Circulation

Circulatory Systems
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Transport
Diffusion
Circulatory system
As organisms increase in complexity diffusion becomes inefficient
– Gases
– Components of immune systems
– Sugars, salts,
– Removal of metabolic waste

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Characteristics of a blood vascular system

• A blood circulatory system consists of the following:
• Two types
– Open →
Arthropods
– Closed →
Vertebrates
• Pump
• Vessels
• Circulatory fluid

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Circulatory system - Open
• Insects and some molluscs
• Blood pumped by heart → blood spaces
• Sinuses
• Blood in direct contact with tissues • Returns to heart via open veins
• No control

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Circulation in vertebrates

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Double circulation
• Blood moves through heart 2x during a circuit
– Lungs
– Body
– Low pressure from lungs,

• Birds
• Warm blooded creatures
• High metabolic rate
– Requires good oxygen supply → aerobic respiration

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Human cardiovascular system
• Human cardiovascular system blood flows
• Muscular heart → arteries → smaller aterioles → arterioles → capillaries
– take blood to the tissues
• Capillaries → venules → veins
• Transport blood from tissues → return the blood to heart.

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Organs parallel not sequential

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The Heart

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The structure of blood vessels
Tunica
externa

Endothelium

Endothelium

• Tunica externa
– Collagen fibres
– outermost layer → forms a connective tissue sheath
– stabilise & anchor the vessel → blending of connective tissue fibres into adjacent tissue.

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The structure of blood vessels
Tunica
externa

Endothelium

Endothelium

• Tunica media
– Smooth muscle, connective tissue +elastic fibres
– stimulated by sympathetic nerve fibres
– very thick in arteries.
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Veins

• Veins carry blood from capillaries to the heart.
– pulmonary veins,
– Venules
– Pressure in veins low
– muscular contractions
– valves

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Varicose veins

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Capillaries
• Capillaries
– Join