14.3 Ovarian and Uterine Cycles Flashcards
Describe the 6 stages of the ovarian cycle?
- primary follicle contains an oocyte and begins producing the sex hormone estrogen
- secondary follicle contains a primary oocyte and produces the sex hormones estrogen and some progesterone
- vesicular (Graafian) follicle develops
- ovulation: secondary oocyte is released
- corpus luteum produces the sex hormones progesterone and some estrogen
- corpus luteum degenerates
What happens as a follicle matures?
- oogenesis
- layers of follicle cells surround the developing oocyte
- the mature follicle eventually ruptures and the secondary oocyte is released
- follicle becomes corpus luteum which eventually degenerates
What is an ovary made up of?
outer cortex and inner medula
What are follicles?
structure in the ovary that contains immature oocytes, site of oocyte production
When does the ovarian cycle occur?
as follicle changes from a primary to a secondary vesicular (Graafian) follicle
What do primary follicles have?
epithelial cells that surround a primary oocyte
What surrounds the oocyte in a secondary follicle?
pools of follicular fluid
Describe what happens in a vesicular follicle.
a fluid-filled cavity increases to the point that the follicle wall balloons out on the surface of the ovary
Describe the steps of ovulation.
- primary oocyte divides, producing two haploid cells, one cell is a secondary oocyte and the other is a polar body
- ## vesicular follicle bursts, releasing the second oocyte
What happens once a vesicular follicle has lost the secondary oocyte?
develops into a corpus luteum
What is a corpus luteum?
glandlike structure that produces progesterone
Describe the steps of oogenesis.
- secondary oocyte enters a uterine tube
- if a sperm enters the secondary oocyte, fertilization occurs and the secondary oocyte completes meiosis
- egg with 23 chromosomes and a second polar body results
- when sperm unites with the egg nucleus, zygote with 46 chromosomes is produced
- if zygote formation and pregnancy do not occur, corpus luteum begins to degenerate after about 10 days
What are the 2 phases of the ovarian cycle?
first half: follicular phase
second half: luteal phase
What happens during the follicular phase?
- follicle-stimulating hormone (FSH) produced by the anterior pituitary, promotes the development of a follicle in the ovary, which secretes estrogen and some progesterone
- as the estrogen level in the blood rises, it exerts negative feedback control over the anterior pituitary secretion of FSH so that the follicular phase comes to an end
What does an estrogen spike cause?
- sudden secretion of a large amount of GnRH from the hypothalamus, an example of positive feedback
- leads to a surge of luteinizing hormone (LH) from the anterior pituitary which causes ovulation at about the 14th day of a 28-day cycle
What happens during the luteal phase?
- LH promotes the development of the corpus luteum, which secretes progesterone and some estrogen
- as the blood level of progesterone rises, it exerts feedback control over the anterior pituitary secretion of LH so that the corpus luteum in the ovary begins to degenerate
What happens as the luteal phase comes to an end?
low levels of progesterone and estrogen in the body cause menstruation to begin
Describe the hormonal control of ovaries.
- hypothalamus produces GnRH, which stimulates the anterior pituitary to produce FSH and LH
- FSH stimulates the follicle to produce primarily estrogen
- LH stimulates the corpus luteum to produce primarily progesterone
- estrogen and progesterone maintain the sex organs and the secondary sex characteristics, and they exert feedback control over the hypothalamus and the anterior pituitary
- feedback control regulates the relative amounts of estrogen and progesterone in the blood
OVARIAN CYCLE
Follicular phase - Days 1-13
- FSH secretion begins
- follicle maturation occurs
- estrogen secretion is prominent
OVARIAN CYCLE
Ovulation - Day 14
LH spike occurs
OVARIAN CYCLE
Luteal phase - Days 15-28
- LH secretion continues
- corpus luteum forms
UTERINE CYCLE
Menstruation - Days 1-5
endometrium breaks down
UTERINE CYCLE
Proliferative phase - Days 6-13
endometrium rebuilds
UTERINE CYCLE
Secretory phase - Days 15-28
- rise in progesterone levels
- endometrium thickens
- glands are secretory
What are the female sex hormones?
estrogen and progesterone
What are the functions of the female sex hormones?
affect the endometrium, causing the uterus to undergo a cyclical series of events known as the uterine cycle
Describe days 1-5 of the uterine cycle.
- low level of female sex hormones in the body causes the endometrium to disintegrate and its blood vessels to rupture
- day 1: flow of blood and tissues passes out of the vagina during menstruation (period)
Describe days 6-13 of the uterine cycle.
- increased production of estrogen by a new ovarian follicle in the ovary causes endometrium to thicken and become vascular and glandular
- this is called the proliferative phase of the uterine cycle
Describe day 14 of the uterine cycle.
ovulation usually occurs in the ovary
Describe days 15-28 of the uterine cycle.
