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3 Menstrual Cycle

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  • 1. Highlights • General considerations. • Menstrual cycle (MC). • Phases of MC ( 2 ????? 4 ). • Main changes in the endometrium. • Hormonal influence. • GnRH/ • GnH/ • LH/FSH/ • PROGESTERONE/OESTROGEN (estrogen)/ • INHIBIN.
  • 2. General considerations. Structure of uterus • The wall of the uterus is made up of three layer: 1. The perimetrium: outermost layer (peritoneum). 2. The myometrium: main thickness of the wall = smooth muscle. 3. The endometrium: innermost layer corresponding to mucous membrane. The endometrium: is the layer which undergoes changes during MENSTRUAL CYCLE ( MC).
  • 3. The endometrium • The constituents of the endometrium are as follows: 1) The surface of the endometrium is covered by a lining epithelium. 2) The stroma fills the interval between surface epithelium and myometrium. It contains numerous simple tubular glands (uterine glands). 3) The arteries that supply the endometrium tend to run vertically towards the surface. Some of these run spirally and supply the whole thickness of the endometrium, while others that remain straight are confined to the basal part.
  • 4. MENSTRUAL CYCLE
  • 5. MENSTRUAL CYCLE The term is applied to cyclical changes that occur in the endometrium every month. The most obvious feature is a monthly flow of blood (menstruation).
  • 6. General considerations. • Reproductive period = the child bearing period. • Menstruation (menses) = flow of blood from the uterus. • Menarche = the onset of menstruation. • Menopause = cessation of menstruation. • Monthly menstruation is the external manifestation of a series of cyclic changes taking place in the uterus: • these changes constitute the menstrual cycle and the ovarian cycle. The most important event in the ovarian cycle is ovulation.
  • 7. The Menstrual Cycle /phases • On the bases of changes taking place in the uterine endometrium, the MC is divided into the following phases: 1. Postmenstrual 2. Proliferative 3. Secretory or premenstrual 4. Menstrual • The changes during phase 1 + 2 take place under the action of Eterogen produced by the developing follicles in the ovary. Hence this period is referred as the FOLLICULAR PHASE of the MC. • During the 2nd half of the MC (following ovulation), the corpus luteum is formed and start secrete Progesterone, • Progesterone, along with Estrogen, produces striking changes in the endometrium, and as these changes take places under the influence of corpus luteum, this half of MC is called the Luteal phase.
  • 8. The Menstrual Cycle (continue) • Just before next bleeding, there is lowering of levels of both progesterone and estrogen, and it is believed that this WITHDRAWAL leads to the onset of menstrual bleeding. • THE DIVISION OF THE MC into the phases above is, however, arbitrary. The changes are continuous, and may be summarized as follows: 1. The endometrium progressively increases in thickness, (0.5 to 1 mm in the postmenstrual phase ), ( 2 to 3mm in the proliferative phase), and 5 to 7mm in the secretory phase. 2. Uterine gland increase in length, diameter and become convoluted . The basal parts of uterine glands remain tubular (straight) and do not undergo these changes. 3. The epithelium is cuboidal in the postmenstrual phase.  columnar in the proliferative phase.  during secretory phase the apical part of cell is shed off and the cell again becomes cuboidal.  glycogen accumulate in the basal portion of the epithelial cell.
  • 9. The Menstrual Cycle (continue) 4.During the postmenstrual phase, stromal cell are uniformly distributed and are compactly arranged. During proliferative phase, the stroma is divided into 3 layers: A. Stratum compactum. (cells are uniformly distributed and compactly arranged). B. Stratum spongiosum. ( cells surrounding the uterine glands body become spongy). C. Stratum basale. (cells remain compact in the deeper part of the stroma).  During secretory phase, these layers become better defined.
  • 10. The Menstrual Cycle (continue) 5. The arteries of the endometrium are small to start with, they grow in length during the proliferative phase. They become tortuous and are called spiral arteries in the secretory phase.  Toward the end of the secretory phase the endometrium is thick, soft, and richly supplied with blood.  The secretory activity of the uterine glands not only makes the endometrium soft, but also provides nutrition to the embryo.  If the ovum is not fertilized, the stratum compactum and stratum spongiosum are shed off and this is accompanied by menstrual bleeding.
