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Unit 1 Section 5: Transport in Animals
The Ciculatory System

Be able to explain the need for transport systems in multicellular animals in terms of
size, level of activity and surface area : volume ratio.

Be able to explain the meaning of the terms 'single circulatory system' and 'double

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The human circulation system is a double circulatory system. One part serves the lungs, and this
is called pulmonary circulation. The other part serves the rest of the body, and is called the
systemic circulation.

Fish, however, have a single circulatory system. Here the blood is pumped out of the…

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Structure of the cardiac muscle
The outer and inner layers of the heart are made up of epithelial cells and connective tissue.
Myocardium comprises of cardiac muscle which can contract and relax for a long time without
fatigue. It is made up of actin and myosin. Cardiac muscle is made…

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The pulmonary vein is connected to the left atrium and brings oxygenated blood back
from the lungs. Unusually for a vein it carries oxygenated blood.

Supplying the cardiac muscle with oxygen
The heart muscle is supplied by its own blood vessels called coronary arteries, which branch off
the aorta shortly…

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to myocardial infarction, or heart attack, because an area of the heart muscle is deprived of
oxygen and so dies leaving scar tissue.

The cardiac cycle


Blood vessels
Arteries carry blood away from the heart. Blood has a high pressure as it is pushed out…

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high-pressure blood
pulses through.
Smooth muscle in Relatively large amount in Small amount. All blood None
wall small arteries and in veins is travelling back
arterioles. Contraction of to the heart, so there is
this muscle reduces the no advantage in being
size of the lumen, which able to divert…

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Red blood cells
Erythrocytes are biconcave discs. Around 78µm in diameter, there are 5 million in each mm3 of
blood and each lives for around 120 days.
Made in the bone marrow.
Red blood cells have no nucleus, mitochondria, rough endoplasmic reticulum or Golgi apparatus
when mature ­ although it…

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Blood pumped by the heart passes along arteries, arterioles and the capillaries. This creates
hydrostatic pressure of around 4.8 kPa at the arterial end of the capillaries, which tends to force
liquid out of the blood. The outward pressure is opposed by two forces:
Hydrostatic pressure of the tissue fluid…

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Enlargement of the thorax during breathing in reduces pressure in the thorax, drawing
lymph into this region and away from the tissues.

Blood Plasma Tissue fluid Lymph
Cells Erythrocytes, None None Lymphocytes
leucocytes and
Location Within heart, Within heart, Outside vessels, Within lymph
arteries, veins and arteries, veins and…

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The walls of the alveoli are made of two types of cell:
Type I pneumocytes ­ squamous epithelial cells
Type II pneumocytes ­ special type of epithelial cell which produces a chemical called
Surfactants reduce the surface tension of substances, most commonly water. They are best
known for their…


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