Ch 53 - Red Blood Cells Flashcards
The packaging of hemoglobin and carbonic anhydrase inside specialized cells called _____________ greatly amplified the capacity of circulating blood to carry oxygen to and carbon dioxide away from peripheral tissues.
erythrocytes
Anemia, a deficiency in the level of circulating hemoglobin (______________), compromises health by reducing the ability of the blood to supply tissues with adequate levels of oxygen.
<120-130 g/L
____________ help staunch the outflow of blood from damaged tissues.
Platelets
Hence, replacements are constantly being produced from precursor _________.
stem cells
Stem cells possess a unique capacity both to produce unaltered daughter cells (__________) and to generate a diverse range of specialized cell types (__________).
self-renewal
Potency
Stem cells may be:
____________ - (capable of producing all the cells in an organism)
____________ - (able to differentiate into cells of any of the three germ layers)
____________ - (produce only cells of a closely related family)
____________ - (produce only one type of cell).
totipotent
pluripotent
multipotent
unipotent
Differentiation of hematopoietic stem cells is regulated by a set of secreted glycoproteins called _____________.
Cytokines
Stem cell factor and several colony stimulating factors collaborate with _______________ to stimulate the proliferation of hematopoietic stem cells in the bone marrow and their commitment to differentiate into one of several myeloid cell types.
interleukins 1, 3, and 6
Binding of _______________ directs myeloid progenitor cells to eventually differentiate into erythrocytes or platelets, respectively.
erythropoietin or thrombopoietin
_____________ Are Devoid of Internal Organelles
Mature Erythrocytes
The structure and composition of red blood cells reflects their highly specialized function: to deliver the maximum quantity of ____________ possible to tissues and aid in the removal _____________, a waste product of cellular respiration, and ________.
oxygen
carbon dioxide
Urea
The interior of a red blood cell contains a massive concentration of hemoglobin, roughly one-third by weight (_______________ for an adult).
30-34 g/dL
As a consequence, _________ are unable to reproduce.
enucleated red blood cells
Their _____________ possesses a much higher ratio of surface area to volume than more spherical geometries.
disc-like configuration
By minimizing the distance to be traversed, these factors promote efficient gas exchange between capillary walls and the rapidly moving (up to ______) erythrocytes.
2 mm/s
Erythrocytes generate ATP exclusively via ___________.
Glycolysis
True or False:
Red blood cells lack mitochondria, and hence the enzymes of the TCA cycle, electron transport chain, β-oxidation pathway, or ATP synthase.
True
Glucose enters red blood cells by ____________, a process mediated by the _______________, also known as glucose permease.
facilitated diffusion
glucose transporter (GLUT1)
The glycolytic pathway in red blood cells also possesses a unique branch, or shunt, whose purpose is to isomerize 1,3-bisphosphoglycerate (1,3,-BPG) to ____________________.
2,3-bisphosphoglycerate (2,3-BPG)
2,3-BPG binds to and stabilizes hemoglobin in the _________.
T-state
Conversion of 1,3-BPG to 2,3-BPG is catalyzed by ______________, a bifunctional enzyme that also catalyzes the hydrolysis of 2,3-BPG to the glycolytic intermediate 3-phosphoglycerate.
2,3-bisphosphoglycerate mutase
A second enzyme, _____________, catalyzes the hydrolysis of 2,3-BPG to the glycolytic intermediate 2-bisphosphoglycerate.
multiple inositol polyphosphate phosphatase
The activities of these enzymes are sensitive to _______, which insures that 2,3-BPG levels rise and fall at the appropriate times during the oxygen transport cycle.
pH
It accounts for ∼2% of the protein of the membrane of the RBC.
GLUT1
GLUT1 exhibits specificity for glucose and related d-hexoses (____________ are not transported).
l-hexoses
The transporter functions at ∼_____% of its Vmax at the physiologic concentration of blood glucose, is saturable, and can be inhibited by certain analogs of glucose.
75%
It is a member of a family of homologous glucose transporters found in mammalian tissues.
GLUT1
GLUT1 is not dependent upon _______, unlike the corresponding carrier in muscle and adipose tissue.
insulin
Its 492 amino acid sequence has been determined.
GLUT1
It transports glucose when inserted into artificial liposomes.
GLUT1
GLUT1 is estimated to contain ____ transmembrane helical segments.
12
It functions by generating a gated pore in the membrane to permit passage of glucose; the pore is conformationally dependent on the presence of glucose and can oscillate rapidly (∼900 times/s).
GLUT1
____________ facilitate CO2 transport.
Carbonic anhydrase
True or False:
Like oxygen, the solubility of carbon dioxide in aqueous solution is low, much too low to accommodate more than a few percent of the CO2 produced by metabolically active tissues.
True
However, the solubility of the hydrated form of CO2, carbonic acid (H2CO3) and its protonic dissociation product, bicarbonate (HCO3−), are relatively ________.
high
The presence in erythrocytes of high levels of the enzyme ______________ enables them both to concentrate waste CO2 by catalyzing its rapid conversion to carbonic acid, and to reverse this process in order to facilitate its expulsion in the lungs.
carbonic anhydrase
While red blood cells carry some CO2 in the form of hemoglobin-bound carbamates, roughly ____% is carried internally as dissolved bicarbonate.
80%
The RBC is highly dependent upon ___________ as its energy source, for which its membrane contains high-affinity glucose transporters.
glucose
___________, producing lactate, is the mode of production of ATP.
Glycolysis
True or False:
Because RBCs lack mitochondria there is no production of ATP by oxidative phosphorylation.
True
The RBC has a variety of transporters that maintain _________ and __________ balance.
ionic and water
Production of ____________ by reactions closely associ-ated with glycolysis is important in regulating the ability of Hb to transport oxygen.
2,3-bisphosphoglycerate
The pentose phosphate pathway of the RBC metabolizes about 5%-10% of the total flux of glucose) and produces NADPH. Hemolytic anemia due to a deficiency of the activity of ______________________ is common.
glucose-6-phosphate dehydrogenas
________________ is important in the metabolism of the RBC, in part to counteract the action of potentially toxic peroxides. The RBC can synthesize ______ and the ______ required to return oxidized glutathione (G-S-S-G) to the reduced state GSH.
Reduced glutathione (GSH) GSH and NADPH
The iron of Hb must be maintained in the ___________. Ferric iron is reduced to the ferrous state by the action of an NADH-dependent ____________________ involving __________ and ___________.
ferrous state
methemoglobin reductase system
cytochrome b5 reductase and cytochrome b5
True or False:
While biosynthesis of glycogen, fatty acids, protein, and nucleic acids does not occur in the RBC, some lipids (eg, cholesterol) in the red cell membrane can’t exchange with corresponding plasma lipids.
False: Some lipids (eg, cholesterol) in the red cell membrane CAN exchange with corresponding plasma lipids.
The RBC contains certain enzymes of nucleotide metabolism (eg, _____________, _____________ and ___________). Deficiencies of these enzymes are involved in some cases of hemolytic anemia.
adenosine deaminase
pyrimidine nucleotidase
adenylyl kinase
When RBCs reach the end of their lifespan, the globin is degraded to _____________ (which are reutilized in the body), the iron is released from heme and reutilized, and the tetrapyrrole component of heme is converted to _____________, which is mainly excreted into the bowel via the bile.
Amino acids
Bilirubin
Newly formed red blood cells retain portions of the __________, __________, _________, etc that were present in their nucleated precursors.
ribosomes, endoplasmic reticulum, mitochondria
