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Fundamentals of Pathology > RBC Structure and Function > Flashcards

RBC Structure and Function Flashcards

1
Q

describe the structure of RBCs

A
  • lacks nucleus, mitochondria and endoplasmic reticulum
  • essentially a ‘bag of Hb’
  • biconcave and 8 micron cells to able to deform and pass through 3 micron capillaries or reticuloendothelial system w/o fragmentation
  • structural properties linked to membrane
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2
Q

what is the function of RBCs?

A
  • to transport respiratory gases to and from tissues
  • RBC traverse the microvascular system w/o mechanical damage and retain shape which facilitates gaseous exchange
  • red cell membrane should be extremely tough but flexible
  • cytoskeletal proteins interactions w membrane lipid bilayer determines flexibility
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3
Q

describe the structure of RBC membranes

A
  • made of 50% proteins, 40% lipids and 10% carbohydrates
  • is a semi permeable layer w proteins scattered throughout
  • outer hydrophilic layer portion composed of glycolipids, glycoproteins and proteins
  • central hydrophobic layer contains proteins, cholesterol and phospholipids
  • inner hydrophilic layer is a made of mesh-like cytoskeletal proteins the support the bilayer
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4
Q

elaborate on the lipids present in the RBC membrane

A
  • phospholipids are arranged in a bilayer
  • there is an asymmetric phospholipid distribution
  • unesterified cholesterol between which is an important determinant of membrane SA and fluidity
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5
Q

what are the phospholipids present in the outer layer of the RBC membrane?

A

uncharged phosphotidyl choline and sphingolipids

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6
Q

what are the phospholipids present in the inner layer of the RBC membrane?

A

charges phosphotidyl ethanol amine and phosphotidyl serine

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7
Q

what are the 2 types of proteins present in the RBC membrane?

A

integral membrane proteins and peripheral proteins

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8
Q

elaborate on intergral membrane proteins

A
  • external from outer surface and traverse the entire bilayer to inner surface
  • the 2 types are: glycophorins (A, B, C) and Band 3
  • glycophorins are the major integral proteins and causes the cell to have a -ve charge
  • other integral proteins include: Na+/K+ ATPase, aquaporin 1, surface receptor TfR
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9
Q

why is it important for RBCs to have a negative charge?

A

to ensure that the RBC does not interact w other cells

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10
Q

what is the function of peripheral proteins?

A

-limited to cytoplasmic surface of membrane and forms the RBC cytoskeleton
-cytoskeleton acts as tough framework to support the bilayer
spectrin, ankyrin, protein 4.1 and actin are the main peripheral proteins with key roles

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11
Q

what are the key roles of the major peripheral proteins?

A

1) spectrin: is the most abundant peripheral protein
- composed of α and β chains
- important in RBC membrane integrity as it binds to other periphery proteins ti form cytoskeleton network of microfilaments
- controls the biconcave shape and deformity of cell and if denatured, the cell becomes spherical and loses flexibility

2) ankyrin: primarily anchors lipid bilayer to membrane skeleton via interaction w spectrin and Band 3
3) protein 4.1: may link the cytoskeleton to membrane by associations w glycophoin and stabilises the interactions w spectrin w actin
4) actin: responsible for contraction and relaxation of membrane

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12
Q

what maintains the SA of the cell?

A

strong cohesion between bilayer and membrane skeleton

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13
Q

where are carbohydrates located on the RBC protein and what is their function?

A
  • located only on the external surface of the cell
  • carbohydrate groups attached to proteins and lipids by glycolysation
  • may contain 2-60 6C monosaccharide untie either branched or straight
  • gives cell it’s identity which is a distinguishing factor between human blood types
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14
Q

what are blood group antigens?

A
  • certain blood group antigens are found w specific membrane structures
  • they can either be proteins (Duffy, Kidd), carbohydrates (ABO, lewis) or combinations of glycolipids and proteins
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15
Q

what is the function of the RBC membrane?

A
  • provides shape and optimum SA:V ratio for respiratory exchange
  • provides deformability and elasticity so that the RBC can pass through microvessels
  • regulates [intracellular cation] by allowing H20 and electrolytes to exchange via pumps
  • controls the volume and H20 content by controlling [Na+] and [K+] via cationic pumps by active transport
  • acts as interface between cell and environment via membrane surface receptors
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16
Q

how can a change in [cholesterol] affect the RBC membrane?

A
  • [membrane cholesterol] ⇌ [plasma cholesterol]
    [cholesterol] determinant of membrane SA and fluidity
  • increase in membrane cholesterol causes an increase in SA and decrease in deformability
    -RBC will appear distorted and cause the formation fo acanthocytes
    -increase in cholesterol and phospholipid is due to target cells
17
Q

what is the cause of hereditary spherocytosis?

A
  • ankyrin deformity or abnormalities
  • A or B specrtin deformity or abnormalities
  • Band 3 abnormalities
  • protein 4.1 abnormalities
18
Q

what is the cause of hereditary elliptocytosis?

A
  • A ro B spectrin mutation caused by a defect of the spectrin dimer
  • A or B spectrin mutation due to defective spectrin-ankyrin association
  • protein 4.2 deformity or abnormalities
19
Q

what features allow RBCs to withstand life w/o structural deformation?

A
  • geometry of the cell (SA:V): facilitates deformation whilst maintaining constant SA
  • membrane deformability: spectrin molecules undergo reversible change in conformation, some are uncoiled and extended and some are compressed and folded
  • cytoplasmic viscosity determined by MCHC (mean corpuscular [Hb]: as MCHC increases, the viscosity increases²
20
Q

what is the purpose of RBC in metabolic pathways?

A

provides energy for maintenance of cation pumps, RBC integrity + deformability, Hb in the reduced state and reduced sulfhydryl (thiol) groups in Hb

21
Q

how does the glycolytic pathway aid RBCs?

A
  • glucose is metabolises and generates 2ATP molecules
  • glycolysis generate 90-95% of energy needed for RBCs
  • functions in maintenance of RBC shape, flexibility and cation pumps
22
Q

how does the pentose phosphate pathway aid RBCs?

A
  • pentose phosphate shunt provides reducing power, NADPH
  • NADPH maintains glutathione in the reduced form GSH
  • RBCs use GSH for protection from oxidative damage
23
Q

how does the methemoglobin pathway aid RBCs?

A
  • maintains iron in ferrous state (Fe2+)

- in absence of enzyme, methemoglobin accumulates and the RBC cannot carry O2

24
Q

how does the Luebering-Rapoport pathway aid RBCs?

A
  • permits the accumulation of 2,3-DPG which is essential for maintaining normal O2 tension, regulating the Hb affinity
  • it is the biochemical pathway for mature erythrocytes, regulates O2 release from Hb and delivery to tissues

Fundamentals of Pathology (7 decks)

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