•Testes (male gonads): secrete male sex hormones
(androgens), produce male gametes (spermatozoa or
sperm) 1/5 billion per day.
•Pathway of Spermatozoa: Testis, Epididymis, Ductus
deferens (vas deferens), Ejaculatory duct, Urethra
•Accessory Organs: secrete fluids into ejaculatory
ducts & urethra:
-Seminal Vesicles: Paired, contribute about 60% of
semen volume. High in fructose, energy for sperm
motility; also prostaglandins to enhance contractions
in female reproductive tract.
-Prostate Gland: Surrounds portion of urethra, size of
walnut. Produces alkaline fluid to give semen proper
consistency. Can enlarge over time as men age. Benign
prostatic hyperplasia (BPH); urinary problems.
Prostate cancer (usually slow growing); similar
symptoms
-Bulbourethral glands : Produce thick lubricant “Pre-
ejaculate” but may contain sperm.
•Temperature Regulation: Normal sperm
development in testes: Requires temperatures 1.1°C
(2°F) lower than body temperature. Muscles relax or
contract: To move testes away or toward body. To
maintain acceptable testicular temperatures.
•Dartos Muscle : a layer of smooth muscle in dermis of
scrotum. Causes wrinkling of scrotal surface.
•Cremaster Muscle : a layer of skeletal muscle deep to
dermis. Tenses scrotum and pulls testes closer to body
(temperature regulation).
•Histology of the Testes: Septa subdivide testis into
lobules. Lobules contain about 800 slender & tightly
coiled seminiferous tubules: Produce sperm; each is
about 80 cm (32 in.) long; testis contains about 1/2
mile of tightly coiled seminiferous tubules.
•Sertoli (sustentacular) cells: “Nurse” cells, part of
seminiferous tubules, helps sperm production,
activated by follicle-stimulating hormone (FSH).
•Leydig (interstitial) cells: Adjacent to seminiferous
tubules, produce testosterone in the presence of
Luteinizing hormone (LH).
•Germ Cells: Undergo spermatogenesis.
Spermatogonia → spermatocytes → spermatids →
sperm.
•Ovaries (female gonads): Release one immature
gamete (oocyte) per month. Produce hormones.
•Uterine tubes : Carry oocytes to uterus: if sperm
reaches oocyte, fertilization is initiated and oocyte
matures into ovum
•Uterus : Encloses and supports developing embryo.
•Vagina : Connects uterus with exterior.
•Ovarian Cycle: After sexual maturation: A different
group of primordial follicles is activated each month.
Divided into: Follicular phase (preovulatory phase).
Luteal phase (postovulatory phase).
•Uterine Cycle: Responds to hormones of ovarian
cycle. Menses and proliferative phase: Occur during
ovarian follicular phase. Secretory phase: Occurs
during ovarian luteal phase.
•Fertilization: Following implantation, the placenta
originates from maternal and fetal tissues. Placenta
produces human chorionic gonadotropin (HCG) which
maintains the corpus luteum in the ovary until the
placenta begins its own production of progesterone
and estrogen.
•Female Menopause : when ovulation & menstruation
cease. Occurs ~45 to 55. Estrogens & progesterone
decline, increased GnRH, FSH, LH. May experience hot
flashes, night sweats, hair loss, mood swings. Cancer
risks with menopausal hormone therapy.
•Male Menopause : Decline in Leydig cell activity can
occur in men beginning at 40 - 50 years of age.
Reduction in circulating testosterone levels. Fatigue,
reduced muscle mass, depression, loss of libido, lower
sperm production. Testosterone replacement therapy
increases risk of heart disease and prostate cancer.
•Puberty: stage when individuals become sexually
mature. Controlled by key hormones: GnRh from
hypothalamus. LH and FSH from anterior pituitary.
Either testosterone or estrogen from the gonads.
These hormones produce, Maturation of the gonads.
Other physical changes (secondary sexual
characteristics).
•Puberty in Girls: First visible change is often
development of breast tissue. Growth of axillary and
pubic hair. Growth spurt of up to 3”/yr common at age
9–11. Start of menstruation (“menarche”).
•Puberty in Boys: First physical change is often growth
of testes, followed by pigmentation of scrotum and
growth of penis. Growth of axillary, pubic, chest, facial
hair. Increase in body musculature. Testosterone
stimulates growth of larynx and vocal cords, lowering
voice. Growth spurt of up to 4”/yr common at age 11
– 13, later than in girls.
•Development of Sexual Organs: Females (XX) are
sometimes called the “fundamental sex”. Without
additional chemical influences, all fertilized eggs
would develop into females. To develop as a male
(XY), an embryo must be exposed to factors initiated
by a single gene on the Y chromosome. Called the SRY
(sex-determining region of the Y chromosome).
•Sexual differentiation (external sexual organs) begins
about 6-7 weeks after fertilization; can be detected via
ultrasound by third month.
•Transit of Sperm: Hundreds of millions of sperm are
released into the vagina, but after 1-2 hours only a few
hundred or thousand enter the fallopian tubes. Acidity
of vagina (about pH 3.8) kills sperm. Blocked by thick
cervical mucus. Phagocytic uterine leukocytes. Sperm
can survive for 3-5 days in fallopian tubes. Oocyte can
only survive one day after ovulation.
•Capacitation: fluids in female reproductive tract
improve sperm motility, thin the acrosome of sperm
to penetrate outer layers of oocyte.
