Transcript the reproductive system

THE REPRODUCTIVE SYSTEM
Ch 25, Human Anatomy
Sonya Schuh-Huerta, Ph.D.
The Reproductive System
• Involved in the production of gametes,
fertilization & procreation of the species
• Primary sex organs:
– Testes
– Ovaries
• Accessory sex organs:
– Glands
– External genitalia
The Male Reproductive System
The Male Reproductive System
• Produce male gamete (= sperm)
• Testes are located within the scrotum
• The scrotum  Skin & superficial fascia
surrounding the testes
– Positioning provides an environment 3˚ cooler than
body temperature!
• Dartos muscle = layer of smooth muscle
• Cremaster muscle = bands of skeletal muscle surrounding
the testes
– Elevates the testes
The Testes
• Contain long coiled seminiferous tubules where
sperm are made
• Enclosed in a serous sac  the tunica vaginalis
• Tunica albuginea  fibrous capsule of the testes
– Divides each testis into 250–300 lobules
• Lobules contain 1–4 coiled seminiferous tubules
• Epididymis
– Comma-shaped structure on posterior testis; where
the sperm go after they have developed in the testis
The Male Reproductive System
Ureter
Urinary bladder
Peritoneum
Seminal vesicle
Ampulla of
ductus deferens
Prostatic urethra
Ejaculatory duct
Membranous urethra
Pubis
Rectum
Urogenital diaphragm
Prostate
Bulbourethral gland
Corpus cavernosum
Corpus spongiosum
Spongy urethra
Anus
Bulb of penis
Ductus (vas) deferens
Epididymis
Testis
Scrotum
Glans penis
Prepuce (foreskin)
External urethral
orifice
Relationship of the Testes to the Scrotum
Urinary bladder
Superficial inguinal ring
(end of inguinal canal)
Spermatic cord
Testicular artery
Ductus (vas)
deferens
Penis
Autonomic
nerve fibers
Middle septum
of scrotum
Pampiniform
venous plexus
Cremaster muscle
External spermatic
fascia
Superficial fascia
containing dartos
Scrotum muscle
Epididymis
Tunica vaginalis
(from peritoneum)
Tunica albuginea
of testis
Internal spermatic
fascia
Skin
Nerves & Vessels
• Arterial supply of the testes
– Testicular arteries
• Testicular veins arise from the pampiniform
plexus
– Pampiniform plexus helps keep testes cool!
• Testes innervated by parasympathetic &
sympathetic divisions of ANS
• The spermatic cord contains:
– Vas deferens
– Testicular blood vessels & nerves
– Runs through inguinal canal
The Testis & Spermatic Cord
Spermatic cord
Spermatic cord
Blood vessels
and nerves
Ductus (Vas)
deferens
Head of epididymis
Efferent ductule
Rete testis
Straight tubule
Body of epididymis
Duct of epididymis
Tail of epididymis
Epididymis
Testis
Seminiferous
tubule
Lobule
Septum
Tunica albuginea
Tunica vaginalis
Cavity of
tunica vaginalis
Testis
Microscopic Anatomy
• Scientists once believed that the sperm
contained a tiny human or all the
material that would give rise to the
human (“spermists”)
A Seminiferous Tubule of the Testis
Seminiferous
tubule
Areolar
connective
tissue
Interstitial
Cells
(Leydig cells)
Myoid cells
Spermatogenic
cells
Sertoli Cell
& nucleus
Sperm
Microscopic Anatomy
• Sertoli Cells
– Surround developing sperm
– Extend from basal lamina to the lumen
– Tight junctions between cells
• Blood-testis barrier (protects sperm from immune system!)
– Assist sperm production
– Secrete testicular fluid &
androgen-binding protein
(ABP)
Microscopic Anatomy
• Interstitial cells:
• Myoid cells  surround seminiferous tubules
– Contract rhythmically
• Leydig cells
– Secrete testosterone (T)! What does T do?
• T secretion regulated by LH (Luteinizing Hormone)
The Epididymis
• Duct of the epididymis is 6 m long (when uncoiled)
• Dominated by pseudostratified columnar epithelium
– Bears tufts of stereocilia  immotile, long
microvilli
• 20-day journey for sperm to move through epidid.
