Lung

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The lung or Lungs, is an organ found with in animals that is the site of gaseous exchange [1]. Every human is born with 2 lungs (a left lung and a right lung) and the lungs are found with in the chest cavity. They are encased in what is known as the thoracic cage; the ribs and the spine make up the outside of the cage and the diaphragm is found beneath the cage to act as a floor.

Contents

External anatomy of the lungs:

The left lung is divided into two lobes- the Superior lobe and the Inferior lobe. Whereas the right lung is divided into three lobes- the Superior, Inferior and the Middle lobe. The Middle lobe is found between the Inferior and Superior lobe [2].

Internal anatomy of the lungs:

This anatomy is more complicated than the external anatomy. The trachea which is found outside the lungs, connecting the lungs to the mouth to allow air flow, branches off into the primary bronchi (which is inside the lung) this branches off further into smaller bronchi, bronchioles and finally the alveoli. The alveoli is the exchange surface where gaseous exchange takes place and the other structures (bronchioles, bronchi and trachea) make up the conducting system - passing air from the outside to the inside and vice versa[3].

Ventilation of the lungs:

During ventilation of the lungs, two antagonistic processes occur one after the other. Inhalation provides fresh air that is rich in oxygen to the lungs and the alveoli whereas exhalation removes stale air from the lungs. During inhalation the diaphragm and the external intercostal muscles contract increasing thoracic volume. This results in the drop of pressure below the atmospheric pressure, forcing air to enter the lungs. The opposite process of exhalation, caused by the contraction of the internal intercostal muscles and relaxation of the diaphragm, leads to the decrease in the volume of the thorax [4][5].

There are three stages of Respiration:

  1. External respiration is the exchange of gasses from the atmosphere into the lungs
  2. Internal transport is the transport of gasses into the blood
  3. BloodInternal respiration is the exchange of gasses from the blood to cells

References

  1. Silverthorn D. (2010) Human Physiology an integrated approach, 5th edition, San Francisco: Pearson.
  2. Silverthorn D. (2010) Human Physiology an integrated approach, 5th edition, San Francisco: Pearson.
  3. Silverthorn D. (2010) Human Physiology an integrated approach, 5th edition, San Francisco: Pearson.
  4. Silverthorn, D. U. (1998) Human physiology: an integrated approach. Upper Saddle River, New Jersey: Prentice Hall.
  5. Allott, A. (2007) IB Study Guide: Biology. Oxford: Oxford University Press.

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