Week 2. Red Blood Cells Flashcards
How does mean cell volume change in diseases?
Decreases in iron deficiency
Increases in B12 anaemia
what are 3 useful red blood cell indices?
Haemoglobin (g/dL)
Mean cell volume (fl)
Red cell count (10^12/L)
Why are reticulocytes called that?
Because of their reticular (mesh-like) network of ribosomal RNA that becomes visible under a microscope with certain stains like-> new methylene blue.
RBC lifespan?
120 days
Romanowsky results for red blood cell?
Pink.
Strength of colour shows how much haemoglobin is in the cell. So faint colour= not much Hb
Size of RBC
- 5um diameter.
2. 0um depth
Hereditary spherocytosis
Most common HA in northern europe. Defects in proteins involved in vertical interactions between membrane cytoskeleton and lipid bilayer. Cell becomes spherical. Die prematurely.
Clinical features and treatments of hereditary spherocytosis
Anaemia. Jaundice. Increased bilirubin because increased rbc destruction.
Splenomegaly-> spleen gets bigger.
Splenectomy last resort.
Stages of erythropoiesis?
Hemocytoblast (stem cell) Proerythroblast (committed cell) (now into developmental pathway) Early erythroblast (ribosome synthesis) Late erythroblast Normoblast (haemoglobin accumulation and ejects nucleus) Reticulocyte Erythrocyte!
Describe the peripheral proteins of the rbc membrane?
- spectrin (alpha and beta. alpha=globular part, beta=chain)
- Protein 4.1 links to cytochrome c
- protein 4.2 links to band 3 via ankyrin and to spectrin.
- Ankyrin links band 3 to 4.3 and then spectrin
- Actin at 4.1 spectrin and 4.2 spectrin links.
When does polychromasia occur?
When the immature reticulocytes are released, resulting in greyish blue coloured cells.
Colour is due to ribosomes still left on the immature RBC. Ribosomal RNA left in reticulocyte.
Reticulocytes under romanowsky stain
Appear slightly bluer than RBCs because of ribosomal rna still left inside.
What is the width of capillaries and red blood cells?
Capillaries are 2-3um wide.
Red blood cells are 7-8 um diameter.
So the red blood cell needs to be tough and flexible
How does plasmodium falciparum invade red blood cells?
Extra reading
1982 study.
When glycophorin B is removed by trypsin treatment RBCs are partly resistant to plasmodium falciparum invasion. When glycoprotein A-> completely resistant.
More modern studies show there are multiple pathways of invasion.
What functions does the rbc membrane have?
- separates cell contents from plasma
- maintains biconcave disc shape
- regulates intracellular cation conc.
- Interface for membrane-bound cell receptors
What is the composition of the rbc membrane?
50% protein
42% lipis
8% carbohydrate
How many RBC membrane proteins are there?
What roles do they have?
Currently more than 50 known proteins. Around 25 of these carry the various blood group antigens
roles= transport (25% of membrane) e.g. band 3, aquaporin
cell adhesion
structural role
Most common phospholipids?
Phosphotidylcholine (PC) 30%
Phosphotidylethanolamine (PE) 28%
Sphingomyelin 25%
Can rbcs make lipids from scratch?
Mature rbc cant make lipids de novo.
There are lipid renewal pathways and cholesterol content of the membrane is regulated by exchange between plasma cholesterol and membrane cholesterol.
Maintains equilibrium. Found to happen more rapidly in old than young rats. May be due to larger pool of free cholesterol in old rats. [Malhotra and Kritchevsky]
Examples of membrane proteins for:
- Transport
- cell adhesion
- Structural role
- transport- Band3, aquaporin 1 (water), glut1 (glucose and L-dehydroascorbic acid), RhAG (gas probably co2)
- Cell adhesion- ICAM 4 (interacts with integrins), BCAM (glycoprotein also known as Lu or laminin-binding protein
- Structural role-
Ankyrin-based macromolecular complex- proteins linking the bilayer to the membrane skeleton through the interaction of their cytoplasmic domains with Ankyrin.
Band 3- assembles glycolytic enzymes
duffy protein (extra)
What system destroys rbs normally?
The reticuloendothelial system (RES)
How do monocytes contribute to the reticuloendothelial system?
Monocytes leave the blood stream and enter tissue and specialise. Can break down rbcs in other organs than spleen e.g. when no spleen body adapts- macrophages in bone marrow. Kupffer cells in liver. (name for monocytes in these places)
What is a haemolytic disorder?
What is compensated haemolysis?
When increased haemolysis.
The body tries to make more RBCs to compensate.
Get haemolytic anaemia when the RBCs are broken down faster than they are made.
What happens when rbcs are about 120 days old?
They burst in narrow spleen channels.
Macrophages in the spleen and liver digest the cell components here. Convert haem to bilirubin. Becomes bile and then faeces. Haem and globin recycled.
