Physiology Flashcards
What is internal respiration?
A biochemical process that uses ‘food’ and oxygen to make ‘energy’ and carbon dioxide
What is external respiration?
The sequence of events that lead to thee exchange of oxygen and carbon dioxide between the external environment and the cells of the body
What are the four steps of external respiration?
- Ventilation
- Gas exchange between alveoli and blood
- Gas transport in the blood
- Gas exchange at at tissue level
Explain Boyle’s Law
At any constant temperature the pressure exerted by a gas varies inversely with the volume of the container the gas is held in.
Which of these two processes is passive? a) Inspiration b) Expiration
b) Expiration
Explain the mechanics of ventilation (the first step of external respiration)
The thorax and the lungs must expand to make the intra-alveolar pressure lower than the atmospheric pressure THORAX:
- Vol. of thorax increased vertically by contraction of diaphragm (phrenic nerve from cervical 3,4 and 5)
- External intercostal muscles contract which lifts the ribs and move out the sternum- aka ‘bucket handle’ mechanism
LUNGS:
- Intra-alveolar pressure pushes outward while the lower intrapleural pressure pushes inward
- Difference in pressure creates a transmural gradient that pushes inward
- compressing the thoracic wall meaning the alveoli stretch to fill the now larger thoracic cavity
What links the lungs and the thorax?
Two forces hold the thoracic wall and the lungs in close opposition:
1) Intrapleural fluid cohesiveness - water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart hence pleural membranes tend to stick together
2) Negative intrapleural pressure - the sub-atmospheric intrapleural pressure create a transmural pressure gradient across the lung wall and the chest wall. So the lungs are forced to expand outwards while the chest is forced to squeeze inwards
What is a pneumothorax and what are the potential causes?
Pneuothorax: air in the pleural space Can be: 1. Spontaneous 2. Traumatic 3. Iatrogenic
Describe a pneunothorax
- Air enters the pleural space from outside or from the lungs 2. This can abolish transmural pressure gradient leading to lung collapse (Lung collapse= the lung collapses to unstretched size & chest wall springs outward)
What are the symptoms and physical signs of a pneumothorax?
Symptoms: shortness of breath, chest pain Physical signs: hyperresonant percussion note, decreased/ absent breath sounds
How do the lungs recoil?
- elastic connective tissue
- alveolar surface tension
What is alveolar surface tension?
- attraction between water molecules at liquid air interface
- in the alveoli this produces a force which resists the stretching of the lungs
- if the alveoli were lined with water alone the surface tension would be too strong so the alveoli would collapse hence surfactant
How does surfactant reduce the alveolar surface tension?
Pulmonary surfactant is a complex mixture of lipids and proteins secreted by type II alveoli -lowers surface tension by interspersing between the water molecules lining the alveoli
Discuss surfactant in relation to small alveoli?
According to the law of LaPlace the smaller alveoli have a higher tendency to collapse -surfactant lowers the surface tension of smaller alveoli more than that of larger alveoli - this precents smaller alveoli from collapsing and emptying their air contents into the larger alveoli
What is the equation for LaPlace’s Law?
P=2T/r P= inward directed collapsing pressure T= surface tension r= radius of the bubble
Describe the opposing forces acting on the lungs.
Forces Keeping Alveoli Open:
- transmural pressure gradient
- pulmonary surfactant
- alveolar interdependence
Forces Promoting Alveolar Collapse:
- elasticity of stretched lung connective tissue
- alveolar surface tension
List the lung volumes
- tidal volume
- inspiratory reserve vol
- expiratory reserve vol
- residual vol
Describe tidal vol
Tidal volume is the volume of air entering or leaving the lungs during a single breath Average value: 0.5L
Describe inspiratory reserve vol.
