Menstrual cycle Flashcards
Describe the reproduction
Reproduction begins with the development of ova in the ovaries. In the middle of each monthly sexual cycle, a single ovum is expelled from an ovarian follicle into the abdominal cavity near the open fimbriae tubae uterinae of the tuba uterina. This ovum then passes through one of the tubae uterinae into the uterus; if it has been fertilized by a sperm, it implants in the uterys, where it develops into a fetus, a placenta, and fetal membranes - and eventually into a baby.
What is a developing egg called?
Oocyte
What is a oocyte?
Oocyte is a developing egg
What differentiates a oocyte into?
Oocyte differentiates into a mature egg called ovarium through a series of steps called oogenesis
What is oogenesis?
Oogenesis is the differentiation of the ovarium
What is oogenesis?
Oogenesis is the differentiation of the oocyte into a mature egg (ovum) to further develop when fertilized.
Questions about the oogenesis
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Describe the female hormonal system
The female hormonal system consists of three hierarchies of hormones
1. A hypothalamuc releasing hormone, called gonadotropin-releasing hormone (GnRH)
2. The anterior pituitary sex hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both of which are secreted in response to the release of GnRH from the hypothalamus
3. The ovarian hormones, estrogen and progesterone, which are secreted by the ovaries in response to the two female sex hormones from the anterior pituitary gland
How does the female hormones differ during different parts of the female monthly sexual cycle?
The various hormones are secreted at drastically differing rates during different parts of the gemale monthly sexual cycle.
- Estrogen peaks at ovulation
- Progesteron peaks after ovulation
What is the monthly rhythmical changes in the rates of secretion of the female hormones and corresponding physical changes in the ovaries and other secual organs called?
The female monthly sexual cycle or the menstrual cycle
What is the duration of the menstrual cycle?
The duration of the cycle averages 28 days. It may be as short as 20 days or as long as 45 days in some women, although abnormal cycle length is frequently associated with decreased fertility.
What is the two significant results of the menstrual cycle?
First, only a single ovum is normally released from the ovaries each month, so normally only a single fetus will begin to grow at a time.
Second, the uterine endometrium is prepared in advance for implantation of the fertilized ovum at the required time of the month.
At what day does the ovum normally realease from the ovaries each month?
The ovum is normally released from the ovaries at day 14 of the menstrual cycle
The ovarian changes that occur during the menstrual cycle is due to what?
The ovarian changes that occur during the sexual cycle depend completely on the gonadotropic hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are secreted by the anterior pituitary gland.
Why are the ovaries inactive throughout childhood and when do they begin being active?
The ovaries are inactive throughout childhood because almost no pituitary gonadotropic hormones are secreted. At age 9 to 12 years, the pituitary begins to secrete progressively more follicle-stimulating hormone and luteinizing hormone, which leads to the onset of normal monthly menstrual cycles beginning between the ages of 11 and 15 years,
What is puberty?
The ovaries are inactive throughout childhood because almost no pituitary gonadotropic hormones are secreted. At age 9 to 12 years, the pituitary begins to secrete progressively more follicle-stimulating hormone and luteinizing hormone, which leads to the onset of normal monthly menstrual cycles beginning between the ages of 11 and 15 years, This period of change is called puberty.
Define menarche
Menarche is the time of the first menstrual cycle
What is the first time of the first menstrual cycle called?
Menarche
How does female sex hormones stimulate the ovaries?
Both follicle-stimulating hormone and luteinizing hormone stimulate their ovarian target cells by combining with highly specific FSH and LH receptors in the ovarian target cell membranes.
In turn, the activated receptors increase the cells’ rates of secretion (stimulate sex hormone synthesis) and usually growth and proliferation of the cells as well.
What is a primordial follicle?
When a female child is born, each ovum is surrounded by a single layer of granulosa cells; the ovum, with this granulosa cell sheath, is called a primordial follicle.
What are primordial follicles surrounded by?
Primordial follicles are surrounded by a single layer of granulosa cells
What are the granulosa cells’, that surrounds primordial follicles, function?
The granulosa cells are believed to provide nourishment for the ovum and to secrete an oocyte maturation inhibiting factor that keeps the ovum suspended in its primordial state in the prophase stage of meiotic division.
What happens in the ovaries after puberty, when FSH and LH from the anterior pituitary gland begin to be secreted in significant quantities?
