Flashcards in Physiology Deck (252):
what is the internal respiration equation?
food + oxygen = energy + carbon dioxide (+ water)
consumption of oxygen and production of carbon dioxide
what does external respiration refer to?
the exchange of oxygen and carbon dioxide between external environment and the cells of the body
how many steps are involved in external respiration?
what is the 1st step of external respiration?
what is the 2nd step of external respiration?
gas exchange between alveoli and blood
what is the 3rd step of external respiration?
gas transport in the blood
what is the 4th step of external respiration?
gas exchange at tissue level
what does ventilation (1st step of external respiration) involve?
the mechanical process of gas exchange between the armosphere and the alveoli
what does 'gas exchange between alveoli and blood' (2nd step of external respiration) involve?
exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries
what does 'gas transport in the blood' (3rd step of external respiration) involve?
the binding and transport of oxygen and carbon dioxide in the circulating blood
what does 'gas exchange at tissue level' (4th step of external respiration) involve?
the exchange of oxygen and carbon dioxide between the blood in the systemic circulation and the body cells
what 3 body systems are involved in external respiration?
What is Boyle's Law?
for a given mass of gas -at a certain temperature- as the volume of the gas increases, the pressure exerted by the gas decreases.
air flows down a pressure gradient ___ pressure to a region of ___ pressure
high pressure to a region of low pressure
when is the intra-alveolar pressure equivalent to the atmospheric pressure?
What does expansion of the thorax and lungs do to the intra-alveolar pressure?
makes it fall below atmospheric pressure (Boyle's Law)
this allows air to move from atmosphere into lungs down pressure gradient
what 2 forces hold the thoracic wall and the lungs in close opposition?
1. intrapleural fluid cohesiveness
2. the negative intrapleural pressure
how does the intrapleural fluid keep thoracic wall and lungs in close opposition?
the water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart, therefore pleural membranes tend to stick together
how does the negative intrapleural pressure keep the thoracic wall and lungs in close opposition?
the sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and chest wall, therefore lungs are forced to expand outwards while the chest is forced to squeeze inwards
what 3 pressures are important in ventilation?
what is the atmospheric pressure at sea level?
what is usually the intrapleural pressure?
when the external intercostal muscle contract what do they cause?
elevation of the ribs, causing the sternum to move upwards and forwards- increases AP dimension of thoracic cavity
what type of process is inspiration?
(brought about by contraction of inspiratory muscles)
what type of process is normal expiration?
(brought about by relaxation of inspiratory muscles)
what 2 properties allows the lung to recoil to their preinspiratory size during expiration?
elastic connective tissue in the lungs
alveolar surface tension
what does the recoil of lungs do to the intra-alveolar pressure?
makes it rise above atmospheric pressure
this allows air to move from lungs to atmosphere down a pressure gradientq
what is a traumatic pneumothorax?
a puncture wound in the chest wall causing a collapsed lung
what is a spontaneous pneumothrax?
a hole in the lung itself causing a collapsed lung
why do holes in either the chest wall of lung wall cause collapsed lungs?
they permit air to enter the pleural cavity and abolish the transural pressure gradient causing the lung to collapse to its unstretched size
what is alveolar surface tension?
attraction between water molecules at liquid air interface on the internal surface of the alveoli producing a force which resists the stretching of the lungs
what would happen if the alveoli were lined with water alone on the internal surface?
surface tension would be too strong and the alveoli collapse
What is LaPlace's Law
P = inward directed collapsing pressure
T = surface tension
r = radius of the alveoli
so collapsing pressure varies directly with surface tension but varies indirectly with to radius
what happens to the tendency of the alveoli to collapse if the radius of the alveoli is decreased?
increased tendency to collapse
what mixture intersperses between the water molecules lining the alveoli and lowers the alveolar surface tension?
what is surfactant made of?
a complex misture of lipids and proteins
what type of cell secretes surfactant?
type II alveoli
in what type of alveoli is surfactant more effective in? (small or big alveoli?)
what does surfactant prevent from happening?
