Chapter Notes for Lecture: E.N. Marieb, HUMAN ANATOMY & PHYSIOLOGY,5^TH Edition, , Benjamine Cummings Publisher, 2001 Prepare from : V.A. Austin’s PowerPpoint Presentation (ISBN: 0-8053-5469-7), CD ROM: Pearson Education, Inc. , 2003

Chapter 28

The Reproductive System

Reproductive System

• Primary sex organs (gonads) – testes in males, ovaries in females

• Gonads produce sex cells called gametes and secrete sex hormones

• Accessory reproductive organs – ducts, glands, and external genitalia

• Sex hormones – androgens (males), and estrogens and progesterone (females)

• Sex hormones play roles in:

• The development and function of the reproductive organs

• Sexual behavior and drives

• The growth and development of many other organs and tissues

Male Reproductive System

• The male gonads (testes) produce sperm and lie within the scrotum

• Sperm are delivered to the exterior through a system of ducts: epididymis, ductus deferens, and the urethra

• Accessory sex glands:

• Empty their secretions into the ducts during ejaculation

• Include the seminal vesicles, prostate gland, and bulbourethral glands

The Scrotum

• Sac of skin and superficial fascia that hangs outside the abdominopelvic cavity at the root of the penis

• Contains paired testicles separated by a midline septum

• Its external positioning keeps the testes 3°C lower than core body temperature (needed for sperm production)

• Intrascrotal temperature is kept constant by two sets of muscles:

• Dartos – smooth muscle that wrinkles scrotal skin

• Cremaster – bands of skeletal muscle that elevate the testes

The Testes

• Each testis is surrounded by two tunics:

• The tunica vaginalis, derived from peritoneum

• The tunica albuginea, the fibrous capsule of the testis

• Septa divide the testis into 250-300 lobules, each containing 1-4 seminiferous tubules

• Seminiferous tubules:

• Produce the sperm

• Converge to form the tubulus rectus

• The straight tubulus rectus conveys sperm to the rete testis

• From the rete testis, the sperm:

• Leave the testis via efferent ductules

• Enter the epididymis

• Surrounding the seminiferous tubules are interstitial cells that produce androgens

• Testicular arteries branch from the abdominal aorta and supply the testes

• Testicular veins arise from the pampiniform plexus

• Spermatic cord – encloses PNS and SNS nerve fibers, blood vessels, and lymphatics that supply the testes

The Penis

• A copulatory organ designed to deliver sperm into the female reproductive tract

• Consists of an attached root and a free shaft that ends in the glans penis

• Prepuce, or foreskin – cuff of skin covering the distal end of the penis

• Circumcision – surgical removal of the foreskin after birth

• Internal penis – the urethra and three cylindrical bodies of erectile tissue

• Erectile tissue – spongy network of connective tissue and smooth muscle riddled with vascular spaces

• Erection – during sexual excitement, the erectile tissue fills with blood causing the penis to enlarge and become rigid

• Corpus spongiosum – surrounds the urethra and expands to form the glans and bulb of the penis

• Corpora cavernosa – paired dorsal erectile bodies bound by fibrous tunica albuginea

• Crura – proximal end of the penis surrounded by the ischiocavernosus muscle; anchors the penis to the pubic arch

Epididymis

• Its head joins the efferent ductules and caps the superior aspect of the testis

• The duct of the epididymis has stereocilia that:

• Absorb testicular fluid

• Pass nutrients to the sperm

• Nonmotile sperm enter, pass through its tubes and become motile

• Upon ejaculation, the epididymis contracts expelling sperm into the ductus deferens

Ductus Deferens (Vas Deferens)

• Runs from the epididymis through the inguinal canal into the pelvic cavity

• Its terminus expands to form the ampulla and then joins the duct of the seminal vesicle to form the ejaculatory duct

• Propels sperm from the epididymis to the urethra

• Vasectomy – cutting and ligating the ductus deferens, which is a nearly 100% effective form of birth control

