Ovulation
INTRODUCTION:
- Ovulation occurs when the ovum surrounded by the corona radiata escapes out of the Graafian follicle.
- It is quickly picked up by the tubal fimbria, which hugs the ovary at ovulation.
- After ovulation, during the luteal phase, the egg will be available to be fertilized by sperm.
- The uterinelining (endometrium) is thickened to be able to receive a fertilized egg.
- If no conception occurs, the uterine lining as well as blood will be shed during menstruation
REGULATION:
- The process of ovulation is controlled by the hypothalamus of the brain and through the release of hormones luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
- Preovulatory phase: FSH.
- Ovulation is triggered by:FSH and LH released from the pituitary gland.
PHASES:
Follicular phase or proliferative phase:
- Lasts from the beginning of menstruation to the start of ovulation.
- Ovum must be supported by the corona radiata and cumulus oophorous granulosa cells.
- Cumulus oophorous granulosa cells cumulus expansion
Ovulation:
- Second phase of the ovarian cycle
- Mature egg is released from the ovarian follicles into the oviduct
- Ovulation is estimated to occur 14 days before the first day of succeeding cycle and this interval is fixed.
- In 40 days of menstrual cycle the ovulation occurs at 26th day
- The lining of the uterus has thickened to prepare for the fertilized egg.
- If no conception occurs, the uterine lining, as well as blood, will be shed.
- The shedding of an unfertilized egg and the uterine wall is the time of menstruation.
- Estrogen levels peak towards the end of the follicular phase.
- Surge in levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
- Lasts from 24 to 36 hours, and results in the rupture of the ovarian follicles, causing the oocyte to be released from the ovary
- All the primary oocytes in the ovary of a newborn are arrested In the late prophase (of meiosis) till puberty.
- At puberty as a result of mid cycle preovulatory surge, meiosis is resumed and completed just prior to ovulation.
- Therefore first polar body is released just prior to ovulation
- The second division starts immediately after it and is arrested in metaphase.
- At the time of fertilization second division is completed which results in the release of oocyte and second polar body.
- Therefore second polar body release occurs only at the time of fertilisation.
- LH surge preceedes ovulation by 34-36 hours.
- LH peak preceedes ovulation by 10-16 hours.
- Prior to ovulation:
- Follicle reaches a size of 18-20mm.
- Endometrium is 9-10 mm thick.
- Endometrium show triple line on USG.
Luteal phase:
- Without the oocyte, the follicle folds inward on itself, transforming into the corpus luteum that produces estrogen and progesterone.
- These hormones induce the endometrial glands to begin production of the proliferative endometrium and later into secretory endometrium, the site of embryonic growth if implantation occurs.
- Maximum function of corpus luteum occurs 9 days after ovulation
- In the absence of pregnancy, will rapidly regress 9 to 11 days after ovulation
- The action of progesterone increases basal body temperature by one-quarter to one-half degree Celsius
- The corpus luteum continues this paracrine action for the remainder of the menstrual cycle, maintaining the endometrium, before disintegrating into scar tissue during menses.
DISORDERS:
The World Health Organization (WHO) has developed the following classification of ovulatory disorders:
- WHO group I: Hypothalamic–pituitary-gonadal axis failure
- WHO group II: Hypothalamic–pituitary-gonadal axis dysfunction.
- WHO group II is the most common cause of ovulatory disorders, and the most common causative member is polycystic ovary syndrome (PCOS).
- WHO group III: Ovarian failure
- WHO group IV: Hyperprolactinemia
METHODS TO DOCUMENT OVULATION:
- Luteinizing Hormone Monitoring Documentation of the LH surge represents a remarkably reproducible method of predicting ovulation.
- Basal Body Temperature: The least expensive method of confirming ovulation is for the patient to record her temperature each morning on a basal body temperature (BBT) chart.
- Midluteal Serum Progesterone
- Ultrasound Monitoring Ovulation can also be documented by monitoring the development of a dominant follicle by ultrasound until ovulation takes place
- A ferning pattern is seen when periovulatory cervical mucus is spread and dried on a microscope slide.
- Endometrial biopsy:EMB near the end of the luteal phase can provide reassurance of an adequate maturational effect on the endometrial lining.
Exam Question
- First polar body is extruded accompanied by ovulation.
- In 40 days of menstrual cycle the ovulation occurs at 26th day.
- Ovulation occurs due to mid cycle FSH and LH surge.
- Fall of temperature at ovulation is by 0.5 degree Fahrenheit.
- Post ovulation, the cervical mucus is thick.
- Maximum function of corpus luteum occurs 9 days after ovulation.
- LH surge preceedes ovulation by 36 hours.
- Time of ovulation is detected by urine LH and urine FSH.
- Best diagnosis of ovulation is by Endometrial biopsy >Ultrasound.
- Tests for ovulation :Fern test , Basal body temperature ,LH surge , Ultrasound Monitoring
- Ovulation can be evaluated by Cervical Mucous.
- Hormonal study(Urinary LH surge) for assessment of female fertility during a menstrual cycle can best predict the timing of ovulation.
- Hypogonadism with normal FSH and oestradiol levels belongs to type II disorders of ovulation as per the WHO classification .
- The mid-cycle shift in the basal body temperature (BBT) after ovulation in women is caused by Progesterone.
- Ovulation occurs 14 days prior to next menstruation.
Don’t Forget to Solve all the previous Year Question asked on Ovulation
