Lecture 15- Reproduction II Flashcards
Female Reproductive System Functions
Produce ova (eggs)
Receive sperm, facilitate fertilization
House and nourish developing embryo, give birth
Lactate, feed young
Ovaries and what they produce
Female gonad (reproductive organ)
Located in abdominal cavity (Held in place by several ligaments)
Produce:
- Gametes via oogenesis
- Sex hormones- estradiol, progesterone
Oviducts (Fallopian tubes)
Extend from uterus to ovaries
Collects secondary oocyte from ovary
Moves to uterus via beating cilia, contractions
Site of fertilization
Uterus
What are the layers?
Pear-shaped, size of fist
Site of embryonic development (expands during pregnancy)
2 layers
Myometrium: Thick wall of smooth muscle (involuntary movement)
Endometrium- Lines lumen
Endometrium
Fertilization vs. no fertilization
Lines lumen- connective tissue, glands, blood vessels
Thickens each month- prepare for pregnancy
Fertilization-> embryo implants
No fertilization-> sloughed off-> menstruation
Cervix
What does it separate?
Lower part of uterus
Closes uterus, separates from vagina
Common site of cancer
99% of cases due to HPV
Vagina
Elastic muscular tube
Extends to outside of body
Receives penis and sperm
Birth canal
Vulva
External genitalia
Covers external openings
Oogenesis-> how is the primary oocyte formed?
Development of mature eggs
In Embryo
Primordial germ cells (2n)
Mitosis-> Oogonia (2n)
Form during development, no new oogonia after birth
Mitosis-> Primary oocyte (2n)
Primary Oocyte
Begin meiosis
Arrest (pause) in prophase I
At birth, 1-2 million primary oocytes
200k by sexual maturity
Dormant until acted on by hormones after puberty
After Puberty
What happens in the ovary?
Occurs in follicle (structure within ovary)
Contains:
Primary oocyte
Follicle cells- protective barrier
Zona pellucida: Thick glycoprotein layer between follicle cells and oocyte
What is the zona pellucida?
Thick glycoprotein layer between follicle cells & oocyte
What happens each month when 6-12 follicles mature?
6-12 follicles mature
Primary oocyte grows, follicle cells proliferate
After 1 week, the largest continues, the others stop
What happens during primary oocyte division?
Primary oocyte completes meiosis I 8-10 hours before release. Completion of meiosis I and onset of meiosis II. Unequal cytokinesis->
1 polar body (n)
1 secondary oocyte (n)
Secondary oocyte starts meiosis II and arrests (pauses) at metaphase II
What happens during ovulation?
As secondary oocyte matures, it moves to surface of ovary.
Follicle cells secrete fluid, estrogens, proteolytic enzymes-> break down ovary wall
The secondary oocyte is ejected into the oviduct as a result.
What happens to the portion of follicle left in ovary after ovulation?
This is this corpus luteum, or yellow body. It develops into a temporary endocrine gland. It secretes estrogens and progesterone (1000x more than estrogens)
Secondary Oocyte (if sperm enters vs. if no sperm enters)
If sperm enters-> completes meiosis II
-> Mature egg containing sperm head- oogenesis complete
If no sperm enters-> disintegrates
Corpus lute dies (luteolysis)
-> Menstruation
New follicle next cycle
Oogenesis Summary
Primordial germ cell
-> Oogonium
-> Primary oocyte
-> Secondary oocyte
-> Ovum
Begins during embryonic development
Finishes at fertilization
Menstrual Cycle Overview
Complex sequence of events
Involves hypothalamus, anterior pituitary, ovaries, uterus
Repeats every 28 days unless fertilization + implantation occur
Prepares female body for pregnancy
Components of Menstrual Cycle- What are the two overlapping parts?
Ovarian cycle and Uterine cycle
List the components of the Ovarian cycle
List the components of the Uterine cycle
OVARIAN CYCLE
Follicular phase- days 1-13- before ovulation
Ovulation- day 14
Luteal phase- days 15-28- after ovulation
UTERINE CYCLE
Menstrual flow phase- days 1-5
Proliferative phase- days 6-13- before ovulation
Secretory phase- days 15-28- after ovulation
Female Sex Hormones- Estrogen
Estrogen is the principle female sex hormone. Main form is estradiol.
