Download Reproductive System

Reproductive System
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Evolutionary success is determined by
reproductive success
Reproductive Strategies in animals:
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Asexual – one parent, offspring genetically identical
to parent
budding – a miniature version of the adult grows
directly on adult (sponges, cnidarians)
fission followed by regeneration (fragmentation) –
animal disintegrates into two or more pieces and
each piece regenerates entire body (some annelids,
flatworms, a few brittle stars)
parthenogenesis – females only, haploid egg cells
develop into adults without being fertilized (bees,
some fish, amphibians, insects, reptiles) – some
species of fish and lizards have completely done
away with males
Parthenogenic Lizards
2. Sexual reproduction – requires union of
egg and sperm (fertilization)
• male produces sperm, female produces
eggs
– Hermaphrodites – have both male and female
gonads
– may self-fertilize (internal parasites) but
usually exchange sperm between individuals
External Fertilization
• gametes unite outside of the parents’
bodies
• more common in aquatic animals (aquatic
inverts, most fish, many amphibians
• vast numbers of eggs and sperm are
released at one time – spawning
• synchronized release of gametes achieved
by signals (pheromones), behaviors
(courtship), and environmental cues
(seasonal changes, daylength)
External Fertilization
Internal Fertilization
• sperm are taken into female’s body and fertilization
occurs internally
• copulation – behavior by which the male deposits
sperm directly into the reproductive tract of female
• spermatophores – some males package their
sperm in a container and drops it on the ground –
female finds it and fertilizes herself by inserting it
into her reproductive cavity
• deposit of sperm must coincide with ovulation
(release of egg) – resulting in the need for mating
behaviors, breeding seasons, or storage of sperm
until eggs are ready (snails, insects)
• fertilized eggs are either enclosed in protective
shell and released or held in female’s body for
embryo. development
Amniotic Egg
land vertebrate eggs (birds, reptiles) consist
of:
• amnion – encloses a fluid-filled chamber
housing embryo
• allantois – retains metabolic wastes of
embryo, has blood vessels near shell for
gas exchange
• yolk sac – encloses embryo’s food supply
• chorion – outer membrane surround
embryo and other membranes
Human Reproductive System
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mammals use internal fertilization and
embryo is retained in female for
development
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
descend at time of birth into scrotum
through inguinal canal – canal closes off
with connective tissue
inguinal hernia – point of weakness,
excessive strain may cause a rupture
(most common hernia in human males)
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)
hypothalamus produces gonadotropic releasing
hormone (GnRH) to anterior pituitary
ant. pituitary release luteinizing hormone (LH) and
follicle stimulating hormone (FSH)
LH stimulates interstitial cells of testes to produce
testosterone
FSH and testosterone stimulates
spermatogenesis
secondary sex characteristics result from
testosterone (beard, pubic 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
hypothalamus begins releasing GnRH at
puberty stimulating ant. pituitary to release
FSH and LH
FSH and LH stimulate the ovaries to
produce estrogen and progesterone –
starts menstrual cycle
estrogen stimulates development of
secondary sex characteristics (pubic hair,
broadening of pelvis, devel. of breasts,
distribution of fat, changes in voice)
Estrous Cycle in Mammals
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rhythmic variation in the condition of the
reproductive tract and sexual readiness
females of most species of mammal will only
accept the male in copulation during brief
periods near time of ovulation – female is in
estrus (“in heat”) – if fertilization does not occur,
uterine lining is reabsorbed
humans and higher primates do not have
distinct heat period – female is somewhat
receptive throughout cycle, if fertilization does
not occur, uterine lining is sloughed off during a
period of bleeding – menstruation
Human Menstrual Cycle
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averages every 28 days
1st day of menstruation is day one of cycle
days 1 – 7 – lining is sloughed off (lining is thin)
Follicular Phase (lasts 9 to 10 days after
menstrual flow) – ant. pituitary releases FSH
stimulating the maturation of several follicles
(only 1 will complete maturation) – also
stimulates ovaries to secrete estrogen
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estrogen stimulates thickening of uterine lining
estrogen stimulates hypothalamus to release GnRH
to stimulate ant. pituitary to release an abrupt surge
of LH – LH surge is followed by ovulation (around the
middle of the cycle)
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Luteal phase (lasts approx. 13 – 15 days)
– after ovulation, LH stimulates ruptured
follicle to form the corpus luteum –
continues to release estrogen and also
progesterone
– progesterone support uterine lining (also
inhibits production of FSH and LH)
– if no fert. occurs – corpus luteum atrophies,
progesterone levels drop and lining is shed
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
Hormonal control of Parturition (birth)
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progesterone inhibits contractions of the
uterus
progesterone levels begin to drop near the
end of the pregnancy
muscle fibers in uterine wall develop
additional receptors for oxytocin (causes
contractions) which is released by the pituitary
gland
uterus becomes more sensitive to oxytocin
and contractions get stronger
uterine muscle fibers produce prostaglandins
in response to oxytocin which further stimulate
contractions