Exam 2: Lecture 21: Reproductive Endocrinology Flashcards
What is a simple neural reflex?
-Employs nerves that release simple neurotransmitters directly onto target tissue
What is a neuroendocrine reflex?
-Requires neurohormone (released by neuron) to enter blood & act on remote target tissue
___ is the control center for repro hormones
The hypothalamus
Neurohormones enter
bloodstream
Explain the steps of a simple neural reflex
- Stimulus (temp. tactile, visual, etc.)
- Sensory neurons (afferent, recognition of stimulus)
- Transmission
- Efferent neurons
- Neurotransmitter
- Target tissue
- Response by target tissue
Explain the steps of a neuroendocrine reflex
- Stimulus (temp. tactile, visual, etc.)
- Sensory neurons (afferent, recognition of stimulus)
- Transmission
- Efferent neurons
- Hypothalamus
- Neurohormone
- Blood
- Target tissue
- Response by target tissue
The ____ is the neural control center for reproductive hormones
hypothalamus
What 3 things have direct effect on reproduction?
-Surge center
-Tonic center
-PVN (paraventricular nucleus)
note: all close to each other & 3rd ventricle
Where is the pituitary?
-Positioned in depression of sphenoid bone, the sella turcica
The ____ separates the lateral portions of the hypothalamus
Third ventricle
What does the Hypothalamo-Hypophyseal Portal System do?
-Allows minute quantities of releasing hormones to act on the anterior pituitary before they are diluted by general circulation
How does the HHP system work? (Hypothalamo-Hypophyseal Portal System)
-Axons from neurons in the surge center & tonic center extend to stalk region where they terminate on blood vessels of HHP system
What is the relationship between PVN & posterior pituitary?
-Axons from neurons originating in hypothalamus (PVN) extend into posterior lobe of pituitary where they release their neurohormones into a capillary plexus
____ does not have a portal system
posterior pituitary
-Neurohormones are deposited directly into systemic circulation
What is positive feedback?
Something influences the stimulation of another
What is negative feedback?
Something influences the suppression of another
What are some characteristics of reproductive hormones?
-Act in small quantities
-Posses short half-lives
-Bind specific receptors
-Can cause release of other hormones
-Can stimulate the gonads
-Can cause sexual promotion (ex: steroids)
-Can help maintain pregnancy
-Luteolysis
What would eliminate pregnancy?
-Luteolysis
What are the 3 ways a hormone is classified?
-Source
-Mode of action
-Biochemical classification
What are the hypothalamic hormones?
-GnRH (causes release of LH & FSH)
What are the pituitary hormones?
-Follicle Stimulating Hormons (FSH)
-Luteinizing Hormone (LH)
-Prolactin
-Oxytocin
What are the gonadal hormones?
-PGF2a (made in uterus)
-Progesterone (made in ovary, CL)
-Estrogen (made in ovary, follicle)
-Equine chorionic gonadotropin (made in placenta)
-Human chorionic gonadotropin (made in placenta)
Where are neurohormones synthesized & released & what are they?
-Synthesized by neurons
-Released directly into blood
-GnRH, FSH, LH, Oxytocin
Where are releasing hormones synthesized, what do they do, and what are they?
-Synthesized by neurons in hypothalamus & cause release of other hormones from anterior pituitary
-Can also be classified as neurohormone b/c synthesized & released by neurons
-GnRH
Where are Gonadotropins synthesized, what do they do, and what are they?
-Synthesized & secreted by specialized cells in anterior lobe of pituitary gland
-Have stimulatory effect on gonads
-FSH, LH
Where are sexual promoters secreted, what do they do, and what are they?
-Secreted by gonads to stimulate reproductive tract, regulate function of hypothalamus & anterior pituitary & regulate reproductive behavior
-Estrogen, Progesterone, Testosterone, eCG, hCG
What are the hormones classified under the pregnancy maintenance hormone mode of action & what does it do?
-High concentration during pregnancy
-Responsible for maintaining pregnancy & assisting female in lactation ability
-Progestins, Placental Lactogen
What are the general metabolic hormones and what do they do?
-Promote metabolic well-being
-Thyroxin, adrenal corticoids, growth hormone
What are the lutyletic hormones & what do they do?
-Cause destruction of the CL
-PGF2a
What is the peptide classification of hormones and what falls under it?
-Very small protein
-GnRH is a decapeptide, Prolactin, Relaxin
What is the glycoprotein classification of hormones and what falls under it?
-A polypeptide protein that has carbohydrate moieties
-Large protein
-FSH, LH, Inhibin
What is the steroid classification of hormones and what falls under it?
-Have a common molecular nucleus
-Progesterone, Testosterone, Estradiol
What is the prostaglandins classification of hormones and what falls under it?
-Lipid based
-PGF2a, Prostaglandin E2
Why does the biochemical classification of reproductive hormones matter?
-The body doesn’t notice the really small hormones
-So, have to give a small hormone to induce ovulation or the immune system will notice
_____ can be taken and through different enzymatic conversions go to pregnenolone, progesterone, testosterone, or estradiol
Cholesterol
Reproductive hormones are required to bind to
specific receptors on their target cells
What do protein hormones do?
