Reproductive
System
Chapter 16
Reproductive System
• Function: produce new individuals of a
species and pass on genetic material
• Structures:
– Gonads: primary sex organs (testes & ovaries)
• Produce gametes: sex cells (sperm & ova)
• Secrete sex hormones (development & function of
reproductive organs; sexual behavior & drives)
– Accessory reproductive organs
• Produce materials to support gametes (i.e. semen)
Male Reproductive Anatomy
• Gonad: testes; gamete: sperm
– Both exocrine (sperm-producing)
function and endocrine (testosteroneproducing) function
• Accessory ducts/glands: aid in
delivery of sperm to body exterior
or to female reproductive tract
Male Reproductive System
•
•
•
Testes
paired oval glands (10-15 g)
develop around 3rd month high on
posterior abdominal wall (descend
during 7th month)
Produce sperm & hormones
– Responds to hormones from pituitary
gland (FSH & LH)
•
•
•
FSH – stimulates spermatogenic cells to
produce sperm
LH – stimulates release of testosterone
(final trigger for spermatogenesis and
enhances spermatogenesis)
Divided into lobules that contain
seminiferous tubules
– Make sperm and empty sperm into rete
testis which leads to duct system
•
Interstitial cells surround
seminiferous tubules and produce
androgens (testosterone)
Cryptorchidism
• Testes do not descend
– 3% of full term infants, 30% premature
– both sides results in sterility
• Chance of testicular cancer 30-50 times higher
• 80% spontaneously descend in first year
• Hormones or surgery needed otherwise
Spermatogenesis
•
•
•
•
•
Sperm production (takes 64-72 days)
Begins during puberty and continues
throughout life
Millions of sperm produced per day
Formed in seminiferous tubules of testis
Spermatogonia: primitive stem cells (mitotically divide
throughout life)
– During puberty, FSH is secreted some new cells become primary
spermatocytes that will undergo meiosis and form four haploid
spermatids (immature)
•
Spermiogenesis (occurs in epididymis): spermatids stripped
of excess cytoplasm and tail forms to form mature sperm;
contain DNA
– Acrosome: releases enzymes that help sperm penetrate through
the capsule of follicle cells that surround the egg
Spermatogenesis
Spermatogonia
Primary Spermatocyte
Spermatid
Secondary Spermatocyte
Spermatozoon
(spermatozoa)
Threats to Spermatogenesis
• Common antibiotics (penicillin &
tetracycline) can suppress sperm formation
• Radiation, lead, certain pesticides,
marijuana, tobacco, excessive alcohol can
cause production of abnormal sperm
Testosterone Production
• interstitial cells in testes produce
testosterone
• activated by luteinizing hormone (LH) –
released by anterior pituitary gland with
FSH (sperm production)
• stimulates adolescent growth spurt,
prompts reproductive organs to develop,
underlies sex drive
• causes secondary male sex characteristics
Duct System
• Accessory organs transport sperm from the body
– Epididymis
• Temporary storage site for immature sperm from testis
• Takes about 20 days to make it through, sperm maturation
occurs and gain ability to swim
– Ductus deferens (vas deferens)
• Empties into ejaculatory duct, which passes through
prostate gland to merge with urethra
• vasectomy
– Urethra
• Extends from base of bladder to tip of penis
• Carries both urine and sperm to body exterior (part of both
systems)
• Bladder sphincter prevents passage of urine/sperm at same
time and prevents sperm from entering bladder
Ducts through which Sperm Travel
Seminiferous
Tubules
Epididymus
Vas deferens
Rete Tubules
Efferent ducts
Ejaculatory Ducts
Urethra
Vasectomy
• Portion of ductus deferens (vas
deferens) removed
• Sperm produced but degenerate
• Can be reversed (45-60%
effective)
Accessory Glands
• Seminal vesicles (60%)
– Located at base of bladder
– Secretion is rich in fructose, vitamin C, prostaglandins, and
other substances that nourish and activate sperm passing
through tract; alkaline (high pH); viscous
• Prostate (25%)
– Encircles upper part of urethra
– Produces fluid that plays role in activating sperm; milky
fluid, slightly acidic (citric acid & enzymes)
– aids in survival in female reproductive tract
• Bulbourethral glands (Cowper’s glands)
– Tiny glands inferior to prostate
– Produce thick, clear, alkaline mucus that cleans urethra of
traces of acidic urine prior to ejaculation
Semen
•
•
•
•
•
Mixture of sperm and accessory gland secretions
Transport medium for nutrients and chemicals that protect
sperm and aid in their movement
Fructose in seminal vesicle secretion provides the sperm’s
energy fuel
Alkalinity of semen (pH 7.2-7.6) helps neutralize the acidic
environment (pH 3.5-4) of female vagina (protects sperm &
maintains motility)
Contains:
–
–
–
–
•
antibiotic chemicals that destroy certain bacteria
hormone relaxin
enzymes that enhance sperm motility
substances that inhibit an immune response in female reproductive
tract
Dilutes sperm to aid in motility
– 2-5 ml semen ejaculated, between 50-150 million sperm per milliliter
Male Infertility
• First step to test fertility in a couple unable to
conceive is semen analysis
– Sperm count: <20 million per milliliter makes
impregnation improbable, 20-40 million borderline
– Motility – at least 60% swimmers
– Morphology – 65-70% not deformed
– Semen volume - low would indicate defect or
inflammation
– pH – slightly alkaline
– Fructose present
– liquefaction within 2 hours – enzyme defect if not
occurring
• May be caused by obstructions of duct system,
hormonal imbalances, environmental estrogens,
pesticides, excessive alcohol, many other factors
External Genitalia
• Scrotum: protection and support of testes
– Divided sac of skin
– Provides testes with temperature below body
temperature (viable sperm cannot be produced at
normal body temperature)
• need temperature 3 degrees lower than body temp.
