12th Zoology

Parathyroid gland

Parathyroid gland

In man the parathyroid gland are small oval yellow-brown bodies
found attached to the posterior surface of the thyroid gland. The parathyroid
gland secrete two hormones namely, 1. Parathormone and 2. Calcitonin.


Purified parathormone is a simple polypeptide chain. It has short
duration of biological activity. The half-life of the hormone is of about 20-30
minutes only.

Physiological effects of Parathormone

Parathormone manifests its regulatory effects at three different loci in
the body namely the skeleton, kidneys and the gastro intestinal tract. In
skeleton, the hormone directly acts upon the bone tissue to stimulate the
activity of osteoclast cells (bone destroying cells). Under the influence of this
hormone calcium is released from the bone matrix into the circulation. As a
result plasma calcium level increases. Thus it helps in the skeletal
remodelling. (parathyroid gland)

In kidney, parathormone induces a marked increase in phosphate
excretion. In the gastro intestinal tract, parathormone stimulates the
absorption of calcium and phosphate from the gut by enhancing the
vitamin D synthesis. As a result, more phosphate and calcium are
transported into the blood stream. Its other physiological effects include its
inhibitory action over the osteoblasts or bone forming cells, bicarbonate
reabsorption and reduction of urine pH, etc.


It is a calcium-lowering hormone secreted by the parafollicular cells
of the parathyroid gland. It is a protein. Its physiological effects are antagonistic
to that of parathormone. It inhibits bone resorption. In kidney, it inhibits the
reabsorption of calcium, phosphorus, sodium, potassium, magnesium and
other ions. It decreases gastric HCl secretion. It also decreases the insulin
and glucagon secretion. (parathyroid gland)


It is a condition where there is an increased amount of parathyroid
hormone in circulation. Excess secretion of parathormone brings about
demineralization of the bones.

The protein matrix of the bone is also absorbed. These changes result in bone cyst and the elevation of the calcium level in the blood. The latter causes calcification of kidneys, arteries, stomach and lungs. (parathyroid gland)


Removal of parathyroids causes the blood calcium levels to fall and
results in tetany. Tetany is characterized by low serum calcium
(Hypocalcemea), reduced urinary excretion of calcium and phosphate,
neuromuscular hyperexcitability, spasms of muscles and cramps etc. (parathyroid gland)

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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