Urethra

• Conveys both urine and semen (at different times)

• Consists of three regions

• Prostatic – portion surrounded by the prostate

• Membranous – lies in the urogenital diaphragm

• Spongy, or penile – runs through the penis and opens to the outside at the external urethral orifice

Accessory Glands: Seminal Vesicles

• Lie on the posterior wall of the bladder and secrete 60% of the volume of semen

• Semen – viscous alkaline fluid containing fructose, ascorbic acid, coagulating enzyme (vesiculase), and prostaglandins

• Joins the ductus deferens to form the ejaculatory duct

• Sperm and seminal fluid mix in the ejaculatory duct and enter the prostatic urethra during ejaculation

Accessory Glands: Prostate Gland

• Doughnut-shaped gland that encircles part of the urethra inferior to the bladder

• Its milky, slightly acid fluid, which contains citrate, enzymes, and prostate-specific antigen (PSA), accounts for one-third of the semen volume

• Plays a role in the activation of sperm

• Enters the prostatic urethra during ejaculation

Accessory Glands: Bulborethral Glands (Cowper’s Glands)

• Pea-sized glands inferior to the prostate

• Produce thick, clear mucus prior to ejaculation that neutralizes traces of acidic urine in the urethra

Semen

• Milky white, sticky mixture of sperm and accessory gland secretions

• Provides a transport medium and nutrients (fructose), protects and activates sperm, and facilitates their movement

• Prostaglandins in semen:

• Decrease the viscosity of mucus in the cervix

• Stimulate reverse peristalsis in the uterus

• Facilitate the movement of sperm through the female reproductive tract

• The hormone relaxin enhances sperm motility

• The relative alkalinity of semen neutralizes the acid environment found in the male urethra and female vagina

• Seminalplasmin – antibiotic chemical that destroys certain bacteria

• Clotting factors coagulate semen immediately after ejaculation, then fibrinolysin liquefies the sticky mass

• Only 2-5 ml of semen are ejaculated, but it contains 50-130 million sperm/mL

Male Sexual Response: Erection

• Enlargement and stiffening of the penis from engorgement of erectile tissue with blood

• During sexual arousal, a PNS reflex promotes the release of nitric oxide

• Nitric oxide causes erectile tissue to fill with blood

• Expansion of the corpora cavernosa:

• Compresses their drainage veins

• Retards blood outflow and maintains engorgement

• The corpus spongiosum functions in keeping the urethra open during ejaculation

Male Sexual Response

• Erection is initiated by sexual stimuli including:

• Touch and mechanical stimulation of the penis

• Erotic sights, sounds, and smells

• Erection can be induced or inhibited solely by emotional or higher mental activity

• Impotence – inability to attain erection

Ejaculation

• The propulsion of semen from the male duct system

• At ejaculation, sympathetic nerves serving the genital organs cause:

• Reproductive ducts and accessory organs to contract and empty their contents

• Bladder sphincter muscle to constrict, preventing the expulsion of urine

• Bulbospongiosus muscles to undergo a rapid series of contractions

• Propulsion of semen from the urethra

Spematogenesis

• The sequence of events that produces sperm in the seminiferous tubules of the testes

• Each cell has two sets of chromosomes (one maternal, one paternal) and is said to be diploid
(2n chromosomal number)

• Humans have 23 pairs of homologous chromosomes

• Gametes only have 23 chromosomes and are said to be haploid (n chromosomal number)

• Gamete formation is by meiosis, in which the number of chromosomes is halved (from 2n to n)

Meiosis

• Two nuclear divisions, meiosis I and meiosis II, halve the number of chromosomes in the four daughter cells

• Chromosomes replicate prior to meiosis I

• In meiosis I, homologous pairs of chromosomes undergo synapsis and form tetrads with their homologous partners

• Crossover, the exchange of genetic material among tetrads, occurs during synapsis

Meiosis I

• Tetrads line up at the spindle equator during metaphase I

• In anaphase I, homologous chromosomes still composed of joined sister chromatids are distributed to opposite ends of the cell

