Reproductive Physiology
Dr. Anderson
Rowan University
Chromosomal Gender Determination
• Gender differentiation is largely determined by week 20 in fetal
development
Y-Chromosome Effects
• Y-Chromosome has
the SRY gene which
causes the
undifferentiated
gonads to turn into
testes when
expressed.
• If this gene is not
expressed, then the
fetus will develop as
a female
Ovaries/Testes
• In the embryo, ovaries start
as mesonephric ducts or
paramesonephric ducts
• If SRY gene is expressed,
mesonephric ducts develop and
hormones cause
paramesonephric ducts to
regress (male child)
• If SRY gene is absent (or not
expressed) the opposite will
happen (female child)
Female Differentiation
• Lack of testosterone,
DHT, and antimullerian hormone
allow the
paramesonephric
ducts to develop
• Uterus
• Fallopian tubes
• Vagina
Further Differentiation
• Once testes are formed, testosterone
will continue to shape the male to
form
• Epididymis
• Seminal vesicle
• Vas Deferens
External Genitalia
• Very similar between males and females! (in derivation)
• Hormonal influences (or lack of) determine the final external genital
arrangement
https://www.youtube.com/watch?v=jFh4iStyW3c
Final Phenotypes
• Given that the genitalia derive from the same tissue…
• How could the development of the genitalia vary?
• Male, female, intersexed
Puberty ( Males)
• Begins at roughly 11-12 years old
• Gonadotropin stimulating hormone causes a marked increase in
testosterone production
• Testosterone causes:
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Increase in facial, axillary and pubic hair length
Apocrine glands increase activity (axillary and perineal regions)
Deeper voice
Increase in testicular and penis size
Muscle and bone growth (size and thickness)
Puberty (Females)
• Begins at roughly 10-11 years old (as early as 8)
• Why so early?
• Gonadotropin stimulating hormone causes a marked increase in
estrogen production
• Estrodiol (estrogen) production causes:
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Axillary and pubic hair appears
Apocrine glands increase activity (axillary and perineal regions)
Deeper voice (larynx increases)
Increase in labia minora and clitoris size
Menarche
Breast tissue develops
Gamete Production
• Sperm and eggs cells are produced
via meiosis, not mitosis
• When sperm and eggs are
produced, genes are randomly
mixed during meiosis I (prophase I)
• This means that every sperm and
egg produced will be unique
Crossing Over
• During meiosis I,
chromosomes lined
up in metaphase can
exchange chromatids
(sections of DNA
containing whole
genes)
• This leads to every
sperm being slightly
different, genetically
Sperm Production
• Sperm are produced in the seminiferous tubules
via meiosis
• Sperm have half of the genetic material of the
father
• So are all sperm the same?
Sperm Production
• Temperature is important! (controlled by cremaster muscle scrotum)
• Optimal temperature is roughly 92° F.
• Activated by the secretion of Follicle-Stimulating Hormone (FSH) and
testosterone
• Androgen-binding protein in the testes increases the amount of
testosterone in the seminiferous tubules
• Up to 200 million sperm produced daily
Sperm Life Cycle
Primary spermatocytes (diploid)
Meiosis I
Secondary spermatocytes (Diploid)
Meiosis II
Haploid spermatids
Sperm Release
• Sperm are stored in the epididymis until
ejaculation
• Sperm cannot swim until they mix with the
“activating” fluids produced by the prostate
and seminal vesicles
• Roughly 0.1 – 10 ml of ejaculate produced,
with up to 300 million sperm/ml
Oogenesis
• Of about 15 follicles that begin to develop, only one dominant follicle
continues after 9 days of the cycle – the others are resorbed into the ovary
• This dominant follicle starts to produce large amounts of estrogen
Mechanics of Sex - Male
• Erection – caused by the release
of nitric oxide which causes
blood vessels to dilate
• Corpora cavernosa of the penis
• Hydrostatic pressure increases
penis size and rigidity enabling
insertion
Mechanics of Sex - Male
• Upon arousal, pre-ejaculate is produced
by Cowper’s glands (bulbo-urethral
gland)
• This fluid is slightly alkaline – why?
Mechanics of Sex - Female
• Arousal leads to production of
vaginal secretions that lubricate it for
penis insertion
• Vaginal secretions are thought to
derive from the blood plasma
• Released upon engorgement of vaginal
blood vessels
• Clitoris will also enlarge and emerge
from the clitoral hood
Birth Control
• Condoms (male and female)
• The “pill”
• Birth control pills
• The Morning After Pill
• The Abortion Pill
• Implants (vaginal, subdermal)- release
hormones that prevent ovulation
• Intrauterine Devices (IUD’s)
• Diaphragm
Conception and Pregnancy
Dr. Robert Anderson
Rowan University
Conception
• Sperm cells are released into
the female reproductive
tract
• After ovulation, egg cells
(oocytes) are most receptive
to fertilization
Conception - Location
• Most often, conception
happens in the ampulla
of the fallopian tube
• What is the point of such
an arduous trip for
sperm cells?