•Contact btwn Sperm & Oocyte: Fertilization usually
occurs in distal fallopian tube, since moving through
entire tube takes about 3 days. Oocyte is surrounded
by two protective layers
-Corona radiata: outer layer of follicular cells, release
chemicals that attract sperm
-Zona pellucida: thick, transparent layer of
glycoprotein that surrounds the oocyte’s plasma
membrane. Sperm must penetrate these two
protective layers to bind to receptors; “acrosome
reaction” is release of enzymes by sperm that digest
glycoproteins.
•Prevention of polyspermy: initial “fast block”
involves change in sodium ion permeability that
depolarizes the membrane. Then, a “slow block”
caused by influx of calcium ion results in cortical
reaction that destroys sperm receptors and creates
impenetrable barrier to additional sperm.
•Fertilization & Twins: The two haploid nuclei (one
maternal, one paternal) are called pronuclei; they
decondense and replicate their DNA in preparation for
mitosis. Their nuclear envelopes disintegrate, the
genetic material intermingles, and fertilization ends
with the creation of the diploid zygote. Most of the
time (about 99%), a woman releases a single egg
during ovulation. Release of two eggs could produce
fraternal twins. No more identical than siblings born at
different times. Identical twins: zygote divides into
separate offspring (much less common).
•Processes of development. Cleavage - Cell division
without growth. Morphogenesis - Shaping of embryo.
Differentiation - Cells take on specific structure and
function. Growth - Increase in size of cells.
•Cleavage & Cell Division: Zygote undergoes rapid
mitotic cell division, but these do not increase the size
of the zygote, called cleavage divisions. Cleavage
produces a solid sphere of cells, still surrounded by
zona pellucida, now called a morula. At 4.5 to 5 days,
cells have developed into a hollow ball of cells,
blastocyst. It is at this stage that it enters the uterus.
•The Blastocyst: has an outer layer of cells called the
trophoblast, an inner cell mass, & a fluid filled cavity
called the blastocoel. The trophoblast and part of the
inner cell mass will form the membranes of the fetal
portion of the placenta, the rest of the inner mass
forms the embryo.
•Implantation: The blastocyst remains free in the
uterus a short time; zona pellucida disintegrates.
Blastocyst nourished by glycogen from glands of the
endometrium. At about 6 days after ovulation
blastocyst implants – orients cell mass toward
endometrium, & secretes enzymes which allow it to
penetrate (digest) the endometrial wall. This
nourishes the blastocyst for about a week after
implantation.
-As early as 8 -12 days after fertilization, the blastocyst
begins to secrete human chorionic gonadotropin or
hCG. hCG keeps the corpus luteum active until the
placenta can produce estrogens and progesterone.
The presence of hCG is the basis for pregnancy tests.
-Inner cell mass forms two cavities: the yolk sac and
the amniotic cavity. In humans the yolk sac produces
blood cells and future sex cells. The amniotic cavity
becomes the cavity in which the embryo floats. Fluid is
produced from fetal urine, and secretions from the
skin, respiratory tract, and amniotic membranes. Cells
of the trophoblast eventually give rise to the placenta.
-Implantation can also occur in uterine tube, cervix, or
the abdominal cavity. Implantation anywhere outside
the uterus is called an ectopic pregnancy. It is possible
for fetus to grow in the abdominal cavity, but growth
inside the uterine tube causes the tube to rupture,
resulting in severe bleeding.
•Primary Germ Layers: In between the yolk sac and
the amniotic cavity is the embryonic disc, which gives
rise to the primary germ layers: Endoderm,
Mesoderm, Ectoderm.
-Ectoderm: gives rise to the skin, the brain, the spinal
cord, subcortex, cortex and peripheral nerves, pineal
gland, pituitary gland, kidney marrow, hair, nails,
sweat glands, cornea, teeth, the mucous membrane of
the nose, and the lenses of the eye.
-Mesoderm: give rise to the digestive tract, the heart
and skeletal muscles, red blood cells, and the tubules
of the kidneys, as well as a type of connective tissue
called mesenchyme.
-Endoderm: gives rise to the epithelial lining of
digestive tract, resp tract, assoc glands of these
systems, lining of bladder.
•Gestation Period: Divided into three trimesters.
During first trimester individual starts out as a zygote,
then morula, blastocyst, & after implantation, an
embryo. Embryonic phase of development lasts from
fertilization until the 8th week of gestation, when it
becomes a fetus. By day 35 the heart is beating, & eye
& limb buds are present. By the end of the first
trimester, the rudiments of all organ systems are
formed and functioning. From then on, fetal
development is primarily a matter of growth.
•The Placenta: The chorion develops into the fetal
part of the placenta. The chorionic villi connect the
fetal circulation to the placenta. The placenta is
composed of both fetal and maternal tissues.
•Functions of the placenta: Transfer gasses. Transport
nutrients. Excretion of wastes. Hormone production, temporary
endocrine organ, estrogen & progesterone. Formation of a
barrier, incomplete, nonselective, alcohol, steroids, narcotics,
anesthetics, some antibiotics & some organisms can cross.
•Fetal Circulation: The umbilical cord stretches between the
placenta and the fetus and contains the umbilical arteries and
veins. Exchange of gases and nutrients between maternal and
fetal blood takes place in the umbilical arteries. Umbilical vein
carries blood & oxygen away from the placenta to the fetus.
•The Birth Process (Parturition): Stage 1: The uterine
contractions press the head against the cervix causing it to
dilate, and the amniotic sac may rupture (“water breaks”)
Usually lasts 6 – 24 hours depending on the number of previous
deliveries. Stage 2: Period from maximal cervical dilation until
the birth of the baby, lasts minutes to an hour, contractions
become more intense and frequent. Stimulated by oxytocin,
positive feedback loop. Stage 3: The expulsion of the placenta,
