Gas Transport Flashcards
List the four functions of blood
- Deliver nutrients and oxygen
- Remove waste products
- Maintain homeostasis
- Circulation
List the 3 functions of erythrocytes:
- Carrying O2 from lungs to body
- Carrying CO2 from body to lungs
- Acid/base buffering
Where does erythropoiesis occur?
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
Outline erythropoiesis
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)
What are the two ways oxygen is transported in blood?
- Dissolved
2. Bound to hemoglobin
Why is dissolved oxygen inadequate?
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
Carbon dioxide transport is done in 3 ways in blood:
- Dissolved
- Bicarbonate (HCO3-)
- Carbamino compounds
How much of arterial and venous blood is made of dissolved CO2?
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
How is Carbamino hemoglobin (Hb-NH-COO−) different between arterial and venous blood?
Accounts for 5% of CO2 in arterial blood and 30% in venous blood
Bicarbonate accounts for ___% of CO2 in arterial blood and ___% in mixed venous
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+
What happens to CO2 once we’re back in the lungs?
- Dissolved CO2 moves down its concentration gradient into the alveoli
- CO2 dissociates from proteins
- HCO3 is converted back to CO2
explain the oxygen hemoglobin dissociation curve using the 3 axes
- 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
How much O2 can blood carry?
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
What does the arterial side of the oxygen-Hb dissociation curve show?
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
What does the venous side of the Oxygen-Hb dissociation curve show?
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
What is P50 on the oxygen-Hb dissociation curve?
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]
What would breathing 100% oxygen do to the oxygen-Hb dissociation curve?
Raises the amount of dissolved O2
May increase dissolved amount to 1.8 mL O2 / 100 mL blood
What does a right shift in the oxygen dissociation curve mean?
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
What does a left shift in the oxygen dissociation curve mean?
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
What constitutes the Respiratory Quotient?
=(volume CO2 produced)/(volume O2 consumed) = 200 mL/250 mL = 0.8
What determines the Respiratory Quotient, specifically?
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)
What is the Haldane effect?
As O2 levels fall (towards O% HbO2) CO2 levels increase -Tissues - pick up CO2
-Pulmonary capillaries – release CO2
List some disorders associated qith RBCs
Anemia of blood loss Anemia of chronic disease hemolytic anemias anemias of diminished erythropoiesis polycythemia
What are the requirements for erythropoiesis?
- adequate nutrition
- vitamin B12 (cynocobalamin, cobalamin) and folate (B9) - required for DNA synthesis
- Iron availability - absorption, transport, storage
*note: folate or B12 deficient results in megaloblastic macrocytic anemia
poor B12 leads to pernicious anemia
What causes microcytic anemia?
deficiency in Iron circulating as transferrin
What causes hypochromic anemia?
deficient transport of transferrin to developing erythroblasts
How does anemia decrease oxygen carrying capacity?
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
Differentiate between Primary polycythemia, secondary polycythemia, and physiologic polycythemia.
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
Explain methemoglobinemia
- 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
define hemachromatosis
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
