Flashcards in Reproductive Endocrinology - Lecture 5 Deck (56):
Where is GnRH made, how and why is it released into the Anterior Pituitary?
In the Hypothalamus, it is released into the capillary bed of the median eminence, then to the second capillary bed in the Pituitary gland. It is released to help the Anterior Pituitary gland to release FSH and LH.
Where are FSH and LH made (2 Gonadotropins)?
In the Anterior Pituitary gland.
Which cells do FSH and LH act on?
The cells in the Gonads, testes in males and ovaries in females
What hormones do the Gonads produce?
Androgens, Estrogens and Progesterone
What are the two forms of GnRH release?
Pulsatile and Surge. There are two centres in the brain in the Hypothalamus that regulate this.
1. Tonic centre
2. Surge centre
How does the Tonic centre in the Hypothalamus release GnRH? And does this occur in males or females?
Responsible for the ongoing Pulsatile nature that occurs throughout the day every 1 to 3 hours. It is a pulsatile release of GnRH.
It occurs in both males and females.
How does the Surge centre in the Hypothalamus release GnRH? And does this occur in males or females?
It is responsible for a large surge or increase of GnRH.
It occurs in females only.
When does the Surge of GnRH occur in females?
Just before ovulation
Do high Estrogen levels result in a negative or positive feedback loop?
POSITIVE feedback loop
Which hormones are required for spermatogenesis?
Testosterone, LH and FSH
What are the 3 important accessory glands important for secretion of semen?
What produces semen?
The sperm plus the proteins and secretions from the glands = produce semen
Where is the mitochondrial spiral located in the sperm?
In the mid piece of the sperm, were energy is produced. to keep the flagellum (tail) moving
What do Androgens like testosterone influence?
1. Primary sex characteristics - internal and external genetalia
2. Secondary sex characteristics - body shape, beard and body hair, muscular development, lowering of voice, libido.
Describe the feedback regulation of the Gonadotropins FSH and LH.
LH and FSH from A. Pituitrary act on the Gonads (ovaries and testes)
LH acts on Endocrine cells to to create peptide and steroid hormones (Estrogens, progesterone & Androges)
The steroid hormones produced by LH act back on A. Pituitary go INHIBIT release of LH and FSH
The steroids produced by LH can act back on hypothalamic cells to INHIBIT GnRH
LH in females acts on Gamete production
FSH acts directly on Gamete production in both males and females
LH and FSH can act on GnRH to INHIBIT its release
When Estrogen is in HIGH concentration, does it INHIBIT or ENHANCE GnRH release? And who does it get help from to do this?
It ENHANCES GnRH release, and progesterone helps too.
What are Inhibins and Activins?
They are both peptide hormones that are made with the help of LH release in endocrine cells.
What do the peptide hormones Inhibins and Activins do?
They influence the release of FSH
In males, what does FSH and LH stimulate?
FSH - stimulates sertoli cells to produce proteins & inhibins.
LH - stimulates Leydig cells to produce testosterone
In females, what does FSH and LH stimulate?
FSH - stimulates ovaries to produce steroids estradiol & progesterone.
Surge (with LH) triggers ovulation
LH - stimulates ovaries to produce steroids.
Surge triggers ovulation
What is Leutinising hormone CRITICAL for?
The surge that produces ovulation
Where does spermatogenesis in the testes occur?
In the Seminiferous tubule.
Describe where in the Seminiferous tubule the Sertoli cells, the Leydig cells, the capillaries and Lumen are.
Capillaries - are around the outside of the tubule
Leydig cells are on the outside too
Sertoli cells are inside together the the spermatocytes
The lumen is in the middle of the tubule
What is the role of Sertoli cells?
Their role is CRITICAL. They provide nutrients and environment that the maturing spermatocytes need.
What is the role of Leydig cells?
They provide Testosterone which contributes to the maturation of sperm.
What do Sertoli cells secrete?
Androgen-binding protein (ABP), inhibin, activin. Testosterone binds to ABP in the tubule.
What makes up semen?