Secreted by follicle cells, corpus lute
At puberty, stimulates growth of:
- Sex organs
- Secondary sex characteristics- breast development, broadening of pelvis, fat and muscle distribution
Stimulates monthly prep for pregnancy- endometrium
Female Sex Hormones- Progesterone
Secreted mainly by corpus luteum
Completes preparation of endometrium for pregnancy
Stimulates endometrial glands to secrete nutrient-rich fluid
What stimulates the production of estrogen and progesterone?
Hypothalamus secretes GnRH (Gonadotropin-releasing hormone). Stimulates anterior pituitary to release FSH and LH (Follicle stimulating hormone and Luteinizing hormone). FSH and LH are secreted and enter ovaries, signal ovaries to produce estrogen and progesterone
New Ovarian Cycle
Hypothalamus releases GnRH (Gonadotropin-releasing hormone). Stimulates Anterior Pituitary to release FSH + LH (Follicle stimulating hormone and luteinizing hormone). This leads to follicle growth. Follicle cells produce estradiol, so there is a slow rise in estradiol during follicular phase as follicle grows.
Now we have high estradiol. The hypothalamus is still secreting GnRH to the AP. FSH and LH are still being released, LH surge. LH surge triggers ovulation.
Maturing follicle enlarges and moves to the ovary surface. Ovulation occurs ~1 day after LH surge. Secondary oocyte is released into oviduct. (Ovulation is due to positive feedback regulation).
Luteal Phase
LH stimulates remaining follicle tissue-> corpus lute
-> Secretes progesterone and estradiol
Hypothalamus releases less GnRH
AP releases less LH, FSH
Why?
Negative feedback to prevent another egg from maturing after pregnancy may have started
If No Pregnancy
Low FSH, LH cause corpus luteum to disintegrate
Estradiol and progesterone decrease
No negative feedback on hypothalamus-> secretes GnRH
-> AP produces FSH
-> Stimulates next ovarian cycle
Uterine Cycle 3 Phases
- Menstrual Flow phase- days 1-5
- Proliferative phase- days 6-13- before ovulation
- Secretory phase- days 15-28- after ovulation
Proliferative Phase
Days 6-13- before ovulation
Coordinated with follicular phase of ovarian cycle
Ovarian hormones stimulate uterus to prepare, support embryo
Growing follicle produces estradiol, causing the endometrium to thicken.
Ovulation- day 14
Secretory Phase
Days 15-28- After ovulation
Coordinated with luteal phase of ovarian cycle
Promoted by estradiol, progesterone from corpus luteum
Endometrium development
Arteries enlarge
Endometrial glands grow
(Preparing for embryo)
If no pregnancy
Corpus luteum disintegrates
Estradiol and progesterone go down
Arteries in endometrial lining constrict
-> Loss of circulation
-> Lining disintegrates
Menstrual Flow Phase
Endometrial tissue, fluid, blood is shed
New follicles begin to grow
Day 1 of menstrual flow= beginning of new ovarian/uterine cycles
What are the female gonads?
Ovaries
When puberty begins, the concentration of _____ begins to rise.
Estrogen (estradiol)
Prior to puberty, each primary oocyte is housed within a _____.
Follicle
Gonadotropin-releasing hormone (GnRH) is secreted by the _____ and travels to the _____.
Hypothalamus / Anterior pituitary
What are the main functions of the ovaries?
Produce ovum & secrete hormones that regulate the menstrual cycle and fertility
What two subcycles compose the menstrual cycle?
Ovarian cycle & Uterine cycle
What is the corpus luteum and what does it secrete?
Temporary endocrine gland that secretes estrogen and progesterone
What is produced when a primary oocyte completes meiosis I?
One polar body (n) and one secondary oocyte (n)
The Fallopian tubes (oviducts) are tubes that stretch from the _____ to the _____.
Uterus to the ovaries
What must occur in order for a secondary oocyte to complete meiosis?
Secondary oocyte must be fertilized by sperm to exit metaphase II and finish meiosis
What are the three stages of the ovarian cycle?
Follicular phase → Ovulation → Luteal phase
The _______ is a glycoprotein layer surrounding the plasma membrane of oocytes and lies between the oocyte and follicle.
Zona pellucida
In the embryonic ovaries, primordial germ cells (2n) divide and differentiate into _____.
Oogonia (2n)
What are the three stages of the uterine cycle?
Menstrual flow phase → Proliferative phase → Secretory phase
True or False: The Fallopian tubes (oviducts) are directly connected to the ovaries
False; the oviducts are not in physical contact with the ovaries
The secretion of gonadotropin-releasing hormone (GnRH) stimulates the anterior pituitary to release _____ and _____.