– Cremaster muscle & change in scrotal surface area
regulate temperature (temperature can cause
infertility)
• Penis
– Delivers sperm into female reproductive tract &
supports urethra
– Shaft, glans penis, prepuce (foreskin) around glans
– Erectile tissue surrounds urethra to enable delivery of
sperm to female reproductive tract
Circumcision
Link
• Part or all of prepuce removed
• Usually performed by eighth day of life
• No consensus on medical benefits
Female Reproductive System
• Gonad: ovaries; gamete: ova
– releases both exocrine products (ova) and
endocrine products (estrogen and progesterone)
– in 3rd month, pre-programmed cells develop and
descend to pelvis and start making follicles (if no Y
chromosome)
• must nurture and protect developing fetus
during pregnancy
• accessory organs: structures to transport,
nurture, or serve the needs of reproductive cells
and/or developing fetus
Female Reproductive System
Sagittal Section
Posterior view
Ovaries
• contain ovarian follicles
– each follicle consists of
immature egg (oocyte)
surrounded by follicle cells
– follicle enlarges as oocyte matures and develops fluidfilled region called antrum
– ovulation: ejection of egg from ovary
– after ovulation, follicle becomes corpus luteum and
degenerates
• attached to uterus with ligament but no real
attachment to fallopian tubes
Ovulation
• approximately every 28 days
• ovum released from ovary and sucked up into
fallopian tube with current produced by fimbriae that
surround ovary and cilia inside tube
• fertilization occurs in fallopian tube (uterine tube)
• egg can drop into
abdominopelvic cavity, be
fertilized, and implant
outside uterus
(ectopic pregnancy)
Ovarian Cyst
• fluid-filled sac on or in ovary
• relatively often, most under 2
inches
• usually
noncancerous
Oogenesis
• formation of eggs (ova)
• one egg is formed per meiosis
• oogonium – predetermined diploid cell
– does not go through 2nd cell division
unless fertilized
– nucleus immediately splits if fertilized (2nd
nucleus expelled)
– unequal cell division – only get one egg
from meiotic division
Oogenesis
Primary Oocyte
Oogonia
Ovum
Secondary Oocyte
Maturation after
Fertilization
Contrasting Spermatogenesis & Oogenesis
Spermatogenesis
- equal division
- 4 sperm
- both divisions
prior to maturity
- 300 million per
day
Oogenesis
- unequal division
- one egg
- only 1 division prior
to fertilization
- 1-2 produced per
month (don’t waste
energy on 2nd division
Duct System
• Uterine Tubes (Fallopian tubes)
– receive ovulated oocyte and provide site for fertilization
• sperm must swim against current created by cilia
– fertilization occurs within 24 hours (due to viability of egg)
– location of surgical sterilization
• Uterus
–
–
–
–
path for sperm & egg (if not fertilized)
receives, retains, and nourishes fertilized egg
initiation of labor (contractions)
wall composed of three layers: perimetrium, myometrium,
endometrium
• endometrium is inner lining: if egg is fertilized, burrows into
endometrium (implantation); if not fertilized, sloughed off
periodically in response to changes in levels of ovarian hormones
in blood (menstruation)
• endometriosis: thickened, fibrous endometrium
Tubal Ligation
• surgical sterilization: fallopian
tubes cut and cauterized
• can be reversed
Toxic Shock Syndrome
• caused by bacterium:
Staphylococcus aureus
• high fever (up to 105),
sore throat, tender
mouth, headache, rash,
abdominal pain, vaginal
irritation
• most common in
females who use
tampons
Mammary Glands
•
•
•
•
organs of reproductive system
Modified sweat glands lie over chest
muscles
15-20 lobes
Respond to hormones
– Oxytocin (hypothalamus) begins lactation
– Prolactin (pituitary) helps oxytocin
to begin lactation and maintain lactation
– Relaxin allows milk to come in
