Animal Reproduction Flashcards
What is a hormone?
Endogenous substance released into circulation. It has a high affinity and specificty of binding to specific target cells and initiates a biological response.
What are the different mechanisms of hormone release?
Endocrine
Neuroendocrine
Paracrine
Neurocrine
Autocrine
What kind of control is reproduction under?
Nervous and endocrine.
What are the two types of reflexes seen by neural control?
Simple neural reflex (does not go passed the spine)
Neuroendocrine reflex (goes up to the hypothalamus to release hormone from adenohypophysis)
Describe the hypothalamus - hypophyseal portal system.
Cells in the hypothalamus release GnRH into the hypothalamic portal system.
GnRH goes directly to adenohypophysis and acts on gonadotropes.
Adenohypophysis releases FSH and LH
FSH and LH travels to ovaries and testes
There is also feedback inhibition by the hormones produced at the testes/ovaries.
Which type of control is longer lasting? Neural or endocrine?
Endocrine. It is also slower.
What hormones are relased by the hypothalamus?
GnRH
The pituitary gland releases _____.
FSH
LH
Prolactin
Oxytocin
What hormones do the ovaries release?
Testes?
Ovary: Estradiol, progesterone, inhibin, testosterone, relaxin.
Testis: testosterone, inhibin, estradiol
What hormones are released by the placenta?
Progesterone
Estradiol
hCG
eCG
Oxytocin
PGF2-a
What hormones are derived from cholesterol?
Progesterone, testosterone, estradiol
What hormones are glycoproteins?
FSH, LH, TSH
What hormones are peptides?
GnRH
Prostaglandins are released by the _____. What happens upon adminsitration of prostaglandins during pregnancy?
uterus
Abortion
Describe the mechanism of action of protein hormones.
Activate protein kinase A via cAMP and GPCR.
cAMP activates it by stimulating regulatory subunit and catalytic subunit.
Eventually leads to the construction of new proteins for reproduction.
Describe the mechanism of action of steroid hormones.
Diffuse through the plasma and nuclear membranes of the target cell.
Bind to nuclear receptor
mRNA production is triggered and protein synthesis begins
What factors determine the magnitude and duration of action of hormones?
Pattern and duration of secretion
Half-life
Receptor density
Affinity receptor-hormone
What are the general hormone secretion pattersn?
- Episodic: hormones under nervous control. Released in sudden bursts or pulse.
- basal: hormone stays low but fluctuates with low amplitude pulses.
- Sustained: e.g. steroids. levels remain high in a steady fashion for long period (days/weeks)
How can hormones be measured?
Blood, saliva, urine, lymph, tear, feces
Radioimmunoassay and ELISA
Hypothalamic Hormones ——> Pituitary
CRH
TRH
GnRH
ACTH
TSH
FSH & LH; Growth hormone
What are the two antagonists released by the hypothalamus? What do they act on?
SS inhibits growth hormone
Dopamine (DA) inhibits prolactin.
What is puberty?
The process to reach reproducte competences.
The requirement is adequate GnRH to stimulate gonadotrophin release from gonadotroph cells.
The most important driver for puberty onset is the ability of presynaptic neurons to provide information to GnRH neurons.
Figure: Two hypothalamic centers are present:
1) Surge center: increases GnRH secretion; not active prior to puberty.
2) Tonic center: gives a basal GnRH release; active prior to puberty.
What is the best definition of puberty in the female?
Age on which female can support gestationwithout deleterious effect.
Age at first estrous (heat)/ovulation is not good definition because ovulation is silent and not easily determined.
What is the best definintion of puberty in the male?
Age when the ejaculte contain a number of spermatozoa able to produce fertilization.
May also be definied as the age when spermatozoa appear in the ejaculate or age at first ejaculation.
How does the sensitivity of the hypothalamic centers change?
Prior to puberty, the tonic center is sensitive to the low amounts of estradiol (inhibitory), which leads to low GnRH and tiny follicles.
Once the tonic center is no longer sensitive to low amounts of estradiol, GnRH production increases, leading to a larger follicle and more estradiol production.
Estrodiol positively feeds back on the peak cnter and ovulation occurs.
What are the factors affecting the onset of puberty in the female?
Body, score, condition (BSC)
Environmental stimulus or social cues
Degree of body fat (metabolic signals have an effect of GnRH neurons and its secretion)
Metabolic status and GnRH activity
Metabolic signals and GnRH activity
What is the lipostatic hypothesis?
Adipose tissue is critical for reporductive maturation due to its metabolic cues (glucose, fatty acids, leptin, kisspeptin)
TRUE/FALSE.
Nutrition has an impact on the achiecement of puberty.
TRUE.
Animals with better nutrition achieve puberty at an earlier age.
______ may stimulate GnRH neurons.
(Hint: the metabolic influence).
Glucose, leptin, Blood fatty acids
(the more adipose tissue, the higher the leptin levels)
These cues are also indicative of an animals nutritional/metabolic status.
