1 chapter 3 the red blood cell: structure and function

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Chapter 3Chapter 3The Red Blood Cell:The Red Blood Cell:

Structure and FunctionStructure and Function

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1. Study Questions1. Study Questions2. Homework 2. Homework AssignmentAssignment3. Exam for Chapter 3 & 3. Exam for Chapter 3 & 55

on Sept 27 on Sept 27

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The Red Blood Cell: The Red Blood Cell: Structure and FunctionStructure and Function

► In this chapter, you will learn the basic In this chapter, you will learn the basic structure and functions of the structure and functions of the erythrocyte. Also covered in this chapter erythrocyte. Also covered in this chapter is the formation and functions of is the formation and functions of hemoglobin. You will learn how changes hemoglobin. You will learn how changes in the structure of hemoglobin affect its in the structure of hemoglobin affect its functions. RBC metabolic pathways are functions. RBC metabolic pathways are discussed. Finally, the processes of RBC discussed. Finally, the processes of RBC destruction will be covered. destruction will be covered.

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Red Cell Red Cell Structure Structure

and and FunctionFunction

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Introduction to RBC FunctionIntroduction to RBC Function

►Three areas of RBC metabolism Three areas of RBC metabolism essential for survival and function: essential for survival and function: RBC membraneRBC membrane Hemoglobin structure and functionHemoglobin structure and function Cellular energetics Cellular energetics

►Defects in any area results in impaired Defects in any area results in impaired RBC survival (RBCs have normal 120 RBC survival (RBCs have normal 120 day life span).day life span).

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RBC Membrane RBC Membrane 1 of 31 of 3

►RBC membrane is a three layer structure: RBC membrane is a three layer structure: an outer hydrophilic portion composed of an outer hydrophilic portion composed of

glycolipid, glycoprotein, and protein glycolipid, glycoprotein, and protein a central hydrophobic layer containing a central hydrophobic layer containing

protein, cholesterol, and phospholipidprotein, cholesterol, and phospholipid an inner hydrophilic layer containing protein an inner hydrophilic layer containing protein

►Membrane is very elastic. Membrane is very elastic. ►Membrane is a semi-permeable lipid bi-Membrane is a semi-permeable lipid bi-

layer supported by a mesh-like layer supported by a mesh-like cytoskeleton. cytoskeleton.

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►Cytoskeleton:Cytoskeleton: Network of proteins on the inner surface Network of proteins on the inner surface

of the plasma membrane, called the of the plasma membrane, called the peripheral membrane proteins peripheral membrane proteins

Responsible for maintaining shape, Responsible for maintaining shape, stability, and deformability of RBC stability, and deformability of RBC

►Lipid bi-layer contains equal amounts Lipid bi-layer contains equal amounts of cholesterol and phospholipids with of cholesterol and phospholipids with proteins scattered throughout. proteins scattered throughout.

See Figure 3-2 on page 60

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►Integral membrane proteinsIntegral membrane proteins:: Extend from outer surface and transverse Extend from outer surface and transverse

entire membrane to inner surface entire membrane to inner surface

►Peripheral proteinsPeripheral proteins:: Limited to cytoplasmic surface of Limited to cytoplasmic surface of

membrane and forms the RBC cytoskeletonmembrane and forms the RBC cytoskeleton

NOTE: They aren’t really “peripheral” to the NOTE: They aren’t really “peripheral” to the RBC, since they are within the RBC RBC, since they are within the RBC membranemembrane

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RBC Membrane ProteinsRBC Membrane Proteins

►The two most important protein The two most important protein constituents include:constituents include:

Glycophorin Glycophorin (an integral membrane (an integral membrane protein) protein)

SpectrinSpectrin (a peripheral membrane protein (a peripheral membrane protein of the cytoskeleton)of the cytoskeleton)

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Integral Membrane Proteins Integral Membrane Proteins 1 of 21 of 2

►Glycophorin is the principle RBC Glycophorin is the principle RBC glycoprotein. Spans entire thickness glycoprotein. Spans entire thickness of lipid bilayer and appears on external of lipid bilayer and appears on external surface of RBC membrane, accounting surface of RBC membrane, accounting for location of many RBC antigens. for location of many RBC antigens.

►Three types of glycophorins identified: Three types of glycophorins identified: A, B, and C. A, B, and C.

►All glycophorins carry RBC antigens All glycophorins carry RBC antigens and are receptors or transport and are receptors or transport proteins.proteins.

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Integral Membrane Proteins Integral Membrane Proteins 2 of 22 of 2

►The plasma membrane is anchored to the The plasma membrane is anchored to the RBC cytoskeleton through the tethering RBC cytoskeleton through the tethering sites of integral proteins located in the sites of integral proteins located in the lipid bilayer. lipid bilayer.

►The lipid bilayer plus the integral proteins The lipid bilayer plus the integral proteins chemically isolate and regulate the cell chemically isolate and regulate the cell interior. interior.

