12th Zoology

Excretion Ureotelism Nephron

Excretion Ureotelism Nephron


As a result of continuous synthesis and breakdown of materials many
waste products are formed in cells. The process by which the cellular
nitrogenous wastes are eliminated is called excretion.

Three main nitrogenous wastes are ammonia, urea and uricacid. Various vertebrates excrete different form of nitrogenous wastes, according to the nature of their habitat and availability of water.


Ureotelism is an adaptation for a semi-terrestrial habitat. Urea
requires only a small quantity of water to form urine and never involves much
water loss; Further, urea is much less toxic than ammonia and it can be
retained in blood for sometime before it is transported and eliminated through
the excretory organs. Though the concentration of urea in the blood is small,
it can be stored safely in the bladder in high concentration. Thus ureotelism is
conditioned by the shortage of water, characteristic of the terrestrial habitat.
Urea Biosynthesis (Ornithine Cycle)

Liver is the principal organ of urea biosynthesis. In the ornithine cycle,
ammonia, formed by deamination in cells and tissues, combines with carbon
dioxide to form carbamyl phosphate. This compound is subjected to a cyclic chemical reactions as provided in the figure. Three molecules of ATP are
spent to convert the toxic ammonia into a molecule of urea.


Nephron is the structural and functional unit of the kidney. There are
about a million nephrons
In general, the kidney performs the following vital functions in the
body :
1. Excretion of waste products resulting from protein metabolism.
2. Regulation of acid-base balance by excretion of H+ ions (acidification)
and bicarbonate ions.
3. Regulation of salt-water balance by hormones secreted both intra-and
4. Formation of renin and erythropoietin and thereby playing a role in the
regulation of blood pressure and erythropoises respectively.

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

Leave a Reply

Your email address will not be published. Required fields are marked *