The size of the corpus luteum is ______ (directly/inversely) proportional to plasma progesterone levels.
Directly.
The larger the corpus luteum, the higher the secretion.
What are the different effects that pheromones could affect the sexual behaviour of the female?
Induce ovulation during anestrous season
Synchronize estrous and ovulation
Concentrate estrous and parturition
What is the effect on puberty when GnRH is immunoneutrolized?
What about when GnRH treatment pusles are given?
Delays sexual maturity and reproduction
Advances puberty
Describe the hormonal secretion pattern in males vs. females.
Males: LH surges are followed by testosterone surges. - Released every 4-6 hours
Females: GnRH causes release of FSH, followed by LH surges.
Spermatogenesis takes approximately ______ weeks.
5-9
What are the phases associated with the differentiation process of sperm formation.
Golgi Phase
Cap Phase
Acrosome Phase
Maturation phase
Describe the golgi phase.
- Spermatid is perfectly spherical and has a well developed golgi apparatus.
- Golgi vessicles fuse and give rise to pro-acrosomic granules. Centrioles migrate to location beneath the nucleas that opposes acrosomic vesicle.
- Dense acrosomic vesicle granules within the large acrosomic vesicle. Proximal centriole gives rise to attachment point for tail; distal centriole gives rise to developing axoneme inside the cytoplasm.
Describe the cap phase.
- Golgi migrates caudally; DC forms axoneme or flagellum that projects away from nucleus and toward lumen of seminiferous tubule.
- Acrosomic vesicle flattens and begins to form a distinct cap with outer and inner membranes, acrosomal contents (enzymes) in between
Describe the acrosomal phase.
- Spermatid nucleus elongates and acrosome covers majority of the anterior nucleus. Manchette forms and extends down toward developing flagella.
- Neck and annulus form - become juncture between middle piece and principal piece. All components are surrounded by plasma membrane.
Describe the maturation phase.
Mitochondria form a spiral assembly around flagellum that defines middle piece.
Postnuclear cap is formed from manchette microtubules.
Annulus forms juncture between middle piece and principal piece.
How many stages are their in the cycle of seminiferous epithelium?
8
What are the different stages of spermatogenesis?
Proliferation: Spermatogonia - different numbers of divisions is species dependent
Meiosis: to primary and secondary spermatocytes
Differentiation: to spermatids
Describe the structure of spermatozoa.
Head: Nucleus, acrosome, post-nuclear cap
Tail: middle piece + pincipal piece + terminal piece.
Describe the induced ovulation pathway.
What are some species that undergo this pathway?
- Copulation stimulates sensory nerves in vagina and cervix.
- Impulses relayed to spinal cord
- Impulses sent to surge center –> increased GnRH secretion –> increased LH –> ovulation
Follicle will not rupture if the female does not receive the male.
Cats, rabbits, camels
Describe the seasonally poleyestrus pathway.
Pineal gland controls GnRH through melatonin secretion.
Differences in length of day alter pineal gland secretions.
Short day breeders (fall) - sheep
Lond day breeders (spring) - horses
What regulatory hormones are secreted from each of the following organs?
- Hypothalamus
- Hypophysis
- Ovary
- Uterus
- GnRH
- FSH and LH
- Estradiol, progesterone, inhibin
- Prostaglandin, PF2α
Describe the follicular phase and luteal phase.
Follicular phase: Corpus luteum regression (luteolysis) to ovulation. Associated with
-↓ progesterone
-↑ FSH, LH → ↑ estrogen (sexual behavior)
estrodiol will eventually reach threshold and cause GnRH secretion, leading to ovulation.
Luteal Phase: After ovulation & corpus luteum formation. Metestrus and diestrus.
Assocated with
- ↑ progesterone
- ↓ estrogen
**Progesterone inhibits FSH and LH
TRUE/FALSE.
Only one follicle grows at a time.
FALSE.
Multiple follicles grow and there is selection of teh dominant one.
What are the stages of each phase? What are the characteristics of each?
Follicular phase:
-Proestrus: Rise in estradiol produced by developing follicles; pulse frequency of GnRH and LH are increasing.
Estrus: behavioral estrus and ovulation (Max E2 concentration and LH peak).
Luteal Phase:
- Metaestrus: Follicle is transformed to corpus luteum
- Diestrus: fully functional CL and high progesterone
What are the functions of the corpus luteum?
Secrete progesterone
Induce embryo growth
Maintain pregnancy
What are the structures leading up to the formation of the corpus luteum?
Pre-ovulatory follicle
Corpus Hemorrhagicum (caused by rupture of blood vessels)
Corpus luteum
During pregnancy, how is the death of the CL prevented?
CL maintains pregnancy through release of progesterone.
Chemical signals are produced to either inhibit PGF2α
What happens if the female is not fertilized?
The endometrium will produce prostaglandins (PGF2α) *stimulated by progesterone after Day 15 in cow*
This is released into the uterine vein
Picked up by the ovarian artery - sent to ovary to cause lysis of CL
What are some cauess of anestrus?