• At the end of meiosis I each daughter cell has:

• Two copies of either a material or paternal homologous pair of chromosomes

• A 2n amount of DNA and haploid number of chromosomes

Meiosis II

• Mirrors mitosis except that chromosomes are not replicated before it begins

• Meiosis accomplishes two tasks:

• It reduces the chromosome number by half (2n to n)

• It introduces genetic variability

Comparison of Mitosis and Meiosis

Spermatogenesis

• Cells making up the walls of seminiferous tubules are in various stages of cell division

• These spermatogenic cells give rise to sperm in a series of events

• Mitosis of spermatogonia, forming spermatocytes

• Spermatids formed from spermatocytes by meiosis

• Spermiogenesis – spermatids forming sperm

Mitosis of Spermatogonia

• Spermatogonia – outermost cells in contact with the epithelial basal lamina

• Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells

• Type A cells remain at the basement membrane and maintain the germ line

• Type B cells move toward the lumen and become primary spermatocytes

Spermatocytes to Spermatids

• Primary spermatocytes undergo meiosis I, forming two haploid cells called secondary spermatocytes

• Secondary spermatocytes undergo meiosis II and their daughter cells are called spermatids

• Spermatids are small round cells seen close to the lumen of the tubule

Spermatogenesis: Spermatids to Sperm

• Late in spermatogenesis, spermatids are haploid but are nonmotile

• Spermiogenesis – spermatids lose excess cytoplasm and form a tail, becoming sperm

• Sperm have three major regions

• Head – contains DNA and has a helmetlike acrosome containing hydrolytic enzymes that allow the sperm to penetrate and enter the egg

• Midpiece – contains mitochondria spiraled around the tail filaments

• Tail – a typical flagellum produced by a centriole

Sustentacular Cells (Sertoli Cells)

• Cells that extend from the basal lamina to the lumen of the tubule that surrounds developing cells

• They are bound together with tight junctions forming an unbroken layer with the seminiferous tubule, dividing it into two compartments

• The basal compartment – contains spermatogonia and primary spermatocytes

• Adluminal compartment – contains meiotically active cells and the tubule lumen

Sustentacular Cells

• Their tight junctions form a blood-testis barrier

• This prevents sperm antigens from escaping through the basal lamina into the blood

• Since sperm are not formed until puberty, they are absent during thymic education

• Spermatogonia are recognized as “self” and are influenced by bloodborne chemical messengers that prompt spermatogenesis

Adluminal Compartment Activities

• Spermatocytes and spermatids are nearly enclosed in sustentacular cells, which:

• Deliver nutrients to dividing cells

• Move them along to the lumen

• Secrete testicular fluid that provides the transport medium for sperm

• Dispose of excess cytoplasm sloughed off during maturation to sperm

• Produce chemical mediators that help regulate spermatogenesis

Brain-Testicular Axis

• Hormonal regulation of spermatogenesis and testicular androgen production involving the hypothalamus, anterior pituitary gland, and the testes

• Testicular regulation involves three sets of hormones:

• GnRH, which indirectly stimulates the testes through:

• Follicle stimulating hormone (FSH)

• Luteinizing hormone (LH)

• Gonadotropins, which directly stimulate the testes

• Testicular hormones, which exert negative feedback controls

Hormonal Regulation of Testicular Function

• The hypothalamus releases gonadotropin-releasing hormone (GnRH)

• GnRH stimulates the anterior pituitary to secrete FSH and LH

• FSH causes sustentacular cells to release androgen-binding protein (ABP)

• LH stimulates interstitial cells to release testosterone

• ABP binding of testosterone enhances spermatogenesis

• Feedback inhibition on the hypothalamus and pituitary results from:

• Rising levels of testosterone

• Increased inhibin

Mechanism and Effects of Testosterone Activity

• Testosterone is synthesized from cholesterol

• It must be transformed to exert its effects on some target cells

• Prostate – it is converted into dihydrotestosterone (DHT) before it can bind within the nucleus

