3.2 - Transport in Animals

• Multicellular organisms require transport systems due to their large size, high metabolic rates, and high demand for oxygen.
• The circulatory system can be open, where blood can diffuse out of vessels like in insects, or closed, where blood is confined to vessels like in fish and mammals.
• The structure of arteries includes thick, muscular walls to handle high pressure without tearing, elastic tissue that allows recoil to prevent pressure surges, and a narrow lumen to maintain pressure.
• The structure of veins includes thin walls due to lower pressure, valves to ensure blood doesn’t flow backwards, and less muscular and elastic tissue as they don’t have to control blood flow.
• The structure of capillaries includes walls only one cell thick, a very narrow lumen, and numerous and highly branched vessels providing a large surface area.
• Arterioles and venules branch off arteries and veins in order to feed blood into capillaries, are smaller than arteries and veins so that the change in pressure is more gradual as blood passes through increasingly small vessels, and have thinner walls due to lower pressure.
• Tissue fluid is a watery substance containing glucose, amino acids, oxygen, and other nutrients that supplies these to the cells, while also removing any waste materials.
• Hydrostatic pressure is higher at the arterial end of a capillary than the venous end.
• Oncotic pressure is changing water potential of the capillaries as water moves out, induced by proteins in the plasma.
• Sinoatrial node (SAN) initiates and spreads impulse across the atria, causing them to contract.
• Atrioventricular node (AVN) receives, delays, and then conveys the impulse down the bundle of His.
• During ventricular systole, the ventricles contract, increasing the pressure which closes the atrioventricular valves to prevent backflow, and opens the semilunar valves, allowing blood to flow into the arteries.
• An electrocardiogram (ECG) is a graph showing the amount of electrical activity in the heart during the cardiac cycle.
• After tissue fluid has bathed cells it becomes lymph, and therefore this contains less oxygen and nutrients and more waste products.
• Cardiac output is calculated as heart rate x stroke volume.
• The heart is relaxed during cardiac diastole, allowing blood to enter the atria and increasing the pressure, which pushes open the atrioventricular valves.
• Purkinje fibres, which branch across the ventricles, receive impulse from AVN, causing the ventricles to contract from the bottom up.
• The heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses, which is referred to as myogenic.
• During atrial systole, the atria contract, pushing any remaining blood into the ventricles.
• Tissue fluid is formed from blood, but does not contain red blood cells, platelets, and various other solutes usually present in blood.
• Fibrillation is defined as an irregular, fast heartbeat.
• When partial pressure is low, oxygen is released from haemoglobin.
• Haemoglobin is present in red blood cells and oxygen molecules bind to the haem groups, carried around the body, then released where they are needed in respiring tissues.
• Carbonic anhydrase is present in red blood cells and converts carbon dioxide to carbonic acid, which dissociates to produce H+ ions.
• The chloride shift is the intake of chloride ions across a red blood cell membrane, which repolarises the cell after bicarbonate ions have diffused out.
• Oxyhaemoglobin dissociation curves show saturation of haemoglobin with oxygen, plotted against partial pressure of oxygen.
• Tachycardia is defined as a fast heartbeat, with a rate over 100 beats per minute.
• Ectopic refers to early or extra heartbeats.
• Bradycardia is defined as a slow heartbeat, with a rate under 60 beats per minute.
• The Bohr effect occurs as partial pressure of carbon dioxide increases, causing haemoglobin to change shape, decreasing its affinity for oxygen, so oxygen is released from haemoglobin.
• Bicarbonate ions (HCO 3 - ) are produced alongside carbonic acid, 70% of carbon dioxide is carried in this form, and in the lungs, bicarbonate ions are converted back into carbon dioxide which we breathe out.
• Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin due to the low partial pressure of oxygen by the time it reaches the foetus.
• These H+ ions combine with the haemoglobin to form haemoglobinic acid, encouraging oxygen to dissociate from haemoglobin.
• As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin.