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Revision notes for biology

Special surfaces for exchange

To keep all cells functioning properly and alive they need...
Oxygen for aerobic respiration
Glucose as a source of energy
Protein for growth and repair
Fats to make membranes and to be a store of energy
Water
Minerals to maintain water potential…

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capillaries in close contact with alveolus wall
capillaries are so narrow that red blood cells are squeezed against the wall making
them closer to the air in the alveoli & reducing rate at which they flow past in the
blood
the total barrier to diffuse is only two flattened cells…

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Tissues in the lungs

Lungs

The trachea, bronchi and bronchioles are airways that always allow passage of
air into the lungs and out again.

To be effective these airways must meet certain requirements:
larger airways must be large enough to allow sufficient air to flow without
obstruction
must divide into…

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Much narrower than bronchi, the larger bronchioles may have some cartilage but
smaller ones have no cartilage. The wall is made mostly of smooth muscle and
elastic fibres. The smallest have clusters of alveoli at their ends.

What is the role of each tissue?
Cartilage; Structural role
Supports trachea and…

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maximum amount of air that can be forcibly exhaled after breathing in as
much as possible. Normally about 5 dm3

- Tidal lung capacity ­ The amount of air your lungs hold during normal
breathing; the amount of air moved in and out of the body in one breath. Normally…

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Respiration is important to produce heat; therefore oxygen and nutrients
need to get to cells quickly; double circulation allows this.

The structure of the mammalian heart

Muscular pump which creates pressure to propel blood through arteries &
around body.
Pressure in arteries produced due to contraction of the left ventricle…

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Atria- muscle is very thin as these chambers do not need to create much pressure.
They push blood into the ventricles.

Right ventricle- walls thicker than atria, enables atria to pump blood out of heart.
Pumps deoxygenated blood to lungs, pressure must be kept down to prevent the
capillaries in…

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Note : When pressure in major arteries is higher than pressure in ventricles, semi
lunar valves are closed.

Control of the cardiac cycle

Myogenic ­ can innate its own contraction, e.g. the heart, it will contract and relax
rhythmically even if it is not connected to the body.
Atrial muscles…

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1) We of depolarization spreads from SAN over atria
2) Ventricles depolarize, contract and pump blood into ventricles
3) Wave reaches AVN and transmitted down bundle of his
4) Wave transmitted along purkinje fibres into ventricles
5) Ventricles depolarize, contract and pump blood into arteries
6) Atria and ventricles depolarize…

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A depressed ST segment can indicate lack of oxygen to heart (myocardial
ischaemia) the drug digoxin can also cause a depressed ST segment. This could also
indicate a heart attack or angina.








Arrhythmias is the condition when the heart beat is too fast or too slow. Some are
considered normal…

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