Female Physiology

Erection

  • erection takes more time than in males

    • a more complex process that involves psychological, emotional, and social factors in addition to physiological events

    • does not require a refactory period

  • sexual arousal leads to increased blood flow

    • engorgement of clitoral cavernosa and labia

    • increased interacavernous pressure causes tumenscence, protusion of glans clitoris, and eversion of labia minora

  • arousal causes vestibular glands to produce lubricating mucus and antimircobial fluids

  • also causes vaginal smooth muscle to relax

  • regulated by both the PNS and CNS

    • coordination of brain activity, spinal cord reflexes, and PNS neurotransmitter release

      • nitric oxide plays a role as in male erection

        • relaxes smooth muscles to increase blood flow, lubrication, and sensitivity; helps release oxytocin

        • lack of NO linked to menopause/vascular dysfunction

          • decreased lubrication, increased discomfort, and/or difficulty achieving orgasm

      • vasoactive intestinal peptide (VIP) enhances vaginal blood flow, lubrication and secretions

    • sacral segments of the spinal cord serve as reflex centers for erection

    • pudendal nerve sends sensory feedback from the clitoris and vagina to the brain

    • hypothalamus, visual cortex, olfactory cortex, and other regions of the brain process stimuli and send signals down the spinal cord

      • parasympathetics from pelvic nerve cause vasodilation allowing lubrication and clitoral engorgement (arousal)

      • sympathetics from hypogastric nerve involved in initial arousal and in orgasm

  • response manifests as engorgement and swelling of genital tissues (especially the clitoris), increased vaginal wall compliance, and production of secretions

    • results from increases in blood flow to the clitoris, vagnia, and labia

      • regulated by vascular smooth muscle tone of erectile tissues and assiociated blood vessels

  • emissary veins and a subtunical venous plexus as in males

    • relaxation of the tunica albuginea allows blood to drain via these vein networks

Sex Hormones

  • gonadotropin-releasing hormone

    • stimulates secretion of LH and FSH

  • luteninizing hormone

    • triggers ovulation and supports pregnancy

  • follicle-stimulating hormone

    • stimulates ovarian follicles to secrete estrogens, progesterones, and androgens

    • suppressed by inhibin

  • progesterone

    • prepares uterus for possible pregnancy

  • androgens (DHEAS, DHEA, DHT, androstenedione, and testosterone)

    • low levels until after menopause, then ovaries primarily secrete androgens

  • estrogens (primarily estradiol)

    • comes from androstenedione

    • triggers many changes during puberty

    • involved in development and function of reproduction system - vital in ovarian cycle

Oogenesis

  • female germ cells arise from the yolk sac

    • colonize gonadal ridges in 5-6 weeks od embryonic development → differentiate and multiply → become primary oocytes

      • development arrests until adolescence

  • divide into secondary oocytes and polar body

    • secondary oocyte proceeds to metaphase II, then arrests until after ovulation

      • completes meiosis II (if fertilized) or dies

      • polar bodies cast off/disintegrate

Folliculogenesis

  • primordial follicles contain the primary oocyte

    • features a single layer of squamous granulosa cells and is a dormant stage prior to birth

  • primary follicles form during ovarian follicle activation as granulosa cells become cuboidal in shape and oocytes are activated

    • develop receptors for FSH and the zona pellucida (surrounds oocyte; separates from the granulosa cells)

  • secondary follicles have muliple layers of granulosa cells and feature theca cells

    • theca cells surrounds the outer most layer and differentiate into the theca externa and theca interna and capillaries form between them

  • tertiary follicles feature fluid-filled cavities called antra (sing. antrum) and grow in size dependent upon the availablity of FSH

    • granulosa cells differentiate into subtypes that behave differently in response to FSH

    • theca cells developreceptors for luteinizing hormone (LH) and start producing androgens in response to LH

  • follicle burst to release oocytes during ovulation

  • ruptured follicles transform into the corpus luteum, which secretes progesterone and some estrogen

    • if the egg is fertilized, corpus luteum becomes corpus luteum gravidiatis to support implantation and early embryogenesis

    • if egg isnt fertilized, the corpus luteum degenerates after ~10 days and becomes the corpus albicans (scar tissue)

Ovarian Cycle

  • occurs monthly unless pregnant

    • averages 28 days (varies from 20-45 days)

    • occurs in the ovaries (3 phases)

      • follicular phase, ovulation, and luteal phase

  • follicular phase (~2 weeks)

    • mentruation during the first 3-5 days

      • shedding of uterine lining

      • uterus replaces lost tissue via mitosis

    • FSH stimulates follicles to grow

      • follicles secrete estradil

    • dominant follicle becomes increasingly senstive to FSH, LH, and estradiol

      • becomes the preovulatory follicle

      • other antral follicle degenerate (atresia)

