Animal Reproductive Structures and Functions - FEMALES Flashcards
Females
in sexually reproducing populations, are the sex with ovaries that produce small numbers of large eggs, which travel down the uterine tube where they are fertilized or released in an aqueous environment
- require investment of time, energy, and nutrients to form eggs
Males
in sexually reproducing populations, are the sex with testes that produce large amounts of small sperm, which are stored in the epididymis until ejaculation
Spermatheca
specialized sperm-storing sac present in females in some invertebrate species; common in insects, mollusks, and worms
- after mating, the female stores the male’s sperm for later use; fertilization can then be times with optimal environmental/food conditions for better offspring survival
- may be stored from one or multiple males depending on the species mating system
- in some species, the female may only mate once in her lifetime and use the sperm from this single mating to fertilize eggs throughout her life
Cloaca
single, shared body opening that functions in the digestive, excretory, and reproductive systems; found in many non-mammal vertebrates (birds + reptiles)
- mating usually involves positioning the cloaca openings opposite of each other for transfer of sperm from male to female
Uterus
structure present in placental mammals, which houses the developing offspring internal to the mother’s body; essentially serves as the location for the development of an amniotic egg retained within the body
- may have two chambers that produce multiple offspring at a time (mice) or only one chamber that produces one offspring at a time (primates)
Gametogenesis
production of gametes (sperm + egg)
- requires meiosis, which produces HAPLOID cells with half the number of chromosomes normally found in diploid cells
- hormones regulate gametogenesis in both male and female reproductive cycles: FSH + LH
Human Female Reproductive Anatomy
include external (breasts, vulva) and internal (ovaries, oviducts, uterus, vagina) structures
- ovaries: produces + develops (matures) eggs
- fallopian tubes (oviducts): site for fertilization: transports egg to the uterus
- uterus: supports developing embryo
- cervix: allows passage between the uterus + vagina
- vagina: receives the penis during intercourse, acts as the birth canal, passes menstrual flow
- breasts: produce and deliver milk
Female Maturity + Puberty
- human females become capable of reproduction at sexual maturity, which follows puberty
- in puberty, the hypothalamus signals the pituitary gland to produce FSH + LH which stimulates the ovaries to produce the female sex hormones estrogen and progesterone
- during puberty, E + P initiate the development of secondary sex characteristics (breasts) + cause the ovaries to being producing mature eggs
Female Maturity: Ovaries + Follicles
the site of egg development + maturation; eggs develop + mature in structures called FOLLICLES which are found throughout the ovary
- each follicle contains 1 immature egg
- egg development in humans occurs in small batches, with 1-2 eggs maturing on a monthly cycle: the Ovarian Cycle
Ovarian Cycle
1st: several follicles become activated to promote the development of the egg inside them
2nd: the most mature follicle will “rupture,” releasing one egg that travels from the ruptured follicle into the oviducts, where it is fertilized if sperm is present. Over a week, the egg will travel through the oviduct into the uterus, where it will implant + result in pregnancy if fertilization occurs. FERTILIZATION MUST TAKE PLACE IN THE OVIDUCT, NOT THE UTERUS
3rd: the ruptured follicle (still in the ovary) becomes the CORPUS LUTEUM, which secretes hormones that prevent menstruation until the egg has had time to fertilize. If fertilization + implantation into the uterine wall occurs, the CL will continue to prevent menstruation. If not, the CL degenerates + menstruation occurs
Female Gametogenesis: Oogenesis
Begins when the female is still an embryo; this occurs in the ovaries, where egg stem cells (OOGONIA) divide by mitosis to produce up to 2 million oocytes (precursor to the egg). The oocytes START the process of meiosis and then pause during M2.
