Dual System

Blood circulation in animals with a dual circulatory system has a number of features. Firstly, it is closed, that is, it does not communicate with the external environment, in contrast to the open blood circulation of some invertebrates. Secondly, it is double - it consists of two separate blood flow circuits. And thirdly, it is complete - arterial and venous blood never mix in it.

Blood circulation forms two circles:

1. Small, or pulmonary circle. Located between the heart and lungs. Blood saturated with carbon dioxide enters the lungs and is enriched with oxygen.

2. Large, or general circle. Transports oxygen-enriched blood from the heart to various organs and tissues of the body and returns venous blood with metabolic products back to the heart.

Thus, the dual circulatory system ensures efficient transport of oxygen and nutrients to the body's cells and removal of metabolic products. This is the most important feature of the organization of the circulatory system of vertebrates and humans.