Female Reproductive System Study Notes

The Female Reproductive System

Lecture Outline

  1. Anatomy Overview

    • Ovaries

    • Uterine tubes

    • Uterus

    • Vagina

    • Vestibule and vulva

  2. Physiology Overview

    • Oogenesis (secondary follicles and hormones/follicular development)

    • Ovulation (LH surge, spontaneous and reflex ovulators, and seasonal transition)

    • Corpus luteum

    • Phases of the estrous cycle (proestrus, estrus, metestrus, diestrus, anestrus)

    • Specifics of selected estrous cycles

Learning Objectives

  1. Explain the primary roles of the ovary.

  2. Describe the path that spermatozoa must traverse in order to reach the ova for fertilization.

  3. Illustrate the anatomical structures that comprise the female reproductive tract and their relationships to one another.

  4. Explain the functional significance of the three layers of the uterus – endometrium, myometrium, and mesometrium.

  5. Describe the peritoneal and neurovascular structures that suspend and support the female reproductive tract, and how these structures relate to one another.

  6. Describe the role of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in follicular development.

  7. Explain the role of estrogen in initiating the luteinizing hormone surge and ovulation.

  8. Illustrate the phases of the estrous cycle, including the primary endocrine events and ovarian structures.

  9. Describe the origin, demise, and endocrinology of the corpus luteum.

  10. How do estrous cycles differ among species?

Background

  • Obstetrician-gynecologists (OB/GYN) and veterinary obstetrics

    • Physicians with specialized knowledge, skills, and professional capability in the care of the female reproductive system and associated disorders.

  • Endocrinology

    • Scientific study of biology and medicine relating to the endocrine system, its diseases, and hormone secretions.

Anatomy – Background

  • The mammalian female reproductive tract produces female gametes (ova), delivers them for fertilization, provides an environment for embryo development, and expels the fetus upon readiness.

  • The organs include:

    • Two ovaries

    • Two uterine tubes (oviducts)

    • Uterus

    • Vagina

    • Vulva

  • Fertilization typically occurs in the uterine tube as the ovum is transported from the ovary.

  • The fertilized ovum develops into a zygote, then into an embryo and fetus, before being expelled through the vagina and vulva during birth (parturition).

Anatomy – Overview (Figure 26-1)

  • Diagram structure includes:

    • Vagina

    • Cervix

    • Uterus

    • Vulva

    • Ovarian structures including oviduct and broad ligament.

Anatomy – Ovaries

  • The ovaries are vital reproductive organs in females analogous to testes in males.

  • They serve dual purposes: they are both endocrine (producing hormones) and cytogenic (producing ova).

  • They have an ovoid shape and are encased in a connective tissue capsule called the tunica albuginea.

Anatomy – Ovaries Structure

  • The ovary's structure comprises:

    • Medulla: Central, highly vascular section.

    • Cortex: Outer section made up of dense, irregular connective tissue interspersed with follicles and interstitial cells that execute endocrine functions.

Anatomy – Uterine Tubes

  • Also known as oviducts or fallopian tubes; transport ova from each ovary to the uterus.

    • Infundibulum: Funnel-shaped opening, acting as a "catcher’s mitt" to guide ova into the tube.

  • Lined with ciliated epithelium and connective tissue layers enabling movement of ova and spermatozoa.

  • The external uterine tube is covered by peritoneum, termed mesosalpinx.

Anatomy - Uterus

  • Comprised of three parts:

    • Body

    • Cervix

    • Two horns (which vary in shape and proportion by species)

  • The uterine wall consists of:

    • Mucous Membrane: Lining

    • Myometrium: Smooth muscle layer

    • Serous Layer: Peritoneal covering.

  • Supports and positions the uterus via the mesometrium, a component of the broad ligament, which includes the mesosalpinx and mesovarium.

Anatomy - Uterus Histology

  • The endometrium, lining the uterus, is glandular, varies in thickness and vascularity in relation to hormonal changes and pregnancy.

