The Reproductive System: Part C 27 The Reproductive System: Part C

Establishing the Ovarian Cycle During childhood, until puberty Ovaries secrete small amounts of estrogens Estrogen inhibits release of GnRH

Establishing the Ovarian Cycle At puberty Leptin from adipose tissue decreases the estrogen inhibition GnRH, FSH, and LH are released In about four years, an adult cyclic pattern is achieved and menarche occurs

Hormonal Interactions During a 28-Day Ovarian Cycle Day 1: GnRH  release of FSH and LH FSH and LH  growth of several follicles, and estrogen release  estrogen levels Inhibit the release of FSH and LH Stimulate synthesis and storage of FSH and LH Enhance further estrogen output

Hormonal Interactions During a 28-Day Ovarian Cycle Estrogen output by the vesicular follicle increases High estrogen levels have a positive feedback effect on the pituitary at midcycle Sudden LH surge at day 14

Hormonal Interactions During a 28-Day Ovarian Cycle Effects of LH surge Completion of meiosis I (secondary oocyte continues on to metaphase II) Triggers ovulation Transforms ruptured follicle into corpus luteum

Hormonal Interactions During a 28-Day Ovarian Cycle Functions of corpus luteum Produces inhibin, progesterone, and estrogen These hormones inhibit FSH and LH release Declining LH and FSH ends luteal activity and inhibits follicle development

Hormonal Interactions During a 28-Day Ovarian Cycle Days 26–28: corpus luteum degenerates and ovarian hormone levels drop sharply Ends the blockade of FSH and LH The cycle starts anew

Early and midfollicular phases Hypothalamus Hypothalamus 5 GnRH Positive feedback exerted by large in estrogen output. 4 8 Travels via portal blood 1 Anterior pituitary 1 5 Progesterone Estrogen Inhibin LH surge FSH LH Ruptured follicle 6 2 2 8 Slightly elevated estrogen and rising inhibin levels. 3 7 Thecal cells Granulosa cells Androgens Corpus luteum Mature follicle Ovulated secondary oocyte Convert androgens to estrogens Inhibin 2 Late follicular and luteal phases Early and midfollicular phases Figure 27.19

(a) Fluctuation of gonadotropin levels: Fluctuating LH FSH (a) Fluctuation of gonadotropin levels: Fluctuating levels of pituitary gonadotropins (follicle-stimulating hormone and luteinizing hormone) in the blood regulate the events of the ovarian cycle. Figure 27.20a

(b) Ovarian cycle: Structural changes in the ovarian Primary follicle Vesicular follicle Corpus luteum Degenerating corpus luteum Secondary follicle Ovulation Follicular phase Ovulation (Day 14) Luteal phase (b) Ovarian cycle: Structural changes in the ovarian follicles during the ovarian cycle are correlated with (d) changes in the endometrium of the uterus during the uterine cycle. Figure 27.20b

Uterine (Menstrual) Cycle Cyclic changes in endometrium in response to ovarian hormones Three phases Days 1–5: menstrual phase Days 6–14: proliferative (preovulatory) phase Days 15–28: secretory (postovulatory) phase (constant 14-day length)

Uterine Cycle Menstrual phase Ovarian hormones are at their lowest levels Gonadotropins are beginning to rise Stratum functionalis is shed and the menstrual flow occurs

Uterine Cycle Proliferative phase Estrogen levels prompt generation of new functional layer and increased synthesis of progesterone receptors in endometrium Glands enlarge and spiral arteries increase in number

Uterine Cycle Secretory phase Progesterone levels prompt Further development of endometrium Glandular secretion of glycogen Formation of the cervical mucus plug

(c) Fluctuation of ovarian hormone levels: Estrogens Progesterone (c) Fluctuation of ovarian hormone levels: Fluctuating levels of ovarian hormones (estrogens and progesterone) cause the endometrial changes of the uterine cycle. The high estrogen levels are also responsible for the LH/FSH surge in (a). Figure 27.20c

