When the blood circulates through a series of vessels of varying diameter, it is termed

Closed circulatory system refers to the type of circulation where blood flows through a continuous system of vessels (arteries, capillaries, and veins) and does not leave the vessels to flow into open spaces around tissues. In closed circulation, blood remains within the vessels as it circulates through the body, ensuring efficient transport of oxygen, nutrients, hormones, and waste products.

Open circulatory system is a type of circulation found in some invertebrates where blood leaves the vessels and flows through open spaces (sinuses) around tissues before returning to the heart. 

Renal portal system refers to a specific circulation found in some vertebrates where blood from the hind limbs or tail flows first through the kidneys before returning to the heart. 

Hepatic portal circulation refers to the circulation of blood from the digestive organs (stomach, intestines) through the portal vein to the liver before it enters the general systemic circulation.