Biology chapter 8

• In single-celled organisms, processes such as diffusion, osmosis, active transport, endocytosis and exocytosis can supply everything the cell needs to import or export.
• These processes are also important in multicellular organisms, transporting substances within and between individual cells.
• As organisms get bigger, the distances between the cells and the outside of the body get greater.
• Diffusion would transport substances into and out of the inner core of the body, but it would be so slow that the organism would not survive.
• The blood sounds return to normal at the point when even the lowest pressure during diastole is sufficient to get through the cuff, which gives the diastolic blood pressure.
• More recently a simpler, digital sphygmomanometer is often used - but the same principles apply.
• A reading of 120/80 mmHg is regarded as being normal.
• The stethoscope is simply built into the cuff applied around the arm.
• Specialised transport systems are needed because the metabolic demands of most multicellular animals are high they need lots of oxygen and food, they produce lots of waste products.
• The surface area to volume (SA:V) ratio gets smaller as multicellular organisms get bigger so not only do the diffusion distances get bigger but the amount of surface area available to absorb or remove substances becomes relatively smaller.
• Molecules such as hormones or enzymes may be made in one place but needed in another.
• Food will be digested in one organ system, but needs to be transported to every cell for use in respiration and other aspects of cell metabolism.
• Waste products of metabolism need to be removed from the cells and transported to excretory organs.
• Most large, multicellular animals have specialised circulatory systems (transport systems) which carry gases such as oxygen and carbon dioxide, nutrients, waste products and hormones around the body.
• Most circulatory systems have features in common: they have a liquid transport medium that circulates around the system (blood), they have vessels that carry the transport medium, and they have a pumping mechanism to move the fluid around the system.
• When substances are transported in a mass of fluid with a mechanism for moving the fluid around the body it is known as a mass transport system.
• Large, multicellular animals usually have either an open circulatory system or a closed circulatory system.
• In an open circulatory system there are very few vessels to contain the transport medium, it is pumped straight from the heart into the body cavity of the animal, and the transport medium returns to the heart through an open-ended vessel.
• These open-ended circulatory systems are found mainly in invertebrate animals, including most insects and some molluscs.
• Insect blood is called haemolymph, it transports food and nitrogenous waste products and the cells involved in defence against disease.
• The body cavity of insects is split by a membrane and the heart extends along the length of the thorax and the abdomen of the insect.
• The haemolymph circulates but steep diffusion gradients cannot be maintained for efficient diffusion.
• The sino-atrial node (SAN) initiates the heartbeat by producing a wave of electrical excitation which causes both of the atria to contract followed by the ventricles as a result of the AVN delay.
• A cuff, which is connected to a mercury manometer, is placed around the upper arm.
• The cuff is then inflated until the blood supply to the lower arm is completely cut off.
• Blood pressure is traditionally measured using a manual sphygmomanometer.
• The signal from each of the electrodes is fed into the machine, which produces an ECG.
• The pressure at which the blood sounds first reappear as a slight tapping sound is recorded.
• The height of the mercury at this point gives the systolic blood pressure in mmg.
• The Purkyne fibres spread out through the walls of the ventricles on both sides, triggering the contraction of the ventricles, starting at the apex.
• Electrocardiograms can be used to measure the spread of electrical excitation through the heart as a way of recording what happens as it contracts.
• The contraction starting at the apex allows more efficient emptying of the ventricles.
• An electrocardiogram (ECG) measures tiny electrical differences in the skin, which result from the electrical activity of the heart.
• A normal ECG is shown in Figure 5 and Figure 7(a).
• Atrial fibrillation is an example of an arrhythmia, which means an abnormal rhythm of the heart.
• Tachycardia is when the heartbeat is very rapid, over 100bpm.
• Electrocardiograms are used to help diagnose heart problems.
• The way in which the wave of excitation spreads through the heart from the SAN, with AVN delay, ensures that the atria have stopped contracting before the ventricles start.
• A stethoscope is positioned over the blood vessels at the elbow.
• Electrodes are stuck painlessly to clean skin to get the good contacts needed for reliable results.