Reproductive System Primary sex organs (gonads) – testes in males, ovaries in females Primary sex organs (gonads) – testes in males, ovaries in females.

Reproductive SystemReproductive System

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

Gonads produce sex cells called gametes and Gonads produce sex cells called gametes and secrete sex hormonessecrete sex hormones

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

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

Reproductive SystemReproductive System

Sex hormones play roles in:Sex hormones play roles in: The development and function of the reproductive The development and function of the reproductive

organsorgans Sexual behavior and drivesSexual behavior and drives The growth and development of many other organs The growth and development of many other organs

and tissuesand tissues

Male Reproductive SystemMale Reproductive System

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

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

Accessory sex glands:Accessory sex glands: Empty their secretions into the ducts during ejaculation Empty their secretions into the ducts during ejaculation Include the seminal vesicles, prostate gland, and Include the seminal vesicles, prostate gland, and

bulbourethral glandsbulbourethral glands

The ScrotumThe Scrotum

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

Contains paired testicles separated by a Contains paired testicles separated by a midline septummidline septum

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

The ScrotumThe Scrotum

Intrascrotal temperature is kept constant by Intrascrotal temperature is kept constant by two sets of muscles:two sets of muscles: Dartos – smooth muscle that wrinkles scrotal skinDartos – smooth muscle that wrinkles scrotal skin Cremaster – bands of skeletal muscle that elevate Cremaster – bands of skeletal muscle that elevate

the testesthe testes

The TestesThe Testes

Each testis is surrounded by two tunics: Each testis is surrounded by two tunics: The tunica vaginalis, derived from peritoneumThe tunica vaginalis, derived from peritoneum The tunica albuginea, the fibrous capsule of the The tunica albuginea, the fibrous capsule of the

testistestis Septa divide the testis into 250-300 lobules, Septa divide the testis into 250-300 lobules,

each containing 1-4 seminiferous tubuleseach containing 1-4 seminiferous tubules

The TestesThe Testes

Seminiferous tubules:Seminiferous tubules: Produce the spermProduce the sperm Converge to form the tubulus rectusConverge to form the tubulus rectus

The straight tubulus rectus conveys sperm to The straight tubulus rectus conveys sperm to the rete testisthe rete testis

The TestesThe Testes

From the rete testis, the sperm:From the rete testis, the sperm: Leave the testis via efferent ductulesLeave the testis via efferent ductules Enter the epididymisEnter the epididymis

Surrounding the seminiferous tubules are Surrounding the seminiferous tubules are interstitial cells that produce androgensinterstitial cells that produce androgens

The TestesThe Testes

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

Testicular veins arise from the pampiniform Testicular veins arise from the pampiniform plexus plexus

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

The PenisThe Penis

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

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

Prepuce, or foreskin – cuff of skin covering Prepuce, or foreskin – cuff of skin covering the distal end of the penisthe distal end of the penis Circumcision – surgical removal of the foreskin Circumcision – surgical removal of the foreskin

after birthafter birth

The PenisThe Penis

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

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

The PenisThe Penis Erection – during sexual excitement, the Erection – during sexual excitement, the

erectile tissue fills with blood causing the penis erectile tissue fills with blood causing the penis to enlarge and become rigidto enlarge and become rigid

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

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

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

The PenisThe Penis

Figure 27.4

EpididymisEpididymis Its head joins the efferent ductules and caps the Its head joins the efferent ductules and caps the

superior aspect of the testissuperior aspect of the testis The duct of the epididymis has stereocilia that:The duct of the epididymis has stereocilia that:

Absorb testicular fluidAbsorb testicular fluid Pass nutrients to the spermPass nutrients to the sperm

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

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

Ductus Deferens and Ejaculatory Ductus Deferens and Ejaculatory DuctDuct

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

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

Propels sperm from the epididymis to the Propels sperm from the epididymis to the urethraurethra

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

UrethraUrethra

Conveys both urine and semen (at different Conveys both urine and semen (at different times)times)

Consists of three regions Consists of three regions Prostatic – portion surrounded by the prostateProstatic – portion surrounded by the prostate Membranous – lies in the urogenital diaphragmMembranous – lies in the urogenital diaphragm Spongy, or penile – runs through the penis and Spongy, or penile – runs through the penis and

opens to the outside at the external urethral orificeopens to the outside at the external urethral orifice

Accessory Glands: Seminal Accessory Glands: Seminal VesiclesVesicles

Lie on the posterior wall of the bladder and Lie on the posterior wall of the bladder and secrete 60% of the volume of semensecrete 60% of the volume of semen Semen – viscous alkaline fluid containing fructose, Semen – viscous alkaline fluid containing fructose,

ascorbic acid, coagulating enzyme (vesiculase), ascorbic acid, coagulating enzyme (vesiculase), and prostaglandinsand prostaglandins

