Physiology Flashcards
what is internal respiration
the internal mechanisms that consume O2 and produce CO2
what is external respiration
the sequence of events that leads to the exchange of O2 and CO2 between external environments and the cells of the body
identify the four steps of external respiration
ventilation, gas exchange between alveoli and blood, gas transport in the blood, gas exchange at the tissue level
describe ventilation
the mechanical process of moving gas in and out of the lungs- from atmosphere to alveolar sacs
what blood vessels involved in gas exchange with alveoli
pulmonary capillaries
what blood vessels involved in gas exchange with tissues
systemic capillaries
what is the first step of external respiration
ventilation
what is boyle’s law
at any constant temperature the pressure of the gas varies inversely with the volume of the gas
how does boyle’s affect ventilation
gases will move from higher to lower pressures
what two factors holds the lungs to the thoracic walls
intrapleural fluid cohesiveness (water molecules in intrapleural fluid are attracted to each other and resist bring separated), the negative intrapleural pressure (the sub-atmospheric intrapleural pressures create a transmural pressure gradient across lung and chest wall)
what is the significance of the transmural pressure gradient against the lung and chest walls (2)
holds them together, pushing lungs out and chest inwards, also pressure play role in ventilation
how can you calculate the transmural pressure gradient across lung wall (transpulmonary pressure)
intra-alveolar (intrapulmonary) pressure - intrapleural (intrathoracic) pressure
how can you calculate the transmural pressure gradient across thoracic wall
atmospheric pressure - intrapleural (intrathoracic) pressure
describe the three pressures in relation to each other before inspiration
intra-alveolar pressure equal to atmospheric pressure and greater than intra-pleural pressure
what must happen for air to flow into the lungs during inspiration?
the intra-alveolar pressure must be less than the atmospheric pressure
describe the process of inspiration
thorax and lungs expand as a result of contraction of inspiratory muscles decreasing the intra-alveolar pressure (air then enters lung until atmospheric pressure is regained)
explain the significance of the transmural pressure gradient across the lung and chest wall
allows lung expansion and prevents collapsing of the lung
describe the process of expiration
the relaxation of inspiratory muscles which causes the recoiling of the lungs and the intra-alveolar pressure to fall back to an atmospheric level
inspiration and (normal resting) expiration- passive or active processes
inspiration active
expiration passive
what is a pneumothorax
air in the pleural space
what does a pneumothorax abolish
the transmural gradient needed for lung expansion
what does a pneumothorax lead to and produce symptom wise
lung collapse, shortness of breath and chest pain
what are the physical signs of a pneumothorax (2)
hyperresonant percussion note, decreased/ absent breath sounds
what muscles are involved with normal resting breathing
diaphragm - major inspiratory muscle; increases vertically the volume of the thorax by contracting
external intercostal muscle- contraction lifts ribs out and moves out the sternum; bucket handle
what allows the lungs to recoil
their elastic nature
what gives the lungs their elastic nature (2)
elastic connective tissue and alveolar surface tension
what is alveolar surface tension made of
the attraction between water molecules at liquid air interface in alveoli produces a force that resists the stretching of the lungs
what is pulmonary surfactant
a complex mixture of lipids and proteins secreted by type 2 alveoli
what is the role of pulmonary surfactant
lowers alveolar surface by interspersing between the water molecules lining the alveoli
why is pulmonary surfactant so important
prevents smaller alveoli collapsing and releasing air into larger alveoli
describe the Law of LaPlace
refers to alveolar stability- smaller alveoli with smaller radii have higher tendency to collapse
describe alveolar interdependence
when an alveoli starts to collapse the surrounding alveoli are stretched then recoil exerting expanding forces in the collapsing alveolus to open it
what are the major inspiratory muscles
the diaphragm and external intercostal muscles
what are the accessory muscles of inspiration and when are they used
sternocleidomastoid, scalenus, pectoral - forceful inspiration
what are the muscles of active respiration
abdominal muscles and internal intercostal muscles
what is tidal volume (TV)
volume of air entering or leaving lungs in a single breath
what is inspiratory reserve volume (IRV)
extra volume of air that can be maximally inspired over and above the resting tidal volume
what is reserve volume (ERV)
extra volume of air that can be actively expired via maximal contraction beyond the normal volume of air after a resting tidal volume
what is residual volume (RV)
Minimum volume of air remaining in lungs after even a maximal expiration
what is inspiratory capacity (IC)
