Human Reproduction
Anatomy of the human male
Main functions:
The production of sperm,
the male gametes;
Spermatogenesis begins at
puberty and continues
until death;
Delivery of functional
sperm to the female
reproductive system
Anatomy of the human male
Anatomy of the human male
Production of Semen (a fluid comprised of):
Sperm, which are expelled through the ducts
during ejaculation (≈1% of semen volume);
Glandular secretions that carry, nourish, and
protect the sperm (mostly sugars & buffers)
Testes (plural):
Glands that produce sperm; located outside
abdominal cavity within the scrotum
 Scrotum ≡ (saclike pouch ≈ 1-3°C below normal
body temperature - sperm can only form at this
lower temperature)
How sperm leave the testes
Seminiferous tubules: carries/stores sperm in testes
Epididymis: a series of coiled ducts for maturation &
temporary storage of sperm
Vas deferens: tube which carries sperm past
connecting lubricating and support glands
How sperm leave the testes
Lubricating and support glands:
(a.) Seminal vesicles: secrete sugar-rich fluid that
protects & nourishes sperm
(b.) Prostate gland: produces an alkaline fluid that
neutralizes both urine in the male urethra and the
acidic environment of the vagina
(c.) Bulbourethral glands: secrete fluids that
lubricates the male urethra and allows easier
coitus (intercourse)
How sperm leave the testes
Urethra: tube in the penis that transports semen out
of the male’s body; also transports urine from the
urinary bladder
Penis: copulatory organ; transient tumescence
Ejaculation: the release of semen through rhythmic
contractions of smooth muscle in the Vas deferens
Anatomy of the human male
Anatomy of the human female
Main functions:
To produce the female
gametes (ova);
To receive sperm;
To provide a suitable
environment in which
a fertilized ovum
might develop during
pregnancy
Anatomy of the human female
Anatomy of the human female
Ovaries:
Contain follicles that nurture ova;
Produces sex hormones;
Functional from puberty to menopause
Anatomy of the human female
Oviducts (Fallopian Tubes):
Convey (move) ova towards the uterus;
Muscular contractions & cilia draw ovum (egg) into
oviduct;
Location for fertilization to occur
Anatomy of the human female
Uterus (womb):
Nourishes development of fertilized zygote;
Opens into the vagina at cervix
Vagina:
Receives the penis during coitus;
Forms the birth canal;
Multiple layers of expandable smooth muscle;
Potential, not defined, space
Anatomy of the human female
Anatomy of the human female
Puberty
Puberty: when secondary sexual characteristics
develop and the potential for sexual reproduction is
reached (sperm production or ovulation)
Changes are controlled by hormones that initiate
development of secondary sex characteristics;
Primary sex characteristics are internal and
external reproductive organs (genitalia)
Puberty in males (♂)
Secondary sex characteristics:
Primary hormone:
testosterone (testes);
2° Characteristics:
increased hair (body,
pubic, & facial), muscle
development, deeper
voice;
Spontaneous ejaculation
Puberty in females (♀)
Secondary sex characteristics:
Primary hormone:
estrogen (ovaries);
2° Characteristics: breast
development, broadened
pelvis, distribution of body
fat; increased hair (body &
pubic);
Menarche (onset of
menstruation)
Reproductive hormones
Testosterone (♂ testes):
Sperm production &
secondary sexual
characteristics
Estrogen (♀ ovaries);
Ova production,
preparing uterus for
fertilized zygote &
secondary sexual
characteristics
Hormonal control of the testes
Stimuli from other
areas in the brain
Androgens, (testosterone
Hypothalamus
most important), stimulate
sperm production
Releasing
hormone
They also maintain
Negative
Anterior
feedback
pituitary
homeostasis by a
negative feedback
mechanism that inhibits
FSH
LH
the secretion of FSH
Androgen
(follicle-stimulating
production
Testis
Sperm
hormone) and LH
production
(luteinizing hormone)
Oogenesis: Production of ova
Oogenesis occurs within the ovaries
 Lifetime supply of primary oocytes is present at
birth that are ‘frozen’ in Prophase I
 One (maybe more) primary oocyte matures each
menstrual cycle to form a secondary oocyte +
polar body
 If the secondary oocyte is fertilized, it completes
meiosis and becomes a haploid ovum + another
polar body

