11/15/2017. Reproductive System. Anatomy of Male Reproductive System. Reproductive Organs of the Male, Sagittal View

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1 Reproductive System What is sex? Biological science perspective Primary sex organs (gonads): testes and ovaries Produce gametes (sex cells): sperm and ova Secrete steroid sex hormones Androgens (males) Estrogens and progesterone (females) Accessory reproductive organs: Internal ducts and glands external genitalia including copulatory organs Anatomy of Male Reproductive System Testes: sperm-producing male gonads that lie within the scrotum Sperm is delivered to body through system of ducts: epididymis, ductus (vas) deferens, ejaculatory duct, and urethra Accessory sex glands: seminal glands, prostate, and bulbo-urethral glands Reproductive Organs of the Male, Sagittal View Scrotum Sac of skin and superficial fascia outside abdominopelvic cavity Contains paired testes 3 C lower than core body temperature necessary for sperm production Midline septum divides scrotum into two compartments, one for each testis 1

Testis, Scrotum and Spermatic Cord Spermatic cord encloses nerve fibers, blood vessels, and lymphatics that supply testes The

one to four seminiferous tubules Interstitial endocrine cells: located in soft tissue surrounding seminiferous tubules Produce

like cells that may squeeze sperm and testicular fluids out of testes Structure of the Testis Sperm is conveyed from

2 Testis, Scrotum and Spermatic Cord Spermatic cord encloses nerve fibers, blood vessels, and lymphatics that supply testes The Testes Each testis is surrounded by tunica vaginalis and tunica albuginea Septa divide testis into ~250 lobules, each containing one to four seminiferous tubules Interstitial endocrine cells: located in soft tissue surrounding seminiferous tubules Produce androgens, such as testosterone Secrete it into interstitial fluid Myoid cells surround each seminiferous tubule Smooth muscle like cells that may squeeze sperm and testicular fluids out of testes Structure of the Testis Sperm is conveyed from seminiferous tubules to straight tubule to rete testis to efferent ductules to epididymis Sperm are stored in tail of epididymis until ejaculation 2

testes to body exterior Epididymis Ductus deferens

3 Structure of the Testis Male Reproductive Structures Male Duct System Ducts carry sperm from testes to body exterior Epididymis Ductus deferens formerly known as vas deferens Ejaculatory duct Urethra 3

4 Epididymis Duct of the epididymis is ~ 6 m in length Microvilli (stereocilia) absorb testicular fluid and pass nutrients to stored sperm Nonmotile sperm enter, pass slowly through (~ 20 days), become motile Can be stored several months During ejaculation, epididymis contracts, expelling sperm into ductus deferens Ductus Deferens and Ejaculatory Duct Ductus deferens (vas deferens) ~ 45 cm long Passes through inguinal canal to pelvic cavity Expands to form ampulla Joins duct of seminal vesicle to form ejaculatory duct Smooth muscle in walls propels sperm from epididymis to urethra Vasectomy: cutting and ligating ductus deferens Nearly 100% effective form of birth control Urethra Conveys both urine and semen (at different times) Has three regions Prostatic urethra: surrounded by prostate Intermediate part of the urethra (membranous urethra): in urogenital diaphragm Spongy urethra: runs through penis; opens at external urethral orifice 4

5 Male Accessory Glands Seminal glands or seminal vesicles On posterior bladder surface Contains smooth muscle that contracts during ejaculation Produces viscous alkaline seminal fluid Fructose, citric acid, coagulating enzyme (vesiculase), and prostaglandins Comprises 70% volume of semen Duct of seminal gland joins ductus deferens to form ejaculatory duct Bulbo-urethral glands Pea-sized glands inferior to prostate Produce thick, clear mucus during sexual arousal Lubricate urethra and glans penis Neutralize traces of acidic urine in urethra Male Accessory Glands Prostate Encircles urethra inferior to bladder Size of peach pit Consists of smooth muscle that contracts during ejaculation Secretes milky, slightly acid fluid Contains citrate, enzymes, and prostate-specific antigen (PSA) Plays a role in sperm activation Enters prostatic urethra during ejaculation Makes up one-third of semen volume Semen (1 of 2) Milky-white mixture of sperm and accessory gland secretions 2 5 ml semen are ejaculated containing million sperm/ml Contains fructose for ATP production, protects and activates sperm, and facilitates sperm movement Alkaline fluid neutralizes acidity of male urethra and female vagina and enhances motility 5

Semen (2 of 2) Characteristics of semen Contain prostaglandins that decrease viscosity of mucus in cervix and stimulate reverse peristalsis in uterus Contains the hormone relaxin and other enzymes