Inspiratory reserve vol. is the extra volume of air that can be maximally inspired over and above the typical resting tidal volume Average vol= 3.0L
Describe expiratory reserve vol
Expiratory reserve volume is the extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume Average vol= 1.0L
Describe the residual volume
Residual volume is the minimum volume of air remaining in the lung even after a maximal expiration NB: increases when elastic recoil of the lungs is lost e.g. in emphysema Average vol= 1.2L
List the lung capacities
~inspiratory capacity ~functional residual capacit ~vital capacity ~total lung capacity
Describe the inspiratory capacity
Inspiratory capacity is the maximum volume of air that can be inspired at the end of a normal quiet expiration Average value= 3.5L
Describe the functional residual capacity
The functional residual capacity is the volume of air in lungs at end of normal passive expiration Average value= 2.2L
Describe the vital capacity
The vital capacity is the maximum volume of air that can be moved during a single breath following a maximal inspiration (VC= IRV + TV + ERV) Average value= 4.5L
Describe Total Lung Capacity (TLC)
The total lung capacity is the total volume of air the lungs can hold (TLC= VC + RV) Average 5.7L
Can total lung capacity be calculated using spirometry?
No. TLC= VC + RV and residual vol. cannot be measured by spirometry
When is spirometry useful in regards to respiratory disease?
- Find the Forced Vital Capacity 2. Find the Forced Expiratory volume 3. Calculate FEV/FVC (normally >70%) 4. Draw a volume time curve 5. Dynamic Lung Volumes are useful in the diagnosis of Obstructive and Restrictive Lung Disease
How does a restrictive lung disease effect spirometry results?
The curve on a graph for FVC, FEV and FEV/FVC is shifted to the right and depressed
List the factors which influence airway resistance
- Radius of the conducting airway
- primary determinant
- Disease (e.g. COPD/asthma) can cause significant resistance to airflow
Define pulmonary compliance
During inspiration the lungs are stretched and compliance is measure of effort that has to go into stretching or distending the lungs. It is the volume change per unit of pressure change across the lungs. The less compliant the lungs are, the more work is required to produce a given degree of inflation.
What factors decrease pulmonary compliance?
- Pulmonary Fibrosis
- Pulmonary Oedema
- Absence of Surfactant
- Pneumonia
- Lung Collapse
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What does decreased pulmonary compliance mean for an individual?
Greater change in pressure is needed to produce a given change in volume (i.e. lungs are stiffer) -causes shortness of breath especially on exertion -may cause a restrictive pattern of lung volumes in spirometry
What does increased pulmonary compliance mean for an individual? And how can it occur?
Compliance may become abnormally increased if the elastic recoil of the lungs is lost and occurs in emphysema. Patients have to work harder to get the air out of the lungs a.k.a hyperinflation of lungs -dynamic airway obstruction will be aggravated in patients with obstructed airway and emphysema caused by COPD -compliance also increases with increasing age
What is pulmonary ventilation?
The volume of air breathed in and out per minute
What is Alveolar ventilation?
The volume of air exchanged between the atmosphere and alveoli per minute.
This is more important than pulmonary respiration as it represents new air available for gas exchange with blood.
Alveolar Ventilation < Pulmonary Ventilation because of anatomical dead space
What is anatomical dead space and why is it significant?
ANATOMICAL DEAD SPACE: Some inspired air remains in the airways where it is not available for gas exchange It means that alveolar ventilation is always less than pulmonary ventilation.
Significance: To increase pulmonary ventilation both the depth and rate of breathing increase but because of dead space it is more advantageous to increase the depth of breathing.
What is the eqn for pulmonary ventilation?
Pulmonary ventilation= Tidal vol (litres/breath) x Resp rate (breaths/min)
e.g. 0.5L x 12 breaths/min= 6L/Min
What is the eqn for alveolar ventilation?
Alveolar ventilation= (Tidal vol - alveolar dead space) x Resp rate
Define ventilation
Ventilation is the rate at which gas is passing through the lungs
Define perfusion
Perfusion is the rate at which blood is passing through the lungs
Describe alveolar dead space
Ventilated alveoli which are not adquately perfused with blood are considered as alveolar dead space.
It v.small & :. of little importance in healthy people but can increase significantly in disease.
This means the match between air in the alveoli & the blood in the pulmonary capillaries is not always perfect.
Describe ventilation perfusion matching in the lungs
Local controls act on the smooth muscles of airways and arterioles to match airflow to blood flow
a) accumulation of CO2 in alveoli as a result of increased perfusion –> decreases airway resistance –> increased airflow
b) increase in O2 conc. in alveoli as a result of increased ventilation –> pulmonary vasoldilation –> increase blood flow to match larger airflow
What is the eqn. for physiological dead space?
