RBC structure and function Flashcards
Structure of red blood cells [5 marks]
- No nucleus, mitochondria or ER
- Cytoplasm rich in haemoglobin
- Biconcave
- Flexible membrane
- High surface area to volume ratio
Function of red blood cells [1 mark]
To carry oxygen and carbon dioxide to and from tissue.
What lipids does the outer hydrophilic portion consist of? [2 marks]
- Phosphatidylcholine
- Sphingomyelin
BOTH UNCHARGED
What lipids does the inner hydrophobic portion consist of? [2 marks]
- Phosphatidylethanolamine
- Phosphatidylserine
BOTH CHARGED
What does increased cholesterol in red blood cells cause?
Acanthocytosis (spiked cells)
What does an increase in cholesterol and phospholipids and a decrease in haemoglobin cause? [1 mark]
Target cells
What are the integral proteins in red blood cells? [5 marks]
- Glycophorin (A, B and C)
- Band 3
- Na+/k+ ATPase
- Aquaporin 1
- Transferrin Receptor
What is the peripheral protein Spectrin and what does it do? [4 marks]
- Most abudant
- Made up of alpha and beta chains
- Binds with other peripheral proteins to form the cytoskeletal network of microfilaments
- Controls biconcave shape and deformability of cell.
What is the peripheral protein Ankyrin and what does it do? [1 mark]
Anchors lipid bilayer to membrane skeleton via spectrin and band 3 interaction
What is the peripheral protein Protein 4.1 and what does it do? [4 marks]
- Links cytoskeleton to the membrane via glycophorin
- Stabilises interaction of spectrin with actin
What is the peripheral protein Actin and what does it do? [1 mark]
It’s responsible for contraction and relaxation of the membrane.
What is the function of the membrane? [3 marks]
- Provides shape
- Provides deformability, elasticity
- Regulates intracellular cation concentration
What causes hereditary elliptocytosis? [2 marks]
- Mutations in genes destabilise the cytoskeleton of erythrocyte
- So they can’t maintain their shape
What causes hereditary spherocytosis? [2 marks]
- Mutations in genes for spectrin or ankyrin means that they can’t link with actin
- This makes erythrocytes more likely to lyse in water
What allows red blood cells to stay alive without structural deterioration? [3 marks]
- Surface area to volume ratio
- Membrane deformability
- Cytoplasmic viscosity determined by Mean Corpuscular Haemoglobin Concentration (higher MCHC = higher viscocity)
Haemoglobin structure [4 marks]
- Globular
- 2 alpha globin chain, 2 beta globin chain
- Haem is a complex of protoporphyrin IX and Fe2+ (Fe2+ in centre with 4 nitrogen)
Why do red blood cells need metabolic pathways?
- To maintain cation pumps
- To maintain Hb in reduced state
- To maintain reduced sulfhydryl groups in Hb
- To maintain RBC integrity and deformability
Glycolytic pathway
- Glucose is metabolised to generate 2 ATP
- Generates 90-95% of energy needed
- Maintain RBC shape, flexibility and cation pumps
Hexose monophosphate stunt (a.k.a. pentose phosphate)
- Provides the reducing power NADPH
- Maintains glutathione in the reduced form
- Red blood cells use reduced glutathione to protect it against oxidative damage
Methaemoglobin Reductase pathway
- Maintain iron in Fe2+
- Without the enzyme, methaemoglobin with Fe3+ accumulate and it can’t carry oxygen
Luebering Rapoport shunt
Permits the accumulation of 2,3-DPG which is essential for maintaining normal oxygen tension, regulating haemoglobin affinity
