Physiology Flashcards
What is meant by internal respiration?
The intracellular mechanisms by which oxygen is consumed and carbon dioxide is produced.
What is meant by external respiration?
The sequence of events that leads to the exchange of oxygen and carbon dioxide between the external environment and the cells of the body. This involves four steps.
Give the four stapes of external respiration?
- Ventilation or gas exchange between the atmosphere and alveoli in the lungs
- Exchange of oxygen and carbon dioxide between air in the alveoli and the blood.
- Transport of oxygen and carbon dioxide between the lungs and tissues
- Exchange of oxygen and carbon dioxide between the blood and the tissues.
This then leads into internal respiration!
What is ventilation?
The process of moving air between the atmosphere and the alveolar sacs.
What is Boyle’s law?
“At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas”
This means as the volume of a gas increases the pressure exerted by it decreases.
What must happen before air will flow into the lungs?
The intra alveolar pressure must become less that the atmospheric pressure for air to flow in. This is because air will always flow down a pressure gradient.
How is the change in atmospheric pressure achieved before inspiration? (Before inspiration intra alveolar pressure and atmospheric pressure are equal)
The thorax and lungs expand duet contraction of inspiratory muscles. This means that the volume has increased and so pressure decreases, resulting in the required gradient.
How does movement of the chest walls expand the lungs?
There is no physical connection but the intrapleural fluid and negative intrapleural pressure mena they are very closely connected.
What two forces hold the thoracic wall and the lungs in close opposition?
- Intrapleural fluid cohesivness. This means the pleural membranes tend to stick together.
- The negative intrapleural pressure. The sub atmospheric intrapleural pressure and so creates a transmural pressure gradient across the lung wall and across the chest wall. This means the lungs are forced to expand outwards when the chest is forced to squeeze inwards.
What is meant by the term transmural pressure gradient across the lung wall?
Intra-alveolar pressure - intrapleural pressure
Across the lung wall, there is an outward push of 760mmHg by the intra - alveolar pressure. There is an intrapleural pressure of 756mmHg which pushes inwards.
This means that overall there in a 4mmHg difference which constitutes a transmural pressure gradients that pushes towards on the lungs, making them stretch to fill the thoracic cavity.
What is meant by the term transmural pressure gradient across the thoracic wall?
Atmospheric pressure - intrapleural pressure
The atmospheric pressure of 760mmHg pushes inwards while the intrapleural pressure of 756mmHg pushes outwards. This 4mmHg difference constitutes a transmural pressure gradient that pushes inward and compresses the thoracic wall.
What does transmural pressure mean?
The pressure on two different sides of a partition. Transpulmonary pressure is the difference between the alveolar pressure and the intrapleural pressure in the lungs. During human ventilation, air flows because of pressure gradients.
What two muscles contract to increase the volume of the thoracic cavity?
The diaphragm
The external intercostal muscles
In inspiration a passive or active process?
Active
In expiration a passive or active process?
passive (as it is brought around by muscle relaxation)
What does recoil of the lungs do to the itra alveolar pressure?
Causes it to rise (as volume has decreases) and so air to move out down a pressure gradient
What two things cause the lungs to recoil during expiration?
Elastic connective tissue in the lungs
Alveolar surface tension
What is alveolar surface tension?
Attraction between water molecules at a liquid air interface. In the alveoli this produces a force which resists the stretching of the lungs.
What reduces the alveolar surface tension?
Surfactant
What is surfactant?
A complex mixture of lipids and proteins which act to intersperse the water molecules lining the alveoli and lowers surface tension.
What secretes surfactant?
Type 2 alveoli
What is infant respiratory distress syndrome?
Babies born prematurely have not yet developed the ability to produce surfactant and so the baby finds it very hard to overcome the high surface tension and to breath.
Give another factor, aside from surfactant, which helps keep the alveoli open:
Alveolar interdépendance. Alveoli are usually found in a group of interconnected alveoli so the expanding forces of individual ones helps keep them all open.
What happens in the case of a traumatic pneumothorax?
A puncture in the chest wall permits air from the atmosphere to flow down its pressure gradients and into the pleural cavity and in doing so abolishes the transmural pressure gradient needed to expand.The lung will collapse to an unstretched size.
What are the muscles of active inspiration?
Abdominal muscles and internal intercostal muscles
What are the accessory muscles of forceful inspiration?
sternocleidomastoid and scalenus muscles.
What does tidal volume mean and what is its usual value?
Volume of air entering or leaving the lungs during a single breath: 500ml
What does inspiratory reserve volume mean and what is its normal value?
Extra volume of air that can be maximally inspired over and above the typical resting tidal volume: 3000ml
What does inspiratory capacity mean and what is its usual value?
Maximum volume of air that can be inspired at the end of a normal, quiet, expiration: 3500ml
IC = IRV + TV
What does expiratory reserve volume mean and what is its usual value?
