Lecture 21: Reproductive Endocrinology (Exam 2) Flashcards
Define simple neural reflex
Employs nerves that release simple neurotransmitters directly onto target tissue
Define neuroendocrine reflex
Req a neurohormone (released by a neuron) to enter blood & act on remote target tissue
How do we get from stimulus to reaction is a simple neural reflex
Stimulus -> sensory N -> spinal cord -> efferent neurons -> target tissue -> reaction
Do the same thing as above but for the neuroendocrine reflex
What is the job of the hypothalamus
The neural control center for repro hormones
Fill out the diagram
Describe the hypothalamic nuclei
Nerve cell bodies found in the hypothalamus
Who does not have a surge center?
Males
What has direct on reproduction
- Surge center
- Tonic center
- PVN
What is the neural control center for repro hormones
Hypothalamus
What separates the lateral portions of the hypothalamus
The third ventricles
Where does the axons from neurons in the surge center & the tonic center terminate
To the stalk region where they terminate on BV of the HHP system
What does the HHP allow
Small quantities of the hormone to act before being diluted in the systemic circulation
Does the posterior pituitary have a portal system
No
Where are neurohormones deposited
Directly into systemic circulation
Where do axons from neurons originating in the hypothalamus (PVN) extend & what do they do
To the posterior lobe where they release their neurohormones into a capillary plexus
T/F: The posterior lobe does not have a portal system
True
Define positive feedback
Something influences the stimulation of another (a hormone goes back and causes the release more/another hormone)
Define negative feedback
- Something influences the suppression of another
- Hormone goes back and stops or slows down the production/release of other hormones or more hormone
What are the characteristics of reproductive hormones
- Act in small quantities
- Possess short half-lives
- Bind specific receptors
- Can cause release of other hormones
- Can stimulate the gonads
- Can cause sexual promotion
- Can help maintain preg
- Luteolysis
What are the different source classifications of hormones
- Source
- Mode of Action
- Biochemical classification
What can we use as FSH & LH & why
Equine & human chorionic gonadotropin b/c they are easier to make
Example of hypothalamic hormones
Gonadotropin releasing hormone (GnRH)
What are examples of pituitary hormones
- FSH
- LH
- Prolactin
- Oxytocin
Examples of gonadal hormones
- Prostaglandin F2 alpha from the uterus
- Progesterone from the ovary & corpus luteum
- Estrogen from the ovary & follicle
- Equine chorionic gonadotropin & Human chorionic gondadotropin from the uterus
What are the different mode of action classifications
- Neurohormones
- Releasing hormones
- Gonadotropins
- Sexual promoters
- Pregnancy maintenance hormones
- General metabolic hormones
- Luteolytic hormones
Describe neurohormones
- Synthesized by neurons & are released directly into the blood to cause a response in a target tissue somewhere else in the body
- GnRH, FSH, LH, & Oxytocin
Describe releasing hormones
- Synthesized by neurons in the hypothalamus & cause release of other hormones from the anterior pituitary
- They can also be classified as neurohormones b/c they are synthesized and released by neurons
- GnRH
Describe gonadotropins
- Synthesized & secreted by specialized cell in the anterior lobe of the pituitary gland
- These have stimulatory effect on the gonads
- FSH & LH
What are sexual promoters
- Secreted by the gonads to stimulate the repro tract, regulate the function of the hypothalamus & anterior pituitary, & regulate repro behavior
- Estrogen, progesterone, testosterone, eCG, & hCG
Describe preg maintenance hormones
- High concentration during preg
- Responsible for maintaining preg & assisting the female in lactation stability
- Progestins & placental lactogen
Describe general metabolic hormones (not reproductive hormones)
- Promote metabolic well-being
- Thyroxin, adrenal corticoids, & growth hormone
Describe luteolytic hormones
- Cause destruction of the corpus luteum
- PGF 2a
What are the biochemical classification or repro hormones
- Peptides
- Glycoproteins
- Steroid
- Prostaglanding
Describe peptides
- Very tiny
- GnRH is a decapeptide
- Prolactin
- Relaxin
Describe glycoproteins
- A polypeptide protein that has carbohydrate moieties
- Large protein
- FSH
- LH
- Inhibin
Describe steroids
- Have a common molecular nucleus
- Progesterone
- Testosterone
- Estradiol
Describe prostaglandins
- Lipid base
- Prostaglandin F2 alpha
- Prostaglandin E2
Why does the biochemical classification of repro hormones matter clinically?
- B/c the body doesn’t notice the really small ones but notices the really big ones
- Keep responding to smaller molecular drugs like GnRH b/c they don’t realize it
- W/ larger molecular drugs like FSH the immune system recognizes them and begins to build antibodies to them which eventually causes the body to stop responding
Which prostaglandin is the good one? Bad one?
