BIOL 80A Final | The Menstrual Cycle

what three endocrine structures interact to control human reproductive cycles in males and females?

the hypothalamus (H), the anterior pituitary gland (P), and the gonads (G)

which gland releases gonadotropin-releasing hormone (GnRH)?

the hypothalamus

what structure does GnRH act upon?

the anterior pituitary gland

what two hormones does the anterior pituitary release into the blood in response to GnRH?

FSH (follicle-stimulating hormone) and LH (luteinizing hormone)

what are the target organs for FSH and LH?

the gonads (ovaries in females, testes in males)

what do FSH and LH trigger the gonads to release?

reproductive hormones (estrogen in females, testosterone in males)

what is GnRH?

gonadotropin-releasing hormone (released by the hypothalamus)

what is FSH?

follicle-stimulating hormone (released by the anterior pituitary)

what is LH?

luteinizing hormone (released by the anterior pituitary)

what is the female reproductive cycle?

(also known as the “menstrual cycle,” this is the sequence of events that occur as the body prepares for the possibility of pregnancy each month.

what is menstruation?

(also known as your “period,” this is the monthly shedding of the lining of your uterus

when does the menstrual cycle typically begin?

at menarche (first menstrual period), usually between ages 10-17 (average age is 12.5)

when does the menstrual cycle typically stop?

at menopause, usually between ages 45-55 (average age is 51)

how much fluid is typically lost during menstruation?

most women lose about 3-4 ounces (4-6 tablespoons or ¼ cup) of menstrual fluid

what is menstrual fluid composed of?

cervical mucus, vaginal secretions, endometrial tissue, and blood

what primarily determines the menstrual cycle?

the rise and fall of specific hormones

how long is the average menstrual cycle?

28 days long, measured from the first day of menstrual flow to the first day of the next

what is considered a “normal” range for menstrual cycle length?

between 21-35 days

how long does “normal” menstrual flow last?

from 3-7 days

what are the two parallel “cycles” within the female reproductive cycle?

the ovarian cycle (what’s happening in the ovaries/eggs) and the uterine cycle (what’s happening with the uterine lining)

do the ovarian and uterine cycles happen at different times?

no, they occur simultaneously and are coordinated over an individual’s menstrual cycle

what is GnRH (gonadotropin-release hormone) and its’ function?

produced by the hypothalamus, signals the anteror pituitary gland to produce the gonadotropins FSH and LH

what is FSH (follicle-stimulating hormone) and its’ function?

produced by the anterior pituitary, stimulates growth of ovarian follicles, particularly important during the follicular phase of the ovarian cycle

what is LH (luteinizing hormone) and its’ function?

produced by the anterior pituitary, stimulates ovarian cells and follicles to produce estrogen; “LH surge” triggered ovulation

what is estrogen and its function?

produced by ovarian cells and follicles, contributes to the maturation of the follicle, and growth of the endometrium during the proliferative phase of the uterine cycle

what is progesterone?

produced by the corpus luteum (degenerating follicle) after ovulation, contributes to the maintenance enrichment of the endometrium during the secretory phase of the uterine cycle

what is the endometrium?

the inner epithelial lining of the uterus, rich in blood vessels, that grows and thickens during the uterine cycle

what is the myometrium?

a thick muscular wall of the uterus located outside the endometrium

what is the function of the growth and enrichment of the endometrium?

it prepares the uterus to receive a fertilized egg (zygote) which will then implant itself

what pituitary hormones stimulate follicles to grow during the follicular phase?

LH (luteinizing hormone) and FSH (follicle-stimulating hormone)

what do follicles produce during the early follicular phase

low levels of estrogen

what is the effect of low estrogen levels on GnRH secretion?

it inhibits GnRH secretion by the hypothalamus, which keeps LH and FSH levels low

what affect do low levels of estrogen have on endometrial arteries?

they cause endometrial arteries to constrict, resulting in menstruation

what are the normal variations in menstrual flow?

flow can be red, pink, or brown; it can be thick, lumpy, or watery; small clots can be normal

what causes menstrual cramps and diarrhea during a period?

the release of hormones called prostaglandins, which cause smooth muscle contractions in the myometrium of the uterus and intestines

how frequently should a tampon be changed to reduce the risk of toxic shock syndrome?

every 4-6 hours

is it normal to bleed through a super tampon or pad every hour in a day?

no, this is not normal and indicates a potentially heavy flow that should be addressed

can a person still get their period if they are pregnant?

getting a period does not necessarily mean you are not pregnant

is it safe to have sex during a period?

yes it is safe (after removing a tampon)

what pituitary hormones drive follicle maturation and ovulation?

LH & FSH stimulate one follicle to mature, and a surge in LH triggers the egg release (ovulation)

what does the dominant follicle’s estrogen do during ovulation?

stimulates GnRH, causing LH/FSH to surge, leading to ovulation; thickens the uterine lining (endometrium)

what is mittelschmerz?

a one-sided pain some women feel during ovulation as the egg is released

what is spinnbarkeit?

the clear, stretchy vaginal discharge that becomes abundant around ovulation, signaling fertility

what pituitary hormone is key in the luteal phase?

LH (luteinizing hormone) stimulates the ruptured follicle to become the corpus luteum

what do estrogen and progesterone from the corpus luterum do?

block GnRH/LH/FSH production (negative feedback) and further develop the endometrium for potential pregnancy

how long does the physical act of ovulation take?

only a few minutes

what can cause fraternal twins?

fertilization of more than one egg released during the same cycle (from one or both ovaries)

what happens during the menses phase?

menstrual flow, triggered by drop in estrogen and progesterone (if no implantation has occured)

what happens during the proliferative phase?

endometrium rebuilds in response to increasing estrogen

what happens during the secretory phase?

estrogen and progesterone prepare the endometrium for implantation; endometrial glands secret a fluid rich in glycogen

how long is the average menstrual cycle?

28 days long (from the first day of menstrual flow to the first day of the next)

how long can a normal menstrual cycle be?

it can be between 21-35 days

when do you ovulate if you have a shorter reproductive cycle (~25 or 26 days)?

before day 14

when do you ovulate if you have a longer reproductive cycle (~30-32 days)?

after day 14

how long does an egg and sperm live after ovulation?

an egg lives about 24 hours after ovulation, and sperm lives 3-5 days

assuming ovulation happens on day 14, what is a woman’s fertile window (the window of time where sex has a high chance of resulting in pregnancy)?

approximately days 10 to 17