hormones
secreted by endocrine glands or nerves
enter the blood and cause cells or target tissues to secrete new products or new hormones
cannot act without a receptor
necessary for successful reproduction
changes in target tissue involve alterations in metabolism
protein hormones
act via plasma membrane receptors
exert effects in the cytoplasm of the target cell
cause changes in the function of target cells
steroid hormones
act through nuclear receptors that regulate transcription factors that regulate gene expression in target cells
slow response - days to weeks
act through plasma membrane responses
rapid response - minute to hours
cause changes in the function of target ce
neural control requires:
primary pathways of nervous involvement:
simple neural reflexes
or
neuroendocrine reflexes
responsibility of the nervous system
translate (transduce) external stimuli into neural signals that bring about a change in the reproductive organs or tissues
sensory neurons
functional component of neural pathways
afferent neurons taking neural signals toward the spinal cord
efferent neurons
functional component of neural pathways
nerves leaving the spinal cord and traveling to the target tissue
target tissues
functional components of neural pathways
organs that respond to a specific set of stimuli or hormone
simple neural reflex
employs nerves that release their neurotransmitters directly onto the target tissue
afferent sensory neurons synapse directly with interneurons in the spinal cord
interneurons synapse with efferent neurons that travel directly to the target tissue
target
neuroendocrine reflex
requires a neurohormone (substance released by a neuron) to enter the blood and act on a remote target tissue
no direct innervation of the target tissue
neurohormone is the messenger between the neurosecretory cell and the target tissue
sensory neurone sy
neurosecretory cells
neurons releasing neurohormones
neurotransmitter
substance of smaller molecular weight that is released from the terminals of nerves that causes other nerves to fire or causes contraction of smooth muscle that surrounds portions of the reproductive tract
neurohormone
small molecular weight materials
released by hypothalamic neurons
released directly into the blood rather than directly onto the target tissue
travel to a target tissue elsewhere in the body
ex: oxytocin
suckling reflex
neuroendocrine reflex
sensory nerves in the teat of the lactating female detect the tactile stimulus of suckling
sensory signals travel to the spinal cord then the hypothalamus to synapse with other nerves
hypothalamic neurons depolarize and oxytocin is r
hypothalamus (role in repro)
neural control center for reproductive hormones
consists of clusters of nerve cell bodies (hypothalamic nuclei)
surge center and tonic center (GnRH)
paraventricular nucleus: oxytocin
each hypothalamic nucleus has a different function and is stimulated by
hypothalamo-hypopyseal portal system
allows minute quantities of releasing hormones to act directly on the anterior pituitary before the GnRH is diluted by the systemic circulation
capillary network where nerve endings from hypothalamus terminate
neuropeptides from the nerves enter the syste
superior hypophyseal artery
delivers blood to the capillary system
divides into smaller arterial capillaries at the pituitary stalk
enables extremely small quantities of releasing hormones to be secreted into the primary portal plexus of the pituitary stalk
hormones then go to the s
posterior pituitary lobe
does not have a portal system
neurohormones are deposited directly into a simple arteriovenous capillary plexus
ex: oxytocin from the paraventricular nucleus
half-life
the time required for 1/2 of a hormone to disappear from the blood or from the body
short in hormones
hormones are quickly degraded after they cause a response
determined by the rate at which it is metabolized
-metabolized in the liver
negative feedback
suppression of GnRH neurons
caused by progesterone on the hypothalamic level
-inhibits GnRH neurons, when levels are high neurons secrete basal levels of GnRH
allows some follicular development
does not allow sufficient follicular development for the secr
positive feedback
stimulation of GnRH neurons
caused by estradiol
makes the surge center release lots of GnRH to induce ovulation (LH surge)
surge center believed to respond mostly to positive feedback
kisspeptins
neuropeptide
secreted by hypothalamic neurons in the periventricular, preoptic, and arcuate nuclei
stimulate GnRH secretion by acting directly on GnRH neurons
regulator of sexual differentiation in the brain, timing of puberty, and adult regulation of gon
