EndocrinologyHormonal Control Of Ovarian and

Endometrial Cycle

Presented By: Girish Kumar K III MSc Biomedical Science

Ovarian Cycle• The ovarian cycle is a series of events in the ovaries

that occur during and after the maturation of the oocyte (egg or ovum).

• It is the development and release of oocytes in the ovary and changes in the follicles.

• Ovarian cycle occurs within 28days and involves both oogenesis, the process of formation and development of oocyte, and preparation of the uterus to receive a fertilized ovum.

• The cycle is consists of follicular phase and luteal phase.

The Endometrial cycle• It is the preparation of the lining of the uterus

(endometrium) for implantation by a fertilized egg and shedding of the lining when implantation has failed.

• The cycle consists of the menstrual (menstruation), proliferative phase and secretory phase.

• The two cycles occurs concurrently and regulated by hormones released by the endocrine system.

• Changes in the ovary is regulated by the hormones from anterior pituitary.

• Changes in endometrium is regulated by hormones from ovary during the ovarian cycle.

Ovarian CycleFollicular Phase• Occurs in the first half of the cycle• Oocyte inside each follicle enlarges and thecal cells

in follicle secretes increased amount of oestrogen.• Zona pellucida and antrum forms• A rapid follicular growth continues during the

follicular phase.• One follicle usually grows more rapidly & matures

about 14 days after onset of follicular development.

Hormonal Control Of Follicular Phase

Ovulation• Walls of the Graffian follicles

ruptures and thereby antral fluid along with the oocytes flows to ovarian surface.

• Fluids and the oocytes are released and the oocytes enters the uterine tube.

• Luteinizing hormone is triggered.• Follicle(s) are released during

ovulation.

Luteal Phase• It is the last 14 days of the ovarian cycle.• Old follicular cells undergoes structural

transformation to form corpus luteum.• Fully functional within four days after ovulation and

continues to increase in size for another 4-5 days.• If released ovum is not fertilized and does not

implant, corpus luteum degenerates within about 14 days after formation.

• Hormonal control: LH causes development of corpus luteum from empty Graafian follicle.

Hormonal Control of Ovulation

Endometrial Cycle• Reflects from hormonal changes during

ovarian cycle.• Averages for 28days.• The cycle consists of three phases.Menstrual phaseProliferative phase (estrogen)Secretory or progestational phase.

(progesterone)

Menstrual phase – In this phase there is a decreased level of oestrogen and progesterone. Uterine lining is shed from 5-7 days.

Proliferative phase – Increased level of estrogen. Endometrium is renewed in the preparation of possible pregnancy.

Secretory phase – Increased level of progesterone. Endometrium is developed. The phase coincides with the luteal phase.

Menstrual phase• Characterized by discharge of blood and endometrial

debris from vagina .• First day of menstruation is considered start of new cycle.

Coincides with end of ovarian luteal phase and onset of follicular phase.

• Triggered by decreased oestrogen and progesterone: hormones decrease when corpus luteum degenerates.

• Release of uterine prostaglandin.• Causes vasoconstriction of endometrial vessels, disrupts

blood supply and causes death of endometrium.• Stimulates mild rhythmic contractions of uterine

myometrium – Helps expel the menstrual flow

Proliferative phase• Begins concurrent with last portion of ovarian

follicular phase.• Uterus prepares for fertilized ovum.• Endometrium starts to repair itself and

proliferate under influence of oestrogen from newly-growing follicles.

• Oestrogen-dominant proliferative phase lasts from end of menstruation to ovulation Peak oestrogen levels trigger LH surge responsible for ovulation

Secretory phase• Endometrium prepares for implantation with increased blood supply. • Glands enlarges and secrete glycogen-rich fluids. • Secretory phase conditions promoted by progesterone – Uterus

enters this phase after ovulation when new corpus luteum is formed.• Corpus luteum secretes large amounts of progesterone and

oestrogen.• Progesterone converts endometrium to highly vascularized, glycogen-

filled tissue.• Endometrial glands actively secrete glycogen.• If fertilization and implantation do not occurs. 1. Corpus luteum degenerates. 2. New follicular phase and menstrual phase begin again.

Timing Of Ovarian and Endometrial cycles

Hormonal control of Endometrial cycle

• FSH - Follicle stimulating hormone growth and development of follicles.

• LH - Luteinising hormone causes ovulation development of corpus luteum.

• Inhibin - Decreases FSH but not LH.

Oestrogen• Stimulate oogenesis and follicle development.

• Promote proliferative-phase uterine conditions.

• Induce expression of uterine progesterone receptors.

• Induce expression of granulosa cell LH receptors.

• Secondary sexual characteristics Breast growth during pregnancy

Progesterone• Promotes secretory-phase uterine conditions.

• Suppresses uterine contraction during pregnancy.

• Promotes growth of glandular breast tissue but suppresses milk production

• Oestrogen secreted first from the follicle, then from the corpus luteum.

• Progesterone secreted from the corpus luteum.

• LH and FSH secreted from the anterior pituitary.

• Oestrogen and progesterone inhibit LH and FSH secretion

1. Which two hormones stimulate the development of follicles in the follicular phase of ovarian cycle?

2. What are the functions of the LH in luteal phase?

3. Role of progesterone and oestrogen in the endometrial cycle? Any two.

Answer:1. FSH and Oestrogen.2. LH causes development of corpus luteum from

empty Graafian follicle.3. Progesterone - Promotes growth of glandular

breast tissue but suppresses milk production -suppresses uterine contraction during pregnancy. Oestrogen - Stimulate oogenesis and follicle development. -Secondary sexual characteristics Breast growth during pregnancy

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