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The Endometrial Cycle (Menstrual cycle)

The Endometrial Cycle (Menstrual cycle). In the endometrial lining of the uterus. Proliferative phase Secretory phase Menstruation. The Endometrial Cycle (Menstrual cycle). Proliferative phase (11 days): Occurs before ovulation. (but after the last cycle which desquamated the epithelium)

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The Endometrial Cycle (Menstrual cycle)

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  1. The Endometrial Cycle (Menstrual cycle) • In the endometrial lining of the uterus. • Proliferative phase • Secretory phase • Menstruation

  2. The Endometrial Cycle (Menstrual cycle) • Proliferative phase (11 days):Occurs before ovulation. (but after the last cycle which desquamated the epithelium) • Epithelial cells and stromal cells proliferate rapidly. • Due to the high levels of _estrogen_ secreted by the ovaries. • The epithelial surface is re-epithelialized in 4-7 days. • By the end of this phase the endometrium has increased greatly in thickness (up to 3-5 mm). • Increased number of stromal cells. • Progressive growth of endometrial glands which produce astringy mucusused to guide spermatozoa. Sherwood’s Human Physiology 20-15 5th Ed. & 20-16 6th Ed.

  3. The Endometrial Cycle (Menstrual cycle) • Secretory phase (12 days):Occurs after ovulation. • Slight proliferation of the endometrium (5-6 mm). • Due to the corpus luteum secretion of estrogens. • Swelling and increased secretion of the endometrium. • Due to the corpus luteum secretion of progesterone. Sherwood’s Human Physiology 20-15 5th Ed. & 20-16 6th Ed.

  4. The Endometrial Cycle (Menstrual cycle) • The glands increase in tortuosity. • Excessive secretion accumulates. • Stromal cells have large cytoplasms full of glycogen and lipids. • The blood supply increases & vessels increase in tortuosity. • The whole purpose for these endometrial changes is to accommodate a fertilized ovum. Usually 3-4 days after ovulation. Sherwood’s Human Physiology 20-15 5th Ed. & 20-16 6th Ed.

  5. The Endometrial Cycle (Menstrual cycle) • Menstrual Phase (5 days): • If no ovum is fertilized about day 26 the corpus luteum involutes and estrogen and progesterone levels fall. • The decrease in estrogen and progesterone levels induce menstruation. • Decreased stimulation of the endometrial cells. • Involution of endometrial cells. • Tortuous blood vessels become vasospastic, resulting in hemorrhage and necrosis of the tissues. • Eventually the necrotic layers separate from the uterus until all the superficial layer of the endometrium have desquamated. • The mass is expelled due to uterine contractions. Within 4-7 days after menstruation starts the loss of blood stops as the endometrium has re-epithelized. Guyton’s Textbook of Medical Physiology81-7

  6. Hormonal Regulation of the Endometrial Cycle • Postovulatory phase • High levels ofestrogenand progesteronesecretion by the corpus luteum and secretion ofinhibin have negative feedback control (on both anterior pituitary and hypothalamus) over the secretion ofFSHandLH. Guyton’s Textbook of Medical Physiology81-3

  7. Hormonal Regulation of the Endometrial Cycle • Follicular growth phase • 3 days before menstruationestrogen,progesterone, andinhibin levels decrease, releasing their control over the anterior pituitary and hypothalamus.FSHand LHlevels increase. • New follicle growth inducesestrogensecretion slowly inhibitingFSHandLHproduction. • (Does not explain preovulatory surge in LH and FSH?) Guyton’s Textbook of Medical Physiology81-3

  8. Guyton’s Textbook of Medical Physiology81-3

  9. Hormonal Regulation of the Endometrial Cycle • Preovulatory phase • It is believed that the high levels ofestrogenor the beginning ofprogesterone secretion is responsible for a positive feedback resulting in a surge ofLHand FSHproduction. Guyton’s Textbook of Medical Physiology81-3

  10. Hormonal Regulation of the Endometrial Cycle Sherwood’s Human Physiology 20-18 5th Ed. & 20-19 6th Ed.

  11. Follicular (O) & Proliferative (U) Phase • Increasing E (from follicle) leading to a peak before ovulation, decreasing FSH • Ovulation • E drop followed by LH & FSH surge and P increase • Luteal (O) & Secretory (U) Phase • E & P increase, LH & FSH decrease • Beginning ofNew Follicular (O) & Menstrual (U) Phase • E & P decrease, LH & FSH increase Summary Sherwood’s Human Physiology 20-15 5th Ed. & 20-16 6th Ed

  12. Non-Ovarian Cycle Functions of Estrogen & Progesterone • Progesterone functions in breast development & and is mainly involved in pregnancy. • Estradiol (the principal estrogen) is involved in development of the secondary sex characteristics of the female. • Increased size of the reproductive organs • Increases osteoblast activity and therefore bone growth • Increases total body protein • Slightly increase metabolic rate • Development of a soft & smooth skin

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