Respiratory Physiology Part 3 Flashcards
if transmural pressure is positive
expanding pressure on the lung
if transmural pressure is negative
collapsing pressure on the lung
At rest of breathing cycle
- diaphragm at equilibrium
- alveolar pressure = atmospheric pressure
- no airflow b/c no pressure difference
- intrapleural space is negative
- FRC
During Inspiration of breathing cycle
- diaphragm contracts
- lung volume increases
- pressure in lung decreases
- intrapleural space becomes more negative
- dynamic compliance
Halfway through inspiration of breathing cycle
alveolar pressure falls below atmospheric
this drives airflow into lung until atmospheric pressure = 0
expiration of breathing cycle
- alveolar pressure becomes positive
- air flows out & returns to FRC
Forced expiration of the breathing cycle
- contraction of expiration muscles raises intrapleural pressure
- if transmural pressure is positive the airways and lungs will remain open
patients with emphysema forced expiration
- airways can collapse
- lung compliance increases
- alveolar & airway pressure lower than normal
- resistance increases (expiration more difficult)
- expire more slowly
O2 in gas exchange
alveolar gas into pulmonary capillary
delivered to tissues
systemic capillary blood into cells
CO2 in gas exchange
delivered from the tissue to venous blood to pulmonary capillary blood
alveolar gas to be expired
Dalton’s Law of Partial Pressure
the partial pressure of gas in a mixture of gases is the pressure that gas would exert if it occupied the total volume of the mixture
barometric pressure
sume of partial pressures O2 CO2 N2 H2O
percentages of gases in dry air at barometric pressure
O2 = 21%
N2 = 79%
CO2 = 0%
since air is humidified in the airways, the water pressure is ___
obligatory and equal to 47 mmHG at 37 degrees
Henry’s Law for Concentration of Dissolved Gases
used to convert the partial pressure of gas in the liquid phase to the concentration of gas in the liquid phase
at equilibrium, the partial pressure of a gas in the liquid phase =
the partial pressure in the gas phase
diffusion of gases - fick’s law
transfer of gases that occurs by simple diffusion
rate of transfer by diffusion is directly proportional to
driving force
diffusion coefficient
surface area available for diffusion
rate of transfer by diffusion is inversely proportional to
the thickness of membrane barrier
the driving force for diffusion of a gas is the ___
partial pressure difference of the gas across membrane
the diffusion coefficient of gas is a combination of ___
usual diffusion coefficient and the solubility of gas difusion
gas concentration
dissolved gas + bound gas + chemically modified gas
dissolved gas
contribute to partial pressure
N2 as a dissolved gas
can only be carried in dissolved form and is never bound or chemically modifies
bound gases
O2, CO2, and CO are bound to proteins in blood
chemically modified gas
CO2 –> HCO3 in RBC by action carbonic anhydrase
gas transport in the lungs
Mixed venous enters the pulmonary capillary
Oxygen is added to pulmonary capillary blood
CO2 is removed from it by transfer across the alveolar/capillary barrier
Systemic arterial blood leaves the pulmonary capillary
dry inspired air
PO2 = 160 mmHg
Humidified tracheal air
air saturated w/ water vapor
O2 reduced
No CO2
humidified air enters alveoli
alveolar air
O2 decreases (going in blood)
CO2 increases (enters alveolar air)
mixed venous blood
blood entering pulmonary capillary - blood returned from tissue to heart
systemic arterial blood
blood that leaves pulmonary capillary that has been oxygenated
diffusion-limited gas exchange
total amount of gas transported across alveolar-capillary barrier that is limited by diffusion process
perfusion limited
total amount of gas transported across alveolar/capillary barrier is limited by blood flow
how to increase the amount of gas transported?
increase blood flow
oxygen is carried in 2 forms
dissolved
bound to hemoglobin
dissolved oxygen
insufficient to meet the demands of the tissues
needs hemoglobin
oxygen bound to Hgb
98% of total O2 content is reversibly bound Hgb
4 subunits of Hgb
4 molecules of O2 per molecule of Hgb
The O2 content of blood is primarily determined by
Hgb and the O2 binding capacity of hgb
amount of O2 delivered to tissues is determined by
blood flow and O2 content of blood ( dissolved O2 + O2-Hgb)
CO2 is carried in blood in 3 forms
- dissolved CO2
- carbaminohemoglobin (CO2 bound to hemoglobin)
- bicarbonate (CO2)
