Phys: Test 3: Lecture 6. Gas Transport By Blood

Front 1

Why is diffusion of O2 not sufficient?

Back 1

• If it were just carried freely in the blood, there would only be .3ml of O2 per 100 ml of blood
o This is insufficient to supply the bodies need
 Ex: that would give you 90ml of oxygen per min, but during exercise consumption may be 3000 ml/min

Front 2

What does Hb do (increase content or PO2?)

Back 2

• Carried with hemoglobin
o Increases the amount of O2 carried in the blood for a certain PO2
 20.8ml of O2/100 ml of blood

Front 3

How does Hb binding allow more O2 to get in?

Back 3

o O2 will bind to the hemoglobin
o Thus the partial pressure difference between the O2 in the plasma and the lung is still high, so diffusion of O2 can still occur
 It will keep happening until all of the hemoglobin is saturated
• Then the diffusion of oxygen will occur until the lung and the capillary have equilibrated to a PP of ~100

Front 4

. Explain the physiological significance of the shape of the O2 dissociation curve

Back 4

o Plateau region
 Acts as a safety net, doesn’t change with drop in lung PO2 (60-100 PO2)
o Steep region
 As you decrease PO2, hemoglobin will give up O2
• Meaning it will readily dump it to the tissue where there is low PO2

Front 5

for what range of PO2 will the saturation of Hb stay the same (on the O2 saturation curve)

Back 5

60-100 mmHg PO2

Front 6

. Explain why caution should be used in interpreting Hb saturation values obtained
using pulse oximetry in the cases of carbon monoxide poisoning

Back 6

Hb saturation only refers to the & Hb BOUND

CO Poisoning: co binds to Hb better than O2; pulsue oximetry doesn't measure diff btw O2 and CO, just what is bound to Hb; so Hb Sat will seem high

Front 7

Explain why caution should be used in interpreting Hb saturation values obtained
using pulse oximetry in the cases of anemia.

Back 7

Hb saturation only refers to the & Hb BOUND

the total Hb will be reduced, but saturation will remain high, so saturation will look normal but total O2 is reduced

Front 8

. Describe the factors that produce a left- or right- shift in the oxygen dissociation
curve

Back 8

• Right shift
o Lower Hb saturation for a given PO2, Hb gives up O2 more readily
o Bohr effect
 Increased H+ or PCO2 will cause this and increased 2,3, BPG

• Left shift
o Higher Hb saturation for a given PO2
o Hb holds on to O2 more readily
o Caused by
 Decreased: H+, PCO2, 2,3 BPG
o This can be seen at high altitudes

Front 9

• What is the P50 value?

Back 9

o Amount of PO2 that Results in 50% saturation of O2 on hemoglobin

Front 10

typical value for Venous PO2

Back 10

40

Front 11

typical value for venous SaO2

Back 11

75%

Front 12

typical value for arterial PO2

Back 12

100

Front 13

typical value for arterial SaO2

Back 13

97.5

Front 14

Describe the forms in which CO2 is transported in the blood. (give prevalence)

Back 14

o Bicarbonate: 60%
 CO2 + H2O  H2CO3HCO3 + H
o Dissolved CO2: 10%
 It is much more solubule in the plasma than O2
o Carbamino: 30%
 Carbon binds to a protein
 Hemoglobin is one that it binds to

Front 15

Explain why red cells can be considered to be the main facilitator of CO2 transport in
the blood.

Back 15

• Because formation of bicarb occurs in the red blood cell (have lots of carbonic anhydrase, the enzyme needed to make bicarb)
• Also because hemoglobin is the primary caramino

Front 16

Describe how the CO2 dissociation curve differs from the oxygen dissociation curve.
Explain the physiological significance of the shape of the CO2 dissociation curve,
and why the PCO2 difference between arterial and venous blood is typically only 6
mmHg.

Back 16

CO2 curve is more linear and has NO PLATEAU
it is also steeper
this means small changes in PCO2 can result in large changes in CO2 content in the blood
this explains why the PCO2 difference for arterial and venous blood is small (6mmHg)
can still unload lots of CO2

Front 17

. Describe the Haldane effect. Explain its physiological significance for gas transport

Back 17

• Ability to carry CO2 is decreased as you add more O2
o Thus oxygenation in the lung helps unload CO2
o Deoxygenation in the tissues helps with loading CO2

Front 18

What is the mechanism underlying the Haldane effect?