►Cytoskeleton provides rigid support and Cytoskeleton provides rigid support and stability to lipid bilayer. Is also stability to lipid bilayer. Is also responsible for deformability properties responsible for deformability properties of the RBC membrane, leading to shape of the RBC membrane, leading to shape change.change.

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Peripheral Proteins Peripheral Proteins 1 of 31 of 3

►The major peripheral proteins that The major peripheral proteins that make up the cytoskeleton include: make up the cytoskeleton include: SpectrinSpectrin AnkyrinAnkyrin Protein 4.1Protein 4.1 ActinActin

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► Spectrin:Spectrin: The most abundant peripheral proteinThe most abundant peripheral protein Flexible, rodlike molecule composed of an alpha Flexible, rodlike molecule composed of an alpha

helix of two polypeptide chainshelix of two polypeptide chains Is an important factor in RBC membrane integrity Is an important factor in RBC membrane integrity

because it binds with other peripheral proteins to because it binds with other peripheral proteins to form the skeletal network of microfilaments on form the skeletal network of microfilaments on the inner surface of RBC membranethe inner surface of RBC membrane

Microfilaments strengthen membrane, protecting Microfilaments strengthen membrane, protecting cell from being brokencell from being broken

Controls biconcave shape and deformability of Controls biconcave shape and deformability of cell cell

Cytoskeletal network also provides stability to Cytoskeletal network also provides stability to lipid bilayer. lipid bilayer.

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►Ankyrin:Ankyrin: Primarily anchors lipid bilayer to Primarily anchors lipid bilayer to

membrane skeleton membrane skeleton ►Protein 4.1:Protein 4.1:

May link the cytoskeleton to the May link the cytoskeleton to the membrane by means of its membrane by means of its associations with glycophorinassociations with glycophorin

►Actin:Actin: Responsible for contraction and Responsible for contraction and

relaxation of membranerelaxation of membrane

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Deformability Deformability 1 of 21 of 2

►Critical to RBC survival as it travels Critical to RBC survival as it travels through microvasculature. Also through microvasculature. Also essential for oxygen delivery. essential for oxygen delivery.

►Loss of ATP (energy) leads to decrease Loss of ATP (energy) leads to decrease in phosphorylation of spectrin, which, in phosphorylation of spectrin, which, in turn, leads to loss of membrane in turn, leads to loss of membrane deformability. Also leads to deformability. Also leads to accumulation of calcium in membrane accumulation of calcium in membrane causing an increase in membrane causing an increase in membrane rigidity and loss of pliability. rigidity and loss of pliability.

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Deformability Deformability 2 of 22 of 2

► Cells lacking flexibility quickly removed from Cells lacking flexibility quickly removed from circulatory system. Spleen responsible for circulatory system. Spleen responsible for removal of RBCs. removal of RBCs.

► Rigid parts of cell membrane may be Rigid parts of cell membrane may be removed, resulting in malformed cells - removed, resulting in malformed cells - spherocytes and "bite" cells. spherocytes and "bite" cells.

► Lack of deformability shortens survival time. Lack of deformability shortens survival time. ► Sometimes deformability is reversible. Sometimes deformability is reversible. ►Discoid shape most efficient form to Discoid shape most efficient form to

maximize ratio of surface area to cell maximize ratio of surface area to cell volume.volume.

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Permeability Permeability 1 of 21 of 2

► RBC membrane freely permeable to water and RBC membrane freely permeable to water and anions (chloride and bicarbonate). anions (chloride and bicarbonate).

► Exchange of anions between internal Exchange of anions between internal environment of cell and external environment environment of cell and external environment facilitated by exchange channels. facilitated by exchange channels.

► RBC membrane relatively impermeable to RBC membrane relatively impermeable to cations (primarily sodium and potassium). Is cations (primarily sodium and potassium). Is through control of sodium and potassium through control of sodium and potassium intracellular concentrations that RBC maintains intracellular concentrations that RBC maintains its volume and water homeostasis. its volume and water homeostasis.

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Permeability Permeability 2 of 22 of 2

►Passive influx of sodium and Passive influx of sodium and potassium cations controlled by cation potassium cations controlled by cation pumps that actively transport sodium pumps that actively transport sodium out of the cell and potassium into the out of the cell and potassium into the cell. Is an energy (ATP) pump. cell. Is an energy (ATP) pump. Transport also requires sodium-Transport also requires sodium-potassium ATPase enzyme. potassium ATPase enzyme.

►Also a calcium-ATPase pump to Also a calcium-ATPase pump to remove calcium cations from interior remove calcium cations from interior of cell to exterior of cell.of cell to exterior of cell.

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Red Cell Membrane LipidsRed Cell Membrane Lipids

►1. Phospholipids1. Phospholipids►2. Glycolipids and 2. Glycolipids and

CholesterolCholesterol

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PhospholipidsPhospholipids

► Erythrocyte membrane lipid consists of bilayer Erythrocyte membrane lipid consists of bilayer of phospholipids intermingled with molecules of of phospholipids intermingled with molecules of cholesterol in nearly equal amounts. Also cholesterol in nearly equal amounts. Also small amounts of free fatty acids and small amounts of free fatty acids and glycolipids. glycolipids.