– Chemical changes that give them the ability to
swim, undergo the acrosome reaction & fertilize
an egg
The Epididymis
Spermatic cord
Blood vessels
and nerves
Ductus (Vas)
deferens
Head of epididymis
Efferent ductule
Rete testis
Straight tubule
Body of epididymis
Duct of epididymis
Tail of epididymis
Testis
Seminiferous
tubule
Lobule
Septum
Tunica albuginea
Tunica vaginalis
Cavity of
tunica vaginalis
The Epididymis & Vas Deferens
Smooth muscle
around the duct
of the epididymis
Loose connective tissue
outside the duct
Stereocilia
Duct of the
epididymis
Sperm in
the lumen
Pseudostratified
columnar epithelium
(a) Duct of the epididymis (110)
Lumen
Smooth muscle
Mucosa
Pseudostratified
columnar
epithelium
Internal
longitudinal layer
Middle
circular layer
Lamina propria
External
longitudinal layer
Adventitia
(connective tissue)
(b) Vas deferens (7)
Vas Deferens (Ductus Deferens)
• Stores & transports sperm
• Joins up with ejaculatory duct
The Vas Deferens
• Trace the course of the Vas deferens
Seminal vesicle
Ampulla of
ductus deferens
Ejaculatory duct
Bulbourethral gland
Vas deferens
The Vas Deferens & Urethra
Ureter
Ampulla of
ductus deferens
Urinary
bladder
Prostate
Prostatic urethra
Orifices of
prostatic ducts
Membranous urethra
Root of penis
Seminal vesicle
Ejaculatory duct
Bulbourethral
gland & duct
Urogenital diaphragm
Bulb of penis
Crus of penis
Bulbourethral
duct opening
Ductus deferens
Corpora cavernosa
Epididymis
Shaft (body)
of penis
Corpus spongiosum
Testis
Spongy urethra
Glans penis
Prepuce
(foreskin)
External
urethral orifice
Accessory Glands
• The Seminal vesicles 
– Lie on the posterior surface of the urinary bladder
– Secretes about 60% of the volume of semen
• Fluid contains 
–
–
–
–
–
Fructose to nourish sperm
Substances that enhance sperm motility
Prostaglandins
Substances that suppress immune responses against semen
Enzymes that clot & then liquefy semen
Accessory Glands
• The Prostate gland 
– Encircles the prostatic urethra
– Secretes about 25–30% of the volume of seminal fluid
– Contains substances that
• Enhance sperm motility
• Enzymes that clot & then liquefy semen
Accessory Glands
• The Bulbourethral glands 
– Pea-sized glands inferior to the prostate gland
– Produce a mucus
• Mucus enters spongy urethra prior to ejaculation
– Neutralizes traces of acidic urine, otherwise this would
kill sperm!
– Also lubricates urethra
Male External Genitalia
• Penis  internal anatomy
– 3 erectile bodies
• 1 corpus spongiosum
– Surrounds spongy urethra
• 2 coropora cavernosa
– Contain sinuses, make up most of the penis
• Male sexual response
– Erection  parasympathetic control, allows blood to
enter corpora cavernosa
– Ejaculation  sympathetic control
Spermatogenesis
• Sperm formation
• 400 million sperm formed per day (that’s ~4,000 sperm per heartbeat!)
– Begins at puberty, continues throughout man’s entire life
– Process takes ~75 days
– Cells undergo meiosis, differentiate, & move toward the lumen
•
•
•
•
•
Spermatogonia
Primary spermatocytes
Secondary spermatocytes
Spermatids
Sperm
TESTIS
gonocyte
1°
spermatogonium spermatocyte
2°
spermatocyte
spermatid
mature sperm
Spermatogenesis
• Divided into 3 stages
– Stage 1  spermatogonia divide by mitosis
• Type A  maintain the germ cells (= stem cells)
• Type B  differentiate into primary spermatocytes
– Stage 2  meiosis I & meiosis II
• Meiosis I  forms 2 secondary spermatocytes
• Meiosis II  each secondary spermatocyte forms 2 spermatids
– Stage 3  Spermiogenesis
•
•
•
•
The 4 spermatids differentiate into mature sperm
Flagellum (tail) formed ( head, midpiece, tail)
Form acrosome
Shed cytoplasm (compact head, with very little cytosol)
Spermatogenesis
Spermatogonium
(stem cell)
Meiosis
(early spermatogenesis)
Spermiogenesis
(late spermatogenesis)
Spermatogenesis
Mitosis
Growth
Enters
meiosis I and
moves to
adluminal
compartment
Meiosis I
completed
Basal lamina
Type A daughter cell
remains at basal lamina
as a stem cell
Type B daughter cell
Primary
spermatocyte
Secondary
spermatocytes
Meiosis II
Early
spermatids
Late spermatids
Sperm
(b) Events of spermatogenesis,
showing the relative position
of various spermatogenic cells
Spermiogenesis
Golgi
apparatus
Approximately 24 days
Acrosomal
vesicle
Mitochondria
Acrosome
Nucleus
1
(a)
2
Spermatid
nucleus
Centrioles
3
Midpiece Head
Microtubules
Flagellum
Excess
Cytoplasm
(cytoplasmic
droplet)
Acrosome
4
Tail
5
6
(b)
7
Control of Spermatogenesis
• Spermatogenesis controlled by 
– Follicle stimulating hormone = FSH (from ant. pituitary)
– Testosterone (from testis)
• Secretions from Sertoli cells also influence
spermatogenesis
