Gas exchange- KTs notes Flashcards
Oxygen moves from the alveolar membranes to the?
Pulmonary capillaries
Path of Oxygen to get into the cells?
Move across capillary membrane Into Pulmonary capillaries Transported by blood to tissues Leaves Tissue capillaries into extracellular fluid Finally crosses plasma membranes To gain entry into cells
CO2 does this bit backwards
How much blood enters cells per minute compared to how much oxygen is added to the blood in the lungs per minute?
Same volume
If patient is in a steady state
What process is responsible for the movement of O2 and CO2 between the alveoli and the blood and the body cells?
Diffusion
The mechanisms of this depends on basic chemical and physical properties of gases
What is Daltons law?
In a mixture of the gases, the pressure exerted by each gas is independent of the pressure exerted by the others.
Therefore the total pressure of the mixture is simply the sum of the individual pressures. These individual pressures are termed partial pressures.
What are partial pressures?
Individual pressures of gases
How will net diffusion occur?
From an area of high to low partial pressure
Henry’s Law?
The amount of gas dissolved will be directly proportional to the partial pressure of the gas with which the liquid is in equilibrium.
When will diffusion equilibrium be reached?
When PO2 liquid is equal to PO2 in gas.
What happens if PO2 in gas is higher than PO2 in liquid phase?
NO net diffusion of 02 into liquid and vice versa
Normal alveolar gas pressures for CO2 and PO2?
PCO2= 40mHg PO2= 105mmHg
Normal gas pressures in air being breathed in?
PCO2= 0.3mmHg PO2= 160mmHg
Why is alveolar PO2 lower than PO2 air breathed in?
Some of the oxygen in the air entering the alveoli leaves them to enter the pulmonary circulation
Factors determining alveolar PO2?
- PO2 of atmospheric air
- Rate of alveolar ventilation
- Rate of total body oxygen consumption
Factors determining alveolar PCO2?
- Alveolar ventilation
- Rate of CO2 production
What happens to partial pressures of gases in hyperventilation?
There is a decrease in the ratio of carbon dioxide production to alveolar ventilation. PCO2 decreases below normal.
What happens to partial pressure of gases in hypoventilation?
There is an increase in the ratio of carbon dioxide production to alveolar ventilation. PC02 increases above normal
Describe the blood that enters the pulmonary capillaries?
Systemic venous blood pumped to the lungs via the pulmonary arteries
High PCO2 and low PO2
Where is complete equilibrium achieved in a normal person? and why?
Before the end of the capillaries
Because the rate at which O2 and CO2 diffuse is so rapid and the blood flow through capillaries is so slow
The more capillaries involved in gas exchange…?
The more O2 and CO2 can be exchanged
Pulmonary capillaries at base of lung?
Closed at rest
Open with exercise and receive blood and enhance gas exchange
What is the flow of blood through the lungs determined by?
Pressure and vascular resistance
What is ventilation determined by?
Lung compliance
Airway resistance
3 pressures that determines the flow of blood to different parts of the lung?
- Hydrostatic pressure in the pulmonary arteries in different parts of the lungs
- Pressure in the pulmonary veins
- Pressure of air in the alveoli. High pressure of the alveoli can act on walls of pulmonary capillaries and collapse them
Systolic and diastolic perfusion pressures in the pulmonary arteries?
- 3kPa = Systolic
1. 0kPa = diastolic
How much pressure will a column of 1cm of blood exert?
0.1kPa
The apex of the lung is better perfused than the base. True or false?
False
Base is better perfused than apex
3 zones of the lung?
Apex
Middle zone
Base
Pressures at the apex of the lung?
Alveolar pressure is similar to arterial pressure
Pulmonary capillaries are relatively compressed- vascular resistance is high
Blood flow is relatively low
If arterial pressure falls below alveolar pressure there will be no blood flow
Pressures in the middle zone of the lung?
Pressure of the pulmonary arteries is relatively higher and exceeds the alveolar pressure
-Therefore blood progressively increases down the zone
Pressures in the base of the lung?
Arterial pressure exceeds alveolar pressure by a considerable margin
Pulmonary vessel is fully open
Blood flow is relatively high
Ventilation and perfusion when the lung is in the upright position?
Falls with height above the base
How fast does perfusion fall compared to ventilation?
Perfusion falls 3 times faster than ventilation
Va:Q ratio meaning?
Ventilation: perfusion ratio
When does the Va:Q ratio increase?
Increases with height above the base of the lung
Va:Q of well ventilated areas with sufficient perfusion in the lung?
1
V:Q ratio of poorly ventilated alveoli that are well perfused?
Less than 1 (base)
V:Q ratio of well ventilated alveoli with poor perfusion?
More than 1 (apex)
What does wasted ventilation mean?
Ventilated alveoli with no blood supply
What is a shunt?
Blood flowing to areas of lung that have no ventilation
What does ventilation-perfusion inequality do?
Lowers the PO2 of systemic arterial blood- CO2 elimation is also impaired but no nearly to the extent of O2 uptake
Local homeostatic responses in the lungs?
Minimize the mismatching of ventilation and blood flow
Small pulmonary blood vessels constrict in response to low PO2 = producing the net effect of supplying less blood to poorly ventilated areas and more blood to well ventilated areas
Pressure equation?
Pressure= flow x resistance
What happens to pulmonary vascular resistance when cardiac output increases? What does this cause?
It falls
-This causes more areas of the lungs to be perfused increasing gas exchange
Fall in resistance is based off of equation Pressure= flow x resistance
