Blood & Lymph Module Rbc Flashcards
When are Reactive oxygen species/oxidants/oxygen radicals
formed ?
During cellular metabolism
3 examples of Reactive oxygen species/oxidants/oxygen radicals?
Superoxide, Hydrogen peroxide, hydroxy radicals
What do O radicals do ?
Damage DNA, proteins and lipids in cells which leads to cell death
What are the 3 main protective enzymes agains reactive oxygen species ?
- Glutathione peroxidase
- Superoxide dismutase
- Catalase
Describe glutathione and where is it found.
• A tripeptide – glutamate + cysteine + glycine
• Present in most cells
2 functions of glutathione
• Very important intracellular reductant(antioxidant)
• Important for stability of red cell membrane
2 forms of glutathione
2forms-
Reduced(GSH)
Oxidized (GSSG) (two mol of GSH joined
by disulfide bond)
2G-SH to G-S-S-G reaction
Uses Se. parallel to reaction H2O2 to 2H2O catalyzed by glutathione peroxidase
Reaction of G-S-S-G to 2G-SH
Catalyzed by glutathione reductase in parallel to NADPH
+ H ion to NADP+ catalyzed by FAD
Ratio of G-SH to GSSG and explain importance
100:1
• Ratio of GSH to GSSG controls the redox potential in cells
• Serves as basis for the antioxidant system, quenching reactive oxygen species
• Red cells are totally dependent on Pentose phosphate pathway (HMP shunt) for their supply of NADPH.
Where is NADPH formed
• produced only via Pentose phosphate pathway in RBC
5 uses of NADPH
- As a high energy molecule
- For reductive biosynthesis
- reducing glutathione
- nitric oxide synthesis
- oxygen-dependent mechanism after leukocyte phagocytosis of microbes
Describe Pentose phosphate pathway (HMP shunt)
GLUCOSE to GLUCOSE-6-PHOSPHATE (G6PD) to 6-PHOSPHOGLUCONATE ( 1NADP+ to 1NADPH) to RIBULOSE-5-PHOSPHATE to nucleotide synthesis
What is G6PD deficiency
• X linked disease recessive
• Deficiency of Glucose-6- phosphate dehydrogenase
enzyme
• G6PD enzyme catalyzes irreversible oxidation of G6P to 6-phosphogluconolactone in pentose phosphate pathway
Consequences of G6PD deficiency
• Leads to deficiency of NADPH
• Oxidative stress = RBC are destroyed = hemolytic anemia
Heinz bodies (most severe in rbc)
What causes G6PD Deficiency
Infection
Favinism
Certain medications (SMX, primaquine)
• Why should RBC be easily deformable?
• For RBC to be easily deformable,
Fluidity by Membrane lipids
Flexibility by Cytoskeletal proteins
Describe RBC cytoskeleton
• Is a semi-permeable lipid bilayer supported by a protein cytoskeleton (contains both integral and peripheral proteins)
• Inside the cell there is an extensive filamentous network called , red cell membrane skeleton ( cytoskeleton)
What is spectrum and its 3 functions
• A major protein of peripheral cytoskeleton
• Found on the inner surface of the membrane
❑ Strengthens
❑ gives elastic properties to membrane
• Helps to maintain shape and flexibility of RBC.
Describe spectrums interactions in rbc
•spectrin bound to Actin and Ankyrin (peripheral membrane proteins)
•Ankyrin and actin are bound to integral proteins.
• α & β chains of spectrin loosely twisted
•Forms an anti parallel dimer.
spectrin binds with other peripheral proteins such as actin to form a skeleton of microfilaments on the inner surface of the membrane.
For spectrin to participate in this interaction, it must be phosphorylated by a protein kinase that requires ATP.
A decrease in ATP leads to decreased phosphorylation of spectrin.
Unphosphorylated spectrin can no longer bind to actin to give the membrane its elastic properties.
This then leads to a loss in membrane deformability and a decreased RBC survival time.
Clinical implication due to spectrin and ankyrin
Hereditary spherocytosis
Very fragile, small round RBC
Hereditary elliptocytosis
RBC are ellpsoidal
What is rbc life span
120 days
How to recognize old RBC and what happens to them
• Old RBC are recognized by membrane changes
- loss of deformability and membrane integrity
• Most are degraded extra vascularly in reticulo- endothelial system (liver and spleen mainly)
To globin which turns to amino acids, to heme which turns to Fe2+ then iron pool and Porphyrins which turns to bilirubin
Explain formation of bilirubin
1st reaction
• occur by microsomal Heme oxygenase
• Heme converted to Biliverdin
Needs O2 & NADPH
Fe2+ is converted to Fe3+.
• Induced by heme
* ** The only CO producing enzyme in human body
( heme to biliverdin , intermediate 2O2 to CO, Fe3+ released , NADPH + H+ to NADP+
2nd reaction
Biliverdin to bilirubin using enzyme cytoplasmic bilirubin reductase
Bilirubin is unique to mammals and functions as antioxidant
How is bilirubin transported in blood and 2 drugs that can interfere and how
• Bilirubin is poorly water soluble
• Thus needs a transporter
• Non covalently binds to Albumin
• 2 binding sites on albumin for bilirubin.
- a high affinity site and low affinity site
• Some drugs displace bilirubin from albumin
Eg: salicylates, sulfonamides.
Explain uptake into hepatocyte ( major parynchemal cells of liver)
Bilirubin- albumin complex
Bilirubin dissociates
Enters hepatoctye by facilitated diffusion
• Is saturable but large capacity
Bilirubin binds to intracellular proteins
Explain bilirubin conjugation in liver
• Formation of Bilirubin diglucuronide / conjugated bilirubin
• Catalyzed by microsomal Bilirubin glucuronyl transferase
• Bilirubin diglucuronide is water soluble
• Induced by phenobarbitol ( an anti epileptic drug)
Effect of lack of Bilirubin glucuronyl transferase
• Deficiency of this enzyme leads to Crigler-Najjar 1, 11
and Gilbert syndrome.
Explain unconjugated bilirubin secretion
• Unconjugated bilirubin not secreted
• Bilirubin diglucuronide is actively secreted in to bile
cannaliculi
• Rate limiting step
What impairs secretion of unconjugated bilirubin to bile
And consequence of lack of transporter protein
Liver disease
Dubin Johnson syndrome
What happens to bilirubin diglucuronide in terminal ilium and large intestine
Bilirubin diglucuronide is ,
1. Deconjugated
2. Reduced
by gut bacteria
Gut bacteria turns
Bilirubin diglucuronide
To
Urobilinogen
Colourless
What happens to urobilinogen large intestine
Most of urobilinogen is,
Urobilinogen to Stercobilin by Gut bacteria
Gives the characteristic brown color of stool.
What happens to urobilinogen in terminal ileum.
Small fraction of urobilinogen is reabsorbed in terminal ileum .
Entero hepatic circulation of urobilinogen
Some urobilinogen excreted in urine.
Converted to Urobilin in urine.
Gives yellow color to urine
Explain jaundice
•= Icterus
• Caused by hyper bilirubinemia
• Due to deposition of bilirubin . (conjugated or unconjugate
or both)
Why does stool become darker with time