– Androgen-binding protein concentrates T near
developing sperm
– Inhibin  inhibits FSH (feedback loop)
Normal Sperm Parameters & Male
Infertility
 > 20 million (20–150 million) sperm per ml (2–3 ml/ejaculate)
 > 50% forward motility
 > 40% normal morphology
Male Infertility Disorders
 Endocrine – Testicular Feminization Syndrome
(androgen receptor does not respond to T)
 Hypothalamic – Kallman’s Syn (no GnRH or olf. neurons)
 Anatomic – Varicocele
 Sertoli Cell Only Syndrome
 Oligospermia = reduced sperm #
human sperm
 Azoospermia = no sperm
 Asthenozoospermia = reduced motility
 Chromosomal Defects = Klinefelter’s Syndrome (XXY)
Causes of Human Infertility
 ~15% of couples are infertile
low sperm quantity
poor morphology
poor motility
 Male infertility contributes to ~½ of cases
Causes of Male Infertility
Unusual
Problems
Ovulatory
Dysfunction
15%
5%
Unknown 10%
Female tubal &
pelvic pathology
35%
Male Factor
35%
 Endocrine
 Hypothalamic/Pituitary
 Anatomic
 Coital Disorders
 Environmental Factors
 Infections/toxins/drugs
 Sperm abnormalities
 Genetic/Chromosomal Defects
 Idiopathic
(Speroff, L., Clin Gynecol Endocrin & Infertility, 1999)
Cancers of the Male
Reproductive System
• Testicular cancer
–
–
–
–
Affects 1 in 50,000 males
Commonly from early-stage spermatogenic cells
Increase of 50% from 1974 to 1990
Cured in 95% of cases
• Prostate cancer
– Slow-growing  arises from peripheral glands
– Increasingly common
– Risk factors
• Fatty diet
• Genetic predisposition
The Female Reproductive System
Leonardo Da Vinci
Female Reproductive System
• Produces female gamete (= oocytes/eggs)
• Functions to support a developing embryo
• Undergoes changes according to the menstrual
cycle
– Menstrual cycle = the monthly cycle as it affects all
reproductive organs in preparation for pregnancy
• Includes:
– Ovaries, uterine tubes (fallopian tubes), uterus, & vagina
The Vagina
• Consists of 3 layers
– Adventitia  fibrous connective tissue
– Muscularis  smooth muscle
– Mucosa  marked by transverse folds
• Consists of lamina propria & stratified squamous
epithelium
• Hymen  an incomplete diaphragm
• Fornix  recess formed at the superior part of
the vagina
The Ovaries
• Small, almond-shaped organs
– Produce eggs/oocytes!!!
• Held in place by ligaments & mesenteries
– Broad, suspensory, & ovarian ligaments
• Ovarian arteries  arterial supply
• Innervated by both divisions of ANS
Female Internal Reproductive Organs
Peritoneum
Uterosacral
ligament
Perimetrium
Rectouterine
pouch
Rectum
Posterior fornix
Cervix
Anterior fornix
Vagina
Anus
Urogenital diaphragm
Greater vestibular
(Bartholin’s) gland
Suspensory ligament
of ovary
Infundibulum
Uterine tube
Ovary
Fimbriae
Uterus
Round ligament
Vesicouterine pouch
Urinary bladder
Pubic symphysis
Mons pubis
Urethra
Clitoris
External urethral
orifice
Hymen
Labium minus
Labium majus
The Female Reproductive System
Suspensory
ligament of ovary
Uterine (fallopian) tube
Ovarian blood
vessels
Mesosalpinx
Fundus
of uterus
Uterine
tube
Lumen (cavity)
of uterus
Ampulla
Ovary
Isthmus
Infundibulum
Mesovarium
Broad
ligament
Fimbriae
Mesometrium
Ovarian ligament
Body of uterus
Ureter
Uterine blood vessels
Isthmus
Uterosacral ligament
Lateral cervical
(cardinal) ligament
Lateral fornix
Cervix
Round ligament of uterus
Endometrium
Myometrium
Perimetrium
Internal os
Cervical canal
External os
Vagina
Wall of uterus
Deep Structures of the Female External
Genitalia & Perineum
Clitoris
Labia minora
Labia majora
Anus
Inferior ramus
of pubis
Bulb of
vestibule
Pubic symphysis
Body of clitoris,
containing corpora
cavernosa
Clitoris (glans)
Crus of clitoris
Urethral orifice
Vaginal orifice
Greater vestibular
gland
Fourchette
Internal Structure of the Ovaries
follicle
B
• Tunica albuginea
oocyte
– Fibrous capsule of the ovary
• Ovarian cortex  periphery, where developing
oocytes are found
• Follicles  multi-cellular sacs housing oocytes
• Ovarian medulla  loose connective tissue
– Contains blood vessels, lymph vessels, & nerves
Structure of the Ovary
Tunica albuginea
Cortex
Oocyte
Degenerating
corpus luteum
(corpus albicans)
Granulosa cells
Antral follicle
Mesovarium &
blood vessels
Mature ovarian
(Graafian)
follicle
Germinal epithelium
Primary follicles
Antrum
Oocyte
Ovarian
ligament
Zona
pellucida
Theca
folliculi
Medulla
Corpus luteum
Ovulated
oocyte
Developing
corpus luteum
Corona
radiata
The Fallopian Tubes (Oviducts)
• Receive ovulated oocyte
• Parts of the fallopian tube 
– Infundibulum = distal end of uterine tube
• Surrounded by fimbriae (finger-like
projections)
– Ampulla = middle 1/3 of uterine tube
• Usual site of fertilization!!!
