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