Flashcards in Lecture 27 blood Deck (29)
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Blood plasma
water + electrolytes (Na+, Cl-, K+, HCO3-, Ca2+), plasma proteins, glucose, urea, etc.
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Formed Elements
erythrocytes (RBCs) - 5,000,000/uL
leukocytes (WBCs) - 5,000-10,000/uL
platelets
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RBCs
are anucleated cells, filled with hemoglobin
blood cells are produced in red bone marrow from hematopoietic stem cells
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hematocrit
= % by volume of RBCs (normally 45%)
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erythropoietin
hormone produced by kidneys, stimulates production and differentiation of RBCs
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polycythemia
high RBC count (high hematocrit)
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anemia
low O2 carrying capacity of blood (low hemoglobin concentration)
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Hemoglobin structure and function
protein composed of 4 polypeptide (globin) subunits (2 a, 2B)
each subunit contains a heme group with iron (Fe2+) at the center
each heme reversibly binds O2 (-> 4 O2 binding sites)
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Oxygen transported by blood
1. O2 dissolved in plasma
2.O2 carried by hemoglobin
3. oxygen-hemoglobin dissociation curve
4.factors that affect O2 affinity of hemoglobin
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O2 dissolved in Plasma
low solubility of O2 in plasma
at Po2 = 100 mm Hg, plasma: 3 mL O2 / L blood
whole blood: 200 mL O2 / L blood
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O2 carried by hemoglobin
99% of O2 in blood is carried by hemoglobin
O2 carrying capacity of blood depends on hemoglobin concentration
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Hemoglobin-O2 binding
deoxyhemoglobin (Hb) + O2 -><- oxyhemoglobin (Hb O2)
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Binding and release of O2 depends on:
1. PO2 of the blood
2. affinity of hemoglobin for O2
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Oxygen Hemoglobin Dissociation Curve
relationship between Po2 of blood and percent O2 saturation of hemoglobin
S-shaped curve results from interactions among hemoglobin subunits -> promotes loading of O2 in the lungs and unloading of O2 in the tissues
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Normal Values (curve) (resting, sea level)
arterial Po2 = 100 mm Hg, 98% O2 saturation
venous Po2 = 40 mm Hg, 75% O2 saturation
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In lungs
Po2 = 100 mmHg
flat part of curve -> nearly 100% saturated
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In tissues
Po2 < 60 mm Hg -> rapid unloading of oxygen as Po2 decreases
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During exercise
tissues Po2 decreases -> more O2 released from Hb -> O2 sat. of venous blood
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Pulmonary disease
Pulmonary disease -> decrease arterial Po2 -> decrease O2 saturation (hypoxemia)
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At high altitude
decrease in arterial Po2 -> decrease O2 saturation
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Factors that affect O2 affinity of hemoglobin
1. increase temp -> decreases affinity (rightward shift of O2 dissociation curve)
2. decrease pH (increase [H+]) -> decreases affinity - (bohr shift)
3. increase PCO2 -> decrease affinity
4. increae 2, 3-DPG -> decreased affinity
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rightward shift
means more O2 will be unloaded from Hb at a given Po2
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in active tissues
increase temp, decrease pH and increase Pco2 promote unloading of O2
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Carbon Dioxide transport by blood
1. dissolved Co2 plasma (10%)
2. bicarbonate (70%)
3. carbamino hemoglobin (20%)
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Bicarbonate
Co2 + H20 -><- H+ + HCO3-
in tissues high PCO2 drives reaction forward to form HCO3-
in lungs, lower PCO2 pull reactions in reverse, HCO3- is converted back into CO2
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carbonic anhydrase
in RBC catalyzes conversion of CO2 to carbonic acid
CO2 is a major source of H+ in the body
increase PCO2 -> decrease pH
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Buffer
hemoglobin acts as a buffer of H+ formed by the reaction
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HCO3-
is transported from RBC out to plasma in exchange for Cl-
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