Red Blood Cells: Structure, Metabolism, Membrane, and Pathophysiology

Flashcards cover RBC structure, metabolism (Embden-Meyerhof), ATP roles, shunts, G6PD deficiency, methemoglobin reductase, Rapaport-Leubering pathway, RBC membrane composition (lipids, glycolipids, transmembrane and cytoskeletal proteins), blood group antigens, and membrane defects.

What is the mature red blood cell's basic structure?

Anucleate, biconcave, discoid.

What fills the RBC and what is its function?

Hemoglobin; transports oxygen and carbon dioxide.

What is the typical diameter of an RBC?

7–8 μm.

Why is there a zone of pallor in the center of RBCs?

Due to their biconcave shape.

What is the lifespan of an erythrocyte?

About 120 days.

What is the Embden-Meyerhof Pathway in RBCs?

Non-oxidative glycolytic pathway; anaerobic glycolysis producing ATP from glucose.

Which glucose transporter facilitates glucose entry into RBCs?

Glut-1.

What is the net ATP yield of glycolysis in RBCs?

4 ATP produced per glucose; net gain of 2 ATP per glucose.

What are the three phases of the Embden-Meyerhof pathway in RBCs?

Phase 1: Glucose → G3P; Phase 2: G3P → 3-PG; Phase 3: 3-PG → Pyruvate.

During which steps is ATP consumed in RBC glycolysis?

Glucose to G3P and G3P to 3-PG.

What are the primary ATP-dependent roles in the RBC membrane?

Maintenance of membrane lipids, driving Na+/K+ pump and Ca2+ flux, and maintaining shape/deformability.

What happens if ATP is deficient in RBCs in vivo and in vitro?

Premature cell death in vivo; loss of viability and ATP depletion in vitro.

What are glycolysis diversion pathways called?

Shunts or diversions off glycolysis.

What is G6PD deficiency?

Most common inherited RBC enzyme deficiency; impairs detoxification leading to hereditary nonspherocytic anemia.

What is the Methemoglobin Reductase Pathway?

Maintains iron in hemoglobin in the reduced Fe2+ state; prevents oxidation to Fe3+ (methemoglobin); enzyme is cytochrome b5 reductase.

What does the Rapaport-Leubering Pathway produce and what is its effect on hemoglobin?

Produces 2,3-BPG, which lowers hemoglobin's oxygen affinity to promote oxygen release to tissues.

Name the oxidative pathway in RBCs and its function.

Hexose Monophosphate Shunt (oxidative pathway); helps prevent denaturation of globin by maintaining redox balance.

What is another RBC metabolic pathway besides Embden-Meyerhof and the HMP shunt?

Methemoglobin Reductase Pathway; Leubering-Rapaport (2,3-BPG) related regulation.

What is the overall RBC membrane geometry and its functional consequence?

Biconcave geometry essential for normal function and 120-day lifespan; facilitates deformability.

What are the three properties of the RBC membrane that contribute to deformability?

Geometry, pliancy, and cytoplasmic viscosity.

What is the macromolecule composition of the RBC membrane?

Proteins ~52%, Lipids ~40%, Carbohydrates ~8%.

Which phospholipids are in the outer membrane layer and which are in the inner layer of RBC membranes?

Outer layer: phosphatidylcholine (PC) and sphingomyelin; Inner layer: phosphatidylserine (PS) and phosphatidylethanolamine (PE).

What role do RBC membrane lipids play and what happens if they are deficient?

Provide tensile strength to the lipid bilayer; cholesterol homeostasis; deficiencies can lead to acanthocytes and target cells.

What are RBC membrane glycolipids and their function?

Glycolipids carry blood group antigens (ABH and Lewis) and contribute to the glycocalyx.

What are the functions of RBC membrane transmembrane proteins?

Transporters, adhesion sites, and signaling receptors; disruption can alter osmotic tension, viscosity, and deformability; glycosylation supports surface carbohydrates.

Name two key transmembrane protein complexes in the RBC membrane.

Ankyrin complex (band 3 and protein 4.2) and Actin complex (band 3 dimers, protein 4.2, adducin).

What are RBC membrane cytoskeletal proteins and their role?

Alpha and beta spectrin form antiparallel heterodimers; spectrin dimers dissociate and reassociate during deformation.

What are common RBC membrane defects and their effects?

Hereditary Spherocytosis: vertical anchorage defects leading to spherical, less stable RBCs; Hereditary Elliptocytosis: horizontal interaction defects leading to elliptically shaped, less deformable RBCs.