(d) The three phases of the uterine cycle: Endometrial glands Blood vessels Menstrual flow Functional layer Basal layer Days Menstrual phase Proliferative phase Secretory phase (d) The three phases of the uterine cycle: • Menstrual: Shedding of the functional layer of the endometrium. • Proliferative: Rebuilding of the functional layer of the endometrium. • Secretory: Begins immediately after ovulation. Enrichment of the blood supply and glandular secretion of nutrients prepare the endometrium to receive an embryo. Both the menstrual and proliferative phases occur before ovulation, and together they correspond to the follicular phase of the ovarian cycle. The secretory phase corresponds in time to the luteal phase of the ovarian cycle. Figure 27.20d

If fertilization does not occur Uterine Cycle If fertilization does not occur Corpus luteum degenerates Progesterone levels fall Spiral arteries kink and spasm Endometrial cells begin to die Spiral arteries constrict again, then relax and open wide Rush of blood fragments weakened capillary beds and the functional layer sloughs

Effects of Estrogens Promote oogenesis and follicle growth in the ovary Exert anabolic effects on the female reproductive tract Support the rapid but short-lived growth spurt at puberty

Induce secondary sex characteristics Effects of Estrogens Induce secondary sex characteristics Growth of the breasts Increased deposit of subcutaneous fat (hips and breasts) Widening and lightening of the pelvis

Effects of Estrogens Metabolic effects Maintain low total blood cholesterol and high HDL levels Facilitates calcium uptake

Effects of Progesterone Progesterone works with estrogen to establish and regulate the uterine cycle Effects of placental progesterone during pregnancy Inhibits uterine motility Helps prepare the breasts for lactation

Female Sexual Response Initiated by touch and psychological stimuli The clitoris, vaginal mucosa, and breasts engorge with blood Vestibular gland secretions lubricate the vestibule Orgasm is accompanied by muscle tension, increase in pulse rate and blood pressure, and rhythmic contractions of the uterus

Female Sexual Response Females do not have a refractory period after orgasm and can experience multiple orgasms in a single sexual experience Orgasm is not essential for conception

Sexually Transmitted Infections (STIs) Also called sexually transmitted diseases (STDs) or venereal diseases (VDs) The single most important cause of reproductive disorders

Gonorrhea Bacterial infection of mucosae of reproductive and urinary tracts Spread by contact with genital, anal, and pharyngeal mucosae

Gonorrhea Signs and symptoms Males Urethritis, painful urination, discharge of pus Females 20% display no signs or symptoms Abdominal discomfort, vaginal discharge, or abnormal uterine bleeding Can result in pelvic inflammatory disease and sterility Treatment: antibiotics, but resistant strains are becoming prevalent

Bacterial infection transmitted sexually or contracted congenitally Syphilis Bacterial infection transmitted sexually or contracted congenitally Infected fetuses are stillborn or die shortly after birth Infection is asymptomatic for 2–3 weeks A painless chancre appears at the site of infection and disappears in a few weeks

Syphilis If untreated, secondary signs appear several weeks later for 3–12 weeks, and then disappear: pink skin rash, fever, and joint pain The latent period may or may not progress to tertiary syphilis, characterized by gummas (lesions of the CNS, blood vessels, bones, and skin) Treatment: penicillin

Chlamydia Most common bacterial STI in the United States Responsible for 25–50% of all diagnosed cases of pelvic inflammatory disease Symptoms: urethritis; penile and vaginal discharges; abdominal, rectal, or testicular pain; painful intercourse; irregular menses Can cause arthritis and urinary tract infections in men, and sterility in women Treatment: tetracycline

Viral Infections Genital warts Caused by human papillomavirus (HPV) Second most common STI in the United States Increase the risk of cancers in infected body regions

Caused by human herpes virus type 2 Viral Infections Genital herpes Caused by human herpes virus type 2 Characterized by latent periods and flare-ups Congenital herpes can cause malformations of a fetus Treatment: acyclovir and other antiviral drugs

