Section 6: RBC structure & function Flashcards
Where is the lipid bilayer located on the red cell?
Function of the lipid bilayer
Outside part the RBCs
-insoluble barrier that separate vastly different environments.
Function of protein membrane skeleton
-gives structure, shape, & deformability
-proteins on surface of cell act as receptors, RBC antigens & enzymes
-contains pumps/ channels for movement of ions b/w interior of the RBC & the plasma
what do Integral proteins do? (give example of one)
they go across the lipid bilayer
ex- sialic acid = gives RBC their negative charge so that they don’t stick together
Peripheral proteins (give example of one)
interact w/ lipids at membrane surface but DON’T penetrate bilayer
ex- spectrin = cytoskeleton which modulates shape & deformability
^ they deform (form biconcave shape) reduce flow resistance
Osmotic balance b/w plasma & cytoplasm in Isotonic vs hypotonic vs hypertonic
-Isotonic (normal) = normal RBC
-Hypotonic (dilute) = RBC swelling
-Hypertonic (concentrated) = shrunken RBC
What are the 4 metabolic pathways of RBCs?
-Embden-Meyerhof pathway
-Hexose monophosphate pathway
-Rapoport - Luebering pathway
-Methemoglobin pathway
Embden - Meyerhof pathway does what in RBCs?
Anaerobic glycolysis = main way RBC gets energy
90-95% of glucose consumption w/ net gain of 2 ATP
Which is the most common enzyme deficiency in the Embden-Meyerhof pathway?
Pyruvate kinase
May result inadequate ATP production? — Dawn clarification
Hexose monophosphate pathway does what in RBCs?
Aerobic glycolysis = combats oxidative injury to RBC
Which is the most common enzyme deficiency in the hexose monophosphate pathway?
A deficiency in (G6PD) can result in Abnormal RBC morphology
Rapoport - Luebering pathway does what in RBCs?
Regulates O2 delivery to tissues
Why is 2,3-biphosphoglycerate (2,3-BPG) an important enzyme?
-important control for Hgb affinity for O2
deficiency can results in inadequate ATP production?
The methemoglobin reductase pathways does what?
Maintains hemoglobin in its reduced (Fe2+) state by reducing Fe3+
Why is methemoglobin reductase enzyme an important enzyme?
It reduces (Fe3+) into (Fe2+) which allows it to carry O2
deficiency can be due to
-hereditary enzyme deficiency
-toxic substance exposure
-abnormal Hgb M disease
What does cyanosis mean?
Met-Hgb can’t carry O2 so the skin gets blue discoloration
Structure of Hemoglobin
- Heme — a protoporphyrin ring (pyrole ring) w/ a central ferrous (Fe2+) iron
- Globin — polypeptide chain w/ (141-146) amino acids
- 1 Hemoglobin-A molecule = 4 heme + 4 polypeptide chains (2 Alpha, 2 Beta)
Note: variations in amino acids create different globin chains
Heme iron
In the ferrous Fe2+ form
Transferrin
Plasma transport protein that carries iron in the ferric form Fe3+
Ferritin
Is (Iron + apoferritin) = major storage form of iron
Hemosiderin
- Intracellular storage form of iron
- Breakdown product of ferritin
Birth hemoglobin type ratios (hint: Hgb X has which polypeptide chains and what percentage of babies have Hgb X?)
- Hgb F (2α, 2γ) is 60-90%
- Hgb A (2α, 2β) is 40-10%
- ratios slowly reverts to adults ratio @ ~6 months
Adult hemoglobin ratios (hint: Hgb X has which polypeptide chains and what percentage of adults have Hgb X?)
- Hgb A (2α, 2β) > 95%
- Hgb A2 (2α, 2δ) ~ 2%
- Hgb F (2α, 2γ) ~ 1-2%
What is respiratory movement?
Process of loading & unloading O2
Describe the process of unloading O2 in the tissues
- Oxygen unloading increases the space between beta chains, which gives room for 2,3-BPG to bind hemoglobin and create deoxyhemoglobin
- Salt bridges form to stabilize
= 2,3-BPG-bound hemoglobin has lower affinity for oxygen
Describe the process of loading O2 in lung
- 2,3-BPG is expelled resulting in oxyhemoglobin
- salt bridges are broken down
- beta chains pull together
- Oxyhemoglobin has high affinity for O2
What is the normal Oxygen dissociation curve P50 reference range?
26-30 mm Hg of tissue PO2
P50 values
PO2 at which Hgb is 50% saturated with O2 under standard condition (Temp & pH)
Reference range: P50 = 26-30mm Hg
Increased abnormal Hgb (of certain types, such as methemoglobin) or pH shifts the oxygen dissociation curve in which direction?
Left shift
Decreased BPG, temp, or P50 shifts the oxygen dissociation curve in which direction?
