Transport, Circulatory System, and Communication – Key Terms

Transport systems

• In this section, transport and communication are considered. 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 communication involves mainly the nervous and endocrine systems; 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.

Blood

• The blood transports substances around the body through a large network of blood vessels.

• In adults the body contains 5 to 61 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 substances 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

• 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