• Neurons – it is converted into estrogen to bring about stimulatory effects

• Testosterone targets all accessory organs and its deficiency causes these organs to atrophy

Male Secondary Sex Characteristics

• Male hormones make their appearance at puberty and induce changes in nonreproductive organs, including

• Appearance of pubic, axillary, and facial hair

• Enhanced growth of the chest and deepening of the voice

• Skin thickens and becomes oily

• Bones grow and increase in density

• Skeletal muscles increase in size and mass

• Testosterone is the basis of libido in both males and females

Female Reproductive Anatomy

• Ovaries are the primary female reproductive organs

• Make female gametes

• Secrete female sex hormones (estrogen and progesterone)

• Accessory ducts include uterine tubes, uterus, and vagina

• Internal genitalia – ovaries and the internal ducts

• External genitalia – external sex organs

The Ovaries

• Paired organs on each side of the uterus held in place by several ligaments

• Ovarian – anchors the ovary medially to the uterus

• Suspensory – anchors the ovary laterally to the pelvic wall

• Mesovarium – suspends the ovary in between

• Broad ligament – contains the suspensory ligament and the mesovarium

• Blood supply – ovarian arteries and the ovarian branch of the uterine artery

• They are surrounded by a fibrous tunica albuginea, which is covered by a misnamed layer of epithelial cells called the germinal epithelium

• Embedded in the ovary cortex are ovarian follicles

• Each follicle consists of an immature egg called an oocyte

• Cells around the oocyte are called:

• Follicle cells (one cell layer thick)

• Granulosa cells (when more than one layer is present)

• Primordial follicle – one layer of squamouslike follicle cells surrounds the oocyte

• Primary follicle – two or more layers of cuboidal granulosa cells enclose the oocyte

• Secondary follicle – has a fluid-filled space between granulosa cells that coalesces to form a central antrum

• Graafian follicle – secondary follicle at its most mature stage that bulges from the surface of the ovary

• Ovulation – ejection of the oocyte from the ripening follicle

• Corpus luteum – ruptured follicle after ovulation

Uterine Tubes (Fallopian Tubes) and Oviducts

• Receive the ovulated oocyte and provide a site for fertilization

• Empty into the superolateral region of the uterus via the isthmus

• Expand distally around the ovary forming the ampulla

• The ampulla ends in the funnel-shaped, ciliated infundibulum containing fingerlike projections called fimbriae

• The uterine tubes have no contact with the ovaries and the ovulated oocyte is cast into the peritoneal cavity

• Beating cilia on the fimbriae create currents to carry the oocyte into the uterine tube

• The oocyte is carried toward the uterus by peristalsis and ciliary action

• Nonciliated cells keep the oocyte and the sperm nourished and moist

• Mesosalpinx – visceral peritoneum that support the uterine tubes

Uterus

• Hollow, thick-walled organ located in the pelvis anterior to the rectum and posterosuperior to the bladder

• Body – major portion of the uterus

• Fundus – rounded region superior to the entrance of the uterine tubes

• Isthmus – narrowed region between the body and cervix

• Cervix – narrow neck which projects into the vagina inferiorly

• Cervical canal – cavity of the cervix that communicates with:

• The vagina via the external os

• The uterine body via the internal os

• Cervical glands secrete mucus that covers the external os and blocks sperm entry except during midcycle

Supports of the Uterus

• Mesometrium – portion of the broad ligament that supports the uterus laterally

• Lateral cervical ligaments – extend from the cervix and superior part of the vagina to the lateral walls of the pelvis

