12th Zoology

Ovulation and fate of the ovum – Menstrual cycle

Ovulation and fate of the ovum – Menstrual cycle

The shedding of the ovum from the ovary is called ovulation. The ovarian
follicle enlarges and reaches the surface of the ovary. The stroma and the theca
of the Graffian follicle ruptures and the ovum is shed from the ovary. As it reaches
the fallopian tube it may get fertilized. The fertilized egg reaches the uterus and
gets implanted on its wall. If the ovum is not fertilized in the fallopian tube it dies
in 12- 24 hours.

Corpus luteum

The corpus luteum is an important structure needed at the time of
pregnancy. It is derived from the empty graafian follicle after ovulation. The
corpus luteum secretes a hormone called progesterone. It is a steroid hormone,
secreted in significant amounts by the corpus luteum and placenta.

Menstrual cycle

The functioning of the reproductive system in human adult female is
characterized by the menstrual cycle. While the changes concerned within ovulation and the formation of the corpus luteum, are going on in the ovary, the uterine endometrium shows striking cyclical changes.

The rhythmical series of changes in the sex organs occur for about 28 days through out the reproductive life of women from puberty to menopause (except during times of pregnancy). It is called the menstrual cycle.

The most prominent feature of this cycle is a monthly flow of blood from
the genital canal. This is called menstruation or menses. A menstrual cycle begins with the onset of menstrual bleeding and ends just before the next menstruation.

The menstrual cycle is usually divided into the following phases on
the basis of changes taking place in the uterine endometrium.
The follicular phase or Proliferative phase ( 5th day – 14th day)

The follicular phase is initiated by the release of follicle stimulating
hormone (FSH) from the anterior pituitary gland. During this phase, a
primary follicle begins to enlarge. While it is growing, the follicles secrete
oestrogen and smaller quantities of progesterone into the blood. Under the
effects of oestrogen from the developing follicle, the endometrium starts
regenerating from the basal portion. Deeper parts of the glands start proliferating.

By day 14, graffian follicle has matured and pushed up against
the ovary surface. The secretion of FSH ceases at the end of follicular phase.
The Luteal phase or Premenstrual phase (15th day – 28th day)

The luteal phase begins at day 14. Under the influence of Leutenizing
hormone (LH) released by the anterior pituitary, rupture of graffian follicle
and release of ovum (ovulation) occurs. After ovulation, the empty follicle is
transformed into a transitory endocrine gland called corpus luteum. The
corpus luteum slowly increases in size and releases a large quantity of
progestrone and smaller amount of oestrogen into the blood.

The progesterone acts on endometrium of the uterus, preparing it to receive the
fertilized ovum. To maintain pregnancy and to prevent the contraction of
uterus, the progesterone hormone is highly essential. If there is no fertilisation,
the corpus luteum degenerates and is reabsorbed by the ovary at the end of
luteal phase.

The menstrual phase (1st – 5th day)

The decline in progesterone and oestrogen initiates shedding of the
endometrium and severe bleeding in a process called mensus or
menstruation. During this phase, all the extra layers are sloughed off along
with unfertilized egg. At the termination of menstruation, the corpus luteum is
converted into a scar tissue called corpus albicans.

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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