Point of Conception
• Acrosome contains
enzymes that penetrate
the jelly coat of the egg
• When one sperm
penetrates the plasma
membrane of the egg,
other sperm are
prevented from entering
• Why?
• Cortical granules “seal”
the egg from other sperm,
preventing polyspermy
Week 1 (GH)
• Sperm has reached egg
and the cells have
fused to become a
zygote
• Cells proliferate via
mitosis (morula stage)
on their way to the
uterus where they will
implant
Week 1 (Continued)
• Morula becomes a multi-cellular,
ring-shaped blastocyst
• The blastocyst “hatches” – frees
itself from the zona pellucida,
allowing to implant into the
endometrium of the uterus (day
8-9)
Week 2 - Implantation
• Surge of progesterone (from
ovulation) makes the lining of
the uterus “receptive” to
implantation (days 20-24 of the
menstrual cycle)
• Gastrulation starts (the
formation of primitive “germ
layers”)
Gastrulation
Week 3
• Ectoderm folding creates the
neural tube
• Brain starts to develop and
differentiate into sections
• Musculoskeletal system starts
to develop
Week 4
• CNS further differentiates into
spinal cord, ganglia and brain
proper – neural tube closes
• Heart begins to beat (first fully
functional organ) at day 23 with
blood vessels
• Liver develops
• Skin starts to form (epithelia)
Week 5
• Heart develops septa (atria and
ventricles)
• Eye lenses form
• Cerebral hemispheres form
• Upper and lower limb buds
grow
Week 5 – Umbilical Cord
• Composed of one umbilical
arteries and two umbilical
veins
• Derived from the zygote and
develops as food stores in
the embryo are used up
• Attaches to the placenta
Placenta
• Close association of blood
vessels between maternal
and fetal portions of the
placenta allows for exchange
• Of what?
• What won’t go through?
Week 6
• Endocrine development (pituitary,
thyroid, parathyroid, thymus,
adrenal glands)
• Tongue forms
• Olfactory nerves enter the brain
Morning Sickness
• Generally starts around week 6
• Sometimes the first sign of
pregnancy!
• Due to increased estrogen levels in
the blood
• Usually gone by week 12
• Why is morning sickness a thing?
Week 7
• Limb bones form
(endochondrial ossification)
• Muscles of abdominal wall
separate
• Mullerian ducts invaginate
the body wall
• Eyelids meet
Week 8
• Gastrointestinal tract
perforates body wall (anus)
• Most components of axial
skeleton visible
• Fingers and toes separate
• Gonads start to differentiate
in accordance with secreted
hormones
Week 9
• Hearing and olfactory anatomy
developed
• Femur length at this point is 6mm
long
• Gender (external) not yet
differentiated
Week 10
• Intestines in abdomen
• Fingernails appear
• Outer ears (pinnae) form
• De novo hormones produced from
pancreas and pituitary (HGH)
Second Trimester (Weeks 12- 16)
• External genitalia differentiate
• Milk teeth are present in the
mandible and maxilla
• Growth hormone levels peak
(pituitary)
• Vellus body hair emerges from skin
Second Trimester (Weeks 17 – 21)
• Vernix caseosa covers skin
• Functions?
• Antimicrobial
• Protection
• ??
• Spleen formed and contains
lymphocytes
Vernix
Second Trimester (Weeks 22 – 26)
• Alveoli start to appear in lungs
• Beginning to secrete surfactant
• Why need surfactant in the lungs?
• Why is it not necessarily important
at this stage?
Second Trimester (Weeks 27 – 38)
• Lungs formed
• Testes descend into scrotum
(male)
• Nails reach end of fingers
• All sulci present in brain
• Thyroid and adrenal hormones
secreted
Birth!
• Much safer than it used to be!
• Up to 50% mortality for mom
AND baby 150 years ago
• Very stressful for mom and
baby (obviously)
Maternal Post-Birth Effects
• Organs move to accommodate
baby
• Breathing difficulties
• Uncomfortable sleeping
Lactation
• Release of prolactin
from the pituitary
causes the
production of milk
• Negative feedback
regulates
production (Milk
loss increases
production and
vice-versa)
Stretch Marks
• Caused by separation of collagen
fibers that lie over rapidly growing
tissue
• Will disappear with time!