• Uterosacral ligaments – paired ligaments that secure the uterus to the sacrum

• Round ligaments – bind the anterior wall to the labia majora

Peritoneal Pouches

• Several cul-de-sacs of peritoneum exist around the uterus

• Vesicouterine pouch – lies between the bladder and the uterus

• Rectouterine pouch – lies between the rectum and the uterus

Uterine Wall

• Composed of three layers

• Perimetrium – outermost serous layer; the visceral peritoneum

• Myometrium – middle layer; interlacing layers of smooth muscle

• Endometrium – mucosal lining of the uterine cavity

Endometrium

• Has numerous uterine glands that change in length as the endometrial thickness changes

• Stratum functionalis:

• Undergoes cyclic changes in response to ovarian hormones

• Is shed during menstruation

• Stratum basalis:

• Forms a new functionalis after menstruation ends

• Does not respond to ovarian hormones

Uterine Vascular Supply

• Uterine arteries – arise from the internal iliacs, ascend the sides of the uterus and send branches into the uterine wall

• Arcuate arteries – branches of the uterine arteries in the myometrium that give rise to radial branches

• Radial branches – descend into the endometrium and give rise to:

• Spiral arteries to the stratum functionalis

• Straight arteries to the stratum basalis

• Degeneration and regeneration of spiral arteries causes the functionalis to shed during menstruation

• Veins of the endometrium are thin-walled with occasional sinusoidal enlargements

Vagina

• Thin-walled tube lying between the bladder and the rectum, extending from the cervix to the exterior of the body

• The urethra is embedded in the anterior wall

• Provides a passageway for birth, menstrual flow, and is the organ of copulation

• Wall consists of three coats: fibroelastic adventitia, smooth muscle muscularis, and a stratified squamous mucosa

• Mucosa near the vaginal orifice forms an incomplete partition called the hymen

• Vaginal fornix – upper end of the vagina surrounding the cervix

External Genitalia: Vulva (Pudendum)

• Lies external to the vagina and includes the mons pubis, labia, clitoris, and vestibular structures

• Mons pubis – round, fatty area overlying the pubic symphysis

• Labia majora – elongated, hair-covered, fatty skin folds homologous to the male scrotum

• Labia minora – hair-free skin folds lying within the labia major: homologous to the ventral penis

• Greater vestibular glands

• Pea-size glands flanking the vagina

• Homologous to the bulbourethral glands

• Keep the vestibule moist and lubricated

• Clitoris

• Erectile tissue hooded by the prepuce

• Homologous to the penis

• Perineum

• Diamond-shaped region between the pubic arch and coccyx

• Bordered by the ischial tuberosities laterally

Mammary Glands

• Modified sweat glands consisting of 15-25 lobes that radiate around and open at the nipple

• Areola – pigmented skin surrounding the nipple

• Suspensory ligaments attach the breast to underlying muscle fascia

• Lobes contain glandular alveoli that produce milk in lactating women

• Compound alveolar glands pass milk to lactiferous ducts, which open to the outside

Breast Cancer

• Usually arises from the epithelial cells of the ducts

• Risk factors include:

• Early onset of menses or late menopause

• No pregnancies or the first pregnancy late in life

• Previous history of breast cancer or family history of breast cancer

• Hereditary factors include mutations to a pair of genes BRCA1 and BRCA2

• 70% of women with breast cancer had no known risk factors

Breast Cancer: Detection and Treatment

• Early detection is by self-examination and mammography

• Treatment depends upon the characteristics of the lesion

• Radiation, chemotherapy, and surgery followed by irradiation and chemotherapy

• Today, lumpectomy is the surgery used rather than radical mastectomy

Oogenesis

• Production of female sex cells by meiosis

• In the fetal period, oogonia (2n ovarian stem cells) multiply by mitosis and store nutrients

• Primordial follicles appear as oogonia are transformed into primary oocytes

• Primary oocytes begin meiosis but stall in prophase I

Oogenesis: Puberty

• At puberty, one activated primary oocyte produces two haploid cells

• The first polar body

• The secondary oocyte

• The secondary oocyte arrests in metaphase II and is ovulated

• If penetrated by sperm:

• The second oocyte completes meiosis II, yielding:

• One large ovum (the functional gamete)