►Different types of phospholipids are found on Different types of phospholipids are found on the inside layer than on the outside layer. The the inside layer than on the outside layer. The orientation of these phospholipids, and ratios orientation of these phospholipids, and ratios of them, are important to proper transport of of them, are important to proper transport of substances in and out of the RBC. substances in and out of the RBC. Abnormalities in the phospholipids may result Abnormalities in the phospholipids may result in decreased deformability and decreased red in decreased deformability and decreased red cell survival (extravascular or intravascular cell survival (extravascular or intravascular hemolysis).hemolysis).

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Glycolipids and CholesterolGlycolipids and Cholesterol

► Most of glycolipids are located in outer half of Most of glycolipids are located in outer half of lipid bilayer and interact with glycoproteins to lipid bilayer and interact with glycoproteins to form many of RBC antigens. form many of RBC antigens.

► Cholesterol equally distributed on both sides of Cholesterol equally distributed on both sides of lipid bilayer. Is 25% of RBC membrane lipid lipid bilayer. Is 25% of RBC membrane lipid content. RBC membrane cholesterol is in content. RBC membrane cholesterol is in continual exchange with plasma cholesterol. continual exchange with plasma cholesterol.

► Cholesterol plays important role in regulating Cholesterol plays important role in regulating membrane fluidity and permeability. membrane fluidity and permeability.

► Accumulation of cholesterol can result in Accumulation of cholesterol can result in formation of target cells, acanthocytes, bite cells, formation of target cells, acanthocytes, bite cells, and spherocytes. and spherocytes.

► Accumulation of cholesterol results in decreased Accumulation of cholesterol results in decreased deformability and may lead to hemolytic anemia. deformability and may lead to hemolytic anemia.

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Hemoglobin Hemoglobin SynthesisSynthesis

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Introduction to Hemoglobin Introduction to Hemoglobin SynthesisSynthesis

►Hemoglobin is a conjugated globular protein. Hemoglobin is a conjugated globular protein. ►Constitutes about 95% of RBC's dry weight. Constitutes about 95% of RBC's dry weight. ►About 65% of Hgb synthesis occurs during About 65% of Hgb synthesis occurs during

nucleated stages of RBC maturation, and 35% nucleated stages of RBC maturation, and 35% occurs during the reticulocyte stage. occurs during the reticulocyte stage.

Textbook pg 64

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Introduction to Hemoglobin Introduction to Hemoglobin Synthesis Synthesis (cont.)(cont.)

►Normal hemoglobin consists of Normal hemoglobin consists of globinglobin (a tetramer of two parts of (a tetramer of two parts of unlike globin polypeptide chains) and unlike globin polypeptide chains) and four four heme groupsheme groups, each of which , each of which contains a contains a protoporphyrin ring protoporphyrin ring plusplus ironiron. Also contains one molecule of . Also contains one molecule of 2,3-DPG2,3-DPG (2,3-diphosphoglycerate). (2,3-diphosphoglycerate).

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Glossary DefinitionsGlossary Definitions

►Globin:Globin: A protein constituent of hemoglobinA protein constituent of hemoglobin There are 4 globin chains in the There are 4 globin chains in the

hemoglobin (Hgb) moleculehemoglobin (Hgb) molecule

►Heme:Heme: The iron-containing protoporphyrin The iron-containing protoporphyrin

portion of the Hgb wherein the iron is in portion of the Hgb wherein the iron is in the ferrous (Fethe ferrous (Fe2+2+) state) state

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Hemoglobin SynthesisHemoglobin Synthesis

►Depends on three processes: Depends on three processes: 1. adequate supply and delivery of 1. adequate supply and delivery of

iron; iron; 2. adequate synthesis of 2. adequate synthesis of

protoporphorins (heme protoporphorins (heme precursor); precursor);

3. adequate globin synthesis 3. adequate globin synthesis

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Iron Delivery and Supply Iron Delivery and Supply 1 of 31 of 3

► Iron delivered to Iron delivered to membrane of RBC membrane of RBC precursor by protein precursor by protein carrier carrier transferrintransferrin. .

►Most of the iron that Most of the iron that crosses membrane and crosses membrane and enters cytoplasm of cell is enters cytoplasm of cell is committed to hemoglobin committed to hemoglobin synthesis. Proceeds to synthesis. Proceeds to mitochondria for insertion mitochondria for insertion into into protoporphyrin protoporphyrin ringring to form to form hemeheme. .

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► Excess iron in Excess iron in cytoplasm aggregates cytoplasm aggregates as as ferritinferritin. Amount of . Amount of ferritin stored depends ferritin stored depends on ratio between level on ratio between level of plasma iron and of plasma iron and amount of iron required amount of iron required by erythrocyte for by erythrocyte for hemoglobin synthesis. hemoglobin synthesis.

