2.2 Female reproductive anatomy and physiology

Female reproductive anatomy is a complex system designed for reproduction and sexual pleasure. From external structures like the clitoris to internal organs like the uterus, each part plays a crucial role in the menstrual cycle, pregnancy, and childbirth.

Hormones regulate the menstrual cycle, influencing egg development and uterine changes. Understanding these processes helps explain fertility, contraception, and reproductive health issues, connecting anatomy to broader sexual and reproductive functions.

External and Internal Female Reproductive Anatomy

External Genitalia (Vulva)

• Mons pubis forms fatty tissue pad over pubic bone
• Labia majora create outer folds of vulva, contain sweat and sebaceous glands
• Labia minora form inner folds, contain nerve endings for sexual arousal
• Clitoris comprises glans, body, and crura, contains 8000+ nerve endings
• Vestibule houses openings of urethra and vagina
• Vaginal opening leads to internal reproductive tract
• Bartholin's glands near vaginal opening secrete lubricating fluid during arousal

Internal Reproductive Organs

• Vagina connects external genitalia to cervix and uterus
  • Muscular, elastic canal approximately 7.5-10 cm long
  • Lined with rugae (folds) allowing expansion during intercourse and childbirth
• Cervix forms lower portion of uterus, produces cervical mucus
• Uterus houses developing fetus during pregnancy
  • Perimetrium (outer serosal layer)
  • Myometrium (middle smooth muscle layer)
  • Endometrium (inner mucosal lining)
• Fallopian tubes (oviducts) connect ovaries to uterus
  • Site of fertilization, lined with cilia to transport egg/embryo
• Ovaries produce and release eggs, secrete estrogen and progesterone
  • Contain primordial follicles housing immature oocytes

Associated Structures

• Breast tissue contains milk-producing lobules and ducts
  • Areola surrounds nipple, contains Montgomery glands
  • Adipose and connective tissue provide shape and support
• Pelvic floor muscles support pelvic organs (levator ani, coccygeus)

Hormonal Regulation of Menstrual Cycle

Hypothalamic-Pituitary-Gonadal Axis

• Hypothalamus releases gonadotropin-releasing hormone (GnRH)
• GnRH stimulates anterior pituitary to secrete:
  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
• Ovaries respond by producing estrogen and progesterone
• Feedback loops regulate hormone levels throughout cycle

Menstrual Cycle Phases

• Follicular phase (days 1-14 of average 28-day cycle)
  • FSH stimulates follicle development in ovaries
  • Estrogen levels rise, promoting endometrial growth
  • Negative feedback initially suppresses LH
• Ovulation (around day 14)
  • Estrogen surge triggers positive feedback
  • LH spike causes follicle rupture and egg release
• Luteal phase (days 15-28)
  • Corpus luteum forms from ruptured follicle
  • Progesterone prepares uterus for potential implantation
  • Estrogen and progesterone levels decline if no pregnancy occurs
  • Endometrium sheds, initiating menstruation

Hormonal Fluctuations and Effects

• Estrogen peaks twice during cycle (mid-follicular and mid-luteal)
• Progesterone rises after ovulation, peaks mid-luteal
• FSH and LH levels fluctuate, with sharp LH surge before ovulation
• Basal body temperature rises 0.5-1°F after ovulation due to progesterone

Oogenesis and Follicular Development

Oogenesis Process

• Begins during fetal development with primordial germ cells
• Oogonia undergo mitotic divisions, form primary oocytes
• Primary oocytes enter meiosis I, arrest in prophase I until puberty
• At puberty, select oocytes resume meiosis each cycle
• Meiosis I completed upon ovulation, forming secondary oocyte
• Meiosis II only completed if fertilization occurs

Follicular Development Stages

• Primordial follicles contain primary oocytes surrounded by flat granulosa cells
• Primary follicles develop cuboidal granulosa cells, form zona pellucida
• Secondary follicles acquire multiple granulosa cell layers, theca cells
• Antral follicles develop fluid-filled cavity (antrum)
• Graafian (preovulatory) follicle is mature, ready for ovulation
  • Contains secondary oocyte suspended in cumulus oophorus

Follicle Selection and Atresia

• Cohort of follicles begins development each cycle
• One dominant follicle selected for ovulation (typically)
• Remaining follicles undergo atresia (programmed cell death)
• Anti-Müllerian hormone (AMH) inhibits excessive follicle recruitment

Pregnancy and Childbirth Physiology

Early Pregnancy Events

• Fertilization occurs in ampulla of fallopian tube
• Zygote undergoes cleavage, forms blastocyst
• Implantation in uterine wall 6-10 days post-ovulation
• Trophoblast cells invade endometrium, initiate placenta formation
• hCG production maintains corpus luteum, supports early pregnancy

Maternal Physiological Adaptations

• Cardiovascular changes
  • Blood volume increases 40-50%
  • Cardiac output rises 30-50%
• Respiratory adjustments
  • Oxygen consumption increases 20%
  • Tidal volume expands, respiratory rate may increase
• Metabolic alterations
  • Basal metabolic rate increases 15-20%
  • Insulin resistance develops to ensure fetal glucose supply
• Renal adaptations
  • Glomerular filtration rate increases 50%
  • Plasma volume expansion may lower hematocrit

Labor and Delivery Stages

• First stage: cervical dilation and effacement
  • Latent phase: slow cervical changes
  • Active phase: rapid dilation to 10 cm
• Second stage: fetal descent and birth
  • Pushing phase, delivery of infant
• Third stage: placental delivery
  • Separation and expulsion of placenta

Postpartum Changes

• Uterine involution reduces uterus size
• Lochia discharge occurs for 2-6 weeks
• Lactation begins, triggered by prolactin surge
• Hormonal shifts may affect mood and metabolism

Lactation and Breastfeeding Physiology

Mammary Gland Development

• Embryonic stage establishes rudimentary ductal system
• Puberty initiates branching of ducts, formation of terminal end buds
• Pregnancy causes extensive ductal branching, alveolar development
• Functional differentiation of alveolar cells occurs late in pregnancy

Lactogenesis and Milk Production

• Stage I lactogenesis begins mid-pregnancy
  • Colostrum production starts
  • High in immunoglobulins, growth factors
• Stage II lactogenesis occurs 2-3 days postpartum
  • Copious milk production begins
  • Triggered by progesterone withdrawal after placental delivery
• Prolactin maintains milk production
  • Levels increase in response to infant suckling
  • Suppressed by dopamine (prolactin-inhibiting factor)

Milk Ejection Reflex

• Infant suckling stimulates sensory nerves in nipple
• Signals travel to hypothalamus, triggering oxytocin release
• Oxytocin causes myoepithelial cell contraction in alveoli
• Milk ejected from alveoli into ducts and sinuses
• Reflex can be conditioned (responding to infant's cry, for example)

Milk Composition and Production Regulation

• Colostrum transitions to mature milk over 7-14 days
• Mature milk composition
  • 87% water, 7% lactose, 4% fat, 1% protein
  • Contains antibodies, enzymes, hormones
• Feedback Inhibitor of Lactation (FIL) regulates supply
  • Accumulation in alveoli signals decreased production
  • Frequent emptying maintains high production
• Prolactin levels influenced by suckling frequency and duration