12th Zoology

Adrenal gland

Adrenal gland

The adrenal gland or supra renal gland is composed of an outer
cortex and an inner medulla. The adrenal cortex forms the major portion of
the total mass of tissue of adrenal gland. In adults three concentric zones are
discernible within the cortex. 1. A thin outer most layer, the Zona
glomerulosa, 2. A thick middle region, Zona fasciculata and 3. A
relatively thick inner layer, the Zona reticularis.

In man, the cells of zona fasciculata and zona reticularis act as a single unit, the main function of which is to form glucocorticoids and to a lesser extent androgens and possibly oestrogens. The mineralocorticoid hormone, aldosterone is secreted by the cells of the zona glomerulosa. The enzymes necessary for its synthesis reside in the cells of the zona glomerulosa. All the adreno corticoid hormones are
steroids. (adrenal gland)

Action of glucocorticoids

The major glucocorticoids are cortisone and certain closely related
steroids. These hormones stimulate the production of glucose from
non-carbohydrate sources such as fats and amino acids. Glucocorticoids
also decrease glucose utilization by tissues in general. All these effects lead
to increased blood glucose level. Cortisone also acts as an anti-inflammatory
agent. (adrenal gland)

Action of mineralocorticoids

The major effect is on the metabolism of sodium ions and indirectly
potassium ions. The major mineralocorticoid hormone is Aldosterone. Its
most important effect is to promote the resorption of sodium ions from the
renal glomerular filtrate. Secondary effects of sodium retention are an
increased chloride retention and a decreased potassium retention by the
kidneys. The most important function of the adrenal cortex is its role in stress
tolerance. (adrenal gland)

Adrenal medulla

The medulla of adrenal gland differs both in morphology and
physiology from the cortex portion. Both cortex and medulla are derived
independently and from totally different tissues in the embryo. The adrenal
medulla in the adult humans and other mammals is invested closely by the
cortical tissue.

The cells of the adrenal medulla are large ovoid and columnar
in type and are grouped into clumps around the blood vessels. The
hormones produced by adrenal medulla are 1. Adrenalin or epinephrine
and 2. Nor adrenalin or nor epinephrine. The two hormones belong to a
group called catecholamines. The various physiological and biochemical
actions of adrenalin or epinephrine are the following: (adrenal gland)

1. Adrenalin stimulates constriction of blood vessels supplying the intestine,
kidneys, viscera and skin and causes dilation of blood vessels supplying
skeletal and heart muscle.

2. It increases the rate, amplitude and frequency of the heart beat.
3. It causes relaxation of the smooth muscles of the digestive tract and brings
peristalsis to a halt
4. It causes relaxation of the bronchi, dilation of the pupil, closure of
sphincters and increases sweating
5. It causes contraction of muscles associated with hair follicles and makes
the hair “stand on end” and causes goose flesh
6. It accelerates respiration and stimulates mental alertness
7. It stimulates the breakdown of glycogen to glucose, thereby increasing
oxygen consumption and heat production.
8. Biochemically it releases the free fatty acids and increases blood glucose
level.
9. Adrenalin prepares an individual during emergency or stress situations.
Hence it is called the fight, flight and fright hormone.

Action of Nor adrenalin or Nor epinephrine

Nor adrenalin has certain effects similar to that of adrenalin. For
example, both the hormones dilate the coronary vessels. However, nor
epinephrine cause vaso constriction in most organs other than heart.

It increases both the systolic and diastolic blood pressures. It exerts a weakly
inhibitory action upon the contractile activity of smooth muscle in the gastro
intestinal tract. However, it does not relax the smooth musculature of the
pulmonary bronchioles. Nor epinephrine exerts very little effect upon
carbohydrate metabolism and oxygen consumption. (adrenal 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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