- occurs in embryonic development - the female mammal is born with every single egg she will ever produce in her lifetime (immature eggs)
M1 is paused until the onset of puberty, where a series of events leads to monthly egg maturation
Oogenesis: After Puberty
- Hormones from the pituitary cause some follicles to begin developing + the oocyte inside the follicle to finish M1
- After completing M1, the oocyte pauses during M2
- Through several follicles are activated each cycle, typically only one will release an oocyte that will travel through the oviduct, still paused in M2
- If the oocyte is fertilized by a sperm cell, it will finish M2 to produce a zygote. If not, it degrades without completing M2
Oogenesis: Unequal Cytokinesis
when each oocyte undergoes meiosis to go from diploid to haploid, each one produces only a single egg; the cytoplasm divides unequally so almost all cytoplasm goes to one daughter cell rather than evenly to both
- POLAR BODY: smaller cell that normally dies as development progresses
Hormonal Control of Oogenesis
oogenesis is controlled by 4 hormones: FSH, LH, estrogen, and progesterone. These hormones regulate the ovarian and menstrual cycles:
- Ovarian: release of eggs
- Menstrual: activities in the uterine lining in preparation for possible pregnancy
Follicle Stimulating Hormone (FSH)
activates follicles within the ovary to promote the development of egg cells, causing eggs to finish M1 and pause during M2
Luteinizing Hormone (LH)
promotes the release of the most mature egg, resulting in ovulation
Progesterone
suppresses the release of more FSH + LH to block the activation of new follicles, allowing time for the ovulated egg to be fertilized in the oviduct and travel to the uterus where it will implant if previously fertilized
Estrogen
the “enhancer” in the ovarian cycle; enhances activation of follicles in response to FSH + suppression of follicles in response to progesterone
- helps with re-growing uterine lining + development of secondary sexual characteristics
Ovarian Cycle Phases
- Follicular Phase
- Ovulation
- Luteal Phase
Follicular Phase
the first half of the OC, named for the fact that the dominant feature is activated follicles:
- FSH is released from the pituitary in the brain. The slowly rising FSH levels prompt the follicles on the ovary surface to grow + begin maturing the egg inside for ovulation
- As follicles grow, they release estrogen, which enhances FSH effects. The more the follicles grow, the more estrogen they release (POSITIVE FEEDBACK LOOP that promotes follicle growth that in turn promotes estrogen release)
- in each follicle, the maturing egg finishes M1 and pauses during M2
Ovulation
middle of the OC, when the high estrogen levels cause a rapid rise + spike in LH + FSH levels
- LH spikes CAUSES OVULATION: one mature follicle ruptures + releases its egg. The other mature follicle degenerates and its egg is lost
- LF + FSH levels fall immediately after ovulation, and estrogen levels decrease when the extra follicles degenerate
- Takes 7 days for the egg to travel through the oviduct from the ovary to the uterus. It must be fertilized while IN THE OVIDUCT. If so, it will complete M2, producing a single mature egg
Luteal Phase
the dominant feature is the CORPUS LUTEUM, the structure that remains from the ruptured follicle
- the CL produces progesterone + estrogen. P inhibits the release of any more FSH + LH, suppressing activation of any new follicles, The uterus prepares to accept the fertilized egg if fertilization occurs.
- FSH + LH inhibition prevents any further eggs + follicles from developing. the CL estrogen increases over the next few days, enhancing the progesterone’s effects
- BIG END QUESTION: DID FERTILIZATION OCCUR?
Luteal Phase: No Fertilization
egg does not implant into the endometrial lining of the uterine wall
- the CL degenerates
- estrogen + progesterone levels decrease
- the progesterone decrease releases the suppression of FSH; the anterior pituitary then releases FSH which starts the ovarian cycle again
Luteal Phase: Yes Fertilization
fertilized egg does implant on the endometrial lining of the uterine wall
- the embryo produces the hormone called HUMAN CHORIONIC GONADOTROPIN (hCG)
- hCG causes the corpus luteum to remain instead of degrading, which causes the ovary to continue producing high levels of progesterone
- prevented initiation of another ovarian cycle during pregnancy
- hCG is unique to pregnancy, and is the hormone detected by pregnancy tests
