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.
Describe the Haldane effect?
Haldane effect is the decrease of the carbon dioxide binding capacity of hemoglobin with the rise in the concentration of oxygen.
i.e. there is decreased carbon dioxide binding when there is high Oxygen levels.
When is the Haldane effect important?
Important in aiding in the unloading of CO2 at the lungs and the binding of O2
Describe the Bohr effect
Bohr effect is the decrease of the oxygen binding capacity of haemoglobin with the increase of the concentration of carbon dioxide or decrease in pH
Hence means increasing acidity enhances the unloading of oxygen from Hb.
Hemoglobin binds with most of the H+ formed within the erythrocytes.
When is the Bohr effect important?
Helps in unloading of O2 at tissues and the pickup of CO2
Describe how carbon monoxide poisoning comes about
CO competes with O2 for the same binding sites on Hb
BUT, Hb has much higher binding affinity for CO
Hb + CO ———HbCO
HbCO= carboxyhemoglobin
Describe the properties of carbon monoxide.
CO is dangerous as it is ‘odorless, colorless, tasteless, non-irritating and non-DETECTABLE
What is the normal body pH kept at?
pH is kept between 7.35 and 7.45
pH levels <7.0 or> 7.8 are not compatible with life
State the need to maintain acid base balance in the body.
*Necessary to sustain life
The pH determines:
*Properties of proteins
-Enzyme activity
-Part of the cell structure
*Permeability of membranes
-Distribution of electrolytes
What is ana acid?
Electrolyte that forms a hydrogen cation and an anion in the presence of water.
Describe weak and strong acid with examples.
WEAK ACID
-Partially ionizes in water
H2CO3
STRONG ACID
-Totally ionizes in water
HCl
What is a base?
A substance that can accept hydrogen ions
Describe weak and strong base with examples.
Weak base
-do not bind well with hydrogen
HCO3-
NH3
Strong base
-binds well with hydrogen
OH- (group 1 metal hydroxides)
What are volatile acids?
Can be eliminated as CO2 gas
How are volatile acids eliminated?
Volatile acids are eliminated through the lungs.
Give an example of a volatile acid.
*Carbonic acid
Carbonic acid dissociates to CO2 and H20
Name the most important buffer that operates both in the lung and the kidney.
Bicarbonate
The components of bicarbonate
Consists of
*H2CO3 and HCO3-
*CO2 is excreted or retained as needed
*HCO3 is excreted or retained as needed
What is respiratory Acidosis?
When does it occur?
Excess CO2 in arterial blood (hypercapnia) occurs mostly as a result of hypoventilation.
The result is an elevated production of CO2-generated H+ leading to an acidic condition respiratory acidosis.
What is respiratory alkalosis?
When does it happen?
Below normal CO2 in arterial blood (hypocapnia) occurs mostly as a result of hyperventilation.
The result is a decreased production of CO2-generated H+ leading to an alkaloid condition respiratory alkalosis.
What is hypercapnia and hypocapnia?
Excess and below normal carbon dioxide levels in blood.