Developmental Aspects: Determination of Genetic Sex One of the 23 pairs of chromosomes in body cells are sex chromosomes: X and Y Females are XX and each egg has an X chromosome Males are XY, so ~50% of sperm contain X, ~50% contain Y

Developmental Aspects: Determination of Genetic Sex X egg + X sperm  XX (female offspring) X egg + Y sperm  XY (male offspring) The SRY gene on the Y chromosome initiates testes development and maleness

Developmental Aspects: Sexual Differentiation Sexually indifferent stage Gonads begin development in fifth week as gonadal ridges Paramesonephric (Müllerian) ducts (future female ducts) form lateral to the mesonephric (Wolffian) ducts (future male ducts) Primordial germ cells migrate to the gonadal ridges to provide germ cells destined to become spermatogonia or oogonia Gonads begin development in seventh week in males, eighth week in females

sexually indifferent stage Mesonephros Mesonephric (Wolffian) duct Gonadal ridge Paramesonephric (Müllerian) duct Metanephros (kidney) Cloaca 5- to 6-week embryo: sexually indifferent stage Figure 27.21 (1 of 5)

Testes Efferent ductules Epididymis Paramesonephric duct (degenerating) Mesonephric duct forming the ductus deferens Urinary bladder Seminal vesicle Urogenital sinus forming the urethra 7- to 8-week male embryo Figure 27.21 (2 of 5)

Ovaries Paramesonephric duct forming the uterine tube Mesonephric duct (degenerating) Fused paramesonephric ducts forming the uterus Urinary bladder (moved aside) Urogenital sinus forming the urethra and lower vagina 8- to 9-week female fetus Figure 27.21 (3 of 5)

Developmental Aspects: Development of External Genitalia Genital tubercle  penis of male; clitoris of female Urethral fold  urethra of male; labia minora of female Labioscrotal folds  scrotum of male: labia majora of female

Genital tubercle Urethral fold Labioscrotal Anus swelling Tail (cut) Urethral groove (a) Indifferent Figure 27.22a

Approximately 5 weeks Glans penis Labioscrotal Urethral swellings (scrotum) Urethral folds Anus Glans penis Penis Scrotum Anus (b) Male development Figure 27.22b

Genital tubercle Urethral fold Labioscrotal Anus swelling Tail (cut) Urethral groove (a) Indifferent Figure 27.22a

(c) Female development Approximately 5 weeks Glans clitoris Urogenital sinus Labioscrotal swellings (labia majora) Urethral folds (labia minora) Anus Glans clitoris Labia majora Labia minora Anus (c) Female development Figure 27.22c

Development Aspects: Descent of the Gonads About two months before birth Testosterone stimulates the migration of the testes toward the scrotum Ovaries also descend, but are stopped by the broad ligament at the pelvic brim Gubernaculum: fibrous cord from each testis to the scrotum or from ovary to labium majus; guides the descent

At birth: male development Urinary bladder Seminal vesicle Prostate Bulbourethral gland Ductus deferens Urethra Efferent ductules Epididymis Testis Penis At birth: male development Figure 27.21 (4 of 5)

At birth: Female development Uterine tube Ovary Uterus Urinary bladder (moved aside) Vagina Urethra Hymen Vestibule At birth: Female development Figure 27.21 (5 of 5)

Development Aspects: Puberty In response to rising levels of gonadal hormones Reproductive organs grow to adult size and become functional Secondary sex characteristics appear Earliest time that reproduction is possible

Menopause Has occurred when menses have ceased for an entire year There is no equivalent to menopause in males

Declining estrogen levels  Menopause Declining estrogen levels  Atrophy of reproductive organs and breasts Irritability and depression in some Hot flashes as skin blood vessels undergo intense vasodilation Gradual thinning of the skin and bone loss Increased total blood cholesterol levels and falling HDL