maximal volume of air that can be inspired after a normal resting expiration
how can inspiratory capacity be calculated
IRV + TV
what is functional residual capacity (FRC)
volume of air in lungs after normal passive expiration
how is functional residual capacity calculated
ERV + RV
what is vital capacity
maximal volume of air that can be moved out of the lungs during a single breath following a maximal expiration
how is vital capacity calculated
IRV + TC + ERV
what is total lung capacity
total volume of air the lungs can hold
how is total lung capacity calculated
VC + RV
what volume cannot be measured by spirometry
residual volume (and therefore total volume)
when does residual volume increase
when the elastic recoil of the lungs is lost
what curve is used in spirometry
volume time curve
what is a forced vital capacity
maximum volume of air that can be forcibly expelled from the lungs after a maximum inspiration
what is forced expiratory volume in one second (FEV1)
volume of air that can be expelled during the first second of a forced vital capacity determination
what is the FEV1/FVC ratio and its usual value
proportion of forced vital capacity that can be expired in the first second (>70%)
what are the dynamic lung volumes
FVC, FEV1
what are dynamic lung values useful in diagnosing
obstructive and restrictive lung disease
what is the usual value for the FEV1/FVC and curve in obstructive lung disease
<70%
curve; same maximal value (FVC) but less steep curve
what is the usual value for the FEV1/FVC in restrictive lung disease
normal (>70%)
curve; same steepness, lower maximal value
what is the primary determinant of airway resistance?
radius of the conducting airway
what does parasympathetic stimulation cause in the airways
bronchoconstriction
what does sympathetic stimulation cause in the airways
bronchodilation
what is more difficult, expiration or inspiration
expiration
during inspiration what pulls the airways open
the thorax
what happens to intrapleural pressure during inspiration
it decreases
what happens to intrapleural pressure during expiration
it increases
what do the lungs do during expiration
recoil
what is dynamic airway compression
when rising pleural pressure during active expiration compresses the alveoli and airway
what does dynamic airway compression result in
make expiration more difficult in patients with airway obstruction
does dynamic airway compression cause problems in normal people
nope
describe how dynamic airway compression is beneficial in healthy individuals
increased airway resistance increases the upstream airway pressure which helps open airways by increasing the driving pressure between the alveoli and airways
give two examples of airway obstructions
asthma, COPD
what happens to the driving pressure when there is an airway obstruction
driving pressure between alveolus and airway is lost over obstructed segment
what does the loss in driving pressure result in
a fall in the airway pressure downstream
what does a fall in airway pressure downstream lead to
airway compression by the rising pleural pressure during active expiration
are diseased airways more likely to collapse
yes
what makes airway obstruction worse
if the patient also has decreased elastic recoil of lungs
what causes reduced elastic recoil (2)
emphysema, obstructed airway caused by COPD
what is the peak flow meter used to measure and in what patients
peak flow rate in patients with obstructive lung disease
what is the compliance of the lungs
measure into the effect that has to go into stretching or distending of the lungs
what is pulmonary compliance measured in
volume change per unit of pressure change across the lungs
less compliant = more/less effort?
more
what can decrease lung compliance (5)
pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia, absence or surfactant
what symptoms can decreased lung compliance produce
shortness of breath
how can decreased pulmonary compliance show in spirometry
restrictive pattern of lung volume (restrictive lung disease)
what can cause increased pulmonary compliance
if the elastic recoil of the lungs is lost- emphysema
what does increased lung compliance result in for the patients
hyperinflation of the lungs- harder to get air out
what is work of breathing
energy expended on breathing
what four factors can increase work of breathing
decreased pulmonary compliance, increased airway resistance, decreased elastic recoil, need for increased ventilation
what is pulmonary ventilation
the volume of air breathed in and out per minute
what is alveolar ventilation
volume of air exchanged between the atmosphere and alveoli per minute (represents new air available for gas exchange with blood)
what is anatomical dead space
parts of airways where the air is not available for gas exchange
how do you calculate pulmonary ventilation
(in liters) tidal volume x respiratory
is alveolar ventilation greater or smaller than pulmonary
less because of dead space
how do you calculate alveolar ventilation
(tidal volume - dead space volume) x respiratory rate
how do you increase pulmonary ventilation
increase depth and rate of breaths
what method of increasing pulmonary ventilation is more advantageous, why?
