Lecture 2 – Reproductive Tract of Females

Overview of Female Reproductive Organs

the primary organs of the female reproductive system are the ovaries, fallopian tubes, uterus, and vagina.

their functions are tightly coordinated by hormonal signals

  • the ovaries are paired organs that are responsible for producing oocytes and secreting the key female sex hormones, estrogen and progesterone

  • the fallopian tubes are muscular tubes that transport the oocyte from the ovary to the uterus

    • typical site where fertilisation occurs

  • the uterus is a muscular, pear-shaped organ where a fertilised egg implants and develops into a fetus

    • provides mechanical protection, nutrition, and waste removal

    • its powerful contractions are essential for childbirth

  • the vagina is a muscular canal that receives the penis during intercourse, serves as the passageway for menstrual fluid, and forms the lower part of the birth canal

Anatomy & Support Structures

the organs aren’t rigidly fixed but are suspended within the pelvic cavity by a network of ligaments, which allows for some movement while maintaining their relative positions this is important because the fallopian tubes aren’t directly connected to the ovaries

  • board ligament

    • a large, double-layered fold of peritoneum that ‘drapes’ over the uterus and encloses the uterine tubes and ovaries

    • acts as a primary stabiliser, preventing lateral movement

  • suspensory ligament

    • extends from the lateral surface of the ovary to the pelvic wall

    • contains the ovarian artery and vein, providing the major blood supply to the ovary

  • ovarian ligament

    • connects the medial surface of the ovary to the lateral wall of the uterus

  • uterine ligament

    • uterosacral, round, cardinal

      • stabilise the position of the uterus, limiting its range of motion

    • usually is anteverted position (angled forward over the bladder)

    • a retroverted uterus (tipped backward) is found in 20–25% of women and is considered a normal variation

The Ovary: Structure and Cycle

the ovary is a small organ with a complex internal structure

  • general epithelium

    • a single layer of cuboidal cells covering the surface

  • tunica albuginea

    • a layer of dense connective tissue beneath the epithelium

  • cortex

    • the outer region containing ovarian follicles at various stages of development

  • medulla

    • the central region, consisting of loose connective tissue and blood vessels

The Ovarian Cycle

females are born with their entire lifetime supply of oocytes. these oocytes are arrested in prophase I of meiosis. from puberty to menopause, a cyclical process occurs:

  • follicle development

waves of primordial follicles are recruited. it takes ~85 days for a follicle to progress from the primordial stage to the point of antrum formation. the stages are:

  1. primordial follicle

oocyte surrounded by a single layer of flattened granulosa cells

  1. primary follicle

oocyte surrounded by a single layer of cuboidal granulosa cells. the oocyte begins to grow

  1. secondary follicle

granulosa cells proliferate to form multiple layers

  1. tertiary follicle

a fluid-filled space called the antrum forms

The Ovarian Cycle – Fertility Charting

  • during the follicular phase of each menstrual cycle, a cohort of developing follicles responds to FSH. one follicle is selected to become dominant and continues to mature while the others undergo atresia. this dominant follicle will eventually ovulate

The Uterus: Structure & Cyclic Changes

the non-pregnant uterus is a pear-shaped organ with a small luminal volume. it's wall is composed of three layers:

  • perimetrium: the outer protective layer

  • myometrium: the thick middle layer of smooth muscle. it’s responsible for:

    • proliferative phase: gentle ‘upward’ contractions that may aid sperm transport

    • secretory phase: ‘downward’ contractions that may aid embryo transport

    • labour: powerful, coordinated contractions for fetal explusion

  • endometrium: the inner mucosal layer, which is highly dynamic. it’s subdivided into:

    • functional zone: the thick, superficial layer that is shed during menstruation if pregnancy doesn’t occur. it’s rich in glands and spiral arteries

    • basal zone: the thin, deep layer adjacent to the myometrium. it’s not shed and serves to regenerate the functional layer after each menstruation

The Menstruation Cycle

this cycle describes the changes in the endometrium, driven by hormones form the ovary

  • menstrual phase

if no pregnancy occurs, the corpus luteum degenerates, causing a sharp drop in estrogen and progesterone. the spiral arteries constrict, causing ischemia and necrosis of the functional zone, which is then shed as the menstrual flow

  • proliferative phase

rising estrogen from the developing dominant follicle stimulates the regeneration and thickening of the functional zone. glands proliferate, and the spiral arteries elongate and become coiled. this phase ends at ovulation

  • secretory phase

after ovulation, the corpus luteum produces progesterone. this hormone transforms the endometrium, making it secretory. the glands produce a glycogen-rich fluid to nourish a potential embryo. the decidual reaction also occurs during this phase

The Decidual Reaction & Window of Implantation

  • a change in the endometrial stroma where fibroblasts swell and accumulate glycogen and lipids. in humans, this occurs spontaneously during the secretory phase, preparing the ‘soil’ for a potential embryo. in most other mammals, it only occurs after implantation

  • a short ~48 hour period when the endometrium is receptive to the implanting blastocyst. this receptivity is mediated by the expression of specific adhesion molecules

The Fallopian Tubes: Transport & Fertilisation

the tube is ~13 cm long and has three distinct regions:

  1. infundibulum

the funnel-shaped end with finger-like projections called fimbriae. the fimbriae sweep over the ovary to capture the oocyte after ovulation

  1. ampulla

the longest and widest part. this is the typical site of fertilisation

  1. isthmus

the narrower portion that connects to the uterus

  • the oocyte/embryo is moved along the tube by a combination of ciliary beating and peristaltic contractions of the smooth muscle wall

The Cervix: Gateway & Barrier

  • the lower portion of the uterus that projects into the vagina

  • a critical feature is the change in epithelial type at the squamocolumnar junction

    • endocervix: lined by a single layer of columnar epithelium

    • ectocervix: lined by multi-layered squamous epithelium

    • transition zone: the area where these two meet. this is the site where most cervical cancers arise

  • functions:

    • sperm regulation: secretes cervical mucus that changes from thick and impenetrable to thin, watery, and alkaline to facilitate sperm passage

    • barrier: protects the upper reproductive tract from infection

    • pregnancy & birth: remains tightly closed during pregnancy to retain the fetus. during labour, it thins and opens to allow passage of the fetus

Ectopic Implantation

  • implantation of the embryo outside the uterine cavity

  • the fallopian tube, often due to scarring or damage that impedes the embryo’s transport to the uterus

  • can occur anywhere in the abdominal cavity, including the ovaries, cervix, or even on the peritoneum, as demonstrated by the remarkable case study of a woman who had an abdominal pregnancy after a hysterectomy

Cervical Cancer & Prevention

  • almost all cervical cancers are caused by persistent infection with high-risk strains of the HPV, primarily serotypes 16 & 18

  • screening

    • the pap smear is a screening tool that collects cells from the transition zone to detect pre-cancerous changes

    • regular screening every three years can reduce the risk of developing cervical cancer by up to 90%

  • prevention

    • HPV vaccines are highly effective at preventing infection with the most common high-risk HPV strains