Seasonal Cyclicity and Menstrual Cycle: Reproductive Physiology and Hormonal Regulation

Seasonal Anestrus-Cyclicity

Prevents females from conceiving when survival of embryo/neonate would be low.

Hyperthermia

Harms oocytes & early embryos.

Seasonal Breeders

Give birth during spring when nutrition is sufficient for lactation/growth of the neonate.

Short‐Day Breeders (fall)

Examples include sheep, goats, deer, and elk.

Long‐Day Breeders (spring)

Examples include horses and hamsters.

Obligatory Seasonal Breeders

Rely on seasonal cues to predict when conditions are favorable to reproduction and rearing young.

Facultative (Opportunistic) Breeders

React directly to changes in an environmental variable, not linked to seasonal cues.

Anestrus in Obligatory Seasonal Breeders

GnRH pulse frequency and LH secretion are low; follicles may grow but fail to obtain pre-ovulatory status.

Photoperiod

Regulated by the duration of light exposure, affecting GnRH pulse frequency, detected by retina.

how does the photoperiod regulate the duration of melatonin release that affects GnRH?

info is sent to superachiasmatic nucleus (SCN) IN the hypothalamus VIA the optic nerve

after the info is recieved at the SCN, where does it go to?

the superior cervical ganglion (SCG)

what happens after info is sent to the SCG?

sympathetic neurons from the SCG project into the pineal gland to regulate melatonin release, ultimately regulating GnRH and gonadotropin secretion

Melatonin

Secreted by the pineal gland in a circadian fashion; minimal during light and maximal during darkness.

Hormone of darkness (melatonin)

Provides accurate information about the light-dark cycle.

Menstrual Cycle

Events that occur in a female's reproductive system between two successive menstrual periods

Amenorrhea

Lack of bleeding.

Dysmenorrhea

Painful menstruation

GnRH

Gonadotropin-releasing hormone that regulates reproductive functions.

Kisspeptin

A neuropeptide that plays a role in the regulation of GnRH secretion.

GnIH

Gonadotropin-inhibitory hormone that impacts reproductive hormone secretion.

Suprachiasmatic nucleus (SCN)

Part of the hypothalamus that receives information about light exposure.

Superior cervical ganglion (SCG)

Sends signals to regulate melatonin release from the pineal gland.

Pineal gland

Gland that secretes melatonin.

Circadian fashion

Refers to biological processes that follow a roughly 24-hour cycle.

Menstruation

Sloughing of endometrium.

Menorrhagia

Excessive menstrual bleeding (> 8-10 days, > 80 mL).

Oligomenorrhea

Little menstrual bleeding.

Menarche

First menstrual bleeding (median = 12.77 years).

Menstrual Cycle Length for 15-19 year olds

35 days.

Menstrual Cycle Length for 30 year olds

30 days.

Menstrual Cycle Length for 35 year olds

28 days.

Menstrual Cycle Hormonal Changes

Includes proliferative and secretory phases.

CL lifespan in human

12-14 days unless pregnancy occurs.

Menstruation Process

Drop in P4 and E2, endometrial PGF2α, vasoconstriction, necrosis.

Lactational Amenorrhea

Method of family planning effective for first 6 months if criteria strictly followed.

Criteria for Lactational Amenorrhea Success

Dependent on frequency of feeding (>6x d/n), contact with infant, mother's nutritional status.

Historical Discovery of Ovum

First discovered in 1827, menstruation connected to ovum in 1863.

Cultural Beliefs about Menstruation

Some tribes believed menstruation was due to demon attacks on the reproductive tract.

what does the estrus cycle begin/end with?

estrus

what does the menstrual cycle begin/end with?

menses

how long is the follicular phase in the estrous cycle?

very short (less than 20% of the cycle)

how long is the follicular phase in the menstrual cycle?

long (50% of cycle length)

when does ovulation occur in the estrous cycle?

the beginning and end of cycle

when does ovulation occur in the menstrual cycle?

in the middle

how long is the luteal phase in the estrous cycle?

very long (80% of the cycle)

how long is the luteal phase in the menstrual cycle?

shorter (50% of cycle)

does the estrous cycle have endometrial sloughing?

NO

why does the menstrual cycle have endometrial sloughing?

there is no pregnancy/embryo present, needs a clean slate so P4 decreases and luteolysis occurs

when is the well-defined period of sexual receptivity in the estrous cycle?

during estrus

when is the well-defined period of sexual receptivity in the menstrual cycle?

THERE IS NONE

where does luteolysis result from in the estrous cycle?

in the uterus

where does luteolysis result from in the menstrual cycle?

in the ovaries (CL self-destructs)

what is the CL lifespan dependent upon?

length of follicular phase