Gas Transport

Question 1

List the four functions of blood

Answer 1

1. Deliver nutrients and oxygen
2. Remove waste products
3. Maintain homeostasis
4. Circulation

Question 2

List the 3 functions of erythrocytes:

Answer 2

1. Carrying O2 from lungs to body
2. Carrying CO2 from body to lungs
3. Acid/base buffering

Question 3

Where does erythropoiesis occur?

Answer 3

Red bone marrow; 120 day life cycle

breakdown occurs in macrophages of spleen, liver or red bone marrow; released hemoglobin is ingested by monocyte macrophages immediately

Question 4

Outline erythropoiesis

Answer 4

Reticulocytes mature into erythrocytes entering the circulation
Erythrocytes mature in the circulation based on oxygen demand
Erythropoietin (EPO) – principle regulator
•Produced by kidneys in response to anemia, low Hb,
decreased RBF, central hypoxia (pulmonary dz,
altitude)
•Regulated by hypoxia inducible factor (HIF)

Question 5

What are the two ways oxygen is transported in blood?

Answer 5

1. Dissolved

2. Bound to hemoglobin

Question 6

Why is dissolved oxygen inadequate?

Answer 6

Solubility x pressure difference between alveolar and arterial (100 mm Hg)= 0.3 mL O2/100 mL blood

dissolved Oxygen delivery = 15 mL O2/min
Oxygen consumption = 250 mL O2/min

Question 7

Carbon dioxide transport is done in 3 ways in blood:

Answer 7

1. Dissolved
2. Bicarbonate (HCO3-)
3. Carbamino compounds

Question 8

How much of arterial and venous blood is made of dissolved CO2?

Answer 8

Dissolved accounts for 5% of CO2 in arterial blood and 10% in mixed venous.

PvCO2 is 45 mm Hg = 2.7 ml CO2 / 100 ml blood

Not enough to rely on dissolved transport alone (we produce 200 ml CO2)

Key concept: Solubility of CO2 is 6 ml CO2 / dl blood / 100 mm Hg

Question 9

How is Carbamino hemoglobin (Hb-NH-COO−) different between arterial and venous blood?

Answer 9

Accounts for 5% of CO2 in arterial blood and 30% in venous blood

Question 10

Bicarbonate accounts for ___% of CO2 in arterial blood and ___% in mixed venous

Answer 10

Bicarbonate (HCO3-) accounts for 90% of CO2 in arterial blood and 60% in mixed venous.

Formed by:

• Dissociation of H2CO3 to H+ and HCO3-
• Formed directly from CO2 and OH- by carbonic anhydrase (CA)
• Formed directly from CO32- + H+

Question 11

What happens to CO2 once we’re back in the lungs?

Answer 11

• Dissolved CO2 moves down its concentration gradient into the alveoli
• CO2 dissociates from proteins
• HCO3 is converted back to CO2

Question 12

explain the oxygen hemoglobin dissociation curve using the 3 axes

Answer 12

• Right Y-axis: O2 content (also in mL O2/100 mL blood) (sometimes expressed as a %)
• Left Y-axis: Hb saturation (%)
• X-axis: PO2 (mm Hg)

*Note: Based on ‘normal’ hemoglobin concentration in blood of 15 g/100 mL blood

Question 13

How much O2 can blood carry?

Answer 13

Hemoglobin in blood is normally 15 g Hb
Pure Hb carries 1.39 mL O2 / g Hb
Actual Hb in blood carries 1.34 mL O2 / g Hb

So, maximally: 1.34 mL O2/ gHb * 15 g Hb/dL blood = ~20.1 (mL O2)/dL blood

Question 14

What does the arterial side of the oxygen-Hb dissociation curve show?

Answer 14

Arterial blood (a on curve) PaO2 = 100 mm Hg
•97.5% saturation
• If 20.1 mL O2 / 100 mL of blood @100% then @97.5% -> 19.6 mL O2 / 100 mL of blood
•+ dissolved blood 0.3 mL O2 / 100 mL of blood
•Total oxygen in arterial blood is 19.9 mL O2 / 100 mL blood

Question 15

What does the venous side of the Oxygen-Hb dissociation curve show?