Oogenesis: Production of ova
Ovum maturation in ovary
releases
progesterone
maintains
uterus
lining
produces estrogen
Reproductive Cycle of the Adult
Human Female



A cyclical pattern of hormone secretion and
reproductive events.
Humans and many other primates have menstrual
cycles.
If implantation of a fertilized zygote does not
occur, the endometrium (lining of uterus) is shed
through the cervix and vagina in the process
called menstruation.
The Menstrual Cycle
•
The series of changes in the female reproductive
system that includes producing an ovum and
preparing the uterus for receiving it.
•
Once an ovum has been released during ovulation,
the part of the follicle that remains in the ovary
develops into a structure called the corpus luteum.
•
The menstrual cycle begins during puberty and
continues for 30 to 40 years, until menopause.
•
At menopause, the female stops releasing ova and
the secretion of female hormones decreases.
The Menstrual Cycle
•
Divided into three phases: the flow phase, the
follicular phase, and the luteal phase.
•
The timing of each phase of the menstrual cycle
correlates with hormone output from the pituitary
gland, changes in the ovaries, and changes in the
uterus.
Menstrual cycle

1.
2.
3.
4.
LH
Controlled by a
complex
interaction of 4 egg development
hormones:
follicle stimulating
hormone (FSH);
estrogen
luteinizing
hormone (LH);
estrogen;
progesterone
Days 0
7
FSH
ovulation = egg release
corpus luteum
progesterone
lining of uterus
14
21
28
Menstrual cycle: Flow phase
Day 1 of the menstrual cycle (1st phase) is the day
menstrual flow begins.
 The shedding of blood, fluid, mucus, and epithelial
cells that make up the endometrium (the internal
lining of the uterus) begins.


Contractions of the uterine muscles help expel the
uterine lining and can cause discomfort in some
females.

The level of FSH in the blood begins to rise, and a
follicle in one of the ovaries begins to mature as
meiosis of the prophase I cell proceeds.
Menstrual cycle: Follicular phase

Follicular (2nd) phase lasts from about day 6 to day
14.

As the follicle containing a primary oocyte continues
to develop, it secretes estrogen, which stimulates
the repair of the endometrial lining of the uterus.

Day 14 ovulation occurs:

Ovulation ≡ follicle enlarges and ruptures ovary
wall; ovum is released to oviduct.
 Mittelschmerz:
ovulation pain
Menstrual cycle: Luteal phase
Luteal (3rd) phase begins after ovulation (≈ day 15).
 Progesterone increases the blood supply of the
endometrium.
 These changes correspond to the arrival of a
fertilized ovum (zygote).


If the ovum is not fertilized, the rising levels of
progesterone and estrogen from the corpus luteum
cause the hypothalamus to inhibit the release of FSH
and LH.
Menstrual cycle: Luteal phase

Without fertilization, the corpus luteum degenerates
and stops secreting progesterone or estrogen.

As hormone levels drop, the thick lining of the uterus
begins to shed.

