A&S2 - Menstrual Cycle

Where are luteinizing hormone (LH) and follicle stimulating hormone (FSH) produced?

Anterior pituitary

Where is gonadotrophin-releasing hormone produced?

Hypothalamus

What is the primary source of progesterone in the later stages of pregancny

The corupus luteum is the primary source of progesterone at the start of pregnancy however the corpus luteum breaks down eventually. So from the 8th week of pregnancy the main source of progesterone is the placenta.

At which stage of the uterine cycle does the menstrual phase occur?

*Days 1-5* The menstrual phase occurs at the very beginning of the uterine cycle. It only occurs if no ovum is fertilised. The proces begins with the breakdown of the corpus luteum which therefore ceases to produce progesterone. The loss of progresterone causes vasoconstriction of the spinal arteries supplying the functional layer of the endometrium. As a result it becomes necrotic and is then lost through the vagina causing the 3-5days of bleeding.

In a normal 28day cycle when would you expect the LH sugre to occur?

*Days 11-13* The LH surge usually occurs on day 12. This occurs due to oestrogen levels reaching a high level which stimulates large amounts of LH production. The high LH levels cause the membrane of the graafian follicle to become thin. As a result 24-28 hours later the LH surge ovulation usually occurs due to the rupture of the graafin follicle.

At which stage in the uterine cycle does the secretory phase occur?

*Days 14-28* The secretory phase of the menstrual cycle begins after ovulation when the ruptured graafian follicle develops into the corpus luteum. The corpus luteum produces progesterone which causes the endometrium to begin secreting various substances ehich make the uterus more receptive to implantation of a fertilised ovum.

At which stage in the uterine cycle does the proliferate phase occur?

*Days 5-14* The proliferate phase begins immediatley after the menstrual phase and invloves increased levels of oestrogen driving repair and growth of the functional endometrial layer.

At which point in the menstrual cycle is a woman most fertile?

*Days 9-16* The most fertile period of the menstrual cycle is from 5 days before ovulation to 1-2 days after. Couples often use this knowledge to increase their chances of conception

Which hormone is the corpus luteum responsible for producing?

*Progesterone* The corpus luteum produces progesterone which causes the endometrium to become receptive to implantation of a blastocyst and prevents menstration occuring.

What are the functions of luteinizing hormone (LH)?

- Formation and maintenance of the corpus luteum - Thinning of the graafian follicles membrane

What are some of the main functions of progesterone?

- Stimulation of oestrogen production - Initation of the secretory phase of the endomentrium - Increased in basal body temperature - Inhibition of LH and FSH production Progesterone is involved in many different processes during the menstrual cycle. It causes increased production of oestrogen and causes the endomentrium to become more receptive to implation of a fertilised ovum. It also inhibits production production of LH and FSH via negative feedback.

What is the physiological purpose of mensturation?

- The menstural cycle is an endocrine cycle regulating reproductive physiological changes. The menstrual cycle is variable amongst women and also within an individual, the "28 days" is an average time course. Like the cycle itself, the time of ovulation can vary anywhere between day 10-19. The uterine lining (functional layer) is replaces every cycle, though this would not be considered he main function of the cycle. The body temperature does increase at ovulation, but it remains high even after this point, it is the time of change that indicated ovulation.

What are the effects of increased levels of oestrogen in the follicular phase of the menstrual cycle?

- Thinning of cervical mucous - Thickening of the endometrium In the follicular phase oestrogen fucntions to increases chances of successful fertilisation. As a result it causes the mucous of the cervix to become thinner allowing easier passage of sperm. It also causes thickening of the endometrium to increase chances of successful implantation of a blastocyst.

In a 28 day menstrual cycle approximately how long would you expect menstruation to last?

In a normal 28 day menstrual cycle would you expect menstruation to last approximately 3-5 days