physiology Flashcards
what does internal respiration refer to?
the intracellular mechanisms which consume O2 and produce CO2
what does external respiration refer to?
to the sequence of events that lead to the exchange of 02 and CO2 between the external environment and the cells of the body
four steps involved in external respiration
ventilation, exchange of O2 and CO2 between air in alveoli and blood coming into lungs, transport of O2 and CO2 in blood between the lungs and tissues, exchange of O2 and CO2 between the blood and tissues
four body systems involved in external respiration
the respiratory system, the cardiovascular system, the haematology system, the nervous system
Ventilation definition
the mechanical process of moving air between the atmosphere and alveolar sacs
are the lung movements active or passive
passive
what muscles are involved in the movement of the lungs?
respiratory muscles
what is inspiration
an active process brought about by contraction of inspiratory muscles
what is normal resting expiration
a passive process brought about by relaxation of inspiration muscles
what are the major functions of nasal breathing
to heat and moisten the air
and to remove particulate matter
what does cilia in nasal epithelium do?
move mucus back to the oropharynx to be swallowed
lung ventilation can be considered in two parts, what are they?
the mechanical process of inspiration and expiration and the control of respiration to a level appropriate for metabolic needs
how does lung volume affect the intrapleural pressure?
the higher the lung volume, the more the lung stretches, creating more negative intrapleural pressure
what are the responses by the lungs governed by
opposing forces
what are the forces that cause lungs to be hindered/ impeded?
elastic resistance (of lungs and chest wall) and non elastic resistance (airway resistance)
How do lungs adhere to the chest wall and follow its movement?
due to transmural pressure gradient and the intrapleural fluid cohesiveness
what is the transmural pressure gradient
the sub atmospheric intrapleural pressure (intrathoracic): creates a transmural pressure gradient across the lung wall and across the chest wall
what is intrapleural fluid cohesiveness?
the water molecules in the intrapleural fluid are attached to each other and resist being pulled apart. Hence the pleural membranes tend to stick together.
what are the three pressures that are important in resp?
atmospheric pressure which is the pressure in the atmosphere, intra alveolar (intrpulmonary) pressure which is the pressure within the lung alveoli and intrapleural pressure (intrathoracic) which is the pressure exerted outside the lungs within the pleural cavity and is usually less than the atmospheric pressure.
usual atmospheric pressure
760mmHg
usual intra alveolar pressure
760mmHg
usual intra pleural pressure
756mmHg
what will occur to the lungs if there’s no transmural gradient
they will collapse
where is there air when there’s a pneumothorax
in the pleural space
what can cause a pneumothorax
it can be traumatic, iatrogenic or spontaneous
how does a pneumothorax occur
air enters the pleural space, abolishing the transmural pressure gradient due to the increase in the intrathoracic pressure, leading to lung collapse
symptoms of pneumothorax
shortness of breath and chest pain
physical signs of a pneumothorax
hyper resonate percussion note and decreased/absent breath sounds
what’s boyles law
at any constant temperature the pressure exerted by gas varies inversely with the volume of the gas.
what occurs to the volume of the gas as the pressure exerted by the gas decreases
volume of gas increases
why does the intra alveolar pressure need to be less than the atmospheric pressure?
because air flows down a pressure gradient from high pressure to low pressure.
how does the intra alveolar pressure drop?
before inspiration the pressures are the same but when inspiring, the inspiration muscles contract causing the thorax and lungs to expand, increasing the volume of the gas in the lungs and hence decreasing the intra alveolar pressure
how does passive inspiration occur?
the lungs recoil, decreasing the size of lungs and hence decreasing the volume of gas in the lungs, this increases the intra alveolar pressure to 761mmHg and causes the gas to leave the lungs down its pressure gradient until the intra alveolar pressure becomes equal with the atmospheric pressure
what causes lungs to recoil during expiration?
elastic recoil of the lungs and alveolar surface tension
what is alveolar surface tension
its the attraction between water molecules at the liquid air interface, in the alveoli this produces a force which resists the stretching of the lungs
what would occur if the alveoli were only lined with water?
the surface tension would be too high, causing the alveoli to collapse
what do type II alveoli secrete
pulmonary surfactant
what is pulmonary surfactant made up of
a complex mixture of lipids and proteins
what does pulmonary surfactant do
it lowers the surface tension by interpreting between the water molecules lining the alveoli, smaller alveoli are more likely to collapse so pulmonary surfactants lower the pressure of these more
what law proves the smaller alveoli have a higher tendency to collapse
law of LaPlace
what can cause respiratory distress syndrome in premature babies?
