MLS 411 Exam 3

Describe the structure of the RBC membrane

• Semi-permeable, phospholipid bilayer

• Supported by a protein cytoskeleton

• Flexible

• Na and Ca accumulate in RBC; H2O and K lost from RBC

• Since RBC is relatively impermeable to Na and K, there is a cationic pump to transport these molecules in/out (requires ATP)

What is the lifespan of a normal RBC?

120 days

What happens to an RBC when there is a loss of ATP?

• Membrane flexibility is lost

• Causes RBCs to be removed by the spleen

What is the function of hemoglobin and 2,3-DPG?

• Gas transport: oxygen delivery to tissues and removal of carbon dioxide

• 2,3-DPG binds to deoxygenated (tense) Hgb to control how Hgb releases oxygen

  • Switches from relaxed Hgb (O₂ saturated) and tense Hgb (O₂ release)

  • More 2,3-DPG = More O₂ is released in tissues, decreased Hgb affinity for O₂

In stored RBC products, 2,3-DPG and ATP levels ____ over time

Decrease

• Levels of 2,3-DPG and ATP are regenerated within 24 hours after the product is transfused, restoring normal Hgb function

• Low levels of 2,3-DPg affect cardiac output, making it important for newborns and cardiac patients to receive fresh blood with high levels of 2,3-DPG

Oxygen Dissociation + Curve

Definition: maintenance of Hgb/Oxygen equilibrium

• RBCs pick up O₂ in lungs (high PO₂) and release it in tissues (low PO₂) in exchange for CO₂ to be brought back to heart and then the lungs

Oxygen Dissociation Curve: relationship between % of Hgb saturated with O₂ vs PO₂ levels

• Influenced by: pH and 2,3-DPG levels

• P₅₀: PO₂ at which 50% of Hgb saturated with O₂

• Right Shift: Hgb has decreased affinity for O₂ = more released to tissues

  • Occurs in: hypoxia, acidosis

• Left Shift: Hgb has increased affinity for O₂ = less released to tissues

  • Occurs in: alkalosis, increased qty of abnormal Hgb, multiple transfusions of 2,3-DPG depleted blood

What is the amount of whole blood in a normal adult?

5000 mL

What is storage lesion?

The harmful biochemical, metabolic, and physical changes RBC undergo while banked in a refrigerator (1-6C)

• Decreased pH (due to increased metabolism of glucose to lactic acid)

• Decreased ATP (glucose consumption is decreased)

• Decreased 2,3-DPG (increases Hgb affinity for O₂)

In plasma:

• K⁺ rises

• Na⁺ falls

• Plasma Hgb rises

What must be preserved when storing RBCs?

• Viability (ATP levels)

• Hgb function (2,3-DPG)

The FDA states that __% to _% of transfused cells must remain in circulation for 24 hours following transfusion

70% to 75%

T/F: During a collection of a whole blood unit, no more than 10.5 mL/kg of body weight may be collected

True (~450-500 mL per collection)

Describe the constituents of approved anticoagulant preservative solutions

1. Sodium citrate: binds calcium and prevents initiation of coagulation

2. Citric acid: creates an acidic environment to slow down glycolysis

3. Dextrose: sugar source for RBC metabolism

4. Monobasic sodium phosphate: buffer to maintain pH

5. Adenine: maintains ATP levels during cell metabolism

What are the different anticoagulants/preservatives? Compare them

• ACD

• CPD

• CP2D

• CPDA-1

• Additive solutions (AS-1/Adsol, AS-3/Nutricel, AS-5/Optisol)

 

	Acid Citrate Dextrose (ACD)	Citrate Phosphate Dextrose (CPD)	Citrate Phosphate 2 Dextrose (CP2D)	Citrate Phosphate Dextrose Adenine (CPDA-1)	Additive Solutions  AS-1 (Adsol)  AS-3 (Nutricel) AS-5 (Optisol)
Contents	Citrate Dextrose	Citrate Phosphate Dextrose	Citrate Phosphate Dextrose	Citrate Phosphate Dextrose  Adenine	Saline Adenine Glucose Mannitol (Except AS-3)
Outdate	21 days	21 days	21 days	35 days	42 days
2,3-DPG Depletion	By end of first week of storage	By end of second week of storage		By end of second week of storage	By end of second week of storage
Notes	Used primarily in apheresis collections	Commonly used for whole blood collection  pH higher than ACD, slower glycolic activity	Has twice the level of glucose in CPD to prolong ATP generation	More glucose than CPD  Adenine helps increase ATP levels	Mannitol slows hemolysis & reduces viscosity; maintains membrane Greater RBC in vivo survival  Hct is ~ 55%

Which preservatives are used to collect blood?

• ACD

• CPD

• CPD2

The majority of plasma is removed, and an additive solution is added to the RBCs

What kind of bags should blood be stored in?

Sterile, pyrogen-free, single use bags made of a plastic material that is permeable to CO₂ in order to maintain higher pH levels during storage