Female Reproduction

Introduction to Female Reproduction

  • The female reproductive system is complex, serving multiple purposes:
      - Producing and delivering gametes (egg cells or ova)
      - Providing nutrition and a safe harbor for fetal development
      - Giving birth
      - Nourishing the infant

Objectives

Students will:

  • Describe the structure of the ovary.

  • Trace the female reproductive tract and describe the gross anatomy and histology of each organ.

  • Name the hormones that regulate female reproductive function and state their roles.

  • Describe the principal signs of puberty.

  • Describe the hormonal events that regulate the ovarian cycle.

  • Describe how the uterus changes during the menstrual cycle.

  • Construct a chart of the phases of the monthly sexual cycle showing the hormonal, ovarian, and uterine events of each phase.

Structural Composition of the Female Reproductive System

Internal Genitalia

  • Ovaries

  • Uterine tubes

  • Uterus

  • Vagina

External Genitalia

  • Clitoris

  • Labia minora

  • Labia majora

  • Occupy the perineum

Primary Sex Organs

  • Ovaries are the primary sex organs that produce egg cells (ova) and sex hormones.

Secondary Sex Organs

  • Other internal and external genitalia.

Figure 28.1

  • Diagram depicting the location of internal and external female reproductive structures.

Ovaries

  • Almond-shaped organs located in the ovarian fossa of the posterior pelvic wall.

  • Each egg develops in its own fluid-filled follicle.

  • Ovulation occurs when the follicle bursts and releases the egg.

Structure of the Ovary

  • Ovarian components include:
      - Medulla
      - Cortex
      - Tunica albuginea
      - Corpus albicans
      - Corpus luteum

Stages of Follicle Development

  • Primordial follicles

  • Primary follicles

  • Secondary follicles

  • Tertiary follicles

  • Mature follicles

Uterine Tubes (Oviducts or Fallopian Tubes)

  • Canal approximately 10 cm long connecting the ovary to the uterus.

  • Muscular tube lined with ciliated cells, highly folded into longitudinal ridges.

The Uterus

Overview

  • The uterus is a thick muscular chamber that opens into the roof of the vagina.

  • Typically tilts forward over the urinary bladder.

  • Functions include:
      - Harboring the fetus
      - Providing a source of nutrition
      - Expelling the fetus at the end of development

  • Pear-shaped organ comprising:
      - Fundus: Broad superior curvature
      - Body (corpus): Middle portion
      - Cervix: Cylindrical inferior end

Uterine Wall Composition

  • Perimetrium: External serosa layer

  • Myometrium: Middle muscular layer, composed mainly of smooth muscle; responsible for labor contractions to expel the fetus.

  • Endometrium: Inner mucosa, consists of simple columnar epithelium and glands.
      - Functional layer (stratum functionalis): Shredded each menstrual period.
      - Basal layer (stratum basalis): Deep layer that remains to regenerate a new stratum functionalis.

Pap Smears and Cervical Cancer

  • Cervical cancer is common among women ages 30 to 50, with risk factors including smoking, early sexual activity, STDs, and human papillomavirus (HPV).

  • Best protection against cervical cancer is early detection via Pap smear.

  • Grades of cervical intraepithelial neoplasia:
      - Class I: Mild dysplasia
      - Class II: Biopsy recommended
      - Class III: May require radiation therapy or hysterectomy.

Mammary Glands

  • Breast tissue overlying pectoralis major, enlarges at puberty.

  • Most of the time contains little mammary gland; develops during pregnancy.

  • Regions of the breast:
      - Body: conical to pendulous with nipple apex
      - Axillary tail: Extension toward armpit

  • Nipple surrounded by areola with heightened sensitivity triggering milk ejection reflex during nursing.

Breast Cancer

  • Occurs in 1 out of 8 or 9 American women, a leading cause of female mortality.

  • Tumors often begin in cells from mammary ducts and can metastasize.

  • Risk factors include BRCA1 and BRCA2 genes, exposure to ionizing radiation, and lifestyle factors (alcohol, fat intake, smoking).

  • Detection includes breast self-examination (BSE) and mammograms.

Puberty

  • Begins around ages 8 to 10 in most American girls.

  • Triggered by rising levels of Gonadotropin-releasing hormone (GnRH), stimulating the anterior pituitary to secrete Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH).

  • FSH prompts ovarian follicles to secrete estrogen, progesterone, inhibin, and androgens.

  • Effects of estrogen:
      - Feminizing hormones with widespread effects on the body; include Estradiol (most abundant), Estriol, and Estrone.

Oogenesis and the Sexual Cycle

Reproductive Cycle

  • Sequence of events from fertilization to childbirth and returning to fertility.

  • The sexual cycle consists of two interrelated cycles controlled by hormone secretion:
      - Ovarian cycle: Events that occur in the ovaries
      - Menstrual cycle: Corresponding changes in the uterus

Oogenesis

  • Egg production, producing haploid gametes through meiosis.

  • Distinctly cyclic, typically releasing one egg monthly.

  • Accompanied by cyclical hormone secretion and changes in the ovaries and uterus, leading to menstrual flow.

Stages of Oogenesis

  • Most primordial germ cells degenerate (atresia) by birth.

  • Egg transitions from primary oocyte to ovum within the ovarian follicle.

  • By puberty, approximately 200,000 oocytes remain, with about 480 expected to undergo ovulation in a lifetime.

The Sexual Cycle and Hormonal Control

  • The sexual cycle averages 28 days (varies from 20 to 45 days).

  • Hormones are regulated hierarchically:
      - Hypothalamus → Pituitary → Ovaries → Uterus.

  • The cycle begins with a follicular phase, ovulation occurs typically on day 14, followed by the luteal phase which lasts until menstruation begins.

Events of the Ovarian Cycle

  • Follicular Phase: Day 1-14

  • Ovulation: Day 14

  • Luteal Phase: Day 15-28

Control of Ovulation

  • Estradiol stimulates a surge of LH and a smaller spike of FSH leading to ovulation.

  • The LH surge induces primary oocyte completion of meiosis I, follicular fluid buildup, and follicle wall weakening leading to ovulation.

Menstrual Cycle

  • Consists of endometrial buildup followed by breakdown and discharge.

  • Divided into four phases:
      - Proliferative Phase: rebuilding the functional layer.
      - Secretory Phase: thickening in response to progesterone.
      - Premenstrual Phase: degeneration of the endometrium.
      - Menstrual Phase: discharge of menstrual fluid.

Average Menstrual Phase

  • Average discharge: 40 mL of blood and 35 mL of serous fluid over approximately 5 days, with the menstruation fluid containing fibrinolysin to prevent clotting.

Endometriosis

  • Endometriosis is the growth of endometrial tissue outside the uterus, causing pain and sometimes infertility (prevalent in 6-10% of women).

  • Believed to result from retrograde menstruation, where menstrual fluid flows backward through the uterine tube into the peritoneal cavity.

Hormones of Pregnancy

  • Human Chorionic Gonadotropin (HCG) secreted by the blastocyst and placenta, detectable in urine 8-9 days after conception.

  • Estrogen levels rise significantly, facilitating tissue growth in the fetus and enlarging maternal structures.

  • Progesterone suppresses the secretion of FSH and LH, preventing follicular development and supporting endometrial proliferation.

Adjustments During Pregnancy

  • Morning sickness, constipation, and heartburn are common symptoms triggered by hormonal changes.

  • Basal metabolic rate (BMR) increases by about 15% in the second half of gestation; healthy average weight gain is about 24 lb.