Left shift
Increased: BPG, temp or P50 shifts the oxygen dissociation curve in which direction?
Right shift
Decreased pH shifts the oxygen dissociation curve in which direction?
Right shift
Methemoglobin (how is it formed, causes, results of toxic levels)
Formed by reversible oxidation of iron to Fe3+ state; Oxidized Fe can’t bind to O2
Causes:
- oxidants such as nitrites
- decreased activity of methemoglobin reductase
- inherited in M disease - Abnormal globin structure
- Results of toxic levels: Decreased O2 delivery to tissues because conformational Hgb molecule changes, and O2 affinity to other heme groups increases, resulting in Left shift. Cyanosis occurs due to methemoglobinemia
Sulfhemoglobin (how is it formed, causes, results of toxic levels)
Formed by irreversible oxidation of Hgb
Causes: Certain drugs/chemicals such as Sulfonamides
Results of toxic levels:
100x less affinity for O2 ~ ineffective for O2 transport, which causes left shift because of decreased oxygen affinity
Carboxyhemoglobin (how is it formed, causes, results of toxic levels)
Formed by binding of Carbon monoxide (CO) to heme iron
Causes: carbon monoxide exposure
Results of toxic levels:
Hgb has 200x more affinity for CO than O2, though CO binds more slowly but stronger. Results in cherry red colored blood (particularly venous blood)
Describe the 2,3 BPG levels, P50 shift, and RBC efficiency when the oxygen dissociation curve shifts to the LEFT. What kind of phenomenon causes this shift?
- Decreased 2,3-BPG = increased Hgb affinity for O2 & decreased O2 release to tissues
Decrease in P50 = increase in O2 affinity - RBC are less efficient because bind oxygen more strongly than in normal curve
- Abnormal Hbg causes this shift
Describe the 2,3 BPG levels, P50 shift, and RBC efficiency when the oxygen dissociation curve shifts to the RIGHT. What is the compensatory shift?
-Increased 2,3-BPG = decreases Hgb affinity for O2 & increases O2 delivery to tissues
Increase in P50 = decreased O2 affinity
-RBCs have become more efficient because less PO2 required to release same amount of oxygen as in normal curve (e.g., at 40 mmHG PO2 in normal curve, release 25% O2 to tissues. In right shift, release ups 50% O2 to tissues at same PO2).
-Hypoxia is the compensatory shift because want to release less oxygen (right shift releases too much oxygen)
What does the P50 value mean?
It is the mmHG of tissue PO2 required for 50% saturation of RBCs. In other words, 50% of RBCs are saturated with oxygen at x mmHG of O2
List the 3 types of modified Hgbs
- Hethemoglobin
- Sulfhemoglobin
- Carboxyhemoglobin
What are other names for conjugated and unconjugated bilirubin?
Conjugated BR = direct
Unconjugated = indirect
What is the byproduct of Hgb catabolism?
Bilirubin
What is the carrier protein of unconjugated (indirect) bilirubin? To which organ does it transport?
Albumin transports indirect BR to the liver
What is cyanosis?
Blue discoloration of the skin
The majority of hemolysis is intravascular or extravascular?
Extravascular
Explain process of extravascular hemolysis
Also pg. 74 in textbook
1. Start in spleen or bone marrow where RBC is lysed and releases heme
2. Transferrin transports iron back to bone marrow, globin chains recycled back in to amino acid pool, and protoporphyrin ring opens to become biliverdin, which gets converted to indirect bilirubin (BR)
3. Albumin carrier protein binds indirect BR and transports to liver
4. Glucuronyl transferase metabolizes indirect BR + glucuronic acid to form conjugated (direct) BR
5. Conjugated BR travels to intestines, where bacteria convert it to urobilinogen.
6. Urobilinogen can be found in stool, rejoin general circulation, or pass through glomerulus in kidneys such that some can be found in urine. No BR found in the stool or urine!
Explain the process of intravascular hemolysis
- Haptoglobin binds Hgb dimers after Hgb broke down, where it transports to liver. The rest of the process is same as extravascular pathway
- If Hgb NOT bound by haptoglobin, then filtered through kidney
- If Hgb NOT filtered through kidney, then oxidized to methemoglobin, which is disassembled into metheme and globin
- Metheme bound by hemopexin and transported to liver
What does hemopexin bind? What happens when hemopexin is depleted?
Binds metheme. When depleted, metheme binds albumin to become methalbumin and gives blood a brown tinge. Will circulate in this form until more hemopexin formed by liver
List the major organs involved in extravascular/intravascular hemolysis
-Spleen
-Liver
-Kidney
-Bone marrow
List carrier proteins in extravascular hemolysis and intravascular hemolysis
Extravascular: transferrin, albumin
Intravascular: Haptoglobin, albumin, hemopexin, transferrin
