Puberty, Estrous Cycles, Reproductive Behavior Flashcards Preview

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Flashcards in Puberty, Estrous Cycles, Reproductive Behavior Deck (51)
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Puberty is a ______

- acquisition of reproductive competence
- occurs when there is secretion of GnRH in appropriate frequency and quantity to stimulate gonadotropin release by the pituitary


The hypothalamus in inherently _____

- has both a surge and tonic center


The male hypothalamus only has a ____

Tonic center
- allows for slow release of GnRH that allows for continuous production of sperm


Fetal testis

Secretes testosterone that defeminizes hypothalamus and eliminates GnRH surge center


Testosterone is converted to ____ in the brain

- allows for defeminization of the brain



In females, binds E2 and prevents crossing of blood-brain barrier
- estrogen does not enter the brain!!


Definitions of puberty in females

- age at first heat (estrus) --> easy to detect
- age at first ovulation --> difficult to detect
- age at which pregnancy can be maintained without deleterious effects --> 65% of adult body weight


What are possible ways to detect ovulation?

- palpate for a corpus luteum
- do a blood sample to detect presence of progesterone
- ultrasound the ovary to see follicle (or absence of)


Process of pubery in males (in order of increasing age)

- expression of behavioral traits
- first ejaculation
- when sperm appear in the ejaculate
- when sperm appear in the urine
- when ejaculate contains a threshold number of sperm (to achieve pregnancy)


Puberty is influenced by

- plane of nutrition (fatness)
- threshold body size and composition
- exposure to environmental and social cues
- genetics


How do genetics influence puberty?

Breed variations
- ex: brahman reach puberty later, large dogs reach puberty later
Scrotal circumference in bulls and early puberty
- larger SC will have female offspring that reach puberty 4 days earlier per increased centimeter size


Environmental and social cues

- season of birth in seasonal breeders (sheep, goats, cats)
- photoperiod in seasonal breeders (sheep, goats, cats)
- presence or absence of opposite sex (ewe, sow, cow, rodents)
- density of same sex groups (small groups = later, large groups = sooner)


Spring born versus fall born ewe lambs

- spring born: breed in fall and deliver in spring
- fall born: will not reach puberty until next fall (1 yr later)
*due to short day breeding season*


What is a major limit on puberty onset?

Failure of hypothalamus to produce sufficient quantities of GnRH to cause gonadotropin release
*GnRH is the limiting step!*


Prepubertal female

- tonic center in hypothalamus releases small quantities of GnRH at low frequency
- provides insufficient stimulation of pituitary
- minimal follicular development cannot release enough E2 to trigger surge center to release large amounts of GnRH


Pubertal transition

- tonic center is very sensitive to neg feedback on GnRH at low levels of E2
- neg feedback is slowly lost = higher levels of GnRH = more E2
- eventually, the E2 is high enough to cause surge center to discharge large quantities of GnRH = ovulation and puberty


Prepubertal male

- small amounts of testosterone/estradiol have neg feedback at hypothalamus
- GnRH neurons are less sensitive to T and E2 as puberty approaches
- more T and E2 required to inhibit GnRH neurons
- decreased sensitivity to neg feedback of T = hypothalamus produces more GnRH and more FSH/LH produced


Age at puberty

- equine: 14 mos
- bovine: 11 mos
- canine/feline: 9 mos
- ovine: 7 mos
- porcine: 7 mos


What is the difference between estrus and estrous?

- estrus = noun (behavior)
- estrous = adjective


Estrus is the period of ________

Sexual receptivity
- referred to as heat when female will stand for breeding


Estrous cycle

Begins with estrus and ends at onset of subsequent estrus
- provides female with repeated chances to become pregnant
- begins after reaching puberty
- continue until advanced age
- occurs in cyclic and sequential manner while in season


What causes interruptions in cyclicity?

- pregnancy
- nursing
- changes in photoperiod
- inadequate nutrition
- stress
- pathology
* all cause anestrus *


General timeline of pregnancy events

- puberty
- cyclicity starts
- breeding occurs
- pregnancy
- parturition
- uterine involution
- lactation
- resumption of cyclicity


Breeding seasons

Initiated when environment will allow for best survival of young
- patterns have developed over many years
- altered by selecting more prolific animals and providing better environment



Multiple periods of estrus each year
- cow, swine, rodents


Seasonally polyestrus

- short day breeders: sheep, goat
- long day breeders: horse, cat



One period of estrus each year
- dog


Follicular phase

- period of CL regression to ovulation
- growing follicle is dominant structure
- estradiol is dominant hormone


Luteal phase

- period from ovulation to CL regression
- CL is dominant structure
- progesterone is dominant hormone


What are the purposes of female behaviors?

- attractiveness
- proceptivity
- receptivity