Download Reproductive System

Reproductive System
Sexual reproduction – requires union of egg
and sperm (fertilization)
• male produces sperm, female produces
eggs
• Sex cells are made in the gonads (ovaries
and testes)
• Eggs and sperm are haploid (made by
meiosis) so when they unite the diploid
number is restored
Male Reproductive System
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main organ: testes
located at the base of the abdominal cavity
develop from same embryonic tissue as
female ovaries
Testes have 2 functional components:
• seminiferous tubules – produces sperm,
only functional at slightly lower body temp.
• scrotal sac approx. 1.5 degrees C cooler
than abdom.
• epididymis – coiled tube where sperm
travel from seminiferous tubules – lie on
top of testes – sperm stored here and
acquire ability to swim
• interstitial cells – secrete male sex
hormone testosterone
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Vas deferens – 2 long ducts that carry sperm
from epididymis to urethra (common duct for
passage of sperm and urine)
urethra passes through penis and empties to
outside
as sperm passes through the vas deferens,
sperm is mixed with seminal fluids to form
semen – seminal fluids are secreted by seminal
vesicles, prostate gland, and Cowper’s gland
(bulbourethral gland)
seminal fluid functions as: vehicle for transport
of sperm, lubricates passages where sperm
pass, acts as a buffer fluid to protect sperm from
acids in female reprod tract, contains fructose
for source of energy
Hormonal control of male reproduction
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during embryological development – small amts of
testosterone cause differentiation of male
structures
testosterone levels remain low until onset of
puberty (no sperm production)
At puberty, testes begin to release testosterone
which begins production of sperm
After puberty, secondary sex characteristics result
from testosterone (beard, pubic hair, underarm
hair, deepening of voice, development of larger
and stronger muscle)
Female Reproductive System
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Ovaries – located in abdom cavity – held in
place by ligaments – produce gametes and
sex hormones
at time of birth, ovaries already contain
hundreds of thousands of oocytes
(primordial egg cells)
each oocyte is enclosed in a follicle – each
month when egg ripens, follicle grows and
fills with fluid and bulges on surface of
ovary – ovulation occurs and egg is
released into body cavity
Follicles in ovary
Ovulation
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egg is taken up by oviducts (Fallopian tubes)
fertilization must occur in upper third of oviduct
for baby to result
egg finishes maturation (completes meiosis II)
with penetration of sperm, nuclei fuse
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Oviducts empty directly into uterus
about the size of a fist
lies in lower portion of abdomen behind bladder
muscular sac with thick walls of smooth muscle,
lined with mucous, contains many blood vessels
location where fertilized egg implants and
develops
•lower end of
uterus connects
to vagina (birth
canal)
•muscular tube
leading to
outside
•cervix –
opening from
vagina to uterus
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Hormonal control of female reproductive
system
At puberty, FSH and LH stimulate the
ovaries to produce estrogen and
progesterone – starts menstrual cycle
estrogen stimulates development of
secondary sex characteristics (pubic and
underarm hair, broadening of pelvis,
development of breasts, distribution of fat,
changes in voice)
Human Menstrual Cycle
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averages every 28 days
1st day of menstruation is day one of cycle
days 1 – 5 lining is sloughed off (lining is thin)
Events during the 1st half of the cycle (approx. days 1 –
14):
– pituitary releases FSH stimulating the maturation of
several follicles (only 1 will complete maturation) –
also stimulates ovaries (follicle) to secrete estrogen
• estrogen stimulates thickening of uterine lining
• estrogen stimulates the release of an abrupt surge
of LH almost midway through the cycle – LH surge
is followed by ovulation (around the middle of the
cycle – about day 14)
• Estrogen inhibits the pituitary from releasing more
FSH (negative feedback)
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Events during the 2nd half of the cycle
(days 15 – 28):
after ovulation, LH stimulates ruptured
follicle to form the corpus luteum –
continues to release estrogen and also
progesterone
– progesterone promotes continued buildup and
support of the uterine lining (also inhibits
production of FSH and LH – negative
feedback)
– if no fert. occurs – corpus luteum
degenerates, progesterone levels drop and
lining is shed and cycle starts over
Hormonal control of pregnancy
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once fertilized, egg immediately becomes impermeable to
other sperm cells – membrane changes consistency –
forms zygote
cell division occurs as zygote travels down oviduct to
uterus – embryo forms – implants in wall of uterus 8 – 10
days after fert.
after implantation – fert. egg forms: embryo, umbilical cord
(blood vessels connect baby and mother), and placenta
(formed from embryonic and uterine tissues – blood
systems of baby and mother come in close contact but
never actually mix – exchange occurs between circ.
systems)
fertilized egg produces human chorionic gonadotropin
(HCG) which keep corpus luteum in place – continues to
produce progesterone to sustain pregnancy – eventually
placenta takes over production of estrogen and
progesterone to maintain uterine lining
In vitro Fertilization (IVF)
• Normal fertilization takes place in the
oviduct
• Sometimes a couple may be infertile –
unable to conceive a baby
• In vitro fertilization involves fertilization of
eggs in the laboratory in a test tube
• IVF is controversial – review ethical issues
in your textbook