depth because of dead space
what is the definition of ventilation
rate at which gas is passing through the lungs
what is the definition of perfusion
the rate at which blood is passing through the lung
which part of the lung has better blood flow and ventilation
bottom
what is alveolar dead space
ventilated alveoli that are not adequately perfused with blood
what is physiological dead space
anatomical dead space and alveolar dead space
when could alveolar dead space become significantly increased
during disease
what matches airflow to blood supple in the lungs
local controls that act on the smooth muscles of airways
increased perfusion leads to what which then causes what
accumulation of CO2 in alveoli
decreases airway resistance leading to increased airflow
what does increased ventilation cause and then lead to
increase in alveolar O2 concentration
pulmonary vasodilation which increases blood flow
what are the four factors that influence gas transfer across the alveolar membrane
partial pressure gradient of O2 and CO2,
diffusion coefficient of CO2 and O2,
Surface area of alveolar membrane,
thickness of alveolar membrane
what does the partial pressure of a gas determine
the pressure gradient of that gas
why is a partial pressure gradient important
how gases move (across membranes etc)
what is partial pressure
the pressure that that gas would exert if it occupied the total volume in absence of all the other gases in the mixture (for non reactive mixtures)
what is daltons law of partial pressures
the total pressure exerted by a gaseous mixture = the sum of all the partial pressures of the components of the mixture
what is the alveolar gas equation
PAO2 = PiO2 - (PaCO2 /0.8)
what does PAO2 represent
partial pressure of O2 in alveolar air
what does PiO2 represent
partial pressure of O2 in inspired air
what does PaCO2 represent
partial pressure of CO2 in arteriole blood
what does 0.8 represent
respiratory exchange ratio (ratio of CO2 produced/ O2 consumed)
do gases move from higher to lower/ lower to higher partial pressures
higher to lower
why is the partial pressure gradient for CO2 much smaller than that of O2
CO2 more soluble in membranes
what is the diffusion coefficient of a gas
measure of the solubility of a gas in a membrane
is the diffusion coefficient of CO2 bigger or smaller than that of O2
bigger (20x)
what is the difference between PAO2 and PaO2
A = alveolar a = arterial
why is there a gradient between PaO2 and PAO2 (is it normal)
small gradient normal as ventilation-perfusion not perfect
big gradient would indicate problems with gas exchange in the lungs or a right to left shunt in the heart
what features of lungs facilitate effective gas exchange
large surface area and thin membranes
how is surface area of airways increased
airways divide repeatedly
where does the entire cardiac output go to
pulmonary circulation
what is ficks law of diffusion
the amount of gas that moves across a sheet of tissue per unit time is proportional to the area of the sheet but inversely proportionate to its thickness
describe alveoli
thin walled inflatable sacs, closely spaced
what do alveolar walls consist of
a single layer of flattened type one alveolar cells
what encircles each alveolus
pulmonary capillaries
what are the 7 non respiratory functions of the respiratory system
route for water and heat loss, enhances venous return, helps maintain normal acid-base balance, enables vocalisations. defends against inhaled foreign matter, nose- organ of smell, removes, modifies, activates or inactivates various materials passing through the pulmonary circulatory system
what is Henry’s law
the amount of gas that dissolves in a liquid is proportional to the partial pressure of the gas at equilibrium with the liquid
as a result of henry’s law if the partial pressure of the gas phase what would happen to the concentration of the gas in liquid phase
would increase proportionally
how is oxygen carried in the blood (2)
dissolved in blood, bound to haemoglobin in red blood cells,
when is haemoglobin considered fully saturated
when all Hb present is carrying maximum O2 load
how many Hb units in one molecule of haemoglobin
4
what is the primary factor that determines the percentage saturation of haemoglobin with O2
PO2
describe the shape of the O2-Hb dissociation curve
sigmoid shape
