36.1: Review of the Female Reproductive System
By the end of this section, you should be able to:
- 36.1.1 Describe the structure and function of the female reproductive system.
- 36.1.2 Discuss common conditions that affect the female reproductive system.
Structure and Function of the Female Reproductive System
The female reproductive system (also referred to as the ovarian reproductive system ) is made up of internal and external organs (see Figure 36.2). The external parts, known also as the vulva (see Figure 36.3), include the labia majora, labia minora, clitoris, vaginal and urethral openings, and the mons pubis. The internal organs are the vagina, cervix, uterus, fallopian tubes, and ovaries (Hoare & Kahn, 2022; Netter, 2022).
The labia majora provide protection to the other external organs. The labia minora cover the openings to the urethra and the vagina. The clitoris is the junction of the labia minora and is the organ that allows sexual arousal to occur. The mons pubis is the small, rounded area made up of fat that sits just above the vulva. Pubic hair grows from the mons (Hoare & Kahn, 2022; Netter, 2022).
The uterus, or womb, is where a fertilized egg implants to develop into the fetus. If an egg is not fertilized and implanted, the uterus sheds its inner lining in the process usually known as menstruation or a period. The vagina is the birth canal, which connects the cervix, the lowest end of the uterus, to the outside of the body. During labor, the cervix gradually dilates to allow the fetus to enter the vagina. Strong contractions push the fetus through the vagina to the point where the fetus is born, meaning it has been delivered outside the body (Betts et al., 2023; Hoare & Kahn, 2022; Netter, 2022).
Hormones
The major hormones affecting the female reproduction system are secreted from three locations in the body. The hypothalamus secretes a hormone known as the gonadotropin-releasing hormone (GnRH) . The anterior pituitary is stimulated by GnRH to secrete two hormones: Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) . Finally, the ovaries (gonads) themselves secrete estrogen and progesterone (gonadotropins) in response to FSH and LH released by the anterior pituitary. Each of these hormones is released during the monthly menstrual cycle, but in different amounts depending on the stage of the cycle. Estrogen and progesterone are gonadotropins.
GnRH is a critical hormone in the hypothalamic-pituitary-gonadal axis, acting as the central regulator. It is responsible for regulating the start of puberty, onset of menstrual cycle, development of sex characteristics, and ovulation. GnRH is also responsible for producing the gonadal sex hormones, LH and FSH (Casteel & Singh, 2023).
FSH and LH stimulate the development of ovarian follicles and the release of mature ova (eggs) from mature follicles. Additionally, FSH and LH prepare the body for pregnancy and support pregnancy until the time of delivery.
Estrogen is produced in three types: estradiol, estriol, and estrone. It initiates the development of the female genitalia and breast tissue and plays many roles during pregnancy to conserve energy for the fetus, increase metabolism, increase uterine motility, and other actions to prepare the body for pregnancy and delivery. Progesterone performs many of the same functions as estrogen does, to promote maturation of sex organs, prepare the body for pregnancy, and maintain a healthy uterine environment for development of the fetus.
The adrenal cortex secretes gonadocorticoids (gonadotropins), which are the sex hormones. Male hormones (androgens/testosterone) and female hormones (estrogen) are secreted in opposite sexes in very small amounts. However, they have minimal effect on the opposite sex (testosterone in females and estrogen in males) because hormones from the testes and ovaries override them. In menopause, androgen has more of a masculinization effect on females because the ovaries secrete less estrogen (Nassar, 2023).
Menstrual Cycle
The menstrual cycle refers to the monthly changes in hormones and reproductive organs that usually occurs on a 28-day cycle. The length of the cycle is different for each client and may be shorter or longer or even irregular for some individuals. The first menstrual cycle is known as menarche and generally begins around age 12, with some clients starting earlier and some not starting until their mid-teens. Each menstrual cycle begins with the first day of bleeding from the uterus. The bleeding is the discharge of blood and endometrial tissue, the lining of the uterus, which had been prepared for the implantation of a fertilized egg. Bleeding lasts around 5 days, though the length of time is individualized. Approximately 14 days after the first day of the cycle, ovulation occurs. The ovary releases an egg, and it travels through the fallopian tubes to the uterus to be fertilized and implanted. If no fertilization occurs, the egg, along with the endometrial content, is expelled from the uterus, and the bleeding starts another menstrual cycle (McLaughlin, 2023; Rosner et al., 2022).