► Two-thirds of total iron Two-thirds of total iron supply is bound to supply is bound to heme in hemoglobin.heme in hemoglobin.

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►Sideroblast:Sideroblast: A ferritin-containing normoblast A ferritin-containing normoblast

(nucleated RBC) in the bone marrow. (nucleated RBC) in the bone marrow. It makes up from 20% to 90% of It makes up from 20% to 90% of

normoblasts in the marrow.normoblasts in the marrow.►Siderocyte:Siderocyte:

A nonnucleated red blood cell containing A nonnucleated red blood cell containing iron in a form other than hematin.iron in a form other than hematin.

Confirmed by a specific iron stain such as Confirmed by a specific iron stain such as the Prussian blue reaction.the Prussian blue reaction.

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Synthesis of Protoporphyrins Synthesis of Protoporphyrins 1 of 31 of 3

► Begins in mitochondria with Begins in mitochondria with formation of formation of delta-delta-aminolevulinic acidaminolevulinic acid from from glycineglycine and and succinyl succinyl coenzyme Acoenzyme A (CoA). Is the (CoA). Is the major rate controlling step in major rate controlling step in heme biosynthesis. heme biosynthesis.

► Enzyme, Enzyme, delta delta aminolevulinic acid aminolevulinic acid synthetasesynthetase (delta ALA) (delta ALA) mediates this reaction. mediates this reaction. Amount of enzyme influenced Amount of enzyme influenced by amount of erythropoietin by amount of erythropoietin and Vitamin B6 available. and Vitamin B6 available.

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► PorphyrinogensPorphyrinogens are are intermediate products in intermediate products in heme synthesis. If any one heme synthesis. If any one of normal enzyme steps in of normal enzyme steps in heme synthesis blocked, heme synthesis blocked, excessive formation of excessive formation of porphyrins can occur. porphyrins can occur. Results in condition called Results in condition called porphyriaporphyria. .

► Protoporphyrinogen IXProtoporphyrinogen IX is is last porphyrinogen formed. last porphyrinogen formed. Becomes Becomes Protoporphyrin Protoporphyrin IXIX. .

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► Once Protoporphyrin IX Once Protoporphyrin IX formed, iron formed, iron (Fe(Fe2+2+) ) is is inserted into its ring inserted into its ring structure. Once iron has structure. Once iron has been inserted, a been inserted, a HEMEHEME molecule has been molecule has been formed. formed.

► At end of heme synthesis, At end of heme synthesis, have small amount of have small amount of excess porphyrin in excess porphyrin in mitochondria. Is mitochondria. Is complexed to zinc. complexed to zinc. Excess is called Excess is called free free erythrocyte erythrocyte protoporphyrinprotoporphyrin (FEP)(FEP). . FEP is elevated when iron FEP is elevated when iron supply depleted.supply depleted.

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Globin Synthesis Globin Synthesis 1 of 111 of 11

►Occurs on RBC-specific Occurs on RBC-specific ribosomes which are ribosomes which are derived from inheritance derived from inheritance of various structural of various structural genes. Each RBC genes. Each RBC contains four alpha, two contains four alpha, two zeta, two beta, two delta, zeta, two beta, two delta, two epsilon, and four two epsilon, and four gamma genes. Resulting gamma genes. Resulting gene products are alpha, gene products are alpha, zeta, beta, delta, epsilon, zeta, beta, delta, epsilon, and gamma globin and gamma globin chains. chains.

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Hemoglobin Hemoglobin ChainChain

Greek SymbolGreek Symbol

AlphaAlpha αα

BetaBeta ββ

DeltaDelta δδ

EpsilonEpsilon εε

GammaGamma γγ

ZetaZeta ζζ

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►Throughout embryonic and fetal Throughout embryonic and fetal development, activation of globin genes development, activation of globin genes progresses from zeta to alpha, and from progresses from zeta to alpha, and from epsilon to gamma to delta to beta. epsilon to gamma to delta to beta.

zeta alpha

betadeltagamma

epsilon

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HemoglobinHemoglobin Globin Chain Globin Chain TypesTypes

Gower IGower I 2 zeta and 2 epsilon2 zeta and 2 epsilon

Gower IIGower II 2 alpha and 2 epsilon2 alpha and 2 epsilon

PortlandPortland 2 zeta and 2 gamma2 zeta and 2 gamma

Hemoglobin F Hemoglobin F (fetal Hgb)(fetal Hgb)

2 alpha and 2 gamma2 alpha and 2 gamma

Hemoglobin A Hemoglobin A (Adult Hgb)(Adult Hgb)

2 alpha and 2 beta2 alpha and 2 beta

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► Epsilon and zeta globins usually appear Epsilon and zeta globins usually appear only during embryonic development. only during embryonic development. Gower IGower I HemoglobinHemoglobin is two zeta and two is two zeta and two epsilon chains. epsilon chains. Gower II HemoglobinGower II Hemoglobin is is composed of two alpha and two epsilon composed of two alpha and two epsilon chains. chains. Hemoglobin PortlandHemoglobin Portland is is composed of two zeta and two gamma composed of two zeta and two gamma chains. chains.