The ovaries (together with some of the follicles within them) begin to grow.
What is the first stage of follicular growth?
The first stage of follicular growth is moderate enlargement of the ovum, which increases in diameter twofold to threehold. That stage is followed by growth of additional layers of granuosa cells in some of the follicles. These follicles are known as primary follicles.
What happens in the first few days of each monthly female menstrual cycle?
The concentrations of both FSH and LH secreted by the anterior pituitary gland increase slightly to moderately, with the increase in FSH slightly greater than that of LG and preceding it by a few days.
These hormones, especially FSH, cause accelerated growth of 6 to 12 primary follicles each month. The initial effect is rapid proliferation of the granulosa cells, giving rise to many more layers of these cells.
In addition, spindle cells derived from the ovary interstitium collect in several laters outside the granulosa cells, giving rise to a second mass of cells called the theca.
What is the theca divided into?
The theca is divided into two layers.
In the theca interna, the cells take on epithelioid characteristics similar to those of the granulosa cells and develop the ability to secrete additional steroid sex hormones (estrogen and progesterone).
The outer layer, the theca externa, develops into a highly vascular connective tissue capsule that becomes the capsule of the developing follicle.
What happens after the early proliferative phase of follicular growth?
After the early proliferative phase of growth, which lasts for a few days, the mass of granulosa cells secretes a follicular fluid that contains a high concentration of estrogen. Accumulation of this fluid causes an antrum to appear within the mass of granulosa cells.
How does the primary follicle develop into the antral follicle?
The early growth of the primary follicle up to the antral stage is stimulated mainly by FSH alone. Greatly accelerated growth then occurs, leading to still larger follicles called vesicular follicles.
Once the antral follicles begin to grow, their growth occurs almost explosively. The ovum also enlarges in diameter another threefold to fourfold, giving a total diameter increase up to 10-fold, or a mass increase of 1000-fold.
What happens about 2 days before ovulation?
About 2 dats before ovulation the rate of secretion of luteinizing hormone by the anterior pituitary gland increases markedly, rising 6- to 10-fold and peaking about 16 hours before ovulation.
Follicle-stimulating hormone also increases about twofold to threefold at the same time, and the FSH and LH act synergistically to cause rapid swelling of the follicle during the last few days before ovulation.
What effect does luteinizing hormone have on the granulosa and theca cells?
Luteinizing hormone converts them mainly to progesterone-secreting cells. Therefore, the rate of secretion of estrogen begins to fall about 1 day before ovulation, while increasing amounts of progesterone begin to be secreted.
What happens to the follicle after expulsion of the ovum?
The remaining granulosa and theca interna cells change rapidly into lutein cells. They enlarge in diameter two or more times and become filled with lipid inclusions that give them a yellowish appearance. This process is called luteinization, and the total mass of cells together is called the corpus luteum.
Describe the development of the corpus luteum
The corpus luteum normally grows to about 1,5 centimeters in diameter, reaching this stage of development 7 to 8 days after ovulation. Then the corpus luteum begins to involute and eventually loses its secretory function and its yellowish, lipid characteristic about 12 days after ovulation, becoming the corpus albicans.
- This causes the ovarian hormones estrogen and progesterone to decrease greatly
What happens to the corpus albicans?
The corpus albicans is during the ensuing few weeks replaced by connective tissue and over months is absorbed.
Describe the synthesis of the estrogens and progestins
Estrogens and progestins are synthesized in the ovaries mainly from cholesterol derived from the blood. During synthesis, mainly progesterone and androgens (testosterone and androstenedione) are synthesized first; then, during the follicular phase of the ovarian cycle, before these two initial hormones can leave the ovaries, almost all the androgens and much of the progesterone are converted into estrogens by the enzyme aromatase in the granulosa cells.
- Because the theca cells lack aromatase, they cannot convert androgens to estrogens. However, androgens diffuse out of the theca cells into the adjacent granulosa cells, where they are converted to estrogens by aromatase, the activity of which is stimulated by follicle-stimulating hormone.
Name the stages of the monthly endometrial cycle and menstuation
- Proliferative Phase (Estrogen Phase) of the endometrial cycle, occuring before ovulation
- Secretory Phase (Progestational Phase) of the endometrial cycle, occuring after ovulation
- Menstrual Phase
Describe the proliferative phase of endometrial cycle
At the beginning of each monthly cycle, most of the endometrium has been desquamated by menstruation. After menstruation, only a thin layer of endometrial stroma remains and the only epithelial cells that are left are those located in the remaining deeper portions of the glands and crypts of the endometrium.
