Physiology Flashcards
What way do gases move in Boyle’s Law?
High Concentration -> Low Concentration
What effect does a pneumothorax have?
Abolishes the transmural pressure, causes lung to collapse
What is the main function of the respiratory system in terms of a simple conversion?
‘food’ + O2 -> ‘energy’ + CO2
What is internal respiration?
The intracellular mechanisms which consume O2 and produce CO2
What is external respiration?
The sequence of events that lead to the exchange of O2 and CO2 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 a tissue level
What is ventilation?
The mechanical process of moving air between the atmosphere and 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
volume up = pressure down
What are the two forces that hold the thoracic wall and the lungs in close opposition?
1) the intrapleural fluid cohesiveness
2) the negative intrapleural pressure
What is inspiration dependant on?
Muscle contraction. It is an active process
Describe inspiration and how this process is done
Increase in lung volume. Contraction of the diaphragm increases the volume of the lungs vertically. External intercostal muscle contraction lifts the ribs and moves outage sternum
How does inspiration affect the intra-avelolar pressure?
It decreases this pressure
Describe expiration
Inspiratory muscles relax, lungs recoil, lung volume decreases and intra-aveolar pressure rises
What causes the lungs to recoil during during expiration?
1) elastic connective tissue in the lungs that makes the whole structure ‘bounce’ back
2) Alveolar Surface Tension (MAIN)
What is Alveolar Surface Tension?
Attraction between water molecules at liquid air interface. Produces a force which resists the stretching of the lungs.
What is the effect of Pulmonary Surfactant?
Reduces the alveolar surface tension
Which size of alveoli have a higher tendency to collapse?
Smaller alveoli
What babies are at risk of Respiratory Distress Syndrome and why?
Premature babies. Foetal lungs are unable to synthesise Surfactant until late into the pregnancy => premature babies may not be able to produce Surfactant => high surface tension => respiratory distress as they have difficulty inspirating and inflating their lungs
What does the Alveolar Interdependence do?
Help keep alveoli open. if an alveolus starts to collapse the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it
What are 3 important pressures in terms of Ventilation
- Atmospheric pressure (pressure of weight of a gas in atmosphere)
- Intra-alveolar pressure (pressure within alveoli)
- Intrapleural pressure (pressure within the pleural sac)
What nerve is Inspiration supplied by
Phrenic nerve from C3,4,5
Describe how the thorax volume is increased (3 ways)
- The diaphragm contracts and lowers, increasing the vertical dimension
- The external intercostal muscles contract, elevating the ribs; increasing side-side dimension
- elevation of ribs in turn causes the sternum to move upwards and outwards; increasing front-back dimension
What happens to the intra-alveolar pressure when the lungs increase in size?
The pressure decreases, since an increase in the size of the lungs also increases the volume of gas present (Boyle’s Law - the air molecules are contained in a larger volume)
What gives the lungs their elastic behavior, and what does this allow them to do?
- Elastic connective tissue
- Alveolar surface tension
- allows the lungs to recoil
What is the pulmonary surfactant
It is a mixture of lipids and proteins secreted by Alveoli type 2
Why is the pulmonary surfactant important
It intersperses between the water molecules on the alveoli; reducing surface tension and preventing smaller alveoli from collapsing and releasing air into bigger alveoli
If it wasn’t there, the alveolar surface tension would be too strong as there would be nothing to decrease the force between the water molecules at the liquid air interface
Name 3 forces that act to open the lungs
- transmural pressure gradient
- pulmonary surfactant
- alveolar interdependance
Name 2 forces that act to close lungs/promote alveolar collapse
- Elasticity of stretched pulmonary tissue fibers
2. Alveolar surface tension
what are the inspiratory muscles?
- external intercostal muscles
- diaphragm
what are the muscles of active expiration?
- internal intercostal muscles
- abdominal muscles
what is active expiration?
the air that is forcefully released after a natural release of air when exhaling (the expiration reserve volume)
i.e. when you breathe out naturally, then force more air out, the forcing bit is ‘active’ and not ‘passive’
what is passive expiration?
the relaxation of the inspiratory muscles, causing air to be expelled from the lungs
Define Residual Volume and it’s normal value (for a healthy adult male)
Residual volume is the volume of air left when all possible air has been expelled from the lungs
- 1200ml
Define Total Lung Capacity and normal value
The maximum volume of air that lungs can hold (vital capacity + residual volume)
- 5700ml
What is a pneumothorax?
A collection air in the lung, arises from a puncture wound in the lung or chest wall
What is pulmonary ventilation?
the volume of air that is breathed in/out per minute
what is the alveolar ventilation?
the volume of air exchanged between atmosphere and alveoli per minute
What effect does increase in breathing rate have on the pulmonary ventilation and alveolar ventilation?
Increases pulmonary ventilation
No change on alveolar ventilation
Why is increasing the depth of breathing more advantageous than increasing the rate of breathing?
