiac muscle. This is a specialized tissue that is capable of rhythmic contraction and relaxation over a long period without fatigue
  • Tendinous cords - When ventricles contract the increased blood pressure causes atrioventricular valves to close simultaneously preventing the backflow of blood into the atria. The tendinous cords prevent valves from inverting into the atria. 
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Functions of Heart Vessels

  • Aorta - Largest artery which transports blood from the heart to the body. 
  • Vena Cava - Two veins that carry deoxygenated blood to the heart from the upper and lower parts of the body. 
  • Pulmonary Artery - Transport deoxygenated blood from the heart to the lungs where gas exchange takes place. 
  • Pulmonary Vein - Transports oxygenated blood from the lungs back to the heart. 
  • Coronary Arteries - Supply heart cells with oxygenated blood and glucose. 
  • Coronary veins - Remove deoxygenated blood from cardiac muscles. 
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Blood Flow from Lungs To Body Tissues

  • Oxygenated blood travels from the lungs to the heart via the pulmonary vein. 
  • Blood leaves the pulmonary vein and enters the left atrium. 
  • Left atrium contracts and forces blood through the left ventricle through the bicuspid valve. 
  • The left ventricle contracts and the bicuspid valve closes forcing the blood upwards into the aorta via the semilunar valve.
  • Oxygenated blood leaves via the aorta to the rest of the body tissues. 
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Blood Flow From Body Tissues To The Lungs

  • Deoxygenated blood returns to the heart in the vena cava
  • Blood then moves from the superior and inferior vena cava to the right atrium. 
  • The right atrium contracts and blood moves into the right ventricle through the tricuspid valve, 
  • The right ventricle contracts, closing the tricuspid valve and forcing blood into the pulmonary artery through the semi lunar valve. 
  • Deoxygenated blood travels in the pulmonary artery towards the lungs. 
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Cardiac Cycle

  • Atrial Systole - Both atria contract forcing the tricuspid valve and bicuspid valves to open. Blood flows from the high-pressure atria to the low-pressure ventricle. Backflow is prevented by valve closure in the veins. 
  • Ventricular Systole - Both ventricles contract, forcing the blood up and out of the heart into arteries. Both valves close due to the pressure from the blood in the ventricles. This prevents the backflow of blood into the aorta. Semilunar valves in the aorta and the pulmonary artery open. 
  • Diastole- Atria and ventricles relax creating a low pressure in the heart. The semilunar valves in the aorta and pulmonary artery close due to blood in the aorta (high pressure) to the ventricles (low pressure). Blood flows from the veins through the atria and into the ventricles as there's higher pressure in veins. 
  • Stroke volume- Volume of blood pumped from the left ventricle per beat. 70ml in a healthy person. Cardiac output is the product of heart rate and stroke volume. It decreases in certain conditions and disease states. Stroke volume correlates with cardiac function. 
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Cardiac Cycle Summary

  • The right atrium receives oxygenated blood from the vena cava. The left atrium receives oxygenated blood from the pulmonary vein. 
  • At this point the Atrioventricular valves are open, the TC is in the right atrium and the BC in the left atrium. 
  • Blood is drawn from the high-pressure atria into the low pressure, relaxed, ventricles. 
  • The atria contract to force the remaining blood into the ventricles. 
  • The ventricles contract forcing the blood out of the semilunar valve through the pulmonary artery and aorta. 
  • Both atria contract and both ventricles contract. Single heartbeat is one contraction (systole) and one relaxation (diastole) 
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Pressure Changes In The Heart

  • TC and BC valves are open when pressure in the atria is higher than in the ventricles. They close when the pressure in the ventricle is greater than the pressure in the atria. 
  • The semi lunar valves open when pressure in the ventricles is greater than the aorta and pulmonary artery. They close when the arterial pressure is greater than ventricular pressure and blood tries to travel backwards. 
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Pressure Changes in Vessels

  • Arteries - The highest pressure occurs in the arteries closest to the heart. A rhythmic rise and fall is corresponding to ventricular contraction and relaxation. 
  • Arterioles - Friction with vessel walls causes a progressive drop in pressure. Arterioles have a large total cross-sectional area and a narrow lumen causing a substantial decrease in the aortic pressure. The pressure in the arterioles depends on whether they are dilated or constricted. 
  • Capillaries- Have a small diameter and friction with walls reduces the flow of blood and decreases pressure. As some fluid is forced out of the capillaries this reduces blood flow and pressure. 
  • Veins - The return flow to the heart is non-rhythmical as they are too far from the heart to be affected by contraction and relaxation. Vein pressure is low but doesn't reach 0 because of the massaging effect of muscles
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Heartbeat Control

  • The heart is myogenic which means that it can initiate its impulses and heartbeat itself.
  • In the walls of the Right atrium is a region of specialised fibres called the sinoatrial node. These act as a pacemaker.
  • A wave of depolarisation arises at the SAN and nerve impulses spread over the atria making them contract. 
  • The electrical stimulation is prevented from spreading to the ventricles by a thin layer of tissue which also acts as an insulation layer. 
  • After a short delay, the nerve impulse reaches the atrial ventricular node between the 2 atria. This passes the impulse onto the ventricles. 
  • From the AVN the impulse passes down the bundle of HIS to the apex of the heart. The bundle branches into perkinge fibres in the ventricular walls which carry the wave of depolarisation upwards through the ventricular muscle. 
  • The impulses cause the cardiac muscle in each ventricle to contract simultaneously from the apex upwards. This forces blood out of the heart.
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ECG Traces

  • The electrical activity that sreads though the heart during the cardiac cycle can be detected via electrodes placed on the skin. The electrical signals can then be shown on cathode ray oscilloscope or a chart recorder, AThsi process is an electrocardiogram or ECG. 
  • P Wave - First part of the trace that shows depolarisation of atrial systole. 
  • QRS Wave - Spread of depolarisation in ventricles causing ventral systole
  • T Wave - Relaxation and repolarisation during ventrical diastole. 
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