erythrocytes (rbc’s) … · 2018-03-15 · no organelle –no mitochondria generate energy...

Erythrocytes (RBC’s)

RBCs are flattened biconcave discs

◦ Flexible structure

◦ Shape provides increased surface area for

diffusion

7.5 µm diameter, 2.5 µm thick

Life cycle – 120 days

Lack a nucleus and other organelles.

33% of weight is hemoglobin molecules (Each

RBC contains 280 million hemoglobins).

Other proteins include antioxidants and those to

maintain RBC shape (spectrin)

Erythrocytes are dedicated to respiratory gas transport (transport O2 to tissues and CO2 from tissues)

Hemoglobin reversibly binds with oxygen and most oxygen in the blood is bound to hemoglobin

Erythrocyte Function

Is a very elastic , semi-permeable lipid bi-layersupported by a mesh-like cytoskeleton

Is a three layer structure:1. an outer hydrophilic portion:glycolipid, glycoprotein and protein

2. a central hydrophobic layer:

protein, cholesterol and PL

3. an inner hydrophilic layer:containing protein

Several proteins are present in the RBC’s

Integral membrane proteins:Extend from outer surface andtransverse entire membrane to innersurface

Peripheral proteins:

Limited to cytoplasmic surface ofmembrane and forms the RBCcytoskeleton

Glycophorin:

Is the principle RBC glycoprotein. Spans entirethickness of lipid bilayer and appears on externalsurface of RBC membrane

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

All glycophorins carry RBC antigens and are receptors or transport proteins

Cytoskeleton:

Network of proteins on the inner surface of theplasma membrane, called the peripheral membraneproteins

Provides rigid support and stability to lipid bilayer

Responsible for maintaining shape and deformabilityof RBC

The most abundant peripheral protein

Flexible, rod like molecule composed of an alpha helix of two

polypeptide chains

1. Spectrin

Microfilaments strengthen membrane, protecting cell from being

broken

Controls biconcave shape and deformability of cell

Is an important factor in RBC membrane integrity because it binds

with other peripheral proteins to form the skeletal network of

microfilaments on the inner surface of RBC membrane

2. Ankyrin :

Primarily anchors lipid bilayer to membrane skeleton

3. Protein 4.1:

May link the cytoskeleton to the membrane by means of

its associations with glycophorin

4. Actin:

Responsible for contraction and relaxation of membrane

Erythrocyte membrane lipid consists of bilayer ofphospholipids intermingled with molecules ofcholesterol in nearly equal amounts. Also, smallamounts of free fatty acids and glycolipids

Different types of phospholipids are found on the insidelayer than on the outside layer

Abnormalities in the PL may result in decreaseddeformability and decreased red cell survival

Most of glycolipids are located in outer half of lipidbilayer and interact with glycoproteins to form manyof RBC antigens

Cholesterol equally distributed on both sides of lipidbilayer (25% of RBC membrane lipid content)

RBC membrane cholesterol is in continual exchangewith plasma cholesterol

Cholesterol plays important role in regulatingmembrane fluidity and permeability

Accumulation of cholesterol results indecreased deformability and may lead tohemolytic anemia

They occur only on the external surface of the red cell

They occur as glycoproteins or glycolipids

The antigens of ABO bloodgroups are examples ofcarbohydrate membranes

Defective or absent spectrin molecule

Leads to loss of RBC membrane, leading tospherocytosis

Decreased deformability of cell

Increased osmotic fragility

Normal biconcave red cell loses membrane fragments

and adopts a spherical shape

Inflexible cells are trapped in the splenic cords, phagocytosed by macrophages

Hereditary disorder of the RBCs (autosomal dominant

trait)

RBCs assume an elliptical shape, rather than the typical

round shape.

Spectrin abnormality or deficiency of protein 4.1

RBC hemolysis occurs in the spleen, thus

splenectomy corrects the hemolysis, but not the

RBC membrane defect

Nonspecific test forinflammatory process

Anticoagulated blood incalibrated tube; rate ofsedimentation of RBCs in 1h

Normal:◦ <15mm/hmale;

◦ <20mm/h female;

◦ add 10 past age 60

X

Any condition that elevates fibrinogen should elevate ESR.

Dramatically ↑ with infection, malignancy, connective tissue disease. Also ↑ with pregnancy, inflammatory disease, and anemia.

A ↓ ESR is associated with blood diseases in which red blood cells have an irregular or smaller shape that causes slower settling ie: sickle cell anemia

The term erythropoiesis (erythro = RBC, andpoiesis = to make) is used to describe theprocess of RBC formation or production.

