L34 Mensuration Flashcards
What are the uterine stages of the menstrual cycle?
Menstrual phase - Approx. Day 1-5
Proliferative phase - Approx. Day 5 - 14. Here there is proliferation of the endometrium.
Secretory Phase - Approx. Day 14 - 28. Here the endometrium is kept safe for the oocyte. If no egg is implanted, the endometrium is shed in the menstrual phase.
What are the ovarian stages of the menstrual cycle?
Follicular phase - Approx. Day 1 - 14. In this phase the follicles are recruited.
Luteal Phase - Approx. Day 14- 28. In this has ether corpus lutetium appears.
What is the endocrine control of menstruation?
The hypothalamus exerts its effect on the anterior pituitary through the pulsatile release of GnRH (Gonadotrophin releasing hormone). The pituitary therefore stimulates the ovary through FSH and LH. The ovary will feed back to the neural structures through predominantly oestrogen release. Oestrogen also effects the furthers.
GnRH is a decapeptide. It is produces in hourly pulses. It is transported to the pituitary via the hypophyseal portal blood system. It is secreted by mid basal hypothalamic neurons. The pulsatile nature can be interrupted by a variety of events such as: bereavement, anxiety, time zone, day/night, exercise and weight change.
What are the structural differences between LH and FSH?
They both glycoproteins with the same alpha chain but have differing beta chains.
What is the role of LH?
- LH which is predominate in the middle of the cycle and from then on. It triggers the release of an egg from the dominant follicle and promotes development of the corpus luteum and the production of progesterone from the corpus luteum - vital to the fertilised egg in terms of subsequent implantation. It ensures ovulation occurs.
What is the role of FSH?
FSH is the predominate hormone in the first half of the cycle. It stimulates follicular activity and thus promoting oestradiol production from granulosa cells. Oestrogen has the proliferative effect on the endometrium.
Describe positive and negative feedback of the menstrual cycle?
Positive feedback occurs midcycle. Negative feedback from oestrogen occurs on the receptors of the hypothalamus reducing the production of GnRH. At a point near the cycle, a high level of oestrogen leads to a surge in LH release which triggers ovulation.
What are the different stages of a developing oocyte?
Primordial follicle -> primary/preantral follicle -> Secondary/antral follicle -> Preovulatory follicle -> Ovulation
Describe follicular development.
The proliferation of the granulosa cells that occurs in the follicular phase ensures that a fluid filled antrum is developed. The capacity for nutrition for the oocyte prior to ovulation takes place. There is also proliferation of thecal cells. Thecal cells are external to the granulosa cells. They form a theca interna which is glandular and highly vascularised and a theca externa which is a fibrous capsule. There is a lot of communication between the cells of the oocyte and between the production of sex steroid cells. This is typically through androgens before they get to female sex steroids, and it is converted mostly within the granulosa cells. Cholesterol is found in the corpus luteum as it is the precursor to all the sex steroids.
What occurs post ovulation?
After ovulation, luteinisation occurs under the influence of LH. There is then an enhanced production of progesterone. If there is no fertilisation that takes place there is no onwards stimulation to continue the survival of the corpus luteum. It then degenerates and fibroses to become the scars within the ovary called the corpus albicans.
What is the role of the endometrium in the different stages of the menstrual cycle?
The endometrium is the lining of the uterus. During the proliferative phase, oestradiol stimulates the endometrium to thicken through proliferation. There is increased number of blood cells, glandular cells and stromal cells. By ovulation the endometrium is 2-3 mm thick. This means there is a stabilised environment for the oocyte to embed into. However in some women who do not ovulate every well, there is a rapid thickening of the endometrium, however is not very stable. This is called anovulatory cycle. Progesterone is the predominate hormone in the secretory phase; the endometrium is far more stable due to its influence. It thickens also slightly. It is also more vascular and nutrient-rich.
If fertilisation does not take place, there is no further stimulus to the corpus luteum. The corpus luteum degenerates and so the levels of progesterone falls. The endometrium then starts to destabilise and there is menstrual shedding. On a microscopic level there is vasodilation after vasospasm of the blood vessels. The necrotic outer layer is separated. Together with uterine contractions, cramping feelings, and the dilatation of the cervix, allows the menstrual tissue to be shed.
What is the role of the cervix?
The cervix is the entry point to the uterus and governs what enters and does not. In mid cycle, cervical mucus is both stringy and runny. The mucus is produced from the columnar glands. This facilitates sperm access at ovulation. The mucus known as spinnbarkeit. The window of opportunity for the sperm is short lived.
The cervical mucus will then develop more tenacious and inelastic luteal phase. They protect the developing embryo and prevents the ascent of microorganisms into the uterine cavity from the vagina. The mucus plug therefore provides a functional barrier. This is all under the influence of progesterone - the inelasticity will occur.
How does oral contraception work?
The combined pill contains an oestradiol and a progesterone. Each of the pills within the combined pill has the same dose of either. The steady state ensure suppression of GnRH release and GSH and LH. This means a hypogonadotropic hypogonadism. The pill prevents ovulation. The continued dose of progesterone means that the cervical mucus remains tenacious and inelastic.
What is the corpus luteum?
A corpus luteum is a mass of cells that forms in an ovary and is responsible for the production of the hormone progesterone during early pregnancy. Progesterone is important in the development and maintain of the endometrium.
When is the chance of conceiving greatest?
The timing of ovulation varies tremendously. The greatest chance of conceiving is mid cycle, around 7-15 days. However there is still the opportunity to get pregnant before or after expected.