reproductive hormones
act in minute quantities
have short half-lives
bind to specific receptors
regulate intracellular biochemical reactions
hormones are classified by
source
mode of action
biochemical classification
hypothalamic hormones
produced by neurons in the hypothalamus
cause the release of other hormones from the anterior pituitary
GnRH
GnRH
neuropeptide of hypothalamic origin
less than 20 amino acids
most important neuropeptide governing reproduction
pituitary hormones
released into the blood from the anterior and posterior pituitary
anterior: FSH, LH, prolactin
posterior: oxytocin
gonadal hormones
originate from the gonads
affect function of the hypothalamus, anterior pituitary, and tissues of the repro tract
initiate the development of secondary sex characteristics that cause maleness and femaleness
female: estrogens, progesterone, inhibin, testos
lactocrine signaling
delivery of bioactive factors from mother to offspring as a specific consequence of nursing and the consumption of colostrum
milk-borne bioactive are transported in colostrum, not blood, and absorbed into neonatal circulation where they act on target tiss
reproductive hormones originate from:
hypothalamus
pituitary
gonads
uterus
placenta
releasing hormones
synthesized by neurons in the hypothalamus
cause release of other neurons in the anterior pituitary
can be classified as neurohormones because they are synthesized and released by neurons
ex: GnRH
gonadotropins
hormones synthesized and secreted by specialized cells in the anterior lobe (gonadotropes)
tropin: having an affinity for or to nourish
stimulatory influence on the gonads
FSH, LH
LH
gonadotropin
pituitary hormone
causes ovulation
stimulates the corpus luteum to secrete progesterone
causes testosterone secretion in males
FSH
causes follicular growth in ovaries
stimulates Sertoli cells in the male
sexual promoters
estrogens, progesterone, testosterone
secreted by the gonads of both sexes
stimulate the reproductive tract
regulate the function of the hypothalamus and anterior pituitary
regulate reproductive behaviour
cause development of secondary sex characteristics
hCG and eCG
human chorionic gonadotropin
equine chorionic gonadotropin
secreted by the early embryo (conceptus)
cause stimulation of the maternal ovary
pregnancy maintenance hormones
high concentrations during pregnancy
responsible for maintenance of pregnancy
sometimes assist in lactation ability
placental lactogen
promotes development of the mammary gland of the gland
lactogenic
general metabolic hormones
promote metabolic well-being
thyroxin: regulates metabolic rate of the animal
adrenal corticoids: mineral metabolism to regulation of inflammatory response
growth hormone (somatotropin): helps regulate growth, lactation and protein metabolism
necessary fo
luteolytic hormones
cause destruction of corpus luteum
prostaglandin F2?: causes decrease in secretion of progesterone by the CL
reproductive hormones cause
release of other hormones (releasing hormones)
stimulation of the gonads (gonadotropins)
sexual promotion (steroids)
pregnancy maintenance
luteolysis (destruction of the CL)
peptide
most important repro peptide: GnRH
prolactin: protein hormone, 1 polypeptide chain, not glycosylated
relaxin: two-chained nonglycosylated polypeptide, primary source is CL
glycoproteins
polypeptide hormones
contain carbohydrate moieties
secreted and synthesized by the anterior pituitary - all have the same ? subunit but different ? subunits
? subunits give glycoproteins give each unique protein its unique function
subunits held together
inhibin
glycoprotein hormone
has the same physiological activity no matter which of two ? subunits are attached
suppresses FSH secretion from the anterior pituitary
activin
protein hormone
found in follicular fluid
2 ? subunits
causes release of FSH pituitary cells in culture, has the opposite effect of inhibin in-vitro
follistatin
glycoprotein
present in ovarian follicular fluid
inhibits FSH secretion from pituitary cells in culture
low physiological activity compared to inhibin
binds to activin to inhibit widespread actions
carbohydrate moieties on glycoproteins
bound to the ? and ? subunits
more glycosylation = longer half-life
biochemical classifications
peptides
glycoproteins
steroids
prostglandins
gonadal steroid synthetic pathway
cholesterol -> pregnenolone -> progesterone -> testosterone -> estradiol
prostaglandins
lipids derived from arachidonic acid
PGE2 lowers blood pressure
PGF2? increases blood pressure
stimulate uterine smooth muscle to contract
influence lipid metabolism
mediate inflammation
ovulation controlled in part by PGE2 and PGF2?