Follicle stimulating hormone (FSH) & Luteinizing hormone (LH)
How does high levels of estrogen (estradiol) and progesterone affect the hypothalamus and anterior pituitary?
Hypothalamus and anterior pituitary are inhibited and stop releasing GnRH & FSH/LH respectively
Oocytes are housed in the _____.
Ovaries
True or False: The concentrations of FSH and LH are very high during the early follicular phase of the ovarian cycle
False; the low concentrations of estrogen (estradiol) and progesterone inhibit the hypothalamus and anterior pituitary from releasing GnRH and FSH/LH respectively
True or False: The layer of the uterus responsible for muscle contractions is the endometrium
False; the layer of the uterus responsible for muslce contractions is the MYOMETRIUM
True or False: In the embryonic ovaries, oogonia undergo meiosis to form primary oocytes
False; in the embryonic ovaries, oogonia (2n) undergo MITOSIS to form primary oocytes (2n)
An oocyte is a cell that undergoes meiosis to become a(n) _____.
Ovum (egg)
True or False: The concentration of progesterone is very low during the follicular phase of the ovarian cycle
TRUE
What is the function of follicles prior to puberty?
Protect primary oocytes
How does the hypothalamus respond to low levels of estrogen (estradiol) and progesterone?
Hypothalamus is inhibited and stops releasing GnRH
The end of the proliferative phase of the uterine cycle is marked by _____.
Ovulation
What is contained in the ovaries?
Follicles and Oocytes
What occurs during the luteal phase of the ovarian cycle?
Follicle tissue becomes corpus luteum and secretes progesterone which inhibits the hypothalamus and prevents another egg from releasing
What happens to primary oocytes during embryonic development?
Primary oocytes (2n) begin MEIOSIS but arrest at prophase I until puberty
What occurs during the menstrual flow phase of the uterine cycle?
Endometrial lining is shed & new follicles begin to grow
What is ovulation and when does it occur?
Ovulation is the process by which ovarian follicles rupture and release mature secondary oocytes from the ovaries in the oviducts (day 14)
How does the anterior pituitary respond to low levels of estrogen (estradiol) and progesterone?
Stops secreting FSH and LH because it is no longer receiving GnRH
What happens to primary oocytes when puberty begins?
Increase in estrogen causes primary oocytes (2n) to finish meiosis I
Estrogen (estradiol) is secreted by the ____ and ____.
Follicle cells & corpus luteum (which are both in the ovaries)
What occurs during the early follicular phase of the ovarian cycle?
The anterior pituitary secretes small amounts of FSH/LH which stimulates follicles to undergo mitosis and grow
What happens at the end of the luteal phase of the ovarian cycle if there is no pregnancy?
Decrease in FSH/LH concentrations cause corpus luteum to disintegrate / Estrogen (estradiol) & progesterone concentrations return to normal / Endometrial lining is shed
Following meiosis I, what happens to the polar body and secondary oocyte?
Polar body is discarded and secondary oocyte begins meiosis II
What are the main functions of estrogen (estradiol) in a female human?
Monthly preparation (thickening) of the endometrium & secondary sex characteristics (physical characteristics after puberty)
How do the hypothalamus and anterior pituitary respond to high levels of estrogren (estradiol) and low levels of progesterone?
Hypothalamus continues to secerete GnRH and anterior pituitary continues to secrete LH/FSH in a positive feedback mechanism
The end of the follicular phase of the ovarian cycle is marked by _____.
A spike in LH and subsequent ovulation (day 14)
What occurs during the proliferative phase of the uterine cycle?
Rise in estrogen (estradiol) concentration causes endometrium to thicken
At which phase of meiosis does the secondary oocyte arrest?
Metaphase II
Progesterone is secreted by the _____.
Corpus luteum
What occurs during the late follicular phase of the ovarian cycle?
Growing follicle cells secrete high levels of estrogen (estradiol) which stimulates the hypothalamus and subsequently the anterior pituitary in a positive feedback mechanism
What happens to the ruptured follicle after ovulation?
Ruptured follicle develops into corpus luteum
What are the main functions of progesterone in a female human?
Prepares uterine lining (after ovulation) & maintains pregnancy
What occurs during the secretory phase of the uterine cycle?
Corpus luteum secretes progesterone and cervical mucus thickens which prepares the endometrium for the implantation of a blastocyst