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► In fetus, major hemoglobin is In fetus, major hemoglobin is Hemoglobin FHemoglobin F (two alpha and two (two alpha and two gamma chains). By age two, Fetal gamma chains). By age two, Fetal Hemoglobin (Hemoglobin F) comprises Hemoglobin (Hemoglobin F) comprises less than 2% of total hemoglobin. less than 2% of total hemoglobin.

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►Beta chain production steadily Beta chain production steadily increases after birth until adult increases after birth until adult percentages are reached between percentages are reached between three months and six months of age. three months and six months of age.

►All normal adult hemoglobins All normal adult hemoglobins ((Hemoglobin AHemoglobin A) consists of two alpha ) consists of two alpha and two non-alpha globin chains. and two non-alpha globin chains.

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►Hemoglobin A has two alpha and two Hemoglobin A has two alpha and two beta chains and comprises 95-97% of beta chains and comprises 95-97% of adult hemoglobin. Hemoglobin A2 has adult hemoglobin. Hemoglobin A2 has two alpha and two delta chains and two alpha and two delta chains and comprises 2-3% of total adult comprises 2-3% of total adult hemoglobin. hemoglobin.

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►Each globin chain links with heme Each globin chain links with heme molecule (protoporphyrin ring with molecule (protoporphyrin ring with iron) to form hemoglobin. iron) to form hemoglobin.

►Entire hemoglobin molecule has two Entire hemoglobin molecule has two alpha chains, two beta chains, and alpha chains, two beta chains, and four heme groups. four heme groups.

►Precise order of amino acids in globin Precise order of amino acids in globin chains critical to hemoglobin chains critical to hemoglobin molecule's structure and function. molecule's structure and function.

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► Rate of globin synthesis directly related to rate Rate of globin synthesis directly related to rate of porphyrin synthesis and vice versa. Is of porphyrin synthesis and vice versa. Is NONO such relationship between iron uptake when such relationship between iron uptake when either globin or protoporphyrin synthesis either globin or protoporphyrin synthesis impaired. impaired.

► Iron accumulates in RBC cytoplasm as ferritin Iron accumulates in RBC cytoplasm as ferritin aggregates. Iron-laden RBC called aggregates. Iron-laden RBC called sideroblastsideroblast and anucleated from called and anucleated from called siderocytesiderocyte. (Will . (Will see iron clusters when cells stained with see iron clusters when cells stained with Prussian Blue stain). Prussian Blue stain).

► Completed hemoglobin molecule is three-Completed hemoglobin molecule is three-dimensional structure. Has a globular shape. dimensional structure. Has a globular shape. Is species specific. Called a dimer structure. Is species specific. Called a dimer structure.

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2,3-Diphosphoglycerate (2,3-2,3-Diphosphoglycerate (2,3-DPG)DPG)

► Is an organic phosphate responsible Is an organic phosphate responsible for hemoglobin's affinity for oxygen. for hemoglobin's affinity for oxygen.

► Is a product derived from Luebering-Is a product derived from Luebering-Rapaport shunt. Rapaport shunt.

► Is located in the central cavity of Is located in the central cavity of hemoglobin molecule. Is bound to hemoglobin molecule. Is bound to beta chains. beta chains.

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Assembly of Hemoglobin Assembly of Hemoglobin Molecule Molecule

1 of 21 of 2

►Formation of hemoglobin requires iron, Formation of hemoglobin requires iron, globin chains, protoporphyrin IX, and globin chains, protoporphyrin IX, and 2,3-DPG. 2,3-DPG.

►To assemble molecule, ferric iron To assemble molecule, ferric iron (Fe(Fe3+3+) must be obtained from ferritin. ) must be obtained from ferritin. Iron is chemically reduced (FeIron is chemically reduced (Fe2+2+), and ), and then inserted as ferrous iron into then inserted as ferrous iron into center of protoporphyrin IX molecule. center of protoporphyrin IX molecule.

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Assembly of Hemoglobin Assembly of Hemoglobin Molecule Molecule

2 of 22 of 2

►When globin chain completed on ribosome, When globin chain completed on ribosome, it is released to cytoplasm. Individual alpha it is released to cytoplasm. Individual alpha and beta chains quickly and spontaneously and beta chains quickly and spontaneously form alpha-beta dimers. Two heme form alpha-beta dimers. Two heme molecules bind to each alpha-beta dimer. molecules bind to each alpha-beta dimer. Two dimers quickly form a tetramer and Two dimers quickly form a tetramer and assume final three dimensional shape. assume final three dimensional shape.

►Last step is insertion of 2,3-DPG molecule Last step is insertion of 2,3-DPG molecule into center cavity of hemoglobin molecule. into center cavity of hemoglobin molecule.