Back 18

Hb picks up CO2 from carbamino compuonds; mops up the H+ produced in conversion of CO2-->HCO3; thus pulls the equilibrium rxn to the right facilitating formation of more bicarb

Front 19

Explain why the PCO2 affects blood pH

Back 19

• CO2 results in the formation of H+ ions because of the bicarb formation reaction

Front 20

Write the equation by which blood pH can be calculated from the bicarbonate and CO2 concentrations

Back 20

pH= 6.1 + log [HCO3] / [CO2]

• Thus pH is dependent on bicarb and CO2 levels

Front 21

Name the ratio of
bicarbonate to CO2 that produces a pH of 7.4

Back 21

• Blood pH will be equal to 7.4 (normal pH) as long as the ratio of HCO3:CO2 is equal to 20

Front 22

Describe how blood pH can be disturbed by alterations in PCO2 or bicarbonate.
Describe how alterations in PCO2 or bicarbonate are typically produced.

Back 22

• PCO2
o Disturbances in PCO2 occur through the extent of alveolar ventilation
o Hyperventilation: decreased PCO2
o Hypoventilation: increased PCO2
o RESPIRATORY
• Changes in HCO3
o Normally a result of metabolic processes (vomiting up acid, etc.)

Front 23

Describe the pH disturbances and compensatory mechanisms in respiratory acidosis and alkalosis.

Back 23

• If the PCO2 is changed, the body will respond by changing the HCO3
o Or vice versa
 Will do this until the ratio is back to 20

Front 24

Describe the pH disturbances and respiratory compensatory mechanisms in
metabolic acidosis and alkalosis.

Back 24

• Disturbances of lung function
o Respiratory acidosis
 Increased PCO2 (hypoventialition)
o Respiratory alkalosis
 Decreased PCO2(hyperventilation)
• Metabolic alkalosis
o Increased HCO3
• Metabolic acidosis
o Decreased HCO3

Front 25

How does the body respond to respiratory acidosis and alkalosis?

Back 25

• Acidosis is a result of lower pH
o so the kidney trys to increase the reabsorption of HCO3
• Alkalosis is higher pH
o Thus the kidney tries to dump HCO3 and decrease reabsorption

Front 26

How does the body respond to metabolic acidosis and alkalosis?

Back 26

Metabolic alkylosis-> hypoventilate to lower the pH

Metabolic acidosis-->hyperventilate to increase pH

Front 27

if you have a respiratory acid/alkylosis how do you fix it?

Back 27

with the kidney

Front 28

if you have metabolic acid/alkylosis what mechanism do you use to fix it?

Back 28

breathing

Front 29

if you have a decreased pH, what kind of acid-base defect do you have? What would you look at next to figure out if it was respiratory versus metabolic? what if the previous value was INCREASED

Back 29

Acidosis
PCO2
Increased PCO2 with acidosis means respiratory acidosis

Front 30

if you have a decreased pH, what kind of acid-base defect do you have? What would you look at next to figure out if it was respiratory versus metabolic? what if the previous value was DECREASED

Back 30

Acidosis
PCO2
decreased PCO2 with acidosis means compensated metabolic acidosis

Front 31

if you have a increased pH, what kind of acid-base defect do you have? What would you look at next to figure out if it was respiratory versus metabolic? what if the previous value was DECREASED

Back 31

Alkalosis
PCO2
with alkalosis and decreased PCO2 you are dealing with respiratory alkalosis

Front 32

if you have a increased pH, what kind of acid-base defect do you have? What would you look at next to figure out if it was respiratory versus metabolic? what if the previous value was INCREASED

Back 32

Alkalosis
PCO2
with alkalosis and increased PCO2 you are dealing with compensated metabolic alkalosis

Front 33

Increased pH and Increased PCO2?

Back 33

compensated metabolic alkalosis

Front 34

decreased pH and decreased PCO2

Back 34

compensated metabolic acidosis

Front 35

increased pH and decreased PCO2?

Back 35

respiratory alkalosis

Front 36

decreased pH and increased PCO2?

Back 36

respiratory acidosis