Physiology Flashcards
What is internal respiration?
The intracellular mechanisms which consume oxygen and produce carbon dioxide
What is external respiration?
The sequence of events that lead to the exchange of oxygen and carbon dioxide between the external environment and the cells of the body
What are the 4 steps of external respiration?
Ventilation
Gas exchange between alveoli and blood
Gas transport in the blood
Gas exchange at the tissue level
Describe ventilation (2)
The mechanical process of moving gas in and out of the lungs. Here, gas exchange occurs between the atmosphere and the air sacs in the lungs
In step 2 of external respiration, where is the gas exchanged?
Between the alveoli and the pulmonary capillaries
Describe the gas transport in the blood
The binding and transport of oxygen and carbon dioxide in the circulating blood
What are the 4 body systems involved in external respiration?
Respiratory
Cardiovascular
Haematology
Nervous
What physics law applies to ventilation and what does it entail?
Boyles Law - at any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas
What does Boyles Law mean practically?
As the volume of the gas increases, the pressure exerted by the gas decreases
What is key to remember with air flow in the respiratory system?
Moves down the pressure gradient from a region of high pressure to low pressure.
How does intra-alveolar pressure compare to atmospheric pressure and why?
Intra-avlevolar pressure is less than atmospheric as air will therefore move passively down the pressure gradient
How is a lower than atmospheric pressure achieved in the alveoli? (4)
Before inspiration, intra-alveolar pressure is the same as atmospheric
During inspiration, the thorax and lungs expand as a result of contraction of inspiratory muscles.
Therefore the volume in which the gas is distributed is greater
Therefore the pressure decreases
What are the two forces holding the lungs and the thoracic wall close together?
Intrapleural fluid cohesiveness
Negative intrapleural pressure
What intrapleural fluid cohesiveness?
The water molecules in the fluid between the two layers of pleural are attracted to each other and therefore resist being pulled apart
What is the negative intrapleural pressure?
Teh sub-atmospheric intrapleural pressure creates a transmural pressure graidient across the lung and chest wall, meaning they are forced to expand outwards while the chest is forced to squeeze inwards
Which force is more important out of the two forces that holds the lung and the thoracic wall together?
The negative intrapleural pressure
What are the intra-alveolar pressures pushing outwards and pushing inwards?
760mmHg outwards
756mmHg inwards
What does the difference in the inwards and outwards intra-alveolar pressures result in?
Transmural pressure gradient that pushes out on the lungs, stretching them to fill the thoracic cavity.
Which three pressures are important in ventilation?
Atmospheric
Intra-alveolar
Intrapleural
What is atmospheric pressure and what is its numerical value?
The pressure exerted by the weight of the gas in the atmosphere on objects - 760mmHg at sea level
What is the intrapleural pressure?
The pressure within the pleural sac (i.e. the pressure exerted on the outside of the lungs, within the thoracic cavity) - 756mmHg
What is inspiration?
The process of breathing in
What does inspiration depend on?
Muscle contraction
How does inspiration start? (2)
The volume of the thorax is increased vertically by the diaphragm contracting, and therefore flattening out its dome shape
What are the nerves involved in diaphragmatic movement?
Phernic nerve from the cervical 3,4 and 5
how are the external intercostal muscles involved in inspiration?
They contract, lifting the ribs and moving the sternum upwards and outwards.
In which direction does the diaphragm move?
Downwards
When does air stop coming into the lungs on inspiration?
When the intra-alveolar pressure is equal to atmospheric pressure
How is expiration brought about?
By a relaxation of the inspiratory muscles
What type of process is inspiration?
Passive
What size do the organs of respiration end up after inspiration and why?
Their pre-inspiratory size due to the cell’s elastic recoil
State the process of expiration
The contracted muscles relax and the elastic recoil of the chest wall and lungs make the intra-alveolar pressure increase
This is due to there being a smaller volume in which the air is present
This means that air will leave the lungs until the intra-alveolar pressure reaches atmospheric again
What is a pneumothorax?
Where there is air in the pleural space
What is the key thing that happens when there is a pneumothorax?
The transmural pressure gradient is abolished.
What happens (in terms of pressure) when there is a pneumothorax?
Air enters the pleural space to equalise the pressure difference between the lungs/atmosphere and the pleural space
What are the two types of pneumothorax?
Traumatic and Spontaneous
What is a traumatic pneumothorax?
When there is a puncture in the chest wall that permits air into the plural cavity
What is a spontaneous pneumothorax?
A hole in the lung wall that allows aur from the lung into the pleural space.
What is a collapsed lung?
When the transmural pressure gradient is abolished, meaning that all three pressures are equal.
What are the consequences of a collapsed lung?
The lung collapses to its unstretched size and the chest wall springs outwards
What are the two things that cause the lungs to recoil during expiration?
The elastic connective tissue in the lungs
The alveolar surface tension
What is the alveolar surface tension?
The force produced by the small water molecules that line the alveolar as they attract each other
What does the alveolar surface tension do?
Resist the stretching of the lungs
What would happen if the alveoli were lined purely with water?
The surface tension would be too strong and the alveoli would collapse