Harvey Chapter 4 Evaluation of Erythrocytes PART I AKG Flashcards
Esterified or non-esterifide cholesterol increases fluidity of the RBC membrane?
Esterified - it is builker and ‘packs’ more loosely
How does the degree of saturation of phospholipid fatty acids affect RBC membrane fluidity?
More saturation –> better ‘packing’ –> decreases fluidity of the membrane
What is the predominant cytoskeletal protein within RBCs?
Alpha and beta sepctrin
This cytoskeletal RBC protein:
- binds spectrin along with protein 4.1
- involved in junctional complexes that link cytoskeleton to cell membrane
Actin
This cytoskeletal RBC protein:
- part of actin junctional complex (binds glycophorins and band 3)
- Binds both ß-spectrin and actin to strengthen the spectrin-actin interaction
Protein 4.1
This cytoskeletal protein attaches ß-spectrin to band 3 tetramers.
Ankyrin
What is the integral membrane protein responible for:
- (1) anchoring cytoskeleton to the membrane
- (2) anion exchange (delivering CO2 to the lungs in exchange for Cl-)
- (3) Binding of glycolytic enzymes, hemoglobin and hemichromes
Band 3 (“anion exchange protein”)
Which integral membrane protein is heavily glycosylated and responsible for:
- Carrying most of the sialic acid residues, and therefore negative charge on the surface of RBCs
Glycophorin
Each RBC contains approximately ____ hemoglobin molecules.
A. 2.5 billion
B. 250 million
C. 250,000
D. 25
B. 250 million
Describe the structure/composition of hemoglobin
- Hemoglobin is a tetramer:
- Two α- and two β-polypeptide globin chains (4 globins total) + 4 heme proteins.
- Each globin is linked to a separate heme that binds oxygen
- The heme prosthetic group is held firmly within a hydrophobic cleft
- Non-polar side of heme is positioned in the hydrophobic pocket of each globin chain
α-globulins in hemoglobin bind and transport _____
ß-globulins in hemoglobin binds _____
CO2
2,3-DPG
List the steps of heme synthesis and where they occur within the cell.
Mitochondria –> cytosol –> mitochondria
- Mitochondria: glycine + succinyl CoA –5-ALA synthase –> delta-ALA
- Cytosol: delta ALA –porphobilinogen synthase–> porphobilinogen –> protoporphyrin IX
- Mitochondria: Protoporphyrin IX + Fe2+ –ferrochelatase enzyme–> heme
List the enzymes that are inhibited by lead in heme synthesis.
What are thhe subsequent consequences?
- 5-ALA synthase
- Porphobilinogen synthase
- Ferrochelatase
- Coproporphyrinogen oxidase
Build up of porphyrins in RBCs, plasma, and/or urine (aka porphyria) - these animals are prone to photosensitivtiy.
Early in hemoglobin synthesis, 5-ALA synthase requires a co-factor to make delta-ALA. What is this cofactor?
B6 (pyridoxine)
How is free hemoglobin as a result of IVH normally cleared?
Binds to haptoglobin and the complex is cleared by macrophages
If free hemoglobin exceeds binding capacity of haptoglobin, hemoglobin is cleared by the kidneys (hemoglobinuria)
Heme catabolism starts with cleavage of the heme ring mediated by ______ which releases linear tetrapyrrole biliverdin, iron, and carbon monoxide. This enzyme is highest in which organ?
heme oxygenase
it’s activity is highest int he spleen; some ativity in the liver, BM, and renal tubular cells
During heme catabolism, once iron is released, it is oxidized to the ____ form and is released and trasnported as ______ and stored as ____ or ____ in the liver and BM for subsequent reuse.
ferric
transferrin
hemosiderin or ferritin
After biliverdin is released from cleavage of the heme ring mediated by heme oxygenase that occurs during heme catabolism, list what happens to biliverdin next in mammals vs birds.
Mammals:
- Biliverdin reduced to bilirubin within macrophages via bilirubin reductase
- Bilirubin binds to albumin to remain soluble in plasma and the complex is transported to the liver
- Hepatocyte uptakes bilirubin and conjugates it to glucuronic acid via glucuronyl transferase
- Hepatocytes transport bilirubin glucuronide into bile canaliculi –> rate limiting step. (small amount is released into circulation)
Birds:
- Birds lack biliverdin reductase, so avian bile contains biliverdin - very green bile compared to yellow/green bile in mammals
Sheep and goats synthesize hemoglobin ___ in response to severe anemia (mediated by EPO).
hemoglobin C
What are the two hemoglobin confirmations? Where do they mostly occur within the body?
