Questions and Answers
What denotes the period from one ovulation to the next in the female estrous cycle?
What hormone is primarily associated with the luteal phase of the estrous cycle?
Which part of the female reproductive system is responsible for producing GnRH?
What role does the Surge Center of the hypothalamus play in the estrous cycle?
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What is released by the posterior pituitary and synthesized in the paraventricular nucleus?
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What characterizes a primary follicle?
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Which hormone is involved in the feedback regulation of the estrous cycle from the uterus?
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Which cells produce estrogen and inhibin in the antral follicle?
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What is the main function of the corpus luteum?
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What happens to subordinate follicles during the development of the dominant follicle?
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What role does inhibin play in the female estrous cycle?
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What is the fate of the corpus hemorrhagicum after ovulation?
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Which hormone does the dominant follicle produce to induce ovulation?
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How does the hypothalamo-pituitary-gonadal axis impact the female estrous cycle during diestrus?
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What hormone is released by the posterior pituitary and plays a role in uterine contraction during childbirth?
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In which phase of the estrous cycle does ovulation occur?
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Which substance is primarily responsible for luteolysis in the cow after day 15?
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What is the primary effect of melatonin on GnRH release in small ruminants?
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What type of ovulation is characterized by the need for an external stimulus for LH release?
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What is the duration of estrous cycle for a ewe?
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What role does inhibin play in the female estrous cycle?
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What is the significance of estradiol in the context of ovulation?
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What happens if there is non-maternal recognition of pregnancy?
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During which phase is estradiol primarily produced?
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What triggers luteolysis of the corpus luteum in non-pregnant females?
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Which hormone is primarily responsible for inducing follicular regression?
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What is the response of the anterior pituitary gland during the estrous cycle?
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What leads to the secretion of oxytocin following ovulation?
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How does the luteal phase differ between mares and cows in terms of oxytocin production?
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What physiological factor is responsible for the induction of ovulation?
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Study Notes
Female Estrous Cycle Overview
- The estrous cycle is defined as the period from the beginning of one estrus to the start of the next, or from one ovulation to the next.
- Key phases include the follicular phase (estrus), characterized by estrogen production, and the luteal phase (diestrus), dominated by progesterone.
- Anestrus is a quiescent phase where no hormones are produced, prevalent in seasonal animals like sheep.
Endocrine Regulation
- The hypothalamus-pituitary-ovarian axis regulates the estrous cycle.
- The hypothalamus releases GnRH (Gonadotropin-Releasing Hormone).
- Anterior pituitary produces FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone).
- Ovaries produce estradiol, progesterone, and inhibin; the uterus produces prostaglandin F2α (PGF2α).
GnRH and Feedback Mechanisms
- Tonic GnRH Center functions continuously, with pulse frequency altered by internal and external factors.
- Surge Center triggers bursts of GnRH for preovulatory LH surge.
- Oxytocin is synthesized in the paraventricular nucleus and released by the posterior pituitary.
Follicular Development
- Primordial follicles consist of oocytes surrounded by a single layer of squamous cells.
- Follicles progress through stages: primary, secondary, and antral, with the latter characterized by fluid accumulation and completion of Meiosis I.
- Antral follicles are gonadotropin-dependent and responsive to FSH and LH.
Ovarian Structures
- Corpus hemorrhagicum forms immediately post-ovulation with blood filling the collapsed antrum.
- Corpus luteum (CL) forms from proliferated theca interna and granulosa cells, primarily producing progesterone.
- Corpus albicans is the remnant of the old corpus luteum after regression.
Phases of the Estrous Cycle
- Diestrus sees progesterone exert negative feedback on LH, facilitating continuous follicular development.
- Estrus phase involves estradiol providing positive feedback for LH; inhibin provides negative feedback for FSH.
Pregnancy vs. Non-Pregnancy
- In non-pregnant females, CL produces progesterone; the anterior pituitary produces FSH for ongoing follicular development.
- If pregnancy is not recognized, the endometrium produces PGF2α, leading to luteolysis and the start of a new estrus cycle.
Luteolysis Mechanisms
- Species differences highlighted; in mares, CL does not produce oxytocin.
- Prostaglandin synthesis varies, affecting luteolysis timing in different species (e.g., cows require PGF2α after day 15).
Seasonal Breeding
- Seasonality in reproductive cycles is mediated by photoperiod.
- Melatonin secretion from the pineal gland influences GnRH release, increasing in short-day breeders (e.g., small ruminants) and decreasing in long-day breeders (e.g., horses).
Ovulation Mechanisms
- Spontaneous ovulators (e.g., cows, horses) experience LH peak and ovulation post-estrogen peak.
- Induced ovulators (e.g., cats, camelids) require an external stimulus for LH release and ovulation.
Estrous Cycle by Species
- Cows exhibit a cycle of 18-24 days (average 21 days), running through proestrus, estrus (heat), metestrus, and diestrus.
- Small ruminants have a cycle of 13-19 days, are seasonal breeders, and reach puberty at 6-12 months.
- Bitches show variable cycles based on breed, monitored through behavior, vaginal cytology, and hormone levels.
- Queens have a seasonally polyestrous cycle, lasting 30-70 days, with estrus detectable by distinct behavioral signs.
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Description
Test your knowledge on the female estrous cycle, including phases such as the follicular and luteal phases. This quiz covers key hormonal changes and their physiological implications. Ideal for students of reproductive physiology.
