Oxygen Transport In Blood

Question 1

How much O2 is dissolved in 1L of blood?

Answer 1

. 3 ml

. O2 is poorly dissolved because it is poorly soluble in body fluids

Question 2

Hemoglobin carrying capacity

Answer 2

. Up to 4 molecules O2
. Single RBC has 280 million Hb molecules
. Hb removes O2 from solution as soon as it enters acting as storage for O2
. Binding of O2 will maintain partial pressure gradient from alveoli to blood causing more O2 to move into blood until there is equilibration btw alveolar PO2 and blood PO2 (bound O2 to Hb does it contribute to blood PO2)

Question 3

Oxygen saturation

Answer 3

. SO2 = amt O2 combined with Hb/ O2 capacity
. Most important factor is PO2 of blood (related to conc. Of O2 physically dissolved in blood)
. Inc. blood PO2 inc. likelihood that O2 will bind w/ Hb (occurs in pulmonary capillaries)
. Dec. blood PO2 dec. likelihood that O2 will bind to Hb (systemic capillaries)

Question 4

Oxygen-Hb dissociation curve

Answer 4

. Steep portion of curve btw PO2 of 0 and 60 mmHg occurs at systemic capillaries where O2 is unloaded to the tissues
. Hb in venous blood is still 75% saturated
. When systemic capillary PO2 dec. large amts of O2 becomes available to meet O2 demands of metabolizing tissues by dissociating from Hb

Question 5

Conditions that affect shape of O2-Hb dissociation curve

Answer 5

. PCO2
.pH
. Temperature
. Conc. Of 2,3-DPG

Question 6

P50

Answer 6

PO2 when the Hb is 50% saturated
. When inc. the curve shifts to the right and higher PO2 is required for Hb to become 50% saturated
. When inc. th curve goes left

Question 7

What conditions shift the O2-Hb curve to the right?

Answer 7

. Fall in pH from metabolically active tissues
. Rise in PCO2 from metabolic tissues
. Rise in temperature
. These dec. O2 affinity

Question 8

What occurs with CO2 when PCO2 inc.?

Answer 8

Productionof CO2 and/or lactic acid inc.
. CO2 combines w/ H2O to form carbonic acid that then dissociates into H and HCO3
. Acidification of tissue results in inc. unloading of O2

Question 9

Bohr effect

Answer 9

. Decrease in O2 affinity of Hb when the pH of the blood falls

Question 10

What conditions shift the O2-Hb curve left?

Answer 10

. Rise in pH
. Dec. in PCO2
. Dec. in temperature
. These inc. O2 affinity

Question 11

What occurs to CO2 when O2-Hb curve shifts left?

Answer 11

. Extra acid-forming CO2 is removed from body
. Local environment is cooler
. Hb has high affinity for O2 in pulmonary capillaries
. Aids i inc. the loading of O2 onto Hb

Question 12

2,3-DPG

Answer 12

. Produced w/in RBC during anaerobic metabolism
. Highly charged anion that binds to deoxy-Hb but not oxy-Hb
. Inc. in conc. Shifts curve to right
. DPG production in RBCs is inc. when total Hb conc. Is low (anemia) or when PO2 is low (high altitude) to facilitate unloading of O2 at tissues
. Excess will reduce O2 binding to Hb in the lung reducing O2 uptake

Question 13

How much O2 is on Hb when it is fully saturated in physiologic conditions?

Answer 13

1.34 ml O2/g Hb

Question 14

What is the normal conc. Of Hb in blood?

Answer 14

15 g Hb/100 ml blood

Question 15

Oxygen capacity

Answer 15

. Maximum amount of O2 that can be combined w/ Hb
. Measured by exposing blood to high levels of PO2 (600 mmHg) to ensure all Hb is maximally bound to O2
. Normally is around 20.1 ml O2/100 ml blood
O2 capacity = 1.34 x Hb conc.

