• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

The heart is a pear-shaped organ located in the thoracic cavity.

Extracts from this document...


The Heart (unit 1) The heart is a pear-shaped organ located in the thoracic cavity. It lies underneath the sternum between the lungs. The heart consists of three layers. 1. The pericardium; which is an outer, double layered bag containing a thin film of fluid. Its function is to reduce friction between the heart and other parts of the thoracic cavity and to maintain the heart shape. 2. The myocardium, or cardiac muscle; contracts in the same way as skeletal muscle. The heart has a pacemaker which sends impulses throughout the myocardium. Because of its united structure, all cells forming the entire myocardium muscle sheet contract together, producing a heartbeat. This is the all or none law. ...read more.


sends out impulses. The S.A. node is located in the right atrial wall. It is the rate at which the pacemaker emits impulses that determines the heart rate. Cardiac output also changes during exercise. Cardiac output is defined as the stroke volume (amount of blood ejected from a ventricle at each heart beat) multiplied by the heart rate. During the initial stages of exercise, increased cardiac output is due to an increase in both heart rate and stroke volume. When the level of exercise exceeds 40% to 60% of the individual's capacity, stroke volume has either plateaued or begun to increase at a much slower rate. Thus further increases in cardiac output are largely the result of increases in heart rate. The more blood pumped, the more oxygen is available to the exercising muscles. ...read more.


This decrease in heart rate is called bradycardia. The heart adapts to aerobic exercise over time so it can pump more blood per stroke. If I play a match at the beginning of the season when I am untrained, cardiac output can increase to four times resting capacity. In the untrained female, it goes from pumping 4 to 5 litres a minute at rest to 16 to 20 litres a minute during exercise, primarily through an increase in heart rate. In trained athletes such as Serena who trains throughout the year, the cardiac output can increase up to eight times the resting output. This is brought about not only by an increase in heart rate, but also by a training-induced increase in the stroke volume - the amount of blood ejected with each heartbeat. Rachel Jones ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Humans as Organisms section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Humans as Organisms essays

  1. Marked by a teacher

    Artificial Cardiac Pacemakers

    5 star(s)

    This could have many disastrous effects, including death, or the return of old symptoms (such as palpitations or shortness of breath). Also, interference from other electrical devices can cause the pacemaker to malfunction. Therefore, certain medical treatments must be avoided, including "electro cauterization" and "shock-wave lithotripsy"36 Many pacemakers contain private

  2. Effects of Exercise on Cardiac Output.

    so there is less of an oxygen debt, therefore there is a steady decrease. As the males have a 151 beats per minute at exercise (9 beats per minute higher than females) it will take the male's heart rates slightly longer to return to their average resting heart rate.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work