Comprehensive Notes on Follicle Development and Ovulation Mechanisms

Species classification based on ovulation count: - Monotoucous species: Characterized by the ovulation of a single dominant follicle. - Polytocous species: Characterized by the ovulation of multiple large follicles.
Follicle presence on ovaries during a cycle: - In fertile animals, the cortex below the surface contains numerous follicles at various stages: primary, secondary, and tertiary follicles. - Some follicles are visible on the ovarian surface, specifically those with a diameter of $>1\,mm$ .
Species-specific variations in follicle visibility and timing: - Spontaneous and induced ovulators: Some species exhibit large follicles specifically during the follicle phase. - Luteal phase dominance: Some species possess large or dominant follicles during the luteal phase. - Litter bearing species: The ovulation rate serves as the primary (1st) limit to the resulting litter size.

Proestrus dynamics: - Early proestrus: Polytoucous species possess dominant/ovulatory follicles during this stage. - Late proestrus: Monotoucous species possess dominant/ovulatory follicles during this stage.
Initiating events for the follicle phase: - Fertility is identified as the fundamental key. - Anterior Pituitary Action: The release of Follicle Stimulating Hormone (FSH) provides the signal allowing follicles to advance. - In season factors: Influenced by the photoperiod. - Physiological state: Post-partum recovery must be complete. - Luteolysis: Occurs in animals that are cycling but not pregnant; this process follows a state of high progesterone prior to the start of a new phase.

Developmental progression: - Follicles leave the resting state (primordial follicles) to enter the growing pool. - Timeframe: The transition from primordial to antral takes approximately $1\,month$ . - Antral follicles: These follicles are sensitive to gonadotropins.
The selection process: - One or more follicles are selected to grow to a large (ovulatory) size. - Selected follicles become Estrogen active. - Inhibin production: Dominant follicles produce inhibin to reduce FSH levels, thereby reducing competition from other follicles.
FSH and LH Receptor distribution based on follicle size: - Small follicles: Possess FSH receptors. - Medium follicles: Possess both FSH and LH R (receptors). - Large follicles: Possess LH receptors.

Horses (Mare): - Follicle phase: During proestrus, which lasts $6\,days$ , the mare develops and selects a single large dominant follicle. - Retention: This follicle is retained until the point of ovulation.
Primates (Women): - Day 15: Recruitment occurs where a group of follicles ( $3$ to $30$ ) are recruited to grow following ovulation. - Day 5: A cohort within the recruited group is selected to advance. - Day 9: Final selection/dominance is established. - Day 14: Ovulation occurs.
The Dog: - Proestrus: Lasts for $9\,days$ , occurring $1$ to $3$ times per year. - Corpus Luteum (CL): Will ovulate and form a corpus luteum on day $60$ .
The Cat: - Seasonal behavior: Characterized by repeated $10\,day$ proestrus periods. - Estrogen peak: An E2 peak occurs on the third day. - Ovulation requirements: The cat ovulates and forms a CL only if mating occurs. - CL duration: The corpus luteum lasts for $60\,days$ , regardless of whether the cat is pregnant or not.

Pre-ovulatory LH surge events: - Estrogen (E2) induces the dilation of ovarian arteries. - This leads to increased blood flow and the development of edema. - Capillaries become leaky, allowing fluid to enter the antrum.
Post LH surge events: - Theca cells undergo a biochemical shift, changing production from androgen to progesterone. - Progesterone induces the production of collagenase. - Collagenase facilitates the breakdown of the tunica albuginea. - Stigma (wound) formation: The follicle wall ruptures at the stigma, resulting in the expulsion of the egg and fluid, which constitutes ovulation.

Breeding seasonality: Typically occurs in spring or fall.
Dominant follicle development: Large follicles develop and produce estrogen (observed in cats, rabbits, and camels).
The neuro-endocrine pathway: - Coital tactile stimulation: Provided by the male during mating. - Neural Action Potential: The stimulation induces an action potential. - Pathway: This potential travels via afferent pathways through the Central Nervous System (CNS). - Hypothalamic response: Neural signals in the hypothalamus induce the release of Gonadotropin-Releasing Hormone (GnRH), which triggers ovulation.
Regulation: The inhibition of ovulation in these species can be achieved through the use of hormones.