Pregnancy
Lactation
Season
Presence of Offspring
Stress
Pathology
Describe true vs. apparent anestrus.
True: Pathological problem - insufficient hormonal stimuli.
Can be treated
Apparent: failure to detect estrus (may be due to retention of CL) or pregnancy
What is the sequence of events after deposition of spermatozoa in the female tract?
- Immediate transport
- Cervix
- Uterus
- Oviduct
- Fertilization
What are the two phases of sperm transport?
Rapid phase: Contraction of the muscluaris of the female tracts allows sperm to reach oviducts minutes after copulation.
Sustained Phase: sperm sent in slow drops from reservoirs in the cervix.
What proteins are present in the cervix and what are their functions?
Sulfomicins: increase viscosity - apical zone.
Sialomicins: decrease viscosity - basal zone - privileged pathways to alow fast transport.
What occurs during capacitation?
Surface molecules fall away int he female tract to allow binding to the zona pellucida of the oocyte. A sign of capacitation is increased motility.
Describe the binding to the zona pellucida.
3 receptors involved:
ZP: species-species recognition.
ZP2: ?
ZP3: leads to acrosome reaction. The sperm is then endocytosed.
What is the syngamia?
The fusion of both pronucleus - occurs after sperm nucleus decondensation and the disulfide cross-links are broken.
What events need to happen before the embryo can implant in the uterus?
Development inside zona pellucida
Hatched Zona Pellucida
Maternal recognition of pregnancy
Formation of extraembryonic membranes
After fertilization, what are the different stages?
Zygote → 2 celled embryo → Morula → Early Blastocyst (cell polarization to form endoderm, ectoderm, mesoderm) → Hatching/hatched Blastocyst
How does the blastocyst hatch?
Through production of proteolytic enzymes that degrade the zona pellucida.
How does uterine attachment vary between species?
Primates - blastocysts implant very soon.
Most other domestic species: preattachment period lasts several weeks and comprises formation of amnion, chorion, and allantochorion.
What are the extraembryonic membranes?
Yolk sac
Amnion
Chorion
Allantois
In the cow, what do the trophoblastic cells of the blastocyst produce to prevent destruction of the corpus luteum?
IFN-τ
This acts on endometrial cells to inhibit the production of oxytocin receptors so that oxytocin does not stimulate PGF2α synthesis.
In the sow, what do the trophoblastic cells of the blastocyst produce to prevent destruction of the corpus luteum?
Estradiol is secreted, which reroutes PGF2α secretion.
Minimum 2 embryos needed for uterine horn to achieve pregnancy.
What prevents corpus luteal degradation in the mare?
Embryo migration, believed that migration of the “conceptus” distributes pregnancy factors.
What is a placenta?
Transient organ of pregnancy that provides interface for metabolic exchange between mother and fetus.
What are the different types of placenta?
What are the zones of the zonary placenta?
- Transfer zone
- Pigmented zone - maternal hemorrhage
- Allantochorion - nonvascular
What are the structures associated with a cotyledonary placenta?
Cotyledon: placental unit with blood vessels and connective tissue.
Placentome: interphase point formed of fetal cotyledon and maternal part (caruncular region)
What are the different classifications of placenta based on layers?
- Epitheliochorial: 6 layers, low levels of bleeding during parturition. Pigs, horses, ruminants. No antibodies are passed. Colostrum is crucial.
- Endotheliochorial: 5 layers. Some Ig transferred and some bleeding during parturition. Dogs/Cats
- Hemocorial: primates and rodents. 3 layers. High bleeding during parturition. Mother’s RBCs contact chorionic capillary directly.
TRUE/FALSE.
Proteins can cross the placenta.
FALSE.
With the exceptiono f a few immunoglobulins, they cannot. The fetus synthesizes proteins using the amino acids from the mother.
TRUE/FALSE.
Lipids do not cross the placenta.
TRUE.
What hormones does the placenta produce?
Ovarion stimulation (hCG/eCG)
Pregnancy maintenance: Progesterone
Fetus Growth: placental lactogens
Assist parturition: prostaglandins, oxytocin, relaxin
After 100 days, how does progesterone secretion change in the mare?
The placenta becomes the primary source of progesterone.
What are the stages of parturition?
Stage 1: myometrial contractions (removal of progesterone block by increased estradiol) - initiated by fetus stress (fetal ACTH –> cortisol secretions)
Stage 2: Expulsion of the fetus, requires strong contractions (also caused by estradiol, includes PGF2α) Relaxin allows pelvic ligament to stretch. This stage is also a reflex - hypothalamus increases production of oxytocin.
Stage 3: Expulsion of fetal membranes
What is the pathway associated with increased secretion of the genital tract and removal of the progesterone block?
Hypothalamus-pituitary-adrenal axis
In the bovine placenta, what are binucleated giant cells?
They migrate from the chorion to the endometrial epitheliam. Thought to secrete placental lactogen and pregnancy specific protein.
