hematology exam 1 - RBC membrane, bone marrow anatomy

RBC membrane major components

glycophorin (A, B, C)

spectrin

ankyrin

actin

tropomodulin, tropomyosin

adducin

band 4.1

band 4.2

band 4.9

band 3

glycophorin

integral protein

main RBC glycoprotein

consists of 20% of the total membrane proteins

spans the entire lipid bilayer and is present on the outside of membrane to interact with RBC antigens and transport them inside the cell

cytoskeleton gives cell support + stability for the lipid bilayer to be able to be flexible and deform when it needs to change shape

movement of the integral proteins within the lipid bilayer rarely occurs

• one of the 3 major glycophorinsn (GPA, GPB, GPC)

• 3 domains: cytoplasmic, hydrophobic, extracellular

  • extracellular: responsible for most of negative surface charge to keep RBCs from sticking to ea. other and vessel wall

• GPC: helps attach the skeletal protein network to the lipid bilayer

spectrin

predominant skeletal protein

flexible rod-shaped protein structure composed of an alpha chain and a beta chain intertwined to form tetramers

• arranged side by side, antiparallel

• twisted, highly flexible, around 100 nm long

fxns like a spring:

• tetramers are tightly coiled and can extend in reverse when membrane is stretched up to a point

important for RBC integrity → acts as an anchor for other important proteins (actin, ankyrin, adducin, and others)

complex connects RBC skeleton network together and stabilizes jxn between spectrin and actin to preserve integrity

band 4.1

interacts w/ spectrin, actin, and GPC

• strengthens bond b/w spectrin and actin for membrane stability

band 3

anion exchange protein: major integral protein of RBC

• transport channel for chloride-bicarbonate

  • occurs during CO2 transport from tissues back to lungs

• major binding site for enzymes and cytoplasmic components

  • regulates glycolytic enzymes, binds Hb, attaches skeletal protein network to lipid bilayer

ankyrin

high-affinity binding site for attachment of spectrin to inner membrane surface

• binds spectrin near region involved in dimer-tetramer interactions

ankyrin is also bound really well to Band 3

actin

similar fxn to actin in other cells

• organized into short, dbl-helical protofilaments of 12-14 actin monomers

• stabilized by other proteins: tropomodulin, adducin, tropomyosin, band 4.9

• binds to end of spectrin dimers

RBC membrane skeleton

consists of structural proteins

horizontal interactions: parallel to membrane’s plane

• skeletal support for lipid membrane

vertical interactions: perpendicular to membrane’s plane:

• attach skeletal lattice network to lipid bilayer

provides viscoelastic properties

helps w/ cell shape, deformability, and membrane stability

• defects:

  • abnormal cell shape, decreased stability, hemolytic anemia

cell/fat ratio of bone marrow and changes from childhood → adulthood

• two types of bone marrow in our body: red and yellow

  • red bone marrow: produces blood cells

  • yellow: stores fat for energy prod and helping develop bone, cartilage, muscles of body

  • bone marrow is made up of all red until abt age 7, yellow eventually replaces red as we age

    • bone marrow around 100% cellular during first 3 months after birth

    • 80% cellular in children up to age 10

    • it slowly declines in cellularity, eventually reaching 50% at age 30

    • 30% cellularity at age 70

hypoplasia

decrease in the # of cells in the bone marrow

• M:E ratio is low

• can result in disorders such as anemia

hyperplasia

increase of # of cells in bone marrow

• M:E ratio is high

• can manifest in 3 diff ways: erythroid, myeloid, and megakaryocytic

myeloid:erythroid ratio

estimate of myeloid elements and their precursors found in the bone marrow as well as erythroid elements and their precursors

• normal ratio: 3:1 to 4:1

• ratio can be changed by diff factors, such as things that impair RBC life span or production, decreases in a certain cell line

• in adults, an M:E ratio of 4:1 is normal for 50% cellularity, which represents 30-40% granulopoeisis and 10-15% erythropoiesis

avg life span of RBC, myelocytes, and platelets

RBC: 120 days

WBC: 6-10 hrs

platelets: 10 days