the smaller alvoli collapsing and emptying their air contents intp the larger alveoli
what causes respiratory distress syndrome of the new born?
premature babies may not have enough pulmonary surfactant and so the baby makes very strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs
when is surfactant synthesised in the developing fetal lungs?
late in pregnancy
what 3 forces keep the alveoli open? (ie overcome surface tension)
transmural pressure gradient
what happens when an alveolus starts to collapse?
the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus causing it to open again
what are the accessory muscles of inspiration?
what are the major muscles of inspiration?
external intercostal muscles
when are the accessory muscles of inspiration used?
during forceful inspiration
what are the muscles of active expiration?
internal intercostal muscles
what device is used to measure lung volumes and capacities?
what one volume can the spirometer not measure?
What is the tidal volume? (TV)
volume of air entering or leaving lungs during a single breath
what is the inspiratory reserve volume? (IRV)
extra volume of air that can be maximally inspired over and above the typical resting tidal volume
what is the average tidal volume? (TV)
what is the average inspiratory reserve volume? (IRV)
what is the inspiratory capacity? (IC)
the maximal volume of air that can be inspired at the end of a normal quiet expiration
(IC = TV + IRV)
what is the average inspiratory capacity? (IC)
(500ml + 3000ml)
what is the expiratory reserve volume? (ERV)
extra volume of air that can be actively expired by aximal contraction beyond the normal volume of air after a resting tidal colume
what is the average expiratory reserve volume? (ERV)
what is the residual volume? (RV)
minimal volume of air remaining in the lungs even after a maximal expiration
what is the average residual volume?
what is the functional residual capacity? (FRC)
the volume of air in the lungs at the end of a normal expiration
(FRC = ERV +RV)
what is the average functional residual capacity?
(1000 + 1200ml)
what is the vital capacity? (VC)
maximal volume of air that can be moved out during a single breath following a maximal inspiration
(VC = IRV + TV + ERV)
what is the average vital capacity?
(3000ml + 500ml + 1000ml)
what is the total lung capacity? (TLC)
maximal volume of air that the lungs can hold
(TLC = VC + RV
TLC = IRV + TV + ERV + RV)
what is the average total lung capacity?
(4500ml + 1200ml)
(3000ml + 500ml + 1000ml + 1200ml)
what is the forced expiratory volume in 1 second? (FEV1)
[a dynamic volume]
the volume of air that can be expired during the first second in a FVC (forced vital capacity)
what is the normal FEV1%?
what does spirometry allow you to create?
a volume time curve
what 3 things does a volume time curve produced from spirometry allow you to determine?
in an obstructive lung disease, what is the FEV%?
in an obstructive lung disease, what happens to the FEV1 and the FVC?
FVC- normal (4500ml)
in a restrictive lung disease, what happens to the FEV1 and the FVC?
in an restrictive lung disease, what is the FEV%?
what does airway flow vary with?
varies directly with pressure
varies indirectly with resistance
(as pressure increases flow increases. as resisance increases flow decreases.)
why does air usually flow in the airways with only a small pressure gradient?
resistance to flow in the airways is normally very low
what does parasympathetic stimulation cause in the smooth muscles of the airways?
what does sympathetic stimulation cause in the smooth muscles of the airways?
in obstructive disease which is more difficult- expiration or inspiration?
what effect happens during active expiration that causes no problem in normal people but is problematic for patients with airway obstruction?
dynamic airway compression
what 2 things does dynamic airway compression cause an increased pressure in?
what is dynamic airway compression not a problem for normal people?
despite the increased airway resistance, the pressure in the alveoli gets high enough so there is no change in air flow
why is dynamic airway compression problematic for patients with airway obstruction?
if there is an airway obstruction, the alveoli pressure wont be high enough to overcome the increased airway resistance- causing air-trapping behind the blackade
in addition to obstructed airways, what other type of airways are more likely to collapse?
what can aggravate the problem of dynamic airway compression in patients with airway obstruction?
if the patient also has decreased elastic recoil of the lungs
(ie patient with emphysema and obstructed airway caused by COPD)
what does a peak flow meter do?
