Valoración de las acciones del Programa en materia de reconversión productiva

We now move on to those body systems which are most affected by the absorption of toxic substances.

Blood is a viscous fluid which circulates throughout most of the body structure. Blood is both a functional organ and a connective tissue, as it contains specific cells. Blood cells are

suspended in a fluid plasma, which together make up the composite fluid which is called blood. Being a fluid, blood is able to take the shape of the vessels or organs in which it is contained. The lack of a specific shape enables blood to enter into any body situation where it is required to function.

 In a healthy adult, the total blood volume is about 8% to 12% of the body weight, with a volume of between 4 and 8 litres.

 The basic composition of the blood is: plasma 55%, blood cells 45%.

 The specific gravity of blood is about 1.055, i.e. a little heavier than water.

 The blood plasma is slightly alkaline, about pH 7.4, a level which is critically maintained to ensure maximum operating efficiency.

Blood consists by weight of:

 Water 91.0%

 Protein 8.0%

 Salts 0.9%

The salts are mainly sodium chloride, sodium hydrogen carbonate and salts of calcium, as well as salts of phosphorus, magnesium and iron. There are traces of organic matter, such as glucose, amino acids, fats, urea, uric acid and cholesterol. The blood also carries oxygen and carbon dioxide; internal secretions such as hormones, enzymes and antigens (antibodies); and blood cells.

Blood cells transported in the blood include:

 Erythrocytes (red cells).

 Leucocytes (white cells).

 Thrombocytes (platelets).

The ratio of the cells in blood is 500 red cells: 1 white cell: 30 platelets.

Erythrocytes

These are biconcave cells (shaped like a doughnut) measuring about 7 µm in diameter and about 2 µm thick, and they do not contain a nucleus. They are made in the red bone marrow, found in the cancellous tissue of long bones, in the bones of the skull, the vertebrae, the ribs and the sternum.

The erythrocytes contain haemoglobin which provides a chemical system which enables oxygen to be transported throughout the body. When oxygen obtained from the lungs is attached to the haemoglobin, it is termed oxyhaemoglobin.

The red cells are the most numerous of the blood cells: 1 mm3 of blood contains about 5 million erythrocytes.

• Haemoglobin

You will remember that haemoglobin is a complex chemical compound which gives the erythrocyte (and the blood) its red colour. The HAEM provides the "active" (or prosthetic) part of the molecule. It is a red pigment, formed by a complex molecule of iron. The GLOBIN is formed from protein molecules. The two molecular systems are joined in such a way that they make a composite functional biochemical structure.

As erythrocytes do not have a nucleus, like other cells do, they are not considered as "living" systems, i.e. they do not divide and reproduce. Red blood cells have a limited "life" of about 120 days, so the body has to mass-produce them to keep the required operational numbers. The replacement rate in a healthy body is about 1½ million per second. Fortunately, much of the raw materials are not lost from the body, so, provided the essentials are kept topped up from the diet, problems do not occur.

Leucocytes

These cells, as the name implies, are white in colour. There are about 8,000 white cells per mm3 of blood. On average, they are larger than red cells, ranging from 8 µm to 20 µm in diameter. The cells contain a nucleus, so they can be considered as "living" cells. There are two main types of leucocyte which together form the main defensive system in combating disease and the effects of toxic actions:

• Granulocytes

These cells constitute about 75% of the white cells. They are produced in the bone marrow and the spleen. Their defensive role involves moving in and out of the blood vessels and wandering freely through the tissues, where they ingest (or "eat") harmful micro-organisms or debris, by a process called phagocytosis (phago means "to eat"). Granulocytes concentrate at the site of infection or injury to attack foreign matter. They ingest to an extent that causes them to die and, in doing so, they form "pus" discharge. The increased microbiological action causes the site to become hot, resulting in

inflammation.

• Lymphocytes

Lymphocytes make up about 25% of the leucocytes. They are derived from the lymph glands, spleen, liver and bone marrow. They are in general not able to ingest foreign matter like the granulocytes, but they protect the body by forming antibodies.

An antibody is a particular protein molecule produced to neutralise the effect of a foreign protein molecule or antigen. The production of antibodies in response to an antigen is called an immune response. As the process takes time to establish, antigens may overwhelm the body and cause severe illness or death.

Immunisation is the process of giving the body a store of antibodies ready to fight off infections before they become dominant in the body. An over-response by the body to antigens is commonly called an allergic, or sensitisation, reaction.

Thrombocytes (Platelets)

Thrombocytes are formed in the bone marrow. Their main function is in the clotting of blood. They are very small cells about 2 to 3 µm in diameter. One mm3 contains about ¼ million cells. The clotting of blood is a complex process depending upon many variable factors. In essence the reaction involves precipitation of a material called fibrogen from the plasma to give fibrin, a fibrous material which entangles blood cells to form a clot. Fibrin can become involved with the structural repair of tissue and form part of the resulting scar. Formation of scar tissue can be termed fibrosis.