6 Semen (2 of 2) Characteristics of semen Contain prostaglandins that decrease viscosity of mucus in cervix and stimulate reverse peristalsis in uterus Contains the hormone relaxin and other enzymes that enhance sperm motility Contains ATP for energy Can suppress female immune response Antibiotic chemicals destroy some bacteria Clotting factors coagulate semen initially to prevent draining out, then liquefy it by fibrinolysin so sperm can finish journey Cell Division in Body Cells: Mitosis Chromosome number 23 HOMOLOGOUS pairs for total of 46 diploid condition Chromosome number unaffected by cell division mother and daughter cells have the same number Increases number of body cells (development) or regenerates tissues (throughout life) Cell Division and the Production of Gametes: Meiosis Gamete formation involves meiosis, which differs from mitosis Involves two consecutive cell divisions (meiosis I and II), but only one round of DNA replication Produces four daughter cells Functions of meiosis Number of chromosomes are cut in half (2n to n) Diploid mother cells to haploid sex cells Prepare for union of two haploid gametes into one diploid zygote Introduces genetic diversity 6

Followed by growth and development of daughter

Homologous Chromosomes in Meiosis Supporting

Random alignment of homologous pairs in meiosis I

variability of gametes (not shown) Results in no

7 Followed by growth and development of daughter cells into mature cells Independent Assortment of Homologous Chromosomes in Meiosis Supporting Genetic Diversity Introduces genetic variability Random alignment of homologous pairs in meiosis I leads to variability of gametes Crossover variability of gametes (not shown) Results in no two gametes being exactly alike All are different from original mother cells 7

Spermatogenesis Reminder: most body cells have 46 chromosomes: Two sets (23 pairs) of

chromosomal number (2n) Gametes have only 23 chromosomes: haploid chromosomal number (n) Only

Spermatogenic cells give rise to sperm Spermatogenesis Spermiogenesis: Transformation of a

nucleus and helmetlike acrosome containing hydrolytic enzymes that enable sperm to penetrate

8 Spermatogenesis Reminder: most body cells have 46 chromosomes: Two sets (23 pairs) of chromosomes One maternal, one paternal: homologous chromosomes Referred to as diploid chromosomal number (2n) Gametes have only 23 chromosomes: haploid chromosomal number (n) Only one member of homologous pair Occurs in seminiferous tubules of testis beginning at puberty Spermatogenic cells give rise to sperm Spermatogenesis Spermiogenesis: Transformation of a Spermatid into a Functional Sperm Major regions of sperm: Head: genetic region that includes nucleus and helmetlike acrosome containing hydrolytic enzymes that enable sperm to penetrate egg Midpiece: metabolic region containing mitochondria that produce ATP to move tail Tail: locomotor region that includes flagellum 8

Spermatogenesis: Summary of Events in the Seminiferous Tubules Role of sustentocytes (also called Sertoli cells) Extend through wall of tubule and surround developing cells Provide nutrients and

9 Spermatogenesis: Summary of Events in the Seminiferous Tubules Role of sustentocytes (also called Sertoli cells) Extend through wall of tubule and surround developing cells Provide nutrients and signals to dividing cells Move cells along to lumen Secrete testicular fluid into lumen for sperm transport Phagocytize faulty germ cells and excess cytoplasm Produce chemical mediators to regulate spermatogenesis Tight junctions that divide tubule into two compartments and form blood testis barrier Basal compartment: area where spermatogonia and primary spermatocytes are located Adluminal compartment: area where meiotically active cells and tubule lumen are located Hormonal Regulation of Testicular Function, the Hypothalamic-Pituitary- Gonadal (HPG) Axis 1. Hypothalamus releases GnRH 2. GnRH binds to anterior pituitary gonadotropic cells stimulating FSH and LH release 3. FSH stimulates sustentocytes to release androgen-binding protein (ABP) ABP keeps concentration of testosterone high near spermatogenic cells, promoting spermatogenesis 4. LH binds to interstitial endocrine cells, prodding them to secrete testosterone 5. Testosterone entering blood stimulates sex organ maturation, secondary sex characteristics, and libido 6. Rising testosterone levels negative feed back on GnRH and on pituitary 7. Inhibin: released by sustenocytes when sperm count high; inhibits GnRH and FSH release The Hypothalamic-Pituitary-Gonadal (HPG) Axis Amount of testosterone and sperm produced by testes reflects balance among three interacting sets of hormones Balance takes 3 years to achieve, after which testosterone and sperm production are fairly stable throughout life Without GnRH and gonadotropins, testes atrophy, and sperm and testosterone production ceases 9

