Respiratory Tract 1: Gas Transport Flashcards
What proteins are used to transport oxygen? What formula is derived from this?
Hemoglobin- 98% of oxygen transported in blood (oxyhemoglobin)
Dissolved in plasma- 2% (0.3 mL/dL)
Total blood Oxygen content= amount dissolved in plasma+ amount bound to hemoglobin
Why do we need hemoglobin to transport oxygen?
- dissolved oxygen reaching circulation each minute is less than 10% of basal needs and would require a cardiac output of 83L/min to maintain basal needs
- Dissolved oxygen is not the sufficient to meet the bodies demands
- Blood oxygen content is increased by the carrier molecule- hemoglobin
Describe hemoglobin
Tetramer( 4 units)
Each monomer contains a heme group (porphyrin ring with Fe held in the center)
2 alpha heme and 2 beta heme and a polypeptide (globin) chain
Each heme can bind 1 molecule of oxygen
What does Oxygen Carrying Capacity mean?
The maximum amount of oxygen that can be bound to hemoglobin
What is oxygen saturation?
Ratio of quantity of oxygen actually bound to the quantity of oxygen that can be potentially bound (come back for formula)
-usually 98% on room air
What is oxygen content?
Amount of oxygen actually bound to hemoglobin + dissolved oxygen
- oxygen content= (binding capacity x % saturation) + dissolved oxygen
What is the average Hb content of blood ?
15g/100ml
- 12-16 g/dL in females
- 13-18 g/dL in men
1 g of Hb can bind …
1.34 ml of O2
How to calculate oxygen carrying capacity?
15g/100ml
- 12-16 g/dL in females
- 13-18 g/dL in men
1g of Hb can bind 1.34 ml of oxygen
=1.34 x 15
= 20.1 ml O2/ 100 ml
How to calculate oxygen content?
O2 content= (binding capacity x % saturation) + dissolved oxygen
-Oxygen content
(98% x 20.1)+ 0.3
=19.7+ 0.3
= 20.1 ml O2 /100 ml
Describe oxygen saturation
A measure of the number of occupied oxygen binding sites in a Hb molecule (comeback for formula)
A patient with anemia has a normal SaO2 because the O2 content and binding capacity are proportionally reduced
What is anemia?
Anemia is strictly defined as a decrease in red blood cell mass
May result from blood loss, increased destruction of RBCs(hemolysis), or decreased production of RBCs
The Hb available can still be saturated
What is cooperative binding?
Once on O2 is bound to Hb it becomes easier for the next O2 to bind
Describe the hemoglobin-oxygen transport
Association (loading)
- blood arrives at lungs with a O2 saturation of about 75%
- Pressure gradient enhances transfer
- Plateau region of the curve
Dissociation
- Blood arrives at tissues where O2 it is needed
- Pressure gradient and environment facilitates transfer
- Steep region of the curve
- Each O2 dissociation event lowers the affinity of the remaining heme groups for bound O2
What is the consequence of P50?
P50- partial pressure of oxygen required to saturate 50% of Hb
- Measure of the affinity of Hb for oxygen
- Low P50= high affinity since less PO2 is needed to reach 50% saturation
- High P50= low affinity since you must give higher PO2 to reach 50% saturation
What can cause a rightward shift in the hemoglobin oxygen dissociation curve?
Decreased affinity for oxygen = offloading if oxygen
Increased metabolism
- temperature increases
- PCO2 increase
- proton increase
- 2,3-bisphosphoglycerate increase (also a feature of chronic hypoxia-altitude, COPD, anemia )
What can cause a leftward. Shift in the hemoglobin oxygen dissociation curve ?
Leftward shift(increased oxygen affinity = binding of O2)
- temperature decrease - PCO2 decrease - proton decrease - 2,3-Disphosphoglycerate decrease - carbon monoxide
What is the Bohr effect?
The effect of CO2 and proton on Hb’s affinity for oxygen
Elevation of those two parameters stimulate Hb to release oxygen
Right shift of the curve and increased P50
How does Carbon monoxide affect oxygen transport?
- Hb binds CO with high affinity (210 times greater than O2)
- CO competes with O2 for binding sites and increases the affinity of Hb for the bound O2
- CO +Hb v carboxyhemoglobin (bright red color)
- Deadly because O2 is not released to the tissues
How is carbon dioxide transported?
- Dissolved carbon dioxide
- Carbonate
- Carbonic acid
- Carbamino Compound
- Mostly transported by Bicarbonate
What is the function of carbon anhydrase?
The combination of carbon dioxide and water occurs slowly in the absence of carbonic anhydrase(CA)
- This enzyme accelerates this reaction by about 1,000 times
- This enzyme is found in high concentration in red blood cells
CO2 + H2O H2CO4 H+ + HCO3^-
Describe carbon dioxide content in carbon dioxide transport
- Relatively linear relationship with PaCO2
- CO2 is more soluble in plasma than O2
- Large amounts of CO2 can be loaded and unloaded from the blood with a small change in PCO2
- Increasing the PO2 causes the blood to unload CO2 (where do we see this?)
- Blood returning to lungs offloads CO2 as it picks up O2
What is the Haldane effect?
The effect of the PO2 on the CO2 equilibrium curve is known as the Haldane effect
- Higher PO2 will shift the curve downward and to the right
- This allows the blood to load more CO2 in the tissues and unload more CO2 in the lungs
What is chloride shift?
The exchange of chloride for bicarbonate in RBCs for maintenance of electrical neutrality
What are respiratory alkalosis and respiratory acidosis ?
The reference range of the pH of arterial blood is 7.35-7.45
Respiratory Acidosis- condition of lowered pH(acidosis) due to decreased alveolar ventilation (hypo ventilation- increased PaCO2)
Respiratory Alkalosis- condition of increased pH (alkalosis) due to increased alveolar ventilation (hyperventilation- decreased PaCO2)
Changes in pH that aren’t respiratory in origin arise from a metabolic imbalance (metabolic alkalosis/acidosis)
What are the buffers to acidosis?
Bicarbonate (HCO3^-)
Intracellular proteins
What is the renal response to acidosis?
Increased excretion of protons
What is the ventilate response to acidosis?
Increased PaCO2
Acidosis (proton increase)
Detected by chemoreceptors
Stimulation of respiratory centers in CNS
Increased ventilation
CO2 excretion via lungs= decreased PaCO2
What is arterial blood gas?
Arterial blood gas is used to assess the levels of carbon dioxide and oxygen in the arterial system
This test can also be used to ascertain the pH and bicarbonate level
What are the ranges of arterial blood gas?
PaO2: 85-95 mm Hg
PaCO2: 35-48 mm Hg
SaO2: 95%-98%
pH: 7.35-7.45
HCO3: 23-28 mEq/L
