Gas Exchange Flashcards
(60 cards)
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
