5) RBC destruction

Question 1

gradually stop working as cell ages

Answer 1

enzymes (cannot make more)
EM pathway
HMS

Question 2

3 mechanisms of RBC removal

Answer 2

• spleen (cells with mild or subtle abnormalities)
• liver (more severely injured cells)
• intravascular hemolysis

Question 3

best at destroying RBCs with minimal defects

Answer 3

spleen

Question 4

when a large number of RBCs are damaged, most will be removed by the ———, because…

Answer 4

liver
35% blood flow compared to 5%

Question 5

——-% of RBC destruction is extravascular

Answer 5

80-90

Question 6

hemoglobin and hemosiderin in urine associated with…

Answer 6

intravascular hemolysis

Question 7

Extravascular heme degradation

• ring broken at alphamethine bridge by ————
• produces ————, reduced to bilirubin by ————
• bilirubin+————- (unconjugated) → liver
• conjugated with ———— → bile duct into ————
• further converted to urobilinogen, stercobilinogen, mesobilinogen
• ————% of urobilinogen reabsorbed, excreted by ———— or returned to ————

Answer 7

• ring broken at alphamethine bridge by heme oxygenase
• produces biliverdin, reduced to bilirubin by biliverdin reductase
• bilirubin-albumin (unconjugated) → liver
• conjugated with glucaronic acid → bile duct into duodenum
• further converted to urobilinogen, stercobilinogen, mesobilinogen
• 10-20% of urobilinogen reabsorbed, excreted by kidneys or returned to liver

Question 8

Extravascular hemoglobin degradation

Carbon atom:
Iron:
Globin:

Answer 8

Carbon atom: exhaled as CO
Iron: returned to marrow, or stored as ferritin or hemosiderin
Globin: AAs returned to plasma protein pool

Question 9

plasma proteins involved in intravascular hemolysis

Answer 9

haptoglobin
hemopexin

Question 10

Haptoglobin
- Glyco——–
- Strong affinity for ——
- Made in ———
- Concentration expressed in…
- Resembles…

Answer 10

• Glycoprotein
• Hgb
• liver
• free haptoglobin (binding capacity)
• Ig

Question 11

Haptoglobin is able to bind…

Answer 11

• oxyHgb
• mHgb
• isolated alpha chains
• alpha-beta dimers

Question 12

Haptoglobin is not able to bind…

Answer 12

• deoxyHgb
• myoglobin
• heme
• hemoglobins H or Bart
• isolated beta chains

Question 13

binding is irreversible; must be broken down by liver

Answer 13

Haptoglobin + Hgb

Question 14

when haptoglobin binding capacity is exceeded…

Answer 14

free Hgb dissociated into dimers, and passes into glomerular filtrate

reabsorbed into tubules, converted to hemosiderin

excreted into urine

Question 15

hemoglobinuria occurs when…

Answer 15

capacity of renal tubules to convert it to hemosiderin is exceeded

Question 16

hemoglobin not bound to haptoglobin nor processed by kidneys…

Answer 16

oxidized to mHgb
dissociated into heme (3+) and globin
heme groups taken up by hemopexin, taken to liver
globins return to AA pool

Question 17

if hemopexin’s capacity for binding heme is exceeded…

Answer 17

heme is bound to albumin (methemalbumin)
held until additional hemopexin is available