L#32 - Ovaries, uterus and vagina

Ovarian reproductive anatomy

  • The reproductive anatomy and physiology of the female is more complex because of pregnancy

  • Ovaries are the gonads that produce ova gametes and secrete the sex hormones estrogen (in the forms of estradiol, estrone, and estriol) and progesterone

  • Internal genitalia are located in pelvic cavity and include ovaries and duct system (uterine tubes, uterus, and vagina).

  • The external sex organs are referred to as external genitalia or vulva

The ovaries

  • The ovaries produce the gametes ova/eggs, and the sex hormones estrogen and progesterone

  • Each ovary contains many ovarian follicles, which each consists of an immature egg, called an oocyte, encased by one or more layers of different cells

  • B/w menarche and menopause, the ovarian and uterine cycles occur approx. each month when a maturing follicle ejects its oocyte from the ovary — the ruptured follicle transforms into a corpus luteum and then a corpus albicans

The uterine tubes

  • The uterine tubes / fallopian tubes / oviducts — form the beginning of the uterine duct system, receive the ovulated oocyte, and provide a site for fertilization to take place

  • The uterus is a thick-walled muscular organ that can receive, retain and nourish a fertilized ovum. The wall of uterus is composed of 3 layers:

    • the outermost, serous perimetrium

    • the bulky, smooth muscle myometrium

    • the mucosal lining, the endometrium

Endometrium

  • The stratum functionalis changes in response to ovarian hormone cycles and is shed during menstruations

  • The stratum basalis forms the new stratum functionalis after menstruation and is unresponsive to ovarian hormones

The vagina

  • The vagina provides a passageway for menstrual blood or delivery of an infant and can also receive a penis and semen during sexual intercourse

  • The epithelial cells of the vaginal mucosa produce a glycogen-rich fluid that is metabolized by bacteria to lactic acid, producing an acidic environment that protects from infection (pH 4.5, like a tomato)

  • During sexual arousal, the vagina lengthens and expands comparably to the size change of penis during arousal

Vulva (external genitalia)

  • The labia majora are 2 elongated folds of skin and are the vulvar counterpart to the scrotum

  • The labia minora, enclosed by the labia majora, are homologous to the underside of the penis

  • Skene’s glands (lesser vestibular glands or female prostate) are homologous to the penile prostate

  • Bartholin’s glands (greater vestibular glands) are homologous to the bulbourethral glands of the penis and produce lubricating mucous

  • Anterior to the vestibule lies the clitoris, a highly innervated erogenous zone of erectile tissue

  • The clitoris includes a glans (the exposed portion), a prepuce (hood) and 2 corpora cavernosa, are all homologous to these structures in the penis

  • Studies of female sexuality and sexual health, including the significance of the clitoris, have been unfortunately sexist and deficient for centuries — finally, this is changing

Ovarian cycle and uterine cycle

  • The ovarian cycle is a set of events that occur in the ovaries. These relate to the development, maturation and ovulation of an oocyte

  • The uterine cycle occurs at the same time as the ovarian cycle but focuses on changes in the uterus to prepare it for a fertilized ovum that can result in pregnancy

Follicular phase of ovarian cycle

  • In the follicular phase of the ovarian cycle, a follicle develops and the oocyte within undergoes meiosis

  • FSH and LH from the anterior pituitary stimulate follicle maturation and estrogen secretion

    • Moderate levels of estrogen exert negative feedback, inhibiting the release of FSH and LH

    • High levels of estrogen exert positive feedback on the pituitary, stimulating LH release, which triggers oocyte maturation and ovulation

Luteal phase of ovarian cycle

  • The luteal phase is characterized by the formation of the corpus luteum, which secretes progesterone and some estrogens, inhibiting FSH and LH

  • If pregnancy doesn’t occur within around 10 days, the corpus luteum transforms into the corpus albicans and progesterone levels drop, FSH and LH levels rise, which stimulates estrogen secretion and restarts the cycle

  • If pregnancy occurs, the corpus luteum persists until the placenta is mature enough to produce hormones

The uterine cycle

  • Days 1-5: the menstrual phase is the time when the endometrium is shed from the uterus

    • Day 1 / Day 0 — the start of menstruation

    • Days 6-14 — the proliferative(preovulatory) phase, when the endometrium regrows

      • ovulation occurs at the end of this stage

    • Days 15-28 — the secretory (postovulatory) phase, when the endometrium prepares for implantation of an embryo

  • If pregnancy does not occur, the corpus luteum declines, and the lack of progesterone causes spiral arteries to cut off delivery of oxygen and nutrients, which results in the death and subsequent sloughing off of the endometrial layer as the uterine cycle starts over

    • about 2/3 of the endometrium is reabsorbed by the body but some tissue is shed in menstruation

  • Estrogen and progesterone levels establish and help regulate the uterine cycle and promote changes in cervical mucous

Anovulatory cycles and short luteal phases

  • In about 1/3 of overtly normal menstrual cycles, ovulation doesn’t occur (anovulation) or the luteal phase is shorter than 10 days, resulting in insufficient progesterone for fertility

  • Anovulation is often linked to changes in hormone levels, sometimes due to stress or dietary issues, w/ or w/ out changes in the uterine cycle

  • PCOS / Polycystic ovarian syndrome — is a common (about 10% of women have it) endocrine disorder defined by anovulation and increased testosterone production by ovaries

Age beginning puberty

  • The age of puberty in females has decreased from 15-17 years old in 1840 to 8-13 years old today

    • approx. 15% begin puberty by age 7

  • Anthropological research suggests puberty around age 12 for the last 20000 years, and it may have been artificially delayed due to malnutrition and pollution in the industrial revolution (around 1760-1840)

  • Milestones for male puberty are less socially rigid — choir records from medieval cathedrals indicate puberty at ages 12-13, similar to today

Pregnancy

  • In Canada, 1 in 7 couples seek to conceive

  • A single, randomly timed act of heterosexual intercourse results in fertilization (conception) about 3% of the time

  • About 50% of conceptions do not implant are are lost in menstruation — this reduces the rate of congenital disorders, which are medical conditions at or before birth, from an estimated 12% to 2-3%

  • 1-2% are ectopic pregnancies that implant outside of the uterus, mostly in the fallopian tubes