Question 16

Oxygen content/oxygen concentration

Answer 16

. At PO2 of 100 mmHg there is additional 0.3 ml of dissolved O2 in blood
. Usually conc. Is 20.4 ml O2/100 ml blood
. O2 content = (1.34 x Hb conc. X SO2) + 0.003 x PO2

Question 17

Carbon monoxide effect on O2-Hb dissociation curve

Answer 17

. 240 times greater affinity for Hb than O2
. Competitive binding w/ O2 for Hb sites
. High levels of HbCO in blood so O2-Hb levels dec. which reduced oxygen content of blood
. PO2 in arterial blood remains normal because PO2 is determined by amount of O2 in physical solution
. Presence of HbCO shifts curve left which interferes w/ unloading of O2 at tissues

Question 18

Hypoxic hypoxia

Answer 18

. Blood contains abnormally low PO2
. Hb is poorly saturated
. Can occur during hypoventilation or when gas exchange in lung is disrupted diffusion limitation, V/Q inequality, shunt)
. Can also occur when PIO2 is low like in high altitude
. O2 administration is helpful
. PAO2, PAO2, CaO2, SO2, and PVO2 all dec.
. In diffusion limitation and a shunt PAO2 does not change
. In V/Q inequality the PAO2 varies

Question 19

Anemic hypoxia

Answer 19

. PO2 is normal but Hb conc. Is low
. Both O2 content and O2 capacity are reduced
. CaO2 and PVO2 dec.
. CO poisoning considered a type of them even though O2 capacity is normal and only O2 content dec.
. O2 administration is helpful

Question 20

Hypoperfusion hypoxia

Answer 20

. Circulatory/ischemic/stagnant hypoxia
. May occur w/ reduction in tissue blood flow
. Could be global effect from dec. in CO from shock or CHF or local effect from obstruction
. O2 administration is not helpful
. PVO2 dec. and nothing else changes values wise

Question 21

Histotoxic hypoxia

Answer 21

. Occurs when toxic substance (cyanide) interferes w/ ability of tissues to utilize O2
. O2 conc. In venous blood is high but the O2 consumption by tissues is extremely low
. Administration of O2 is not helpful

Question 22

T/F Hypoxemia is caused by different types of hypoxic hypoxia and none of the other types of hypoxia

Answer 22

T

Question 23

Types of hypoxemia

Answer 23

. Hypoventilation
. Dec. inspired PO2
. Ventilation/perfusion inequality 
. Shunt
. Diffusion limitation

Question 24

Hypoventilation

Answer 24

. Causes inc. alveolar and PCO2
. Alveolar PO2 and arterial PO2 dec.
. Causes: drugs that produce central depression (morphine, barbiturates), damage to chest wall or paralysis of respiratory muscles

Question 25

Dec. inspired partial pressure effect for hypoxemia

Answer 25

. Inspiring air w/ dec. PO2 causes hypoxemia

. Cause: breathing high altitude where total barometric pressure is dec.

Question 26

Ventilation-perfusion inequality

Answer 26

. Most common cause of hypoxemia
. Normally there is slight mismatch that causes arterial PO2 to be slightly less than average alveolar PO2
. Is they are grossly mismatched, impairment of both O2 and CO2 transfer results
. Lung cannot maintain as high an arterial PO2 or as low an arterial PCO2 compared to lung w/o mismatch

Question 27

Shunt effect on hypoxemia

Answer 27

. Mixed venous blood that enters arterial circulation w/o becoming deoxygenated
. Produces a depression in arterial PO2
. Hypoxemia cannot be completely abolished by breathing 100% O2 bc shunted blood bypasses ventilated alveoli

Question 28

Diffusion limitation

Answer 28

. Usually does not cause hypoxemia due to reserve ability of pulmonary capillaries to take up O2
. May result if thickness of alveolar respiratory membrane is inc. or SA of alveolar membrane is dec.
. More likely to occur if patient is exercising
. Alveolar and arterial PO2 inc.