measures the maximum speed at which a patient can move air out of lungs- peak flow rate
what does a decrease in peak flow rate show?
possible obstructive lung disease
what does peak flow rate in normal adults vary with?
age, sex, height
what is pulmonary compliance?
a measure of effort that has to go into stretching or distending the lungs
what type of pattern of lung volumes with a decreaed pulmonary compliance show?
what do pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia and absence of surfactant do to the pulmonary compliance?
decrease pulmonary compliance
in restrictive disease which is more difficult- expiration or inspiration?
what occurs in emphysema?
increased compliance due to loss of elastic recoil (hard to get air out of the lungs- hyperinflation)
what physiological factor can cause pulmonary compliance to increase?
what is the name of the area of the airways where there is inspired air but it is not available for gas exchange?
anatomical dead space
Pulmonay ventilation (L)=
tidal volume (L/breath) x respiratory rate (breath/min)
what is the normal pulmonary ventilation rate under normal resting conditions?
why is alveolar ventilation less than pulmonary ventilation?
anatomical dead space
alveolar ventilation =
(tidal volume - dead space volume) x Resp Rate
what is the normal alveolar ventilation rate under normal resting conditions?
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 the alveoli per minute
to increase pulmonary ventilation (ie during exercise) both tidal volume (depth) increases and resp rate increase. which is more advantagous?
tidal volume (depth)
[because of the dead space]
what is perfusion?
the rate at which blood is passing through the lungs
what is considered as alveolar dead space?
ventilated alveoli which are not adequately perfused with blood
physiological dead space =
anatomical death space + alveolar dead space
what usually increases significantly in disease? (anatomical or alveolar dead space)
alveolar dead space
what type of controls act on the smooth muscle of airways and arterioles to match airflow to blood flow? (ventilation to perfusion matching)
what happens when perfusion > airflow?
increased perfusion causes accumulation of CO2 in the alveoli
the increased CO2 causes decreased airway resistance leading to increased airflow
what happens when airflow > perfusion?
increased ventilation causes increased alveolar O2 concentration
increased alveolar O2 concentration causes increased blood flow to match larger airflow
what is alveolar oxygen sats are potent pulmonary vasoconstrictors?
what alveolar oxygen sats are potent pulmonary vasodilators?
what alveolar CO2 sats are potent bronchodilators?
what alveolar CO2 sats are potent bronchoconstrictors?
what tissue cell oxygen sats are potent systemic vasodilators?
what tissue cell oxygen sats are potent systemic vasoconstrictors?
what 4 factors influence the rate of gas exchange across the alveolar membrane?
1. partial pressure gradient of O2 and CO2
2. diffusion coefficient for O2 and CO2
3. surface area of alveolar membrane
4. thickness of alveolar membrane
what is Dalton's law of parital pressures?
the total pressure exerted by a gaseous mixture = the sum of the partial pressures of each individual component in the gas mixture
(P total = P1 + P2 + P3...)
what is the partial pressure of a gas in a mixture of gases that don't react with each other?
the pressure that gas wold exert if it occupied the total volume for the mixture in the absence of the other components
what contributes to about 47mmHg of the total pressure in the lungs?
water vapour pressure
what is the pressure of inspired air?
(without the water vapour)
considering oxygen makes up 21% of the air concentration, what is the the partial pressure of inspired oxygen (PiO2)?
[remember without water vapour, the pressure of inspired air = 712mmHg]
0.21 x 731= 150mmHg
What is the alveolar gas equation?
PAO2 = PiO2- [PaCO2/0.8]
what is the normal arterial PCO2?
at a normal arterial PCO2 what is the PAO2?
PAO2 = 150mmHg - [40/0.8]
what is the PAO2?
the partial pressure of O2 in alveolar air
what is the PiO2?
the partial pressure of O2 in inspired air
what is PaO2?
the partial pressure of O2 in arterial blood
what is PaCO2?
the partial pressure of CO2 in arterial blood
what does the respiratory exchange ratio (RER) mean?
the ratio of CO2 produced and O2 consumed
for someone eating a mixed diet what is the average respiratory exchange ratio?
how do you convert mmHg pressure to kPa?
kPa = mmHg/7.5
what is the normal venous pressure of oxygen?
what is the O2 partial pressure gradient across the pulmonary capillaries (from alveoli to blood)?