developing fatal lungs are unable to produce surfactant until late in pregnancy and so premature babies may not have enough pulmonary surfactant causing very high surface tension and lungs can collapse.
what keeps alveoli open?
surfactant, alveolar interdependence, transmural pressure gradient
what’s alveolar interdependence
once an alveolus begins to collapse it stretches in its surrounding alveoli, these then recoil causing the collapsing alveolus to open
what’s promotes alveolar collapse
surface tension and elastic recoil of chest walls and lungs
major inspiratory muscles
diaphragm and external intercostal muscles
accessory inspiratory muscles
pectoral, scalenus and sternocleidomastoid
muscles pf active expiration
internal intercostal muscles and abdominal muscles
what is the tidal volume and its average value
is the volume of air entering or leaving lungs during a single breath, it’s on average 0.5L
what is the inspiratory reserve volume and its average value
this is the volume of air that can be maximally inspired over and above the typical resting tidal volume, it’s on average 3L
what is the expiratory reserve volume and its average value
this 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, it’s average value is 1L
what is the residual volume and what is it’s average value
the residual volume is the volume of air remaining in the lungs even after a maximal expiration, the average value for this is 1.2L
what is the inspiratory lung capacity and its average value
the maximum volume of air that can inspired at the end of a normal quiet inspiration IC= IRV + TV, its average value is 3.5L
What is the functional residual capacity and its average value
volume of air in lungs at the end of normal passive expiration FRC= ERV + RV, its average value is 2.2L
What is the vital capacity and its average value?
the maximum volume of air that can be moved out during a single breath following a maximal inspiration VC= IRV + TV + ERV, average value is 4.5L
what is the total lung capacity and its average value?
this is the total volume of air the lungs can hold TLC= VC + RV, average value is 5.7L
what cannot be ,measured using spirometry
residual volume and hence can’t measure total lung capacity or functional residual capacity.
FVC definition
maximum volume that can be forcibly expired from the lungs following maximum inspiration
FEV1
the volume of air that can be expired during the first second in an FVC determination
FEV1/FVC
the proportion of FVC that can be expired in the first second
what value is FEV1/FVC x 100 normally
> 75%
what is the FEV1/FVC% for someone with asthma or COPD
<75%
how can spirometry help tell difference between obstructive or restrictive lung diseases
because obstructive such as asthma are reversible and so its FEV1/FVC% should go back to normal after taking an inhaler whereas restrictive such as COPD will not, also the FVC of COPD is lowered whereas it does not lower for asthma
what is a primary determination of airway resistance
the smaller the airway, t he greater the resistance and hence greater the pressure
what causes bronchodilation
parasympathetic stimulation
what makes active expiration more difficult for patients with airway obstruction
dynamic airway compression
why does dynamic airway obstruction make active expiration harder for patients with an obstructed airway
because if there’s an obstruction the driving pressure between the alveolar and the airway is lost over the obstructive segment. This causes a fall in airway pressure along the airway downstream resulting in airway compression by the rising pleural pressure during active expiration.
what can make active expiration even harder for patients with an obstructed airway on top of dynamic airway obstruction
if the patient has decreased elastic recoil in the lungs
what does the peak flow meter measure
the peak flow rate which allows us to assess airway function
what diseases is peak flow meter useful for
obstructive lung disease (asthma and COPD)
how does a patient use a peak flow meter
they take a short sharp breath into it and the three best attempts are taken
what is compliance
the measure of the effort that has gone into stretching or distending the lungs
what is lung compliance ?
the change in lung volume per unit change in transmural pressure gradient across the lung wall (i.e. the difference between intra alveolar sonf intrapleural pressure)
what does less compliance mean for the lungs?
more work is required to produce a degree of inflation
what can cause decreased pulmonary compliance
pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia or absence of surfactant
what does a decrease in pulmonary compliance cause?
