Enzymes usually only catalyse one type of reaction. The enzyme has an active site with a unique shape that fits onto the substrate of the reaction. For the reaction to work the substrate has to fit into the enzymes active site.
It is alkaline to neutralise hydrochloric acid from the stomach. It also emulsifies fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of fat breakdown by lipase.
If the pH in an enzyme is too high or too low it interferes with the bonds holding the enzyme together, changing the shape of the active site and denaturing the enzyme.
The heart pumps blood around the body in a double circulatory system. The right ventricle pumps blood to the lungs where gas exchange takes place. The left ventricle pumps blood around the rest of the body.
Blood flows into the two atria from the vena cava and the pulmonary vein. The atria contract, forcing the blood into the pulmonary artery and the aorta, then out of the heart. The blood then flows into the organs.
The lungs are in the thorax (which is separated from the rest of the body by the diaphragm), they are protected by the rib cage and surrounded by the pleural membranes.
The intercostal muscle contract (the ribs go up and out) and the diaphragm flattens when you breath in, the intercostal muscles and diagram relax when exhaling.
Alveoli are sacs surrounded by a network of blood capillaries, where gas exchange happens. Oxygen diffuses out of the alveolus from a high concentration into the blood (low concentration), carbon dioxide diffuses out of the blood into the alveolus (from high to low).
When the blood reaches the body cells oxygen is released from the red blood cells (high concentration) to the body cells (low concentrations) co2 does the opposite.
The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate.
Arteries carry blood away from the heart. The heart pumps blood out of the heart at high pressure, so artery walls are strong and elastic, The walls are thick compared to the lumen and contain thick layers of muscle to make them strong and elastic fibres to allow them to stretch and spring back.
Veins carry blood to the heart. The pressure is lower, so the walls rent as thick, and they have a bigger lumen then arteries. They also have valves to help keep the blood flowing in the right direction.
Capillaries are involved in the exchange of substances in the tissue. They are very small, have small lumen and one cell thick walls. The walls are permeable so that substances can diffuse in and out. They supply food and oxygen and take away waste like CO2. The walls being one cell thick increases rate of diffusion as distance it happens over is decreased.
Valves in the heart can be damaged or weakened by heart attacks, infection, or old age. This damage causes the valves to stiffen, so it wont open properly. Or a valve may become leaky, allowing blood to flow in both directions.
The valves can be replaced by ones taken from humans or other mammals. It is a much less drastic procedure than a whole heart transplant, but it is still a major surgery and there can be problems with blood clots.
Plasma is a pale straw-coloured liquid that carries everything in the blood. It carries blood cells, platelets, nutrients like glucose and amino acids, carbon dioxide, urea, hormones, proteins, antibodies, and antitoxins
Red blood cells carry oxygen from lungs to the cells of the body. It is biconcave to provide a large surface area for absorbing o2. They don't have a nucleus so there is more space for carrying oxygen.
They contain a red pigment called haemoglobin. In the lungs it binds to oxygen to become oxyhaemoglobin, in body tissues the reverse happens, releasing oxygen in the cell.