Endocrine control of reproduction Flashcards
Gonadotropin-releasing hormone (GnRH) length
10 amino acids
What hormone is the key regulator of reproduction in vertebrates?
GnRH
True or false: GnRH is the exact same sequence in every species
False
- the primary sequence of 24 different GnRH molecular forms have been elucidated in different species
Where do similarities lie between the primary structure of GnRH between different species?
Similarity exists between sequences at N- and C- terminal regions
- Evolutionary conservation
- Important for specificity of hormone receptor
Where is GnRH synthesized?
In the neurosecretory neurons in the hypothalamus, reaches anterior pituitary via hypothalamic-hypophyseal portal system
How is GnRH released and what does it stimulate?
GnRH is released in a pulsatile manner to stimulate release and synthesis of LH and FSH from gonadotropes in the anterior pituitary
- In humans, its one pulse every 90 mins.
True or false: GnRH used to be called LHRH before
True, this was before they knew that GnRH stimulated FSH production/release as well
What 8 main conditions are GnRH analogs used to treat?
- Precocious and delayed puberty
- Hypogonadism
- Anovulation
- Amenorrhea
- The premenstrual syndrome
- Inadequate luteal function
- Endometriosis
- Hormone-dependent neoplasia
How do opiates effect the release of GnRH?
They inhibit the pulsatile release of GnRH
How does estrogen affect GnRH?
Estrogen stimulates Kiss peptin, and Kiss peptin stimulates GnRH
What are kiss peptins?
- Kiss peptins are produced by secretory neurons in the hypothalamus
- Kiss peptin neurons synapse with GnRH neurons
Androgens (stimulate/inhibit) hypothalamus to produce GnRH
Androgens inhibit hypothalamus to produce GnRH
Estrogen can increase __ secretion
What is this important for?
LH
- This is important to bring about the ovulatory surge of gonadotropins
The effect of estrogen is mediated by increased production of…
Kiss peptins
LH and FSH production are inhibited by a combination of…
Estrogen and progesterone
What are pregnancy pills based on?
Based on a combination of estrogen and progestogens that inhibit ovulation
- Pills add a higher level of progesterone (LH inhibitory hormone)
In males, an androgen surge inhibits…
The pulsatile release of GnRH and LH
- The effect of androgens are primarily inhibitory
Inhibin and activin are…
Gonadal peptides
Where are inhibin and activin produced?
Produced in both human female ovary and male testis
Inhibin and activin are (dependent/independent) on/of GnRH
Independent
Inhibin and activin superfamily
Transforming growth factor-β (TGF-β) superfamily
Inhibin function
Inhibits secretion of FSH without affecting LH
Activin function
Stimulates secretion of FSH independent of GnRH in addition to other actions, without affecting LH
Label diagram on slide 15
During each ovarian cycle after puberty, a number of ________ depart from the ________ and start rapid pattern of _________ growth and development
During each ovarian cycle after puberty, a number of primordial follicles depart from the resting pool and start rapid pattern of gonadotropin-dependent (FSH) growth and development
After the follicle grows into a Graafian follicle from the primordial stage, it must achieve… (2 things)
Ovulation or become atretic
Most follicles undergo…
Atresia (degeneration that includes loss of the oocyte)
- Only few reach the preovulatory Graafian follicle stage
Label diagram on slide 16
Describe the four steps of ovarian development from primary follicle to Graafian follicle
- Primary follicle to begin with
- Theca and granulosa cells become more numerous and small spaces appear in the follicle. This structure forms the secondary follicle.
- The spaces become filed with follicular fluid and enlarge to form a single large cavity the antrum.
- The follicle enlarges to approximately 20-25 mm in diameter containing an oocyte of ~120 µm in diameter and become preovulatory (Graafian) follicle
When does meiosis start in an organism?
During the organism’s embryonic stage
During the embryonic stage of a female embryo, what stage does the ovum remain in? It remains in this stage until when?
Prophase I, and remains arrested until lit reaches a Graafian follicle form -> called re-initation of meiosis and is started by an ovulatory surge of LH
After ovulation, the ovum remains in what stage? It remains in this stage until when?
Gets arrested at metaphase II, and meiosis restarts only if the egg is fertilized.
True or false: Meiosis of a follicle to form an ovum results in 2 daughter cells
False, one of the daughter cells becomes a polar body (small in size) and detaches
How long is the menstrual cycle?
25-30 days
The menstrual cycle is divided into two parts, the ___ phase and the ___ phase
Follicular phase and the luteal phase
Follicular phase length
12-16 days
Luteal phase length
10-16 days
What separates the follicular phase and the luteal phase?
Ovulation
What does the follicular phase involve?