it means a greater change in pressure is needed to produce a given change in volume (i.e. lungs are stiffer). This causes shortness of breath especially on exertion
how does a decrease in pulmonary compliance affect a spirometry
it may cause a restrictive pattern of lung volumes
when does compliance abnormally increase
if elastic recoil of the lungs is lost (if a patient has an emphysema)
what does abnormally increased pulmonary compliance do
it means the patient has to work harder to get air out of the lungs- hyperinflation of the lungs
what is work of breathing
a reflection of energy required to overcome the impeding elements of the resp system
examples of when work of breathing is increased
during decreased pulmonary compliance, increased airway resistance, decreased elastic recoil and when there’s a need for increased ventilation
what’s dead space
the air that remains in the airway and is not available for gas exchange
calculation for pulmonary ventilation
PV= tidal volume x respiration rate
calculation for alveolar ventilation
AV = (tidal volume- dead space) x respiration rate
pulmonary ventilation definition
volume of air breathed in and out per min
alveolar ventilation definition
volume of air exchanged between the atmosphere and alveoli per minute
how do you increase pulmonary ventilation
increase both tidal volume (depth of breathing) and the resp rate
how do you increase alveolar ventilation
due to dead space its more advantageous to increase the depth of breathing (tidal volume)
what does the transfer of gases between the body depend on?
ventilation and perfusion
what is perfusion
the rate at which blood is passing through the lungs
are blood flow and perfusion constant throughout the lung
no they vary throughout the bottom to the top of the lung
what does the variation of blood flow and perfusion throughout the lung result in
that the average arterial and alveolar pressures of O2 are not exactly the same, normally this effect is not significant but it can be in disease.
what is alveolar dead space
alveoli which are ventilated but not adequately perfused with blood
what is alveolar dead space like for healthy people
it’s small and of little importance
how could you calculate the physiological dead space
the anatomical dead space + the alveolar dead space
how can alveolar dead space increase
in disease
what does accumulation of CO2 due to increased perfusion cause at the alveoli?
this decreases airway resistance, increasing airflow
what does increase in alveolar O2 due to increased ventilation cause?
this causes pulmonary vasodilation which increases blood flow to match larger airflow
what occurs if perfusion is greater than ventilation?
CO2 increases and O2 decreases, dilation of local airway due to CO2 increase and construction of local blood vessels due to O2 decrease, the airflow increases and blood flow decreases to try and even out
what occurs if ventilation is greater than perfusion ?
O2 increases, dilating the local blood vessels, increasing blood flow and CO2 decreases, constricting local airways, decreasing airflow
what occurs to pulmonary arterioles as O2 is increased/ decreased
O2 increased- vasodilation and decreased O2- vasoconstriction
what occurs to systemic arterioles as O2 is increased/decreased
O2 decreased- vasodilation and )2 increased- vasoconstriction
what is partial pressure
the partial pressure of a gas determines the pressure gradient for that gas
what is the partial pressure of gas in a mixture of gases that don’t react with each other?
the pressure that gas (1) would exert if it occupied the total volume for the mixture in absence of other components
total pressure exerted by all the gases calculation
total pressure= P1 + P2 + P3.. + Pn
what is the alveolar gas equation?
PaO2= PiO2- [PaCO2/0.8]
how would you calculate PiO2 in the alveolar air
pressure inspired= atmospheric pressure- water vapour pressure , then PiO2= pressure inspired x percent of O2
why is the partial pressure gradient of CO2 much smaller than the partial pressure of O2?
CO2 is more soluble in membranes than O2, so has a larger Diffusion Coefficient
what would a large gradient between PAO2 and PaO2 suggest?
this would indicate problems with gas exchange or problems with the exchange of blood from left to right side of the heart.
Fick’s law
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 increases the surface area in lungs
the alveoli
4 factors that influence the rate of gas transfer across the alveolar membrane
partial pressure gradient of O2 and CO2, diffusion coefficient, surface area of alveolar membrane and thickness of alveoli membrane
what occurs to rate of transfer as partial pressure increases
rate of transfer increases
what can decrease surface area of alveolar membrane
emphysema, lung collapse and pneumonectomy
what increases thickness of alveolar membrane
same stuff that decreases lung compliance (pulmonary oedema, pulmonary fibrosis and pneumonia)
what is Henry’s Law?
the amount of gas dissolved in a given type and volume of liquid (blood) at a constant temp is proportional to the partial pressure of the gas in equilibrium with the liquid
O2 is present in the blood in what forms?
