WEEK 2: VENTILATION, GAS EXCHANGE, ACID AND BALANCE Flashcards
What is diffusion?
A process in which the substance moves through a semipermeable membrane or in a solution without any help from transport proteins.
What is partial pressure gradient?
A partial pressure gradient is the difference in the concentration of a gas in a mixture of gases, in which the gas is at a higher pressure in one location and a lower pressure in another location.
What is the gas exchange through the alveolar-capillary spaces is driven by?
Gas exchange through the alveolar-capillary spaces is driven by pressure differences.
What is the conversion factor between kPa and mmHg?
1 atm= 101.325
760 Millimeter of mercury is equal to 1 Atmosphere
What is the partial pressure difference for Oxygen and Carbon dioxide in venous and arteriolar blood?
PAO2 = 13.33 kPa (100 mmHg)
PaO2 = 5.3 kPa (40 mmHg)
ANSWER= 8kPa
PACO2 = 5.3 kPa (40 mmHg)
PaCO2 = 6.1 kPa (46 mmHg)
ANSWER= 0.8kPa
Describe Fick’s law
The rate of gas transfer across a tissue plane or membrane (Vgas) is directly proportional to the difference in partial pressures of the gas on the two sides of the membrane (P1 – P2) and the membrane’s diffusing capacity.
State the formula for Fick’s law.
The formula for Fick’s law for gas exchange is:
Vgas = (P1 - P2) x [(A XD)/ T]
What is diffusing capacity?
How well oxygen and Carbon dioxide are transferred between the blood and the lungs.
Describe factors that influence rate of gas exchange across the alveolar membrane.
1.Partial pressure gradients of oxygen and carbon dioxide.
2.Surface area of the alveolar membrane
3.Thickness of the barrier separating the air and blood across the alveolar membrane.
4.Difussion constant
Why are approximately equal amounts of O2 and Co2 transferred across membrane.
This is because the diffusion constant of C02 is 20x that of O2 offsetting the Partial pressure gradient of C02.
How is most oxygen transported?
Most oxygen is transported bound to hemoglobin
What is Hb and Hb02?
Hb=reduced hemoglobin or deoxyhemoglobin,
HbO2=oxyhemoglobin
Hb + O2———–HbO2
How much oxygen is dissolved in plasma?
Very little (only 1.5%) is physically dissolved in Plasma
What is the major driving force that determines %Hb saturation?
The PO2 is the major driving force that determines %Hb saturation
What is chloride shift?
The chloride shift is a process that helps to maintain a normal balance of electrolytes in the body.
Describe the direct of movement of the following at internal in external respiration.
*Oxygen
*Carbon dioxide
*Chloride shift
EXTERNAL RESPIRATION
Chloride shift and Carbon dioxide towards the alveolusOxygen towards the pulmonary capillary wall
INTERNAL RESPIRATION
*Chloride shift and Carbon dioxide towards the systemic capillary wall
*Oxygen towards the tissues
Describe the O2-Hb dissociation curve.
The oxygen-hemoglobin dissociation curve is a curve that plots the proportion of hemoglobin in its saturated (oxygen-laden) form on the vertical axis against the prevailing oxygen tension on the horizontal axis.
It is an important tool for understanding how our body transports and uses oxygen.
*The flat region at low oxygen tensions represents the binding of oxygen to hemoglobin in the lungs.
*The steep region at intermediate oxygen tensions represents the release of oxygen from hemoglobin in the tissues.
Describe the 3 regions of the O2-Hb dissociation curve.
3 regions:
*The region >100mmHg
*The plateau region (60 to 100mmHg)
*The steep region (0 to 60mmHg)
Hemoglobin is partially saturated from 0-60mmHg and fully saturated from 60mmHg upwards.
Describe the following in the alveoli.
*PAO2, PACO2, Temperature and H+ concentration.
*Effect on hemoglobin.
In the alveoli high pO2, low pCO2, low temperature and less H+ concentration
Favors the formation of oxyhemoglobin.
Describe the following in the tissues.
*PAO2, PACO2, Temperature and H+ concentration.
*Effect on hemoglobin.
In the tissues low pO2, high pCO2, high H+ and high temperature
Favors the dissociation of oxygen from oxyhemoglobin.
Describe how much carbon dioxide is transported using the 3 different modes in blood.
Physically dissolved 10%
Bound to hemoglobin 30%
As bicarbonate ions 60%
Name the compound formed when carbon dioxide binds to the hemoglobin molecules.
Carbaminohemoglobin
Hb-CO2
Where exactly in the hemoglobin molecules does the Carbon dioxide bind?
On the terminal amino acids on the 2 alpha and 2 beta globin chains.
Describe how carbon dioxide is transported as bicarbonate ions.
The greatest percentage of CO2 (about 60%) is transported in plasma as bicarbonate ions. As the CO2 difuses into the systemic circulation it enters into the red blood cells and reacts with water in the presence of the enzyme carbonic anhydrase (CA) to form carbonic acid which in turn dissociate into H+ and HCO3-.Thus the blood picks up CO2. Some HCO3-moves out into the blood plasma down to its concentration gradient.
In exchange chloride ions (Cl -) move from the plasma into the RBC’s. This exchange of negative ions which maintains the electrical balance between the blood plasma and RBC is known as the chloride shift.
As the blood passes through pulmonary capillaries in the lungs, all these reactions are reversed and CO2 is exhaled.