In humans, erythropoiesis occurs almostexclusively in the red bone marrow

A hemocytoblast is transformed into a committed cell called theproerythroblast

Proerythroblasts develop into early erythroblasts

The developmental pathway consists of three phases

◦ Phase 1: ribosome synthesis in early erythroblasts

◦ Phase 2: hemoglobin accumulation in late erythroblasts andnormoblasts

◦ Phase 3: ejection of the nucleus from normoblasts and formation ofreticulocytes

Reticulocytes then become mature erythrocytes

Reduces O2

levels in blood

Erythropoietin

stimulates red

bone marrow

Enhanced

erythropoiesis

increases RBC

count

Normal blood oxygen levelsStimulus: Hypoxia /

decreased availability of O2 to

blood/or increased tissue

demands for O2

Start:

Kidney (and liver to a

smaller extent) releases

erythropoietin

Increases

O2-carrying

ability of blood

Hemolysis is the breakage of the RBC’s membrane, causing the

release of the hemoglobin and other internal components into the

surrounding fluid.

Hemolysis is visually detected by showing a pink to red tinge in

serum or plasma

In-vivo hemolysis may be due to pathological conditions, such as

autoimmune hemolytic anemia or transfusion, drugs and

infections…

(a) without hemolysis: red blood cell suspension seemsred and opaque.

(b) without hemolysis: RBCs sedimented spontaneously for60 min. Note that the supernatant is not colored.

(c) hemolysis: RBC suspension become transparent byhemolysis.

(a) (b) (c)

RBC membranes have glycoprotein antigens

These antigens are:

1. Unique to the individual Human Blood Groups

2. Recognized as foreign if transfused into another individual

3. Promoters of agglutination and are referred to as agglutinogens

Presence or absence of these antigens is used to classify bloodgroups

Humans have 30 varieties of naturally occurring RBC antigens butthe important ones are the ABO and the rhesus (Rh) blood systems

According to the ABO blood typing

system there are four different

kinds of blood types depending on

the antigen of the RBC

membrane: A, B, AB or O

ABO blood grouping system

Is the precursor of both A substance (A antigen) and Bsubstance (B antigen)

Is formed by the action of Fucosyl Transferase thatcatalyses addition of fucose residue to the terminalgalactose residue of H substance precursor

Fucose

Added by Fucosyl transferase

H antigen

Is formed by the action of N-acetyl-DGalactosamineTransferase (GalNAC transferase) thatcatalyses addition of GalNAC to the terminal Gal residue ofH substance

GalNAc

(N-Acetyl-D galactosamine)

A antigen

Is formed by the action of Galactosyl Transferase thatcatalyses the transfer of Gal residue to the terminalgalactose residue of H substance

B antigen

D-GalactoseAdded by Galactosyl

transferase

Blood group A

• you have A antigens on the surface of your

RBCs

•and B antibodies in your blood plasma

AB0 blood grouping system

Blood group B

• you have B antigens on the surface of your

RBCs

•and A antibodies in your blood plasma

Blood group O

•you have neither A or B antigens on the

surface of your RBCs

•but you have both A and B antibodies

in your blood plasma

AB0 blood grouping systemBlood group AB

• you have both A and B antigens on the

surface of your RBCs

•no A or B antibodies at all in your blood

plasma

Blood transfusions – who can receive

blood from whom?

People with blood group O: "universal donors“

People with blood group AB: "universal receivers"

How common is your blood type?

46.1%

38.8%

11.1%

3.9%

Is the second most significant blood group system in human

transfusion

Rh antigens are transmembrane proteins

The D antigen (RhD) is the most important

If it is present, the blood is RhD positive (~80% of the population) , if

not it's RhD negative

So, for example, some people in group A will have it, and will therefore

be classed as A+ (or A positive), while the ones that don't, are A- (or A

negative) and so it goes for groups B, AB and O

A person with Rh+ blood can receive blood from a person with Rh- blood without any problems

A person with Rh- blood can develop Rh antibodies in

the blood plasma if he or she receives blood from a

person with Rh+ blood, whose Rh antigens can trigger

the production of Rh antibodies

hemolysis

Rh- mothers who have had a pregnancy with/are pregnant

with a Rh+ infant are given Rh immune globulin (RhIG) at 28

weeks during pregnancy and within 72 hours after delivery to

prevent sensitization to the D antigen.

It works by binding any fetal red cells with the D antigen

before the mother is able to produce an immune response and

form anti-D IgG

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Maternal antibodies destroy fetal red blood cells

◦ Results in anemia.

◦ Anemia limits the ability of the blood to carry oxygen to the baby's organs and

tissues.

Baby's responds to the hemolysis by trying to make more red blood

cells very quickly in the bone marrow and the liver and spleen.

◦ Organs enlarge - hepatosplenomegaly.