what is the significance of the sigmoid shape (2)
flatter upper proportions means that a moderate fall in alveolar PO2 will not much affect oxygen loading, sites become occupied
steep lower part means that the peripheral tissues get a lot of oxygen for a small drop in capillary PO2, cooperativity
what is oxygen delivery to tissues a function of
oxygen content of arterial blood and cardiac output
how to you calculate oxygen delivery index
DO2I = CaO2 x CI (cardiac index (cardiac output to body surface area))
what determines the O2 content of the arterial blood
concentration of haemoglobin and percentage saturation of haemoglobin with O2
what affects the delivery of O2 to the tissues
respiratory disease, heart failure or anaemia
how do you calculate the oxygen content of arterial blood
CaO2 = 1.34 (one gram of Hb carries 1.34 ml of oxygen whenn fully saturated) x (conc of Hb) x SaO2 (Hb saturated with O2)
how can respiratory disease decrease oxygen delivery
decrease arterial PO2 and therefore Hb saturation with O2
how does heart failure impair oxygen delivery
decreases cardiac output
how is the bohr effect seen on a O2-Hb dissociation curve
shift to the right
what is the bohr effect
increased release of O2 by conditions at the tissues
what conditions cause the bohr effect (4)
increases in carbon dioxide partial pressure in the blood, decrease in blood ph, increased in temperature, increase in 2,3-Biphosphoglycerate
how is foetal haemoglobin (HbF) different to adult haemoglobin (HbA) (2)
in structure (two alpha and two beta subunits) and affinity (higher) for O2
what does a foetal O2-Hb dissociation curve look like compared to normal
shifted to the left due to higher affinity
why does HbF have a higher affinity for O2
as interactes with 2,3-Biphosphogylcerate
what is the significance of HbF’s higher affinity for O2
allows transfer of of oxygen from mother to foetus even when the PO2 is low
whats the difference between O2-Hb and O2-myoglobin dissociation curves
O2-myoglobin curve is hyperbolic
explain the shape of the O2-myoglobin curve
only one haem group- no cooperation, releases O2 at very low PO2- short term storage during anaerobic conditions
how is CO2 carried in the blood (give percentages for each carriage)
solution (10%), as bicarbonate (HCO3-) (60%), as carbamino-haemoglobin (30%)
describe bicarbonate formation
CO2 diffuses into r.b.c. and reacts with water and is converted into carbonic acid by carbonic anhydrase. Carbonic acid then dissociates into hydrogen ions and bicarbonate (HCO3-). Chlorine shift replaces the HCO3- with chlorine from outside the cell resulting in the release of bicarbonate into blood.
what are carbamino compounds made of
CO2 + terminal amine groups in blood proteins
what is the amino group in carboamino-haemoglobin
globin
what is the role of Hb in blood buffering
binds with the hydrogen ions forms in bicarbonate formation
describe the CO2 dissociation curve
linear compared to O2-Hb dissociation
what is the haldane effect
removing O2 from Hb increases Hb’s ability to pick up CO2 and CO2 generated H+
how does the haldane affect show on CO2 dissociation curves
oxygen shifts the curve to the right
how does the haldane effect work in synchrony with the Bohr effect and what is the result
as the bohr effect facillitates the removal of O2 from Hb at a tissue level and pushes the O2 disscoiation curve to the right. Thus Bohr liberates O2 and helps in the uptake of CO2
how is the liberation of CO2 facilitated at the lungs
as where Hb binds to O2 thus weakening its ability to bind to CO2 and H+
what generates the rhythm of breathing and where is it located
the pre-botzinger complex. located near upper end of medulla respiratory complex
what is the pre-botzinger complex
a network of neurons
what part of the medulla is thought to control the rhythm of breathing
the medulla oblongata
what is excited when rhythm is generated by the pre-botzinger complex
the dorsal respiratory group neurons
what happens when the dorsal respiratory group neurons fire in bursts
contraction of inspiratory muscles- inspiration
what happens when firing of the dorsal neurons stops
passive expiration
what does increased firing from the dorsal neurons excite
the ventral respiratory group neurons
what does the excitation of the ventral respiratory neuron group lead to