-Bind to plasma membrane bound receptors
What do steroid hormones do?
-Travel freely through plasma membrane into cytoplasm & bind directly to specific nuclear receptors
Binding of hormones results in
new protein synthesis
Steroid hormones can bind to
-Membrane receptors & nuclear receptors
What is the fast response steroid hormone action?
-Binds to a membrane receptor causing protein production
What are examples of fast response steroid hormone action?
-Estradiol - increased myometrial contractions (period cramps)
-Progesterone - decreases myometrial contractions
What is the slow response steroid hormone action?
-Binds to nuclear receptor inside cell causing protein production
What are examples of slow response steroid hormone action?
-Estradiol - mucous secretion by female tract
-Progesterone - uterine gland secretion
____ ultimately regulates GnRH
CNS
The tonic center is in
Female & male
The surge center is in
Females only
Hypothalamic nuclei nerve cell bodies are found
in the hypothalamus
What are the clusters of specific hypothalamic nuclei?
-GnRH
-TRH
-CRH
Where do hypothalamic nuclei axons terminate
Terminate on capillaries in the H-HPS (Hypothalamo-Pituitary Gonadal Axis)
-Picogram amounts released
-Neurohormones released into blood
____ regulates reproduction primarily based upon a positive & negative feedback system
Hypothalamo-Pituitary Gonadal Axis
Hormones can have _____ feedback on different areas
both positive & negative feedback on different areas
What are the key players in the HPG axis?
-GnRH
-Gonadotropins
-Oxytocin
-Gonadal hormones
What is GnRH and where is it?
-Gonadotropin Releasing Hormone
-Hypothalmic nuclei
What are the gonadotrops and where are they?
-FSH, LH, Prolactin
-Anterior pituitary
Where is oxytocin?
-Made in paraventricular nucleus & transported to posterior pituitary for release into bloodstream
What are the gonadal hormones?
-Testosterone, estrogen, etc.
The strength of hormone action depends on
-Pattern & duration of secretion
-Half-life
-Receptor density
-Receptor-hormon affinity
Steroid hormones are metabolized
by the liver
Protein hormones are degraded
in the liver & kidneys
Which of the following does the pituitary secrete?
A. Oxytocin, FSH, & LH
B. Testosterone & Inhibin
C. FSH and Progesterone
D. Estrogen & Inhibin
E. LH & GnRH
A. Oxytocin, FSH & LH
The tonic center releases ____ amounts of GnRH
small
The surge center releases ____ amounts of GnRH
large
What is the difference in the male and female hypothalamus?
-Males do not have a surge center
Why do males not have a surge center?
-Testosterone defeminizes hypothalamus during embryogenesis & eliminates GnRH surge center in male
-Female has no testes, so does not produce testosterone
What is the mechanism of “defeminization”?
-Testosterone produced by testes in developing male fetus penetrate BBB (blood brain barrier)
-Once testosterone is in brain, it is converted to Estradiol
-So, estradiol actually defeminizes the hypothalamus and causes the surge center to not develop
Why does estradiol in females not defeminize the surge center?
-In female, estradiol is bound by alpha-fetoprotein which prevents the estradiol from crossing the BBB
____ surges just before the huge release of LH
Estrogen
What is puberty in domestic species?
-Process of acquiring reproductive competence
Most mammalian systems are functional at birth, what is the exception?
-Reproductive system
Puberty is a ____ and _____ maturation process
gradual and multifactorial (not a single event)
Onset of puberty is dependent upon
the ability of hypothalamic neurons to produce GnRH in sufficient quantities to support gametogenesis
What are the many female definitions of puberty?
-Age at 1st heat
-Age at 1st ovulation
-Age at which female can support pregnancy w/out problems
What are the many male definitions of pregnancy?
-Age when behavioral traits evident
-Age at 1st ejaculation
-Age when spermatozoa 1st appear in ejaculate or urine
-Age which threshold # of spermatozoa reached in ejaculate
What is the physiologic definition of puberty for male & female?
Specific hypothalamic nuclei are capable of releasing adequate quantities of GnRH to
-Cause gonadotropin release (FSH & LH)
-Ultimately, cause ovulation & spermatogenesis
Development of hypothalamic nuclei are dependent on
-Threshold body size
-Nutritional factors
-Environmental cues
-Photoperiod
-Genetics
In the male, the physiologic onset of puberty is brought about because
of decreased hypothalamic sensitivity to negative feedback by Testosterone/Estradiol
What happens physiologically before puberty?
-GnRH neurons in tonic & surge centers of hypothalamus release low amplitude & low frequency pulses of GnRH
What happens physiologically after puberty?
-Tonic center controls basal levels of GnRH which are higher than in prepubertal females b/c the pulse frequency increases
-Surge center controls the preovulatory surge of GnRH
What time frame is required for the pulse frequency to become high enough for puberty to be achieved?
~2 months
In the prepubertal female, the surge center is sensitive to ____. BUT what?
-Sensitive to estradiol
-BUT surge center cannot release ovulatory quantities of GnRH b/c ovary cannot secrete high enough levels of Estradiol
What are possible influences of metabolic signals upon GnRH neurons?
-Blood glucose concentrations
-Blood leptin
-Blood fatty acids