- Prostaglandin E2 is good
- Prostaglandin F2 is bad & block w/ NSAIDs
What are the actions of hormones
- Protein hormones - binding of hormones results in new protein synthesis
- Steroid hormones travel freely through plasma membrane into cytoplasm & bind directly to specific nuclear receptors
- Binding of hormones results in NEW PROTEIN synthesis
What is req to bind specific receptors on their target cell
Repro hormones
Which hormone bind to the outside & which on the inside
- Protein: Bind outside to plasma membrane bound receptors
- Steroid: Travel freely through the plasma mem into the cytoplasm & bind directly to the specific nuclear receptors
What activates the protein kinase chain
The protein hormone binding to the transmembrane receptor
Where do steroid hormones bind
To membrane receptors & nuclear recptors
Describe the fast response of the steroid hormone action & give examples
- Binds to a membrane receptor causing protein production
- Ex: estradiol increases myometrial contraction & progesterone decreases myometrial contractions
Describe the slow response of the steroid hormone action & give examples
- Binds to nuclear receptor inside the cell causing protein production
- Ex: estradiol causes mucous secretion by female tract & progesterone causes uterine gland secretion
How does the CNS regulate the repro system
- Receives, processes, & interprets sensory inputs from olfactory, visual, feedback systems, & photoperiods
- Ultimately regulates GnRH
Describe hypothalamic nuclei
- Nerve cell bodies found in the hypothalamus
- Clusters of specific nuclei exist like for GnRH, TRH, & CRH
- Axons terminate on the capillaries in the HHPS - picogram amounts released & neurohormones are released into the blood
T/F: The same hormone can have positive feedback in one area but negative feedback in another
True
How does the hypothalamo-pituitary gonadal (HPG) axis regulate repro
By using positive & negative feedback systems
What are the key players in the HPG axis
- GnRH - Hypothalamic nuclei
- Gonadotropins - Anterior pituitary
- Oxytocin
- Gonadal hormones
What does the strength of the hormone action depends on
- Pattern & duration of secretion
- Half-life
- Receptor density
- Receptor-hormone affinity
How are steroid hormones metabolized
- By the liver
- By-products excreted in feces & urine
How are protein hormones degraded
- Degraded in the liver
- FSH & LH have very short 1/2 lives
- hCG & eCG have longer half-lives
What does the tonic center release
Releases small amounts of GnRH
What does the surge center release
Releases large amounts of GnRH
T/F: Males have a surge center
False they don’t
Why do males not have a surge center?
- Testosterone defeminizes the hypothalamus during embryogenesis & eliminates the GnRH surge center in the male
- The female doesn’t have testes so she doesn’t produce testosterone
How do females have surge centers if it is estradiol that eliminates the surge center in males
In the female estradiol is bound by alpha-fetoprotin which prevents the estradiol from crossing the blood brain barrier
T/F: Males & females have the same baseline but females drop a bunch more of LH b/c of estrogen during ovulation
True
What is puberty
- The process of acquiring reproductive competence
- Most mammalian systems are functional @ birth
- Puberty is a gradual & multifactorial process
What is the onset of puberty dep on
The ability of the hypothalamic neurons to produce GnRH in sufficient quantities to support gametogenesis
What are the definitions of a female hitting puberty
- Age @ first heat
- Age @ first ovulation
- Age @ which a femal can support preg without probs
What are the definitions of a male hitting puberty
- Age when behavioral traits are evident
- At @ first ejaculation
- Age when spermatozoa first appear in ejaculate or urine
- Age in which the threshold # of spermatozoa reached in ejaculate
What happens if prepubertal animals are given exogenous GnRH
- They will produce FSH & LH
- This is known to be the major factor limiting onset of puberty
Specific hypothalamic nuclei are capable of releasing adequate quantities of GnRH to what
- Cause gonadotropin release (FSH & LH)
- Cause ovulation & spermatogenesis
What does the dev of nuclei dep on
- Threshold body size
- Nutritional factors
- Envi cues
- Photoperiod
- Genetic
Describe the GnRH release before puberty & after puberty
- Before: GnRH neurons in the tonic & surge centers of the hypothalamus release low amplitude & low freq pulses of GnRH
- After (males only): The tonic center controls basal levels of GnRH which are higher than in prepubertal females b/c the pulse freq increases. The surge center controls the preovulatory surge of GnRH. onset of puberty occurs b/c of decreased hypothalamic sensitivity to negative feedbak by testosterone/estradiol
How long is req for the pulse freq to become high enough for puberty to be achieved
2 M
Describe the surge center in the prepubertal female
- The center is quite sensitive to estradiol
- The surge center cannot release ovulatory quantities of GnRH b/c the ovary cannot secrete high enough levels of estradiol
T/F: there is a relationship btw/ plane of nutrition, growth, & ADG w/ the onset of puberty in dairy heifers
True
What are possible influence of metabolic signals upon GnRH neurons
- Blood glucose concentrations (might stimulate glucose sensing neurons that in turn stimulate GnRH neurons)
- Adipocytes secrete leptin - leptin stimulates neuropeptide Y neurons or directly stimulates GnRH neurons
- The exact mechanisms have not been described
- Kisspeptin neurons are thought to act directly on GnRH neurons
- Blood fatty acids may stim neurons that in turn stimulate the GnRH
What is the theory on high amounts of leptin
The higher the leptin the faster she will enter puberty
T/F: Phermones can decrease the age of the onset of puberty
True