Plasma Testosterone and Sperm Production Levels Versus Age in Male Humans Mechanism and Effects of Testosterone Activity (1 of 3) Testosterone, synthesized from cholesterol, is transformed at some

10 Plasma Testosterone and Sperm Production Levels Versus Age in Male Humans Mechanism and Effects of Testosterone Activity (1 of 3) Testosterone, synthesized from cholesterol, is transformed at some target cells Converted to dihydrotestosterone (DHT) in prostate and estradiol in some brain neurons Prompts spermatogenesis and targets all accessory organs Has multiple anabolic effects throughout body Deficiency leads to atrophy of accessory organs, semen volume declines, and erection/ejaculation are impaired; treatment: testosterone replacement Mechanism and Effects of Testosterone Activity (2 of 3) Male secondary sex characteristics: features induced in nonreproductive organs by male sex hormones (mainly testosterone) Appearance of pubic, axillary, and facial hair Enhanced growth of chest hair; deepening of voice Skin thickens and becomes oily Bones grow, increase in density Skeletal muscles increase in size and mass Boosts basal metabolic rate Basis of sex drive (libido) in males 10

androgens in small amounts, production is insufficient to maintain normal testosterone-mediated

11 Mechanism and Effects of Testosterone Activity (3 of 3) Testosterone Masculinizes embryonic brain Continues to exert effect well into adulthood Although adrenal glands also produce androgens in small amounts, production is insufficient to maintain normal testosterone-mediated functions Organs of the Female Reproductive System, Midsagittal Section Internal Female Reproductive Organs 11

Ovaries Each ovary is held in place by several ligaments Two poorly defined regions Outer cortex: houses forming gametes Inner medulla: contains large blood vessels and nerves Ovarian follicles:

12 Ovaries Each ovary is held in place by several ligaments Two poorly defined regions Outer cortex: houses forming gametes Inner medulla: contains large blood vessels and nerves Ovarian follicles: Contain immature egg (oocyte) surrounded by cells Follicles go through several stages of development Primordial follicle: single layer of follicle cells plus oocyte More mature follicles: several layers of granulosa cells plus oocyte Ovulation and Corpus Luteum Follicles in Different Developmental Phases Female Duct System Tube system includes: Uterine tubes Each tube ~10 cm (4 in) long receives ovulated oocyte and are usual site of fertilization Oocyte is carried along toward uterus by smooth muscle peristalsis and ciliary action Nonciliated cells of tube function to nourish oocyte and sperm Uterus Vagina 12

The Uterus Hollow, thick-walled, muscular organ Function is to receive, retain, and nourish fertilized ovum Regions of uterus Body: major portion Fundus: rounded superior region Isthmus: narrowed

Perimetrium Myometrium interlacing layers of smooth muscle Contracts rhythmically during childbirth Endometrium: mucosal lining Fertilized egg burrows into endometrium and resides there during

13 The Uterus Hollow, thick-walled, muscular organ Function is to receive, retain, and nourish fertilized ovum Regions of uterus Body: major portion Fundus: rounded superior region Isthmus: narrowed inferior region Cervix: narrow neck, or outlet; projects into vagina Cervical glands secrete mucus that blocks sperm entry except during midcycle The Uterus Uterine wall Three layers of wall Perimetrium Myometrium interlacing layers of smooth muscle Contracts rhythmically during childbirth Endometrium: mucosal lining Fertilized egg burrows into endometrium and resides there during development Stratum functionalis (functional layer) Changes in response to ovarian hormone cycles Shed during menstruation Stratum basalis (basal layer) Forms new stratum functionalis after menstruation Unresponsive to ovarian hormones Endometrium 13

The Vagina Thin-walled tube 8 10 cm (3 4 inches) in length Functions as birth canal, passageway for menstrual flow, and organ of copulation Layers of wall Fibroelastic adventitia Smooth muscle

14 The Vagina Thin-walled tube 8 10 cm (3 4 inches) in length Functions as birth canal, passageway for menstrual flow, and organ of copulation Layers of wall Fibroelastic adventitia Smooth muscle muscularis Stratified squamous mucosa with rugae Vaginal secretions are acidic in adult females, but alkaline in adolescents Mucosa near vaginal orifice forms incomplete partition called hymen that ruptures with intercourse External Genitalia Female external genitalia, also called vulva or pudendum, include: Mons pubis: fatty area overlying pubic symphysis Labia majora: hair-covered, fatty skin folds Labia minora: skin folds lying within labia majora Vestibule: recess within labia minora Greater vestibular glands Flank vaginal opening Release mucus into vestibule for lubrication Clitoris: anterior to vestibule Glans of the clitoris: exposed portion Prepuce of the clitoris: hoods glans Perineum External Genitalia 14