• A tiny second polar body

Ovarian Cycle

• Monthly series of events associated with the maturation of an egg

• Follicular phase – period of follicle growth
(days 1–14)

• Luteal phase – period of corpus luteum activity
(days 14–28)

• Ovulation occurs midcycle

Follicular Phase

• The primordial follicle becomes a primary follicle

• Primary follicle becomes a secondary follicle

• The theca folliculi and granulosa cells cooperate to produce estrogens

• The zona pellucida forms around the oocyte

• The antrum is formed

• The secondary follicle becomes a vesicular follicle

• The antrum expands and isolates the oocyte and the corona radiata

• The full size follicle (vesicular follicle) bulges from the external surface of the ovary

• The primary oocyte completes meiosis I, and the stage is set for ovulation

Ovulation

• Ovulation occurs when the ovary wall ruptures and expels the secondary oocyte

• Mittelschmerz – a tinge of pain sometimes felt at ovulation

• 1-2% of ovulations release more than one secondary oocyte, which if fertilized, results in fraternal twins

Luteal Phase

• After ovulation, the ruptured follicle collapses, granulosa cells enlarge, and along with internal thecal cells, form the corpus luteum

• The corpus luteum secretes progesterone and estrogen

• If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving a scar (corpus albicans)

• If pregnancy does occur, the corpus luteum produces hormones until the placenta takes over that role
(at about 3 months)

Establishing the Ovarian Cycle

• During childhood, ovaries grow and secrete small amounts of estrogens that inhibit the hypothalamic release of GnRH

• As puberty nears, GnRH is released; FSH and LH are released by the pituitary, which act on the ovaries

• These events continue until an adult cyclic pattern is achieved and menarche occurs

Hormonal Interactions During the Ovarian Cycle

• Day 1 – GnRH stimulates the release of FSH and LH

• FSH and LH stimulate follicle growth and maturation, and low-level estrogen release

• Rising estrogen levels:

• Inhibit the release of FSH and LH

• Prod the pituitary to synthesize and accumulate these gonadotropins

• Estrogen levels increase and high estrogen levels have a positive feedback effect on the pituitary, causing a sudden surge of LH

• The LH spike simulates the primary oocyte to complete meiosis I, and the secondary oocyte continues on to metaphase II

• Day 14 – LH triggers ovulation

• LH transforms the ruptured follicle into a corpus luteum, which produces inhibin, progesterone, and estrogen

• These hormones shut off FSH and LH release and declining LH ends luteal activity

• Days 26-28 – decline of the ovarian hormones

• Ends the blockade of FSH and LH

• The cycle starts anew

Uterine (Menstrual) Cycle

• Series of cyclic changes that the uterine endometrium goes through each month in response to ovarian hormones in the blood

• Days 1-5: Menstrual phase – uterus sheds all but the deepest part of the endometrium

• Days 6-14: Proliferative phase – endometrium rebuilds itself

• Days 15-28: Secretory phase – Endometrium prepares for implantation of the embryo

Menses

• If fertilization does not occur, progesterone levels fall, depriving the endometrium of hormonal support

• Spiral arteries kink and go into spasms and endometrial cells begin to die

• The functional layer begins to digest itself

• Spiral arteries constrict one final time then suddenly relax and open wide

• The rush of blood fragments weakened capillary beds and the functional layer sloughs

Gonadotropins, Hormones, and the Ovarian and Uterine Cycles

Extrauterine Effects of Estrogens and Progesterone

• Estrogen levels rise during puberty

• Promote oogenesis and follicle growth in the ovary

• Exert anabolic effects on the female reproductive tract

• Uterine tubes, uterus, and vagina grow larger and become functional

• Uterine tubes and uterus exhibit enhanced motility

• Vaginal mucosa thickens and external genitalia mature

Estrogen-Induced Secondary Sex Characteristics

• Growth of the breasts

• Increased deposition of subcutaneous fat, especially in the hips and breasts

• Widening and lightening of the pelvis

• Growth of axillary and pubic hair

Female Sexual Response

• The clitoris, vaginal mucosa, and breasts engorge with blood

• Vestibular glands lubricate the vestibule and facilitates entry of the penis

• Orgasm – accompanied by muscle tension, increase in pulse rate and blood pressure, and rhythmical contractions of the uterus