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HemoglobiHemoglobin Functionn Function

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Hemoglobin Function Hemoglobin Function 1 of 91 of 9

►Primary function is delivery and Primary function is delivery and release of oxygen to tissues and the release of oxygen to tissues and the facilitation of carbon dioxide excretion. facilitation of carbon dioxide excretion.

►One of most important controls of One of most important controls of hemoglobin affinity for oxygen is RBC hemoglobin affinity for oxygen is RBC organic phosphate: 2,3-organic phosphate: 2,3-diphosphoglycerate (2,3-DPG). diphosphoglycerate (2,3-DPG).

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►Unloading of oxygen by hemoglobin Unloading of oxygen by hemoglobin accompanied by widening of space accompanied by widening of space between beta chains and binding of between beta chains and binding of 2,3-DPG to beta chains. Resulting 2,3-DPG to beta chains. Resulting hemoglobin molecule known as hemoglobin molecule known as ""tense formtense form“, which has a lower “, which has a lower oxygen affinity. Also known as oxygen affinity. Also known as deoxyhemoglobindeoxyhemoglobin. .

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Tense Form

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►When hemoglobin binds oxygen, 2,3-DPG When hemoglobin binds oxygen, 2,3-DPG and beta chain bonds break. Beta chains and beta chain bonds break. Beta chains close up and 2,3-DPG expelled. Is close up and 2,3-DPG expelled. Is ""relaxed formrelaxed form" of hemoglobin. Has a " of hemoglobin. Has a high affinity for oxygen. Is also called high affinity for oxygen. Is also called oxyhemoglobinoxyhemoglobin. .

►Conversion between tense form and Conversion between tense form and relaxed form referred to as respiratory relaxed form referred to as respiratory movement. movement.

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Relaxed Form

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►Relationship between hemoglobin and Relationship between hemoglobin and oxygen has a sigmoid curve shape - is oxygen has a sigmoid curve shape - is called the called the oxygen dissociation oxygen dissociation curvecurve. Shape of curve means lots of . Shape of curve means lots of oxygen can be delivered to tissues oxygen can be delivered to tissues with small drop in oxygen tension.with small drop in oxygen tension.

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Oxygen Dissociation CurveOxygen Dissociation Curve

% Sat

Tissue pO2

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Oxygen Dissociation CurveOxygen Dissociation Curve

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► In lungs, where pO2 (oxygen In lungs, where pO2 (oxygen tension) very high, hemoglobin tension) very high, hemoglobin almost 100% saturated with almost 100% saturated with oxygen. As RBCs travel to tissues oxygen. As RBCs travel to tissues where oxygen tension drops, where oxygen tension drops, hemoglobin saturation drops to hemoglobin saturation drops to about 75%, releasing oxygen to about 75%, releasing oxygen to tissues. tissues.

► Is normally occurring process. Is normally occurring process.

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► In hypoxia, a compensatory "In hypoxia, a compensatory "shift to shift to rightright" of hemoglobin dissociation " of hemoglobin dissociation curve occurs to relieve tissue oxygen curve occurs to relieve tissue oxygen deficit. Right shift of curve, mediated deficit. Right shift of curve, mediated by increase in 2,3-DPG, results in by increase in 2,3-DPG, results in decrease in hemoglobin's affinity for decrease in hemoglobin's affinity for oxygen and an increase in oxygen oxygen and an increase in oxygen delivery to tissues. delivery to tissues.

► Shifts to right commonly occur in Shifts to right commonly occur in hypoxia, anemia, acidosis, and rise in hypoxia, anemia, acidosis, and rise in body temperature. body temperature.

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► In "shift to left" of hemoglobin dissociation In "shift to left" of hemoglobin dissociation curve, see an increase in hemoglobin-curve, see an increase in hemoglobin-oxygen affinity and decrease in amount of oxygen affinity and decrease in amount of oxygen being delivered to tissues. oxygen being delivered to tissues.

► Conditions causing a "Conditions causing a "shift to leftshift to left" " include alkalosis, increase in the amount of include alkalosis, increase in the amount of abnormal hemoglobins (methemoglobin or abnormal hemoglobins (methemoglobin or carboxyhemoglobin), increased amount of carboxyhemoglobin), increased amount of Hemoglobin F, or multiple transfusions of Hemoglobin F, or multiple transfusions of 2,3-DPG depleted stored blood. 2,3-DPG depleted stored blood.

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► Hemoglobin-oxygen affinity also Hemoglobin-oxygen affinity also expressed by expressed by PP5050 values. Pvalues. P5050 is point at is point at which hemoglobin is 50% saturated with which hemoglobin is 50% saturated with oxygen. Increase in Poxygen. Increase in P5050 values values represents a decrease in hemoglobin-represents a decrease in hemoglobin-oxygen affinity (shift to right). Decrease oxygen affinity (shift to right). Decrease in Pin P5050 values represents increase in values represents increase in hemoglobin-oxygen affinity (shift to left). hemoglobin-oxygen affinity (shift to left).

