Chlorophyll is the green colouring matter of plant leaves and absorbs the light necessary for photosynthesis.
Chlorophyll absorbs mainly red, violet, and blue light and reflects green light. The great abundance of chlorophyll in leaves and its occasional presence in other plant tissues, such as stems, causes these plant parts to appear green. In some leaves, chlorophyll is masked by other pigments.
Chlorophyll is a large molecule composed mostly of carbon and hydrogen. At the centre of the molecule is a single atom of magnesium surrounded by a nitrogen-containing group of atoms called a porphyrin ring. The structure somewhat resembles that of the active constituent of haemoglobin in the blood. A long chain of carbon and hydrogen atoms proceeds from this central core and attaches the chlorophyll molecule to the inner membrane of the chloroplast, the cell organelle in which photosynthesis takes place. As a molecule of chlorophyll absorbs a photon of light, its electrons become excited and move to higher energy levels. This initiates a complex series of chemical reactions in the chloroplast that enables the energy to be stored in chemical bonds. Research Chlorophyll
Anaemia is the medical condition of lacking red blood cells or haemoglobin or both. I anaemic conditions the blood can carry less oxygen round the body, and is slower in removing the waste substances such as carbon dioxide from the tissues and organs. Research Anaemia
Anoxia (hypoxia) is the lack of a normal supply of oxygen to body tissues, or the inability of the tissues to use the oxygen. Anoxic anoxia occurs when blood flowing through the lungs does not pick up enough oxygen. This can happen when there is a reduced amount of oxygen in the air, such as at altitudes above 3,000 meters. The blood also can fail to pick up sufficient oxygen because of defects in the lungs or because of obstruction of the air passages involved in breathing. Rapid, deep breathing is a common symptom of anoxic anoxia. The condition is often accompanied by cyanosis, a bluish colouration of the skin. Severe cases may lead to loss of consciousness and even death. Anaemic anoxia occurs when the blood cannot carry its normal load of oxygen. This happens when the blood has insufficient amounts of haemoglobin, or when the haemoglobin is altered by carbon monoxide or other poisons. Stagnant anoxia develops when the blood flows so slowly that it loses most of its oxygen before completing its course through a tissue. Part of the tissue thus receives little or no oxygen. An example of stagnant anoxia occurs during cold temperatures when blood vessels under the fingernails and in the lips constrict, causing cyanosis in those body parts. Histotoxic anoxia is caused by poisons that make the tissues incapable of using the oxygen supplied. Cyanide is one such poison. Research Anoxia
The transfer of blood from one individual to another first became a practical proposition during the Great War. The recognition of four major blood groups indicated that there were limitations on blood transfusion which necessitated very careful examination of the blood of the two individuals concerned. In the early days of transfusion after preliminary grouping, the blood was transferred from the donor to the recipient by the ' direct' method, using a two-way tap and syringe, so that the blood was not exposed to the air and had no opportunity for clotting. The 'indirect' method was later introduced in which the donor's blood was received into a solution of sodium citrate which prevented it from clotting by inactivating the calcium. Within an hour or so the blood was then injected into the veins of the recipient. Prior to the second World War, most large hospital centres in Great Britain maintained a panel of blood donors who were willing to come to the hospital at any hour of the day or night for emergency transfusion. The relatives of patients also were called upon, if with the right blood group, to give their blood.
The necessities of war, and the greater demands of surgery for blood transfusion led to the establishment of ' blood banks', in which are stored large quantities of blood taken at a convenient time from thousands of volunteers. With suitable refrigeration, blood may be stored for three weeks with safety and such blood is quite suitable for the treatment of shock and conditions of blood loss. Certain other disorders, mainly medical conditions affecting the formation of red cells in the bonemarrow, are preferably treated with the transfusion of fresh blood: this seems to possess properties which become lost in storage. Blood transfusion performs a double purpose. It replaces the oxygen-carrying red cells and its fluidfraction, the plasma, contributes protein which maintains the circulating blood volume, thus preventing the escape of water into the tissues. Plasma or serum may be separated from the whole blood and dried. In this form it was used extensively during the Second World War because it could be stored indefinitely and could be reconstituted by the addition of distilled water when infusion was needed in the treatment of shock. By the extraction of the fluid portion of the whole blood, the cell content may be concentrated. Such a preparation is known as packed cells. This has become of particular value if it is necessary to raise the haemoglobin rapidly without raising the blood volume unduly. Such a procedure may be required in the treatment of severe anaemia arising from toxaemia. Research Blood Transfusion
Haemoglobin is a protein used by all vertebrates and some invertebrates for oxygen transport. In vertebrates it occurs in red blood cells (erythrocytes), giving them their colour. In the lungs or gills where the concentration of oxygen is high, oxygen attaches to haemoglobin to form oxyhaemoglobin. This process effectively increases the amount of oxygen that can be carried in the bloodstream. The oxygen is later released in the body tissues where it is at a low concentration, and the deoxygenated blood returned to the lungs or gills. Haemoglobin will combine also with carbon monoxide to form carboxyhaemoglobin, but in this case the reaction is irreversible. Research Haemoglobin
Jaundice is a yellowing of the skin, conjunctivae, and mucous membranes caused by excessive amounts of bile pigments in the blood tissues. These pigments, normally present in blood as a result of the breakdown of haemoglobin in red blood cells, are filtered through the liver and excreted. Excessive amounts of these pigments produce four types of jaundice. In haemolytic jaundice there is increased production of bile pigment because of red blood-cell damage. This damage can be caused by antibodies created by a mismatched blood transfusion. In infants the antibodies can be caused by prenatal mismatch between the Rhfactor in the infant' s blood and that of the mother. Newborns can also be jaundiced as a consequence of the condition known as hyperbilirubinemia. In these cases, there is a temporary defect in synthesis of the enzyme that breaks down bile to an excretable form. Hepatocellular jaundice occurs when liver cells are damaged either by viruses or by excessive intake of alcohol and lose the ability to filter pigment. Obstructive jaundice
follows physical obstruction of the ducts that transport pigment from the liver to the intestine. Blockage can be due to gallstones, tumour, or inflammation. Research Jaundice
Thalassaemia (Cooley's Anemia) is a hereditary disease, common in many parts of the world, resulting from defects in the synthesis of the red blood pigment haemoglobin. Research Thalassaemia
Abbreviations
Research Chlorophyll