It increases both the pulmonary ventilation and the alveolar ventilation rather than just pulmonary ventilation
What is the Anatomical Dead Space?
it is where some inspired air remains, this air is not available for gas exchange
What is the Alveolar Dead Space?
it consists of ventilated alveoli that are not adequately perfused with blood
Why can Alveolar Dead Space become significant?
In healthy people, this dead space is very small, however with disease, this can increase in size
What does the transfer of gases in the body depend on?
Ventilation and perfusion
What is Ventilation?
the rate at which gas passes through the lungs
What is Perfusion?
the rate at which blood passes through the lungs
Explain the principles of Ventilation Perfusion Matching
the lungs aim to match the levels of O2 and CO2 in the blood
Why might arterial and alveolar pressure levels not be the same, despising the ventilation perfusion matching?
ventilation and perfusion can vary from the top to the bottom of the lungs, resulting in slightly different pressures. This is normal
Define Dalton’s Law
The total pressure exerted by a gaseous mixture = the sum of partial pressures in each component of the gas mixture
e.g. Ptotal = P1 + P2 + P3 ……
Name the 4 factors influencing gas transfer:
- Partial pressure gradient
- Diffusion coefficient
- Surface area of the alveolar membrane
- Thickness of Alveolar membrane
What is partial pressure?
The pressure that the gas would exert if it occupied the total volume for the mixture
(so the pressure of O2 if it was just O2 in the container, not a mix of O2, NO2, Hydrogen etc etc)
Why is CO2’s partial pressure gradient smaller than that of O2?
CO2 is much more soluble
Explain the Diffusion Coefficient
A value relative to the solubility of gas in membranes
Explain how the surface area of the Alveolar membrane influences gas transfer
Alveoli have thin membranes due to type 1 alveolar cells = more effective gas transfer
they help increase the surface area for gas exchange
what is the difference between type 1 and 2 alveolar cells?
type 1 = thin membrane
type 2 = secrete pulmonary surfactant
What is Fick’s law of diffusion?
larger surface area = more gas moves
thicker wall = less gas moves
positive correlation between surface area and gas exchange, inverse relationship between wall thickness and gas exchange
How to calculate the partial pressure of O2 in alveolar blood
partial pressure of O2 breathed in - partial pressure of CO2 in arterial blood
divide by Respiratory Exchange Ratio (RER)
What is the physiological dead space? (what does it consist of)
the anatomical + alveolar dead space
Name 3 non-resp functions of the respiratory system
- route for water loss and heat elimination
- enhances venous return
- helps maintain homeostasis - acid/base balance
Under what conditions would myoglobin be used to provide O2 and for how long can this method be sustained?
- Anaerobic
- short-term storage =) cannot be sustained for long
Which law states that: the amount of a given gas dissolved in a given type and volume of liquid at a constant temperature is: proportional to the partial pressure of the gas in equilibrium with the liquid?
Henry’s Law
Using Henry’s Law- describe how increasing the partial pressure in the gas phase would effect the concentration of the the gas in the liquid phase
It would increase proportionally
What two forms is O2 present in the blood?
1) bound to haemoglobin (~98.5%)
2) physically dissolved (~1.5%)
What type of curve is the haemoglobin dissociation curve?
Sigmoidal
What is the primary factor that affects saturation?
partial pressure of O2
If a patient suffers from anaemia what would we expect their PO2 to be compared to a normal, healthy individual
The same, it is the lack of haemoglobin in the blood that is causing insufficient oxygen supply to the tissue not the saturation.
What two things is the O2 content of arterial blood dependant on?
1) Haemoglobin Concentration
2) Saturation of haemoglobin with O2
How would heart failure impair the delivery of oxygen to the tissues?
This decreases cardiac output
The binding of one O2 molecule to haemoglobin will affect the affinity of haemoglobin for O2 in what way?
Increases the affinity
How does foetal Hb differ from adult Hb? (3 things)
- It has two alpha and two gamma subunits
- it has a higher affinity for O2
- it interacts less with 2-3 biphosphoglycerate
What are the 3 ways that CO2 can be transported in the blood?
solution, bicarbonate and carbamino compounds
What is the catalyst in the formation of carbonic acid
Carbonic anhydrase
What is carbamino
a combination of CO2 and terminal amine groups
Why does reduced Hb bind more CO2 than non-reduced Hb?
Removing O2 increases the ability of Hb to pick up CO2 and CO2 generated H+ ions
What network of neurons controls the rhythm of breathing and where is it situated?
The Pre-Botzinger complex at the top of the medulla
What is the brain stem made up of?
The midbrain, Pons, Medulla oblongata, Spinal cord
How is inspiration caused
the firing of dorsal neurons in bursts
How does passive expiration occur
the gaps in between firing of dorsal neurons
How does active expiration occur
the ventral respiratory neurons fire; the stimulation of these terminates inspiration
what is apneusis?
A long inspiration followed by a short expiration
What stops apneusis from happening?
The PC - pneumotaxic centre
Which kind of receptors increases the ventilatory rate when there is a decrease in blood pressure?
Baroreceptors
Which kind of receptors are stimulated when there is capillary congestion and pulmonary oedema or PE?
Juxtapulmonary receptroes
