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Anatomy of Hair
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  1. Anatomy of Hair

  2. This is a cross section of a hair showing all three layers

  3. Image of a Hair Follicle

  4. Each Follicle contains a muscle and a sweat gland • Arrector Pili – the muscle that lifts your hair on end when you’re cold or scared

  5. Sebaceous gland – produces oily secretion that cleans hair

  6. Apocrine Gland Produces scent hormones called pheromones

  7. Epidermis Outer layer of skin Made up of 5 dead layers – of keratin packed cells

  8. Dermis – follicle sits in the dermal layer Directly beneath the epidermis. Packed with nerve endings and blood vessels

  9. Hair Follicle – the organ of hair growth

  10. Layers of Hair Follicle Internal and External Root Sheath – molds and forms growing hair Papilla – Actively dividing cells that produce hair Blood Vessels – feed the growing hair Bulb – Bottom of Hair Follicle – contains the papilla and blood vessels Hair Shaft – Made up of Cuticle, Cortex, Medulla

  11. Layers of the Hair Follicle

  12. The Cuticle of Human Hair is rough --- which is why we use Conditioner

  13. Human, Cat, Dog, Mouse • Animals have characteristic cuticle scales that scientists can use to determine the source of hair evidence

  14. Forensic Scientists make a glass slide prep to view animal hair on a Comparison Microscope

  15. In some cases Forensic Scientists make a cast of the cuticle pattern • Cellulose cast

  16. Medulla Patterns • Broken • Intermittent • Continuous

  17. The Medulla of Human Hair is very thin or is not present

  18. Pigment cells are found in the medulla and the cortex

  19. Animal Hair vs. Human Hair • Animal Hair falls into 3 main categories, Guard Hairs, Wool Hairs, Whisker hairs • Human Hairs don’t have a structured medulla ( some human hairs have no Medulla) • - Animal Medulla’s are quite structured

  20. Medulla patterns + other animals

  21. Cat

  22. Rabbit

  23. Rabbit • Cuticle • Pattern >

  24. Deer

  25. Human

  26. 500

  27. Ovoid bodies found in Dog Hair

  28. Ovoid bodies are abundant in Cattle hair

  29. Hair is made of Protein • Hair is made of tight, closely packed dead cells that are made up of myofibrils or bundles of helical keratin

  30. Myofibril - • Bundles of protein filaments that make up muscles and hair

  31. Protein • Long chain of amino acids • Make up muscles, skin, hair nails and all the enzymes in your body

  32. What are amino acids again? • Amino acids make up Protein • Keratin is protein and is therefore made up of amino acids in the form of a helix

  33. As hair grows, new helical Keratin is added quickly • Papilla cells whip out 10 turns of the protein every second!!!

  34. Hair is extremely STRONG • Try to break a piece apart…

  35. Hair gets strength from 3 kinds of Chemical bonds • 1) Individual Keratin Molecules are held together by Hydrogen Bonds

  36. 1) Hydrogen Bonds form between the Amino Acids that make up Proteins

  37. 3) DiSulfide Bridges • Link a Specific Amino Acid together • Cysteine ---Cysteine • When Hair stretches, These bridges break apart • These are COVALENT bonds

  38. 2) Hydrogen Bonds between Helices • Hair is stiff because of H bonds between individual Helices of Keratin. When your hair gets wet, these H bonds break apart and your hair gets limp and looses some of its structure • Why does WATER cause The H bonds in hair to be Rearranged?

  39. Proteins have 4 levels of organization • Primary level --- Sequence of amino acids… polypeptides are thousands of aa’s long… and correct order is crucial

  40. Secondary level • Amino acids react with each other forming • Alpha helices • Beta Sheets

  41. Third level • More folding

  42. Quaternary Structure • Many Poly peptides together • I.e. Keratin

  43. Hemoglobin is a protein that is made up of 4 polypeptides

  44. Hair stretches… • When you stretch hairs H- bonds between helices break, allowing the helix to extend.

  45. Hair Can be Straight or Curly • Hair that is straight has a circular shape • Hair that is curly has an elliptical hair shaft

  46. Curly haired people also have MORE disulfide bridges than straight haired people

  47. When people get a Perm (anent)… Heat is used to Physically change hair • 2 lotions are applied • First Lotion breaks their disulfide bridges

  48. When is hair evidence important in a case? • Animal or Human determination • Body area determination • Race association with hair