Ovulation Physiology Notes

Introduction

Ovulation is the process by which the Graafian follicle in the ovary ruptures and, the ovum is released into the abdominal cavity. Ovulation occurs on the 14th day of the menstrual cycle in a normal cycle of 28 days.

The ovum, which is released into the abdominal cavity, enters the fallopian tube through the fimbriated end of the tube. Usually, only one ovum is released from any one of the ovaries. LH is responsible for ovulation.

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Process Of Ovulation

Prior to ovulation, a large amount of LH is secreted (luteal surge). This causes changes in the Graafian follicle leading to ovulation.

Stages of ovulation:

1. Graafian follicle moves towards the periphery of the ovary
2. New blood vessels are formed in the ovary by actions of LH and progesterone
3. These blood vessels protrude into the wall of the follicle
4. This increases the blood flow to the follicle
5. Now, prostaglandin is released from granulosa cells of the follicle
6. It causes leakage of plasma into the follicle
7. Just before ovulation the follicle swells and protrudes against the capsule of the ovary. This protrusion is called a stigma
8. Hen, progesterone activates the proteolytic enzymes present in the cells of theca interna
9. These enzymes weaken the follicular capsule and cause degeneration of the stigma
10. After about 30 minutes, fluid begins to ooze from the follicle through the stigma
11. It decreases the size of the follicle causing a rupture of the stigma
12. A new, ovum is released from the follicle along with fftjKf and plenty of small granulosa cells into the abdominal cavity.

Hormonal Regulation Of Ovulation

The hormonal regulation of ovulation is discussed in the previous chapter.

Determination Of Ovulation Time

Usually, ovulation occurs on the 14th day of the menstrual cycle if the cycle occurs in 28 days period. There are various methods to determine the ovulation time.

In human beings, usually indirect methods are adopted such as:

1. Determination of basal body temperature
2. Determination of hormonal excretion in urine
3. Determination of hormonal level in plasma
4. Ultrasound scanning.
5. Cervical mucus pattern

Determination Of Basal Body Temperature

• The body temperature is measured for a few days during the mid-period of the menstrual cycle. Temperature is
• measured in the morning by placing the thermometer in the rectum or vagina. There is a slight fall in the basal temperature just prior to ovulation.
• And, the temperature increases after ovulation. The alteration in the temperature is very mild and it is about ± 0.3-0.5°C. The increase in temperature is due to the thermogenic effect of progesterone.

Determination Of Hormonal Excretion In Urine

At the time of ovulation, there is an increase in the urinary excretion of metabolic end products of estrogen and progesterone. The end products of estrogen metabolism are estrone, estriol, and estradiol. The end product of progesterone metabolism is pregnanediol.

Determination Of Hormonal Level In Plasma

Plasma level of FSH, LH, estrogen, and progesterone is measured. The hormonal level is altered at the time of ovulation and after ovulation.

At the time of ovulation:

1. FSH level decreases
2. LH level increases L- Estrogen level increases.
3. After vitiation:

Progesterone level increases.

Ultrasound Scanning

The process of ovulation can be observed in ultrasound scanning.

Cervical Mucus Pattern

When the cervical mucus spread on a slide is examined under a microscope, it shows a fern pattern. This pattern disappears after ovulation.

Significance Of Determining Ovulation Time

Family planning by rhythm method may be well adopted by determination of ovulation time.