– Isthmus = medial 1/3 of uterine tube; narrows
Microscopic Anatomy of Uterine Tubes
• Muscular & ciliated  aids in transport of oocyte & embryo!
Muscularis
Mucosa
Ciliated
columnar
epithelium
Nonciliated
epithelium
Lamina
propria
(a) Cross section through the ampulla
(10)
(b) Enlargement of the mucosa
(180)
The Uterus
• Lies anterior to rectum, posterior to bladder
• Anteverted (anteflexed) usual position of
uterus
• Parts of the uterus 
– Fundus = rounded superior portion
– Cervix = “neck” of uterus
• Cervical canal = connects with vagina inferiorly
• Internal os = opening connecting with uterine cavity
• External os = inferior opening of cervix (at top of vagina)
Supports of the Uterus
• Uterus is supported by
– Mesometrium  anchors uterus to lateral
pelvic walls
– Lateral ligaments  horizontal from cervix &
vagina
– Round ligaments  bind uterus to the anterior
pelvic wall
Uterine Wall
• Wall of the uterus composed of:
– Perimetrium, myometrium, & endometrium
• Embryo burrows into endometrium
• Endometrium has 2 layers
– Functional layer
– Basal layer
Uterine Wall
• Uterine arteries  send branches to
uterine wall & divide into arcuate arteries
• Radial arteries reach the endometrium &
branch into 
– Straight arteries  to basal layer
– Spiral arteries  to functional layer
• Undergo degeneration (& are shed) and then
regeneration with the menstrual cycle
The Uterine Wall
Lumen of uterus
Epithelium
Lumen of uterus
Epithelium
Capillaries
Uterine glands
Uterine glands
Functional
layer of the
endometrium
Venous sinusoids
Lamina propria of
connective tissue
Lamina propria of
connective tissue Spiral (coiled)
artery
Straight artery
Endometrial vein
Smooth muscle
fibers
Basal layer
of the
endometrium
Portion
of the
myometrium
Radial artery
Smooth muscle
fibers
Arcuate artery
Radial artery
Uterine artery
The Female Menstrual Cycle &
Oogenesis
• Monthly menstrual cycle
– The recurring cycle of physiological changes to uterus, ovaries, & other
reproductive organs due to hormonal fluctuations in ovaries, that occur
from the beginning of one menstrual period to the next
• Ovarian cycle  stimulates maturation of
ovarian follicles & oocytes
• Uterine cycle  prepares uterine wall for
implantation
The Ovarian Cycle
• Follicular phase
– 1st half of the ovarian cycle
– 6–12 primordial follicles stimulated to develop
– Growth stimulated by FSH from ant. pituitary
– Primordial follicle  primary follicle
– As follicles grow larger  they gain granulosa &
thecal cells  layers of follicle that secrete
hormones (estrogens, etc.)
The Follicular Phase (cont…)
• Primary follicles  secondary follicles
– Corona radiata  coat of granulosa cells
surrounding oocyte
• Secondary follicles enlarge & become 
– Antral follicles (Antrum = fluid-filled cavity)
– Then, become mature Graafian follicle  ready to
be ovulated
– Only 1 dominant Graafian follicle ovulated (usually!)
