The Structure of Hair

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The Structure of Hair

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The Structure of Hair

  1. 1. Structure of Hair Dr. Ali N. Syed Dr. Narjis A. Askar www.dralisyed.com (revised July 3, 2008)
  2. 3. The Cuticle <ul><li>The cuticle covers the hair fiber. </li></ul><ul><li>It is 5-10 layers in thickness (1). </li></ul><ul><li>In African descent hair there are less cuticle layers (2 layers) in the kink. Function: </li></ul><ul><li>It is responsible for shine and protects the inner structure. </li></ul>1. C.R. Robbins in chemical and Physical Behavior of Human Hair.
  3. 4. Structure of Cuticle <ul><li>The Cuticle is made up of the following layers: </li></ul><ul><li>1. The Epicuticle </li></ul><ul><li>2. The A-Layer </li></ul><ul><li>3. The Exocuticle </li></ul><ul><li>4. The Endocuticle </li></ul><ul><li>The Cell Membrane Complex </li></ul>Endocuticle Exocuticle Epicuticle A-Layer CMC
  4. 5. Epicuticle <ul><li>It is a thin material that covers the surface of hair. </li></ul><ul><li>Chemically composed of lipids and Fibrous proteins. </li></ul><ul><li>Function: It makes the cuticle resistant to chemical attacks. </li></ul>Epicuticle CMC
  5. 6. Surface Membrane of Cuticles Source:Menacham Lewin. 2007. P.339
  6. 7. A-Layer <ul><li>It is present beneath the epicuticle. </li></ul><ul><li>Contains 35% cystine. </li></ul><ul><li>The covalent crosslinking of proteins gives toughness to this layer. </li></ul><ul><li>Function: Makes the hair resistant to physical and chemical attacks. </li></ul>A-Layer CMC
  7. 8. Exocuticle <ul><li>Present beneath the A-Layer. Contains 15% cystine. Function: </li></ul><ul><li>Gives toughness to the cuticle. </li></ul>Exocuticle CMC
  8. 9. Endocuticle <ul><li>Present beneath the exocuticle, it is a soft layer. </li></ul><ul><li>Contains 3% Cystine. </li></ul><ul><li>This is the only layer that swells in the presence of water and the swelling causes the cuticle layers to stand out. </li></ul>Endocuticle CMC
  9. 10. Cell Membrane Complex <ul><li>It is present in between the cuticle cells. </li></ul><ul><li>Made up of polysaccharides and lipids. </li></ul><ul><li>Contains an important lipid called 18-MEA. </li></ul><ul><li>Does not give any toughness to the cuticle. Function: </li></ul><ul><li>It acts as a cement between the cuticle layers and holds them together. </li></ul><ul><li>Helps in the transfer of actives from cuticle to cortex. </li></ul>CMC
  10. 11. <ul><li>In the case of high pH products like permanent colors, relaxers, bleaches, and permanent waves, penetration occurs through the swollen layers of the cuticle. </li></ul>Penetration through the cuticle layers
  11. 12. <ul><li>Shampoos and conditioners tend to penetrate through the channels between cuticle layers and then through the junction of cuticle layers and the cortex. </li></ul>Penetration through the Cuticle Layers Penetration through the cuticle layers
  12. 13. Passage of Shampoo and Conditioner Ingredients from Cuticle to Cortex <ul><li>Passage of shampoo and conditioner ingredients occurs through the edges of cuticle layers into the Cortex through the junction of CMC with Cortex. </li></ul>Passage of shampoos and conditioners CMC Endocuticle Exocuticle Epicuticle A-Layer
  13. 14. The Cortex <ul><li>The Cortex occupies 75% of hair. </li></ul><ul><li>It consists of spindle shaped cells separated by CMC of the cortex. </li></ul><ul><li>These cells are the cortical cells - Ortho and Para cortical cells. </li></ul><ul><li>The cortex is mostly made up of keratin protein. </li></ul><ul><li>The major component of each cortical cell is the Macrofibril. </li></ul>
  14. 16. Ortho and Para Cortical Cells – TMA Source: Menachem Lewin. (2007). Fiber Chemistry. P. 334
  15. 17. The Cortex – Hair Types <ul><li>Straight hair (Japanese, Chinese) are exclusively made up of Paracortical cells. </li></ul><ul><li>African descent hair are made up of equal rows of Ortho cortical and Paracortical cells </li></ul><ul><li>Wavy hair (mixed race) are made up of Paracortical cells with a narrow row of Orthocortical cells. </li></ul>Orthocortex Paracortex Cortical CMC
  16. 18. Differences Between Ortho and Para Cortical Cells: <ul><li>Paracortical cells are present in the inside of the crimp. </li></ul><ul><li>More cystine than ortho </li></ul><ul><li>Matrix in para is more than ortho. </li></ul><ul><li>High thermal stability due to greater degree of stabilisation by disulfides . </li></ul><ul><li>Orthocortical cells are present in the outside of the crimp </li></ul><ul><li>Less cystine. </li></ul><ul><li>Matrix is less. </li></ul><ul><li>Low thermal stability due to low cystine </li></ul>Paracortical Orthocortical
