last ditch effor

Estrus vs. Estrous

Estrus is the noun describing the period of sexual receptivity ("heat"). Estrous is the adjective describing the entire cycle.

Polyestrus

Having regular estrous cycles throughout the entire year (e.g., cattle, swine, rodents).

Seasonally Polyestrus

Displaying clusters of estrous cycles only during specific seasons of the year.

Short-day Breeders

Animals that begin cycling in the Fall as day length decreases (e.g., sheep, goats).

Long-day Breeders

Animals that begin cycling in the Spring as day length increases (e.g., mares).

Monoestrus

Having only one estrous cycle per year (e.g., dogs, wolves, bears).

Follicular Phase

Phase from corpus luteum (CL) regression to ovulation; dominated by antral follicles and estradiol (E2).

Luteal Phase

Phase from ovulation to CL regression; occupies ~80% of the cycle and is dominated by the corpora lutea and progesterone (P4).

Proestrus

Stage of the estrous cycle where ovulatory follicles form, progesterone drops (luteolysis), and estradiol increases.

Metestrus

Stage of the cycle directly after ovulation characterized by CL formation and the start of progesterone secretion.

Diestrus

The longest stage of the estrous cycle; characterized by a fully functional CL and sustained high progesterone.

Anestrus

A period of interrupted cyclicity where the ovaries are inactive with no ovulatory follicles or functional CL.

Silent Ovulation

Ovulation occurring without behavioral estrus (common in the first cycle of a season); happens because the brain lacks progesterone priming to make it sensitive to estradiol.

Induced Ovulators

Animals that do not ovulate unless copulation occurs (e.g., cats). Without mating, they enter a period called postestrus instead of a luteal phase.

Limiting Factor of Puberty

The structural and functional maturation of the hypothalamus (specifically its tonic and surge centers).

Brain Defeminization

Fetal testicular testosterone enters the male brain, is converted to estradiol via aromatase, and destroys the AVPV kisspeptin neurons, preventing surge center development.

Alpha-fetoprotein (αFP)

A glycoprotein in fetal females that binds to estrogen, preventing it from crossing the blood-brain barrier, thereby protecting the development of the GnRH surge center.

Tonic Center Secretion (Post-Puberty)

Characterized by low amplitude, high frequency pulses of GnRH in both males and females.

Surge Center Secretion (Post-Puberty)

Characterized by high amplitude, low frequency pulses of GnRH that trigger the preovulatory LH surge (females only).

Critical Weight/Fat Hypothesis

The theory stating a minimum threshold of body weight and fat composition (e.g., 17% in women) is required to trigger menarche/puberty.

Whitten Effect

The acceleration or synchronization of puberty in juvenile females introduced to a male's urine pheromones.

Simple Neural Reflex

A pathway where a neuron directly innervates a target tissue and releases neurotransmitters from its nerve terminals (e.g., ejaculation, scrotal temperature response via tunica dartos).

Neuroendocrine Reflex

A pathway where sensory neurons signal efferent neurons to synapse on hypothalamic neurons, forcing neurosecretory cells to release neurohormones into the blood (e.g., oxytocin-mediated milk ejection).

Hypothalamo-Hypophyseal Portal System (HHPS)

A specialized capillary network allowing minute amounts of releasing hormones to pass directly from the hypothalamus to the anterior pituitary without dilution in systemic blood.

Hormone Affinity

The degree of chemical attraction and structural fit between a hormone and its specific receptor.

Hormone Agonist

A synthetic analog that binds a receptor and mimics or enhances the native hormone's biological effect (e.g., Pitocin mimicking oxytocin).

Hormone Antagonist

A synthetic analog that binds a receptor and blocks or weakens the native hormone's action (e.g., RU-486/Mifepristone blocking progesterone).

Genomic (Classical) Pathway

Steroid action mechanism where the hormone diffuses into the cell, binds a nuclear receptor, interacts with DNA, and drives slow mRNA/protein synthesis (hours to days).

Non-Genomic Pathway

Steroid action mechanism where the hormone binds a membrane receptor to rapidly alter ion channels or trigger second-messenger systems (seconds to minutes).

2-Cell, 2-Gonadotropin Model

The mechanism of estradiol synthesis where LH stimulates theca interna cells to produce testosterone, which diffuses to granulosa cells where FSH stimulates its conversion into estradiol.