– Rest undergo atresia  cell death
Graafian follicle
OVARY
gonocyte
primordial
follicle
1° follicle
2° follicle
Antral follicle
mature
ovum
ovulation
The Ovarian Cycle
• Ovulation
– Occurs about halfway through each ovarian
cycle (~Day 14)
– 1 mature oocyte ruptures from follicle & exits
from 1 ovary
• Enters peritoneal cavity
– Swept into oviduct by fimbria
– Sudden increase in LH (from
ant. pituitary) is signal for
ovulation!
ovulation movie
The Ovarian Cycle
• Luteal phase
– Occurs after ovulation, in last half of the
ovarian cycle
– Remaining follicle becomes a corpus luteum
• Secretes progesterone
• Prepares uterus for implantation of an embryo
– If no implantation
• Corupus luteum dies
The Ovarian Cycle
2 Primary
1 Primordial
follicle
follicles
2
3
3 Secondary follicle
Theca folliculi
4
Primary oocyte
1
4 Antral follicle
Zona pellucida
8
5
7
Antrum
Secondary oocyte
6
7
7 Corpus luteum (forms
from ruptured follicle)
Secondary oocyte
Corona radiata
6 Follicle ruptures;
secondary oocyte ovulated
5 Mature ovarian follicle carries out
meiosis I; ready to be ovulated
Plasma hormone level
The Ovarian Cycle
LH
FSH
Days 1
5
Menstrual
phase
10
Proliferative
phase
15
20
Secretory
phase
25
(a) Fluctuation of gonadotropin levels: Fluctuating levels
of pituitary gonadotropins (follicle-stimulating hormone and
luteinizing hormone) in the blood regulate the events of the
ovarian cycle.
28
Primary
Vesicular
Corpus
follicle
follicle
luteum
Secondary
Ovulation
Degenerating
follicle
corpus luteum
Follicular
phase
5
Days 1
Menstrual
phase
Ovulation
(Day 14)
10
Proliferative
phase
15
Luteal
phase
20
25
Secretory
phase
28
(b) Ovarian cycle: Structural changes in the ovarian follicles
during the ovarian cycle are correlated with (d) changes in
the endometrium of the uterus during the uterine cycle.
Oogenesis
• Takes many years to complete (~12–51 years!)
• Primary oocytes are arrested (stalled) in meiosis I
• Surge of LH also causes primary oocyte to
compete meiosis I
• Oogenesis produces 1 ovum & 3 polar bodies
– Polar bodies do not contribute to developing embryo
– Are shed & lost
• Meiosis II is completed only upon fertilization
Oogenesis
Before birth
Meiotic events
Follicle development
in ovary
Oogonium (stem cell)
Follicle cells
Oocyte
Mitosis
Primary oocyte
Primordial follicle
Primary oocyte
(arrested in prophase I;
present at birth)
Primordial follicle
Growth
Infancy and
childhood
(ovary inactive)
Each month
from puberty
to menopause
Primary follicle
Primary oocyte
(still arrested in
prophase I)
Secondary follicle
Spindle
Meiosis I (completed
by one primary oocyte
each month in response
to LH surge)
First polar body
Meiosis II of polar
body (may or may
not occur)
Polar bodies
(all polar bodies
degenerate)
Mature ovarian
follicle
Secondary oocyte
(arrested in
metaphase II)
Ovulation
Sperm
Meiosis II
completed
(only if
sperm
penetration
occurs)
Second Ovum
polar body
Ovulated secondary
oocyte
The ruptured follicle
becomes a corpus
luteum and ultimately
degenerates.
Degenating
corpus luteum
The Uterine Cycle
•
•
•
•
Series of cyclic phases of the endometrium
Phases coordinate with the ovarian cycle
Endometrial phases directed by FSH & LH
Phases of uterine cycle
– Menstrual phase  days 1–5
• Stratum functionalis is shed
– Proliferative phase  days 6–14
– Secretory phase  days 15–28
The Uterine Cycle
Structural & hormonal changes
Blood vessels
Plasma hormone level
Endometrial
glands
Menstrual
flow
Estrogens
Progesterone
Days 1
5
10
15
20
25
28
Menstrual
Proliferative
Secretory
phase
phase
phase
(c) Fluctuation of ovarian hormone levels: Fluctuating
levels of ovarian hormones (estrogens and progesterone)
cause the endometrial changes of the uterine cycle. The
high estrogen levels are also responsible for the LH/FSH
surge in (a).
Functional
layer
Basal layer
Days
1
5
Menstrual
phase
10
Proliferative
phase
15
20
Secretory
phase
25
(d) The three phases of the uterine cycle
Menstrual: Shedding of the functional layer of
the endometrium.
Proliferative: Rebuilding of the functional layer of the
endometrium.
Secretory: Begins immediately after ovulation.
Enrichment of the blood supply and glandular secretion of
nutrients prepare the endometrium to receive an embryo.
