Chapter 16: The reproductive
system
(Slides by Jennifer Wade, modified by
Paul Nagami)
The reproductive system
• The main organs of the reproductive system
are the gonads: ovaries and testicles
• The gonads make gametes: eggs & sperm
• Most human cells have 46 chromosomes (two
sets of 23 chromosomes each, one set from
each parent).
• Gametes only have one set of 23
chromosomes, which are passed down to
offspring
• Meiosis is a special term for the cell division
that gives rise to gametes
Sexual reproduction in diploid
organisms
• Cells that give rise to
gametes are called
germline cells
• The letter n is used to
indicate the number of
copies of each
chromosome a cell in an
organism has. n = 23 in
humans.
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Testes are the male gonads
• Housed in the scrotum
• Seminiferous tubules are
where meiosis actually occurs
to make sperm
• They travel to the epididymis
where they mature (takes
about 20 days)
• Mature sperm leave the testis
through the vas deferens
• The spermatic cord attaches
the testis to the body, as well
as housing the vas deferens &
blood vessels and nerves
• Vas deferens empties into the ejaculatory duct,
surrounded by smooth muscle
• The seminal vesicles, prostate, and bulbourethral glands
make fluids that help the sperm move and survive. Semen
is sperm + seminal fluid.
• The urethra delivers semen, as well as urine, to the
outside of the body
Signals from the
anterior pituitary,
controlled by the
hypothalamus,
trigger sperm
development
In males, FSH and LH
trigger testosterone
release and sperm
production. Too much
testosterone blocks
FSH/LH production!
Female reproductive anatomy
• Ovaries are the female gonads, where eggs (ova) develop.
They then travel through the fallopian tubes
• Fertilization usually occurs in the fallopian tubes; the ovum
migrates to the uterus, where it implants in the
endometrium
Female reproductive anatomy
• The cervix separates the uterus from the vagina
• Females also have a urethra, but unlike in males, it plays
no reproductive function
Oogenesis: Making Eggs
Oo = egg
Genesis = making
Oogenesis = making
eggs
Oogenesis begins
before birth; women
make their supply of
primary oocytes
early. One matures
per month (usually)
and women run out
at menopause.
The monthly cycle & menstruation
• Fertile women undergo a series of hormonal
changes each month; these changes help
prepare the body for pregnancy if the ovum is
fertilized after ovulation.
• Main hormones: FSH and LH from anterior
pituitary, and estrogen and progesterone from
the gonads.
Hormones from the anterior pituitary
control the cycle
FSH triggers maturation of the follicle and egg.
FSH + LH spike triggers ovulation (release of the egg)
Maturation of the ovum
After meiosis produces the egg and the follicle ruptures,
the remains of the follicle become the corpus luteum,
which releases hormones.
Estrogen and progesterone are made
in the ovaries
Rising estrogen triggers FSH + LH release
Progesterone + estrogen prepare the body for pregnancy
Fall in progesterone triggers menstruation
Changes in the endometrium
The buildup of the endometrium provides a safe “landing zone”
for the fertilized zygote to implant and grow. Blood vessels give
nutrients to the growing embryo. In absence of pregnancy, this
lining breaks down.
Fertilization usually happens in the fallopian tube, and leads to a
series of rapid divisions, of cleavage, in the developing zygote. The
resulting hollow ball of cells that implants in the uterus is called a
blastocyst.
The uterus expands during pregnancy