II. Hormonal Control of Female Reproductive Cycles
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a. Upon reaching sexual maturity, human males carry out Gametogenesis __; females produce gametes in __
When does ovulation occur?
What happens if no pregnancy occurs?
- a. Ovulation occurs only after endometrium starts thickening and develops a rich blood supply, preparing the uterus for the possible implantation of an embryo
- i. No pregnancyà uterine lining sloughed offà another cycle
1. Cyclic shedding from uterus= __
- (flow from cervix-->vag)
Two closely linked reproductive cycles in human females
- i. Changes in the uterus= menstrual cycle (uterine cycle)
- 1. Avg. 28 days
- Cyclic events in the ovaries define the ovarian cycle
a. __ links two cycles to each other, synchronizing __ and __with the establishment of a__ that supports __
- Hormone activity
- ovarian follicle growth
- uterine lining
- embryonic development
Explain the ovarian cycle.
- i. Begins with release from hypothalamus of GnRH
- ii. Causes anterior pituitary to secrete small amounts of FSH and LH
- iii. FSH stimulates follicle growth, aided by LH
- iv. Cells of the growing follicles start to make estradiol
When cells of the growiing follicles start to make estradiol in the ovarian cycle, what happens?
1. Slow rise in estradiol secreted during most of the follicular phase, the part of the ovarian cycle during which follicles grow and oocytes mature (usually only one follicle of many matures)
What do low levels of estradiol do?
- 1. Low levels of estradiol inhibit secretion of the pituitary hormones, keeping FSH and LH levels low
- 2. During this portion of the cycle, regulation of hormones controlling reproduction parallels regulation observed in males
i. When estradiol secretion by growing follicle begins to rise steeply,__levels increase
What does this result in?
- FSH and LH
- 1. Whereas low level of estradiol inhibits the secretion of pituitary gonadotropins, a high concentration has the opposite effect: it stimulates gonadotropin secretion by acting on the hypothalamus to increase its output of GnRH
When secretioin for gonadotropins is stimulated, what is the effect?
- a. The effect is greater for LH because the high concentration of estradiol increases the GnRH sensitivity of LH-releasing cells in the pituitary
- i. In addition, follicles respond more strongly to LH at this stage because more of their cells have receptors for this hormone
1. Increase in LH caused by increased estradiol secretion from growing follicle is __ --> result: __
- positive feedbackà
- final maturation of the follicle
i. __, containing a fluid-filled cavity, enlarges, forming a bulge near the surface of the ovary
__phase ends at __, about a day after the __
- Maturing follicle
- LH surge
What is the response to the peak in LH levels?
- 1. the follicle and adjacent wall of the ovary rupture, releasing the secondary oocyte
What is the pain experienced at or near ovulation time?
this pain is felt on the left or right side, corresponding to whichever ovary has matured a follicle during that cycle
Which phase follows ovulation
What does LH stimulate?
under continued stimulation by LH, what happens>
- i. LH stimulates the follicular tissue left behind in the ovary to transform into a corpus luteum, a glandular structure
- The luteum secretes progesterone and estradiol
a. As progesterone and estradiol levels rise, what happens?
What does this negative feedback do?
- the combination of these steroid hormones exerts negative feedback on the hypothalamus and pituitary, reducing the secretion of LH and FSH to very low levels
- prevents another egg from maturing when a pregnancy may be under way
1. Near end of __phase, low __levels cause the __to __, triggering a sharp decline in __ and __ concentrations
- corpus luteum
- estradiol and progesterone
a. The decreasing levels of ovarian steroid hormones liberate the __ from the ___ effect of these hormones
i. Pituitary can then begin to secrete enough __to stimulate the growth of new __in the ovary, initiating the next __
- hypothalamus and pituitary
- negative feedback
- ovarian cycle
a. The Uterine (Menstrual) Cycle
i. Prior to ovulation, ovarian steroid hormones stimulate the uterus to __
ii. __secreted in increasing amounts by growing follicles signals the __
1. In this way, the __ of the ovarian cycle is coordinated with the __ of the uterine cycle
- prepare for support of an embryo
- endometrium to thicken
- follicular phase
- proliferative phase
i. Steps 9-10
1. After ovulation, (9) estradiol and progesterone secreted by the __ stimulate __, including __
- corpus luteum
- continued development and maintenance of the uterine lining
- enlargement of arteries and growth of endometrial glands
What do endometrial glands do?
a. secrete a nutrient fluid that can sustain an early embryo even before it implants in the uterine lining
Thus the __phase of the ovarian cycle is coordinated with the __phase of the uterine cycle
1. Upon disintegration of the corpus luteum, the rapid drop (10) in ovarian hormone levels causes __
arteries in the endometrium to constrict
a. Deprived of its circulation, much of the uterine lining __, and the uterus, in response to __secretion, __.
Small blood vessels in the endometrium constrict, doing what? --> what does it lead to?
- releasing blood that is shed along with endometrial tissue and fluidà
- menstruation—the menstrual flow phase—of the uterine cycle
1. During menstruation, what occurs?
a. First day of menstruation is day 1 of __
- a new group of ovarian follicles begins to grow
- new uterine and ovarian cycle
i. Overall, the hormonal cycles in females coordinate __ with __, the organ that accommodates an embryo if the egg cell is fertilized
1. If embryo not implanted in __by the end of the __phase, what happensà next cycle
- egg maturation and releases
- changes in the uterus,
- a new menstrual flow commences
i. About 7% of women of reproductive age suffer from __, a disorder in which some cells of the uterine lining migrate to an abdominal location that is abnormal (__)
What does some cells of the uterine liniing migrating to an abnormal position, such as the abdomen cause?
1. This causes the ectopic tissue to respond to hormones in bloodstream; and, like the uterine endometrium, the ectopic tissue swells and breaks down each ovarian cycle, resulting in pelvic pain and bleeding into the abdomen
i. After about 500 cyclesà menopause, which is?
1. Ages 46-54 when ovaries __--> decline in __production
- the cessation of ovulation and menstruation
- lose responsiveness to FSH and LHà
i. Other species retain reproductive capacity throughout life, but not humans
1. What is the hypothesis?
Hypothesis: during early human evolution, undergoing menopause after several kids allows mom to care better and increase survival
i. Menstrual vs. Estrous Cycles
1. In all female mammals, the __ thickens before __, but only humans and some other primates have __cycles
1. Other mammals have __cycles, in which in absence of a pregnancy, what happens?
- the uterus reabsorbs the endometrium and no extensive fluid flow occurs
1. Whereas human females may engage in sex throughout menstrual cycle, mammals with estrous cycles usually __
a. This period, called __, is the only time the female is receptive to matingà “__” with slight rise in female temp
- copulate only during the period surrounding ovulation
4. __ and __ of estrous cycles vary widely among mammals
Length and frequency
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