Oogenesis Oogenesis: production of female gametes takes years to complete Begins in fetal period Oogonia (2n ovarian stem cells) multiply by mitosis and store nutrients Primary oocytes develop in

15 Oogenesis Oogenesis: production of female gametes takes years to complete Begins in fetal period Oogonia (2n ovarian stem cells) multiply by mitosis and store nutrients Primary oocytes develop in primordial follicles that become surrounded by follicle cells Primary oocytes begin meiosis but stall in prophase I At birth, female presumed to have lifetime supply of primary oocytes Each month after puberty, a few primary oocytes are activated One from this group is selected each month to become dominant follicle that resumes meiosis I Events of Oogenesis Oogenesis produces one viable ovum with three polar bodies Unequal divisions ensure oocyte has ample nutrients for 6- to 7-day journey to uterus Polar bodies degenerate and die The Ovarian Cycle Ovarian cycle: monthly (~28 day) series of events associated with maturation of egg Two consecutive phases, with ovulation occurring midcycle between phases Follicular phase: period of vesicular follicle growth (days 1 14) Luteal phase: period of corpus luteum activity (days 14 28) Only 10 15% women have 28-day cycle Follicular phase varies, but luteal phase is always 14 days from ovulation to end of cycle 15

Ovarian Cycle: Development and Fate of Ovarian Granulosa cells Follicles Follicular cells Stages of Follicle Development Secondary follicle becomes vesicular follicle Connective tissue and granulosa

16 Ovarian Cycle: Development and Fate of Ovarian Granulosa cells Follicles Follicular cells Stages of Follicle Development Secondary follicle becomes vesicular follicle Connective tissue and granulosa cells condense to form theca folliculi Zona pellucida: thick, glycoprotein-rich membrane secreted by oocyte, encapsulating it Early vesicular follicle formed when clear fluid begins to accumulate between granulosa cells Antrum continues to expand with fluid isolating oocyte Isolated oocyte with its surrounding granulosa cells called corona radiata When follicle is full size (2.5 cm or 1 inch), it bulges from external ovary surface It is ready to be ovulated Follicular Phase of the Ovarian Cycle During follicular phase, several vesicular (antral) follicles are stimulated to grow Triggered by rising levels of anterior pituitary hormone FSH follicle stimulating hormone FSH levels drop around middle of follicular phase Causes only one antral follicle, dominant follicle, to be selected to continue on How dominant follicle is chosen is still uncertain Primary oocyte of dominant follicle completes meiosis I to form 2 oocyte and polar body Granulosa cells then send signal to oocyte, causing it to stop at metaphase II 16

17 Ovulation Rising levels of LH cause ovary wall to rupture, expelling secondary oocyte with its corona radiata to peritoneal cavity some women experience a twinge of pain at ovulation 1 2% of ovulations release more than one secondary oocyte, which, if fertilized, result in fraternal twins Luteal Phase of the Ovarian Cycle After ovulation, ruptured follicle collapses, and antrum fills with clotted blood Remaining granulosa cells and internal thecal cells enlarge to form corpus luteum Corpus luteum secretes progesterone and some estrogen If no pregnancy occurs, corpus luteum degenerates into corpus albicans (scar) in 10 days If pregnancy occurs, corpus luteum produces hormones that sustain pregnancy until placenta takes over, at about 3 months Regulation of Female Reproductive System Hormonal Regulation of Ovarian Cycle Establishing the ovarian cycle Before puberty, ovaries secrete small amounts of estrogen, inhibiting hypothalamic release of GnRH As puberty nears, if leptin levels are adequate, hypothalamus becomes less estrogen-sensitive, so GnRH is released, stimulating FSH and LH release by pituitary FSH and LH stimulate follicles to grow, mature, and secrete sex hormones FSH stimulates granulosa cells to release estrogen LH stimulates thecal cells to produce androgens, which granulosa converts to estrogens Events continue until an adult cyclic pattern is achieved and menarche occurs 17

Regulation of the Ovarian Cycle Hormonal Regulation of Ovarian Cycle Negative feedback inhibits gonadotropin release Increasing levels of plasma estrogen levels exert negative feedback inhibition on

