Gas Exchange Flashcards
how does gas exchange occur in the lungs?
due to differences in the partial pressure of gases
what is the atmospheric (barometric) pressure at sea level?
760 mmHg
Dalton’s Law of Partial Pressures
in a mixture of gasses, each gas will contribute to the total pressure of the system in direct proportion in the mixed gas;
[Pressure] x [Gas %] = Partial pressure of gas
what is the significance of partial pressures of gas?
direction of diffusion is determined by partial pressure of the gas (gas movement from high to low pressure); the only reason oxygen comes from alveolus into blood and deposit into tissue is b/c there is a [ ] gradient for O2 extremely high in the atmosphere and lowest at the tissues
partial pressure gradient - as atmospheric air enters the alveoli:
partial pressure of O2 decreases due to increase in p.p. of H2O and CO2 (p.p. CO2 increases due to addition from blood)
partial pressure gradient - as air moves from alveoli to atmosphere:
p.p. of O2 increases due to mixing w/ dead space air, p.p. CO2 decreases due to mixing w/ dead space air
what is the significance of CO2 being more soluble than O2?
- there is a tight range for CO2 b/c of carbonic acid equation; small changes in CO2 levels also change pH of body
- the partial pressure of CO2 is not as affected by diffusion
what is the effect of blood flow on gas exchange?
as blood flows past alveoli, and there is time, pressures will equilibriate
what is the effect of increased diffusion barrier on gas exchange?
due to pulmonary edema
ventilation-perfusion mismatch
sometimes there are regions of the lung where there is an imbalance b/w how well it is ventilated and how well it is perfused - this is described as an abnormal V/Q ratio
high V/Q ratio
there is not enough perfusion of a well-ventilated area:
low V/Q ratio
not enough ventilation of a well-perfused area:
how to correct for a V/Q mismatch
- pulmonary arterioles relax if PaCO2 is low or PaO2 is high
- pulmonary arterioles constrict if PaCO2 is high or PaO2 is low
how do the pulmonary arteries respond when moving to higher elevation?
- airways wide open for ventilation but oxygen levels are low: sensed by pulm.
- arterioles and constrict to shunt blood to other areas getting good adequate oxygenation (unable to) → pulm.
- hypertension
- can lead to right sided heart failure
what would happen to pulmonary arteriolar pressures in COPD?
- issues w/ airway ventilation due to collapsed airways and low O2 levels in alveoli = all the pulmonary vessels start to constrict the arterioles
CO2 transport in the blood
carried in the blood dissolved, as bicarbonate, or bound to hemoglobin as carbamino-Hb
carbonic anhydrase
enzyme that catalyzes the reaction between carbon dioxide and water to form carbonic acid
O2 transport in the blood
carried in the blood dissolved or bound to hemoglobin (majority)
hemoglobin
iron containing protein:
heme - reversibly binds oxygen in relation to partial pressure, higher affinity for CO
globin - globular protein chains (2 alpha, 2 beta)
forms of hemoglobin
adult, fetal and sickle
cooperativity
after Hb binds one oxygen, it becomes easier to bind the next three (this results in a non-linear O2-Hb dissociation curve)
flat top dissociation curve
the flat top allows lots of oxygen pick up with respiratory failure, and the steep portion allows tissue to pull off as much oxygen as needed
steep slope dissociation curve
hemoglobin is normally 100% saturated; at rest 25% oxygen is released from Hb to tissues(65% during exercise)
right-shifted dissociation curve
this is due to tissues with high-metabolism due to increased PCO2, increased temperature and decreased pH
what is the purpose of breathing control?
to ensure that alveolar ventilation is at an appropriate level for the amount of tissue respiration occurring at any given time (maintain ABG levels)
breathing components of medulla
ventral and dorsal RG
dorsal respiratory group (DRG)
pacemaker cells
ventral respiratory group (VRG)
sends outputs to accessory muscles during forced breathing
what influences the smoothness, intensity, and frequency of the respiratory groups in the medulla?
the pontine respiratory group
respiratory inputs to the pons and medulla
cerebral cortex, hypothalamus, peripheral chemoreceptors, baroreceptors, muscle & joint receptors lung stretch & irritant receptors
cerebral cortex
voluntary control of breathing
hypothalamus
breathing influenced by stress, emotion and pain
role of peripheral chemoreceptors in breathing control
responsible for fine control of breathing
baroreceptors
changes in BP during respiratory cycle
muscle and joint receptors
when activity increases, breathing increases
lung stretch receptors
prevents over inflation of lungs when breathing
irritant receptors
triggers the cough reflex
central chemoreceptors
located on the ventral surface of the medulla and sense CSF levels; monitors PaCO2 via H+ (CO2 + H2O <=> HCO3- + H+) (chemoreceptors provide input to maintain constant PaCO2 of 40mmHg)
peripheral chemoreceptors
located in the carotid and aortic bodies; monitor PaCO2, decrease in arterial pH and decrease of PaO2; disturbances are restored by increasing ventilation
80% of our atmosphere is what?
nitrogen
20% of our atmosphere is what?
oxygen and carbon dioxide
does PO2 decrease or increase as we inhale?
decreases
- increase in PH20 in water and PCO2
Does PCO2 increase or decrease as we inhale?
increase
- due to addition from blood
Does PO2 increase as we exhale air?
increases
- mixes with dead space
Does PCO2 increase or decrease as we exhale?
decreases
- mixing with dead space
Where is PO2 higher?
in the alveoli than blood, higher in blood than tissues
Where is PCO2 higher?
higher in the tissues than blood, higher in blood than alveoli
How is elastic tissue around the lobule supplied?
bronchial arteries supply, drained by pulmonary veins
pulmonary vein does what?
collects oxygen rich blood
- called arteriole blood b/c it goes to arteries and service tissues to provide them with oxygen
pulmonary artery does what?
bring up physiologically venous blood
- collects blood from right side of the heart which comes back from tissue
- deoxygenated blood
venous blood is
spent
pulmonary edema
- extra fluid coming in from vascular space ending up in alveoli
- oxygen doesnt dissolve well in the water
- partial pressure of oxygen is reduced by half of the time it gets to the tissue
- becomes cyanotic
Where does high ventilation of perfusion ratio occur?
at the apex of the lung and due to pulmonary embolism
Where does low ventilation of perfusion ratio occur?
at the base of the lung and due to asthma or lung cancer
High ventilation to perfusion ratio
- high O2 making smooth muscle relax
- more blood flow going across alveoli that is well ventilated
Low ventilation to perfusion ratio
- Low O2 making smooth muscle in arterioles to constrict
- reduces blood flow to the alveolus and shunts to others getting fresh air
How does CO2 dissociate?
high conc in tissue to low conc in the blood
What is the gas exchange membrane lining the alveolus?
type one pneumocyte
When does CO2 have a high concentration?
in the blood and low conc in alveoli
How much O2 is dissolved and how much is carried by hemoglobin?
dissolved (1.5%)
bound (98.5%)