When rbcs burst in spleen, what is recycled?
Haem–> Iron –> erythropoiesis
Globin –> amino acids –> protein synthesis
What are the functions of the integral proteins?
Band 3-
Transmembrane anion channel. Gas exchange, allows chloride ion in place of bicarbonate ion, important for gas exchange. Binds peripheral proteins (via ankyrin and 4.2)
Glycophorins- link the membrain skeleton to the lipid bilayer through interaction with proteins 4.1 and 4.2
Transferrin receptor- binds transferring molecules, iron transport later
What are the functions of glycolytic pathway in RBC? and where?
- NADPH production- hexose monophosphate shunt
- ATP production- Embden-meyerhof pathway, maintains shape and flexibility, most glucose used.
- 2,3 DPG production- rapaport-lueberg shunt.
Stabilizes the molecule so favours low oxygen affinity. Useful in respiring tissues.
Describe G6PD deficiency one of the enzymopathies
Glucose-6-phosphate dehydrogenase (G6PD) deficiency.
X-linked inheritance, enzyme activity deficient.
Resistance to malaria.
Was known as Favism because Fava beans increase it.
Rapid haemolysis-> blood film you see bite cells/blister cells
Heinz bodies bind to cell, make it rigid.
Get blood in urine.
Macrophage marks them for destruction, takes a bit out.
Pyruvate kinase deficiency
Defect of Embden-Myerhof pathway. Deveroty varies- mild to sever jaundice. Autosomal recessive Reduced ATP so RBC less flexible. So haemolysis. Lose biconcave disc, appeare larger.
Splenectomy and blood transfusions to treat.
Auto-immune haemolytic anaemia
Acquired not hereditary. Antibody against own red blood cells.
Warm and cold types Categorized whether antibody react more strongly with RBC at 37’C or 4’C
When is Hb made?
65% erythroblast stage
35% reticulocyte stage
What family is Hb in? What is it’s structure?
Part of Porphyrins protein family.
Has 2 alpha globin chains and 2 beta globin chains. 4 haem molecules.
What are the steps of haemoglobin synthesis?
Glycine + B6 + Succinyl CoA to delta- ALA (then leaves mitochondria) Porphobilinogen Uroporphyrinogen Copraporphyrinogen (back into mito) Protoporphyrin Fe is brought into mitochondria by transferrin and links to protoporphyrin. This makes Haem. (leaves mito) Haem joins 2alpha 2 beta globin chains made by ribosomes and. Haem+globin= Haemoglobin
Where are haem and globin made?
What is the structure of haem?
Globin- ribosomes
Haem- mitochondria because it contains ALA-synthase.
Haem structure= protoporphyrin ring with an iron atom in the centre.
What happens to the haem broken down?
Haem broken down to bilirubin.
It’s conjugated and becomes part of the gut bile.
Converted to stercobilinogen-> stercobilin. Pooed out.
Some is reabsorbed and urinated out as urobilinogen->urobilin, if it is not pooed out.
Summarise differnce between integral and peripheral framework of rbc membrane?
INtegrals found within bilayer, anchored in. Peripherals aren’t embedded, on outside. Peripherals have interactions with integral proteins. Peripheral have horizontal framework. Integral- vertical interaction.
What 2 key interactions link the membrane skeleton to lipid bilayer?
Ankyrin (band 3) and spectrin beta
Glycophorin C and protein 4.1
What does spectrin do?
It’s the most abundant peripheral protein.
Flexible rod of alpha and beta.
Allows RBC to form arrowheads in capillaries.
Alpha and beta allow strength and flexibility
What does 4.1 do?
Stabilises the actin/spectrin junction
What does beta spectrin attach to?
Attach to ankyrin which connects to band 3
What does 4.2 do?
Enhances the interaction of beta spectrin with ankyrin (and band 3)
Give 3 integral proteins (types) of rbc
Band 3= anion channel
Glycophorins=link membrane skeleton to lipid bilayer via 4.1 and 4.2
Transferrin=iron transporter
Describe properties of integral and peripheral proteins
Integral- penetrate lipid bilayer anchored by interactions with bilayer small part either end that extends into plasma (often glycosylated) or into cytoplasm. 60-80% total proteins in membrane
Peripheral-
Not embedded in bilayer
Linked by interactions with integral proteins
Interact to form cytoskeleton
What is hereditary stomatocytosis (extra)
A number of inherited autosomal dominant conditions which affect the RBC membrane.
The membrane “leaks” sodium and potassium ions. The cell becomes swamped with salt and water and lyses. Takes on an odd shape like a mouth or “stoma”
When are osmotic fragility tests used?
To diagnose thalassemia or hereditary spherocytsosis,
Blood samples added to solutions of different salt concentrations. See if they are fragile.
