Lecture 3: Female Reproductive System & Readings Flashcards
What is ovarian steroidogenesis?
the production of steroid hormones like estrogen and progesterone
Ovarian steroidogenesis is a two-cell, two-gonadtropin model. Explain
The two cells required for ovaraian steroidogenesis are:
1. theca cells -
2. Lutenizing hormone
3. Granulosa cells
4. Follicle-stimulating Hormone
Explain the role of Theca cells in ovarian steroidogenesis.
Theca cells are stimulated by lutenizing hormone and convert cholesterol to androgens.
Theca cells stop at androgen as they do not have the ability to make estrogen
Explain the role of Granulosa Cells in steroidogenesis
granulosa cells are stimulated by follicle-stimulating hormone and convert androgens (from theca cells)
In the female reproductive tract the hormone produced from cholesterol is
Progesterone
Estradiol is produced from:
testosterone
Androstenedione will produce testosterone which will then produce estradiol
True or False
True
Why are steroids easily able to transverse potential membranes?
Steroids are lipids
Where are Progestins, Androgens and estrogens produced in the female reproductive tract?
In the ovarian follicle
Name the hormone that is produced by all major ovarian cell types: follicular granulose cells, theca cells and corpus luteum
Progestins - Progesterone
What crucial role does progesterone play in the female reproductive tract?
As a product of the corpus lute - during the luteal phase of the menstrual cycle & for the maintenance of pregnancy
What is the hormone that is most important as a precursor for the synthesis of estradiol?
Testosterone (Androgens)
Folliclular Atresia is associated with too much:
Testosterone
What is the hormone essential for the stimulation of follicular development and the onset of puberty
Estrogen - estradiol
The hypothalamic-pituitary-gonadal axis set into motion at puberty are similar in both male and female reproductive systems.
True or False?
True
In the female reproductive tract when the body levels of adipose tissue and leptin are low what happens?
Puberty is delayed
In the female reproductive tract which hormone will inhibit the hypothalamus from releasing GnRH?
estrogen
Gonadotropins (FSH and LH) levels increase for about four years. During this time females are still not ovulating. What does this mean?
During this time they are not able to become pregnant
What is menarche?
The first menstrual period
when does the female reproductive cycle become regular?
About 3 years after menarche
The levels of FSH and LH and ovarian hormones remain stable throughout the females life span.
True or False
False
The levels of FSH and LH, as well as ovarian hormones will fluctuate in reposnse to both negative and positive feedback mechanisms
Describe the regulation of the ovarian cycle.
GnRH stimulates FSH and LH secretion
FSH and LH stimulate follicle growth, mature and secrete sex hormones which cause them to release estrogen
Explain the negative feedback mechanism on regulation of ovarian cycle
Negative feedback inhibits gonadotropin release. As estrogen levels rise they signal the hypothalamus and anterior pituitary to inhibit the release of FSH
Inhibin released by the granulosa cells in reposnse to FSH will control the levels of FSH during this period and only the dominant cycle will survive the dip in FSH
Explain the positive feedback mechanism regulating the ovarian cycle
Positive feedback stimulates gonadotropin release. Once the dominant follicle becomes a mature vesicular follicle just before ovulation and produces high level of estrogens and exert positive feedback of the hypothalamus and anterior pituitray
What hormone triggers ovulation and formation of the corpus lutem?
LH (lutenizing hormone)
What does an LH surge cause?
the primary oocyte of the mature vesicular follicle from its resting state and it completes its first meiotic division forming a secondary oocyte
What is the goal of each menstrual cycle?
To prepare the body for pregnancy
What are primordial follicle?
The first follicles to develop in the fetus. A small fraction of the available dormant primordial follicles are recruited into a pool of growing follicles
How long will the recruiting of primordial follicles occur?
continues throughout the lifespan until the supply of primordial follicles is depleted (menopause)
A follicle has one of two fates. What are they?
- Atresia
- Ovulation
What is atresia?
Apoptosis (programmed cell death) of the oocyte and its surrounding cells. This is the outcome for 99.9% of all follicles
Can recruited follicles undergo atresia?
Yes.
Recruited follicles can undergo atresia at any stage in their development
What happens to all recruited cells before puberty?
They will all undergo atresia
Why is there only about 400, 000 primordial follicles at puberty
because recruited cells will undergo atresia before puberty starts. The are dying before they are capable of producing life
At which age will a female have the full complement of primordial follicles?
6 months of age
What are Oogonia?
diploid stem cells of the ovaries and multiple rapidly by mitosis
What do Oogonia transform into?
Primary oocytes
What are the 3 key differences between ogenesis and spermatogenesis?
- The production of primary ooctes occurs only in the fetus.
- In primary oocytes, meiosis is arrested (stops) in late prophase I and resumes only years later
- In secondary oocytes, meiosis is arrested in metaphase II and is only completed if fertilization occurs
At what stage are oocytes arrested?
Late prophase Iof meiosis
What triggers the resumption of meiosis the first time?
Triggered by a surge of lutenizing hormones
(LH surge)
What is the fate of most primary oocytes?