Physiological dead space= anatomical dead space + alveolar dead space
Does O2 have different effects on systemic arterioles compared to pulmonary arterioles?
If so, how?
YES
Identify the four factors which influence the gas transfer across the alveolar membrane.
- Partial Pressure Gradient of O2 and CO2
- Diffusion Coefficient for O2 and CO2
- Surface Area of Alveolar Membrane
- Thickness of Alveolar Membrane
Define partial pressure of a gas
Partial pressure of a gas is the pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature
Explain how to find an average partial pressure of oxygen in the alveolar air
What you need to know/be aware of:
- air in resp tract is saturated with water
- water vapour pressure contributes aprox. 47mmHg to total pressure in the lungs
- 0.8 is the Respiratory Exchange Ratio-RER- for someone eating a mixed diet (ratio of CO2 produced/O2 consumed)
1) Pressure of inspired air= atmospheric pressure- water vapour pressure
760- 47=713mmHg
2) Partial pressure of inspired oxygen= partial pressure of inspired air x atm. pp02
713x 0.21 (O2 makes up approx. 21% of gases in atmosphere)= 150 mmHg
3) Alveolar Partial Pressure of O2= Partial Pressure of O2 in Inspired Air - (Partial Pressure of CO2 in arterial blood/RER)
150- (40/0.8)
= 150- 50
=100mmHg at sea level
Explain how the partial pressure of O2 and CO2 influences the gas transfer across the alveolar membrane
Gases move from higher to lower partial pressures- down a partial pressure gradient
Explain difussion coefficient in relation to O2 and CO2
The partial pressure gradient for CO2 is much smaller than that of O2 because CO2 is more permeable in membranes than O2.
The solubility of gas in membranes is known as Diffusion Coefficient for the gas.
The diffusion coefficient for CO2 is 20x more than that of O2
Explain how the difussion coefficient of O2 and CO2 influences the gas transfer across the alveolar membrane
A small gradient between alveolar ppO2 and arterial pp02 is normal
A big gradient between alveolar ppO2 and arterial ppO2 would indicate problems with gas exchange in lungs or a right to lift shunt in the heart
Explain how the surface area of the alveolar membrane & thickness of alveolar membrane influences the gas transfer across the alveolar membrane
Fick’s Law of Diffusion
The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness
What four factors influence the rate of gas transfer across the alveolar membrane? and how?
-
Partial pressure gradient of O2 and CO2
- rate of transfer increases as partial pressure increases
-
Diffusion Coefficient (solubility of gas in membranes)
- rate of transfer increases as diffusion coefficient increases
- difusion coefficient of CO2 is 20 times that of O2
-
Surface area of alveolar membrane
- rate of transfer increases as surface area increases
- exercise increases surface area- deeper breathing
- SA decreases with emphysema, lung collapse etc
-
Thickness of alveolar membrane
- rate of transfer decreases as thickness increases
- thickness increases with pulmonary oedema. pulmonary fibrosis, pneumonia
Identify the non-respiratory functions of the respiratory system
- Route for water loss and heat elimination
- Enhances venous return (Cardio physiology)
- Helps maintain normal acid-base balance (Resp & Renal physiology)
- Enables speech, singing & other vocalizations
- Defends against inhaled foreign matter
- Removes, modifies, activates, or inactivates various materials passing through the pulmonary circulation
- Nose serves as the organ of smell
State Henry’s Law
“At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.”
Explain the effect of partial pressure on gas solubility
As stated in Henry’s Law, as ppO2 increases the solubility of the gas increases.
Is all oxygen transported in the body simply dissolved in the blood? Why?
No. *Henry’s Law*
3ml O2 per litre of blood at PO2 of 13.3kPa
- resting conditions (cardiac output= 5L/min): 15 ml/min of O2 taken to tissues as dissolved O2
- strenuous exercise (cardiac output= 30L/min): 90ml/min would be taken to tissues as dissolved O2
- BUT resting O2 consumption of our body cells= 250ml/min hence wahhh???? haemoglobin!!
How is O2 transported in the blood? What is the makeup of these transport types?
