12th Zoology

Melanin functions

Melanin functions

Melanin is the brown black, non-haemoglobin-derived pigment
normally present in the hair, skin choroid of the eye, meninges and adrenal
medulla. It is synthesized in the melanocytes and dendritic cells, both of which
are present in the basal cells of the epidermis.

Melanin is stored in the form of cytoplasmic granules in the phagocytic cells called the melanophore, present in the under lying dermis. Melanocytes possess the enzyme tyrosinase necessary for the synthesis of melanin from the amino acid called tyrosine Tyrosine tyrosinase Melanin

Various disorders of melanin pigmentation cause generalized and
localized hyperpigmentation and hypopigmentation.

Generalized hyperpigmentation

a) In Addison’s disease, there is generalized hyperpigmentation of the skin,
especially in areas exposed to light and buccal mucosa.
b) Hyper pigmentation on skin of face, nipples and genitalia during pregnancy
under the influence of oestrogen.
c) In chronic arsenical poisoning, there is characteristic rain-drop pigmentation
of the skin.

Generalized hypopigmentation

Albinism is an extreme degree of generalized hypo pigmentation in
which tyrosinase activity of the melanocytes is genetically defective and no
melanin is formed. Albinoes have blonde hair, poor vision and severe
photophobia. They are highly sensitive to sunlight. Chronic sun exposure
may lead to pre-cancerous lesions, squamous and basal cell cancers of the
skin.

Localised hypopigmentation

a) Leucoderma is a form of partial albinism and is an inherited disorder.
b) Vitiligo is local hypopigmentation in the skin.
c) Acquired local hypopigmentation can result from various causes such as
leprosy, healing of wounds, radiation dermatitis, etc.

Related Topics in Zoology:

Bio Zoology All Important Topics


  1. Human Physiology Introduction

  2. Nutrition

  3. Carbohydrates Poly hydroxyaldehydes (or) ketones

  4. Proteins (Polypeptides)

  5. Lipids

  6. Vitamins – Functions Of Vitamins

  7. Deficiency of Vitamin

  8. Minerals – Water – Role of water

  9. Balanced diet

  10. Obesity

  11. Digestive System

  12. Dental Caries (Tooth decay)

  13. Root Canal Treatment

  14. Peptic ulcer

  15. Hernia and Types

  16. Appendicitis (Appendix)

  17. Gall Stones

  18. Hepatitis

  19. Fractures – Types of fractures

  20. Mechanism of fracture

  21. Dislocation of joints

  22. Arthiritis

  23. Rickets and Osteomalacia – Orthopedics

  24. Muscles

  25. Mechanism of muscle contraction

  26. Types of muscle contraction

  27. Myasthenia Gravis

  28. Respiration – Process of pulmonary respiration

  29. Mechanism of Breathing

  30. Regulation of Respiration

  31. Pneumonia Tuberculosis Symptoms Treatment

  32. Bronchitis – Acute bronchitis, Chronic Bronchitis Causes

  33. Circulatory System – Functioning of Human heart

  34. Cardiac Cycle

  35. Coronary blood vessel and its significance

  36. Myocardial infarction

  37. Angina pectoris

  38. Angiogram – Angioplasty

  39. Atherosclerosis

  40. Heart block Echo cardiography Heart Valves

  41. Rheumatic Heart Disease (RHD), ICCU – (Intensive Coronary Care Unit)

  42. Blood Pressure

  43. Heart transplantation

  44. Pulse rate

  45. Cardio Pulmonary Resuscitation (CPR)

  46. Blood – Composition of plasma – Blood cells

  47. Clotting of Blood or Haemostasis

  48. Thrombosis

  49. Nervous system Co-ordination systems

  50. The Brain – Fore Brain, Midbrain, Hindbrain

  51. Memory

  52. Sleep – Types of sleep

  53. Stroke – Brain haemorrhage

  54. Alzheimer – Meningitis (Brain fever)

  55. Conditioned reflex

  56. Electroencephalography EEG

  57. Right and Left brain concept

  58. Spinal cord functioning

  59. Chemical co-ordination – Functions of Endocrine glands

  60. Hypothalamus

  61. Pituitary gland – hormone

  62. Hormones of Neurohypophysis – vasopressin

  63. Thyroid gland

  64. Parathyroid Gland

  65. Pancreas

  66. Adrenal gland

  67. Gonads

  68. Receptor Organs – Eye

  69. Photochemistry of Retinal visual Pigments

  70. Errors of refraction

  71. Optometry – Retinopathy

  72. Cataract – Lens Replacement – Glaucoma – Nyctalopia

  73. Eye Infections and Eye Care

  74. Ear

  75. Mechanism of hearing

  76. Defects of the ear

  77. Hearing Aid – Noise pollution

  78. Skin and functions of skin

  79. Melanin functions

  80. Effects of solar radiation / UV radiation – Skin grafting

  81. Dermatitis

  82. Tongue – Mechanism of Stimulation

  83. Excretion Ureotelism Nephron

  84. Mechanism of urine formation

  85. Renal Failure, Dialysis, Kidney Machines

  86. Kidney stone – Kidney transplantation

  87. Diabetes mellitus

  88. Functioning of male reproductive system

  89. Functioning of female reproductive system

  90. Ovulation and fate of the ovum – Menstrual cycle

  91. Fertilization

  92. Birth control

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