The Reproductive System
Reproductive system becomes fully active
during puberty
Primary Sex Organs (Gonads): testes in
males & ovaries in females
Gonads produce gametes & secrete
sex hormones
Testes produce sperm through spermatogenesis
Ovaries produce ova through oogenesis
Accessory Reproductive Organs: ducts,
glands & external genitalia
Anatomy of the Male Reproductive System
Scrotum: sac of skin & superficial
fascia that houses testes in left & right compartments created by the
presence of a midline septum.
Temperature of scrotum must be ~ 3°C
lower than core body temperature for production of viable sperm
Temperature maintained by contraction & relaxation
of dartos & cremaster muscles
Dartos
Smooth muscle layer in fascia -
wrinkles skin, contraction draws scrotum up to reduce heat loss,
relaxation allows scrotum to assume a lower position, decreasing temperature
Cremaster
SkM from internal oblique, suspends
testes, contraction pulls testes close to abdominal wall, relaxation
allows descent away from body, decreases temperature
Testes: lie within scrotum; produce male gametes
(sperm)
Each testis is surrounded by 2 tunics:
outer tunica vaginalis formed from peritoneum & inner tunica albuginea,
formed from fibrous CT
Septa divide each testis into 250-300
lobules
Each lobule contains 1-4 seminiferous
tubules, where sperm is produced
Seminiferous tubules from each lobule converge
to form tubulus rectus that conveys sperm to posterior rete testis
Sperm travels then from rete
testis to efferent ductules to epididymis
Interstitial cells (Leydig
cells): surround seminiferous tubules; produce androgens (testosterone)
Testicular arteries arise
from abdominal aortas & supply blood to testes; testicular veins drain
testes
Spermatic cord: connective
tissue sheath enclosing blood vessels, lymphatics & nerves
Testicular cancer is most common
cancer in young men; treatment is surgical removal of tumor followed by radiation & chemotherapy
Penis: copulatory organ; releases sperm produced by testes
Male external genitalia: penis & scrotum
Male perineum: diamond-shaped region
bounded by pubic symphysis, coccyx & ischial tuberosities
Penis made up of attached root & free
body or shaft ending in enlarged tip called glans penis
Prepuce (foreskin): cuff of skin covering
penis; may be removed by circumcision
Erectile tissue: network of connective
tissue & smooth muscle with vascular spaces that become filled with blood
during sexual excitement
Corpus spongiosum:
surrounds spongy urethra
Corpora cavernosa:
paired dorsal erectile bodies
Male Duct System
Epididymis: coiled
tube that delivers immature sperm from testis to ductus deferens
During this journey sperm gain ability to swim.
Ductus Deferens (vas deferens):
propels live sperm from epididymis to urethra.
The ductus deferens is a long tube that runs from
epididymis upward anterior to pubic bone into pelvic cavity, loops over ureter & descends
posteriorly along bladder, where it joins with seminal vesicle to form ejaculatory
duct.
The ejaculatory duct passes into prostate gland & empties
into urethra.
Accessory Glands
Seminal Vesicles: lie
on posterior wall of bladder
Secrete seminal fluid: a yellowish viscous
alkaline fluid containing fructose (sugar), ascorbic acid, a coagulating enzyme & prostaglandins.
Sperm & seminal fluid mix in ejaculatory
duct & enter prostatic urethra during ejaculation.
Prostate Gland: encircles
urethra just inferior to bladder
Secretes a milky, slightly acidic fluid containing
citrate, enzymes & prostate-specific antigen (PSA) that enters prostatic
urethra during ejaculation
Prostate gland hypertrophy affects nearly
every elderly male
Treatments include microwaves,
drugs & transurethral needle ablation (TUNA)
Prostate cancer is third most
common cancer in men
Bulbourethral Glands (Cowper's
glands): small glands inferior to prostate gland
Produce thick clear mucus prior to ejaculation
that neutralizes acidic urine in urethra
Semen: mixture of sperm & accessory gland secretions
Provides nutrients & transport
medium for sperm & chemicals that facilitate movement.
