WJEC BY2 Notes for 2.3 (Part One - Animals)

This topics quite big so i've only done the first half so far... will do plant transport asap :)

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  • Created on: 15-05-12 17:17
Preview of WJEC BY2 Notes for 2.3 (Part One - Animals)

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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
Earthworms have a closed circulatory system where blood is contained in blood vessels under
pressure. Organs are not in direct contact with the blood and respiratory gases are transported in
the blood.
Humans have a double circulatory system with a 4 chambered heart. Right side of the heart
pumps blood to the lungs (pulmonary circulation) and the left side pumps blood to the rest of
body (systemic circulation)

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Advantages of double circulatory systems:
High blood pressure sustained
Faster circulation
Oxygenated and deoxygenated blood kept separate
Oxygen distribution improved…read more

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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 of blood from ventricles to
atria. Left side of heart has bicuspid valves and two flaps and right side of heart has tricuspid valve
which has 3 flaps.…read more

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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.…read more

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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 from the left atrium.
The left atrium contracts pushing the remaining blood into the right ventricle through the
With the left atrium relaxed and with the bicuspid valve closed the left ventricle
contracts.…read more

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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 vein, helping blood to
return to the heart
Carries deoxygenated blood from body tissues to the
heart at a low blood pressure
Narrow lumen to increase cross sectional area ­ more
contact with blood…read more

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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 time.
The electrical stimulation is prevented from spreading to the ventricles by a thin layer of
connective tissue.…read more

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Formation of tissue fluid:
Dissolved solutes are all exchanged between the blood and the cells in the capillary beds.…read more

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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.…read more

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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 kPa. As
blood passes through the capillaries surrounding the alveoli the haemoglobin binds/associates to
the oxygen to become 95% saturated.
Middle of graph: In the tissues, e.g.…read more



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

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