Under the influence of estrogens, secreted in increasing quantities by the ovary during the first part of the monthly ovarian cycle, the stromal cells and the epithelial cells proliferate rapidly. The endometrial surface is re-epithelialized within 4 to 7 days after the beginning of menstruation.
Then, during the next week and a half, before ovulation occurs, the endometrium increases greatly in thichness, owing to increasing numbers of stromal cells and to progessive growth of the endometrial glands and new blood vessels into the endometrium.
- At the time of ovulation, the endometrium is 3 to 5 millimeters thick
Describe the secretory phase of the endometrial cycle
During most of the latter half of the monthly cycle, after ovulation has occurred, progesterone and estrogen toghether are secreted in large quantities by the corpus luteum. The estrogens cause slight additional cellular proliferation in the endometrium during this phase of the cycle, whereas progesterone causes marked swelling and secretory development of the endometrium.
- At the peak of the secretory phase, about 1 week after ovulation, the endometrium has a thickness of 5 to 6 millimeters.
The whole purpose of all these endometrial changes is to produce a highly secretory endometrium that contains large amounts of stores nutrients to provide appropriate conditions for implantation of a fertilized ovum during the latter half of the monthly cycle.
Describe the menstruation phase
If the ovum is not fertilized, about 2 days before the end of the monthly cycle, the corpus luteum in the ovary involutes and the ovarian hormones (estrogens and progesterone) decrease to low levels of secretion - menstruation follows.
Menstruation is caused by the reduction of estrogens and progesterone, especially progesterone, at the end of the monthy ovarian cycle.
- The first effect is decreased stimulation of the endometrial cells by these two hormones
- Followed rapidly by involution of the endometrium to about 65 percent of its previous thickness
- Then, during the 24 hours preceding the onset of menstuation, the tortuous blood vessels leading to the mucosal layers of the endometrium become vasospastic
The vasospasm, the decrease in nutrients to the endometrium, and the loss of hormonal stimulation initiate necrosis in the endometrium, especially of the blood vessels. As a result, blood at first seeps into the vascular layer of the endometrium and the hemorrhagic areas grow rapidly over a period of 24 to 36 hours.
Gradually, the necrotic outer layers of the endometrium separate from the uterus at the sites of the hemorrhages until, about 48 hours after the onset of menstuation, all the superficial layers of the endometrium have desquamated.
What does a normal menstruation contain?
During normal menstruation, approximately 40 milliliters of blood and an additional 35 milliliters of serous fluid are lost.
- The menstrual fluid is normally nonclotting because a fibrinolysin is released along with the necrotic endometrial material
Within 4 to 7 days after menstruation starts, the loss of blood ceases bevause, by this time, the endometrium has become re-epithelialized.
How is gonadotropin releasing hormone secreted by the hypothalamus?
The hypothalamus secretes gonadotropin releasing hormone in pulses lasting 5 to 25 minutes that occur every 1 to 2 hours.
The neuronal activity that causes pulsatile release of GnRH occurs primarily in the mediobasal hypothalamus, especially in the arcuate nuclei of this area. Therefore, it is believed that these arcuate nuclei control most female sexual activity, although neurons located in the preoptic area of the anterior hypothalamus also secrete GnRH in moderate amounts.
Describe the effect of estrogen on luteinizing hormone and follicle-stimulating hormone
Estrogen in small amounts has a strong inhibitory effect on the production of both LH and FSH. Also, when progesterone is available, the inhibitory effect of estrogen is multiplied, even though progesterone by itself has little effect. These feedback effects seem to operate mainly on the anterior pituitary gland directly, but they also operate to a lesser extent on the hypothalamus to decrease secretion of GnRH, especially by altering the frequency of the GnRH pulses.
How does the corpus luteum inhibit FSH and LH secretion?
Corpus luteum secretes inhibin the same way that Sertoli cells secrete inhibin in the male testes. This hormone inhibits the secretion of FSH and, to a lesser extent, LH by the anterior pituitary gland. Therefore, it is belived that inhibin might be especially important in causing the decrease in secretion of FSH and LH at the end of the monthly female menstrual cycle.