• 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 Diseases: Gonorrhea

• Bacterial infection spread by contact with genital, anal, and pharyngeal mucosal surfaces

• Signs and symptoms:

• In males – painful urination, discharge of pus from the penis

• In females – none (20%), abdominal discomfort, vaginal discharge, abnormal uterine bleeding

• Left untreated, can result in pelvic inflammatory disease

• Treatment: antibiotics, but resistant strains are becoming more prevalent

Sexually Transmitted Diseases: Syphilis

• Bacterial infection transmitted sexually or contracted congenitally

• Infected fetuses are stillborn or die shortly after birth

• A painless chancre appears at the site of infection and disappears in a few weeks

• Secondary syphilis shows signs of pink skin rash, fever, and joint pain

• A latent period follows, which may progress to tertiary syphilis characterized by gummas (CNS, blood vessel, bone, and skin lesions)

• Treatment: penicillin

Sexually Transmitted Diseases: Chlamydia

• Most common STD in the U.S.

• Responsible for 25–50% of all diagnosed cases of pelvic inflammatory disease

• Symptoms include urethritis; penile and vaginal discharges; abdominal, rectal, or testicular pain; painful intercourse; and irregular menses

• Can cause arthritis and urinary tract infections in men, and sterility in women

• Treatment is with tetracycline

Sexually Transmitted Diseases: Viral Infections

• Genital warts – caused by human papillomaviruses (HPV); infections increase the risk of penile, vaginal, anal, and cervical cancers

• Genital herpes – caused by Epstein-Barr virus type 2 and characterized by latent periods and flare-ups

• Congenital herpes can cause malformations of a fetus

• Has been implicated with cervical cancer

• Treatment: acyclovir and other antiviral drugs

Developmental Aspects: Genetic Sex Determination

• Genetic sex is determined by the sex chromosomes each gamete contains

• There are two types of sex chromosomes: X and Y

• Females have two X chromosomes; males have one X and one Y

• Hence, all eggs have an X chromosome; half the sperm have an X, and the other half a Y

• A single gene on the Y chromosome, the SRY gene, initiates testes development and determines maleness

Developmental Aspects

• 5^th week – gonadal ridges form and paramesonephric (Müllerian) ducts form in females, mesonephric (Wolffian) ducts develop in males

• Shortly later, primordial germ cells develop and seed the developing gonads destined to become spermatogonia or oogonia

• Male structures begin development in the 7^th week; female in the 8^th week

• External genitalia, like gonads, arise from the same structures in both sexes

Development of External Genitalia: Male

• Under the influence of testosterone

• Genital tubercle enlarges forming the penis

• Urethral groove elongates and closes completely

• Urethral folds give rise to the penile urethra

• Labioscrotal swellings develop into the scrotum

Development of External Genitalia: Female

• In the absence of testosterone

• Genital tubercle gives rise to the clitoris

• The urethral groove remains open as the vestibule

• The urethral folds become labia minora

• The labioscrotal swellings become labia majora

Development Aspects: Descent of the Gonads

• About 2 months before birth and stimulated by testosterone, the testes leave the pelvic cavity and enter the scrotum

• Gubernaculum – fibrous cord that extends from the testes to the scrotum

• Spermatic cord – blood vessels, nerves, and fascial layers that help suspend the testes

• Ovaries also descend, but are stopped by the broad ligament at the pelvic brim

Developmental Aspects: Puberty

• Reproductive organs grow to adult size and become functional

• Secondary sex characteristics appear

• Characteristics of puberty

• Males – enlargement of the testes and scrotum, appearance of axillary and facial hair, and growth of the penis