A level Biology exam revision resources written by A level Examiners





 

The heart is a hollow pear-shaped muscular organ, that is situated between the lungs in the middle of the chest. It's role is to pump blood through the body, supplying cells with metabolites and removing waste.

The heart has four chambers: a small upper chamber (atrium), and a large lower chamber (ventricle) on each side. The adult human heart is approximately the size of a clenched fist. The anatomical knowledge needed for A level includes all the labelling in figure 3 below.

Figure 3 : Anatomical knowledge of the heart
Circulation, the heart

As the heart is a pump it can be viewed from an engineering viewpoint.

General Description:

2 pumps linked in series, self lubricating, self regulating, operational lifetime approximately 75-86yrs

Dimensions:

Inverted cone shape,
Base width approximately 100mm,
Max. length approximately 155mm, Weight approximately 300g

Performance data:

Cardiac Output (CO or Q) = Stroke Volume (SV (ml)) x Heart Rate (HR (beats per minute))

Resting Cardiac Output approximately 5-8 lm-1 (peak approximately 30 lm-1)

Resting Stroke Volume approximately 80-120 ml

Resting Heart Rate approximately 68 bpm

Construction material:

Cardiac muscle, special feature no fatigue or oxygen debt

The type of muscle that the heart is constructed from allows the continuous pumping action of the heart to be maintained throughout life without pause or rest. Table 1, compares cardiac muscle with skeletal muscle.

Table 1 : Comparing cardiac muscle with skeletal muscle
Comparing cardiac muscle with skeletal muscle. Type of muscle, Control,	skeletal, voluntary, cardiac, involuntary. Type of muscle, Initiation of contraction,	skeletal, nerve impulses (from brain), cardiac, autorhythmic contractions (myogenic from s.a. node). Type of muscle, Arrangement of fibres,	skeletal, parallel, cardiac, interwoven, intercalating. Type of muscle, Mitochondria,	skeletal, less/smaller, cardiac, more/larger.

Figure 4 : Cardiac Muscle Fibres
heart

Cardiac muscle cells are all interconnected as can be seen in figure 4, above. They are able to conduct nerve impulses from cell to cell. So if an impulse is released (from the pacemaker) it will spread through the cardiac muscle causing contraction as it spreads.



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