  17. 19. <ul><li>Para microfibrils are arranged in hexagonal form (The straight hair has only para microfibrils) </li></ul><ul><li>Ortho microfibrils are arranged as whorls (African descent hair has equal rows of ortho and para). </li></ul>Differences Between Ortho and Para Cortex:
  18. 20. Hexagonal Array of Microfibrils. Source: Menachem Levin.2007: Fiber Chemistry, p344
  19. 21. The Intermediate Filaments or Microfibrils <ul><li>The Intermediate filaments are embedded in the matrix as rods. </li></ul><ul><li>Contain disulfide bonds and have a highly crosslinked structure. </li></ul><ul><li>Do not swell in water. </li></ul><ul><li>The Intermediate filaments are made up of 32 protein chains. </li></ul>
  20. 22. CMC of the Cortical Cells <ul><li>The Cortical cells are separated by Cell Membrane Complex of the Cortex. </li></ul><ul><li>The Cortical CMC is similar to Cuticular CMC but it is not as regular as Cuticular CMC. </li></ul><ul><li>It is made up of lipids and Proteins. </li></ul><ul><li>It does not contain 18-MEA which is exclusively present in Cuticular CMC. </li></ul>Cortical CMC
  21. 23. The Macrofibrils <ul><li>The Macrofibrils are made up of Intermediate filaments or Microfibrils and Matrix. </li></ul><ul><li>They are separated from each other by Intermacrofibrillar Matrix. </li></ul><ul><li>The intermediate filaments (microfibrils) are highly organized structures. </li></ul><ul><li>The matrix is a less organized structure. </li></ul><ul><li>The Intermediate filaments (microfibrils) are surrounded by the Matrix . </li></ul>Macrofibrils Microfibrils Intermicrofibrillar matrix Matrix
  22. 24. The Matrix: <ul><li>The matrix occupies a large portion of the Macrofibrils. </li></ul><ul><li>It contains a high amount of Cystine. </li></ul>Macrofibrils Microfibrils Intermicrofibrillar matrix Matrix
  23. 25. <ul><li>It contains disulfide bonds and is present as a lightly cross-linked gel. </li></ul><ul><li>Because of a less crosslinked structure it swells in water. </li></ul>The Matrix:
  24. 26. <ul><li>The Intermediate filaments are made up of 32 protein chains. </li></ul><ul><li>They are made up of four protofilaments. </li></ul><ul><li>Each protofilament is made up of two protofibrils which form an octamer. </li></ul><ul><li>Each protofibril is made up of a coiled coil dimer. </li></ul><ul><li>Each dimer contains a protein chain. </li></ul><ul><li>Each protein chain is made up of a two strand  -Helix </li></ul>The Intermediate Filaments or Microfibrils . Protein Chain Coiled-coil (Dimer) Profilament (Tetramer) Protofibril (Octamer) Microfibril 70 A
  25. 27. <ul><li>Monomer </li></ul><ul><li>Dimer (2) </li></ul><ul><li>Tetramer or Protofilament (4) </li></ul><ul><li>Protofibril contains 2 protofilaments (4*2=8) </li></ul><ul><li>Intermediate filament contains 4 protofibrils (8*4=32) </li></ul>The Intermediate Filaments or Microfibrils
  26. 28. MICROFIBRIL
  27. 29. MICROFIBRIL Microfibril Protofibrils (4) Protofilament (8) Coiled - Coil (Dimer) (16) a Helix (32) Hierarchy <ul><li>The Intermediate filaments are made up of 32 protein chains. </li></ul><ul><li>They are made up of four protofilaments. </li></ul><ul><li>Each protofilament is made up of two protofibrils which form an octamer. </li></ul><ul><li>Each protofibril is made up of a coiled coil dimer. </li></ul><ul><li>Each dimer contains a protein chain. </li></ul><ul><li>Each protein chain is made up of a two strand a -Helix </li></ul>
  28. 30. The  -Helix Dimer <ul><li>Each  -helix is made up of polypeptide chains of proteins. </li></ul><ul><li>The  -Helix is coiled and has a spacing of 1.5A° between two coils. </li></ul>
  29. 31. The Polypeptide Chains <ul><li>The Polypeptide chains of  -Helix are made up of small units called Proteins. </li></ul><ul><li>Proteins are straight chain Polymers made up of the smallest unit the Amino acids </li></ul><ul><li>Proteins are linked together by the Peptide Bond. </li></ul>
  30. 32. The Amino acids <ul><li>There are 21 different Amino acids in hair and the Amino acid Cystine is present in the highest concentration. </li></ul><ul><li>Amino acids contain a C-atom to which is attached a H-atom, a NH 2 group, a COOH group and a side chain R group. </li></ul>
  31. 33. The Medulla <ul><li>It is present in the center of the fiber. </li></ul><ul><li>It contains hollow spaces filled with air separated by a proteinaceous network. </li></ul><ul><li>It does not contain any Cystine. </li></ul>
  32. 34. The Melanin Granules <ul><li>Melanin is a natural pigment found mainly in the Cortex and sometimes in the Cuticle of dark hair. </li></ul><ul><li>Melanin is of two types: </li></ul><ul><li>Eumelanin the brown- black pigment found in dark hair. </li></ul><ul><li>Pheomelanin the yellow-red pigment found in blond and red hair. </li></ul>

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