(100mmHg - 40mmHg)
what is the normal venous pressure of CO2?
what is the CO2 partial pressure gradient across the pulmonary capillaries (from blood to alveoli)?
what 2 partial pressure of oxygen are the same?
PAO2 and PaO2 = 100mmHg
what 2 partial pressures of CO2 are the same?
PAO2 and PaO2 = 40mmHg
what is the O2 partial pressure gradient across systemic capillaries (from blood to tissue cell)?
(100mmHg - <40mmHg)
what is the CO2 partial pressure gradient across systemic capillaries (from tissue cell to blood?)
(46mmHg - <40mmHg)
what is the diffusion co-efficient?
the solubility of gas in membranes
compare the diffusion co-efficients of CO2 and O2?
CO2 diffusion coefficient = 20x diffusion coefficient for O2
(ie CO2 is more soluble in membranes than O2)
why is a small gradient between PAO2 and PaO2 normal?
ventilation-perfusion match is usually not perfect
what does a big gradient between PAO2 and PaO2 indicate?
problems with gas exchange in the lungs or a right to left shunt in the heart
what is 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 proportionate to its thickness
what type of alveolar cells does gas exchange occur across?
type 1 alveolar cells
what happens to the rate of gas transfer across the alveolar membrane as the partial pressure gradient increases?
rate of gas transfer increases
what happens to the rate of gas transfer across the alveolar membrane as the surface area increases?
rate of gas transfer increases
what happens to the rate of gas transfer across the alveolar membrane as the thickness increases?
rate of gas transfer decreases
what happens to the rate of gas transfer across the alveolar membrane as the diffusion coefficient increases?
rate of transfer increases
what is the main influence for the rate of oxygen transfer across the alveolar membrane?
the partial pressure gradient
what is the main influence for the rate of carbon dioxide transfer across the alveolar membrane?
the diffusion coefficient
what are the 7 non-respiratory functions of the respiratory system?
1. route for water loss and heat elimination
2. enhances venous return
3. helps maintain normal acid-base balance
4. enables speech, singins and other vocalizations
5. defends agasint inhaled foreign matter
6. remoes, modifies, activates or inactivates various materials passing through the pulmonary circulation
7. nose serves as the organ of smell.
What is Henrys Law?
the amount of a given gas dissolved in a given type and volume of liquid (at a constant temp) is proportional to the partial pressure of the gas in equilibrium with the liquid
what happens to the concentration of gas in a liquid, if the partial pressure of the gas in equilibrium to the liquid is increased?
the concentration of gas in a liquid will also increase
when a gas is in a equilibrium between the gaseous phase and the liquid phase, what is the partial pressure of the gas in solution equal to?
the partial pressure of the gaseous phase
as the partial pressure increases, what happens to the amount of O2 dissolved in the blood? (Henry's law)
dissolved O2 increases
in what forms is O2 present in the blood?
bound to haemoglobin (98.5%)
physically dissolved (1.5%
how many haem groups does each haemoglobin molecule contain?
4 haem groups
when is haemoglobin considered fully saturated?
when all the Hb present is carrying its maximum O2 load
what is the primary factor which determins the percent saturation of haemoglobin?
what is the average resting PO2 at systemic capillaries?
what is the normal PO2 at pulmonary capillaries?
what is the DO2I?
Oxygen delivery index
CaO2 x Cl
what is CaO2?
oxygen content of arterial blood (ml/L)
what is Cl?
the cardiac index - related the cardiac output to the body surface area (L/min/meter^2)
what is the normal range for cardiac index? (CI)
1.34 x [Hb] x SaO2
one gram of haemoglobin carries how much oxygen when fully saturated? (in millilitres)
what is SaO2?
the percentage of Hb saturated with O2?
what is SaO2 determined by?
what 3 broad reasons can oxygen delivery to the tissues be impaired by?
what does binding of one molecule of oxygen (O2) to Hb do to the affinity of Hb for O2?
increases the affinity of Hb for O2
(co-operativity, sigmoid curve)
what happens to the haemoglobin molecule when all sites are occupied?
how many chains does haemoglobin contain?
