11 - Gas Exchange Flashcards
(27 cards)
What are the molecules of the atmosphere
mostly nitrogen
20% oxygen
0.03% carbon dioxide
Why does gas exchange occur
exchanges of gasses between the alveoli, blood and tissues occurs due to differences in partial pressures of gasses
how to measure atmospheric pressure
- pan of mercury with test tube
- test tube with all the atmosphere taken out of it inverted into the pan of the plate with mercury
- atmosphere presses down on the surface of the mercury
- sending it up the tube to sea level (760 mmHg)
What is Dalton’s law of partial pressures
our atmosphere is a mixture of gasses (nitrogen, oxygen, water vapour, co2)
- each gas contributes to the total pressure of the system in direct proportion to its percentage in the mixed gas
[pressure] x [gas %] = partial pressure of gas
Whats the significance of partial pressure
the direction of diffusion of a gas is determiend by the partial pressure of the gas (from high to low)
- difference of partial pressures drives movement of gasses
Describe the partial pressure gradient as atmospheric air enters the alveoli
Po2 decreases
- due to increase in Ph2o (water added when breathed in)
- due to increase in Pco2
Pco2 increases
- due to addition from blood
Describe the partial pressure gradient as air moves from the alveoli to the atmosphere
Po2 increases
- due to mixing with dead space air
Pco2 decreases
- due to mixing with dead space air
What happens as blood flows past the alveoli in external respiration
CO2 from ‘venous’ blood (pulmonary artery) does into the alveoli
O2 is captured from the alveoli
- ‘arterial’ blood (pulmonary vein) has increased O2 and decreased CO2
What would happen to external respiration in a person with edema
surfactant increases in alveoli –> becomes a barrier for gas exchange
- CO2 can still exchange (dissolves easily in water)
- O2 cannot dissolve in water —> cannot equilibrate into the blood (not enough oxygen in blood)
What would happen in a high V/Q ratio
alot more ventilation for the amount of blood flow
not enough perfusion of a well-ventilated area
- apex of lung
- pulmonary embolism (blood clot in deep vein that moves up to lung)
What would happen in a low V/Q ratio
not enough ventilation to the lung that is getting good blood flow
not enough ventilation of a well perfused area
- base of lung
- asthma (smaller tubes)
- lung cancer (cancer growing into tubes and blocks ventilation)
How to correct V/Q mismatch
intrinsic mechanism built into lungs in vasculature the pulmonary arterioles that go up to the capillary beds
- have sensors for o2 and co2 levels
arterioles relax if PaCO2 is low or PaO2 is high
- high V/Q ratio
arterioles constrict if PaCO2 is high or PaO2 is low
- low V/Q ratio
What happens to pulmonary arterioles when a person moves to higher elevation
less atmospheric pressure
partial pressure is less
pulmonary arterioles will sense and constrict but no where to shunt blood to better area in lungs (but no better area)
- leads to pulmonary hypertension
(altitude sickness)
What happens to pulmonary arteriolar pressure in COPD
gets smaller and permanently smaller over time (constriction) –> pulmonary hypertension
effects ventilation over time
How is CO2 transported in blood
CO2 dissolved in plasma (7%)
Incognito as sodium bicarb HCO3- (70%)
CO2 bound to hemoglobin – carbamino-Hg (22%)
How is O2 transported by the blood
O2 dissolved in the plasma (1.5%)
O2 bound to hemoglobin (98.5%)
Describe the structure of hemoglobin
globin - 4 globular protein chains
- 2 alpha, 2 beta
heme - loose binding site with oxygen (easily reversible)
- binds oxygen in relation to partial pressure (when partial pressure really high, favours O2 binding) (when partial pressrue really low - tissues - favours the oxygen letting go of the hemoglobin)
- higher affinity for carbon monoxide (230x)
What are the forms of hemoglobin
A= adult –> different in men and women
F= fetal –> higher affinity for O2 than A form
S= sickle 00> crystallizes within the cell (deoxy)
How does hemoglobin change in different saturations of blood O2
low blood O2 (unsaturated, appears bluish) - no O2 bound
- in outer space
when exercising tissuess, partial pressure of O2 can drop 20mmHg
(65% of O2 is released to tissues)
at rest, 75% sat with O2 in tissues
(only ever release 25% O2 in an individual)
high blood O2 (fully saturated, appears bright red) - 4 O2 bound
- almost 100% sat at lungs
a single hemoglobin molecule can be 0%, 25%, 50%, 100% saturated with oxygen
- after hemoglobin binds one oxygen, it becomes easier to bind the next three
How is oxygen saturation measured
oxygen sat is a measure of how much hemoglobin (on average) is bound with oxygen
What are the benefits of the non-linear shape of the O2-Hb dissociation curve
- flat top
- allows lots of O2 pick up even with significant respiratory disease (would make it difficult to ventilate alveoli) - steep slope
- allows tissue to pull off as much O2 as needed
What happens when tissues are at a high level of metabolism (intense exercise)
increaseed PCO2
Increased temperature of tissues
decreased pH (increased H+)
affects hemoglobins ability to hold onto oxygen
curve shifts to the right
- allows further oxygen to dissociate from hemoglobin to meet the tissues needs
What controls breathing rhythm
respiratory centers of the brainstem (medulla and pons) to determine an appropriate frequency and depth of breathing to support tissue respiration
Dorsal respiratory group (DRG)
- active in quiet breathing
- outputs to internal intercostals and diaphragm
- allow you to take a breath in
- active for inspiration and shuts off to empty into lungs
Ventral respiratory group (VRG)
- deep breathing
- talk to accessory muscles
- contains pacemaker cells
Pontine respiratory group
- in the pons
- receive inputs from body (pH of blood, temperature..) to adjust breathing rate
What are the sensory inputs to the pons
inflation reflex
- stretch receptors in lung, sends inhbiotry response
cough reflex
- in trachea when there is something in
proprioceptors
- exercise to increase breathing rate
peripheral chemoreceptors in aortic arch
- fine control of paO2 and paCO2
(changes in blood pressure)
temperature, pain, emotion, stretching the anal sphincter