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume: 1000ml
What does residual volume means and what is its usual value?
Minimum volume of air remaining in the lungs after a maximal expiration: 1200ml
What is functional residual capacity and what is its average value?
Volume of air in the lungs are the ends of a normal, passive expiration: 2200ml
FRC +ERV +RV
What is vital capacity and what is its normal value?
Maximum volume of air that can be moved out during a single breath following maximal inspiration: 4500ml
(VC = IRV + TV + ERV)
What is total lung capacity and what is its value?
Maximum volume of air that the lungs can hold: 5700ml
(TLC = VC +RV)
What is forced expiratory volume in one second/Dynamic volume and what is its usual value?
The volume of air that can be expired during the first second of expiration in an FVC (forced vital capacity) determination.
FEV% =FEV1/FVC. This ratio should be over 75%
What would the FEV1:FVC ration be like in someone with asthma?
Less than 75%
What would the FEV1/FVC ratio be like in someone with restrictive lung disease?
Normal
What would be lower in someone with a restrictive lung disease?
Both the FVC and the FEV1 but the ratio would be normal
What would the spirometry results be in someone with obstructive lung disease?
Normal or low FVC, Low FEV1
But low ratio
What spirometry pattern would you seen in someone with a combination of obstructive and restrictive lung disease?
Low FVC
Low FEV1
Low ratio
What does parasympathetic stimulation do to the airways?
Causes bronchoconstriction.
What does sympathetic stimulation do to the airways?
Causes bronchodilation.
Is expiration or inspiration more difficult?
Expiration
What happens to the intrapleural pressure during inspiration?
It falls
What happens to the intrapleural pressure during expiration?
It rises
What is dynamic airway compression?
It is normal, and causes no problem in healthy people but can be problematic in disease states. Normally it helps by increasing the driving press between the alveolus and the airway.
How many attempts need to be taken to get a peak flow result?
Best of three
What is lung compliance?
A measure of effort that has to go into stretching or distending the lungs. The less compliant the lungs are the more work is required to give a degree of inflation. It means a larger change of pressure is needed to produce a given change in volume.
What disease states would decrease pulmonary compliance?
- Pulmonary fibrosis (scarring)
- Pulmonary oedema
- Lung collapse
- Pneumonia
- Absence of surfactant
What spirometry pattern does decreased pulmonary compliance give?
Restrictive
Why does compliance of the lungs become abnormally increases? Give a disease state in which this can occur:
If the elastic recoil of the lungs is lost. This occurs in emphysema.
What can be a consequence of patients having to work harder to get air out of the lungs?
Hyperinflation
When would dynamic airway obstruction be aggravated?
Patients with obstructive airway diseases such as COPD and asthma.
Give four situations where the work of breathing is increased:
- Decreased pulmonary compliance
- Airway resistance increases
- Decreases elastic recoil
- When there is need for increased ventilation.
What is meant by anatomical dead space?
Some inspired air remains in the airways where it is not available for gas exchange.
What is the equation for pulmonary ventilation?
Pulmonary ventilation = tidal volume x Respiratory rate
Why is alveolar ventilation less than that of pulmonary ventilation?
Due to the presence of anatomical dead space
What is the equation fro alveolar ventilation?
(Tidal volume - dead space) x respiratory rate
What is a normal respiratory rate under resting conditions?
12
What is pulmonary ventilation?
The volume of air breathed in and out in one minute
What is alveolar ventilation?
The volume of air exchanged between the atmosphere and alveoli per minute. (This is the important one!)
What two things does the transfer of gases anywhere in the body depend on?
Ventilation
Perfusion
What is ventilation?
The rate at which gas in passing through the lungs
What is perfusion?
The rate at which blood is passing through the lungs.
What is alveolar dead space?
Ventilated alveoli which are not adequately perfused with blood (match between air in the alveoli and blood in the pulmonary capillaries is not always perfect!) In healthy people this is no problems but could increase in disease.
What is physiological dead space?
Anatomical dead space + Alveolar dead space
What local controls act on the smooth muscles of the airways and arterioles to match ventilation and perfusion?
- Accumulation of carbon dioxide in alveoli (due to increased perfusion) decreases airway resistance and increases airflow.
- Increase in alveolar oxygen as a result of increased ventilation causes pulmonary vasodilation which increases blood flow.
What effect does decreased oxygen have on the systemic arterioles?
Vasodilation
What four factors influence the rate of gas exchange across the alveolar membrane?
- Partial pressure gradient of oxygen and carbon dioxide
- Diffusion coefficient for oxygen and carbon dioxide
- Surface area of alveolar membrane
- Thickness of alveolar membrane
What is partial pressure of a gas?
The pressure that a gas would exert if it occupied the total volume for the mixture in the absence of other components.It determines the pressure gradient for one gas in a mixture of gases.
