||1. The blood
The circulatory system transports blood throughout the body. Blood takes oxygen from the respiratory system and the nutrients from the gastrointestinal tract. In addition, it collects wastes and transports them to the kidneys in order to expel them through the urine. Likewise, it collects carbon dioxide and transports it to the lungs to expel it through respiration.
The body of a man has about five liters of blood. It is composed of:
- Red blood cells are responsible for transporting oxygen. In a drop of blood, there are between 5 and 6 million of red blood cells.
- White blood cells are larger than red blood cells. There are about seven thousands of them in a drop. They defend the body against infections: they envelop microbes and devour them.
- Platelets are very small cells. There are about three hundred thousands of them in each drop. Its mission is to plug the wounds of the veins and arteries.
- Plasma is a colorless liquid consisting of water and dissolved salts. It is responsible for leaving the wastes in the kidneys.
2. Indicate the element of blood: red blood cells, white blood cells, platelets or plasma