The maturation of the oocyte and ovulation
The follicular phase is primarily…
Estrogenic
The luteal phase is predominantly…
Progestogenic
During the follicular phase, there is an increase in [this hormone] mainly, which stimulates [this hormone] to enhance the production of [this hormone]
During the follicular phase, there is an increase in estrogen mainly, which stimulates kiss peptin to enhance the production of GnRH
During the end of the follicular phase, there is a slight increase in [this hormone] which causes a dip in [this hormone]
During the end of the follicular phase, there is a slight increase in inhibin which causes a dip in FSH
There is a decline in [this hormone] after ovulation
There is a decline in estrogen after ovulation
GnRH pulse frequency increases during the ____ phase, and low during the ____ phase
GnRH pulse frequency increases during the follicular phase, and low during the luteal phase
The increase in estrogen during the follicular phase stimulates an increase in the secretion of [this hormone] which….
The increase in estrogen during the follicular phase stimulates an increase in the secretion of LH which stimulates ovulation
The corpus luteum secretes which hormone during the luteal phase?
Progesterone
What effect does estrogen have on the endometrium?
It allows for hyperplasia and hypertrophy of endometrial cells
- Endometrium becomes thick and vascularized
What do endometrial cells provide to the implanted embryo?
Nutrition
Progesterone prevents…
Contractile filaments in uterine smooth muscle from contracting
The decline in progesterone at the end of the luteal phase results in…
Spasms because contractions aren’t being prevented anymore
- Leads to menstruation because endometrial cells die
What results in the ovulatory surge of LH/FSH?
Higher estradiol levels towards the end of the follicular phase stimulates kiss peptins which in turn stimulate GnRH, resulting in the ovulatory surge of LH/FSH
Basal body temperature (increases/decreases) during ovulation
Increases
At the beginning of the follicular phase, (FSH/LH) is higher than (FSH/LH)
At the beginning of the follicular phase, FSH is higher than LH
The increase in FSH during the follicular phase (past LH levels) is initiated by [this hormone]
Activin
Ovulation depends on which classes of molecules?
Prostaglandins and cytokines
Surge of LH and FSH results in…
Meiotic maturation and ovulation
After ovulation, granulosa and theca cells undergo _____ and form _____ cells called ______ which produce _____ and a larger amount of _____
After ovulation, granulosa and theca cells undergo luteinization and form luteal cells called Corpus Luteum which produce estrogen and a larger amount of progesterone
The life span of a human corpus luteum is how many days? What happens after this time?
14 days
- After, it spontaneously regresses and results in a decline in progestogen and estrogen levels
What happens to progesterone levels during pregnancy and how?
If pregnancy occurs, chorionic gonadotropin secretion from chorion of embryo prolongs progesterone secretion by sustaining the corpus luteum even as FSH and LH decline, and maintains the pregnancy
The morning after pill is a progesterone _______, which functions to…
The morning after pill is a progesterone antagonist, which functions to contract endometrial cells. This aborts the embryo.
Contraceptive vs. contragestive
Contraceptive: prevents conceptions of embryo
Contragestive: prevents implantation of embryo
All steroid hormones are derived from ______ and differ only in the ______
All steroid hormones are derived from cholesterol and differ only in the ring structure and side chains attached to it.
All steroid hormones are ____ soluble
lipid
True or false: enzymes involved in steroid hormone synthesis have differential regulation based on follicular or luteal phase
True
- controls what steroids are produced during each phase
What are the steps for steroid hormone synthesis? (6 steps)
- Cholesterol becomes pregnenolone (C21) through sidechain cleavage
- Pregnenolone (C21) becomes progesterone (C21) through activity of 3β- hydroxysteroid dehydrogenase (3β-HSD)
- Progesterone (C21) either becomes corticosterods (C21), or becomes 17α-hydroxyprogesterone (C21) through activity of 17α-hydroxylase
- 17αhydroxyprogesterone (C21) becomes androstenedione (C19) through activity of C17,20-lyase
- Androstenedione (C19) becomes testosterone (C19) or estrone (c18) through activity of aromatase
- Testosterone becomes estradiol (C18) through activity of Aromatase
Cholesterol conversion to progesterone happens in the _____, while progestrone conversion into androgens/estrogens happens in the _______.
Cholesterol conversion to progesterone happens in the gonads and adrenal cortex, while progestrone conversion into androgens/estrogens happens in the gonads.
True or false: there’s a much higher concentration of aromatase enzyme in males compared to females
False
- There’s a much higher concentration of aromatase in females compared to males
Androgens have C__ strands, while estrogens have C__ strands
Androgens have C19 strands, while estrogens have C18 strands
Progestogens and corticosteroids are C__ steroids
C21
What are the 4 main effects of estrogens?