Sperm, secretions from glands and proteins
What does the mid piece of the sperm contain and why?
It contains a large number of mitochondria which produce energy for the flagellum (sperm tail) to beat.
In male reproduction, FSH primarily acts on?
Sertoli and granulosa cells
Which cells type in the testes synthesises Testosterone?
In male reproduction, where is LH release and what cells does it act on?
LH in males is released from the Anterior Pituitary and it acts on Leydig cells.
In the hormonal control of reproduction, negative feedback loops exist. Explain the long feedback loops of the Gonadal hormones.
The Gonadal hormones Estrogen, progesterone and Androgens act back on the A. Pituitary and Hypothalamus to alter secretions of GnRH, FSH and LH.
What happens when Gonadal hormone levels are low? As they climb, what happens then?
The Pituitary gland secretes FSH and LH. As the Gonadal hormone levels rise, negative feedback usually inhibits GnRH release.
Do higher levels of Estrogen exert a positive or negative feedback on GnRH?
They can do both. Moderate concentrations of Oestrogen have a negative feedback however if it rises rapidly to a threshold level and stays that way for at least 36 hours, the feedback will be positive.
What do testes produce?
Hormones and sperm
Approximately how many compartments are in the seminiferous tubules?
What do ovaries produce?
Hormones and eggs
What part of the cycle is the follicular phase?
It is the first part where there is follicular growth in the ovary.
What is the Luteal phase?
It follows ovulation and is where the ruptured follicle is transformed into the Corpus Luteum. If pregnancy does not occur, the CL ceases to function after about two weeks and the cycle begins again.
How many phases does the Uterine cycle have?
1. Menses - the beginning of the follicular phase in the ovary corresponds to menstrual bleeding from the uterus.
2. Proliferative phase - the latter part of the ovary's follicular phase. New cells are added to the lining. This is before ovulation.
3. Secretory phase - After ovulation, hormones from the Corpus Luteum convert the thickened endometrium into a secretory structure.
Explain hormonal control in the menstrual cycle
1. Follicular phase - Estrogen is dominant.
2. Ovulation is triggered by surges of LH and FSH.
3. Luteal phase Progesterone is dominant although Estrogen is still present.
What is the role of Anti-Mullerian hormone (AMH)?
It is produced in ovarian follicles in the first part of the ovarian cycle to prevent too many follicles developing at one time.
Basically it regulates follicle development.
What important job does the Corpus Luteum have?
It continues the production of Estrogen and Progesterone, Progesterone is the main hormone however.
What happens when the Corpus Luteum regresses and atrophies?
It stops the production of Estrogen and Progesterone.
How is Estrogen important in the female reproductive cycle?
1. It REDUCES FSH and LH secretion
2. It INCREASES follicle production of estrogens
3. It also ENHANCES GnRH responsiveness when its levels are very high
The uterus is made up of which 3 sections?
1. Uterine wall
2. Endometrium - which changes considerably during the ovarian cycle
3. Uterine cavity
What happens during menses?
The uterine wall closes off, blood vessels close off and bleeding occurs.
At the same time follicle formation takes place.
This is the beginning of the cycle.
From ovulation to fertilisation, Estrogen and Progesterone is continuing to INCREASE. What is producing this?
The Corpus Luteum is producing these two hormones.
What does the Placenta produce and why?
The Placenta produces Human Chorionic Gonadotropin,. This prevents the Corpus Luteum from atrophying so it continues to produce Estrogen and Progesterone.
During gestation, are Estrogen and Progesterone levels HIGH or LOW?
What hormone is used in pregnancy tests?
hCG - Human Chorionic Gonadotropin
What is HPL - Human Placental Lactogen important for?
1. breast development
2. milk production
3. mothers metabolism to ensure there is sufficient Glucose and energy for the fetus.
How many weeks after fertilisation does the Corpus Luteum degenerate and what takes over to continue producing high levels of Estrogen and Progesterone?
Around 7 weeks and then the Placenta takes over
Where is Human Chorionic Gonadotropin released from?
Is Human Chorionic Gonadotropin released in high or low amounts?