Fructose provides fuel.
Prostaglandins decrease viscosity of
mucus at uterine cervix & stimulate reverse peristalsis of uterus & uterine
tubes to move sperm through female reproductive tract.
Alkalinity of semen due to bases (spermine)
helps neutralize acidic environment of male urethra & female vagina
Seminalplasmin: antibiotic in semen
that destroys bacteria
Contains clotting factors to clot & fibrinolysin
to liquefy semen
Physiology of Male Reproductive System
Male sexual response
Erection: results from engorgement of erectile
bodies in penis with blood
During sexual excitement, a parasympathetic reflex
releases nitric oxide, which dilates arterioles supplying erectile tissue
Corpora cavernosa expand, enlarging & stiffening penis
and compressing drainage veins
Ejaculation: propulsion of semen from male
duct system
Sympathetic spinal reflex sends
impulses to nerves serving genital organs: reproductive ducts & accessory
glands contract, emptying contents into urethra.
Bladder sphincter muscle constricts, preventing urine release
of reflux of semen into bladder
Bulbospongiosus muscles of penis undergo series of contractions,
propelling semen along urethra
Spermatogenesis: sperm formation
by meiosis in seminiferous tubules of testes
Begins occurring during puberty & continues
throughout life
Normally ~ 400 million sperm produced each
day
Terms:
diploid (2n): normal
chromosome number in most body cells; 46 in humans, or 23
pairs of homologous chromosomes (paternal & maternal
chromosome of same chromosome number)
haploid (n): chromosome
number in gametes; each human gamete only contains 23 total
chromosomes (only 1 of each homologous pair)
chromatid: one
chromosome of a duplicated chromosome
meiosis: forms
gametes; reduces chromosome number from 2n to n in gametes
meiosis I: reduction division
(2n to n)
synapsis:
during prophase, homologous chromosomes pair & exchange genetic information
tetrads or bivalents - cross
over - at similar regions
independent assortment:
during metaphase, homologous chromosomes line up in pairs at metaphase plate;
either maternal or paternal chromosome of each homologous pair can be on a
given side of equator
both synapsis and independent assortment lead to genetic
variation in gametes
meiosis II: equatorial division
(chromatids distributed equally)
mitotic-like division; duplicated
chromosomes separated
Summary of Events in Seminiferous
Tubules
Mitosis of spermatogonia:
forming spermatocytes
Spermatogonia divide to form type
A cell & type B cell
type A cell remains
in basal compartment in spermatogonia population
type B cell moves
to adluminal compartment & becomes primary spermatocyte, destined to
form 4 sperm cells
Meiosis: spermatocytes
to spermatids
Meiosis I: primary spermatocyte forms
2 secondary spermatocytes
Meiosis II: each secondary spermatocyte
forms 2 spermatids
Spermiogenesis: spermatids
to sperm
Each spermatid undergoes changes to
form sperm cell
At one end of nucleus, head region forms,
including a tightly enclosed nucleus with an acrosome (contains
hydrolytic enzymes for penetration of egg cell) at top
At other end, tail region forms, with a flagellum forming
from centrioles & attached to the head region by a midpiece containing
many mitochondria (supplying energy for moving flagellum)
Role of sustentacular
cells
Sustentacular cells (Sertoli
cells) surround cells of seminiferous tubules & connect
to one another by tight junctions which form 2 compartments (basal & adluminal)
Junctions form blood-testis barrier that prevents
immune cell targeting of sperm
Hormonal Regulation of Male Reproductive Function
Gonadotropin-releasing hormone (GnRH) release
from hypothalamus controls release of follicle-stimulating hormone (FSH) & luteinizing
hormone (LH) from anterior pituitary
FSH stimulates sustentacular
cells to release androgen-binding protein (ABP), which causes spermatogenic
cells to bind testosterone & begin spermatogenesis
LH binds to interstitial
cells & stimulates them to secrete testosterone
Testosterone feeds
back (negative feedback) to hypothalamus & anterior pituitary, inhibiting