  • Uterine glands facilitate secretion of a fluid known as uterine milk, critical during estrus and pregnancy.

  • In ruminants, caruncles: un-glandular, mushroom-like projections for placental attachments.

Anatomy – Uterus: Cervix

  • Serves as a muscular sphincter leading into the vagina, closed except during estrus and parturition.

  • Features anatomical differences based on species (e.g., circular ridges in ruminants vs. smooth in mares).

Anatomy – Vagina

  • Connects the uterus and vulva, functioning as the birth canal.

  • Acts as a sheath for the male penis during copulation.

Anatomy – Vestibule and Vulva

  • The vestibule is positioned between the vagina and external genitalia.

  • The vulva comprises the labia meeting midline with features such as the suburethral diverticulum seen in certain species.

Anatomy Recap

  • See Figure 26-1 for labeled anatomical structures and cross-sectional views of the female reproductive tract.

Physiology – Background

  • Ovaries both generate mature ova and hormones required for reproduction.

  • Oogenesis: The formation and development process of ova.

Physiology – Estrous Cycle Overview

  • Estrus (heat): Period of sexual receptivity.

  • Estrous cycle: Interval from one estrus period to another.

  • Classifications:

    • Monoestrus: One cycle per year (e.g., foxes, bears).

    • Polyestrus: Several cycles annually (e.g., pigs, cattle).

    • Seasonal polyestrus animals exhibit cyclic estrus related to season changes (e.g., sheep, goats).

    • Anestrus: Inactivity between cycles for non-breeding animals.

Physiology – Oogenesis

  1. Initiation in the fetus where primordial germ cells migrate to the ovaries, forming primary follicles around unstimulated oocytes.

  2. Oocyte (primary oocyte) enlarges and initiates meiosis but halts, remaining arrested until maturation and ovulation.

  3. Follicular development leads to the production of polar bodies; in contrast to spermatogenesis, only one viable ovum is produced per cycle.

  4. Hormonal interactions initiate secondary follicle development, culminating in the production of the zona pellucida around oocytes due to secretions from granulosa cells.

Physiology – Hormonal Involvement in Oogenesis

  • The hormonal interplay during oogenesis includes the control from the hypothalamus and the initial production of gonadotropin hormones (FSH, LH) upon GnRH release.

  • FSH and LH foster proper follicular growth, granulosa cell proliferation, and become active in the production of estrogen through their effects on thecal cells.

Physiology – Phases of Ovarian and Estrous Cycle

  • The ovarian cycle phases align with the estrous cycle and include:

    • Follicular Phase: FSH stimulates follicle growth; - Luteal Phase: Progesterone is secreted from the corpus luteum after ovulation.

  • Hormonal changes are orchestrated through the follicular development, ovulation, and the establishment of the corpus luteum.

Ovulation

  • Characterized by an LH surge leading to the maturity and release of the secondary oocyte.

  • The LH surge triggers luteinization and progesterone production pre- and post-ovulation.

  • Species variations exist in the timing and hormonal feedback mechanisms triggering ovulation.

Corpus Luteum

  • Functions as an endocrine organ, primarily producing progesterone.

  • Corpus luteum forms post-ovulation, with its fate hinging on whether the egg is fertilized.

  • Regression of the corpus luteum leads to a downturn in progesterone, stimulating the restart of the estrous cycle when pregnancy is not achieved.

Phases of the Estrous Cycle

  • The cycle is divided into proestrus, estrus, metestrus, diestrus, and anestrus, with species differences intricately noted.

Specific Estrous Cycle Characteristics

  • Detailed characteristics and cycle lengths vary per species, encompassing cattle, sheep among others for comparative studies.

Avian Anatomy and Physiology

  • Overview of female avian reproductive anatomies wherein typically only the left ovary and oviduct remains functional, pivotal in egg production and related processes

Additional Learning Objectives Recap

  • Reiterate on roles of hormones and structures in the ovaries, the uterine cycle, and species-specific reproductive behaviors.