If fertilization occurs the endometrium begins
secreting a fluid rich in nutrients for the embryo.
Female reproductive cycle
egg
matures &
is released
(ovulation)
estrogen
builds up
uterus lining
Feedback
corpus
luteum
ovary
progesterone
FSH & LH
maintains
uterus lining
fertilized egg
(zygote)
HCG
yes
pituitary
gland
pregnancy
GnRH
hypothalamus
no
corpus luteum breaks down
progesterone drops
menstruation
corpus
luteum
progesterone
maintains
uterus lining
Female hormones

FSH & LH
 released from
pituitary gland;
 stimulates ova
development &
hormone release;
 peak release =
release of ova
(ovulation)
Female hormones

Estrogen
 released from
ovary cells around
developing ova;
 stimulates growth
of lining of uterus;
 decreasing levels
initiate
menstruation
Female hormones

Progesterone
 released from
corpus luteum in
ovaries
 stimulates blood
supply to lining of
uterus;
 decreased levels
sustains
menstruation
Hormonal coordination of the
menstrual and ovarian cycles
FSH (follicle stimulating
hormone) produced by
pituitary gland
stimulates development
of follicle
 LH (luteinizing
hormone) stimulates
the development of the
corpus luteum;
stimulates ovulation

Hormonal coordination of the
menstrual and ovarian cycles
Estrogen: secreted by
ovaries, stimulates
development of uterine
lining before
implantation
 Progesterone: secreted
by corpus luteum,
maintains uterine lining
during pregnancy

Fertilization





Fertilization is the union of a sperm and an ovum
to form a diploid zygote.
Fertilization results in a zygote and triggers
embryonic development.
Occurs normally inside of fallopian tube (oviduct).
Fertilization is NOT pregnancy!
(PATHWAY) Tens of millions of sperm enter the
vagina  cervix  uterus  oviducts (fertilization)
sperm + ovum zygote
23(n) + 23(n)  46(2n)
Fertilization

Only one of the
many millions of
sperm entering
the vagina will
penetrate this
human ovum to
initiate
fertilization
Fertilization

The shape of a human
sperm cell is adapted
to its function
 Sperm cell is
enzymes, DNA &
mitochondria!
Multiple Fertilizations

If two (or more) ova are
released in the same
cycle and fertilized 
fraternal siblings
(different DNA)
 If one ova is fertilized
and mitotically divides
into two (or more)
separate zygotes 
identical siblings (same
DNA)
Fertilization
Implantation
Implantation: The fertilized zygote implants into
thickened uterine lining and the embryo starts to
secrete the hormone human chorionic
gonadotropin (HCG) (the hormone used for
pregnancy tests)
 HCG keeps the corpus luteum functional and
continuing to secrete progesterone.
 By the third or fourth month, the placenta takes
over for the corpus luteum, secreting enough
estrogen and progesterone to maintain the
pregnancy.


Implantation = Pregnancy!
Embryonic Development
Development: series of orderly, precise steps that
transform a zygote into a multicellular embryo
 Embryo ≡ early development stages of a
multicellular organism
 Includes:
1. cell division (mitotic)
2. cell growth
3. cell differentiation ≡ altering of unspecialized
mitotic embryonic cells into specialized cells,
tissues,& organs

Early Embryonic Development

Cleavage is the first major
phase of embryonic
development
 It is the rapid succession
of cell divisions (Mitotic)
 It creates a multicellular
embryo from the zygote
 NO growth
 Embryonic growth
cannot occur until
implantation occurs
ZYGOTE
Blastocoel
BLASTULA Cross section
of blastula
(hollow ball)
Early Embryonic Development

Stages:
1. Morula ≡ solid ball of
cells
2. Blastula ≡ single layer
of cells surrounding a
fluid-filled cavity called
the blastocoel
3. NO growth; still
dividing original single
cell mass
ZYGOTE
Blastocoel
BLASTULA Cross section
of blastula
(hollow ball)
Embryonic Development

Gastrulation is the
second major phase of
embryonic development
 The cells at one end
of the blastula move
inward
Embryonic Development
Organs start to form
after gastrulation
 Embryonic tissue layers
begin to differentiate
into specific tissues and
organ systems

Embryonic Membranes
Amnion ≡ fluid filled
sac for protection
Chorion
 Chorion ≡ will form the
embryo’s part of the
Amnion
placenta
Yolk sac
 Yolk sac ≡ produces
first blood cells & germ
cells