2 alpha chains
2 beta chains
(4 in total)
what is the functional ion of a haem group?
What does the Bohr effect do?
causing a shift of the haemoglobin saturation sigmoid curve to the right (ie decreased affinity for oxygen and therefore increased release of O2)
what 4 factors cause the Bohr effect?
where does the Bohr effect usually hapen?
(they want the increased release of oxygen from haemoglobin)
how many haem groups does myoglobin have per molecule?
one haem group
which has cooperative binding- haemoglobin or myoglobing?
what shape is a haemoglobin dissociation curve?
what shape is a myoglobin dissociation curve?
when does myoglobin release O2?
at a very low PO2
what is the function of myoglobin?
provides short-term storage for O2 for anaerobic conditions
where is myoglobin physiologically present?
skeletal and cardiac muscles
what does presence of myoglobin in the blood indicate?
what are the 3 ways CO2 is transported in the blood?
as bicarbonate (60%)
as carbamino compounds (30%)
compare the solubility of carbon dioxide to oxygen?
CO2 is 20 times more soluble than O2
what is the equation for the transformation of carbon dioxide into bicarbonate?
CO2 + H2O (reversible with) H2CO3 (reversible with) H+ + HCO3-
what enzyme converts CO2 + H20 to H2CO3?
where does the conversion of carbon dioxide to bicarbonate take place?
in red blood cells
a byproduct of the conversion of cardbon dioxide to bicarbonate is a H+ atom, what does this bind with?
Hb to make HbH
how are carbamino compounds formed?
by combination of CO2 with terminal amine groups in blood proteins
what is formed when carbon dioxide combines with the globulin of haemoglobin?
in which form is the haemoglobin more readily able to bind CO2?
reduced Hb (ie with no oxygen molecules attached) more readily binds with CO2 than HbO2
What is the Haldane effect?
removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+
what do the Bohr effect and the Haldane effect work in synchrony to facilitate?
the liberation of O2 and the uptake of CO2 and CO2 generated H+ at tissues
what neurones generate the breathing rhythm (act as a pacemaker) for respiration?
pre-botzinger complex in the medullary respiratory centre
what causes contraction of inspiratory muscles and therefore causes inspiration?
firing of the dorsal respiratory group neurones in the medullary respiratory centre
what causes relaxation of inspiratory muscle and therefore causes passive expiration?
ceased firing of the dorsal respiratory group neurones in the medullary respiratory centre
what neurone group does increased firing of the dorsal respiratory group neurones in the medullary respiratory centre excite?
the ventral respiratory group neurones
what causes contraction of internal intercostals and abdominal muscles and therefore causes active/forceful expiration?
firing of the ventral respiratory group neurones in the medullary respiratory centre
the rhythm that is generated in the medulla can be modified from neurones where else in the brain?
What signal from the pons stimulates the termination of inspiration? (ie causes dorsal neurones to stop firing)
firing of neurones from the pneumotaxic centre of the pons
when is the pneumotaxic centre in the pons stimulated?
when dorsal respiratory neurones fire
what type of breathing occurs without the pneumotaxic centre?
breathing is prolonged inspiratory gasps with brief expiration
what is the main function of the pneumotaxic centre?
inhibition of inspiration
what impulses excite the dorsal neurones in the medullary respiratory centre?
firing from neurones from the apneustic centre in the pons
what is the main function of the apneustic centre?
what are the 4 types of involuntary (reflex) modifications of breathing?