Join the ductus deferens to form the Join the ductus deferens to form the ejaculatory ductejaculatory duct

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

Accessory Glands: Prostate Accessory Glands: Prostate GlandGland

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

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

Plays a role in the activation of spermPlays a role in the activation of sperm Enters the prostatic urethra during ejaculationEnters the prostatic urethra during ejaculation

Accessory Glands: Bulbourethral Accessory Glands: Bulbourethral Glands (Cowper’s Glands)Glands (Cowper’s Glands)

Pea-sized glands inferior to the prostatePea-sized glands inferior to the prostate Produce thick, clear mucus prior to ejaculation Produce thick, clear mucus prior to ejaculation

that neutralizes traces of acidic urine in the that neutralizes traces of acidic urine in the urethraurethra

SemenSemen Milky white, sticky mixture of sperm and Milky white, sticky mixture of sperm and

accessory gland secretionsaccessory gland secretions Provides a transport medium and nutrients Provides a transport medium and nutrients

(fructose), protects and activates sperm, and (fructose), protects and activates sperm, and facilitates their movementfacilitates their movement

Prostaglandins in semen:Prostaglandins in semen: Decrease the viscosity of mucus in the cervixDecrease the viscosity of mucus in the cervix Stimulate reverse peristalsis in the uterusStimulate reverse peristalsis in the uterus Facilitate the movement of sperm through the Facilitate the movement of sperm through the

female reproductive tractfemale reproductive tract

SemenSemen The hormone The hormone relaxinrelaxin enhances sperm motility enhances sperm motility The relative alkalinity of semen neutralizes the acid The relative alkalinity of semen neutralizes the acid

environment found in the male urethra and female environment found in the male urethra and female vaginavagina

Seminalplasmin – antibiotic chemical that destroys Seminalplasmin – antibiotic chemical that destroys certain bacteriacertain bacteria

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

Only 2-5 ml of semen are ejaculated, but it contains Only 2-5 ml of semen are ejaculated, but it contains 50-130 million sperm/ml50-130 million sperm/ml

Male Sexual Response: ErectionMale Sexual Response: Erection

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

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

Nitric oxide causes erectile tissue to fill with bloodNitric oxide causes erectile tissue to fill with blood Expansion of the corpora cavernosa:Expansion of the corpora cavernosa:

Compresses their drainage veinsCompresses their drainage veins Retards blood outflow and maintains engorgementRetards blood outflow and maintains engorgement

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

Male Sexual ResponseMale Sexual Response

Erection is initiated by sexual stimuliErection is initiated by sexual stimuli Erection can be induced or inhibited solely by Erection can be induced or inhibited solely by

emotional or higher mental activityemotional or higher mental activity Impotence – inability to attain erectionImpotence – inability to attain erection

EjaculationEjaculation The propulsion of semen from the male duct The propulsion of semen from the male duct

systemsystem At ejaculation, sympathetic nerves serving the At ejaculation, sympathetic nerves serving the

genital organs cause:genital organs cause: Reproductive ducts and accessory organs to Reproductive ducts and accessory organs to

contract and empty their contentscontract and empty their contents The bladder sphincter muscle to constrict, The bladder sphincter muscle to constrict,

preventing the expulsion of urinepreventing the expulsion of urine Bulbospongiosus muscles to undergo a rapid series Bulbospongiosus muscles to undergo a rapid series

of contractions of contractions Propulsion of semen from the urethraPropulsion of semen from the urethra

SpermatogenesisSpermatogenesis

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

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

Humans have 23 pairs of homologous chromosomesHumans have 23 pairs of homologous chromosomes Gametes only have 23 chromosomes and are said to Gametes only have 23 chromosomes and are said to

be haploid (be haploid (nn chromosomal number) chromosomal number) Gamete formation is by meiosis, in which the number Gamete formation is by meiosis, in which the number

of chromosomes is halved (from 2of chromosomes is halved (from 2nn to to nn))

Meiosis – InterphaseMeiosis – Interphase

Two nuclear divisions Two nuclear divisions halve the number of halve the number of chromosomeschromosomes

Chromosomes Chromosomes replicate prior to replicate prior to meiosis Imeiosis I

Figure 27.7.1

Meiosis – Prophase IMeiosis – Prophase I

Homologous Homologous chromosomes chromosomes undergo synapsisundergo synapsis

Tetrads are formed Tetrads are formed with homologous with homologous partnerspartners

Crossing over takes Crossing over takes place during place during prophase Iprophase I