(around 48 hours after birth)
•
•
Men have non-functional mammary
glands
Breast milk provides IgA antibodies
and nutrients difficult to replicate in
infant formula
Female Hormones
• FSH: stimulates follicles to have 1st cell
division to produce secondary oocyte
• LH: increases at ovulation
• Estrogen: released by ovary; controls
uterine cycle; builds endometrial lining
– Appearance of secondary sex characteristics
• Progesterone: released by ovary (and
placenta); controls uterine cycle; maintains
pregnancy if fertilization occurs
Female Hormones
Fertilization
• Spermatozoon and ovum merge into single nucleus
• Occurs in fallopian tube about 12-24 hours after
ovulation
• Only 1% of 300-500 million sperm reach secondary oocyte
• Sperm cannot merge with egg until in female
reproductive tract for 10 hours
– capacitation: functional change sperm undergo in female
reproductive tract; membrane formed round head of
sperm and enzymes released to help penetrate cells
around oocyte; enzymes liquefy semen so sperm become
more motile
• Oocyte secretes chemical to attract sperm
• Syngamy: only one sperm fertilizes egg (entry of other
sperm blocked to prevent polyspermy)
Zygote
• Fertilized egg (day zero)
• First cell of the individual
• Two nuclei fuse
Morula
• Developing embryo reaches uterus
around 3 days after ovulation
• Approximately 16 cells; uses uterine
secretions for nutrition and continues
dividing
Blastocyst
• Embryo hollows out to form a
ball-like structure once it has
about 100 cells
• Secretes hormone: human
chorionic gonadotropin (hCG)
– Stimulates corpus luteum of
ovary to continue producing
hormones
– Pregnancy tests
• Attaches to the endometrium
day 7 after ovulation
• Inner cell mass of blastocyst
begins to form the three
primary germ layers
Implantation
• Completed and uterine mucosa has
grown over embry0 by day 14 after
ovulation (normally day to start
menstruating)
• Enzymes secreted to penetrate
uterine lining and
immunosuppressors secreted to
prevent woman’s body from rejecting
embryo as “foreign”
Gastrulation
• Within one week of implantation
(around day 12)
• Gut begins to form (tube) – will
become digestive system
• embryonic disc – germ layers
(cells surrounding tube)
Primary Germ Layers
Neurilation
• Neurilation: nervous system
development (18-20 days)
– Organs start development
(organogenesis)
Embryonic Membranes
•
Yolk sac: early food source for embryo
– Early site of blood formation prior to spleen taking over
– Developmental circulatory system of embryo prior to placenta
•
Amnion: becomes amniotic sac
– Shock absorber for fetus, regulates temperature, prevents adhesions
– Amniocentesis
•
Chorion: Embryo’s contribution to
placenta
– Surrounds embryo and later
becomes part of placenta
– Chorionic villi testing
•
Allontois: Embryo’s contribution
to umbilical cord
– Small outpouching of yolk sac
– Early blood formation (helps yolk
sac)
– Becomes connection in placenta for
blood (umbilical cord)
Placenta
•
•
•
•
•
•
•
Developed by 3 months
Comes from chorion and endometrium of mother
Allows oxygen and nutrients to diffuse into fetal blood
from maternal blood with no mixing of blood
Small and nonpolar substances can pass through (i.e.
drugs and alcohol)
Protective barrier
(most microorganisms
cannot cross)
Stores nutrients
Produces hormones
necessary to maintain
pregnancy
Umbilical Cord
• Comes from allantois and mother’s
tissue
• Three vessels (one vein & two
arteries)
– Nutrients diffuse into umbilical vein
(towards fetus) and wastes leave
through umbilical arteries (away from
fetus)
• Wharton’s jelly around umbilical
cord (connective tissue)
Fetal Alcohol Syndrome
Leading cause of birth defects…and most preventable!
Gestation: 38-42 Weeks
• 266 days on
average
• Birth:
oxytocin &
positive
feedback!
labor