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

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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

•      5th week – gonadal ridges form and paramesonephric (Mόllerian) 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 7th week; female in the 8th 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

•    Females – enlarging of the breasts, menarche, and dependable ovulation

Menopause

•      Ovulation and menses cease entirely

•      Without sufficient estrogen, reproductive organs and breasts atrophy

•    Irritability and depression result

•    Skin blood vessels undergo intense vasodilation (hot flashes occur)

•    Gradual thinning of the skin and bone loss

•      Males have no equivalent to menopause