Figure 27.7.2.1

Meiosis – Metaphase IMeiosis – Metaphase I

Tetrads line up at the Tetrads line up at the spindle equator during spindle equator during metaphase Imetaphase I

Figure 27.7.2.2

Meiosis – Anaphase IMeiosis – Anaphase I

Homologous Homologous chromosomes chromosomes composed of joined composed of joined sister chromatids are sister chromatids are distributed to opposite distributed to opposite ends of the cellends of the cell

Figure 27.7.2.3

Meiosis – Telophase IMeiosis – Telophase I Nuclear membrane Nuclear membrane

forms around forms around chromosomal masseschromosomal masses

Spindle break downSpindle break down Chromatin reappearsChromatin reappears With telophase and With telophase and

cytokinesis completed, cytokinesis completed, two haploid daughter two haploid daughter cells are formed (with cells are formed (with 22nn amount of DNA) amount of DNA)

Figure 27.7.2.4

Meiosis IIMeiosis II Mirrors mitosis except that chromosomes are Mirrors mitosis except that chromosomes are

not replicated before it beginsnot replicated before it begins Meiosis accomplishes two tasks:Meiosis accomplishes two tasks:

It reduces the chromosome number by half (2It reduces the chromosome number by half (2nn to to nn)) It introduces genetic variabilityIt introduces genetic variability

Meiotic Cell Division: Meiosis IIMeiotic Cell Division: Meiosis II

Figure 27.7.3

SpermatogenesisSpermatogenesis

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

These spermatogenic cells give rise to sperm These spermatogenic cells give rise to sperm in a series of eventsin a series of events Mitosis of spermatogonia, forming spermatocytesMitosis of spermatogonia, forming spermatocytes Meiosis forms spermatids from spermatocytesMeiosis forms spermatids from spermatocytes Spermiogenesis – spermatids form spermSpermiogenesis – spermatids form sperm

Mitosis of SpermatogoniaMitosis of Spermatogonia

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

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

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

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

Spermatocytes to SpermatidsSpermatocytes to Spermatids

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

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

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

Spermiogenesis: Spermatids to Spermiogenesis: Spermatids to SpermSperm

Late in spermatogenesis, spermatids are Late in spermatogenesis, spermatids are haploid but nonmotilehaploid but nonmotile

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

Spermiogenesis: Spermatids to Spermiogenesis: Spermatids to SpermSperm

Sperm have three major regionsSperm have three major regions Head – contains DNA and has a helmetlike Head – contains DNA and has a helmetlike

acrosome containing hydrolytic enzymes that acrosome containing hydrolytic enzymes that allow the sperm to penetrate and enter the eggallow the sperm to penetrate and enter the egg

Midpiece – contains mitochondria spiraled around Midpiece – contains mitochondria spiraled around the tail filamentsthe tail filaments

Tail – a typical flagellum produced by a centrioleTail – a typical flagellum produced by a centriole

Sustentacular Cells (Sertoli Cells)Sustentacular Cells (Sertoli Cells)

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

They are bound together with tight junctions forming They are bound together with tight junctions forming an unbroken layer with the seminiferous tubule, an unbroken layer with the seminiferous tubule, dividing it into two compartmentsdividing it into two compartments The basal compartment – contains spermatogonia and The basal compartment – contains spermatogonia and

primary spermatocytesprimary spermatocytes Adluminal compartment – contains meiotically active cells Adluminal compartment – contains meiotically active cells

and the tubule lumenand the tubule lumen

Sustentacular CellsSustentacular Cells

Their tight junctions form a blood-testis barrier Their tight junctions form a blood-testis barrier This prevents sperm antigens from escaping This prevents sperm antigens from escaping

through the basal lamina into the bloodthrough the basal lamina into the blood Since sperm are not formed until puberty, they Since sperm are not formed until puberty, they

are absent during thymic educationare absent during thymic education Spermatogonia are recognized as “self” and Spermatogonia are recognized as “self” and

are influenced by bloodborne chemical are influenced by bloodborne chemical messengers that prompt spermatogenesismessengers that prompt spermatogenesis

Adluminal Compartment Adluminal Compartment ActivitiesActivities

Spermatocytes and spermatids are nearly Spermatocytes and spermatids are nearly enclosed in sustentacular cells, which:enclosed in sustentacular cells, which: Deliver nutrients to dividing cellsDeliver nutrients to dividing cells Move them along to the lumenMove them along to the lumen Secrete testicular fluid that provides the transport Secrete testicular fluid that provides the transport

medium for spermmedium for sperm Dispose of excess cytoplasm sloughed off during Dispose of excess cytoplasm sloughed off during

maturation to spermmaturation to sperm Produce chemical mediators that help regulate Produce chemical mediators that help regulate

spermatogenesisspermatogenesis