release of GnRH & tropic hormones
Some target cells require conversion
of testosterone to another steroid (dihydrotestosterone (DHT) in prostate,
estrogen in brain) to exert its effects
Testosterone also controls appearance
of secondary sex characteristics in males & boosts metabolism
Inhibin released by
sustentacular cells inhibits release of FSH from anterior pituitary & GnRH
from hypothalamus
Anatomy of Female Reproductive System
Ovaries: female gonads; produce oocytes & female sex
hormones (estrogens & progesterone)
Flank uterus on each side; held in place
within peritoneal cavity by parts of broad ligament (suspensory
ligament & mesovarium)
Ovarian ligament anchors
ovary to uterus
Ovarian arteries (branch from
abdominal aorta) & ovarian branch of uterine arteries serve
ovaries
Ovaries surrounded externally by tunica
albuginea & germinal epithelium
Outer cortex houses
follicles; inner medulla contains blood vessels & nerves
Ovarian follicles:
in cortex; contain immature egg (oocyte) encased by one or more cell layers
(1 layer = follicle cells; more than 1 layer = granulosa cells)
Primordial follicle:
one layer of squamous cells enclose oocyte
Primary follicle:
2 or more layers of cuboidal or columnar cells surround oocyte
Secondary follicle:
has central fluid-filled cavity (antrum)
Vesicular (Graafian) follicle:
follicle bulges from ovary surface; oocyte sits on stalk of granulosa cells
at one side of antrum
Ovulation: ejection
of oocyte from follicle & ovary
Corpus luteum:
structure formed from follicle cells following ovulation; eventually degenerates
Female Duct System
Uterine Tubes (Fallopian
tubes or Oviducts): receive ovulated oocyte
from ovary & provide site for fertilization
Infundibulum: open
funnel-shaped structure with ciliated fingerlike projections called fimbriae that
drape over ovary
Oovulated oocyte is cast into
peritoneal cavity; cilia of fimbriae sweep oocyte into uterine tube
Ampulla: expanded
curved portion of uterine tube where fertilization normally
occurs
Isthmus: constricted
region that leads into uterus
Smooth muscle sheets in wall of uterine tube & mucosa
with ciliated cells aid in carrying oocyte toward uterus
Uterine tubes are covered by peritoneum & supported
by mesentery called mesosalpinx
Uterus: hollow, thick-walled
organ in pelvis that receives, retains & nourishes a fertilized ovum
Consists of fundus, body & cervix from
superior to inferior
Cervix (neck) projects into vagina
Cervical canal communicates
with vagina via external os & with uterus via internal os
Cervical cancer:
caused by certain types of human papillomavirus (HPV);
can be diagnosed by Pap (Papanicolau)
smear
Mucosa contains mucus-secreting cervical glands
Supports of uterus:
mesometrium of broad ligament, lateral cervical ligament, uterosacral ligaments & round
ligaments
Uterine wall: composed of
3 layers:
Perimetrium:
outermost serous layer; visceral peritoneum
Myometrium:
middle smooth muscle layer; contraction of muscle bundles expels baby during
childbirth
Endometrium:
mucosal lining of uterine cavity; simple columnar epithelium; site of implantation
of embryo for development
Stratum functionalis (functional
layer): undergoes cyclic changes in response to ovarian hormones;
shed during menstruation
Stratum basalis (basal layer):
forms new functional layer after menstruation
Blood supply: uterine arteries > arcuate
arteries(myometrium) > radial branches(endometrium) > straight arteries (basal
layer) & spiral (coiled) arteries (functional layer)
Vagina: thin-walled
tube between bladder & rectum extending from cervix to body exterior
Provides passageway for delivery of baby,
for menstrual flow & for delivery of semen (& sperm) to uterine tube
Urethra is embedded
in anterior wall
Wall consists of outer fibroelastic adventitia,
smooth muscle muscularis & mucosa of stratified squamous epithelium with
ridges (rugae)
Cervical mucous glands supply mucus to mucosa;
pH of vagina is normally acidic due to metabolism of sugars by resident bacteria
(prevents infection)