Hormones play a key role in the menstrual cycle through increased or decreased secretion from the hypothalamus, anterior pituitary, and ovaries. At the start of each cycle, the ovaries increase the production of estrogen until about day 14, when ovulation occurs; estrogen production then sharply decreases. During the second half of the cycle, estrogen secretion increases until about day 20 and then decreases to its lowest point when menstruation restarts, marking day 1 of a new cycle. Progesterone secretion, in contrast, is low until just before ovulation and then increases sharply, reaching a peak on about day 20. It then decreases gradually and remains low until the next ovulation at days 12–14 (McLaughlin, 2023; Rosner et al., 2022).
GnRH, LH, and FSH stimulate target cells (the cells that respond to a specific hormone) in the ovaries, causing the increased production of estrogen and progesterone. The hormone GnRH is secreted in bursts that vary in amplitude and frequency. The variations of amplitude and frequency also impact the start of other hormonal changes that regulate the menstrual cycle. Testosterone and progesterone decrease the frequency of GnRH bursts, whereas estrogens increase the frequency (Casteel & Singh, 2023). Additionally, LH and FSH increase the number and size of the target cells. Both LH and FSH secretion rise slightly at the start of the menstrual cycle, decrease, and then sharply increase immediately before day 14, or ovulation. They decrease significantly and rapidly after ovulation and remain steady until just before the start of a new cycle (McLaughlin, 2023; Rosner et al., 2022).
Figure 36.4 shows the phases of hormonal secretion.
Link to Learning
Dr. Paulien Moyaert is a Belgian nuclear medicine resident and science communicator. In this video, Dr. Moyaert explains the hormonal changes that occur during the menstrual cycle .
Pregnancy
Pregnancy means that an egg produced by the ovary has been released, fertilized by sperm, and implanted into the lining of the uterus and has begun to grow into a fetus. During pregnancy, the client will not have monthly menstrual cycles.
Three main groups of medications are related to pregnancy and will be discussed later in the chapter: contraceptives for clients who do not want to become pregnant, fertility medications for females who need help to become pregnant and maintain the pregnancy, and medications used during labor and delivery.
Menopause
Once a client has passed the age when they have regular monthly cycles, they have entered perimenopause . During perimenopause, the monthly menstrual cycle generally becomes irregular. A client may experience a missed cycle for one month and then have a period the following month. Cycles may occur closer together, the actual bleeding time may be shorter, and the amount of bleeding may decrease. Menopause is diagnosed once a client has not had any monthly cycles for 12 consecutive months (Peacock & Ketvertis, 2022; Mayo Clinic, 2023b; North American Menopause Society (NAMS) 2022 Hormone Therapy Position Statement Advisory Panel, 2022).
Menopause can occur in a client as early as their 30s until their mid-50s, with an average age of 51 years. Clients who experience menopause younger than age 40 are considered to have early menopause, usually the result of a genetic or chromosomal problem. Surgical menopause happens when the ovaries are surgically removed. Additionally, induced menopause may occur as the result of medications or radiation therapy that damages the ovaries. Whatever the reason for menopause, the signs and symptoms will be the same (Peacock & Ketvertis, 2022; Mayo Clinic, 2023b; NAMS 2022 Hormone Therapy Position Statement Advisory Panel, 2022).
During menopause, certain conditions develop that are the result of decreased hormones, specifically estrogen and progesterone. Vaginal dryness, hot flashes, night sweats, mood changes, weight gain, trouble sleeping, and thinning hair are what most clients experience during menopause. The intensity of each menopausal condition is individualized, so comparing one person’s experience to another person’s is not supportive to individual clients (Hariri & Rahman, 2023; NAMS 2022 Hormone Therapy Position Statement Advisory Panel, 2022; Mayo Clinic, 2023b; Peacock & Ketvertis, 2022).
One primary concern of menopause is the loss of bone mass, which can lead to fractures. This topic will be covered in more detail in the next section.
Link to Learning
Dr. Jen Gunter discusses what happens to the bodies of clients during menopause.