Physiology Flashcards
What is external respiration?
Exchange of oxygen and carbon dioxide between body cells and the external environment
What is internal respiration?
The intracellular mechanisms that consume oxygen and produce carbon dioxide.
Which 4 body systems are involved in external respiration?
- Respiratory system 2. Cardiovascular system 3. Haematology system 4. Nervous system
In terms of respiration what does the term “ventilation” refer to?
The mechanical process of moving air between the alveoli and the atmosphere
What is Boyle’s Law?
At a constant temperature, the pressure exerted by a gas varies inversely with the volume the gas is contained within. (as volume increases, exerted pressure decreases)
Using Boyle’s Law, describe why the lungs must expand to allow air to enter them during inhalation.
As the volume of the lungs (and thoracic cavity) increase, the pressure decreases. This means atmospheric pressure is high than intrathoracic pressure. Gas (air) flows down the pressure gradient into the lungs
Which two forces hold the thoracic walls and the lungs in close contact?
- The intrapleural fluid cohesiveness (fluid tension) 2. The negative intrapleural pressure
A transmural pressure gradient exists between lung walls. What is this?
A difference in pressure between any separtation
What causes the increase in thoracic volume during inspiration? (2)
- Contraction of the diaphragm 2. External intercostal muscle contraction
During expiration, which two factors contribute to the recoil of the lungs?
- Elastic properties of the involved muscles 2. Alveolar surface tension
What sort of situation would result in a lung collapse?
Any situation involving pleural pressure equalising with or exceeding atmospheric pressure e.g. a puncturing wound
What is alveolar surface tension?
The attraction between water molecules at the liquid air interface of the alveoli - water molecules pull towards each other
What does alveolar surface tension allow for?
A resistance to lung stretching - the water molecules are attracted together so oppose stretching forces
What does the law of LaPlace state?
Smaller alveoli have a higher tendency to collapse due to the increased proximity of the water molecules
What is pulmonary surfactant and where is it produced?
Pulmonary surfactant is a complex mixture of lipids and proteins. It is produced by type II alveoli
What is the effect of pulmonary surfactant?
It reduces surface tension by “diluting” the effect the water molecules have by interspersing them
Why do some infants suffer from respiratory distress syndrome?
Foetal lungs cannot synthesise surfactant meaning premature babies do not have enough surfactant in their lungs. Breathing will them become strenuous as the babies must overcome the high surface tension (of the water droplets) to inflate the lungs
Describe alveolar interdependence
Alveolar interdependence describes the fact that adjacent alveoli protect each other from collapse. If one alveoli begins to collapse, others around it will compensate and stretch. As volume increases in the surrounding alveoli, pressure decreases meaning air flows to the collapsed alveoli to reinflate it. This is due to the pressure gradient.
What are the three types of muscles involved in respiration?
- Accessory muscles (scalenus, sternocleidomastoid) 2. Major muscles (diaphragm, external intercostal muscles) 3. Muscles of active expiration (abdominal muscles, internal intercostal muscles)
What is the tidal volume?
The volume of air entering or leaving the lungs in a normal breath (around 500ml)
What is the inspiratory reserve volume?
This is the extra volume of air that can be breathed in over and above the tidal volume (around 3000ml)
What is the inspiratory capacity?
The maximum volume of air that can be breathed in (inspiratory reserve volume + tidal volume)
What is the expiratory reserve volume?
This is the extra volume of air that can be breathed out over and above the tidal volume (around 1000ml)
What is the residual volume?
This is the minimum volume of air remaining in the lungs even after a maximal expiration - it is always present
What is functional residual capacity and how is it calculated?
Resting lung volume (Expiratory reserve volume + residual volume)
What is vital capacity and how is it calculated?
This is the total volume of air available to be expired in the lungs (inspiratory reserve volume + tidal volume + expiratory reserve volume)
What is total lung capacity and how is it calculated?
This is the total volume of air the lungs can hold (vital capacity + residual volume) Around 5.7 litres
Why is total lung capacity hard to measure in real life?
Residual volume must be known and this cannot be measured
What could lead residual volume to increase?
Reduction in elastic recoil of the lungs - as in emphysema
Which two measurements can be plotted on volume/time curve, and what are they?
FVC - forced vital capacity - maximum volume of air inspired, the maximum volume of air that can be forcibly expelled FEV1 - Volume of air that can be expelled (after full inspiration) in one second
For normal healthy patients, FEV1/FVC x 100 should equal what?
80%
What does a low FEV1/FVC ratio indicate?
Obstructive lung disease
What type of results do individuals with restrictive lung disease give for a FEV1/FVC ratio test?
Normal, if not slightly elevated. They can instead be diagnosed by an initially low FVC
What is the primary determinant of airway resistance?
The radius of the conducting airway
How does the autonomic nervous system affect the resistance to airflow?
Sympathetic - decreases resistance (bronchodilation) Parasympathetic - increases resistance (bronchoconstriction)
Why are sufferers from obstructive lung conditions likely to suffer from collapsing airways?
Driving pressure (during exhalation) upwards from obstruction cannot occur. Relative airway pressure falls onward from obstruction leading to airway compression due to rising pleural and lung pressure. This problem is exacerbated if elastic recoil of airways is also lost as in emphysema.
How is peak flow rate measured?
Using a peak flow meter
Describe how to use a peak flow meter
A short sharp block is given into the meter The score on the scale at the side is taken 3 attempts are given to allow for poor initial technique The best value is recorded This test can highlight obstructive lung disease
What is pulmonary compliance?
This is a measure of the effort required to stretch or distend the lungs
What are the two methods to measure pulmonary compliance clinically?
- Static - the change in volume for any given pressure is measured (measures elastic resistance only) 2. Dynamic - change in volume for any given pressure during the movement of air (measure both elastic resistance and airway resistance)
The less compliant the lungs are the _____ work must be done to inflate them
More
List 3 factors that decrease pulmonary compliance
Pulmonary fibrosis Pulmonary oedema Lung collapse Pneumonia Absence of surfactant
How may a patient present clinically if they have less complaint lungs
Breathless Low exercise tolerance
When would pulmonary compliance increase?
When elastic recoil is lost
Describe a condition in which pulmonary compliance is increased
Emphysema Hyperinflation occurs causing increased difficulty during exhalation Age also increases compliance
List 3 factors which will increased the required work done by the lungs
- Decreased pulmonary compliance
- Increased pulmonary compliance
- Increased airway resistance (potentially when bronchoconstricted)
- Decreased elastic recoil
- Increased elastic recoil
- Need for increased ventilation (low O2)