Answer 15

Venous blood (v on curve) PvO2 = 40 mm Hg
•@75% saturation
•20.1 mL O2 / 100 mL of blood @100%, then @75%= 15.1 mL O2 / 100 mL of blood
•+ dissolved blood 0.1 mL O2 / 100 mL of blood
•Total oxygen in venous blood is 15.2 mL O2 / 100 mL blood

Question 16

What is P50 on the oxygen-Hb dissociation curve?

Answer 16

P50 = 50% O2 saturation
Occurs generally at PO2 = 27 mm Hg
O2 content is 10 mL O2 / 100 mL blood [based on Hb = 15 g]

Question 17

What would breathing 100% oxygen do to the oxygen-Hb dissociation curve?

Answer 17

Raises the amount of dissolved O2

May increase dissolved amount to 1.8 mL O2 / 100 mL blood

Question 18

What does a right shift in the oxygen dissociation curve mean?

Answer 18

Represents decreased affinity of Hb for O2
Associated with anemia
Advantageous for unloading oxygen

Conditions:
•Increased temperature
•Decreased pH (acidity) – Bohr effect
•Increased PCO2

Increased 2,3-diphosphoglycerate (or 2,3-bisphosphoglycerate)
•Increased by low PO2 in RBC stimulating glycolysis
•Chronic hypoxia, anemia
•Largest effect on venous/tissue side of the curve

Question 19

What does a left shift in the oxygen dissociation curve mean?

Answer 19

Represents increased affinity of Hb for O2
Advantageous for holding on to oxygen

Conditions:
•Methemoglobinemia
•HbF
•Polycythemia
•Decreased body temperature
•Increased pH
•Decreased PCO2

Small amounts of CO will displace one O2 molecule from a fully saturated Hb molecule.
•Reduces the binding capacity for O2 molecules
•Also causes LARGE left shift in the O2 curve

Question 20

What constitutes the Respiratory Quotient?

Answer 20

=(volume CO2 produced)/(volume O2 consumed) = 200 mL/250 mL = 0.8

Question 21

What determines the Respiratory Quotient, specifically?

Answer 21

Determined by the type of fuel being used e.g. fat vs carbs

carbs - 1:1 ratio (RQ = 1)
fat 7:10 ratio (RQ = 0.7)
protein 9:10 ratio (RQ = 0.9)

Question 22

What is the Haldane effect?

Answer 22

As O2 levels fall (towards O% HbO2) CO2 levels increase -Tissues - pick up CO2
-Pulmonary capillaries – release CO2

Question 23

List some disorders associated qith RBCs

Answer 23

Anemia of blood loss
Anemia of chronic disease
hemolytic anemias
anemias of diminished erythropoiesis 
polycythemia

Question 24

What are the requirements for erythropoiesis?

Answer 24

1. adequate nutrition
2. vitamin B12 (cynocobalamin, cobalamin) and folate (B9) - required for DNA synthesis
3. Iron availability - absorption, transport, storage

*note: folate or B12 deficient results in megaloblastic macrocytic anemia
poor B12 leads to pernicious anemia

Question 25

What causes microcytic anemia?

Answer 25

deficiency in Iron circulating as transferrin

Question 26

What causes hypochromic anemia?

Answer 26

deficient transport of transferrin to developing erythroblasts

Question 27

How does anemia decrease oxygen carrying capacity?

Answer 27

Hemoglobin concentration is proportional to blood oxygen content.
½ Hemoglobin concentration ~~ ½ blood oxygen content BUT % saturation doesn’t change.

Cyanosis may not be present because SaO2 is high

Question 28

Differentiate between Primary polycythemia, secondary polycythemia, and physiologic polycythemia.

Answer 28

Primary:

• genetic (low EPO)
• extra RBCs
• more blood; more viscosity; normal CO

Secondary:

• Hypoxia (high EPO)
• extra RBCs
• CO likely abnormal

Physiologic:

• high altitude adaptation
• extra RBCs
• normal CO

Question 29

Explain methemoglobinemia

Answer 29

• increased methemoglobin (up to ~25%)
• decreased O2 availability to tissues & leftward shift of oxygen-Hb dissociation curve
• blood is chocolate colored and can appear blue in caucasians
• mutant M form of Hb
• variants of methemoglobin reductase
• oxidation of Fe2+ of Hb

Question 30

define hemachromatosis

Answer 30

Iron overload leading to liver cirrhosis, skin pigmentation & diabetes mellitus.

• can be primary/genetic
• secondary from blood transfusions, ineffective erythropoiesis, increased iron
• neonatal - develops in utero, unknown cause