Allantois
Embryonic Membranes
Allantois ≡ will form
the umbilical cord
(ropelike structure
Chorion
that attaches embryo Amnion
to uterus)
 Umbilical cord brings Yolk sac
nutrients in/wastes
out of fetus
 Ties into hepatic artery
& vein in fetus bellybutton

Allantois
The Placenta
Placenta ≡ A growing
fetus exchanges
nutrients, oxygen, and
wastes with the
mother through the
placenta
 Made of maternal and
fetal tissues
 Substances pass both
ways, but blood does
not mix

Placenta

Nutrients, wastes, & gasses diffuse across capillaries
Fetal Development
Gestation is pregnancy
 It begins at implantation and continues until
parturition (birth)
● Pregnancy in humans usually lasts about 280 days,
calculated from the first day of the mother’s last
menstrual period.
 Embryonic development of essential organs occurs
in early pregnancy.
 The embryo may encounter risks from faults in its
genes & from mother’s exposure to environmental
factors.

Human fetal development is divided
into equal trimesters

First trimester (0 to 3 months)
 The most rapid changes occur during the first
trimester (most developmentally important)10
weeks
4 weeks
10 weeks
7 weeks
eeks10 weeks

10 weeks
Human fetal development is divided
into equal trimesters

Second trimester (4 to 6 months)
 Increase in size of fetus
 General refinement of human features
12 weeks
Human fetal development is divided
into equal trimesters

The fetus spends much of the 2nd & 3rd trimesters
just growing…
…and doing flip-turns & kicks inside amniotic sac
Week 20
Human fetal development is divided
into equal trimesters
24 weeks (6 months; 2nd trimester)
• Fetus is
covered with
fine, downy
hair called
lanugo
• Its skin is
protected by a
waxy material
called vernix
Human fetal development is divided
into equal trimesters

Third trimester (7 to 9 months)
 30 weeks
 (7.5 months)
Human fetal development is divided
into equal trimesters

32 weeks (8 months)
The fetus sleeps
90-95% of the day
& sometimes
experiences REM
sleep, an
indication of
dreaming
Human fetal development is divided
into equal trimesters

Third trimester
 Growth and
preparation for
birth
 Provides time for
maternal body to
prepare for birth
Nooo!!! I don’t
want to go to
Murdoch’s class!
Three stages of labor
Dilation of the cervix is
the first stage
 Cervix starts at less
than 1 cm dilation
(open) and reaches full
dilation at 10 cm
 Longest stage of
labor (6-12 hours or
longer; maybe
MUCH longer!)

Three stages of labor

Expulsion is the second
stage
 Period from full
dilation of the cervix
to delivery of the
infant
 Uterine contractions
occur every 2-3
minutes (positive
feedback)
Three stages of labor

Expulsion is the second
stage
 Mother feels urge to
push down with her
abdominal muscles
 Infant is forced down
and out of uterus and
vagina within a period
of about 20 minutes
Three stages of labor

The delivery of the
placenta is the final
stage of labor
 Usually occurs
within 15 minutes
after the birth of
the baby
 Some placenta’s are
saved and frozen as
they are a source of
stem cells
Labor & Birth: Positive Feedback
positive feedback
The end of the journey!
And you think
9 months of
Biology is hard!
Lactation: the ‘mam’ in mammal
• Lactation ≡ milk production
• Lactation is another positive
feedback system
• Suckling stimulates the
hypothalamus pituitary
gland to release oxytocin
• Oxytocin stimulates
mammary glands to secrete
milk
• Continued suckling continues
milk production
Yes, males have mammary glands too!
Growth and Aging
Once a baby is born,
growth and learning
continue.
 Human growth varies
with age and is
somewhat gender
dependent.
 Females develop
earlier

An adult ages
As an adult ages, his or her
body undergoes many
distinct changes:
-Slower metabolism
-White hair
-Thinner bones
-Vision & hearing diminish