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what is external respiration?

Sequence of events that lead to the exchange of O2 and CO2 between external environment and the cells of the body


what is internal respiration?

Intracellular mechanisms which consumes O2 and produces CO2


What are the 4 steps of external respiration?

1) Ventalation- gas exchange between atmosphere and air sacs(alveoli) in the lungs
2) Exchange of O2 and CO2 between the air in the alveoli and blood coming to the lungs
3) Transport of O2 and CO2 in the blood between the lungs and the tissues
4) Exchange of O2 and CO2 between the blood and the tissues


What 4 systems are involved in external respiration ?

Respiratory, cardiovascular, haematology, nervous


What is Boyles law?

At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas


What 2 forces hold the thoracic wall and lungs together?

-Intrapleural fluid cohesiveness- water molecules in the intrapleural fluid are attracted to each other and so resist being pulled apart
-negative intrapleural pressure- sub atmospheric intrapleural pressure creates transmural pressure gradient across lung wall and chest wall and so lungs forced to expand outwards and chest forced to squeeze inwards


What happens during inspiration?

Volume of the thorax is increased vertically by contraction of the diaphragm and the contraction of external intercostal muscles lift the ribs and move out the sternum. This increase in the size of lungs cause intra-alveolar pressure to fall and air enters lungs down a pressure gradient and stops when pressure becomes equal.


What happens during expiration?

The chest wall and lungs recoil making the intra-alveolar pressure rise and air leaves lungs down the pressure gradient


What causes the lungs to recoil?

Elastic connective tissue and alveolar surface tension


what reduces alveolar surface tension and how does it do this?

Surfactant- it intersperses its lipids/proteins between water molecules lining the alveoli


What value is atmospheric pressure?

760mm Hg


what is pneumothorax and what does it cause?

air in the pleural space abolishes the transmural pressure gradient and causes a collapsed lung


what is traumatic pneumothorax?

puncture wound in chest wall


what is spontaneous pneumothorax ?

Hole in lung


what is the law of Laplace?

the smaller alveoli (smaller radius) have a higher tendency to collapse