Animal Reproduction
Modes of Reproduction
• 2 modes:
– asexual reproduction
•
•
•
•
fission
budding
regeneration
parthenogenesis
Modes of Reproduction
• sexual reproduction
– fertilization
• internal and external
• hermaphroditism
– sequential hermaphroditism
Reproductive Systems
• simplest animals do not have gonads
(produce gametes)
– polychaetes’ gametes develop from
undifferentiated cells lining the coelom
• more complex animals have gonads
and a system of ducts and glands
Reproductive Systems
• non-mammalian vertebrates possess a
cloaca
• mammals have separate openings for
each system
Spermatogenesis
• sperm structure:
– head
• acrosome
– midpiece
– tail
Oogenesis
• production of an ovum
• occurs in the ovaries
Regulation of Male Reproductive System
Regulation of Female
Reproductive System
• pattern of hormone secretion is cyclic
• menstrual cycle
• endometrium is shed if no implantation
occurs (menstruation)
• estrous cycle
– endometrium is reabsorbed
Menstrual Cycle
• average length is 28 days
• refers to changes in uterus
• 1. Menstrual flow phase
– menstrual bleeding
• 2. Proliferative phase
– endometrium regenerates
• Secretory phase (about 2 weeks long)
– glands in endometrium secrete glycogen
Ovarian Cycle
• 1. Follicular phase
– several follicles begin to grow
– ends in ovulation
• 2. Luteal phase
– follicle cells remaining after ovulation
develop into corpus luteum
Hormonal Control
• Follicular phase
– FSH and LH secreted in response to
GnRH
– follicle cells have only FSH receptors
– follicle cells secrete estrogens
– slow rise in estrogen levels, keeping FSH
and LH levels steady
Hormonal Control
– positive feedback- sharp increase in
estrogens cause sharp increase in FSH and
LH (increases GnRH release)
– LH receptors develop on follicle cells
– high LH causes final follicle maturation
– ovulation occurs about 1 day after LH
surge
Hormonal Control
• Luteal phase
– LH stimulates follicle cells to form corpus
luteum
– corpus luteum releases progesterone and
estrogens
– negative feedback- production of
progesterone and estrogen inhibits release
of LH and FSH
Hormonal Control
– corpus luteum disintegrates in 8-10 days,
releasing negative feedback
– FSH production resumes and the cycle
continues over again
• ovarian cycle and menstrual cycle are
sychronized
Hormonal Control
• follicular phase and proliferative phase are
linked
– estrogens cause endometrium to thicken
– uterus is prepared for implantation before
ovulation
• luteal phase and secretory phase are linked
– estrogens and progesterone maintain endometrial
lining
Hormonal Control
• rapid drop in ovarian hormones after
corpus luteum disintegrates causes
arteries in endometrium to spasm,
depriving endometrium of blood
• menstruation results
Menopause
• cessation of ovulation and menstruation
• ovaries lose responsiveness to FSH and
LH