rapidly degraded in t
pheromones
directly influence the reproductive processes
substances secreted to the outside of the body
volatile, detected by the olfactory system (vomeronasal organ) by members of the same species
influence the onset of puberty, identification of females in estrus
endocrine glands
composed of many cells that synthesize and secrete hormones
hormones enter the blood and are transported to every cell in the body
-only cells with certain receptors respond (hormone receptors located on target tissues)
protein hormone receptors
integrated into the plasma membrane of the target cell
receptor domains: 3 distinct domains of receptors
-extracellular domain: specific site that binds to a specific hormone
-transmembrane domain: changes its configuration and activates G-proteins (other
steps of action for protein hormones
1: hormone-receptor binding
-hormone diffuses out of the blood and binds to a specific membrane receptor on the surface of target cells
-receptors for gonadotropins are sparsely distributed on the surface of target cells
2: adenylate cyclase activation
-h
steroid hormone receptors
nuclear receptors - slow response
membrane receptors - fast response
target cells contain both
steroid hormone fast response
similar to protein hormone action
membrane receptor
1: steroid binding to membrane receptors
2: adenylate cyclate activation
3: protein kinase activation
4: changes in Ca2+ channel permeability
myometrium has membrane estradiol receptors
estrogen binds an
steroid hormone slow response
nuclear receptor
1: steroid transport
-carried by plasma proteins in blood and interstitial fluid to the membranes of all cells
-binding to plasma protein extends steroid half-life
2: movement through the cell membrane & cytoplasm
-steroid disassociates f
what does the strength of hormone action depend on?
pattern and duration of secretion
half-life
receptor density
receptor-hormone affinity
episodic hormone secretion
associated with hormones under nervous control
neuropeptides released in sudden bursts (episodes), causing pituitary hormones to be released the same way
pulsatile secretion: typical pattern of episodes into a predictable pattern
-required for an animal t
basal (tonic) hormone secretion
hormone level stays low
fluctuates with low amplitude pulses
ie GnRH secretion of the tonic center
sustained hormone secretion
hormone remains elevated in a steady, stable fashion for a long period of time (days, weeks)
steroids
-glands secrete them continuously rather than as a function of neural activity
i.e. high progesterone during diestrus or pregnancy
what is hormonal potency influenced by?
receptor density
-varies as a function of cell type and degree to which hormones up-regulate or down-regulate synthesis of hormone receptors
-influenced by animal nutrition and condition
hormone receptor affinity
hormones antagonists
analogs that bind to the specific receptor and initially cause the same biological effect as the native hormone
some promote greater physiological activity because they have greater affinity for the hormone receptors
antagonists
analogs that have greater affinity for the hormone receptor and promote weaker biological activity than the native hormone
decrease the response of target cells by blocking the native hormone and causing decreased activity than the native hormone would
Fate of steroids after secretion
steroid secreted by gonad -> steroid enters blood and goes to target tissue -> steroid causes change in target tissue -> steroid in blood passes through liver -> liver renders steroid H2O soluble -> reenters blood and enters kidney or bile -> excreted in
2 ways the liver inactivates steroids
1) any double bond within the steroid becomes saturated, rendering it inactive
2) sulfate or glucuronide residue is attached
-glucuronide form of the steroid is water soluble and can be secreted into urine
chorionic gonadotropins
hCG, eCG
have longer half-lives than pituitary gonadotropins
used as superovulatory drugs because their physiological activity lasts longer in-vivo than GnRH
hCG is small enough to be filtered out in the kidney and eliminated in the urine
reducing the half-life of a gonadotropin
removing polysaccharide side chains (glycosylation sites)
they will bind to liver cells and are internalized and degraded
ways that hormones can be detected
blood, saliva, milk, urine, lymph, tears, fecees (RIA and ELISA)
radioimmunoassay
RIA
requires the use of radioactive hormones
radioactive hormone competes with unlabeled animal hormone in the test tube
amount radioactive hormone that binds is inversely proportional to the amount of animal hormone
enzyme-linked immunosorbent assay (ELISA) steps
1: two types of antibodies are required. One reacts specifically with a hormone (hormone antibody). The other reacts with the hormone-antibody complex and this hormone has an enzyme attached to it (enzyme hormone)
2: the hormone antibody (a protein) is ti
ELISA
designed to determine the presence or absence of specific hormones under a variety of conditions
can determine the quantity of a hormone present
advantages of RIA:
-no radioisotopes are required
-test can be conducted on site with minimal training
-no hea