bound to haemoglobin and physically dissolved
how is most O2 transported
it’s bound to haemoglobin
percent of O2 bound to haemoglobin compared to carried in dissolved form
bound to haemoglobin- 98.5% whereas carted in dissolved form- 1.5%
how many harm groups does haemoglobin contain
4
when is haemoglobin considered fully saturated
when all the haemoglobin present is carrying its maximum O2 load
what is a primary factor that determines percent saturation of haemoglobin
PO2
what occurs to % haemoglobin saturation as partial pressure increases?
the % haemoglobin sat increases as more haemoglobin present is carrying O2.
how much O2 is taken to tissues under resting conditions
15ml/min
how much O2 is taken to tissues under strenuous exercise
90ml/min
what is resting O2 consumption of our body cells
250ml/min
oxygen delivery index calculation
DO2I= CaO2 (oxygen content of arterial blood) x Cl (cardiac index)
what determines the O2 content of arterial blood?
Hb concentration and saturation of Hb with O2 ( and saturation depends on partial pressure)
how much )2 does a gram of Hb carry when fully saturated
1.34
what does the partial pressure of inspired oxygen depend on
total pressure (atmospheric pressure) and proportion of oxygen in gas mixture (about 21% in atmosphere)
what can oxygen delivery to tissues be impaired by
decreased partial pressure of inspired oxygen and respiratory disease as these can decrease arterial PO2 and hence decrease Hb saturation with O2 and O2 content of the blood.
how may anaemia affect oxygen delivery to tissues
it will impair it as it decreases Hb concentration and so decreases O2 content of the blood
how does heart failure affect oxygen delivery to tissue
heart failure impairs it as it decreases cardiac output
what shape does Hb binding cause on a graph
sigmoid
why when one O2 binds to Hb does affinity of Hb increase for another O2
due to cooperativity
what does the flat upper portion of the Hb sigmoid graph mean
it means the MODERATE FALL IN ALVEOLAR P02 WILL NOT HAVE MUCH AFFECT OXYGEN LOADING
what does the steep lower part of the Hb sigmoid graph mean
it means that the peripheral tissues get a lot of oxygen for a small drop om capillary PO2
what can shift the Hb saturation curve to the right, increasing release of O2 at tissues?
increase in PCO2, increase in [H+], increase in temperature, increase in 2,3- niphosphoglycerate
what does 2,3-biphosphoglycerate do
it decreases affinity of Hb to oxygen
why does HbF have a higher affinity for oxygen than Hb
because it interacts less with 2,3- biphopsphoglycerate
how does HbF differ in structure from Hb
HbF has 2 alpha subunits and 2 gama subunits while Hb has beta subunits
what does the HbF dissociation curve look like compared to the Hb dissociation curve
the HbF dissociation curve lies more to the left
where is myoglobin found
in skeletal and cardiac muscles
how many haem groups per myoglobin
1 haem group per myoglobin
why is the myoglobin dissociation curve hyperbolic
because there’s no cooperativity binding of O2
when does myoglobin release O2
at very low PO2
what does myoglobin provide
a short-term storage of O2 for anaerobic conditions
what does the presence of myoglobin in the blood indicate
muscle damage
in what ways is CO2 transported in blood and what % of CO2 is transported in each way
solution 10%, bicarbonate 60%, carbonic compounds 30%
how does henrys law apply to CO2
the amount of CO2 dissolved in blood is proportional to its partial pressure
how much more soluble is CO2 in blood than O2
roughly 20 times
how is bicarbonate formed in red blood cells
CO2 + H2O H2CO3H+ + HCO3
how are carbamino compounds formed
by combination of CO2 with terminal amine groups in blood proteins
what can reduced Hb bind more to than HbO2
CO2
do carbon compounds require enzymes
no, they are rapid even without
what’s the Haldane effect
removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+
what happens when the Boher effect and Haldane effect work together
they facilitate O2 liberation and uptake of CO2 and CO2 generates H+ at tissues
what occurs to Hb at the lungs
Hb pick up O2, weakening the ability to bind CO2 and H+
where do oxygen and CO2 bind to on the Hb molecule
O2 binds to the haem part, CO2 binds to the globing part
what part of the brain generated rhythm for breathing
the medulla
what network of neutrons generate rhythm
a network of neurons called the pre-botzinger complex
where are is the pre-botzinger complex located
near the upper end of the medullary respiratory centre
