The body and its constituents Communication a chemical substances synthesised by body cells, In this section, transport and communication are consid- waste materials produced by body cells to be ered. Transport systems ensure that all cells have access eliminated from the body by excretion to the internal and external environments; the blood the circulatory system and lymphatic system are involved. Blood cells. There are three distinct groups, classified All communication systems involve receiving, collating according to their functions(Fig. 1.5) and responding to appropriate information Erythrocytes(red blood cells) are concerned with the There are different systems for communicating with transport of oxygen and, to a lesser extent, carbon dioxide the internal and external environments. Internal commu- between the lungs and all body cells nication involves mainly the nervous and endocrine sys- Leukocytes(white blood cells) are mainly concerned tems, these are important in the maintenance of with protection of the body against microbes and other homeostasis and regulation of vital body functions. potentially damaging substances that gain entry to the Communication with the external environment involves body. There are several types of leukocytes which carry the special senses, and verbal and non-verbal activities, out their protective functions in different ways. These and all of these also depend on the nervous system cells are larger than erythrocytes and are less numerous Thrombocytes(platelets)are tiny cell fragments which Transport systems play an essential part in the very complex process of blood clotting The blood transports substances around the body Circulatory system( Ch 5) hrough a large network of blood vessels. In adults the This consists of a network of blood vessels and the heart body contains 5 to 61 of blood (Ch. 4). It consists of two (Fig. 1.6) uspendedin fluid called plasma and cells which are plasma Blood vessels. There are three types arteries, which carry blood away from the heart Plasma. This is mainly water with a wide range of sub- veins, which return blood to the heart stances dissolved or suspended in it. These include capillaries, which link the arteries and veins n nutrients absorbed from the alimentary cana Capillaries are tiny blood vessels with very thi in wa consisting of only one layer of cells. They are the site of Thrombocytes Erythrocytes red blood cells) Heart Blood vessels Lymphocyte Neutrophil subtype of white blood cells Figure 1.5 Blood cells after staining in the laboratory viewe Figure 1.6 The circulatory systemThe body and its constituents _8 Communication In this section, transport and communication are consid￾ered. Transport systems ensure that all cells have access to the internal and external environments; the blood, the circulatory system and lymphatic system are involved. All communication systems involve receiving, collating and responding to appropriate information. There are different systems for communicating with the internal and external environments. Internal commu￾nication involves mainly the nervous and endocrine sys￾tems; these are important in the maintenance of homeostasis and regulation of vital body functions. Communication with the external environment involves the special senses, and verbal and non-verbal activities, and all of these also depend on the nervous system. Transport systems Blood The blood transports substances around the body through a large network of blood vessels. In adults the body contains 5 to 6 1 of blood (Ch. 4). It consists of two parts —a sticky fluid called plasma and cells which are suspended in the plasma. Plasma. This is mainly water with a wide range of sub￾stances dissolved or suspended in it. These include: • nutrients absorbed from the alimentary canal • oxygen absorbed from the lungs • chemical substances synthesised by body cells, e.g. hormones • waste materials produced by body cells to be eliminated from the body by excretion. Blood cells. There are three distinct groups, classified according to their functions (Fig. 1.5). Erythrocytes (red blood cells) are concerned with the transport of oxygen and, to a lesser extent, carbon dioxide between the lungs and all body cells. Leukocytes (white blood cells) are mainly concerned with protection of the body against microbes and other potentially damaging substances that gain entry to the body. There are several types of leukocytes which carry out their protective functions in different ways. These cells are larger than erythrocytes and are less numerous. Thrombocytes (platelets) are tiny cell fragments which play an essential part in the very complex process of blood clotting. Circulatory system (Ch. 5) This consists of a network of blood vessels and the heart (Fig. 1.6). Blood vessels. There are three types: • arteries, which carry blood away from the heart • veins, which return blood to the heart • capillaries, which link the arteries and veins. Capillaries are tiny blood vessels with very thin walls consisting of only one layer of cells. They are the site of Figure 1.5 Blood cells after staining in the laboratory viewed through a microscope. Figure 1.6 The circulatory system