TYPES OF CIRCULATORY SYSTEM IN ANIMALS
Open circulatory system e.g. in insects and molluscs.
Closed circulatory system found in most higher animals. This involves movement of blood within vessels. These vessels are arteries, arterioles, capillaries, veins and venules. It occurs in all vertebrates.

CLASS ACTIVITY
In a tabular form, state five differences between open and closed circulatory systems

VERTEBRATE CLOSED CIRCULATORY SYSTEMS
There are two types of closed circulatory systems in vertebrates, they are:
Single circulation e.g. in fish. Here blood moves in one direction from the heart through the ventricle to the gill for oxygenation (i.e. gill filaments) and to the body for cell and tissue use. The blood is returned to the heart through the single auricle for another cycle.

Note:
This type of circulation shows that the heart is two chambered.
During blood circulation in fish, the liver receives oxygenated blood directly from the gills and from deoxygenated but nutrient rich blood from the gut; just like the case of other vertebrates. More so, the kidneys receive oxygenated blood directly from  the gills and deoxygenated blood from the tail.
2. Double circulation e.g. in mammals. Here, blood moves in two directions, i.e.
I. heart and lung. This is called pulmonary circulation
II. heart and body. This is called systemic circulation

Note: this type of circulation shows that the heart is double chambered, that is two auricles and two ventricles.
PULMONARY CIRCULATION: it is the movement/circulation/flow of de-oxygenated blood from the heart to the lungs to pick oxygen, and back to the heart.
SYSTEMIC CIRCULATION: it is the movement of oxygenated blood from the heart to the body for use, and return back to the heart de-oxygenated.
Note the explanations on pulmonary and systemic explain the sequence involved in double circulation