At normal arterial ppO2 of 13.3kPa & normal haemoglobin conc. of 150g/litre O2 conc. in blood should be aprox. 200ml/litre
98.5%= bound to haemoglobin; 1.5%= dissolved in blood
Describe the structure of haemoglobin
- 4 chains; 2 Beta & 2 Alpha
- Each chain has a haem group
- Each haem group has an Fe2+ which can bind to an O2 molecule
- Haemoglobin is considered fully saturated when all the haemoglobin present is carrying its max. O2 load
Describe/draw an oxygen haemoglobin dissociation curve
- Haemoglobin on y-axis
- Blood ppO2 on x-axis
- sigmoidal shape
- starts at 0/0
- 13.3kPa is normal ppO2 at pulmonary capillaries and this is on flat part of graph
- 5.3kPa is average resting ppO2 at systemic capilaries which is on slope
What must you be aware of in regards to O2 conc. and Haemoglobin saturation?
3 different individuals can have 100% saturation but different O2 conc.
a) has 100g of haemoglobin/litre and 100% satured but aprox. 100ml of O2/litre
b) has 150g of haemoglobin/litre and 100% satured but aprox. 200ml of O2/litre
c) has 200g of haemoglobin/litre and 100% satured but aprox. 250ml of O2/litre
What two elements affect the O2 content of arterial blood?
- Haemoglobin conc.
- Saturation of Hb with O2
What can impair O2 delivery to the tissues?
- Decreased partial pressure of inspired O2
- Resp disease -these can decrease arterial ppO2 & hence decrease haemoglobin saturation with O2 and O2 content of the blood
- Anaemia -this decreases haemoglobin conc. & hence decreases O2 content of the bloood
- Heart failure -this decreases cardiac output
What is co-operativity?
binding of one O2 to haemoglobin increases the affinity of that haemoglobin molecule for O2
Explain the significance of the sigmoidal shape of the oxygen dissociation curve
- flat upper portions means moderate falls in alveolar ppO2 will not mch affect oxygen loading
- steep lower part means that the peripheral tissues get a lot of oxygen for a small drop in capillary ppO2
What is the Bohr Effect??
A shift of the oxygen dissociation curve to the right
i.e. increased release of O2 because of:
- increased pCO2,
- Increased hydrogen ion conc
- Increased temp
- Increased 2,3- biphosphoglycerate
- the more metabolically active a RBC is; the higher 2,3- biphosphoglycerate conc. is
Describe foetal haemoglobin
- different structure to adult haemoglobin
- has 2 alpha & 2 gamma subunits
- interacts with 2,3- biphosphoglycerate less than adult haemoglobin
- hence higher affinity for O2 than adult haemoglobin (O2 dissociation curve shifted to the left) -this means O2 can be passed from mother’s blood to foetus’s even if ppO2 is low
What is myoglobin’s main purpose?
Provide a short-term storage of O2 for anaerobic conditions
Describe the structure & location of myoglobin
- One haem group per myoglobin molecule
- Present in skeletal &
- Cardiac muscles
How does myoglobin provide a short-term storage of O2 for anaerobic conditions?
Its dissociation curve is hyperbolic & so releases O2 at very low ppO2
What does myoglobin in the blood indicate?
Myoglobin in the blood indicates muscle damage!!!!!
What are the means of CO2 transport in the body?
- Solution- 10%
- Bicarbonate- 60%
- Carbamino compounds- 30%
Describe CO2 transport in solution.
CO2 aprox. 20 times more soluble than O2
Aprox. 10% of carried CO2 is in solution
Describe CO2 transport via bicarbonate.
Catalyzed by carbonic anhydrase
Reaction occurs in RBC
Most CO2 is transported in the blood as bicarbonate
Describe CO2 transport via carbamino compounds.
Carbamino compounds form when CO2 combines with terminal amine groups in blood proteins
esp. globin of haemoglobin!
- This gives carbamino-haemoglobin
- Rapid even without an enzme
- Reduced Hb can bind more CO2 than Hb02
Describe the Haldane Effect
‘Removing O2 from Hb increases the ability of Hb to pick-up CO2 and CO2 generated H+’
Explain how the Haldane Effect works in synchrony with the Bohr effect
They work in synchrony at tissue level to facilitate the uptake of CO2 & CO2 generated hydrogen ions and release O2