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Abnormal Abnormal HemoglobiHemoglobi

nsns

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Abnormal HemoglobinsAbnormal Hemoglobins

►Are three clinically significant Are three clinically significant abnormal hemoglobins that abnormal hemoglobins that are unable to transport or are unable to transport or deliver oxygen: deliver oxygen: 1.1. Carboxyhemoglobin Carboxyhemoglobin 2. 2. Methemoglobin, and Methemoglobin, and 3.3. Sulfhemoglobin Sulfhemoglobin

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CarboxyhemoglobinCarboxyhemoglobin

►Oxygen bound to hemoglobin replaced by Oxygen bound to hemoglobin replaced by carbon monoxide (CO) carbon monoxide (CO)

►Replacement process relatively slow and Replacement process relatively slow and dependent upon blood concentration of dependent upon blood concentration of carbon monoxide carbon monoxide

►Heme binds to carbon monoxide about Heme binds to carbon monoxide about 200 times tighter than it binds to oxygen 200 times tighter than it binds to oxygen

► Is a reversible condition (oxygen Is a reversible condition (oxygen inhalation)inhalation)

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MethemoglobinMethemoglobin

►Formed when iron of hemoglobin Formed when iron of hemoglobin molecule oxidized to ferric state (Femolecule oxidized to ferric state (Fe3+3+) )

►Can occur as result of overload to oxidant Can occur as result of overload to oxidant stress (ingesting strong oxidant drugs) or stress (ingesting strong oxidant drugs) or to enzyme deficiency in RBC metabolic to enzyme deficiency in RBC metabolic pathways pathways

► Is a reversible condition (with Is a reversible condition (with administration of strong reducing administration of strong reducing substances)substances)

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SulfhemoglobinSulfhemoglobin

►Occurs when sulfur content in blood Occurs when sulfur content in blood builds up (ingestion of sulfur-builds up (ingestion of sulfur-containing drug or chronic containing drug or chronic constipation) constipation)

► Is an irreversible condition (RBCs must Is an irreversible condition (RBCs must be removed from circulation)be removed from circulation)

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RBC RBC Metabolic Metabolic PathwaysPathways

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Introduction to RBC Metabolic Introduction to RBC Metabolic Pathways Pathways 1 of 21 of 2

►Necessary for generation of ATP Necessary for generation of ATP (energy) (energy)

►Necessary for RBC to maintain: Necessary for RBC to maintain: hemoglobin function hemoglobin function membrane integrity and deformability membrane integrity and deformability RBC volume RBC volume

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Introduction to RBC Metabolic Introduction to RBC Metabolic Pathways Pathways 2 of 22 of 2

►Generate energy through Generate energy through anaerobic breakdown of glucose anaerobic breakdown of glucose

►Four pathways involved in RBC Four pathways involved in RBC metabolism: metabolism: Phosphogluconate pathway Phosphogluconate pathway Embden-Meyerhof pathway Embden-Meyerhof pathway Methemoglobin reductase pathway Methemoglobin reductase pathway Luebering-Rapaport pathwayLuebering-Rapaport pathway

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Phosphogluconate PathwayPhosphogluconate Pathway(or Hexose Monophosphate (or Hexose Monophosphate

Pathway)Pathway)►Produces pyridine nucleotides - one Produces pyridine nucleotides - one

of the main lines of defense for RBC of the main lines of defense for RBC against oxidative injury which may against oxidative injury which may be caused by infections or oxidant be caused by infections or oxidant drugs drugs

►Deficiency in this pathway results in Deficiency in this pathway results in deficiency of glutathione which deficiency of glutathione which results in globin denaturation and results in globin denaturation and precipitation as aggregates inside precipitation as aggregates inside the RBC (Heinz bodies) the RBC (Heinz bodies)

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Embden-Meyerhof PathwayEmbden-Meyerhof Pathway

►90% of the ATP needed by the RBC 90% of the ATP needed by the RBC is generated through this pathway is generated through this pathway

►Also generates NADH which is used Also generates NADH which is used in other metabolic pathways in other metabolic pathways

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Methemoglobin Reductase Methemoglobin Reductase PathwayPathway

► Important in maintaining heme iron in Important in maintaining heme iron in the reduced or ferrous functional state the reduced or ferrous functional state

►Dependent on the hexose Dependent on the hexose monophosphate pathway for monophosphate pathway for production of pyridine nucleotides production of pyridine nucleotides

► In absence of enzyme methemoglobin In absence of enzyme methemoglobin reductase, have an accumulation of reductase, have an accumulation of methemoglobin (iron in the ferric or methemoglobin (iron in the ferric or oxidized state) oxidized state)

►Methemoglobin is non-functional, Methemoglobin is non-functional, having lost ability to transport oxygen having lost ability to transport oxygen

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Leubering-Rapaport ShuntLeubering-Rapaport Shunt

►Causes an accumulation of RBC Causes an accumulation of RBC organic phosphate 2,3-DPG which organic phosphate 2,3-DPG which is very important for hemoglobin's is very important for hemoglobin's affinity for oxygen affinity for oxygen

7878

ErythrocytErythrocyte e

SenescencSenescencee

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Introduction to Erythrocyte Introduction to Erythrocyte SenescenceSenescence

►Average life span of RBC is 120 days. Average life span of RBC is 120 days. ►Are continually aging (senescence). Are continually aging (senescence). ►Old RBCs removed by macrophages Old RBCs removed by macrophages

located in thelocated in the reticuloendothelial reticuloendothelial systemsystem (RES) ( (RES) (spleenspleen most important most important organ). organ).

