Female Reproductive System: Organs and Functions

The female reproductive system includes the ovaries, fallopian tubes, uterus, vagina, accessory glands, and external genitalia.

The female reproductive system includes the ovaries, fallopian tubes, uterus, vagina, accessory glands, and external genitalia.

• External genitalia
  • The vulva (pudendum) is a term that refers to the external organs that may be visible in the perineal area 
    • Mons pubis
      • The rounded part of the vulva where pubic hair grows
  • Labia
    • Labia majora (large “lips”) are two large folds of fat and fibrous tissue that protect the other external reproductive organs
    • Labia minora (nymphae, or small “lips”) are two small skin folds located between the labia majora and the opening of the vagina
  • Hymen
    • A thin membrane at the entrance to the vaginal opening that is not always present
  • Clitoris
    • An erectile structure located below the front joining of the labia minora that is a sensitive structure analogous to the male penis
  • Vestibule and urethra
    • The vestibule is located between the clitoris and the opening of the vagina, which is where the urethral opening (where urine exits the body) is found
  • Skene and Bartholin glands
    • Skene glands secrete lubrication at the opening of the urethra
    • Bartholin glands secreting lubrication to the vagina
  • Vestibular bulbs
    • Two masses of erectile tissue 
• Internal genitalia
  • Vagina (birth canal)
    • Extends from the vulva externally to the cervix internally and lies at a 90o angle in relation to the uterus
  • Uterus (womb)
    • A hollow, inverted pear-shaped female reproductive organ that lies in the midline of the body
    • During reproductive years, it changes in response to hormonal stimulation throughout a woman’s monthly cycle
    • It is where a fetus develops
  • Cervix
    • The lower portion of the uterus, separating the body of the uterus from the vagina
    • A canal in the center allowing the passage of sperm to enter the uterus to fertilize an egg and menstrual blood to exit
  • Fallopian tubes (also called oviducts or uterine tubes) 
    • Function primarily to transport sperm toward an egg, which is released by the ovary, and then to allow passage of the fertilized egg back to the uterus for implantation
  • Ovaries
    • There are two located on either side of the uterus, responsible for housing and releasing eggs (ova), needed for reproduction
    • They also produce female hormones
    • At birth, a female has approximately 1-2 million eggs, but only 300 will mature and be released for the purpose of fertilization

A menstrual cycle is counted from the first day of menstruation to the first day of the next. An average menstrual cycle lasts 21 to 35 days. 

There are four main phases of the menstrual cycle:

• Menstruation
  • Passage of the thickened lining of the uterus (endometrium) from the body through the vagina
  • Menstrual fluid contains blood and cells from the lining of the uterus 
  • A menstrual period lasts on average between three to seven days 
• Follicular phase
  • Begins on the first day of menstruation and ends with ovulation
  • The pituitary gland releases follicle stimulating hormone (FSH) that stimulates the ovary to produce around five to 20 follicles (tiny nodules or cysts), which bead on the surface
  • Each follicle houses an immature egg and most of the time one follicle will mature into an egg, while the others die
  • This usually occurs around day 10 of a 28-day cycle
  • The growth of the follicles stimulates the lining of the uterus to thicken in preparation for potential pregnancy
• Ovulation
  • The release of a mature egg from the surface of the ovary
  • This occurs mid-cycle, about two weeks before menstruation starts
  • During the follicular phase, estrogen levels rise and gonadotrophin-releasing hormone (GnRH) is released, which prompts the pituitary gland to produce raised levels of luteinizing hormone (LH) and FSH.
  • High levels of LH trigger ovulation within two days and the egg passes into the Fallopian tube toward the uterus
  • An egg usually only lives about one day and if it is not fertilized by a sperm in that time, it will die
  • This is the most fertile window during a menstrual cycle 
• Luteal phase
  • During ovulation, an egg bursts from its follicle, but the ruptured follicle stays on the surface of the ovary and transforms into a structure known as the corpus luteum which releases progesterone and small amounts of estrogen
  • These hormones maintain the thickened lining of the uterus, waiting for a fertilized egg to stick
  • If a fertilized egg implants, hormones are released to maintain the thickened lining of the uterus
  • If pregnancy does not occur, the lining of the uterus sheds during menstruation and the cycle repeats 

A pregnancy is considered full-term at 40 weeks. There are three stages, called trimesters, of pregnancy, each marked by certain fetal developments. 

First Trimester

The first trimester refers to the first three months and the time in which the baby grows the fastest. About 5 weeks after sperm fertilizes an egg (conception), the embryonic stage of pregnancy begins and runs from about the 5th to the 10th week of pregnancy. 

During the embryonic stage, when the baby is called an embryo) a number of changes occur:

• The cells of the embryo (embryonic stem cells) multiply quickly and develop into the hundreds of different types of cells needed to form a human body
• The major organs, heart, bones, muscles, nervous system, face, arms and legs, and sexual organs begin to form
• The placenta forms
• The amniotic sac forms
• At the end of the embryonic stage (about week 10 of the pregnancy) the baby is about 1 inch long

Second Trimester

After the embryonic stage, the fetal stage begins (when the baby is called a fetus), which runs from the 11th week of pregnancy until birth. By the end of the first trimester, the fetus can weigh about 0.5 to 1 ounce and measure an average of 3 to 4 inches in length.

The second trimester of pregnancy, weeks 13 through 26, is a time when the baby continues to quickly grow and develop. The mother may feel the baby's first fluttering movements between 16 to 20 weeks. The 20th week marks the halfway point of a pregnancy. 

Fetal development during the second trimester includes:

• The placenta is fully developed
• The fetus develops reflexes including swallowing and sucking
• The fetus can respond to certain stimuli
• The fetus kicks, moves, and can turn from side to side
• The brain undergoes its most important period of growth from the fifth month on
• Hair grows on the head of the fetus
• Eyelids begin to open and eyebrows and eyelashes are visible
• The fetus develops all its organs and systems 
• By the end of the second trimester, a fetus will be about 13 to 16 inches long and weigh about 2 to 3 pounds

The mother will usually begin to feel better and the pregnancy will show more. 

Third Trimester

The third trimester, weeks 27 to 40, is the final stretch of a pregnancy. The uterus expands from about 2 ounces before pregnancy to 2.5 pounds at the time of birth as the fetus continues to grow in size and weight. 

Fetal development during the third trimester includes:

• The brain continues to develop
• The fetus can see and hear
• A fetus can suck its thumb and is able to cry
• The kidneys and lungs continue to mature
• The bones of the skull remain soft to so it the fetus can more easily pass through the birth canal
• By week 36, the head may drop into the pelvic area (called lightening)
• By weeks 38 to 40 weeks, the fetus’ fine, soft hair on the body and limbs (lanugo) has disappeared almost completely
• By 38 to 40 weeks, the lungs have matured completely
• The head will usually turn downward during the last couple of weeks of pregnancy

At the end of the third trimester, a fetus is about 19 to 21 inches long and the average weight is 6 to 9 pounds.