    • later in the phase, LH spikes

      • induces primary oocyte to complete meiosis I

      • causes follicular fluids to rapidly build up

      • triggers WBCs to weaken follicle wall

    • follicle detaches and releases chemicals that encourage the uterine tube to move closer and surround the follicle

  • ovulation (around day 14)

    • mature follicle swells, then ruptures ad releases egg into the abdominal cavoty

    • fimbriae sweep over burst follicle to pick up secondary oocyte and move into the uterine tube

    • muscle contractions of the tube push the secondary oocyte towards the uterus

      • if encounters sperm → fertilization

      • if doesnt encounter sperm → reabsorbed

  • luteal phase (~ 2 weeks; day 15-28)

    • starts after ovulation and ends when mentruation begins (unless pregnant)

    • remainder of the dominant follicle becomes the corpus luteum

      • produces progesterone and some estrogen

    • prepares the uterus for pregnancy

      • thickens uterine linging (progesterone)

      • thickens cervical mucus to prevent bacteria

    • if a fertilized ovum impants, it will start secreting human chorioonic gonadotropin (HCG) to keep the corpus luteum functioning

    • if not pregnant:

      • hormone levels decline

        • negative feedback on pituitary

          • corpus luteum shrinks around day 22-26

            • ceases functioning and becomes known as the corpus albicans

      • uterine lining shed during mentrual cycle

        • marks the end of the luteal phase

Mentrual Cycle

  • occurs in the uterus concurrently with the ovarian cycle

    • involves menstuation, which occurs during the follicular phase (following the luteal phase)

  • buildup, breakdown, and vaginal discharge of the endometrium (4 phases)

  • begins during puberty and lasts until menopause

  • four phases of the mentrual cycle:

    • proliferative phase → rebuilding of the endometrium stimulated by estrogen

    • secretory phase → progesterone stimulates thickening of the endometrium

    • premenstrual phase → endometrial degeneration

    • menstual phase → discharge of endometrium and menstrual fluids

      • fibrinolysin prevents clotting in this phase

Puberty

  • puberty - period in which adolescents reach sexual maturity

    • secondary sex characteristics develop externally as the breasts, ovaries, uterus, and vagina mature

      • enlarging breasts, widening hips, growth of pubic and axillary hair, and general growth spurt

    • regulated by LH and FSH

      • levels increase in early puberty

    • regulate GH secretion

  • starts earlier and peaks sooner in girls

  • occurs in the same stages as males

  • onset influenced by:

    • genetics/epigenetics

      • mother’s onset is a strong predictor

      • smoking while pregnant can lead to early onset

    • nutrition/general health

      • better nutrition/health typically earlier onset

      • leptin stimulates GnRH

        • obese onset earlier

        • underweight onset later

      • stress suc as a family conflicts tied to earlier onset

Menopause

  • typically occurs around age 51 or 52

    • 5% of women with early menopause between ages of 40 and 45

    • 1% of women experience premature menopause before age 40

  • perimenopause occurs prior to the onset of menopause (often between 40 and 44)

    • ovaries gradually begin producing less estrogen, but kepp releasing oocytes until menopause begins

    • typically lasts about 4 years

  • some women continue experiencing symptoms post-menopause

  • loss of function in the ovarian follicles and subsequent decline in estrogen levels

    • diminished number of primary follicles leaves nothing to respond to FSH

    • LH surges cease → no ovulation → less estrogen produced → cessation of menes

    • less estradiol and inhibn disrupts negative feedback to the hypothalamus → increase in production of FSH and LH

  • loss of estrogen affects many systems:

    • ovaries, breasts, and mucosal layer of the vagina may being to atrophy

      • dry/itchy vagina, stress incontinence or increased frequency/urgency with urination, dyspareunia (painful intercourse), dysuria (painful urination)

    • increased osteoclastic activity → loss of bone mass and decrease in height

    • induces vasoconstriction, increased rigidity for arteries, and increases LDL levels

    • hot flashes, night sweats, heart palpitations, elevated bp, weight gain, migraines, and mood/sleep disturbances

  • various supports treatments

    • short term hormone therapies such as combination estrogen/progestin (if uterus is healthy) or estrogen alone (if no uterus because may incluce cancer)

    • selective estrogen receptors modulators (“SERMs”) to moduate estrogen without stimulating endometrial growth (cancer risk)

    • non-hormone short-term treatments such as SSRIs or gabapentin

    • treatments for osteoporosis, such as osteoclastic activity disrupters, ca/vitamin D supplements, and increasing intake of estrogen-related foods (e.g soy)

    • treatments for vasomotor symptoms, such as vitamin E and olmega-3 fatty acid supplements