- Enlargement and maintenance of the vagina, uterus, uterine tubes, ovaries and external reproductive organs (primary sexual characteristics).
- Development of the breasts and the ductile system of the mammary glands.
- Increased deposition of adipose tissue in various subcutaneous layers, particularly in the breasts, thighs and buttocks (responsible for the formation of the female physique)
- Influence skin texture and vascularization, skeletal growth, hair distribution, electrolyte balance, feedback action on pituitary and brain, etc.
True or false: breast tissue increases during the follicular phase
True
- Due to increase in estrogen
True or false: during menopause, women get wrinkles, osteoporosis and low vascularization
True
- Due to decrease in estrogen
What are the 4 main effects of progestogens?
- Promote secretory changes in the endometrium, preparing the uterus for implantation of the fertilized ovum
- Reduces uterine contraction and prevents expulsion of the implanted ovum
- Promotes secretion of nutrients by cells lining the fallopian tube
- Promotes development and secretion of alveolar tissue, and general swelling due to secretory development in breast tissue (develops structures that can nurse the young)
What are the functions of the testis? (2 general functions, 4 points for 2nd reason)
- Provide spermatozoa
- Secrete hormones (both steroid and peptide hormones like activin) that:
a) Promote development and maintain the male reproductive characteristics.
b) Promote development and maintain the male secondary sexual characteristics.
c) Regulate gonadotropin secretion and release.
d) Exert influences on a number of nonreproductive components, including liver, kidneys, skin, skeletal muscle, bone, brain.
Increased androgen production can (increase/decrease) natural opiate production
Increase
In males, testosterone is a precursor to which molecule?
Dihydrotestosterone (DHT)
True or false: DHT is only present in males
True
Effect of androgens (testosterone and dihydrotestosterone/DHT) on libido
Act on CNS to increase sexual activity (libido) -> Both males and females have increased libido due to testosterone
Effect of androgens (testosterone and dihydrotestosterone/DHT) on bone growth
Affects bone growth - fusion of epiphysis (both estrogens and androgens cause the apoptosis of cartilaginous cells in the epiphysis)
Effect of androgens (testosterone and dihydrotestosterone/DHT) on reproductive tract during adulthood
Maintains the reproductive tract during adulthood
Effect of androgens (testosterone and dihydrotestosterone/DHT) on voice
Lowers voice
Effect of androgens (testosterone and dihydrotestosterone/DHT) on behaviour
Affects CNS - aggressive behaviour
Effect of androgens (testosterone and dihydrotestosterone/DHT) on hair growth
Affects hair growth (beard, axillar, chest, pubic, etc.) and hair loss in forehead
Effect of androgens (testosterone and dihydrotestosterone/DHT) on gonadotropin secretion and release
Regulate gonadotropin secretion and release
Effect of androgens (testosterone and dihydrotestosterone/DHT) on anabolic effect and growth
Exerts anabolic effect and growth (male physique)
Effect of androgens (testosterone and dihydrotestosterone/DHT) on primary and secondary sexual characteristics
Control development of the primary and secondary male sexual characteristics
Effect of androgens (testosterone and dihydrotestosterone/DHT) on penis/scrotum
Penile and scrotal growth
Effect of androgens (testosterone and dihydrotestosterone/DHT) on prostate, seminal vesicle, bulbouretheral gland, Sertoli cell maturation and androgen binding protein synthesis
Stimulate development of prostate, seminal vesicle, bulbouretheral gland, Sertoli cell maturation (critical for sperm production) and androgen binding protein synthesis
What causes menopause?
As females age, the number of germ cells left in their ovary for fertilization decreases. Menopause is caused by a complete cessation of germ cells in the ovary (they run out).
- No follicles mean no estrogen/progesterone produced so there are many symptoms associated)
What is andropause?
As males age, their testosterone secretion decreases (but they can still produce sperm)
What are the common health effects of menopause? (6)
- Hot flashes
- Urinary problems (because vasculature is affected)
- Vaginal dryness (females become more prone to urinary infection)
- Mood changes, sleep disturbances, stress, depression (rare)
- Increase in heart disease and stroke
- Osteoporosis affects about 25% of menopausal women.
Effect of androgens on spermatogenesis
Stimulates spermatogenesis
There are much more (theca/granulosa) cells than (theca/granulosa) cells in the follicle
Granulosa, theca
Granulosa cells secrete…
Testosterone
- Have large number of aromatase enzymes which convert the testosterone into estrogen
Draw GnRH pulse frequency throughout follicular and luteal phases
Draw the gonadotropic hormones (FSH and LH) throughout follicular and luteal phases
Draw the ovarian hormone levels (inhibin, estrogen, progesterone) throughout the follicular and luteal phases