What is the relationship between the confirmations and oxygen affinity and 2,3-DPG affinity?
- R (relaxed): lungs
- High O2 affinity
- Low affinity for 2,3-DPG
- T (tense): metabolically active tissue
- Low O2 affinity (deoxyHgb)
- High affinity for 2,3-DPG
2,3DPG is an organic phosphate that binds to hemoglobin and ____\_ oxygen-binding affinity of hemoglobin in RBCs.
decreases
2,3-DPG is highest in which species and lowest in which?
- Highest in: rabbits, pigs, horses rats
- Moderate in: humans and dogs
- Very low in: cats and ruminants
- Low to absent in birds (birds can use insoitol pentaphosphate as an alternative to 2,3 DPG)
Hypophosphatemia and acidosis ___ 2,3-DPG synthesis
Increases in [phosphate] and alkalemia (e.g., hypoxia - respiratory alkalosis) ____ 2,3-DPG synthesis.
decrease
increase
Define the Bohr effect
A decrease in hemoglobin oxygen-affinity in response to a lowered blood pH resulting from an increased concentration of CO2 in the blood.
*so hemoglobin oxygen binding affinity is inversely related to aciditiy (H+) and CO2. Acidity and/or high CO2 in blood (as seen in metabolically active tissues) shifts the oxygen-hemoglobin dissociation curve right (promote T conformation to let go of oxgyen). Conversely, low CO2 and higher pH (as seen in the lungs), shifts the O2-hemoglobin dissociation curve to the left (promote R conformation - to hold onto oxygen).
Please draw the oxygen-hemoglobin dissociation curve. Label the x and y axis, and draw and describe what drives the curve to shift to the left and right (DPG, pH, CO2, temp).
What are the three man functions of erythrocytes?
- Transport O2 to tissue
- Transport CO2 to the lungs
- Buffering hydrogen ions (Deoxyhemoglobin is a weaker acid than oxyhemoglobin → when oxyhemoglobin releases O2 in tissues, the formation of deoxyhemoglobin results in increased binding of H+, buffering the effects of H2CO3 and allows for the isohydric transport of CO2)
Which species have high intracellular potassium d/t high Na/K ATPase activity?
Horse
Pig
Some ruminants
Japanese and korean dogs
Some dogs have increased glutamate tarnsport, which results in high reduced glutathione (GSH) concentrations. This promotes the replication of which organism within RBCs?
Babesia gibsoni
What is the primary substrate for energy needs of all RBCs in mammals? What is the exception?
Glucose
Except pig RBCs, which use inosine.
Pig RBCs are poorly permeable to glucose because they lack functional glucose transporter.
Glucose enters RBCs and is phosphorylated to G6P via hexokinase. It can then either be metabolized via ____ pathway or ____ pathway.
Embden-Meyerhof pathway (anaerobic glycolysis)
Pentose phosphate pathway
Mature RBCs undergo kreb’s cycle for energy. T/F
False - they use embden-meyerhof pathway (anaerobic glycolysis) becuase they do not have nucleus, ribosomes, mitochondria, and ER.
____ blood inorganic phosphate concentration and ____ blood pH stimulate anaerobic glycolysis via EMP.
↓ or ↑
↑
Hemolytic anemia in diabetic dogs and cats and post-parturient cattle and a cat with hepatic lipidosis results from decreased ______ which decreases RBC glycolic rates and ultimately decreases ATP generation.
Phosphorous (hypophsophatemia)
Methemoglobin is formed when hemoglobin iron is oxidized from the ___ to the ___ state.
ferrous (2+) to the ferric (3+)
NADPH generated by the ____ in RBCs provides electrons to protect against oxidants by maintaining glutathione and thioredoxin in their reduced states.
Pentose phosphate pathway (PPP)
About 3% of hemoglobin (Fe2+) is oxidized to methemoglobin (Fe3+) each day; methemoglobin is reduced back to hemoglobin in a reaction requiring both __________ and _______ generated by anaerobic glycolysis.
cytochrome-b5 reductase and NADH