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BY2.3 ­ Mass flow and transport ­ Part One (animals)

Mass flow system ­ transport of substances in the flow of a fluid generated by a force, requiring
energy (e.g. heart pumping blood)

Circulatory systems

Insects have an open circulatory system, dorsal tube-shaped heart and fluid-filled body cavity


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Advantages of double circulatory systems:

High blood pressure sustained
Faster circulation
Oxygenated and deoxygenated blood kept separate
Oxygen distribution improved

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The heart ­ structure and function

Atria ­ thin walled, receive blood

Ventricles ­ thick walled to generate high pressure when walls contract (left ventricle larger as the
right needs higher pressure as blood is travelling all around the body, not just lungs)

Atrioventricular/tricuspid and bicuspid valves ­ prevent backflow…

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Atrial systole: The SAN contracts and transmits electrical impulses
throughout the atria, which both contract simultaneously, pumping blood into
the ventricles. The ventricles are electrically insulated from the atria by a thin
layer of connective tissue, so they do not contract at this time:

o Chamber Atria
o Volume decreases…

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The following describes the flow of blood through the left side of the heart:
The left atrium is relaxed and receives oxygenated blood from the pulmonary vein.
When full, the pressure forces open the bicuspid valve/atrio ventricular valve between
the atrium and ventricle.
Relaxation of the left ventricle draws blood…

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Thin smooth layer of muscle in the walls, easily compressed by muscle
Thin layer of elastic tissue in the walls, easily compressed by muscle
Semi lunar valves ­ low blood pressure, so prevents blood to backflow
Venous return ­ blood helped by contraction of muscles
against the bone, squeezing the…

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In the wall of the right atrium is a region of specialised cardiac fibres called the sinoatrial node
(SAN) which acts as a pacemaker.
A wave of electrical stimulation arises at this point and then spreads over the two atria causing
them to contract more or less at the same…

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Formation of tissue fluid:
Dissolved solutes are all exchanged between the blood and the cells in the capillary beds.
Substances first diffuse from the capillaries into the tissue fluid
From here they dissolve into the cells


permeable walls
a large surface area for exchange of materials
blood flows very…

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4) There is some excess tissue fluid, this excess drains into lymph vessels, which are found in all
capillary beds. They have very thin walls and tissue fluid can easily dissolve inside, forming
lymph. Lymph is then returned to the circulatory system where it drains into the Subclavian Vein.


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In the tissues:
As PO2 decreases, going into tissues, more O2 is dissociated
In the lungs:
Hb has a higher affinity for O2 and is fully saturated at low PO2


Top right part of the graph: In the alveoli of the lungs, oxygen concentration is high at 14…




Great mixture of diagrams - some with colour. Well set out.

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