1.4 Types of circulatory systems

Open circulatory system

• Circulatory fluid is not always contained within blood vessels.

• The fluid (haemolymph) flows into body cavities and bathes the organs directly.

• Found in insects and most other arthropods.

• Blood pressure is relatively low and transport is generally slower.

Closed circulatory system

• Blood remains enclosed within blood vessels.

• Blood is pumped by a heart through arteries, capillaries and veins.

• Found in humans, other vertebrates and annelids such as earthworms.

• Allows blood to flow at higher pressure and enables more controlled distribution to organs.

Double circulation

Blood passes through the heart twice per complete circuit. It has two loops:

• Pulmonary circulation: heart → lungs → heart.

• Systemic circulation: heart → body tissues → heart.

Double circulation advantages

• Blood is re-pressurised after the lungs, allowing oxygenated blood to travel to the body at high pressure.

• Oxygen and glucose can be delivered rapidly to respiring cells.

• Oxygenated and deoxygenated blood are kept separate, so body tissues receive blood with a high oxygen concentration.

• This supports a high metabolic rate and helps mammals maintain a constant body temperature.

Double circulation disadvantages

• Requires a more complex circulatory system, including a four-chambered heart.

• Requires more energy to maintain than a simpler circulatory system.

Single circulation advantages

• Simple circulatory pathway.

• Blood passes through the heart once per complete circuit.

Single circulation disadvantages

• Blood pressure decreases as blood passes through the gill capillaries.

• Blood reaches body tissues at relatively low pressure.

• Slower delivery of oxygen and glucose to respiring cells.

• Less suitable for supporting a high metabolic rate.

Pulmonary circulation

• PA:transports deoxygenated blood to the lungs

• PV: transports oxygenated blood to the heart

Systemic circulation

• Aorta: transports oxygenated blood from heart to body

• Vena Cava: transports deoxygenated blood to heart

• Renal artery: transports deoxygenated blood to kidneys ( contains waste products)

• Renal vein: transports filtered deoxygenated blood away from the kidneys