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

The Mammalian Heart and Circulatory System

Extracts from this document...

Introduction

The Mammalian Heart and Circulatory System The heart is a muscular structure that contracts in a rhythmic pattern to pump blood. Hearts have a variety of forms: I am going to look at the mammalian heart which is comprised of four chambers. The heart is the centre of the cardiovascular system. On average the heart beats over 100 000 times a day and pumps 3780 litres of blood through 100 000 kilometres of blood vessels. The circulatory system functions in the delivery of oxygen, nutrient molecules, and hormones and the removal of carbon dioxide, ammonia and other metabolic wastes. It also helps to maintain fluid balance, regulate body temperature, and it assists in the defence of the body against invading microorganisms. Mammals have a double circulatory system: a pulmonary system, which carries blood between the heart and lungs, and a systemic system, which carries blood between the heart and the rest of the body. Capillaries are the points of exchange between the blood and surrounding tissues. Material crosses in and out of the capillaries by passing through or between the cells that line the capillary. The structure of the heart is shown in the diagram below: Mammals have a double circulation, which means that the right hand side of the heart pumps deoxygenated blood to the lungs in the pulmonary artery to pick up oxygen and release carbon dioxide. The oxygenated blood then returns to the left-hand side of the heart in the pulmonary vein. ...read more.

Middle

E.g. during heavy exercise, the heart rate and the breathing rate will increase significantly. When the atria and ventricles are in diastole, blood at a low pressure in the veins flows into the atria which fill with blood and increase this pressure, meanwhile the atrioventricular valves are shut. With rising atrial pressure these valves are then pushed open and the ventricles start to fill with blood. During the 0.3 seconds of contraction, there is both atrial systole followed by ventricular systole. The sinoatrial node initiates an electrical impulse that travels across the atrial walls. This contracts the myocardium of each atrium and atrial systole then forces all remaining blood past the atrioventricular valves into the ventricles. The semi-lunar valves are closed during this. The electrical impulse passes from the atrioventricular node to the bundle of His then to the purkinje fibres. There is a slight delay at the AV node to ensure that both contract at the same time. The myocardium of the ventricles contract, the bicuspid and tricuspid valves remain closed, and the pressure increases in the ventricles and pushes open the semi-lunar valves. This whole contraction results in blood flow out of the heart and into the pulmonary and systemic circulatory systems. Cardiac contractions are initiated by an electrical impulse that originates from the sinoatrial node (pacemaker). The waves spread out over the two atrial walls so that they contract. There is a band of fibres between the atria and ventricles, which have a high electrical resistance so the waves cannot spread from the atria to the ventricles. ...read more.

Conclusion

Nutrients, wastes, and hormones are exchanged across the thin walls of capillaries. Capillaries are microscopic in size, although blushing is one manifestation of blood flow into capillaries. Control of blood flow into capillary beds is done by nerve-controlled sphincters. This is the capillary structure: The extensive network of capillaries in the human body is estimated at between 50,000 and 60,000 miles long. Blood leaving the capillary beds flows into a progressively larger series of venules that in turn join to form veins. Veins carry blood from capillaries to the heart. With the exception of the pulmonary veins, blood in veins is deoxygenated. The pulmonary veins carry oxygenated blood from lungs back to the heart. Venules are smaller veins that gather blood from capillary beds into veins. Pressure in veins is low, so veins depend on nearby muscular contractions to move blood along. The veins have valves that prevent back-flow of blood. The structure of veins: As blood gets farther from the heart, the pressure likewise decreases. Each contraction of the ventricles sends pressure through the arteries. Elasticity of lungs helps to keep pulmonary pressures low. Systemic pressure is sensed by receptors in the arteries and atria. Nerve messages from these sensors communicate conditions to the medulla in the brain. Signals from the medulla regulate blood pressure. In these blood vessels vital substances are transported in the blood to the tissues around the body. This is for processes such as respiration to take place. Substances include glucose, oxygen taken to the tissues, and carbon dioxide and metabolic waste, which are taken back from the tissues as waste products. ...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 means the pacemaker is only active when it needs to be, when the heart rate is too slow. This type of pacemaker is called a demand pacemaker.16 Most pacemakers are internal (surgically implanted inside the body), however some are external (worn outside the body)

  2. Marked by a teacher

    The circulatory system.

    4 star(s)

    The artery has an inner lining called the endothelium, then a layer of involuntary muscle and elastic fibres so the artery can expand and contract.

  1. Describe how the structure of arteries, veins and capillaries enables them to fulfil their ...

    If you are in a high risk category already then smoking or being overweight will make the probability of the disease occurring even greater. Smoking a cigarette increases the heart beat 15-30 beats per minute, blood pressure also increases which damages the artery walls.

  2. Stem Cell Research

    people believe that this shows a lack of respect for embryos, and therefore human life. They believe that this devaluation of human life will lead to more significant changes in the future, where the vulnerable are sacrificed to benefit others.21 If we accept this action now, then people believe that

  1. Blood - moving around our bodies via the circulatory system, consisting of the arteries, ...

    They are responsible for defending the body against infecting organisms and foreign agents, in both the tissues and the bloodstream. Converse to red blood cells, nuclei are present in leukocytes and they can be classified into two groups: granulocytes and agranulocytes.

  2. human body system

    parts of the body, and deoxygenated blood back to the right atrium of the heart. The pulmonary artery brings deoxygenated blood from the heart's right pump, this divides into two branches, one for each lung. Just as the bronchial tree divides into ever smaller branches (alveoli)

  1. The cardiovascular system is made up of the heart and the blood vessels, such ...

    Strength required to support pressure * Blood is pumped away from the heart * Blood contains oxygen (except in the case of the pulmonary artery) Veins * Three Layers, they are thinner and less muscular. * Valves prevent backflow of blood Capillaries * Single-celled layer, suitable for gas and nutrient exchange.

  2. The Pick Up

    He chuckles. Time itself seems to have stilled in the darkness. From nowhere a blood-curdling screech pierces the silence as a huge, dark shape whizzes by Derek's ear. Immediately Derek drops to the ground, his heart pounding like a jackhammer.

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