◦ New red blood cells released prematurely from bone marrow and are unable to

do the work of mature red blood cells.

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Baby's responds to the hemolysis by trying to make more red blood

cells very quickly in the bone marrow and the liver and spleen.

◦ Organs enlarge - hepatosplenomegaly.

◦ New red blood cells released prematurely from bone marrow and are unable to

do the work of mature red blood cells.

◦ The heart begins to fail and large amounts of fluid build up in the baby's tissues

and organs resulting in a condition known as Hydrops Fetalis. A fetus with

hydrops is at great risk of being stillborn.

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Whole Blood

Blood Component

RBC; PLT(platelets); FFP (Fresh Frozen

Plasma); Leukocyte; concentrate

Use of whole blood is considered to be

a waste of resources

Type of Blood Transfusion

Cellular components

Red cells

Platelets

White cells

Fresh plasma

Fresh frozen plasma

Cryoprecipitate Cryosupernatant

Factor VIII Albumin

Concentrate Immunoglobulins

other concentrates

The preparation of blood components from whole blood

Blood type and Rh factor status crossmatched

Blood transfusion reactions:

◦ Fever and chills within first 15 minutes

◦ hives and itching during or after transfusion

Most dangerous: ABO incompatibility

RBCs clump and block capillaries

Decreased blood flow to vital organs

Manifestations: lumbar, abdominal and/or chest pain,

fever, chills, urticaria, nausea and vomiting

Occurs after 100 – 200 ml of incompatible blood

infused

1. Stop transfusion immediately

2. Continue IV infusion with normal saline

3. Notify physician of client’s signs and symptoms

4. Provide care for client as indicated

5. Complete reaction form according to institution protocol.

6. Obtain urine specimen from client and send for free

hemoglobin.

No organelle – no mitochondria

Generate energy through anaerobic breakdown of glucose (2ATP+lactate)

ATP is used as substrate for Na+, K+ or the Ca2+

dependant ATPases that maintain intracellular concentrations of these cations

The glucose uptake by RBC’s through high affinity glucose transporter is independent on insulin

Four pathways involved in RBC metabolism:

1. Pentose Phosphate Pathway

2. Glycolysis pathway

3. Methemoglobin reductase pathway

4. 2,3 BPG pathway is unique for RBC

In red cells 1,3 BPG is converted to 2,3BPG which unites with oxy Hband helps release of oxygen at tissues.

The rate of synthesis and hydrolysis of 2,3 DPG are very sensitive topH: a fall of pH inhibits mutase and stimulates phosphatase causingdecrease of 2,3 DPG

2,3 BPG pathway

H2O2 glutathioneperoxidase

2 H2O

2 GSHGSSGglutathione

reductase

NADPH + H+NADP+

pentose pathway

Hydrogen peroxide

Aerobic respirationDrugs, fava beans

02-

02

Superoxide radicals

➢ When erythrocytes are exposedto chemicals that generate highlevels of superoxide radicals, GSH(Reduced Glutathione) is requiredto reduce these damagingcompounds

➢Glutathione Peroxidase catalyzesdegradation of organichydroperoxides by reduction, astwo glutathione molecules areoxidized to a disulfide GSSG

➢The PPP is responsible for

maintaining high levels of NADPH

in red blood cells for use as a

reductant in the glutathione

reductase reaction.

Pentose Phosphate Pathway

Detoxification

The major role of PPP in RBCs isthe production of NADPH whichprotect these cells fromoxidative damage by providingGSH for removal of H2O2

Important in maintaining heme iron in the reduced or ferrous

functional state

The metHbFe3+ is reduced to deoxyHbFe2+ by the flavoprotein,

MetHb reductase (MW 185Kda) (NADH cytochrome b5 reductase)

NAD+

NADH+H+ 2 cytob5Fe3+

2 cytob5Fe2+

2 Hb Fe2+

2 met Hb Fe3+

(Glycolysis)

Mutations causes a deficiency in G6PDH (X-linked), with consequent

impairment of NADPH production

Detoxification of H2O2 is inhibited, and cellular damage results - lipid

peroxidation leads to erythrocyte membrane breakdown and

hemolytic anemia.

Most G6PD-deficient individuals are asymptomatic - only in

combination with certain environmental factors (sulfa antibiotics,

herbicides, antimalarials, *divicine) do clinical manifestations occur.

*toxic ingredient of fava beans

RBC Metabolic Pathways Disorders

This deficiency causes the entire glycolysis pathway to cease working so that

little to no ATP is produced

Consequently, the defective red cells are destroyed in the spleen causing

anaemia and the spleen enlarges (splenomegaly) because it is overworked

The excessive destruction of red blood cells (hemolysis) results in the

breakdown of hemoglobin stored in these cells