stimulation of internal intercostals, abdominal = forceful expiration
what is thought to modify the rhythm of breathing
neurons in the pneumotaxic centre of the pons
what does stimulation of the pneumotaxic centre cause
terminates inspiration
when is the pneumotaxic centre stimulated
when dorsal respiratory neurons fire
name and describe the condition which would result from a lack of modification of rhythm
apneusis- breathing is prolonged inspiratory gasps with brief expiration
what do impulses from the apneustic centre excite and result in
inspiratory area of medulla, prolonged expiration
name the stimuli that influences respiratory centres from its description;
cerebral cortex, limbic system, hypothalamus
higher brain centres
name the stimuli that influences respiratory centres from its description;
guard against hyperinflation
stretch receptors in the walls of the bronchioles and bronchi
name the stimuli that influences respiratory centres from its description;
stimulated by pulmonary capillary congestion, pulmonary oedema and pulmonary emboli
Juxtapulmonary (J) receptors
name the stimuli that influences respiratory centres from its description;
stimulated by joint movement
joint receptors
name the stimuli that influences respiratory centres from its description;
increased respiratory rate due to drop in blood pressure
baroreceptors
what is the hering-breuer reflex
activated during inspiration, afferent discharge inhibits inspiration
how do impulses from moving limbs affect breathing
increase
list the 5 factors that could increase ventilation during breathing
body movement reflexes, adrenaline, cerebral cortex impulses, increase in body temp, (later) accumulation of CO2 and H+ generated by muscles
what is the cough reflex triggered by
irritations of airways or tight airways
what does afferent discharge stimulate
short intake of breath, closure of the larynx, contraction o abdominal muscles, opening of larynx ans expulsion of air
what is the chemical control of respiration an example of
negative feedback control system
what are the controlled variables in the negative feedback system of the chemical control of respiration
blood gas tensions, especially CO2
what do chemoreceptors sense
values of gas tension
where are peripheral chemoreceptors located
in the carotid and aortic bodies
what do peripheral chemoreceptors sense
tension of oxygen and CO2, and H+ conc in the blood
where are the central chemoreceptors located
near the surface of the medulla in the brain stem
what do central chemoreceptors respond to
H+ conc of the cerebrospinal fluid (CSF)
how is the cerebrospinal fluid separated from the blood
via the blood brain barrier
describe the relative permeability of CO2, H+ and HCO3-
impermeable to H+ and HCO3-
CO2 diffuses readily
why is CSF less buffered than blood
as contains less proteins
what does hypercapnia result in
an increase in ventilation
at what level of PO2 are peripheral chemoreceptors stimulated and what does this result in
> 8 kPa increase in ventilation
what does partial pressure of inspired oxygen depend on
total pressure and proportion of oxygen in gas mixture
what is hypoxia at high altitudes caused by
decreased partial pressure of inspired oxygen
what is the acute response to hypoxia
increased ventilation and cardiac output
list the chronic adaptations to high altitude hypoxia (5)
increased RBC production, 2,3-Biphosphoglycerate produced within RBC (eases O2 offloading to tissues), increased number of capillaries, increased number of mitochondria (more efficient use of O2, kidneys conserve acid (increasing arterial pH)
how to peripheral chemoreceptors adjust acidosis
via the addition of non carbonic acid H+ to the blood
what are the physical effect of stimulation of the peripheral chemoreceptors by H+
hyperventilation to increase elimination of CO2
can CO2 generate H+
yes
what does the elimination of CO2 also result in
a reduction of the H+ load in the body
what is the dominant control of ventilation
arterial PCO2
when does arterial PO2 affect central chemoreceptors
severe hypoxia depresses respiratory centre
why does arterial H+ only affect the peripheral not central chemoreceptors
as H+ cannot cross blood brain barrier
hoe does 2,3 BPG affect an O2-Hb dissociation curve
shifts it to the right
what might become important for people with chronic CO2 retention
hypoxic drive
