Tag: body fluids and circulation

Closed circulatory system has blood closed in all vessels within vessels of different sizes. In this type, the blood is pumped through vessels by heart. This type of circulatory system is more structured and controlled. 

An open circulatory system describes a system where blood and interstitial fluid (fluid found between cells in the body) are allowed to mix in an organism. Organisms that have an open circulatory system don't have true blood since it is mixed with other fluids. The blood in these organisms is defined as haemolymph. Two of the largest phyla in the world, arthropoda and mollusca, have an open circulatory system. Arthropods include most insects and sea organisms like crabs and lobsters. Molluscs are organisms with two shells that are hinged together. Examples include clams and oysters. However, not all molluscs have an open circulatory system. Two major members of the mollusc family, octopus and squid, have a closed circulatory system. 

Insects have an open circulatory system, which differs in both structure and function from the closed circulatory system found in humans and other vertebrates. In an open system, blood (usually called haemolymph) flows freely within body cavities, where it makes direct contact with all internal tissues and organs.

Leeches belong to Phylum Annelida and have closed circulatory systems that carry blood, nutrients etc to all parts of the body.

In a closed circulatory system, blood is always contained within vessels - arteries, veins, capillaries.

In an open circulatory system, the blood is not confined within blood vessels. The blood bathes the organs and tissues directly. Because of this the blood and the interstitial fluid have no distinction. Thus, the term hemolymph is used. The hemolymph is pumped by the heart through the vessels into the sinuses and then to the surrounding cells where the exchange of materials occur. The hemolymph is taken back to the heart through the ostia that close via the valves during heart contraction.

Oxygen carrying pigment haemoglobin are present as separate entities and not found dissolved in plasma like inorganic salts. 

The open circulatory system is common to molluscs and arthropods. Open circulatory systems (evolved in crustaceans, insects, mollusks and other invertebrates) pump blood into a hemocoel with the blood diffusing back to the circulatory system between cells. Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood. So, the blood is not segregated from interstitial fluid.

A. The systolic blood pressure is the pressure that develops in arteries when the ventricles contract and the diastolic pressure develops when the ventricles relax. The normal range of blood pressure is 120/80 mm Hg. In hypertension, the blood pressure elevates to 130-140 mm Hg systolic and 90-100 mm Hg diastolic pressure.