animal reproduction. modes of reproduction 2 modes: –asexual reproduction fission budding...
TRANSCRIPT
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