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CVS- Cardiovascular > S1: The Red Blood Cell - Structure and Function > Flashcards

S1: The Red Blood Cell - Structure and Function Flashcards

1
Q

Describe the structure of mammalian red blood cells

A
  • Biconcave disc shaped
  • Flexible membrane
  • High surface area to volume ratio
  • Lack nucleus, mitochondria and ER
  • Cytoplasm is rich in haemoglobin
  • 8 micron in diameter
  • Able to deform and pass through 3 micron capillaries without framentation
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2
Q

Do prokaryotic organisms have RBC?

A

RBC are unique amongst eukaryotic cells

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3
Q

What is the primary function of red blood cells?

A

Transport of respiratory gases to and from the tissues

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4
Q

List properties of RBC that allow it to transport gases

A
  • Capable of traversing the microvascular system without mechanical damage, and retain a shape which facilitates gaseous exchange
  • The red cell membrane should be extremely tough yet highly flexible
  • Interactions between the membrane and cytoskeletal proteins determines the strength and flexible
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5
Q

What is the structure of red cell membrane?

A

A semipermeable lipid bilayer with proteins scattered throughout.

  • Outer hydrophilic portion composed of glycolipids, glycoproteins and proteins
  • Central hydrophobic layer containing proteins, cholesterol and phospholipids
  • Inner hydrophilic layer of mesh like cytoskeletal proteins to support lipid bilayer
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6
Q

How are lipids distributed in RBC membrane?

A
  • Asymmetric phospholipid distribution
  • Free cholesterol between
  • Uncharged phospholipids in outer layer
  • Charged phospholipids in inner layer
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7
Q

What percentage of the RBC membrane is lipids?

A

40%

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8
Q

Give 2 examples of uncharged phospholipids

A

Phosphatidyl Choline and Sphingomyelin

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9
Q

Give 2 examples of charged phospholipids

A

Phosphatidyl Ethanolamine and Phosphatodyl Serine

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10
Q

What happens to cholesterol in RBC membrane when there is an increase in free plasma cholesterol?

A

Membrane cholesterol exist in free equilibrium with plasma cholesterol.

An increase in free plasma cholesterol results in an accumulation of cholesterol in the RBC membrane.

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11
Q

What happens to RBC with increased cholesterol?

A

Acanthocytosis- RBC with spiked membrane due to abnormal thorny projections

The RBC are now called spur cells

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12
Q

What are integral membrane proteins?

A

Proteins that extend from outer surface and traverse entire membrane to inner surface

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13
Q

What are the 2 major integral membrane proteins?

A
  1. Glycophorins (A, B and C)
  2. Band 3=3 anion transporter

Others: Na+/K+, Aquaporin 1, Surface receptors e.g. TfR

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14
Q

What are peripheral proteins?

A

Proteins limited to cytoplasmic surface of membrane and forms the RBC cytoskeleton

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15
Q

List major peripheral proteins

A
  • Spectrin
  • Ankyrin
  • Protein 4.1
  • Actin
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16
Q

What is spectrin?

A
  • Most abundant peripheral protein
  • Composed of alpha and beta chains
  • Important in RBC integrity (binds to other peripheral proteins to form cytoskeletal network of microfilaments)
  • Controls biconcave shape and deformability of cell
17
Q

What is Ankyrin?

A
  • Peripheral Protein

- Primarily anchors lipid bilayer to membrane skeleton via interaction with spectrin and band 3

18
Q

What is Protein 4.1?

A
  • Peripheral Protein
  • May link the cytoskeleton to the membrane by means of its associations with glycoproteins
  • Stabilises interaction of spectrin and actin
19
Q

What is actin?

A
  • Peripheral Protein
  • Responsible for contraction and relaxation of membrane
  • Strong cohesion between bilayer and membrane skeleton maintains surface area
20
Q

What are the functions of the RBC membane?

A

1) Shape - provides optimum surface area to volume ratio for respiratory exchange and is essential to deformability
2) Deformability and elasticity - Allows for passage through micro vessels (capillaries)
3) Regulates intracellular concentration
4) Acts as the interface between the cell and its enviroment between the cell and its enviroment via membrane surface receptors

21
Q

Name two RBC membrane abnormality diseases

A
  1. Hereditary elliptocytosis is an inherited blood disorder in which an abnormally large number of the patient’s erythrocytes are elliptical rather than the typical biconcave disc shape.
  2. Hereditary Spherocytosis is caused bymutationsin genes relating to membrane proteins that allow for the erythrocytes to change shape. The abnormal erythrocytes are sphere-shaped (spherocytosis) rather than the normal biconcave disk shaped.
22
Q

Describe haemoglobin (Hb) structure

A
  • Globular haemoglobin

- 4 polypeptide subunits (2 a-globin chains, 2 b-globin chains)

23
Q

What are haemoproteins?

A

A group of specialised proteins that contain haem as a tightly bound prosthetic group

24
Q

What is haem?

A

A complex of protoporphyrin IX and ferrous iron (Fe2+)

The iron is held in the centre of haem by bonds to 4 nitrogens of a porphyrin ring

25
Q

What is the main function of haemoglobin?

A

It delivers oxygen to tissues

26
Q

How does haemoglobin bind oxygen?

A

When oxygenated 2,3-DPG is pushed out; the B chains move closer

B chains are pulled apart when O2 is unloaded, permitting entry of 2,3-DPG results in lower affinity of O2

27
Q

How many oxygen molecules can haemoglobin bind to?

A

4 O2 molecules

28
Q

What does 2,3-DPG do?

A

When it enters the cell, it lowers affinity of haemoglobin for O2

29
Q

What factors affect the normal position of the Hb-oxygen dissociation curve?

A
  • Concentration of 2,3-DPG
  • H+ ion concentration (PH)
  • Co2 in red blood cells
  • Structure of Hb
30
Q

What are the conditions for decreased P50 (increased affinity)?

A

Lower temperature
Lower pCO2
Lower 2,3-DAG
Higher PH

31
Q

What is a major haemoglobin abnormality?

A

Sickle cell anemia

32
Q

What does red blood cells metabolic pathways provide energy for?

A

○ Maintenance of cation pumps
○ Maintenance of Hb in reduced state
○ Maintenance of reduced sulfhydryl groups in Hb and other proteins
○Maintenance of RBC integrity and deformability

33
Q

What are the key metabolic pathways?

A
  1. Glycolytic or Embden-Meyerhof Pathway
    1. Pentose phosphate pathway
    2. Methaemoglonin Reductase Pathway
      1. Luebering-Rapoport Shunt
34
Q

What are the main actions of metabolic pathways in RBC?

A
  • use enzymes to supply energy for the system

- reduce oxidants in the system

35
Q

Explain the glycolytic pathway

A
  • generates the majority of energy needed by RBC
  • glucose is metabolised and generates two molecules of ATP
  • functions in the maintenance of RBC shape, flexibility and the cation pumps
36
Q

Explain the pentose phosphate pathway

A
  • GSH protect RBCs from oxidative damage
  • Pentose phosphate shunt provides the reducing power NADPH
  • NADPH maintains glutathione in the reduced form GSH
37
Q

Explain the methaemoglonin reductase pathway

A
  • Maintains iron in the ferrous (Fe2+) state

- In the absence of this enzyme, methaemoglobin accumulates and it cannot carry oxygen

38
Q

Explain the luebering-rapoport shunt

A
  • Permits the accumulation of 2,3-DPG essential for maintaining normal oxygen tension, to regulate haemoglobin affinity

CVS- Cardiovascular (24 decks)

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