Open and Closed Circulatory System: All you will need to know

Circulatory System: Larger animals need a higher and faster supply of nutrients and oxygen to their tissues. They also need the rapid removal of respiratory and nitrogenous wastes. As a result, blood has evolved as a specialised circulatory fluid. But the circulatory system consists of the heart, blood, and blood arteries. This is also for controlling and pumping blood to the tissues. It has been developed. There are two types of blood circulatory systems. Threrefore, open circulatory system and a closed circulatory system are the two types of circulatory systems. Circulatory systems of living things differ from one another.

Many clams and other invertebrates have an open circulatory system. However, humans have a closed one. Blood is surrounded inside blood vessels. The vessels are also in a secure circulatory system. In an open circulatory system, blood arteries open into slots rather than capillaries. This allows blood to touch tissues directly. Blood also travels via capillaries connected by arteries and veins in a closed circulatory system. The pace of circulation in an open circulatory system is sluggish. But it is fast in a closed circulatory system.

If you want to know more about this topic, you’re welcome here. Read on as we explore the facts about the different circulatory systems.


Open and Closed Circulatory System Definition

Most animals are multicellular. They are complex creatures that require a system to carry nutrients. They also need to waste materials throughout their bodies. The circulatory system has developed through time. This also happens to form simple diffusion through cells in early animal development. Thus building a sophisticated network of blood arteries that reaches every region of the human body. This vast network transports oxygen and nutrients to cells, tissues, and organs. Thus the network also eliminates carbon dioxide and waste. These are byproducts of respiration. We may compare the circulatory system to a freeway that travels throughout the human body.

The heart is also at the centre of the human circulatory system. The heart, the size of a clenched fist, is protected behind the rib cage. However, it pumps blood throughout the body and to the heart itself. It is made up of specialised and distinct cardiac muscle. Heart contractions are triggered by intrinsic electrical impulses that are regulated by the brain and endocrine hormones. Understanding the fundamental anatomy and function of the heart is very crucial. It also helps in comprehending the circulatory and respiratory systems of the body.

The circulatory system’s gas exchange is also an important function. However, oxygen and carbon dioxide pass directly between their bodily tissues. The external environment in creatures lives without specific respiratory organs. However, we must deliver oxygen from specialised respiratory organs such as lungs and gills to body tissues.

Open and Closed Circulatory System Architecture

The circulatory system is a creation of a network of cylindrical vessels. Arteries, veins, and capillaries also branch out from the heart. This is a closed-loop system in which blood does not move freely. It stays in a cavity in all vertebrate animals and certain invertebrates. Blood also confines inside blood vessels in a closed circulatory system. It circulates unidirectionally (in one direction) from the heart. It goes around the systemic circulatory route before returning to the heart.

Read Also: Analogous Structures: Definition & Examples

Arthropods (insects, crustaceans, and most molluscs) have an open circulatory system. In an open circulatory system, blood is pumping into a cavity called a hemocoel. This is rather from being contained in blood vessels. Because it interacts with the interstitial fluid, blood is termed hemolymph. The hemolymph circulates throughout the organs within the body cavity. The heartbeats, and the animal moves, reentering the heart through openings called Ostia. This mobility enables the exchange of gases and nutrients. A closed circulatory system consumes more energy to run. Thus it maintains an open circulatory system.

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Open circulatory system

The open circulatory system in arthropods is the central system. The fluid in this cavity is also popular as the hemocoel. Hemocoel bathes the organs directly with oxygen and nutrients. Thus there is no difference between blood and interstitial fluid. This mixed fluid is popular as hemolymph or haemolymph. The animal’s muscular movements aid hemolymph mobility during locomotion. However, the ability to redirect flow from one region to another is not available. Blood gets back toward the heart as the heart relaxes through open-ended pores.

Hemolymph is a fluid that fills the body’s inner hemocoel and surrounds all cells. Water, inorganic salts and organic substances make up hemolymph. This also consists mostly of carbohydrates, proteins, and lipids. Hemocyanin is the major oxygen transporter molecule.

Hemocytes are free-floating cells found in the hemolymph. Therefore, they play a role in the immunological system of arthropods.

Closed circulatory system

All vertebrates, as well as of annelids (such as earthworms) and cephalopods (such as squids, octopuses, and cousins), have closed circulatory systems. They keep flowing blood confined within heart chambers or blood arteries. It works exactly like humans. Even so, the circulatory systems of fish, amphibians, reptiles, and birds indicate different phases of development.

The blood is pumped via the capillaries of the gills. It goes on to the veins of the body tissues in fish. It uses only one circuit. Single-cycle circulation is the term for this type of system. As a result, the heart of a fish has only one pump (consisting of two chambers).

A twofold circulatory system is utilisable in amphibians and most reptiles. However, the heart is not always entirely parted into two pumps. Amphibians have a heart with three chambers.

The ventricular septum of the heart is partial in reptiles. But the pulmonary artery has a sphincter muscle. This opens up a second potential path for blood flow. Instead of blood flowing through the pulmonary artery to the lungs, the sphincter may be constrained. It allows blood to pass through the incomplete ventricular septum into the left ventricle. It can also go out through the aorta. This implies blood travelling from the capillaries to the heart and back to the capillaries.

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Open and Closed Circulatory System Difference

Open and closed circulatory systems help in moving materials and fluids from one region of the body to another. In the available circulatory system, this fluid is haemolymph; in the closed circulatory system, it is blood. The heart serves as a pumping mechanism in both circulatory systems. The primary difference between an open and closed circulatory system is that tissues in an open circulatory system directly touch the haemolymph during the material exchange. In contrast, blood does not come into direct contact with tissues during the material exchange in a closed circulatory system.

Open and Closed Circulatory System Definition

The open circulatory system is where the hemolymph flows in the organs and tissues directly. No interstitial fluid interferes between blood and tissues.

A closed circulatory system is the type of system where blood circulates in closed vessels. It is also distinct from the interstitial fluid.

Open and Closed Circulatory System Location

Arthropods and molluscs have open circulatory systems.

Closed circulatory systems are seen in vertebrates and annelids.

Open and Closed Circulatory System Mechanism

Blood is pumped into a bodily cavity through an open circulatory system. The heart pumps blood through arteries in a closed circulatory system.

Open and Closed Circulatory System – Capillary System

A dorsal blood artery is part of the open circulatory system. Both dorsal and ventral blood veins are part of the closed circulatory system.

Open and Closed Circulatory System – Tissues

Tissues in an open circulatory system are together with blood. Blood does not come into direct touch with tissues in a closed circulatory system.

Open and Closed Circulatory System – Exchange of Materials

In an open circulatory system, only nutrients are transferred directly between blood and tissues. In a closed circulatory system, gases and nutrients are transferred via tissue fluid.

Open and Closed Circulatory System – Gas transportation

The open circulatory system does not carry gases. The closed circulatory system transports gases.

Circulatory Fluid

Haemolymph is the fluid that circulates in an open circulatory system. Blood is the fluid that circulates in a closed circulatory system.


The haemolymph has no respiratory pigments. Respiratory pigments are found in the blood, which is important in gas transport.

Blood Regulation

In an open circulatory system, the amount of blood cannot regulate itself. Hence, the contraction and relaxation of blood arteries regulate blood flow.

Blood Flow

In an open circulatory system, blood flow is exceptionally sluggish.

In a closed circulatory system, blood flow is fast.

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Open and Closed Circulatory System Examples in Animals

Examples of animals with open circulatory systems:

  • The Arthropods
  • The Mollusks
  • Most Insects

Examples of animals with closed circulatory systems:

  • All vertebrates (humans, rabbits).

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