Hymen: incomplete mucosal partition
covering vaginal orifice that is normally ruptured during first sexual intercourse
External Genitalia (Vulva)
Mons pubis: fatty rounded area overlying pubic
symphysis
Labia majora: elongated skin folds running
posteriorly from mons pubis & enclosing labia minora
Labia minora enclose recess called vestibule,
which contains the external opening of urethra (anteriorly) & vagina (posteriorly)
Clitoris: small protruding erectile tissue
(corpora cavernosa) hooded by prepuce formed by junction of labia minora folds
Perineum: diamond shaped region surrounding
external genitalia
Mammary Glands
Present in both sexes; normally only function
in females
Produce milk & nourish newborn baby
Composed of modified sweat glands contained
within a rounded skin-covered breast, anterior to pectoral muscles
Glands consist of lobes separated form each
other by fat & fibrous CT forming suspensory ligaments that support
breasts
Lobules within lobes contain alveoli that
produce milk when a woman is lactating following childbirth
Milk collects in lactiferous sinuses & is
passed into lactiferous ducts, which open to the
outside of the nipple
Invasive breast cancer is the most common
cancer of U.S. women, usually arises from epithelial
cells of ducts
Known risk factors include:
early onset menses & late menopause; no pregnancies or first pregnancy
later in life; previous history of breast cancer; family history of breast
cancer (possible risk factors include overexposure to estrogens, cigarette
smoking & alcoholism)
Hereditary forms (~ 10% of all
cases) often stem from mutations in breast cancer susceptibility genes
BRCA1 & BRCA2 (mutations in these genes put women at risk for developing
breast or ovarian cancer at some time in their lives).
Can be detected by breast self-examination & mammography
Treatment includes radiation & chemotherapy,
and surgery (radical mastectomy has been mostly replaced by lumpectomy or,
if necessary, simple mastectomy)
Physiology of Female Reproductive System
Oogenesis: ovum formation
by meiosis in follicles of ovaries
Oogonia in fetal period
in females rapidly divide & transform into primary oocytes in primordial
follicles (~ 2 million by birth)
Primary oocytes begin meiosis I, but arrest in
prophase I
Starting at puberty, "one" follicle is
chosen each month (from ~ 250,000 remaining) to complete meiosis I,
resulting in a secondary oocyte receiving most of
the cytosol & a small polar body
The secondary oocyte begins
meiosis II, but arrests in metaphase II (awaiting fertilization in oviduct
to complete meiosis II); the polar body may divide to form 2 smaller
polar bodies
The secondary oocyte is ovulated & is
picked up by uterine tube; if fertilization occurs, following sperm entry meiosis
II is completed, forming the ovum and another polar
body
The end result of complete oogenesis
is 3 small polar bodies & one very large ovum (only the ovum is
a functional female gamete); the ovum contains most of the cytosol, with
ample nutrients for the 7 day journey to the uterus
Ovarian Cycle:
Monthly series of events
associated with maturation of egg
Follicular phase: period
of follicle growth; days 1-14 (may vary considerably)
Primordial follicle becomes
primary follicle
Primary follicle becomes secondary
follicle
Secondary follicle becomes vesicular
follicle
Ovulation: bulging ovary
wall ruptures & releases secondary oocyte into peritoneal cavity; ~ day
14
fraternal twins:
more than one oocyte ovulated, & each fertilized by different sperm (~1-2%
of ovulations are multiple oocytes)
identical twins:
one oocyte fertilized by one sperm, & during early embryogenesis cells
divide into separate embryos
Luteal phase: period of corpus
luteum activity; days 14-28
After ovulation, ruptured follicle
collapses, antrum fills with clotted blood & follicle grows into endocrine
gland called corpus luteum
Corpus luteum secretes progesterone & some
estrogen
If pregnancy occurs, corpus
luteum continues to produce hormones until placenta can
assume its role; otherwise, corpus luteum degenerates within ~ 10 days
