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5.2. The blood

The blood

Blood is a liquid connective tissue that circulates in the blood vessels of all vertebrates. It is red because red blood cells have hemoglobin, a protein to which oxygen binds.

Composition of blood

An adult person has about 5.5 liters of blood , which is made up of:

  • The blood plasma, yellowish liquid consisting of water in which many dissolved substances are: mineral salts, nutrients (glucoseamino acidsvitamins), waste substances, hormones, etc.
  • The cells blood, which are of three types:
    • Red blood cells or red blood cells or erythrocytes: These are the most numerous cells (about 5 million per mm3 of blood). They have no nucleus and contain hemoglobin, an iron-containing red pigment, which carries O2.
    • White blood cells or leukocytes: There are several types of white blood cells and they have a defensive function. We have about 6000-7000 white blood cells per mm3 of blood.
    • Platelets or thrombocytes: They are not really cells, but fragments of cells. They intervene in blood clotting , preventing blood from being lost in any hemorrhage. We have 200,000 to 300,000 platelets per mm3 of blood.

Functions of blood

The main functions of blood are:

  • It carries nutrients to all cells in the body.
  • Carries respiratory gases. The oxygen is bound in the lungs, the hemoglobin in red blood cells to form oxyhemoglobin, deep red, and is carried to the cells. There, as there is a lower concentration of oxygen inside the cell, the oxygen is released and passes into the cells. Carbon dioxide, on the other hand, dissolves well in blood plasma, and goes from cells to the lungs.
  • It collects the waste products of metabolism, which it takes to the excretory system to eliminate them, in addition to the CO2 that it eliminates through the lungs.
  • It takes part in the defense of the organism.
  • It carries hormones, substances secreted by the endocrine system.
  • Regulates the temperature, distributing the heat from warmer areas to colder ones. In this way, it achieves a body temperature of about 37 ºC, the best for the development of chemical reactions of metabolism.

Answer in your notebook

5.1.- Name the components of blood and explain the function of each component.

Answer in your notebook

5.2.- In places that are at high altitude, the oxygen pressure is lower. Why do some athletes prepare in these places before a major competition?