Blood & Lymph Module Rbc

Question 1

When are Reactive oxygen species/oxidants/oxygen radicals
formed ?

Answer 1

During cellular metabolism

Question 2

3 examples of Reactive oxygen species/oxidants/oxygen radicals?

Answer 2

Superoxide, Hydrogen peroxide, hydroxy radicals

Question 3

What do O radicals do ?

Answer 3

Damage DNA, proteins and lipids in cells which leads to cell death

Question 4

What are the 3 main protective enzymes agains reactive oxygen species ?

Answer 4

1. Glutathione peroxidase
2. Superoxide dismutase
3. Catalase

Question 5

Describe glutathione and where is it found.

Answer 5

• A tripeptide – glutamate + cysteine + glycine

• Present in most cells

Question 6

2 functions of glutathione

Answer 6

• Very important intracellular reductant(antioxidant)
• Important for stability of red cell membrane

Question 7

2 forms of glutathione

Answer 7

2forms-
Reduced(GSH)

Oxidized (GSSG) (two mol of GSH joined
by disulfide bond)

Question 8

2G-SH to G-S-S-G reaction

Answer 8

Uses Se. parallel to reaction H2O2 to 2H2O catalyzed by glutathione peroxidase

Question 9

Reaction of G-S-S-G to 2G-SH

Answer 9

Catalyzed by glutathione reductase in parallel to NADPH
+ H ion to NADP+ catalyzed by FAD

Question 10

Ratio of G-SH to GSSG and explain importance

Answer 10

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.

Question 11

Where is NADPH formed

Answer 11

• produced only via Pentose phosphate pathway in RBC

Question 12

5 uses of NADPH

Answer 12

• As a high energy molecule
• For reductive biosynthesis
• reducing glutathione
• nitric oxide synthesis
• oxygen-dependent mechanism after leukocyte phagocytosis of microbes

Question 13

Describe Pentose phosphate pathway (HMP shunt)

Answer 13

GLUCOSE to GLUCOSE-6-PHOSPHATE (G6PD) to 6-PHOSPHOGLUCONATE ( 1NADP+ to 1NADPH) to RIBULOSE-5-PHOSPHATE to nucleotide synthesis

Question 14

What is G6PD deficiency

Answer 14

• 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

Question 15

Consequences of G6PD deficiency

Answer 15

• Leads to deficiency of NADPH

• Oxidative stress = RBC are destroyed = hemolytic anemia
Heinz bodies (most severe in rbc)

Question 16

What causes G6PD Deficiency

Answer 16

Infection
Favinism
Certain medications (SMX, primaquine)

Question 17

• Why should RBC be easily deformable?

Answer 17

• For RBC to be easily deformable,
Fluidity by Membrane lipids
Flexibility by Cytoskeletal proteins

Question 18

Describe RBC cytoskeleton

Answer 18

• 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)

Question 19

What is spectrum and its 3 functions

Answer 19

• 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.

Question 20

Describe spectrums interactions in rbc

Answer 20

•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.

Question 21

Clinical implication due to spectrin and ankyrin

Answer 21

Hereditary spherocytosis
Very fragile, small round RBC

Hereditary elliptocytosis
RBC are ellpsoidal

Question 22

What is rbc life span

Answer 22

120 days

Question 23

How to recognize old RBC and what happens to them

Answer 23

• 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

Question 24

Explain formation of bilirubin

Answer 24

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

Question 25

How is bilirubin transported in blood and 2 drugs that can interfere and how

Answer 25

• 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.

Question 26

Explain uptake into hepatocyte ( major parynchemal cells of liver)

Answer 26

Bilirubin- albumin complex
Bilirubin dissociates
Enters hepatoctye by facilitated diffusion
• Is saturable but large capacity
Bilirubin binds to intracellular proteins

Question 27

Explain bilirubin conjugation in liver

Answer 27

• Formation of Bilirubin diglucuronide / conjugated bilirubin
• Catalyzed by microsomal Bilirubin glucuronyl transferase
• Bilirubin diglucuronide is water soluble
• Induced by phenobarbitol ( an anti epileptic drug)

Question 28

Effect of lack of Bilirubin glucuronyl transferase

Answer 28

• Deficiency of this enzyme leads to Crigler-Najjar 1, 11
and Gilbert syndrome.

Question 29

Explain unconjugated bilirubin secretion

Answer 29

• Unconjugated bilirubin not secreted
• Bilirubin diglucuronide is actively secreted in to bile
cannaliculi
• Rate limiting step

Question 30

What impairs secretion of unconjugated bilirubin to bile
And consequence of lack of transporter protein

Answer 30

Liver disease

Dubin Johnson syndrome

Question 31

What happens to bilirubin diglucuronide in terminal ilium and large intestine

Answer 31

Bilirubin diglucuronide is ,
1. Deconjugated
2. Reduced
by gut bacteria

Gut bacteria turns
Bilirubin diglucuronide
To
Urobilinogen
Colourless

Question 32

What happens to urobilinogen large intestine

Answer 32

Most of urobilinogen is,
Urobilinogen to Stercobilin by Gut bacteria
Gives the characteristic brown color of stool.

Question 33

What happens to urobilinogen in terminal ileum.

Answer 33

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

Question 34

Explain jaundice

Answer 34

•= Icterus
• Caused by hyper bilirubinemia
• Due to deposition of bilirubin . (conjugated or unconjugate
or both)

Question 35

Why does stool become darker with time