Anatomy and physiology of pelvic floor
Overview of Female Reproductive Anatomy
The female reproductive system consists of both internal and external structures that play distinct roles in reproduction.
External Organs:
• Vulva: The external genitalia includes the labia majora, labia minora, clitoris, vaginal opening, and urethral opening.
o Labia Majora & Minora: The folds of skin that protect the inner structures.
o Clitoris: A highly sensitive organ involved in sexual pleasure.
o Vaginal Opening: The opening that leads to the vagina.
o Urethral Opening: Located just above the vaginal opening, through which urine is expelled.
Internal Organs:
• Vagina:
o A muscular canal that connects the external genitalia to the uterus. It serves as the passageway for menstrual fluid, sexual intercourse, and the birth canal during childbirth.
• Cervix:
o The lower part of the uterus that opens into the vagina. It acts as a barrier between the vagina and uterus. During pregnancy, it remains closed and firm to hold the fetus. It dilates during labor to allow passage of the baby.
• Uterus:
o A hollow, muscular organ that is responsible for housing and nourishing a developing fetus during pregnancy.
Parts of the Uterus:
Endometrium: The innermost layer, where the fertilized egg implants.
Myometrium: The middle layer, made of smooth muscle, responsible for contractions during labor.
Perimetrium: The outer layer of the uterus.
• Fallopian Tubes:
o Two tubes that extend from the uterus toward the ovaries. They are the site of fertilization. The egg released from the ovaries travels through these tubes, where it may meet sperm for fertilization.
• Ovaries:
o Paired organs located on either side of the uterus. They produce eggs (ova) and secrete hormones like estrogen and progesterone, which regulate the menstrual cycle.
• Broad Ligaments:
o These ligaments support the uterus, ovaries, and fallopian tubes in the pelvic cavity. They help maintain the positioning of these organs during pregnancy.
Female Reproductive Physiology
The physiology of the female reproductive system is largely governed by a complex interplay of hormones that regulate menstruation, ovulation, pregnancy, and menopause.
A. Menstrual Cycle
The menstrual cycle is the process in which the female body prepares for pregnancy each month. It involves a series of hormonal changes that lead to ovulation and the shedding of the endometrium if pregnancy does not occur.
• Follicular Phase:
o Duration: First half of the cycle (approximately 14 days, though it can vary).
o Key Hormones: Estrogen and Follicle-Stimulating Hormone (FSH).
o Events: The pituitary gland secretes FSH, which stimulates the ovaries to mature a follicle containing an egg. As the follicle matures, it produces estrogen, which thickens the endometrial lining of the uterus in preparation for pregnancy.
• Ovulation:
o Duration: Mid-cycle, around day 14 in a 28-day cycle.
o Key Hormone: Luteinizing Hormone (LH) surge.
o Event: A spike in LH triggers the release of a mature egg from the follicle (ovulation). The egg is then captured by the fallopian tube where it may meet sperm for fertilization.
• Luteal Phase:
o Duration: Last half of the cycle (approximately 14 days).
o Key Hormones: Progesterone and Estrogen.
o Events: After ovulation, the ruptured follicle becomes the corpus luteum, which secretes progesterone to maintain the endometrial lining for potential implantation of a fertilized egg. If fertilization doesn’t occur, the corpus luteum degenerates, leading to a drop in progesterone and estrogen, resulting in the shedding of the endometrial lining (menstruation).
• Menstruation:
o If no pregnancy occurs, the endometrium is shed, and menstrual bleeding occurs, marking the start of a new cycle.
B. Pregnancy Physiology
Pregnancy involves a series of physiological changes that support the development of the fetus.
• Implantation and Early Pregnancy:
o After fertilization, the zygote travels through the fallopian tube to the uterus and implants into the thickened endometrium.
o Human Chorionic Gonadotropin (hCG): The placenta begins to produce hCG, which helps maintain the corpus luteum and prevents menstruation.
• Hormonal Changes in Pregnancy:
o Estrogen and Progesterone: Levels of estrogen and progesterone increase, supporting uterine growth and the maintenance of pregnancy.
o Relaxin: This hormone helps relax the ligaments and joints to accommodate the growing baby, leading to increased flexibility, especially in the pelvis and hips.
• Physical Changes:
o Uterine Growth: The uterus expands significantly to accommodate the growing fetus.
o Postural Changes: The body adjusts to the growing belly, which can lead to changes in posture (e.g., lordosis, or inward curvature of the lower back).
o Increased Blood Volume: Blood volume increases by 30-50%, and the heart rate increases to supply oxygen to the fetus.
o Pelvic Girdle Pain: Due to ligamentous laxity, some women experience pain in the pelvis.
• Labor and Delivery:
o The cervix dilates and effaces (thins) to allow the baby to pass through the birth canal.
o The myometrium (muscle layer of the uterus) contracts to help expel the baby.
o Hormones like oxytocin increase the frequency and intensity of contractions during labor.
C. Postpartum Physiology
• Involution of the Uterus:
o After childbirth, the uterus shrinks back to its pre-pregnancy size, a process called involution. This process may take up to 6 weeks.
• Pelvic Floor Recovery:
o After childbirth, particularly vaginal delivery, the pelvic floor muscles may be weakened, and pelvic organ prolapse or incontinence can occur. Physiotherapy focuses on pelvic floor rehabilitation to regain strength and function.
• Lactation:
o The mammary glands produce milk in response to hormonal signals (primarily prolactin). Lactation requires proper positioning, good posture, and effective breast health management.
Hormonal Regulation of Reproduction
Several key hormones control the processes of menstruation, ovulation, pregnancy, and postpartum recovery.
• Hypothalamic-Pituitary-Gonadal Axis:
o The hypothalamus in the brain releases Gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gland to secrete FSH and LH. These hormones control the ovarian cycle, including follicle maturation, ovulation, and corpus luteum formation.
• Estrogen:
o Produced mainly by the ovaries, estrogen regulates the menstrual cycle, promotes the thickening of the endometrial lining, and supports the development of female secondary sexual characteristics.
• Progesterone:
o After ovulation, the corpus luteum secretes progesterone, which prepares the endometrium for implantation of a fertilized egg and maintains pregnancy.
• hCG (Human Chorionic Gonadotropin):
o Produced by the placenta, hCG maintains the corpus luteum during early pregnancy and prevents menstruation. It is the hormone detected in pregnancy tests.
• Prolactin:
o Responsible for milk production after childbirth. Prolactin levels rise during pregnancy and stimulate the mammary glands to produce milk.
• Oxytocin:
o Known as the "love hormone", it is involved in uterine contractions during labor and delivery and also in the milk ejection reflex during breastfeeding.