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Why have a heart and circulation?

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Dr Speller

on 6 September 2018

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Transcript of Why have a heart and circulation?

Why have a heart and circulation?
In vertebrates blood retained in blood vessels; blood vessels + heart = circulatory system
This allows generation of higher pressure so blood travels faster – increases efficiency
Heart  arteries arterioles  capillaries (large number; site of exchange between blood and cells)  venules  veins  heart
Valves – in heart and veins – ensure one way flow

Q 1.3: Fish have two-chambered hearts and mammals have four-chambered hearts. Sketch what the three-chambered heart of an amphibian might look like.
Blood can pass slowly through the region where gas exchange occurs maximising the transfer of oxygen and carbon dioxide although this causes a large pressure drop so blood has to be returned to the heart and then be pumped under high pressure around the rest of the body enabling the organism to be very active.
Q 1.2: What are the advantages of having a double circulatory system?
Some mixing of oxygenated blood (from lungs) with deoxygenated blood (from the body) in the ventricle.

Q 1.4: What might be the major disadvantage of this three-chamber system?
Movement of oxygen, carbon dioxide and other products carried by blood relies on diffusion in an open system - diffusion is only fast enough for small animals (rate of diffusion is inversely proportional to the distance)

Q 1.1: Why do only small animals have an open circulatory system?
In larger organisms diffusion is too slow to move materials throughout the body fast enough and in sufficient quantities to support high metabolic rates.

Such organisms have mass flow transport system involving fluid (i.e. blood) which is made to move around body by a pump (i.e. heart).

This is a circulatory system.

Why many animals have a heart and circulation...


They are thin enough and small enough for sufficient materials to diffuse to and from every cell

They have a large surface area to volume ratio so sufficient oxygen can diffuse in across the entire surface...

Small organisms (such as flatworms) do not need a circulatory system because...

Why many animals have a heart and circulation...

Learning objective:

1.1 Understand why many animals have a heart and circulation (mass transport to overcome limitations of diffusion in meeting the requirements of organisms).

What needs to be transported?
Open circulatory systems
Insects, snails and other animal groups have a heart that pumps blood (hemolymph) into the cavities surrounding the animal's organs.
Closed circulatory systems
Many animals, including all vertebrates, have blood enclosed in vessels - a closed system.
Closed circulatory systems
Closed systems generate higher blood pressure as blood is forced down narrow tubes.
This means blood flows faster and is therefore more efficient at delivering substances to cells in the body.
Closed circulatory systems
Two types:
Compare an animal with a closed system to one with an open system.
Points for thought:
• The pattern of circulation in mammals is often referred to as a ‘double circulation’; blood flows from the heart to the lungs, back to the heart and then out to the rest of the body, before returning again to the heart. Other types of vertebrates have evolved different patterns of circulation.
• Evolution is a theory — a hypothesis with scientific evidence to support it.
• Evolutionary theory holds that all vertebrate groups share ancestry at some point in the past.
• The physiology of living vertebrates may give indirect evidence about the physiology and evolutionary relationships of extinct animals.
• Our mammalian pattern of circulation is sometimes affected by congenital defects — defects people are born with.
• It is important to diagnose and, when appropriate, treat them
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