18 Regulation of the Ovarian Cycle Hormonal Regulation of Ovarian Cycle Negative feedback inhibits gonadotropin release Increasing levels of plasma estrogen levels exert negative feedback inhibition on FSH and LH release Inhibin from granulosa cells also inhibits FSH release Only dominant follicle can withstand this dip in FSH Other developing follicles deteriorate Positive feedback stimulates gonadotropin release Estrogen levels continue to rise as a result of continued release by dominant follicle When levels reach a critical high value, a brief positive feedback occurs on brain and anterior pituitary Triggers LH surge Hormonal Regulation of Ovarian Cycle LH surge triggers ovulation and formation of the corpus luteum High estrogen levels trigger release of stored LH, and some FSH, by anterior pituitary at midcycle Surge triggers ovulation Shortly after ovulation: Estrogen levels decline LH transforms ruptured follicle into corpus luteum LH stimulates corpus luteum to secrete progesterone and some estrogen almost immediately Progesterone helps maintain stratum functionalis Maintains pregnancy, if it occurs 18

19 Hormonal Regulation of Ovarian Cycle Negative feedback inhibits LH and FSH release Negative feedback from rising plasma progesterone and estrogen levels inhibits LH and FSH release If no fertilization occurs: Corpus luteum degenerates when LH levels start to fall Causes a sharp decrease in estrogen and progesterone, which in turn ends blockage of FSH and LH secretion, causing cycle to start all over again The Uterine (Menstrual) Cycle Uterine (menstrual) cycle: cyclic series of changes in endometrium that occur in response to fluctuating ovarian hormone levels 1. Days 1 5: menstrual phase Ovarian hormones are at lowest levels Gonadotropin levels are beginning to rise Stratum functionalis detaches from uterine wall and is shed Menstrual flow of blood and tissue lasts 3 5 days By day 5, growing ovarian follicles start to produce more estrogen The Uterine (Menstrual) Cycle 2. Days 6 14: proliferative (preovulatory) phase Rising estrogen levels prompt generation of new stratum functionalis layer As layer thickens, glands enlarge, and spiral arteries increase in number Estrogen also increases synthesis of progesterone receptors in endometrium Thins out normally thick, sticky cervical mucus to facilitate sperm passage Ovulation occurs at end of proliferative phase on day 14 19

20 The Uterine (Menstrual) Cycle 3. Days 15 28: secretory (postovulatory) phase Phase that is most consistent in duration Endometrium prepares for embryo to implant Rising progesterone levels from corpus luteum prompt: Functional layer to become a secretory mucosa Endometrial glands to enlarge and secrete nutrients into uterine cavity Thickened mucus to form cervical mucus plug that blocks entry of more sperm, pathogens, or debris The Uterine (Menstrual) Cycle 3. Days 15 28: secretory (postovulatory) phase If fertilization does not occur: Corpus luteum degenerates toward end of secretory phase; progesterone levels fall Causes spiral arteries to kink and spasm Endometrial cells die, and glands regress Spiral arteries constrict again, then relax and open wide, causing a rush of blood into weakened capillary beds Blood vessels fragment, and functional layer sloughs off Uterine cycle starts all over again on first day of menstruation 20

21 Effects of Estrogens and Progesterones Estrogens: Promote oogenesis and follicle growth in ovary Exert anabolic effect on female reproductive tract Support rapid short-lived growth spurts at puberty Induce secondary sex characteristics Growth of breasts Increased deposit of subcutaneous fat (hips and breasts) Widening and lightening of pelvis Progesterone works with estrogen to establish and regulate uterine cycle Promotes changes in cervical mucus Effects of placental progesterone during pregnancy Inhibits uterine motility Helps prepare breasts for lactation Developmental Aspects of Reproductive System Embryological and Fetal Events Determination of genetic sex Of 46 chromosomes in fertilized egg, two are sex chromosomes (other 44 are autosomes) X chromosome (large) Y chromosome (quite small) If fertilizing sperm delivers an X chromosome, fertilized egg will contain XX, and embryo will develop ovaries X egg + X sperm XX (female offspring) If fertilizing sperm delivers a Y chromosome, fertilized egg will contain XY, and embryo will develop testes X egg + Y sperm XY (male offspring) Males are XY: so ~50% of sperm contain X chromosome, and ~50% contain Y chromosome 21

Primary sex organs (gonads): testes and ovaries. Accessory reproductive organs: ducts, glands, and external genitalia

Male Reproductive System Primary sex organs (gonads): testes and ovaries Produce sex cells (gametes) Secrete steroid sex hormones Androgens (males) Estrogens and progesterone (females) Accessory reproductive