L4 - Circulatory System

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Describe the role of the circulatory system in providing cells with nutrients and removing wastes

In an open circulatory system, blood vessels transport all fluids into a cavity.

When the animal moves, the blood inside the cavity moves freely around the body in all directions.
The blood bathes the organs directly, thus supplying oxygen and removing waste from the organs.
Blood flows at a very slow speed due to the absence of smooth muscles, which, as you learnt previously, are responsible for contraction of blood vessels.
Most invertebrates (crabs, insects, snails etc.) have an open circulatory system. The fly below shows a schematic of an open circulatory system delivering blood directly to tissues.

Closed circulatory systems are different to open circulatory systems because blood never leaves the blood vessels.

Instead, it is transferred from one blood vessel to another continuously without entering a cavity.
Blood is transported in a single direction, delivering oxygen and nutrients to cells and removing waste products.
Closed circulatory systems can be further divided into single circulatory systems and double circulatory systems.

Single circulatory pathways as shown in the diagram above consist of a double chambered heart with an atrium and ventricle.

Fish possess single circulation pathways.
The heart pumps deoxygenated blood to the gills where it gets oxygenated.
Oxygenated blood is then supplied to the entire fish body, with deoxygenated blood returned to the heart.

A double circulatory system means that on any complete journey around the body, the blood will flow through the heart twice.
This system ensures a high pressure to body (to get there!), yet a low pressure to lungs (so they are not damaged!).
Pulmonary circulation: carries deoxygenated blood from the heart to the lungs to be oxygenated, and then back to the heart.
Systemic circulation: carries oxygenated blood from the heart to the cells to be used, and deoxygenated blood back to the heart
The right-side receives deoxygenated blood that has travelled around the body and pumps it to the lungs to collect oxygen and dispose of carbon dioxide.
The left side receives oxygenated blood from the lungs and sends it around the body to replenish cells with oxygen needed for respiration.
The blood from the left and the right side never mix.