- increased production of progesterone by the corpus luteum in the ovary causes the endometrium of the uterus to double or triple in thickness (from 1mm to 2-3 mm) and the uterine glands to mature, producing a thick mucus secretion
- called the secretory phase of the uterine cycle
- endometrium is now prepared to receive the developing embryo
- if this doesn’t occur, corpus luteum in the ovary degenerates and the low level of sex hormones in the female body results in the endometrium breaking down during menstruation
What is estrogen largely responsible for?
secondary sex characteristics in females including body hair and fat distribution
Why do females have a more rounded appearance than males?
because of a greater accumulation of fat beneath the skin
Why does the pelvic cavity usually have a larger size in women compared to men?
pelvic girdle becomes wider and deeper in females
What do females develop during puberty?
axillary and pubic hair
What is required for breast development?
estrogen and progesterone
Describe the female hormone levels during the ovarian uterine cycles.
- during follicular phase of ovarian cycle, FSH released by anterior pituitary promotes the maturation of a follicle in the ovary
- ovarian follicle produces increasing levels of estrogen, which causes the endometrium to thicken during the proliferative phase of the uterine cycle
- after ovulation and during the luteal phase of the ovarian cycle, LH promotes development of corpus luteum which produces increasing levels of progesterone, which causes endometrium to become secretory
- menstruation and proliferative phase begin when progesterone production declines to a low level
What happens during menstruation?
- arteries that supply the uterine lining constrict and capillaries weaken
- blood spilling from the damaged vessels detaches layers of the lining, not all at once, at random patches
- endometrium, mucus, and blood descend from the uterus, through the vagina, creating menstrual flow
What is fibrinolysin?
enzyme released by dying cells that prevent the blood from clotting
What causes the pain and discomfort during menstruation?
in the uterus, prostaglandins cause muscles to contract
When does an embryo begin to develop?
if fertilization occurs, it begins development as it travels down the uterine tube to the uterus
What receives the developing embryo?
endometrium, it becomes implanted in the lining several days following fertilization, and pregnancy begins
What does the placenta do?
sustains the developing embryo and later fetus, and originates from both maternal and fetal tissues
What is the placenta?
the region of exchange of molecules between fetal and maternal blood, although the 2 rarely mix
What is human chorionic gonadotropin (HCG)?
at first, the placenta produces this, which maintains the corpus luteum in the ovary until the placenta begins its own production of progesterone and estrogen
What can detect the presence of HCG?
a pregnancy test can detect HCG in the blood or urine by 10 days after fertilization
What are the 2 effects of the progesterone and estrogen produced by the placenta?
- they shut down the anterior pituitary so that no new follicle in the ovaries matures
- maintain endometrium so that the corpus luteum in the ovary is no longer needed
What are uterine contractions induced by?
stretching of the cervix, which also brings about the release of oxytocin from the posterior pituitary
What does oxytocin do?
stimulates uterine contractions, which push the fetus downwards and the cervix stretches even more
What 3 events indicate that baby delivery will occur soon?
- uterine contractions are occurring about every 5 minutes and becoming stronger
- amnion, which contains amniotic fluid, ruptures, causing water to flow out of the vagina
- plug of mucus from the cervical canal leaves the vagina, which prevents bacteria and sperm from entering the uterus during pregnancy
What happens to the breasts during pregnancy?
they enlarge as the ducts and alveoli increase in number and size
What is prolactin?
hormone that is needed for lactation to begin, and the production of this hormone is suppressed because of the feedback control that the increased amount of estrogen and progesterone during pregnancy has on the pituitary
What does the anterior pituitary do once the baby is born?
begins secreting prolactin
What is colostrum?
thin, yellow, milky fluid rich in proteins, including antibodies, produced by the breasts
What does the continued production of milk require?
a suckling child, when a breast is suckled, nerve endings in the areola are stimulated and a nerve impulse travels along the neural pathways from the nipples to the hypothalamus, which directs the pituitary gland to release oxytocin
What happens when oxytocin arrives at the breast?
it causes contraction of the lobules so that milk flows into the ducts where it may be drawn out of the nipple by the suckling child
What does breast milk do for babies?
- contain antibodies produced by the mother
- babies have immature immune systems, less stomach acid to destroy foreign antigens, and also unsanitary habits
- breast milk can help protect babies from some illnesses during their development
What does suckling also cause?
uterine contractions that can help the mother’s uterus return to its normal size
What is menopause?
period in a woman’s life during which the ovarian and uterine cycle cease, usually occurs between ages 45 and 55
What happens during menopause?
ovaries become unresponsive to gonadotropin hormones and they no longer secrete estrogen and progesterone
What happens at the onset of menopause?
uterine cycle becomes irregular, but as long as menstruation occurs, it is still possible for a woman to conceive
What do hormonal changes during menopause often produce?
physical symptoms called ‘hot flashes’ caused by circulatory irregularities, dizziness, headaches, insomnia, sleepiness, and depression
What might the use of combined drugs by postmenopausal women cause?
increases in breast cancer, heart attacks, strokes, and blood clots
