Week 2 Lesson 17 In-Class Ovaries Estrogen and Progesterone

Introduction

  • Topic: Hormones and Regulation of the Female Gonads (Ovaries)

Learning Outcomes

  • Students will be able to:

    • Identify normal structure and features of the ovaries.

    • Recognize sexual steroid hormones produced by the ovaries.

    • Understand phases of the estrous cycle and changes in the ovaries.

    • Describe folliculogenesis, ovulation, luteolysis, and maternal recognition of pregnancy.

    • Explain the main functions and effects of estrogen and progesterone in mature females.

Components of the Female Reproductive System

  • Ovaries: Produce oocytes and hormones.

  • Oviducts: Site of fertilization and early embryo development

    • Contain infundibulum (catching oocyte), ampulla (fertilization site), and isthmus.

  • Uterus: Site for embryo attachment and fetal development

    • Comprises horns, body, and cervix.

  • Vagina: Functions as the copulatory organ.

  • External Genitalia: Facilitates sperm access and protects against infections.

Structure and Function of the Ovaries

  • Location: Paired gonads in the dorsal abdominal cavity, caudal to the kidneys.

  • Functional Structures:

    • Follicles (site of oocyte development)

    • Corpus Luteum (CL): Produces hormones post-ovulation.

  • Ovary Composition:

    • Cortex: Contains follicles and corpus luteal structure.

    • Medulla: Highly vascularized with numerous nerve endings.

Estrous vs. Menstrual Cycle

  • Estrous Cycle: Defined by reproductive behavior, endometrium does not shed.

  • Menstrual Cycle: Characterized by shedding of the endometrial lining.

Phases of the Estrous Cycle

  • Estrous Cycle:

    • Cyclical ovarian activity from reproductive receptivity (estrus) to non-receptivity.

    • Estrous behavior is linked to high estrogen from ovarian follicles.

  • Estrous Cycle Phases:

    • Follicular Phase:

      • Proestrus: Short or absent in queens; more than a week in bitches.

      • Estrus: Female is sexually receptive.

    • Luteal Phase:

      • Metestrus: Transitional phase with developing corpus lutea.

      • Diestrus: Characterized by the presence of CL and high progesterone.

      • Anestrus: Period of reproductive quiescence.

Folliculogenesis and Ovulation

  • Folliculogenesis: Sequential growth of ovarian follicles during the reproductive cycle.

  • Ovulation: Initiated by a surge in LH triggered by high estrogen levels, leading to oocyte release.

  • Processes Involved:

    • Induced Ovulation: Occurs in queens, rabbits where copulation triggers ovulation.

    • Spontaneous Ovulation: Regular ovulation without copulation.

Hormones of the Ovaries

  • Estrogen: Produced mainly in ovarian follicles, regulates reproductive tract and behavior.

  • Progesterone: Produced in corpus luteum, vital for maintaining pregnancy and inhibiting estrus.

Mechanisms and Effects of Estrogen

  • Target Tissues: Uterus, vagina, brain, and hypothalamus; increases blood perfusion, smooth muscle motility, and stimulates sexual receptivity.

  • High levels of estrogen create positive feedback for LH release, leading to ovulation.

Mechanisms and Effects of Progesterone

  • Inhibits GnRH and LH/FSH surges, maintaining pregnancy conditions.

  • Stimulates endometrial glands and prevents uterine motility.

Luteolysis Process

  • Regression of corpus luteum, typically induced by prostaglandin F2 alpha in several species.

  • Initiated by oxytocin, leading to increased PGF2alpha, resulting in decreased progesterone levels and activation of the hypothalamic-pituitary axis to start a new cycle.

Maternal Recognition of Pregnancy

  • Involves the embryo signaling the mother to prevent PGF2alpha release, vital for maintaining the corpus luteum and thus progesterone levels.

Conclusion

  • Understanding the estrous cycle, hormone functions, and processes of ovulation/luteinization is crucial for reproductive management in veterinary medicine.