Both the menstrual and proliferative phases occur before ovulation,
and together they correspond to the follicular phase of the ovarian
cycle. The secretory phase corresponds in time to the luteal phase
of the ovarian cycle.
28
Oocyte Loss & Infertility
• Follicles lost by atresia/cell death (~1,000/month lost)
• Follicles/oocytes lost throughout life
• Quality & quantity of oocytes  ovarian reserve
• Ovarian reserve correlated with fertility
• Many reproductive disorders/diseases where #
of follicles reduced  subfertility or infertilty
• Variability among women  genes & environment
The Life History of a Woman’s Oocyte Pool
Fetal Life
Conception 12 wks 20 wks
Birth
Puberty
Age ~12
Peak Fertility
20’s
Fertility Decline
30’s
Menopause
Age ~51
1 million
oocytes/follicles
PGCs
~1,000
oogonia enter
meiosis & differentiate
Ovulation begins
500,000 oocytes
~25,000 oocytes
Ovulation ends
<1,000 oocytes
PGC migration
& proliferation
5-7 million
(Langman’s Medical Embryology, 2007)
www.istockphoto.com
Egg Number Declines with Age
•
•
We can measure a woman’s oocyte pool
Studies of genetic & environmental links
Follicle Counts in Women
60
50
Transvaginal Ultrasound Image
of Antral Follicles
40
AFC
AFC (Antral Follicle Count) =
Non-invasive window into
oocyte pool
R2 = 0.27
R2 = 0.28
30
20
10
0
25
30
35
40
45
Age (years)
(Schuh-Huerta et al., Hum Reprod 2011 & Hum Genet 2012)
Causes of Female Infertility
Female Infertility-Related Disorders
 Various reproductive system cancers and/or radiation therapy (now
fertility preservation being done  cryopreservation of eggs)
 Endocrine – Polycyctic Ovarian Syndrome (high androgen levels, cystic
(ovaries, metabolic/hormonal abnormalities)
 Anatomic – Congenital defects, Pelvic inflammatory disease (& scarring)
 Endometriosis – endometrial tissue growing outside of uterus
 Premature Ovarian Failure = loss of all follicles before age 40
 Early Menopause = loss of all follicles before age 45
 Chromosomal Defects = Turner’s Syndrome (XO)
 Female-produced Anti-sperm antibodies
Fertilization, Pregnancy & Childbirth
Donating Eggs or Sperm
Egg Donors
Compensated
$6,500–$8,000
Sperm Donors
Compensated
$100/sample
$1,200/month
for 3X/week
Fertilization
• Events leading to fertilization 
– Sperm binds to the zona pellucida (coat of egg)
– Undergoes the acrosome reaction
• Releases enzymes to penetrate zona pellucida
– Fusion of oocyte & sperm
– Cortical & Zona Reactions of egg
• Enzymes prevent other sperm from binding to the egg &
the zona becomes hardened (prevents polyspermy &
protects developing zygote/embryo)
– Fertilization  chromosomes of male & female
gametes join (2 pronuclei fuse; diploid chromosome
complement restored)
Close Encounters of the Zygotic Kind
Mammalian Fertilization
1. Sperm Capacitation
1. Capacitation
2. Chemoattraction
2. Chemoattraction
3. Sperm-ZP
Binding
3. Sperm-Zona Pellucida Binding
4. Acrosome Reaction
5. Penetration of the ZP
6. Sperm-Oocyte Binding &
Fusion
6. Sperm-Oocyte
Binding & Fusion
Ca2+
4. Acrosome
Reaction
7. Egg Activation
8. Zona Reaction
5. Penetration
of ZP
(Dick Bowen, Colorado State)
7. Egg Activation
8. Cortical & Zona Reaction
Fertilization
Sperm
Corona radiata
Zona pellucida
First polar
body
Oocyte in
second meiotic
division
(b)
Sperm nucleus
Acrosome
Acrosomal
reaction
Granulosa cells
of corona radiata
Zona pellucida
Extracellular
space
Oocyte plasma
membrane
Cortical granule
Oocyte cytoplasm
Cortical
Fusion of oocyte
and sperm plasma reaction
membranes
Sperm nucleus engulfed
by oocyte cytoplasm
Early Embryonic Development
(a)Zygote
(fertilized egg)
Uterine
tube
(b)4-cell stage
2 days
(d)Early blastocyst
(morula hollows out
and fills with fluid).