  • 11. The Menstrual Cycle (continue) • During menstrual bleeding: • The endometrium is shed off bit by bit, • The blood with the shreds flows out through the vagina. • At the end of menstruation; the endometrium that remains is only 0.5mm thick. It consists of the stratum basale and along with the basal portions of the uterine glands. • The cervical mucosa is not affected.
  • 12. The mechanism for onset of menstrual bleeding • A few hours before the onset of menstrual bleeding the spiral arteries constricted. • Blood supply to the Superficial parts of the endometrium is cut off. • This ischemia leads to degeneration of the endometrium and also damage the wall of the blood vessels themselves. • When arteries relax and blood again flows, it leaks out through the damaged vessels. • This leaking is responsible for gradual shedding of the endometrium.
  • 13. Time of Ovulation in Relation to Menstruation • The period between ovulation and next menstrual bleeding is constant at about 14 days. • But the time of ovulation does not have a constant relationship with the preceding menstruation. • It is difficult to predict the date of the next ovulation from the date of menstruation unless the woman has very regular cycle. • There are many methods of finding out the exact time of ovulation; the TEMPERATURE METHOD is the most commonly used.
  • 14. CLINICAL CORRELATION • Importance of Determining the Time of ovulation and ‘SAFE PERIOD’. • WHEN PREGNANCY IS NOT DESIRED: • Fertilization can occur only if intercourse takes place during a period between 4 days before ovulation to 2 days after ovulation. • The remaining days have been regarded as SAFE PERIOD. • This forms the basis of so called RHYTHEM- METHOD. • WHEN PREGNANCY IS DESIRED; • The couple can be advised to have intercourse during the days most favorable for conception.
  • 15. Hormonal Control of Ovarian and Uterine cycles • The ovarian and uterine cycles run parallel to each other; both are of 28 days. • The uterine cycle is dependent on the ovarian cycle. • These cycles are under the control of various hormones. The HYPOTHALAMUS acts as a major center for the control of reproduction. It secretes Gonadotropin-releasing hormone (GnRH).  Pituitary gland (adenohypophysis) secretes Gonadotrophic hormones (GnH).  Which are the FOLLICULAR STIMULATING HORMONE (FSH) and the LUTEINIZING HORMONE (LH).
  • 16. Hormonal Control of Ovarian and Uterine cycles  Estrogens are secreted by the maturing ovarian follicles. This takes place under the influence of LH. (Repair and proliferation of the endometrium) (the stroma thickens, glands elongate, spiral arteries grow).  Estrogen level rises to a peak about 2 days before ovulation.  This leads to LH surge 24 to 36 hours before ovulation.  LH surge leads to ovulation ( graafian follicle is transformed into the corpus luteum).  LH stimulates progesterone secretion by corpus luteum.  Progesterone secretion predominates ( still some estrogen is secreted).  The combined action of both hormones stimulate the endometrial glands to secrete glycogen rich mucoid material.
  • 17. Hormonal Control of Ovarian and Uterine cycles (continue) If fertilization occurs: • the corpus luteum does not regress, • It continues to secrete progesterone and estrogen. • The secretory phase of the endometrium continues , • And the menstruation does not occur. If fertilization does not occurs: • The granulosa cells produce the protein INHIBIN, • Inhibin act on the anterior pituitary gland and inhibits the secretion of gonadotrophins (FSH & LH). • This leads to regression of the corpus luteum, fall in the blood level of estrogen and progesterone, and regress of the endometrium and triggers menstruation.
  • 18. CLINICAL CORRELATON / CONTRACEPTION!!!!!!!!!!!! • Use of hormone for contraception: • Ovulation/ pregnancy can be prevented by administering contraceptive pills. • Progesterone is the most important ingredients of such pills. • Better results are obtained when a small amount if estrogen is also given. • Norethisterone acetate 1mg === progesterone. • Estradiol 50µg ==============estrogen. • 28 pills of which 21 contain hormones, and 7 pills do not (for use in the last 7 days). • Started in the 5th day of the cycle. • Taken continuously without break as long as contraception is desired. • Menstruation occurs during the 7 days without hormones. • If pills are taken regularly, the menstrual cycle is regular every 28 days. • Contraceptive pills have almost 100% success in suppressing maturation of follicles and ovulation. • There are many side effects of these pills.
  • 19. Note from slide number 28 up to 44 are free general information. The End Thank you Next lecture: Formation of Germ Layers