Atresia
What is the fate of most oocytes in which resumption of meiosis was initiated by LH surge
Only the dominant follicle completes maturation and ovulates a secondary oocyte. The non dominant oocytes the resume meiosis will fail to develop and undergo atresia before ovulation
Explain the development of Primary Follicles.
- Oocytes increase in size and accquires a zona pelluicda
- granulosa cells start to divide and form seveal layers outside oocyte
- ovarian insterstitial cells closest to the growing follicle differentiate to form theca cells
During the changes called a primary follicle, the continued maturation of this follicle requires
FSH - follicle-stimulating hormone
What is an antrum
a fluid filled cavity
Why is it important to have an atrum in a maturing follicle?
It plays several roles in follicular development and successful ovulation.
1. Hormonal Enviornment
2. Follicle Selection
3. Oocyte Support and positioning
4. facilitates ovulation
Explian the role of an antrum in hormonal environment?
the fluid of the antrum contains high levels of estrogen, growth hormones and enzymes. helping oocyte maturation and granulosa cell function
Explain the role of an antrum in follicle selection?
The presence of an antrum helps identify a dominant follicle. A large antrum and higher estrogen level give it a competitive edge
Explain the role of the antrum in oocyte support and positioning
the antrum helps physically cushion and nouris the oocyte (egg cell) and helps position the cumulus oophorus in preparation of ovulation
How does the antrum facilitate ovulation?
Right before ovulation, the fluids pressure increases, contributing to the rupture of the follicle and release of the oocyte. The enzymes in the fluid help weaken the folliclular wall
The basement membrane divides follicles into 2 compartments. what are they?
- inner granulosa cell compartment
- Outer theca cell compartment
explain the role of the inner granulosa cell compartment.
It is non-vascularized to create a barrier protecting the oocyte from an immune response
convert androgens to estradiol under FSH
Describe the theca cell compartment
vascularized because hormone production requires cholesterol delivery
responsive to LH. produces androgens which granulosa cells later convert to estrogens
How does Theca cell produce Testosterone?
Cholesterol -
- progenenolone - - progesterone -
17a - OH- progesterone
Androstenedione -
Testosterone
How does graulosa cell produce estradiol?
cholesterol - pregnenolone -
progesterone - androstenedione - estrone - estradiol or
androstenedione -testosterone - estradiol
Emerging Dominant Follicle becomes the preovulatory follicle. How?
Estradiol levels rise rapidly and FSH switches to inducing receptprs for LH on granulosa cells. The LH further stimulates estrogen and progesterone production and the state is set of LH surge which triggers ovulation
Explain the function of LH on the female reproductive tract
- resumption of meiosis - extrusion of the polar body
- Progesterone production by granulosa cells
- increase in antral fluid volume
- release of hydrolictic enzymes
Explain the minor FSH surge
the minor FSH surge will ensure sufficient LH receptors for luteal phase
and stimulates the synthesis of hyaluronic acid - for cumulus expansion
what are cumulus cells?
a subset of granulosa cells. they are the inner most layer of the granulosa cell that physically surround the oocyte
what is the cumulus oocyte complex
the functional unit that is ovulated during the menstrual cycle and is essential for successful fertilization
If the oocyte is fertilized what would be detected in the urine
hCG - human chorionic gonadotropin
What is the role of hCG
rescues the corpus lutem unit there is enough placental progesterone to maintain the pregnancy
What is the proliferative Phase?
the preovulation phase
Days 5-14
the endometrium rebuilds itself by generating a new functional layer and spiral arteries increase
what hormone largely influences proliferative phase
estrogen
During the proliferative phase the cervical mucosa begins the thin due to estrogen levels. Why does this matter?
to facilitate sperm passge into the uterus
When does ovulation occur
at the end of proliferative phase (Day 14)
How long is the proliferative phase
14 days
What is the secratory phase?
post ovulation phase
occurs days 15-28
the endometrium for an empbryo to implant
what hormone largely affects the secretory phase
progesterone from the corpus luteum
what happens to the cervical mucosa and why?
as a result of progesterone levels the cervical mucosa thickens - which help block entry of sperm, pathogen and other foreign material
If fertilization has not occured when will the corpus luteum degenerate?
at the send of secretory phase
The thickened cervical mucosa lining that which help block entry of sperm, pathogen and other foreign material is known as:
the cervical plug
why is it called the secrtory phase?
the endometrial glands in the utuerus become highly active and begin secreting nutrients
Outline the hormonal regulation of puberty
FSH stimulates estrogen secretion by granulosa cells
LH stimulates theca cells to produce androgens which serve as percuroses to estrogen synthesis
During puberty what is estradiol responsible for?
growtha nd maturation of breast and repoductive organs
fat redistribution
bone matuurations
Explain the concept of perimenopause
extends from early 40s onward
when ovarian function begins to wane due to the deprevation of estrogen
What are some symptoms of perimenopause?
hot flashes
insomnia
irritability
poor libido
headaches
When does menopause occur?
meadian age of 51.4
Explain some of the consequences of decreased estrogen has on the whole body after menopause.
vaginal dryness and icnreased vaginal infections
increased urinary frequency
atherosclerosis can lead to strokes
osteoporosis