►As old RBCs removed, are replaced by As old RBCs removed, are replaced by younger RBCs from the bone marrow. younger RBCs from the bone marrow.

►Two major pathways for RBC removal: Two major pathways for RBC removal: Extravascular Hemolysis Extravascular Hemolysis Intravascular HemolysisIntravascular Hemolysis

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Extravascular Hemolysis Extravascular Hemolysis 1 of 31 of 3

►90% of destruction of RBCs occurs here. 90% of destruction of RBCs occurs here. ►Old or damaged RBCs phagocytized by Old or damaged RBCs phagocytized by

RES cells and digested by lysosomes. RES cells and digested by lysosomes. ►Hemoglobin molecules disassembled Hemoglobin molecules disassembled

and broken down into component parts. and broken down into component parts. ► Iron returned by transferrin to bone Iron returned by transferrin to bone

marrow. marrow. ►Globin broken down into amino acids Globin broken down into amino acids

and returned to amino acid pool. and returned to amino acid pool.

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►Protoporphyrin ring disassembled into Protoporphyrin ring disassembled into carbon monoxide, which is expelled. carbon monoxide, which is expelled. The remaining component,The remaining component, biliverdin biliverdin, , is converted to is converted to bilirubinbilirubin and carried and carried by albumin to liver. In liver, bilirubin by albumin to liver. In liver, bilirubin conjugated to conjugated to bilirubin glucoronidebilirubin glucoronide and excreted with bile into intestines. and excreted with bile into intestines. Bilirubin glucoronide converted by Bilirubin glucoronide converted by bacteria into bacteria into urobilinogenurobilinogen and and excreted in the stool. Small amount excreted in the stool. Small amount recycled back to liver and then recycled back to liver and then excreted through kidneys in urine. excreted through kidneys in urine.

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►Both unconjugated (prehepatic) and Both unconjugated (prehepatic) and conjugated bilirubin (posthepatic) can conjugated bilirubin (posthepatic) can be measured in plasma and used as an be measured in plasma and used as an indicator of the amount of indicator of the amount of extravascular hemolysis occurring. extravascular hemolysis occurring.

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Intravascular Hemolysis Intravascular Hemolysis 1 of 21 of 2

►Only 5-10% hemolysis occurs in this pathway. Only 5-10% hemolysis occurs in this pathway. ► RBCs break down within lumen of blood vessel, RBCs break down within lumen of blood vessel,

releasing hemoglobin directly into bloodstream. releasing hemoglobin directly into bloodstream. ►Hemoglobin disassociates into globin dimers and Hemoglobin disassociates into globin dimers and

picked up by protein carrier - haptoglobin. picked up by protein carrier - haptoglobin. ►Hemoglobin-haptoglobin complex too big to be Hemoglobin-haptoglobin complex too big to be

excreted through kidneys. Complex carried to excreted through kidneys. Complex carried to liver where it is further catabolized. liver where it is further catabolized.

► At this point, pathway in liver identical to At this point, pathway in liver identical to extravascular pathway. extravascular pathway.

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Intravascular Hemolysis Intravascular Hemolysis 2 of 22 of 2

►Haptoglobin levels decrease in intravascular Haptoglobin levels decrease in intravascular hemolysis. hemolysis.

► As haptoglobin levels diminish, hemoglobin As haptoglobin levels diminish, hemoglobin appears in plasma (hemoglobinemia) and is appears in plasma (hemoglobinemia) and is filtered through kidneys and reabsorbed by filtered through kidneys and reabsorbed by renal tubular cells. renal tubular cells.

►Hemoglobin may also appear in urine Hemoglobin may also appear in urine (hemoglobinuria). (hemoglobinuria).

► Always have hemoglobinuria with Always have hemoglobinuria with hemoglobinemia. hemoglobinemia.

►Hemoglobin in plasma may give plasma a Hemoglobin in plasma may give plasma a pink, red, brown, or black color. Urine may pink, red, brown, or black color. Urine may have pink, red, brown, and black color also. have pink, red, brown, and black color also.

1 chapter 3 the red blood cell: structure and function

Documents

rbc membrane integrity

protein membrane

rbc antigens

plasma membrane

rbc cytoskeletonnote

network of proteins

principle rbc glycoprotein

transverse entire membrane