Physiology Flashcards
what is internal respiration?
the intracellular mechanisms that consume oxygen and produce CO2
what is external respiration?
the sequence of events that leads to the exchange of oxygen and CO2 between the external environment and the cells of the body
what are the four steps of external respiration?
ventilation
gas exchange (alveoli to blood)
gas transport in blood
gas exchange (blood to tissue)
what is ventilation?
the mechanical process of moving air in and out of the lungs
what body systems are involved in external respiration?
respiratory
cardiovascular
haematological
nervous
when can air flow into the lungs?
when intra-alveolar pressure is less than atmospheric pressure
what does contraction of the inspiratory muscles cause?
expansion of the thorax and the lungs
what does boyle’s law state?
at any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas
what are the two forces that hold the thoracic wall and the lungs in close opposition?
intrapleural fluid cohesiveness
negative intrapleural pressure
how does intrapleural fluid cohesiveness work?
water molecules in intrapleural fluid are attracted to each other and resist being pulled apart, causing the pleural membranes to stick together
how does negative intrapleural pressure work?
sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the wall of the lung and the chest, forcing the lungs to expand when the chest squeezes inwards
is inspiration an active or passive process?
active
what does inspiration depend on?
muscle contraction
what effect does contraction of the diaphragm have on the volume of the thorax?
increases it vertically
which nerve innervates the diaphragm?
the phrenic nerve
what does contraction of the external intercostal muscles cause?
lifts the ribs up
moves the sternum out
what is the mechanism by which the lifts move up and the sternum moves out called?
the bucket handle mechanism
what effect does increasing the size of the lungs have on intra-alveolar pressure and why?
it decreases, because the air molecules are now contained in a larger volume
when does air stop entering the lungs in inspiration?
when the intra-alveolar pressure is equal to atmospheric pressure
how does expiration occur?
passive
caused by relaxation of inspiratory muscles
what happens when the lungs recoil in expiration?
intra-alveolar pressure rises and air leaves the lungs down its pressure gradient
when does air stop leaving the lungs in expiration?
when intra-alveolar pressure is equal to atmospheric pressure
what two things cause the lungs to recoil during expiration?
elastic connective tissue in the lungs
alveolar surface tension
what is a pneumothorax?
air in the pleural space
what are the three possible causes of a pneumothorax?
spontaneous
traumatic
iatrogenic
how can a pneumothorax progress to lung collapse?
air entering the pleural space can abolish the transmural pressure gradient
what type of pneumothorax may be asymptomatic?
very small
name two possible symptoms of a pneumothorax
shortness of breath
chest pain
name two possible signs of a pneumothorax
hyperresonant percussion
decreased breath sounds
what is alveolar surface tension?
the attraction between water molecules at the liquid air interface of an alveoli
what does alveolar surface tension produce?
a force which resists the stretching of the lungs
what reduces alveolar surface tension and prevents collapse?
surfactant
state laplace’s law
P=2T/r
what does each letter in Laplace’s law represent?
P=inward directed pressure
T=surface tension
r-radius of alveoli
which size of alveoli has a higher tendency to collapse?
smaller
what cell produces surfactant?
type 2 alveoli
how does surfactant lower alveolar surface tension?
it intersperses between water molecules lining the alveoli
when do developing foetal lungs start to synthesise surfactant and what effect can this have?
late in pregnancy
premature babies might not have enough
what causes respiratory distress syndrome of the new born?
lack of pulmonary surfactant
how does alveolar interdependence keep the alveoli open?
if one starts to collapse, the alveoli surrounding it are stretched and then recoil, exerting expanding forces on the one collapsing causing it to open
what factor most increases pulmonary ventilation?
tidal volume
what are the major inspiratory muscles?
diaphragm
external intercostal muscles
what are the accessory muscles of inspiration?
sternocleidomastoid
scalenus
pectoral
when do the accessory muscles of inspiration contract?
only during forceful inspiration
what are the muscles of active expiration?
abdominal muscles
internal intercostal muscles
what is the tidal volume?
the volume of air entering/leaving the lungs during a single breath
what is inspiratory reserve volume?
the extra volume of air that can be maximally inspired above tidal volume
what is expiratory reserve volume?
the extra volume of air that can be expired beyond the tidal volume
what is residual volume?
the volume of air remaining in the lungs, even after a maximal expiration
what is inspiratory capacity?
the maximum volume that can be inspired after a normal expiration
what do you get if you add IRV and TV?
inspiratory capacity
what is functional residual capacity?
the volume of air in the lungs at the end of a passive expiration
what do you get when you add ERV and RV?
functional residual capacity
what is vital capacity?
the max volume of air that can be exhaled after a maximal inspiration
what do you get when you add IRV + TV + ERV?
vital capacity
what is total lung capacity?
the total volume of air the lungs can hold
what do you get when you add VC + RV?
TLC
what is the average value of TLC?
5700ml
what volume cannot be measured by spirometry and what does this mean?
residual volume
means TLC also can’t be measured
when does residual volume increase?
when elastic recoil of the lungs is lost
name a disease where elastic recoil of the lungs is lost
emphysema
name two dynamic lung volumes
FVC
FEV 1
what does FVC stand for?
the forced vital capacity
what is FVC?
the max volume that can be expired from the lungs after a max inspiration
what is FEV1?
the volume of air that can be forcefully expired in the first second of expiration
what is the FEV1/FVC ratio?
the proportion of the FVC that can be expired in the first second
what is the normal value for the FEV1/FVC ratio?
over 70%
what does a FEV1/FVC ratio under 70% suggest?
obstructive lung disease
what are the dynamic lung volumes like in obstructive disease?
