Today we will discuss about the menstrual cycle of female Homo in this blog.
Periodica discharge of blood along with other materials (including one unfertilized ovum) from the female genital tract is called menstruation. Regular repetition of events from one menstruation to the next is called menstrual cycle. This uterine event is the most prominent change in the reproductive cycle of a female.
Duration and flow:
Menstrual bleeding is normally painless and contains no clot. Periodically and duration of bleeding is very often remarkable constant in a particular woman, but highly variable in different woman. The cycle is usually of 28 +/-4 days duration, duration of bleeding is 4 days and amount of bleeding is 4 to 40 ml. If the bleeding is greater than 80 ml, it is taken as abnormal. The blood is mainly arterial and contains shedded endometrium. It is rich in prostaglandins and fibrnolysins. The fibrinolysins prevent coagulation if the bleeding is normal, but fails to do so if the amount of bleeding increases. In that case clots are also passed and the condition is then taken as abnormal.
Subdivisions of the cycle:
- A) Preovulatory part: *) Bleeding phase: 4 days, 1st to 4th day, may vary from 1 to 9 days
*) Proliferative phase: 10 days, 5th day to ovulation i.e. 14th day (it may vary
- B) Post ovulatory part *) Secretory phase: 14 day: 15th to 28th This part is remarkable constant in all
women and bleeding starts 14 days after ovulation.
Description of the cycle:
Follicular phase or Proliferative phase: The proliferatve phase starts after the cessation of menstruation. Its
duration is about 10 days, but varies widely. Endometrium starts healing slowly at first and then proliferates rapidly from 5th to 14th day. During this period, the simple tubular glands grow and there is also growth of blood vessels. Stomal cells and surface epithelium cells also proliferate. The endometrium, which was 2 mm thick initially become 4 mm thick. There is increased contrations of the myometrium. This probably helps in sperm movement. These changes are brought about by the oestrogen from the simultaneously developing follicle under the influence of FSH. Oestrogen in this phase leads to synthesis of progesterone receptors in the endometrial cells. Liquification of cervical secretion also occurs in this phase, so that sperms can enter inside the uterus for fertilization. Ovulation indicates the end of this period.
Secretory phase or Luteal phase: This phase last for about 14 days and is usually constant. It starts after the
ovulation and extends upto the next bleeding. During this phase further thickening of the endometrium (upto 5mm) takes place. Glands secrete mucus, increase in length and diameter, become tortuous, and are filled with secretions. The stoma cells proliferate, spiral arteries become more coiled and dialated. All these changes in the oestrogen primed endometrium are caused by oestrogen and progesterone form the corpus luteum. These changes are to prepare the endometrium, so that he implantation of the fertilized ovum can take place. Progestone also inhibits the myometrium, this prevents expulsion of the implanted ovum. Cervical secretions become thick and prevents entry of sperms.
Mittelschmerz: intermenstrual pain ); an abdominal pain occurring at the time of ovulation, resulting from irritation of the peritoneum by bleeding from the ovulation site. It is common during ovulation for some time following puberty.
Menses or Menstrual Phase or Bleeding phase: If the ovum is not fertilized, the corpus luteum (CL)
regresses from the 24th day of the cycle. (Maintenance of CL beyond this, needs chorionic gonadotrophin). Due to regression of the CL, oestrogen and progesterone secretion decreases and ultimately becomes very low. The endometrium shrinks without hormonal support (gets thinner) and the coiled arteries become further coiled. There is also spasm of the arteries, thus stoppage of blood flow, which leads to focal necrosis of the endometrium and haemorrhage. Necrotic foci then then coalesce and menstrual bleeding starts with subsequent dilation of the arterioles. This occurs after luteolysis i.e. due to loss of hormonal (oestrogen and progesterone) support to the endometrium.
The cause of the bleeding is necrosis due to cessation of blood flow. This occurs may be due to further coiling of arteries or may be due to vasospasm due to prostaglandin liberated locally. The last one seems to be the most important factor. Prostaglandins also cause contraction of myometrium. In abnormal situation where prostaglandin synthesis increases, there is severe spasm of myometrium leading to pain (dysmenorrhea) during menstruation.
- Ovarian cycle:
Development of Graafian follicle à maturation of the oum à ovulation à formation CL à regression of CL à Development of Graafian follicle
- Uterine Cycle:
Shedding of endometrium (bleeding) à regeneration of endometrium ie. Proliferative change à secreting change à shedding (bleeding).
- Anovulatory cycle: If ovulation does not take place the cycle is tehn called anovulatory cycle. Here CL does not form, so progesterone is not available. Endometrium continues to grow under the influence of oestrogen. When it becomes very much thick, it sloughs and bleeding starts. This type of cycles are normally seen at the start (around puberty) and at the end (before menopause) of the reproductive life.
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