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