4 days
Blastocyst
cavity
Sperm
Fertilization
(sperm
meets and
enters egg)
Oocyte
(egg)
(e)Implanting blastocyst
(consists of a sphere
of trophoblast cells and
an eccentric cell cluster
called the inner cell
mass). 7 days
Ovary
Trophoblast
Ovulation
Uterus
Endometrium
Cavity of
uterus
Blastocyst
cavity
Inner cell
mass
Implantation
• Blastocyst begins implantation
– ~6 days after conception
• Blastocyst consists of:
– Inner cell mass & outer trophoblast
– Trophoblast forms 2 layers 
• Cytotrophoblast = inner layer; along with
extraembryonic mesoderm forms chorion & chorionic villi
• Syncytiotrophoblast = outer layer; invades & erodes the
endometrium
The Placenta
• Exchanges across the chorionic villi between
maternal & fetal blood
– Provide fetus with nutrients & O2
– Dispose of its wastes
– Allow hormonal signals to be sent to the mother
• By Week 13 the placenta is fully formed &
functional
Implantation & Growth of Placenta
Endometrium
Maternal
blood vessels
Maternal
blood vessels
Proliferating
syncytiotrophoblast
Cytotrophoblast
Amniotic cavity
Bilayered
embryonic disc
Endometrial epithelium
(a) Implanting 71/2-day blastocyst.
The syncytiotrophoblast is eroding
the endometrium.
Lacuna
(intervillous space)
containing maternal
blood
Proliferating
syncytiotrophoblast
Amnion
Cytotrophoblast
Amniotic cavity
Bilayered
embryonic disc
Yolk sac
Extraembryonic
mesoderm
Chorion
being formed
(b) 12-day blastocyst. Implantation is complete. Extraembryonic
mesoderm is forming a discrete layer beneath the cytotrophoblast.
Amniotic cavity
Primary
germ layers
Chorionic villus
Ectoderm
Chorion
Mesoderm
Amnion
Endoderm
Forming
body stalk
Yolk sac
Allantois
Extraembryonic
mesoderm
Lumen of uterus
Lumen of uterus
Extraembryonic
coelom
(c) 16-day embryo. Cytotrophoblast and associated mesoderm have become the
chorion, and chorionic villi are elaborating. The body stalk forms the basis of the
umbilical cord.
Implantation & Growth of Placenta
Decidua basalis
Maternal blood
Chorionic villus
Umbilical blood
vessels in
umbilical cord
Amniotic sac
Amniotic cavity
Yolk sac
Extraembryonic
coelom
Lumen
of uterus
Chorion
Decidua
capsularis
(d) 41/2 -week embryo. The decidua capsularis, decidua basalis, are well
formed. The chorionic villi lie in blood-filled intervillous spaces within the
endometrium. The embryo is now receiving its nutrition via the umbilical
vessels that connect it (through the umbilical cord) to the placenta.
The 13-Week Placenta
• Embryonic & maternal tissues contribute to the placenta
Placenta
Decidua basalis
Chorionic villi
Yolk sac
Amnion
Amniotic
cavity
Umbilical
cord
Decidua
capsularis
Extraembryonic
coelom
Uterus
Lumen of
uterus
(e) 13-week fetus – placenta now fully formed and functional
Anatomy of the Placenta
Placenta
Chorionic
villi
Decidua
basalis
Maternal
arteries
Maternal
veins
Myometrium
Umbilical
cord
Decidua
capsularis
Uterus
Lumen of
uterus
Chorionic villus
containing fetal
capillaries
Maternal blood
in lacuna
(intervillous space)
Fetal arteriole
Fetal venule
Amnion
Umbilical cord
Stratum basalis
of endometrium
Maternal portion
of placenta
(decidua basalis)
Fetal portion
of placenta
(chorion)
Umbilical arteries
Umbilical vein
Connection to
yolk sac
Anatomy of the Placenta
• Placental barrier consists of:
– All 3 layers of the chorionic villi
• Sugars, fats, & O2 diffuse from mother to fetus
• Urea & carbon dioxide diffuse from fetus to mother
• Syncytiotrophoblast  secretes substances that
regulate events of pregnancy
• Maternal antibodies transported across placenta
• Viruses, alcohol, & heroin cross the placental barrier
Pregnancy & Childbirth
•
•
•
•
Gestation  266 days (40 weeks)
High levels of progesterone & estrogen maintain pregnancy
Parturition  childbirth
Labor  events that expel the infant from the uterus
Umbilical
cord
Placenta
Uterus
Pubic
symphysis
Cervix
Vagina
(a) Dilation (early)
Sacrum
(b) Dilation (late)
Childbirth
• Early Labor
• Active Labor (regular, increasingly
painful contractions; > 4 cm dilated)
• Delivery of baby
• Delivery of placenta
• Avg time of labor ~ 7–12 hrs
Perineum
Uterus
(c) Expulsion
Placenta
(detaching)
Umbilical
cord
(d) Placental
The Mammary Glands
• Breasts  modified sweat glands
– Glandular structure  undeveloped in
nonpregnant women
– Milk production  starts at or after childbirth
– Before milk production  secretion of
callostrum (loaded with mom’s antibodies)
The Mammary Glands
First rib
Skin (cut)
Pectoralis major muscle
Suspensory ligament
Adipose tissue
Lobe
Areola
Nipple
Opening of
lactiferous duct
Lactiferous sinus
Lactiferous duct
Lobule containing alveoli
Hypodermis
(superficial fascia)
Intercostal muscles
Cancers of the Female
Reproductive System
• Ovarian cancer  arises from cells in the
germinal epithelium
• Endometrial cancer  arises from the
endometrium of the uterus
• Cervical cancer  slow-growing, arises from
epithelium at tip of the cervix; often associated
with HPV
Cancers of the Female
Reproductive System
• Breast cancer  2nd most common cause
of cancer deaths in women!
