Tag: circulatory pathways

A) The hepatic portal system is the venous system that returns blood from the digestive tract and spleen to the liver. It is present in mammals.

Both Hemichordata and Arthropoda has an open circulatory system. In this system the heart pumps blood into an open cavity called a hemocoel.

The circulatory patterns are of two types open or closed. Open circulatory system is present in arthropods and molluscs in which blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses. Annelids and chordates (example humans) have a closed circulatory system in which the blood pumped by the heart is always circulated through a closed network of blood vessels. This pattern is considered to be more advantageous, as the flow of fluid can be more precisely regulated.

Vertebrates, and a few invertebrates, have a closed circulatory system. Closed circulatory systems have the blood closed at all times within vessels of different size and wall thickness. In this type of system, blood is pumped by a heart through vessels, and does not normally fill body cavities. In fish, blood flows from the heart to the gills for gas exchange, then to the rest of the body, and finally back to the heart. This is called a single circulation since the blood flows through the heart only once during each complete trip around the body. Amphibians evolved a double circulation; blood flows from the heart to the gills or lungs for gas exchange, then back to the heart to be repressurized before flowing to the rest of the body. The vessels that serve the respiratory organs are called the branchial circuit (for gills) or pulmonary circuit (for lungs). Vessels that serve the rest of the body are called the systemic circuit. The amphibian heart and most reptilian hearts have only three chambers, two atria and one ventricle and there is some mixing of oxygen-rich and oxygen-poor blood in the single ventricle. Endothermic vertebrates, the birds and mammals, have higher metabolic rates and require stricter separation of the pulmonary and systemic blood. Thus, they have four-chambered hearts. Oxygen-rich blood flows through the other ventricle to the systemic circuit.

An open circulatory system is present in arthropods in which blood is pumped by the heart passes through large vessels into open spaces or body cavities called sinuses. Annelids and chordates have a closed circulatory system in which the blood pumped by the heart is always circulated through a closed network of blood vessels.

In closed circulatory system, blood flows through closed chambers called as vessels. In open circulatory system, the blood flows in the closed vessel which further opens into a body cavity called haemocoel.

Valves are essential in circulatory systems to ensure unidirectional flow. They are found in the hearts of vertebrates, the lymphatics of vertebrates, and in various vessels of both vertebrates and some invertebrates.

Blood flows slowest in the capillaries because the total cross-sectional area of the capillary bed is much larger than that of arteries or veins, which is necessary for efficient exchange of nutrients and gases.