12th Zoology



Both testes and ovaries, in addition to their role as reproductive
gamete producing organs, function as endocrine structures also.


The testis in males, in addition to the germinal epithelial cells,
contains groups of epithelioid cells called the interstitial or leydig cells. These
cells constitute the endocrine tissue of the testis. The leydig cells secrete the androgenic hormone testosterone. The androgens are C19 steroids. In the
normal post pubertal males, the rate of secretion of testosterone ranges from
4-9 mg per day. (Gonads)

Action of testosterone

1. Testosterone causes embryonic development of male reproductive
2. It promotes the development of the secondary sexual characters of males,
including physical development, hair distribution, masculine voice and male
behaviour at puberty. (Gonads)


The ovaries are paired, oblong in shape and situated in the pelvic
portion of the abdominal cavity. It releases hormones such as oestrogen
and progesterone. (Gonads)

1. Oestrogen

Under the influence of the FSH from the adenohypophysis, the ovum
grows and becomes enclosed in the Graffian follicle. Associated cells of the
follicle produce a steroid hormone called estrogen. The oestrogens are C18
steroid compounds. It is responsible for the growth of female reproductive
organs and for the appearance of secondary sexual characters.

2. Progesterone

After the discharge of the ovum from the Graafian follicle and after
fertilisation, the ruptured follicle cells form a new structure called corpus
luteum. It produces the pregnancy hormone progesterone. Progesterone is
also synthesized and secreted by the placenta during the later part of
gestation. This hormone is a C-21 steroid compound.
Progesterone is responsible for the premenstrual growth in the
non-pregnant woman’s uterus. The development of the placenta during
pregnancy and the embedding of the fertilized ovum in the uterus
(implantation).  (Gonads)

3. Relaxin

The corpus luteum of the pregnant woman secretes another hormone,
relaxin in addition to progesterone. Relaxin helps in relaxing the muscles and
ligaments of pelvic organs during childbirth (parturition). (Gonads)

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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