– 97% occurs in women over 50
– Treatment
• Surgical removal of the mass (lumpectomy or
mastectomy)
• Radiation therapy
• Administration of selected hormones
• Chemotherapy
Breast Cancer
(a) Mammogram procedure
Malignancy
(b) Film of normal breast
(c) Film of breast with tumor
Embryonic Development of the
Sex Organs
• Sexual Differentiation
• Embryo at 5–6 weeks is sexually
indifferent
– Mesonephric (Wolffian) ducts  future
male ducts
– Paramesonephric (Mullerian) ducts 
future female ducts
Embryonic Development of the Sex Organs
Mesonephros
Mesonephric
(Wolffian) duct
Gonadal ridge
Paramesonephric
(Müllerian) duct
Metanephros
(kidney)
Cloaca
5- to 6-week embryo:
sexually indifferent stage
Embryonic Development of the Sex Organs
• Development of the external genitalia
Genital
tubercle
Urethral fold
Labioscrotal
swelling
Anus
Tail (cut)
Urethral groove
(a) Indifferent external genitalia;
Approximately 5 weeks
Sexual Differentiation
• Male sexual differentiation  begins in Week 7
• SRY = Sex Determining Region of the Y
Chromosome  initiates male differentiation
– Wolffian ducts become 
• Epididymis
• Vas deferens
• Ejaculatory duct
– Mullerian ducts  degenerate
Sexual Differentiation
• Female sexual differentiation  begins Week 8
– Cortical portion of immature ovaries form
ovarian follicles
– Mullerian ducts become 
• Uterus
• Fallopian tubes
• Superior part of vagina
– Wolffian ducts  degenerate
Sexual Differentiation
Glans penis
Glans clitoris
Labioscrotal
swellings
(scrotum)
Urethral folds
Labioscrotal
swellings
(labia majora)
Anus
Urogenital sinus
Urethral folds
(labia minora)
Anus
Glans penis
Glans clitoris
Penis
Scrotum
Labia majora
Anus
Anus
(b) Male development
Labia minora
(c) Female development
Puberty
• Sexual maturation  changes that occur during the
period of life between ages ~10–18
• Begins with pulsatile secretion of GnRH from brain
• Reproductive organs grow to their adult size
• Events of puberty occur in the same sequence in
all individuals
– Age at which events of puberty occur varies widely
– Age of puberty has decreased dramatically
Puberty
• Male secondary sex characteristics
– Enlargement of the scrotum &
testes (age ~13)
– Appearance of pubic, axillary, &
facial hair
– Lengthening of vocal folds  deepening voice
– Musculoskeletal system increases in mass
– Sexual maturation  mature sperm in seminal fluid
Puberty
• Female secondary sex characteristics
– Budding breasts (avg age ~11)
– Other estrogen-induced secondary sex characteristics
• Increase in subcutaneous fat
• Widening & lightening of the pelvic girdle bones
• Appearance of axillary & pubic hair
• Estrogen-induced growth spurt from age ~12-17
– Menarche  the first menstruation (avg age ~12)
Strong correlations between
industrialization, better nutrition,
body fat (BMI), and decreased
age of menarche.
more fat  tells your brain
you’re ready to reproduce!
…What hormones/signals might
be involved?
Reproductive Life Span &
Menopause
• Female reproductive peak  late 20’s
• Late 30’s  increases in:
–rate of follicle loss
–miscarriage rates
–trisomies & other genetic defects
–complications of pregnancy & prematurity
–high risk pregnancy (multiples)
–infertility
• Ovulation & menstruation cease  age ~46–54
– No more follicles; ovaries stop secreting estrogen!
• Reproductive organs & breasts begin to atrophy
• Osteopenia, osteoporosis, & cardiovascular disease risk
Questions?
What’s Next?
Today’s Lab: Reproductive System
Mon Lecture: Endocrine System
Mon Lab: Endocrine System & Presentations