FVC = normal FEV1 = low FEV1/FVC = low
what are the dynamic lung volumes like in restrictive disease?
FVC = low FEV1 = low FEV1/FVC = normal
what are the dynamic lung volumes like in combined obstructive and restrictive disease?
FVC = low FEV1 = low FEV1/FVC = low
what equation can be used to calculate airway resistance?
F = deltaP/R
F = flow P = pressure R = resistance
what is the main determinant of airway resistance?
the radius of the conducting airway
what does parasympathetic stimulation of the bronchus cause?
bronchoconstriction
what does sympathetic stimulation of the bronchus cause?
bronchodilation
what happens to intrapleural pressure in inspiration?
falls
what happens to intrapleural pressure in expiration?
rises
what is a peak flow meter used for?
estimating peak flow rate, which assesses airway function
what is pulmonary compliance?
a measure of the effort that goes into stretching or distending the lungs
what is anatomical dead space?
areas in airways where gas exchange cannot occur
how is pulmonary ventilation calculated?
tidal volume times RR
why is alveolar ventilation less than pulmonary ventilation?
due to presence of anatomical dead space
how is alveolar ventilation calculated?
(tidal volume - dead space volume) X RR
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
how can pulmonary ventilation be increased?
increase depth and rate of brreathing
what is ventilation?
the rate at which gas passes through the lungs
what is perfusion?
the rate at which blood passes through the lungs
what is alveolar dead space?
ventilated alveoli which are not adequately perfused with blood
what is physiological dead space?
anatomical dead space + alveolar dead space
what is the effect of decreased oxygen on pulmonary and systemic arterioles?
pulmonary = vasoconstriction
systemic = vasodilation
what is the effect of increased oxygen on pulmonary and systemic arterioles?
pulmonary = vasodilation systemic = vasoconstriction
what is dalton’s law of partial pressure?
the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in the gas mixture
what is PAO2?
the partial pressure of oxygen in alveolar air
what is the alveolar gas equation?
PAO2 = PiO2 - [PaCO2/0.8]
what is PiO2?
the partial pressure of carbon dioxide in inspired air
what is PaCO2?
partial pressure of CO2 in arterial blood
which is more soluble in membranes - CO2 or oxygen - and why?
CO2
diffusion coefficient for Co2 is 20x higher than oxygen
what is the diffusion coefficient of a gas?
the solubility of the gas in membranes
what is fick’s law of diffusion?
the amount of gas that moves across tissue in unit time is proportional to the area, but inversely proportional to its thickness
what makes up the wall of the alveoli?
a single layer of flattened type I alveolar cells
what is henry’s law?
the amount of a gas dissolved in a liquid at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid
how is most oxygen transported in blood?
bound to haemoglobin in RBCs
what are the two ways in which oxygen is present in blood?
bound to Hb
dissolved
how many haem groups in each Hb molecule, and how many oxygen molecules can each haem group bind?
four
one oxygen molecule each
i.e. one Hb = four oxygen
what is the main factor that determines Hb saturation with oxygen?
PO2
what is meant by cooperativity as exhibited by haemoglobin?
binding of one oxygen increases affinity for oxygen
what does the oxygen haemoglobin dissociation curve look like?
sigmoid curve
flattens when all sites occupied
what is DO2I and how is it calculated?
the oxygen delivery index
CaO2 x CI (cardiac index)
how much oxygen is carried by a fully saturated gram of Hb?
1.34ml
what is CaO2 and how is it calculated?
the oxygen content of arterial blood
1.34 x [Hb] x Sa)2
what is the bohr effect?
a shift of the oxygen Hb currve to the right
caused by increased release of oxygen
what four factors can cause the bohr effect?
increased PCO2
increased [H+]
increased temperature
increases 23bpg
describe the structure of foetal haemoglobin (HbF)
two alpha and two gamma subunits
has a higher affinity for oxygen
when is HbF replaced?
within the first few months after birth
where is myoglobin found?
skeletal and cardiac muscles
how many haem groups are there per myoglobin molecule?
one
describe the shape of the myoglobin dissociation curve
hyperbolic
when does myoglobin release oxygen?
at very low Po2
this provides short term storage for oxygen for anaerobic conditions
what does the presence of myoglobin in blood indicate?
muscle damage
what are the three ways that CO2 can be transported in the blood and which is most common?
in solution (least) as bicarbonate (most common) as carbamino compounds
which is more soluble - CO2 or oxygen?
CO2 - around 20 times more soluble than oxygen
what enzyme is involved in the formation of bicarbonate from CO2 and water?
carbonic anhydrase
where does the formation of bicarbonate from CO2 and water occur?
in red blood cells
how are carbamino compounds formed?
combining of CO2 with terminal amine groups in blood proteins
name a carbamino compound
carbamino-haemoglobin
what is the major rhythm generator of inspiration and expiration?
medulla
what neurons generate the breathing rhythm?
the pre botzinger complex
where is the pre botzinger complex located?
the upper end of the medullary respiratory centre
what two groups of neurons in the pons can modify the breathing rhythm?
pneumotaxic centre
apneustic centre
what does stimulation of the pneumotaxic centre do?
terminates inspiration
what does stimulating the apneustic centre do?
prolongs inspiration