Hormonal Regulation of Ovarian
Cycle
GnRH released from hypothalamus
stimulates FSH & LH release from anterior pituitary
FSH & LH stimulate follicle
growth & estrogen secretion
Estrogen levels
rise & feed back to anterior pituitary, inhibiting release (while
stimulating production) of FSH & LH; in ovary, estrogen secretion is enhanced
by maturation of follicles under the influence of FSH
Inhibin release
by granulosa cells of follicle also inhibits FSH release
As estrogen levels peak (about midcycle),
a burstlike release of accumulated LH (& FSH) from anterior pituitary stimulates
secondary oocyte formation & ovulation; LH also transforms the ruptured
follicle into a corpus luteum
Release of progesterone, estrogen & inhibin from corpus
luteum inhibits release of FSH & LH from anterior pituitary
As LH blood levels decline, corpus luteum
degenerates, & declining levels of progesterone & estrogen remove
block to FSH & LH release; cycle begins again
Uterine (Menstrual) Cycle:
cyclic changes in uterine endometrium in response to ovarian hormones in blood
Menstrual phase (days 1-5):
uterus sheds all but deepest layer of endometrium; detached tissue & blood
pass out through vagina as menstrual flow
Proliferative phase (days
6-14): as estrogen blood levels rise, endometrium
rebuilds itself
Ovulation occurs in ovary at
end of this phase (day 14)
Secretory phase (days 15-28):
increasing progesterone levels prepare endometrium for embryo implantation,
creating blood vessels & stimulating nutrient secretion from uterine glands;
also, cervical plug of mucus reforms to block further sperm entry
Extrauterine Effects of Estrogen & Progesterone
In addition to promotion of oogenesis & follicle
growth in ovaries, estrogen also exerts anabolic effects on
female reproductive tract (increasing size of the duct system in preparation
for childbirth) & promotes appearance of secondary sex characteristics
in female
Progesterone inhibits motility
of uterus & promotes mammary gland activity
Female Sexual Response
Erectile tissue in clitoris & breasts
engorge with blood (similar to male response in penis), while increased activity
of vestibular glands lubricates vestibule
Sexually Transmitted Diseases (STDs or Venereal Diseases (VDs):
infectious diseases spread through sexual contact
Gonorrhea:
caused by bacterium Neisseria gonorrheae
Syphilis:
caused by bacterium Treponema pallidum
Chlamydia:
caused by parasitic bacterium Chlamydia trachomatis
Genital Warts:
caused by human papillomavirus (HPV) (certain types also cause invasive cervical
cancer)
Genital Herpes:
caused by human herpesviruses (herpes simplex virus)
Bacterial pathogens treated with antibiotics,
while viral pathogens are generally treated with antiviral medications
Developmental Aspects of the Reproductive
System:
Chronology of Sexual Development
Embryological and Fetal Events
Sex is determined by the sex chromosomes at conception; females
have two X chromosomes and males have an X and a Y chromosome.
Sexual Differentiation of the Reproductive System
The gonads of both males and females begin to develop during
week 5 of gestation.
During week 7 the gonads begin to become testes in males, and
in week 8 they begin to form ovaries in females.
The external genitalia arise from the same structures in both
sexes, with differentiation occurring in week 8.
About two months before birth the testes begin their descent
toward the scrotum, dragging their nerve supply and blood supply with them.
Puberty: the period of life (between 10-15
years of age) when the reproductive organs grow to their adult size & become
functional in response to gonadal hormones.
Menopause: the time of life in females (usually between 46-54
years of age) when menstruation (& ovulation) ceases
Gradual decline in estrogen levels causes
the reproductive organs & breasts to atrophy, with many other possible
effects
Hormone replacement therapy may be used
to alleviate the signs & complications, but may increase risk of some hyperproliferative
diseases (breast cancer)