1. Hering-Breuer Reflex
2. joint receptors reflex
3. stimulation of respiratory centre
4. cough reflex
what 5 ways can the respiratory centre be involuntary stimulated to increase ventilation during exercise?
impulses from cerebral cortex
accumulation of CO2 and H+ generated by active muscles
what is the Hering-Breuer reflex?
pulmonary stretch receptors detect how much the lung has expand and when the lung has inflated sufficiently they send an afferent trigger which inhibits inspiration
what is the purpose of the Hering-Breuer reflex?
to prevent over-inflation of the lungs,
but not active during normal respiratory cycle
What is the joint receptor reflex?
impulses from moving limbs reflexly increase breathing
what does the joint receptor reflex contribute to?
the necessary increased ventilation during exercise
why does recovery phase of exercise take time for ventilation rate to return to normal?
takes time to wash the chemical triggering increased ventilation out
what is the function of the cough reflex?
helps clear airways of dust, dirt or excessive secretion
when is the cough reflex activated?
irritation of the airways or tight airways
what is the events that occur during a cough reflex?
1. irritation of airways/tight airways
2. afferent discharge
3. short intake of breath
4. closure of larynx
5. contraction of abdominal muscles to increase intra-alveolar pressure
6. opening of the larynx
7. expulsion of air at high speed
what type of feedback control is the chemical control of respiration?
what do chemoreceptors do?
sense the values of gas tensions
what are the controlled variables in the chemical feedback control of respiration?
blood gas tensions
where are peripheral chemoreceptors located?
arch of aorta
what do peripheral chemoreceptors sense?
tension of oxygen and carbon dioxide
[H+] in the blood
where are central chemoreceptors located?
near the surface of the medulla of the brainstep
what do central chemoreceptors respond to?
[H+] of the cerebrospinal fluid (CSF)
how is the cerebrospinal fluid separated from the blood?
by the blood-brain barrier
what is the blood-brain barrier impermeable to?
what diffuses readily across the blood brain barrier?
what happens when CO2 diffuses across the blood brain barrier?
dissociated into H+ ions
as there is a low protein content of the CSF the ions produced arent buffered well and so stimulate the central chemoreceptor
what is the term used to describe high carbon dioxide concetrations in the blood?
as hypercapnia increases slightly what happens to ventilation?
to remove excess CO2
what happens to the respiratory centre neurones when there is severe hypoxia?
become depressed and so there is a poor ventilation
as a general trend, what happens when PO2 increases?
(ignore extreme hypoxia)
as altitude increases what happens to the partial pressure of oxygen?
what type of chemoreceptors cause the effect of hypoxic drive of respiration?
(only they can detect oxygen levels, central only detect CO2 levels through CO2 generated H+)
when is the hypoxic drive of respiration stimulated?
when PaO2 < 8kPa
when does the hypoxic drive of respiration become important?
in patients with chronic CO2 retention (ie COPD)
why does hypoxia at high altitudes occur?
decreased partial pressure of inspired oxygen (PiO2)
what is the acute response to hypoxia at high altitudes?
hyperventilation + increased cardiac outpus
what are 5 chronic adaptations to high altitude hypoxia?
2. increase 2,3-biphosphoglycerate produced within RBC
3. increased number of capillaries
4. increased number of mitochondria
5. kidneys conserve aid
why is polycythaemia a useful adaptation to high altitude hypoxia?
increases O2 carrying capacity of the blood
why is increased 2,3-biphosphoglycerate production within the RBS a useful adaptation to high altitude hypoxia?
allows O2 to be offloaded more easily into tissues
why is increased number of capillaries a useful adaptation to high altitude hypoxia?
allows blood to diffuse more easily
why is increased number of mitochondria a useful adaptation to high altitude hypoxia?
allows O2 to be used more efficiently
why is metabolic conservation of acid a useful adaptation to high altitude hypoxia?
decreases pH (metabolic acidosis) which allows O2 to be ofloaded more easily into tissues
what receptors cause the H+ drive of respiration?
what is the function of the H+ drive of resiration?
adjusts for acidosis caused by the addition of non-carbonic acid H+
(eg lactic acid or diabetic ketoacidosis)
what does the H+ drive of respiration cause?
hyperventilation and incresaes elimination of CO2 from the body (reduces body acid content)