Topic 13- Reproduction II (Female)

Outcomes:

• compare and contrast female reproductive structures

• sequence oogenesis

• hypothesize and diagnose the impact of variability on oogenesis

• sequence the menstrual cycle

• hypothesize and diagnose the impact of variability on the menstrual cycle

• sequence female endocrinology

• hypothesize and diagnose the impact of variability on female endocrinology and reproductive cycles

• compare and contrast ovarian and uterine cycles

I. Female Reproductive System

A. Functions

• Egg production

• Receives penis and sperm

• Nourishes embryo

• Lactation (milk production)

B. Anatomy

• Ovary:

  • Female gonads that house oocytes

  • Secretes estradiol and progesterone

• Follicles:

  • Structures where eggs mature

  • Contains multiple developing oocytes

• Oocyte:

  • Cell that undergoes meiosis to form an egg

• Oviducts (Fallopian tubes):

  • Transport secondary oocyte via cilia

• Uterus (Womb):

  • Myometrium: Smooth muscle that contracts during labor

  • Endometrium: Lining with blood vessels, glands, and tissues

• Cervix:

  • Narrow opening at the bottom of the uterus

• Vagina:

  • Birth canal

• Vulva:

  • External genitalia

II. Oogenesis (Egg Development)

A. Meiosis Review

• 2n cell → 4 haploid cells

• In oogenesis, only one egg is produced; the others become polar bodies

B. Prior to Puberty

• In the embryonic ovary, primordial germ cells divide → form oogonia

• Primary oocytes begin meiosis I but stop at prophase I

• At birth:

  • 1-2 million primary oocytes exist, but only 200,000 remain at puberty

  • Each oocyte is housed in a follicle

  • Follicle cells provide protection

  • Zona pellucida (glycoprotein layer) surrounds the oocyte

• At puberty:

  • Each month, 6-12 follicles begin to mature, but only one completes development

C. During and After Puberty

• At puberty, estrogen levels rise

• Primary oocyte completes meiosis I, forming:

  • Secondary oocyte (haploid)

  • First polar body (degenerates)

• The secondary oocyte begins meiosis II, stopping at metaphase II → it is ovulated

• Ovulation:

  • Secondary oocyte is released, surrounded by zona pellucida and follicle cells

  • Moves into the oviduct

  • Remains in metaphase II until fertilized

D. After Ovulation

• In the ovary, the remaining follicle becomes the corpus luteum (temporary endocrine gland)

  • Corpus luteum secretes estrogens and progesterone

  • Prepares for pregnancy and prevents another egg from releasing

• If no fertilization occurs, the secondary oocyte degenerates

III. Menstrual Cycle

A. Overview

• Unique to humans and primates

• Controls ovulation and endometrial thickening

• Prepares for pregnancy

B. Components of the Menstrual Cycle

• Hormonal regulation:

  • Hypothalamus releases GnRH → stimulates the anterior pituitary

  • Anterior pituitary releases:

    • LH (Luteinizing Hormone)

    • FSH (Follicle-Stimulating Hormone)

• 28-Day Cycle:

  • Ovarian Cycle:

    • Follicular phase → Ovulation → Luteal phase

  • Uterine Cycle:

    • Menstrual flow → Proliferative phase → Secretory phase

IV. Female Endocrinology

A. Female Sex Hormones

• Ovaries respond to FSH and LH by secreting:

  1. Estrogen (Estradiol)

     • Secreted by follicle cells and corpus luteum

     • Stimulates endometrial growth

     • Develops secondary sex characteristics

  2. Progesterone

     • Secreted by the corpus luteum

     • Prepares uterine lining

     • Maintains pregnancy

• Hormonal Regulation:

  • High estradiol, low progesterone → Stimulates hypothalamus

  • High estradiol, high progesterone → Inhibits hypothalamus

B. Ovarian Cycle (28 Days)

1. Early Follicular Phase (Day 1-5)

• FSH and LH released from anterior pituitary

• Follicle cells secrete low estradiol

• Negative feedback: Low estradiol & progesterone inhibit the anterior pituitary

2. Late Follicular Phase (Day 5-13)

• Follicles grow, increasing estradiol but keeping progesterone low

• Positive feedback: High estradiol stimulates the hypothalamus

• LH surge occurs on Day 13

3. Ovulation (Day 14)

• 1 day after LH surge, ovulation occurs

• High estradiol, low progesterone → increases GnRH → triggers LH and FSH release

4. Luteal Phase (Day 15-28)

• Follicle tissue transforms into the corpus luteum

• Secretes progesterone and estradiol

• Negative feedback: Inhibits the hypothalamus to prevent another egg release

• If no pregnancy occurs:

  • Low LH and FSH trigger corpus luteum degeneration

  • Estradiol and progesterone levels drop → Cycle restarts at Day 1

V. Uterine Cycle (Menstrual Cycle)

A. Menstrual Flow Phase (Day 1-5)

• Endometrial lining sheds → menstruation begins

• New follicles begin to grow

• Negative feedback on hypothalamus

B. Proliferative Phase (Day 6-13)

• Uterus prepares for embryo implantation

• High estradiol levels → Endometrial lining thickens (positive feedback)

• Ovulation occurs on Day 14

C. Secretory Phase (Day 15-28)

• Corpus luteum secretes high estradiol & progesterone

• Endometrial glands secrete nutrients to sustain an early embryo

• If no pregnancy occurs:

  • Hormone levels drop

  • Endometrial lining disintegrates → Cycle restarts